RESEARCH ARTICLE

Do smoking intensity-related differences invigilance indicate altered glucocorticoidreceptor sensitivity?

MARTIN REUTER, JUERGEN HENNIG & PETRA NETTER

Department of Psychology, University of Giessen, Germany

Abstract

The relationship of critical flicker fusion frequency (CFF) and a pharmacologically induced cortisol suppression

by means of dexamethasone (DEX) and metyrapone (MET) was investigated during nicotine deprivation in a

between-subjects design in 60 male smokers divided into light, medium and heavy smokers. DEX reduced

vigilance in medium smokers and improved it in heavy smokers compared to placebo, whereas MET was more

detrimental in heavy smokers. The hypothesis was put forward that the intensity of nicotine consumption is

related to differences in glucocorticoid and mineralocorticoid receptor sensitivity.

Introduction

Findings from animal studies (e.g. 1,2) and

experiments in humans3 have outlined the

importance of glucocorticoids in mediating

drug-seeking behaviour and the rewarding prop-

erties of psychostimulant drugs. It could be

demonstrated that stress-elicited corticosterone

release is correlated positively with drug self-

administration4 and that administration of corti-

costerone could initiate drug-seeking behaviour

in animals being resistant to drug self-adminis-

tration. Disruption of the hypothalamic – pituitary

axis (HPA-axis) by means of adrenalectomy

(ADX) or application of the corticosterone

synthesis inhibitor metyrapone decreases drug-

seeking behaviour as well as the rewarding

properties of drugs of abuse (e.g. 2,4 – 6). There

is also evidence that metyrapone ameliorates the

increase in craving during nicotine deprivation in

human smokers.3 It is assumed that the HPA-axis

triggers drug self-administration by influencing

the mesolimbic dopamine (DA) system. It could

be demonstrated that glucocorticoids stimulate

DA release in the nucleus accumbens7 and DA

transmission.1 The neuroanatomical substrate for

the interaction of glucocorticoids and DA are

glucocorticoid receptors, which are located on

mesencephalic dopaminergic neurones.8

Moreover, it is postulated that chronic drug

abuse can increase as well as decrease dopami-

nergic receptor sensitivity in the mesolimbic

dopamine (DA) system.9 Increase is assumed to

be the biochemical basis of sensitization to the

behavioural effects of the drugs10 and decrease to

withdrawal symptoms and tolerance.11 However,

findings demonstrating a sensitization or desen-

sitization of central glucocorticoid receptors as a

function of the intensity of drug abuse have not

been reported, although nicotine consumption

releases not only DA but also cortisol.12

Received for publication 7th August 2003. Accepted 5th January 2004.

Correspondence to: Dr Martin Reuter, Justus-Liebig-University of Giessen, Department of Psychology,Otto-Behaghel-Str. 10F, D-35394 Giessen, Germany. Tel: ++496419926154; Fax: ++496419926159;E-mail: martin.reuter@psychol.uni-giessen.de

Addiction Biology (March 2004) 9, 35 – 41

ISSN 1355–6215 print/ISSN 1369-1600 online/04/010035-07# Society for the Study of Addiction to Alcohol and Other Drugs Taylor & Francis LtdDOI: 10.1080/13556210410001674077

Besides its role in drug-seeking behaviour (for

a review see 13) and in stress responses, stimula-

tion of the HPA-axis may have an effect on sleep

cycles14,15 and may affect central nervous effects

such as vigilance, arousal, attention and mem-

ory.16 However, findings from experimental

studies using a pharmacological challenge of the

HPA axis showed that stimulation of glucocorti-

coid receptors does not consistently alter vigi-

lance. Born et al.17 reported increased cortical

arousal as measured by auditory evoked poten-

tials (AEPs), augmented self-reported concentra-

tion and reduced tiredness during a vigilance task

after administration of hydrocortisone (20 mg/

40 mg) as compared to placebo. The perfor-

mance in the vigilance task itself tended to be

superior in subjects with high cortisol levels

although this effect was not significant. The

authors conclude that the effects of hydrocorti-

sone on both AEPs and self-report measures

suggest an excitatory influence on brain stem and

thalamic mechanisms mediating the stimulus-

induced cortical arousal. Findings from in vitro

experiments demonstrating a glucocorticoid in-

duced increased neuronal excitability18 corrobo-

rate this hypothesis, as well as studies from

animal research which have shown an increased

firing rate of mesencephalic neurones after

administration of hydrocortisone.19,20 However,

Steiner et al.21 reported a dexamethasone (DEX)-

induced decrease in the firing rate of the

mesencephalic reticular formation. The contra-

dicting effects of hydrocortisone and DEX on

indicators of cortical arousal could be explained

by the different affinity of the drugs to the

different glucocorticoid receptors. There are two

classes of intracellular corticosteroid recep-

tors:22,23 the mineralocorticoid receptor (MR;

