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CHAPTER 1

INTRODUCTION

1.1 DEPRESSION – AYURVEDA

Vishada is one of the Vatananatmaja Vikaras and it is further said that Vishada is

the main factor that increases the range of all the diseases“Vishado

Rogavardhanaanaam Shreshthah”[1]. Dalhana commented “Asiddhi Bhayat

Vividheshu Karyasu Sado Apravrutihi” i.e a condition originated from apprehension

of failure, resulting in incapability of mind and body to function properly with

significant reduction in activity. Symptomatic representation of the state of Vishada

is explained in Shrimad Bhagvad Geeta. Depression is a state of low mood and

aversion to activity that can affect a person’s thoughts, behaviour, feelings and

physical well-being. It may include feeling of sadness, anxiety, emptiness,

hopelessness, worthlessness, guilty, irritability or restlessness [2]. The symptoms of

Vishada which are found in various references in Indian science when compared to

depression almost appear similar, so we can correlate Vishada with depression.

According to contemporary science depression is a serious mental health concern that

will touch most people‘s life directly or indirectly.

Charaka Samhita mentions “Vishada” as one of the Nanatmaja Vata Vikara and

it is further said that, Vishada is the main factor that increases the range of all the

diseases. Sushruta has mentioned it under the Mano Vikaras. Further he mentioned

that Vishada is common among Tamasika Manasa Prakruti.Whereas Vagbhata has

stated that person with predominant Tamasa Guna are more prone to suffer from

Vishada commenting on Anumanagamya Bhavas in Charaka Samhita says “Bhayam

Vishadena ” i.e. understanding the feeling of fear in a person by seeing his depressed

state or behaviour [3].

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1.2 DEPRESSION – AN OVERVIEW

Depression, sometimes referred as unipolar depression, is a heterogeneous

syndrome rather than a single disease and has been characterized as a collection of

“physiological, neuroendocrine, behavioural and psychological symptoms” [4]. It is

a common mental disorder characterized by sadness, loss of interest in activities and

by decreased energy and is differentiated from normal mood changes that are part of

life by the extent of its severity, the symptoms and the duration of the disorder.

Moreover, depression often comes with symptoms of anxiety. These problems can

become chronic or recurrent and lead to substantial impairments in an individual’s

ability to take care of his or her everyday responsibilities. [5]. Affected individuals

differ remarkably regarding the profile of clinical features, severity and course of

illness as well as their response to treatment and reintegration efforts.

Depression is a group of brain disorders with varied origins, complex genetics

and obscure neurobiology. It is a chronic and potentially debilitating form of

psychiartric disorders. Any form of stressful life event is considered as the very initial

sign of depression, thereby depression is often thought as stress related disorder [6].

Depressive illness can cause loss of productivity, enjoyment and intimacy of

individual. [7].

Majority of depressed patients have sleep disturbances, including reduced amount

of slow wave sleep (SWS), increased rapid eye movement (REM) sleep amount and

shortened REM sleep latency [8]. Although depression is a very different

phenomenon, it also shares many connections with sleep and they both influenced by

biological and environmental factors. Each phenomenon can also influence the other,

such as the sleep symptoms listed by the DSM-V criteria under depression. DSM- V

criteria plays great importance in diagnosis of depression.

1.3 EPIDEMIOLOGY

According to the World Health Organization (WHO) depression affects 121

million people worldwide. It is one of the top 10 causes of morbidity and mortality.

The high prevalence of suicide in depressed patients (up to 15%) coupled with

complications arising from stress and its effects on the cardiovascular system have

suggested that it will be the second leading cause of death by the year 2020 [9]. It

would fourth rank among all the medical illnesses in terms of its disabling impact on

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the world population. Depression can lead to suicide and is responsible for 850,000

deaths every year 7.15% of the population of most developed countries suffers with

depression. 80% of depressed people are not currently having any treatment. The

prevalence of depression is reported as 7.5 percent in Australia, 8 percent in Canada

and 5.4-8.9 percent in the United States [10, 11]. In India prevalence of all psychiatric

disorder is 65.4 per 1000 population out of which, total 51% i.e. 31.2 per 1000

population is affected by depressive illness [12].

Depression is common in people in their 20s, 30s and 40s although depression

can occur at any age. People who were born in the later part of the 20th century

seemed to have higher rates of depression and suicide than those of the previous

generation, in part, because of high substance abuse and the rising demands in the

standards of living. At least one in ten outpatients have depression but most of the

cases are unrecognized or inappropriately treated. Every year, 5.8% males and 9.5%

females experience episodes of depression worldwide. This imposes a large

economic burden on the society, it decreases the productivity and the functional

decline and it increases the mortality [13].

The one-year prevalence rate is about 5% and recurrence rates up to 85% have

been reported. Epidemiological studies suggest that, patients with lifetime history of

depression have greater risk of developing cardiac problems and these are not merely

the effects of associated life style and substance use co-morbidity [14, 15].

1.4 ETIOLOGY

Depression has multifactorial aetiology arising from environmental,

psychological, genetic and biological factors. As outlined below in Fig. 1, research

over the past decade has clarified that depression is associated with neurotransmitter

imbalances, Hypothalamic- Pituitary- Adrenal (HPA) axis disturbances, dysregulated

inflammatory pathways, increased oxidative and nitrosative damage,

neuroprogression and mitochondrial disturbances [16].

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Figure 1.1 Multiple pathways associated with Depression

1.4.1 Neurotransmitters in depression

The main focus of neurotransmitter research has been driven by the ‘monoamine

hypothesis’ of depression, which states that a deficit of monoamine neurotransmitters;

mainly serotonin, norepinephrine and dopamine, underlies depression [17].