Type I) and the glucocorticoid receptor (GR;

Type II), which vary in distribution in different

brain areas, in binding affinities to various

endogenous and synthetic ligands and in function

within the organism. MRs exert primarily tonic

(permissive) influences, whereas GRs are in-

volved primarily in feedback action on stress-

activated brain mechanisms.23 DEX binds only to

the GR receptor, whereas cortisol binds to both

receptor subtypes. In physiological states cortisol

binds predominantly to the MRs and in stress

conditions the GR receptors are also occupied by

cortisol. Due to the stimulatory effects of the

MRs it can be assumed that vigilance is enhanced

by occupation of the MRs and decreased by

stimulation of the GRs. Moreover, it can be

hypothesized that administration of hydrocorti-

sone in dosages of 20 or 40 mg leads to such a

cortisol excess that both receptors are occupied

with the result that stimulating and dampening

effects neutralize each other with the conse-

quence that no significant alterations in vigilance

as measured by CFF are detectable.17,24

Therefore, altered vigilance (as an indicator of

cortical arousal) assessed by critical flicker fusion

frequency (CFF) after suppression of cortisol

release should be an appropriate indicator of

glucocorticoid receptor sensitization/desensitiza-

tion in smokers who permanently stimulate their

HPA-axis by smoking. This can be achieved by

either blocking cortisol synthesis by the 11-b-hydroxylase inhibitor metyrapone or by inhibiting

endogenous cortisol release via a centrally acting

negative feedback mechanism (e.g. by means of

the GR agonist DEX). This has different im-

plications for the involvement of different gluco-

corticoid receptor subtypes. DEX selectively

stimulates the GR and metyrapone has no direct

effect on either receptor subtype, although both

drugs lower cortisol levels. Moreover, DEX

blocks central CRF via negative feedback which

results in lowered ACTH levels. The amount of

availability of these neuropeptides also influences

cortical arousal.25

Therefore, the aim of this study was to test if

the degree of nicotine dependence in smokers is

related to distinct changes in the sensitivity of

central glucocorticoid receptor subtypes as in-

dicated in changes of vigilance after pharmacolo-

gical manipulation of the HPA-axis. This should

be investigated in a state of nicotine deprivation

to warrant that possible pharmacological effects

are not masked by effects of nicotine.

It was hypothesized that a pharmacologically

induced decrease in cortisol levels is associated

with deterioration of vigilance, at least in light

smokers, whose receptor sensitivity might be

comparable to non-smokers. With respect to the

medium- and heavy smokers we expect a gradual

desensitization of the glucocorticoid receptors

with the most pronounced desensitization in

heavy smokers. It was supposed that the MR is

most probably a candidate for desensitisation,

because the MR is stimulated under physiological

states as well as after smoking or in stressful

situations. Moreover, it is conceivable that

desensitization of the MR has implications for

the functionality of the GR. The sensitivity of the

36 Martin Reuter et al.

GR is also either reduced due to chronic cortisol

excess or the receptor function is reversed (i.e.

the GR has now excitatory effects), a phenomen-

on often observed with desensitized receptors

during withdrawal.9 If the degree of receptor

sensitization is a linear function of the degree of

nicotine dependence, as hypothesized above, then

a reversed functionality of the GR with a resulting

increase in vigilance with DEX should be

observable in medium smokers and most pro-

nounced in heavy smokers. For light smokers

with a hypothesized receptor sensitivity compar-

able to that of non-smokers stimulation of the GR

receptor should result in a deterioration of

vigilance following cortisol suppression.

Method

A sample of 60 healthy male smokers (age: 18 –

35 years, mean age 23.5 years; all subjects

smoked for at least 5 years and were not taking

any medication) was assigned randomly to either

1.5 mg of the centrally acting synthetic gluco-

corticoid dexamethasone (DEX) or 1 g of the

peripherally acting blocker of cortisol synthesis

metyrapone (MET) or placebo (n=20 each) in a

between-subjects design. There were no differ-

ences in age or in body weight between groups.

DEX was administered during the evening before

the day of the experiment (at 10.00 p.m.) and

MET in doses of 500, 250 and 250 mg at

different time-points during the experiment (1,

2 and 2.5 hours after the last standard cigarette

smoked after arrival). The dosages and the dosing

regimens used followed those applied typically in

the dexamethasone suppression test and other

experimental studies with metyrapone in healthy

human subjects (e.g. 26 – 28).