1.4.1.1 Serotonin

Several studies have demonstrated that, serotonergic dysfunction plays the major

role in the pathogenesis of depression. Tryptophan, a precursor of serotonin, was found

to be low in depressed patients and tryptophan depletion has been known to cause

relapse in patients with a history of depression. Genetic variants of tryptophan

hydroxylase, a rate-limiting enzyme in the synthesis of serotonin, were also found to

be associated with suicidal behaviour [18, 19, 20]. Furthermore, previous studies

focusing on serotonin metabolism have suggested that metabolism decreased in

depressed patients when a low level of 5-Hydroxy indoleacetic acid (5-HIAA), the

major metabolite of serotonin, was found in the cerebrospinal fluid. Serotonin receptors

have also been found to relate to depression. Positron emission tomography (PET) has

demonstrated the reduction of 5-HT1A receptor binding in patients with depression,

both pre-synaptically in the raphe nuclei and post- synaptically in several cortical

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regions [21, 22]. Moreover, some researches have shown that, long-term antidepressant

treatment leads to the down regulation of the 5-HT2A receptor and up regulation of the

5-HT1A receptor. In terms of the serotonin transporter (5- HTT), single photon

emission computed tomography (SPECT) studies found reduced serotonin transporter

binding sites in depressed patients [23, 24]. This decreased reuptake of serotonin is

believed to be a compensatory mechanism to counteract transmission deficits in some

serotonergic systems. In addition, gene-environment interaction studies have suggested

that, subjects exposed to environmental stress are more likely to develop depression if

they have at least one allele of a ‘low-efficiency’ version of the serotonin transporter

[25].

1.4.1.2 Norepinephrine

Norepinephrine is also believed to play a major role in the pathophysiology of

depression. Previous research has demonstrated a correlation between the down

regulation of postsynaptic β-adrenergic receptors and clinical antidepressant responses,

as well as the clinical effectiveness of antidepressants with noradrenergic effects (e.g.

Desipramine, Venlafaxine, Duloxetine). Moreover, an increased density of α 2 -

adrenergic receptors has also been reported in depressed patients and suicide victims.

This up regulation may be due to a relative deficiency of norepinephrine in the synaptic

clefts. Finally, the reduction of urinary excretion of the metabolite 3-Methoxy-4-

hydroxy phenyl glycol (MHPG) was found in patients with depression. Although some

subgroups of patients manifested elevated circulating levels of norepinephrine and its

metabolites [26, 27].

1.4.1.3 Dopamine

Previous studies have suggested that, dopamine activity may be reduced in

depression. Medications and diseases that reduces dopamine concentrations (e.g.

reserpine, parkinsonism) were found to be associated with depressive symptoms. In

contrast, drugs that increase dopamine concentrations (e.g. tyrosine, amphetamine,

bupropion) have shown antidepressant efficacy [28].

1.4.2 HPA Disturbances

1.4.2.1 Physiology of stress response and HPA axis

In response to stressful stimuli the periventricular hypothalamus secretes

corticotropin-releasing hormone (CRH) into the hypothalamo–pituitary portal

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circulation, which triggers the release of adrenocorticotropic hormone (ACTH), which

then stimulates the release of cortisol from the adrenal cortex. CRH initiates events that

release glucocorticoids from the adrenal cortex and as a result of the great number of

effects exerted by glucocorticoids, several mechanisms have evolved to control HPA

axis activation and integrate the stress response. Physiological and behavioural

components of the stress response are multiple and complex and as such may be

mediated by several mechanisms [29, 30, 31].

1.4.2.2 Depression and HPA axis activity

Over activity of the HPA axis within individuals with major depressive disorder

has been documented since late 1950s. The past few decades have brought about

numerous indications of impaired activity of various components of the HPA axis and

are evidenced by the following: elevated total and free cortisol concentrations in urine,

plasma and cerebrospinal fluid. Both elevated levels and blunted awakening cortisol;

elevated concentration of cerebrospinal fluid. Increased activity of the HPA axis may

be partly related to reduce feedback inhibition by endogenous glucocorticoids that

serve as potent negative regulators of HPA axis activity, in particular the synthesis and

release of CRH in the paraventricular nucleus [32]. Evidence from dexamethasone

suppression tests (DST and DEX/CRH) suggests that glucocorticoid-mediated

feedback inhibition is impaired in depression in that HPA axis activity is not suppressed

by pharmacological stimulation of glucocorticoid receptors (GR). It has been suggested

that, because individuals with depression exhibit impaired HPA axis negative feedback

through elevated levels of cortisol, that the number or function of GR are reduced in

patients with antidepressant treatment increases glucocorticoid signal in the brain by

increasing GR expression and function, eventually leading to increased negative

feedback on the HPA axis [33].

1.4.2.3 Depressive symptom remission and HPA axis

It has been proposed that, hypercortisolemia in depression should be considered

a state marker and not a trait marker as it has been shown to normalize in patients with

symptom improvement [34]. Evidence suggests that, compared to individuals with

residual symptoms, those who remit have a more pronounced normalization of an

initially dysregulated HPA axis, although inconsistencies have been found [35]. A

potential link between alterations of the limbic-HPA system and the serotonergic

hypothesis of depression has been suggested and treatments targeting these

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components may be beneficial. Investigations have found that, improved HPA system

regulation as measured by DEX/CRH test, was associated with treatment response after

5 weeks and a higher remission rate at the end of hospitalization. Change in HPA

system regulation as assessed by repeated DEX/CRH tests may be a potential

biomarker that predicts relapse and clinical outcome [36].

1.4.3 Oxidative & Nitrosative stress

Decreased antioxidant status and elevated oxidative and nitrosative stress are

found in patients with depression [37]. This is evidenced by reduced plasma

concentrations of important antioxidants such as vitamin C, vitamin E, and coenzyme

Q10 and by reduced antioxidant enzyme activity such as glutathione peroxidase. These

deficiencies in antioxidant defence impair protection against reactive oxygen species

(ROS), leading to damage to fatty acids, proteins and DNA. Depression is also

associated with increased levels of lipid peroxidation, comprising elevations in

malondialdehyde and increased oxidative damage to DNA, characterised by increased

levels of 8-Hydroxy-2-deoxyguanosine. Increased plasma levels of peroxides and

xanthine oxidase also associated with depression. The efficacy of antioxidant therapies

for depression is unknown, although N-acetylcysteine, a powerful antioxidant, was

found to be useful for depressive episodes in bipolar disorder and zinc, which serves

as a strong antioxidant, also has antidepressant activity [38, 39].

1.4.4 Neuroprogression

Neurogenesis and neuronal plasticity are compromised in depression, with

subsequent neuro degeneration [40]. This results in stress-induced alterations to the

number and shape of neurons and glia in brain regions of depressed patients and

decreased proliferation of neural stem cells. Brain-derived neurotrophic factor (BDNF)

is the most abundant and widely distributed neurotrophin in the central nervous system,

involved in neuronal survival, growth and proliferation. BDNF levels are low in people

with depression. However, BDNF levels increase with chronic administration of

several classes of antidepressants, including monoamine oxidase inhibitors, SSRIs,

tricyclic agents and SNRIs. Early life and chronic stress, which is often typical in

patients with depression, also has detrimental effects on BDNF [41, 42].

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1.4.5 Mitochondrial disturbances

Mitochondria are intracellular organelles that generate most of the cell‘s supply

of adenosine triphosphate (ATP) and are also involved in a range of other processes

such as signalling, cellular differentiation, cell death and the control of the cell cycle

and cell growth. High concentrations of mitochondria are found in the brain which

increases its vulnerability to reduction in aerobic metabolism [43]. Depression is

associated with mitochondrial dysfunction or disease with evidence of deletions of

mitochondrial DNA and lower activities of respiratory chain enzymes and ATP

production. Depressed patients presenting with somatic complaints also have low ATP

production rates in biopsied muscles. In addition, rates of depression increased in

patients with mitochondrial disorders [44].

1.4.6 Immuno-inflammation

Increased inflammation in depression has been confirmed in three recent meta

analyses. Elevated levels of C-reactive protein (CRP), interleukin-1 (IL-1) and

interleukin-6 (IL-6) were reported in a meta-analysis on depression in clinic and

community samples, levels of tumour necrosis factor-α (TNF-α) and IL-6 were

significantly higher in depressed patients than control and blood levels of soluble

interleukin-2 receptors, TNF-α and IL-6 were higher in a meta-analysis on patients with

depressive disorder than controls [45]. Depression is also characterised by a Th-1-like

cell-mediated response, with evidence of increased production of interferon-γ (IFN-γ),

increased IFN-γ/IL-4 ratios and increased neopterin levels. In addition, anti-depressant

medications have anti-inflammatory effects. An elevated immuno-inflammatory

response in depression is further supported by investigations into kynurenine pathway

metabolites or TRYCATS (tryptophan catabolites along the IDO pathway) [46].

TRYCATS are produced by the breakdown of tryptophan, involving the enzyme

indoleamine- 2, 3-dioxygenase (IDO). IDO is expressed in multiple cell types including

macrophages, dendritic cells, astrocytes and microglia and is strongly activated by the

pro-inflammatory cytokine IFN-γ and to a lesser extent TNF-α, IL-1 and IL-6. These

TRYCATS have both neurotoxic and neuro- protective qualities. Preliminary research

has demonstrated a relationship between depression and low levels of the

neuroprotective TRYCAT, kynurenicacid (KYNA) and high levels of the excitotoxic

TRYCAT, quinolinicacid (QUIN) [47].

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1.5 NEUROPHARMACOLOGY OF SLEEP

1.5.1 Definition of sleep

Sleep is not one homogeneous state, but rather a progression through various

states with extremely unique characteristics. On the basis of behavioural and

physiological criteria divided into rapid eye movement sleep (REM) and non-rapid

eye movement sleep, (NREMS). REM sleep derives its name from the frequent bursts

of eye movement activity that occur. It is also referred to as paradoxical sleep because

the electroencephalogram (EEG) during REM sleep is similar to that of waking. In

infants, the equivalent of REM sleep is called active sleep because of prominent phasic

muscle twitches. NREM sleep, or orthodox sleep, is characterized by decreased

activation of the EEG; in infants it is called quiet sleep because of the relative lack of

motor activity.

1.5.1.1 Stages of Sleep

Within REM and NREM sleep, there are further classifications called stages. For

clinical and research applications, sleep is typically scored in epochs of 30 seconds

with stages of sleep defined by the visual scoring of three parameters: EEG,

electrooculogram (EOG) and electromyogram (EMG) recorded beneath the chin.

During wakefulness, the EEG shows a low voltage fast activity or activated pattern.

Voluntary eye movements and eye blinks are obvious. The EMG has a high tonic

activity with additional phasic activity related to voluntary movements. When the eyes

are closed in preparation for sleep, alpha activity (8-13 cycles per second [cps])

becomes prominent, particularly in occipital regions.

1.5.1.2 NREM Sleep

NREM sleep, which usually precedes REM sleep, is subdivided into

progressively deeper stages of sleep: N1 stage, N2 and stage N3 (deep or delta-wave

sleep). Sleep usually entered through a transitional state, N1 sleep, characterized by

loss of alpha activity and the appearance of a low voltage mixed frequency EEG

pattern with prominent theta activity (3-7 cps) and occasional vertex sharp waves may

also appear. Eye movements become slow and rolling, and skeletal muscle tone

relaxes. Subjectively, N1 may not be perceived as sleep although there is a decreased

awareness of sensory stimuli, particularly visual, and mental activity.Motor activity

may persist for a number of seconds during N1. Occasionally individuals experience

sudden muscle contractions, sometimes accompanied by a sense of falling and/or

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dreamlike imagery; these hypnic (hypnosis = mental state like sleep) jerks are

generally benign and may be exacerbated by sleep deprivation.