The experiment started at 12.25 p.m. After

3 hours and 45 minutes of smoking deprivation

CFF was assessed by three measurements of

increasing and decreasing flicker fusion frequen-

cies each. There was no delay between the six

CFF measurements. CFF threshold values were

recorded by a ZAK Leeds Psychomotor Tester.

The same procedure was obtained at the corre-

sponding time on the day before the experiment

as a baseline measurement. The mean of the six

measurements was computed for both post-

deprivation and the baseline trial and the

difference in CFF between both trials served as

a dependent variable. On both days the time of

the last smoked cigarette was controlled. On the

day of the baseline measurement the subjects

smoked their last cigarette 30 minutes before the

CFF was assessed. The time between last

cigarette and testing was short enough to avoid

withdrawal and long enough to exclude nicotine

effects on vigilance. On the experimental day all

subjects smoked a cigarette before the onset of

the deprivation phase.

The degree of nicotine dependence was

assessed by the number of cigarettes smoked

per day. Categories of light, medium and heavy

smokers were defined in analogy to categories 1 –

3 in the respective item of the Fagerstrom test for

nicotine dependence (FTND29), which was used

to record the number of cigarettes smoked per

day. According to the FTND criterion, light

smokers (n=23) smoked 10 – 20, medium smo-

kers (n=26) 21 – 30 and heavy smokers (n=11)

31 or more cigarettes per day. The ordinal

variables cigarettes/day (CIG/d) and drug (place-

bo, DEX, MET) were defined as independent

variables in a two-factorial ANOVA design.

Furthermore, an adjective checklist (EWL30),

assessing subjective drug effects and possible

drug-induced adverse somatic side effects, was

administered at baseline, during the deprivation

period and after smoking. The study was

approved by the Ethics Committee of the Ger-

man Psychological Society.

Results

Both MET and DEX significantly suppressed

cortisol levels in comparison to placebo (placebo:

M=157.40 SEM=12.65, DEX: M=62.31

SEM=12.65, MET: M=74.71 SEM=12.65;

F=16.70; p5 0.001). The two-factorial analysis

of variance yielded a significant interactionDRUG

6 CIG/d (F=4.02; p=0.007), but no significant

main effects. As depicted in Fig. 1 and Table 1,

there were no differences between the three drug

conditionswith respect toCFF in the light smokers

group, whereas in medium smokers the highest

decrease in CFF, indicating lowest vigilance, was

observed in the DEX condition and in heavy

smokers in the MET condition. Post hoc compar-

isons via LSD tests31 showed that CFF was

significantly more reduced with DEX in compar-

ison toMETand to placebo in themedium smoker

group and significantly reduced with MET in

comparison to DEX in heavy smokers.

To exclude the possibility that differential

effects between baseline and test values or

Nicotine consumption and glucocorticoid and mineraloid receptor sensitivity 37

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��� ���� ��� ��� ��� ���� ��� ��� ���

Figure 1. Changes in vigilance during smoking deprivation measured by CFF. Interaction of drug 6 cigarettes/day (F=4.02;p=0.007); post-hoc tests: *p5 0.05; **p5 0.001.

Table 1. CFF (Hz) (mean of six trials) mean and SEM at baseline and at the end of the deprivation from nicotine according todrug and habitual smoking intensity

Placebo DEX MET

Baseline M SEM M SEM M SEM

SmokersLight 34.25 0.97 33.87 1.12 35.45 0.81Medium 31.62 1.23 34.19 1.40 32.93 1.13Heavy 33.95 1.33 32.90 1.28 33.61 0.80

End of deprivationSmokers M SEM M SEM M SEMLight 30.39 0.82 29.72 1.33 311.17 1.03Medium 30.73 0.56 27.97 1.63 298.99 0.70Heavy 30.31 0.89 32.05 2.02 281.88 0.44

38 Martin Reuter et al.

between subgroups of smokers were caused by

differences in withdrawal during deprivation, or

that withdrawal interacts with particular drug

effects, an additional analysis of covariance was

computed with degree of withdrawal/craving as a

covariate. The craving measure used was a

computer choice paradigm (for more details see3,32) based on a questionnaire measure of craving

by Griffiths et al.33 The effect of the covariate

(craving) was not significant and the effect of the

interaction drug 6 cigarettes/day was not de-

creased after including the covariate (F=4.00;

p=0.007), indicating that the amount of with-

drawal did not influence the observed differential

effects in vigilance. A two-factorial analysis of

variance showed that there were neither main

effects of drug or of cigarettes/day on craving nor

an interaction between drug6 cigarettes/day (see

Table 2). With respect to the subjective effects,

neither a significant drug effect nor an interaction

drug 6 cigarettes/day 6 time was observed.