After a few minutes of N1, sleep usually progresses to N2, which is heralded by the

appearance of sleep spindles (12-14 cps) and K-complexes (high amplitude negative

sharp waves followed by positive slow waves) in the EEG. N2 and subsequent stages

of NREM and REM sleep are all subjectively perceived as sleep. Particularly at the

beginning of the night, N2 is generally followed by a period comprised of N3. Slow

waves (< 2 cps in humans) appear during these stages, which are subdivided according

to the proportion of delta waves in the epoch; N3 requires a minimum of 20% and not

more than 50% of the epoch time occupied by slow waves. N3 is also referred to as

slow wave sleep (SWS), delta sleep, or deep sleep, since arousal threshold increases

incrementally from N1 through 4. Eye movements cease during N2-3, and EMG

activity decreases further.

1.5.1.3 REM sleep (or) N-R sleep

REM sleep is not subdivided into stages, but is rather described in terms of tonic

(Persistent) and phasic (episodic) components. Tonic aspects of N-R sleep include the

activated EEG similar to that of N1, which may exhibit increased activity in the theta

band (3-7 cps), and a generalized atonia of skeletal muscles except for the extra ocular

muscles and the diaphragm. Phasic features of N-R include irregular bursts of rapid

eye movements and muscle twitches. Normal sleep patterns vary from species to

species. As already discussed, humans go through five stages in approximately ninety

minute cycles throughout the night. Mice, however, spend far more time asleep, and

when they do sleep, the majority of it is NREM sleep. One strongly correlated aspect

of sleep is body and brain size and the average cycle time in NREM sleep- the smaller

the animal, the shorter the cycle [48].

1.5.2 Physiology of Sleep

Human and animal sleep depends on two major factors: a circadian regulator,

defining the diurnal rhythm and a homeostatic regulator defining the relationship

between wake time and sleep time.

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Figure 1.2 Sleep stages in Human sleep with Duration in each stage.

1.5.2.1 Homeostatic Regulation of Sleep

Sleep is understood to be restorative, but precisely what is being restored is

uncertain. As a homeostatic process, sleep allows the body to return to equilibrium

when it is disturbed. For instance, sleep deprivation tends to be followed by extra

compensatory sleep to make up for the loss, albeit not on a minute-to-minute basis. The

homeostatic component, named Process S (sleep), is believed to derive from a substrate

or protein that registers a homeostatic “need to sleep” during periods of extended

wakefulness that is subsequently relieved during sleep. As NREM sleep appears to take

precedence over REM sleep following acute sleep loss, it is probable that the

homeostatic mechanisms for the two sleep states differ. The underlying mechanisms

remain unclear. However, studies have shown that adenosine acting in the basal

forebrain is a key mediator of homeostatic control. Increased adenosine release

accompanies the accumulation of the need to sleep, suggesting that the nucleoside,

adenosine, may be involved in the homeostatic control of sleep expression [49]. During

periods of wakefulness, glycogen, the body’s principal store of energy, is exhausted.

As glycogen is broken down into adenosine, extracellular levels of adenosine begin to

accumulate in the basal forebrain, leading to the replenishment of glycogen levels with

recovered sleep. Experimental models showed that, the injection of adenosine or an

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adenosine A1 receptor agonist into the rat basal forebrain or the cat VLPO,

respectively, promoted sleep by inhibiting multiple wake-promoting regions of the

brain or exciting sleep-promoting cell groups. Adenosine also may excite VLPO

neurons by disinhibiting GABAergic inputs. Therefore, by inhibiting the basal

forebrain arousal system and triggering the VLPO nucleus, adenosine may act as

homeostatic regulator of the sleep need. Recent evidence has shown that the sleep

promoting effects of adenosine are further enhanced through its action at the A1

receptor, which triggers an intracellular cascade leading to increased adenosine A1

receptor production. Other mediators of homeostatic drive may be identified in the

future [50].

1.5.2.2 Circadian Sleep Regulation

A second component of the sleep-wake regulatory mechanism, involves circadian

influences. The SCN, which directs the circadian program, has been called the brain’s

“master clock”. Circadian timing, in which neurons fire in a 24-hour cycle, is organized

in a hierarchy of tissue-specific structures located throughout the body. These tissue-

specific rhythms are coordinated by the SCN based on light input from the outside

world during daytime and by melatonin secretion during the dark cycle [51]. Damage

to the SCN eliminates the circadian rhythms of many behaviours, including sleep. In

particular, lesions of the retinohypothalamic tract (RHT) of the SCN, which processes

light input, cause animals to exhibit free-running behaviours, demonstrating that the

SCN is necessary for synchronization of circadian rhythms to the solar day.

Many physiological processes have a diurnal pattern and are governed by 24 hour

clock, including body temperature, endocrine and autonomic functions, sleep,

cognitive processes and alertness. The diurnal pattern has a key role in assisting an

organism to adapt to environmental circumstances. Many core psychological functions

in healthy individuals such as mood, alertness and cognitive performances follow a

diurnal pattern, being best in the morning and declining throughout the course of the

day to an evening nadir. There is similarly a diurnal pattern to the stress response,

which may be of particular relevance to stress related disorders such as depression. The

circadian clock has a genetic foundation. A range of genes, including the so-called

‘clock’ genes, regulate the length of the circadian period. Variants of this gene

determine a person’s diurnal preference, i.e. being a ‘night owl’ or a ‘morning lark’,

and these genes are further implicated in the pathophysiology of mood disorders [52].

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1.5.3 Sleep Changes as Biomarker for Depression

The relationship between sleep and depression is bidirectional, where sleep

disturbances are one of the core features of depressive illness. While

Polysomnographic (PSG) studies in adults with depression have demonstrated

significant differences on several sleep parameters. These studies have traditionally

examined sleep macro- architecture, which describes the latencies and durations of

sleep stages. Disturbances in duration of PSG parameters, such as total sleep time

(TST), sleep efficiency (SE), non-rapid eye movement (NREM) sleep (N1–3) and

rapid eye movement(REM) sleep as well as the frequency of REMs( REM density)

[53].

Numerous studies undertaken in depressive patients have suggested that a

common comorbidity of depression is a dysregulation of the circadian timing system.

In nearly 80% of depressed patients have profound disturbances in sleep architecture

have been documented. Depressed patients often complain of difficulties in falling

asleep, frequent nocturnal awakenings and early morning wakefulness.