Discussion

The present study supports the hypothesis that

the degree of nicotine addiction is reflected by

changes in the sensitivity of central glucocorticoid

receptors. Moreover, the present findings suggest

that adaptation of glucocorticoid receptor sensi-

tivity does not affect both glucocorticoid receptor

subtypes equally in all nicotine addicts but that

the sensitivity of the MR or the GR is changed

depending on the degree of addiction. Although

both drugs, MET and DEX, significantly sup-

pressed cortisol levels in comparison to placebo

(F=16.70; p5 0.001), a decline of vigilance was

prevented in the group of the heavy smokers by

DEX. This indicates that in heavy smokers the

synthetic glucocorticoid DEX, binding selectively

to GRs, could serve as a surrogate for the blocked

cortisol. On the other hand, MET, which blocks

endogenous cortisol peripherally without stimu-

lation of either of the glucocorticoid receptors,

resulted in the most pronounced decrease of CFF

in this group. In medium smokers DEX could

not compensate the lack of cortisol. On the

contrary, CFF was most decreased in medium

smokers after intake of DEX. This result suggests

that in medium smokers the normal negative

feedback function of the GR (resulting in

decrease of arousal) is operating, whereas in

heavy smokers the GR might compensate for a

desensitized MR receptor. The hypothesis of a

desensitized MR in the heavy smokers is sug-

gested by their severe decrease of vigilance in the

condition of complete cortisol suppression by

MET, as a reversal of receptor function-related

behaviour is often observed with desensitized

receptors during withdrawal.9 The finding sug-

gests that blockade of the GRs by DEX antag-

onizes MR-mediated glucocorticoid functions, as

it is the case in medium smokers. This is in line

with animal studies in which DEX could also be

shown to antagonize MR mediated drug-seeking

behaviour.34 The hypothesized strongest dete-

rioration of vigilance after cortisol suppression in

the group of light smokers was not observed. We

assumed that receptor sensitivity of light smokers

is comparable to that of non-smokers and that a

lack of glucocorticoids should therefore cause low

vigilance. Instead, in light smokers a drug effect

was not observable. Clearly, other neurotrans-

mitter systems relevant for vigilance are able to

compensate a lack of glucocorticoids.

Given that there were no baseline differences

in subjective self-reports of activity, alertness and

mood when starting the test session, it can be

excluded that DEX, which has been reported to

reduce slow-wave sleep,15 had a significant

negative effect on the quality of sleep the night

before the experimental testing with ensuing

negative effects on vigilance performance.

In summary, the data corroborate the assump-

tion that chronic drug abuse is related not only to

changes in sensitivity of DA but also of glucocorti-

coid receptors, which might have implications for

the development of sensitization or tolerance. We

are fully aware that only more molecular experi-

ments can provide further evidence for the

proposed rather speculative assumptions on the

relationship between the degree of addiction and

Table 2. Changes in craving: mean (money spend for acigarette) and SEM of difference scores (end of deprivation fromnicotine – baseline) according to drug and habitual smoking

intensity

Placebo DEX MET

Smokers M SEM M SEM M SEM

Light 2.22 0.29 1.60 0.27 2.50 0.43Medium 1.86 0.32 2.00 0.32 2.00 0.25Heavy 2.00 0.43 2.33 0.49 2.25 0.43

Nicotine consumption and glucocorticoid and mineraloid receptor sensitivity 39

changes of MR and GR receptor sensitivity. It

should be pointed out that our conclusions were

based only on a single vigilance task (CFF), and

that no non-smoker control group was included

into the study. Another shortcoming of the study

was the small number of subjects in the subgroups

of heavy smokers. Given the small sample size in

this group, the results from the heavy smokers have

only a descriptive character, despite the fact that

variance homogeneity was warranted (Levene test:

F=0.12, df = 2,8, p=0.883) indicates that the

reported differences in vigilance seem to be

reliable.

Nevertheless, we are convinced that the find-

ings could encourage further research on altered

glucocorticoid receptor sensitivity in smokers by

using more diverse measures of vigilance and

cognitive performance, and could be extended to

experiments using specific receptor blocking

agents.

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Nicotine consumption and glucocorticoid and mineraloid receptor sensitivity 41