Both epidemiological and electroencephalographic studies implicate sleep

disturbance in the pathogenesis of depression. PSG studies in depressed patients show

a reduction in the absolute number of delta waves during the first NREM sleep period

and a general decrease in delta activity throughout the night. Additionally, an

alteration in the temporal distribution of REM sleep with impairment of the timing of

the REM/NREM sleep cycle was documented. It has been suggested that, patients

with decreased REMOL prior to treatment are prone to develop subsequent episodes

of depression and experiencing rapid relapses after remission. The presence of sleep

abnormalities in the first degree relatives of depressed patients (even those who never

experienced the illness) suggests that these sleep changes can be viewed as “markers”

of depression. The decrease in slow wave activity during the first NREM period and

the increase of REM sleep occur more frequently in early depression although the

significance of this is not clear[54].

Functional neuroimaging studies using positron emission tomography have

indicated that MDD patients have higher rates of brain glucose metabolism during the

first NREM sleep period as compared to non-depressed controls, a change associated

with decreased slow wave activity. Despite this associational evidence, whether sleep

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disturbance has a causal role on depression is still not completely resolved. However,

the clinical management of depression should entail an awareness of the reciprocal

relationship between insomnia and the depressive episodes. It has been suggested that

the existence of abnormalities in the timing of REM/NREM sleep cycle [55, 56].

1.6 Role of Melatonergic system in Sleep regulation and Depression

Melatonin or N-acetyl-5-methoxytryptamine, is a hormone principally produced

and released by the pineal gland. It is a major neurohormone influencing the activity

of SCN neurons. The effect of melatonin is exerted via two distinct melatonin

receptors, MT1 and MT2 [57] . Melatonin inhibits (via MT1 receptors) as well as

phase-shifts (via MT2 receptors) the electrical activity of SCN neurons. In transgenic

mice lacking MT1 receptors, melatonin does not elicit acute inhibitory responses but

can still shift the phase of circadian rhythmicity in SCN firing rate. Therefore, MT2

receptors in the SCN are considered responsible for the phase-shifting and entrainment

effects of melatonin. The firing rate of the SCN decreases in the transition from NREM

to REM sleep, as shown by the simultaneous recording of electroencephalographic

activity and SCN electrical activity in male Wistar rats [58, 59]. These observations,

however require further confirmation in primates, since the relative amount of REM

sleep in rodents is quite limited. The role of the SCN in the regulation of sleep was

first studied in squirrel monkeys. In this primate species SCN lesions, on the one hand,

resulted in the loss of consolidated sleep/wake periods and, on the other hand, caused

a prolonged sleep compared to animals with an intact SCN. The evidence supported

the conclusion that the circadian signal arising from the SCN promotes wakefulness

during the day and facilitates consolidation of sleep during the subjective night.

Indeed, the mechanisms by which the SCN regulates sleep appear to be complex. The

primary projections from the SCN involve hypothalamic and extrahypothalamic

structures (e.g., the basal forebrain or midline thalamic nuclei) that are involved in the

regulation of sleep/wake cycle, autonomic regulation, psychomotor performance and

melatonin secretion. The main purpose of the SCN output system is to integrate

environmental cues with the circadian system, thus conferring maximum flexibility to

the response. Hence, the neural pathways from the SCN, which promote wakefulness

are complemented by those involved in SCN promotion of sleep. The sleep-promoting

action of the SCN also depends upon melatonin whose circadian secretion is regulated

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by the SCN. Signals from the SCN have been shown to influence physiology and

behaviour including melatonin synthesis, temperature and sleep [60].

Figure 1.3 Synthesis of Melatonin.

1.6.1 Melatonin: biosynthesis, metabolism and mechanism of action

Melatonin was isolated in 1958 by Lerner and his associates, and its chemical

nature was identified as N-acetyl-5-methoxytryptamine. Axelrod (1974) demonstrated

that the pinealocytes have the necessary enzymatic components for the biosynthesis

of melatonin. The sequence of events for the biosynthesis of melatonin is as follows:

Tryptophan is taken up from the circulation and is converted into serotonin.

Serotonin is converted into N-acetylserotonin by the enzyme arylalkylamine N

acetyltransferase(AA NAT);

N-acetylserotonin is converted to melatonin by the enzyme hydroxy-indole-O-

methyltransferase.

Melatonin has both lipophilic and hydrophilic properties. Once formed it is

released into capillaries and can reach all tissues of the body within a very short

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period [61]. In the circulation, melatonin is partially bound to albumin and can also

bind to hemoglobin. The secretion of melatonin occurs mainly during the night, with

maximum plasma levels normally found between 02:00 and 03:00 AM [62]. An

episodic secretion of melatonin during the night has also been noted. The half-life of

melatonin after intravenous infusion is about 30 min. However, a recent study

indicated that melatonin exhibits a bi-exponential decay with a first distribution half-

life of 2 min and a second metabolic half-life of 20 min [63]. A positron emission

tomography (PET) study indicated that melatonin enters the brain from the circulation;

brain radioactivity was high within 6–8 min after the injection of 11C melatonin. In

the liver, melatonin is first hydroxylated and then conjugated with sulfate and

glucuronide. In human urine, 6-sulfatoxymelatonin (aMT6 s) has been identified as

the main metabolite. In the brain, melatonin is metabolized into kynurenine

derivatives.

It is of interest that the well-documented antioxidant properties of melatonin are

shared by some of its metabolites including cyclic 3-hydroxymelatonin, N1-acetyl-

N2-formyl-5-methoxykynuramine and, with a highest potency, N1-acetyl- 5-

methoxykynuramine [64, 65]. Although melatonin synthesis occurs in a number of

tissues (i.e. the retina, skin and gut), circulating melatonin is almost totally derived

from the pineal gland as indicated by its disappearance after pineal removal. Since

there is no storage of melatonin in the pineal gland, and since the circulating melatonin

is degraded rapidly by the liver, plasma (or saliva) levels of melatonin as well as

urinary levels of aMT6 s reflect appropriately the pineal biosynthetic activity.

Melatonin levels are higher at night than during the day in all animal species studied,

regardless of being diurnal, nocturnal or crepuscular. The circadian pattern of pineal

AANAT, and consequently of melatonin production and secretion, is abolished by

lesions of the SCN. Environmental 24 h light/dark (L/D) cycle acts thus as the

pervasive and pre-eminent Zeitgeber that regulates melatonin synthesis [66]. The

circadian activity of the SCN is synchronized to the L/D cycle mainly by light that is

perceived by the retina. The signal generated in the retina is transmitted to the SCN

through a monosynaptic retinohypothalamic tract that originates from the ganglion

cell layer in the retina and uses glutamate as a neurotransmitter.

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Recently, it has been found that a sub-group of retinal ganglion cells containing

melanopsin and that innervate the SCN are involved in the photic transmission of light

signals to the SCN. Animal studies demonstrate that the neural pathway connecting

the SCN with the pineal gland starts by a gamma-aminobutyric acid GABA-ergic

projection from the SCN to the paraventricular nucleus (PVN). In addition, the SCN

connects through the subparaventricular zone to the dorsomedial nucleus of the

hypothalamus, which is crucial for producing circadian rhythms of sleep and waking,

locomotor activity, feeding and corticosteroid production [67]. Indeed, physiological

and immunohistochemical studies have revealed that GABA is the principal

transmitter in SCN cells. To control pineal function, efferent fibers from the PVN go

through the medial forebrain bundle and reticular formation and make synaptic

connection with the cells of the intermedio-lateral columns of the cervical spinal cord,

from where preganglionic sympathetic fibers arise and project to the superior cervical

ganglia (SCG).

The postganglionic sympathetic fibers from SCG reach the pineal gland and

release norepinephrine (NE). Activation of pineal beta-adrenergic receptors results in

elevation of cyclic AMP and increases in the synthesis and activity of pineal AA NAT.

Alpha1-adrenergic receptors are also detectable in the pineal gland and potentiate

β-adrenergic receptor activity through the increase of Ca2C activity and the activation

of protein kinase. Beta-adrenergic blockers have been shown to suppress the nocturnal

synthesis and secretion of melatonin in humans, suggesting a similar regulation of

pineal melatonin production [68]. During the light phase, the SCN electrical activity

is high, and under these conditions NE release is inhibited. During the scotophase, the

SCN activity is inhibited and NE release in the pineal is augmented [69]. Exposure to

light (that stimulates the SCN) during the dark phase inhibits NE release in the pineal

gland. Melatonin secretion is suppressed by light intensities ranging from outdoor

levels to, under certain circumstances, those seen indoors. Light-induced suppression

of pineal melatonin synthesis and secretion in humans has a peak sensitivity to short

wavelength light (446–477 nm) [70]. Melatonin is thus produced and released from

the pineal gland during the time of electrical ‘quiescence’ of the SCN occurring in

darkness and is therefore been referred to as the ‘hormone of darkness’. Pineal

melatonin production was shown to be independent of sleep or sleep deprivation.

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Melatonin production exhibits considerable inter-individual differences with more

than 10-fold variability in nocturnal melatonin concentrations among individuals. A

genetic cause of this variability is suggested by the lower variability found in siblings

as compared to the general population [71]. Melatonin sleep promoting effects

involves interaction with specific receptors in the cell membrane. Melatonin may also

interact with nuclear hormone receptors, with a number of intracellular proteins such

as calmodulin, dihydronicotinamide riboside:quinone reductase 2 and tubulin-

associated proteins and is a potent antioxidant acting as a free radical scavenger as

well as via induction of antioxidant enzymes [72]. With the exception of membrane

receptors, the relevance of any of these interactions to the sleep promoting effects of

the hormone is unknown. The sleep promoting and circadian effects of melatonin have

been attributed to the two subtypes of human melatonin receptors (MT1 and MT2).

MT1 mRNA is mostly expressed in the SCN while MT2 mRNA is distributed in the

SCN and other areas of the CNS, as well as in the periphery. It is believed that at the

SCN MT1 receptors are related to amplitude of SCN circadian rhythmicity, while

MT2 receptors are involved in entrainment of circadian rhythms [73].

1.6.2 Melatonin and Sleep

Melatonin has been implicated in a number of physiological functions like

regulation of circadian rhythms, sleep and body temperature, sexual maturation,

immune function, antioxidant mechanisms, regulation of mood, cardiovascular

functions, etc [74]. Among these various functions, the soporific and sleep/wake

rhythm regulating functions of melatonin have gained wide scientific attention

resulting in numerous studies undertaken in animals and in human subjects. The

finding that melatonin is secreted primarily during night time, the close relationship

between nocturnal increase of endogenous melatonin, and the timing of human sleep

and the sleep-promoting effects of exogenous melatonin prompted many investigators

to suggest melatonin is involved in the physiological regulation of sleep. The onset of

night time melatonin secretion occurs approximately 2 h before individual’s habitual

bed time and has been shown to correlate well with the onset of evening sleepiness.

Suppression of melatonin production by procedures like treatment with β-blockers has

been shown to correlate with insomnia. Conversely, increasing plasma melatonin

concentrations by suppressing melatonin metabolizing enzymes in the liver resulted

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in increased sleepiness [75]. The period of wakefulness immediately prior the

‘opening of the sleep gate’ is referred to as the wake-maintenance zone or ‘forbidden

zone’ for sleep. During this time the sleep propensity is lowest and the activity of SCN

neurons is high [76]. The transition phase from wakefulness/arousal to high sleep

propensity coincides with the nocturnal rise in endogenous melatonin. In several

studies, a temporal relationship between the nocturnal increase of endogenous

melatonin and opening of the sleep gate was found in most subjects. Upon

administration of melatonin in the afternoon, the sleep gate was advanced by 1–2 h,

while exposure to 2 h of evening bright light between 08:00 and 10:00 PM delayed

the next day rise in nocturnal melatonin and the opening of sleep gate. It was therefore

proposed that melatonin promotes sleep by inhibiting the circadian wakefulness

generating mechanism. This effect is presumably mediated by MT1 receptors at the

SCN level. Melatonin appears to promote sleep by inhibiting the firing of SCN

neurons. This effect is most probably linked to the activation of GABAergic

mechanisms in the SCN, as shown by a number of studies. It therefore appears that

melatonin has a pivotal role in the circadian sleep timing mechanism through its

activity on the SCN. However, there are melatonin receptors in additional human brain

areas, e.g. hippocampus [77].

1.7 Neopterin – Biomarker for Depression

Important reciprocal relationships exist between the hypothalamo-pituitary-

adrenal cortical HPA axis and humoral and cellular components of the immune

system. The production of HPA axis-activating cytokines in febrile illness and organ

transplantation and the immunosuppressive effect of pharmacological doses of gluco-

corticoids are well known [78].Specific cytokines activate specific levels of the HPA

axis; e.g. the stimulation of CRH secretion by interleukin IL-1 and IL-6 and

stimulation of ACTH secretion by IL-2 and IL-6. HPA axis hyperactivity is the most

prominent neuroendocrine abnormality in depression, occurring in 30-50% of

patients. Though considerable work has been done attempting to clarify immune

changes as biological markers of depression, the results have not been consistent.

Neopterin is a reliable, easy-to-measure and well-established soluble marker of

immune activation [79]. Neopterin, a biopterin precursor, is released by macrophages

and reflects activation of the cell-mediated immune system (T-lymphocytes). It is a

product of GTP hydrolysis by cyclo-hydrolase, which is stimulated by interferon-γ

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(IFN- γ). IFN- γ is secreted by activated T-lymphocytes; therefore, elevated plasma

neopterin is considered to represent activation of T-lymphocytes, although it is

secreted primarily by myeloid cells. Elevated neopterin thus reflects putative

activation of the inflammatory cytokine network, including IL-1, IL-6 and tumor

necrosis factor TNF, which in turn act on the central nervous system. Plasma neopterin

often is elevated in states of activated cell-mediated immunity, such as autoimmune

illness, organ transplantation and viral infections including the human

immunodeficiency virus HIV. It also is elevated in patients with anorexia nervosa,

another psychiatric illness in which HPA axis activation occurs [80].

Neopterin (10, 20, 30-D-erythro-trihydroxypropylpterin) was first isolated from

human urine in 1965. Chemically neopterin represents an unconjugated pteridine

which is synthesized from guanosine triphosphate (GTP) through the GTP

cyclohydrolase I pathway. Thereby, GTP is converted to 7,8-dihydroneopterin

triphosphate by GTP cyclohydrolase I (GCH-I) as the first and rate-limiting step of

the pathway leading to the formation of 5,6,7,8-tetrahydrobiopterin GTP

cyclohydrolase I can be induced by IFN-γ in various cells and species. However unlike

most other cells, human monocyte-derived macrophages and dendritic cells do not

express the subsequent enzymes of the pathway such as 6- pyruvoyl-tetrahydropterin

synthase, which also is relatively insensitive to IFN-γ. As a consequence, following

dephosphorylation of 7, 8-dihydroneopterin triphosphate and oxidation leads to

formation of neopterin [81].

1.8 Depression and Cognitive Changes

Depression unquestionably may affect the ability to think, concentrate, make

decision, formulate ideas, reason, and remember. Other cognitive symptoms of

depression are represented by negative self-evaluation, worthlessness, thoughts of

death, suicidal ideation, ruminative thinking over minor past failings, delusions (50%

of patients tend to focus on fixed ideas of guilt and sinfulness, poverty, somatic

concerns, and feelings of persecution), and hallucinations [82]. Cognitive

dysfunctions are generally assessed by a neuropsychological examination including

an interview of the patient's background and present situation, a behavioural

observation, and the administration of a battery of neuropsychological tests. In an

attempt some researchers employed the P300 event-related electroencephalographic

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potential for cognitive processes [83]. The P300 component of the Event-Related

Potential (ERP) is a positive deflection which occurs when a subject detects an

informative task-relevant stimulus. Real-time recording of ongoing brain activity can

be used to investigate changes in ERPs related to the completion of a specific cognitive

task. ERPs have millisecond temporal resolution, and can therefore be used to monitor

the neural processes engaged in cognitive functions and capture rapid changes in

cerebral activity.

The ERP task most frequently used to elicit the P300 wave is the oddball task, in

which participants are confronted with a repetitive sequence of standard stimuli (e.g.,

a 1000 Hz sound that occurs 80% of the time) and a few deviant stimuli (e.g., a 2000

Hz sound that occurs 20% of the time). Participants must detect the deviant stimuli as

quickly as possible (typically by pressing a button or keeping count mentally).

Because the subjects must explicitly assess the situation, categorize the pertinent

stimuli, and make a decision, the P300 wave is thought to represent real-time

processing of working memory and voluntary attention as well as a decisional

‘‘response-related stage’’ that indexes memory updating and/or cognitive closure

mechanisms. More precisely P300 amplitude is related to stimulus probability,

stimulus significance, task difficulty, motivation, vigilance and also handedness.

The P300 latency is mainly influenced by the task complexity and is only weakly

influenced by response selection processes. Moreover, P300 latency could be heritable

[84]. The P300 wave can provide a highly useful means for monitoring the efficiency

of cognitive processing. Indeed, many studies have shown the relevance of the P300

as a biological marker for pathophysiological mechanisms. There is general agreement

that a reduction in the P300 amplitude is: (1) a state marker (i.e., a biological marker

that is altered during the disease but stabilizes after clinical remission) of depression

(2) a trait marker (i.e., a biological parameter that is altered during and after the

disease) of schizophrenia, and (3) a vulnerability marker (i.e., a biological variable

that is altered before the emergence of the disease) for alcoholism. These markers, if

present, could be used to aid diagnosis, predict prognosis, or choose the most

appropriate treatment for the psychiatric disorder.

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However, some results concerning the P300 component are controversial. For

instance, while a significant number of studies have found reduced P300 amplitudes

in patients with depression other studies have failed to replicate this finding. There are

similar contradictory results regarding P300 evoked in visual oddball tasks as well as

P300 latency. Indeed, several studies have reported that P300 latency is not altered in

depression, but rather reaction time is changed. One possible explanation for these

heterogeneous results is the clinical sub-types of the depressed patients included in

these studies. Many individuals with a history of depression use multiple medications,

have co-morbid psychiatric disorders, and have complicated family histories [85].

1.9 Alternative Therapy for Depression

Depressive disorders are very common in clinical practice, with approximately

11.3% of all adults afflicted during any one year [86]. The majority of patients suffer

from mild to moderate forms and are treated in primary care settings. Such patients

are often reluctant to take synthetic antidepressants in their appropriate doses due to

their anticipated side effects including inability to drive a car, dry mouth, constipation

and sexual dysfunction. As a therapeutic alternative, effective herbal drugs may offer

advantages in terms of safety and tolerability, possibly also improving patient

compliance [87, 88]. The advent of the first antidepressants- the Monoamine Oxidase

Inhibitors (MAOIs) and Tricyclic Antidepressants (TCAs) in the 1950s and 1960s

represented a dramatic leap forward in the clinical management of depression.

The subsequent development of the Selective Serotonin Reuptake Inhibitors

(SSRIs) and the Serotonin Norepinephrine Reuptake Inhibitor (SNRI) venlafaxine in

the past decade and a half has greatly enhanced the treatment of depression by offering

patients medications that are as effective as the older agents but are generally more

tolerable and safer in an overdose [89,90]. The introduction of atypical

antidepressants, such as bupropion, nefazadone, and mirtazapine, has added

substantially to the available pharmacopoeia for depression. Nonetheless, rates of

remission tend to be low and the risk of relapse and recurrence remains high. Thus,

there is a need for more effective and less toxic agents [91].

Depression is the most common condition among patients seeking treatment with

complementary and alternative therapies. Despite effective allopathic antidepressant

management plans, complete remission rate with allopathic pharmacotherapy remains

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low [92].Some of the reasons for the use of CAM include the relatively lower

incidence of adverse effects, perceived effectiveness, and the desire for egalitarian

relationships with medical practitioners, a holistic approach to the individual's

problems and dissatisfaction with conventional healthcare [93]. However, despite this

upsurge in the number of CAM consultations, providers of conventional healthcare

have failed to address the issue. Given their frequent use, CAM approaches warrant

the same level of evaluation as conventional treatments. Service users, planners,

general practitioners and mental health professionals need to be informed about which

treatments are effective, which are not, and which ones have been adequately

evaluated [94].The last decade has witnessed a significant growth of interest in

Complementary and Alternative Medicine (CAM) worldwide.

The 3 most widely used CAM approaches in depression are Relaxation, Exercise

and Herbal remedies [95]. Out of this, Herbal medicines are gaining growing interest

because of their cost-effective, eco-friendly attributes and true relief from disease

condition. Ayurveda usage is among the oldest Indian indigenous systems of medicine

with documented history of about 5000 years and 80% of the population still depends

upon Ayurveda for their health concerns [96]. Many plants have folklore claim in the

treatment of several dreadful diseases but they are not scientifically exploited and/or

improperly used. The use of traditional herbal medicines for the treatment of

depression is well documented. A number of plants have been identified in ancient

herbal texts from all over the world that were used to “settle the spirit,” “lift the mood,”

and “clear the mind”. Many of these herbs have been found to possess potent

chemicals which influence various organ systems that play a key role in mood,

anxiety, and mental function [97].

Recently, several herbal medicines showing promising antidepressant effects in

preclinical studies have been entered into clinical trials. It has been found that some

antidepressant herbal medicines combat depression via known

psychopharmacological actions such as inhibition of monoamine re-uptake (such as

serotonin, dopamine and noradrenaline), augmentation of binding and sensitization of

serotonin receptors, inhibition of monoamine oxidase, and modulation of neuro-

endocrine system. Other actions of the herbs may encompass GABAergic effects,

cytokine modulation (particularly in depressive disorders with a comorbid

inflammatory condition), as well as opioid and cannabinoid system effects. Moreover,

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particular group of herbal preparations, termed as adaptogens, are thought to play a

primary role in the reactions of the body to repeated stress and adaptation mainly due

to their association with the HPA-axis that is a part of the stress system. Therefore,

these plant drugs deserve detailed studies in the light of modern medicine [98,99].

The present Polyherbal formulation was developed at the National Facility for

Tribal and Herbal Medicine, Banaras Hindu University, Varanasi, India in

collaboration with Interdisciplinary Institute of Indian System of Medicine (IIISM),

SRM University, Chennai, India. The formulation was European patented

(EP1569666B1) for the management of Neurological Disorders. It is a polyherbal

formulation made into tablet dosage form, from freeze dried hydro- alcoholic extracts

of Bacopa monnieri whole plant, Hippophae rhamnoides leaves and fruits and

Dioscorea bulbifera rhizome in collaboration through a Memorandum of

Understanding (MoU) with a traditional health care practitioner, using high ethical

standards. The acute, short- term toxicity, pharmacological profile in animals as well

as clinical studies for the formulation showed good results with a very high therapeutic

index [(T.12016/25/2010-DCC (AYUSH)]. The polyherbal formulation exhibits

better therapeutic value on neurological disorder. It may also show positive benefits

on depression symptoms, sleep pattern and biomarkers. Existing knowledge also

advice that traditional herbal medicines are more effective and shows less toxic

effects. Hence the present study was aimed to evaluate the effect of polyherbal

formulation on Psychological parameters, Cognitive functioning, Sleep pattern,

Depression scores and its regulation of biomarkers in mild to moderate depressed

patients.