NEURAL CONTROL OF NEURAL CONTROL OF SALIVARY SECRETIONSALIVARY SECRETION

PARASYMPATHETIC CONTROLPARASYMPATHETIC CONTROLSYMPATHETIC CONTROLSYMPATHETIC CONTROLEXCITATION SECRETION COUPLINGEXCITATION SECRETION COUPLINGSALIVARY REFLEXESSALIVARY REFLEXESBUFFERING ACTION OF SALIVABUFFERING ACTION OF SALIVA

2

0 10 20 30 40

020

4060

80100

K

Cl

HCO3

NaC

once

ntr

atio

n (

mE

q/l

)

Classic experiment in which the concentration of ions in human parotid saliva was measured at different flow rates produced by parasympathetic

stimulation (Thaysen et al., 1954)

Flow of saliva (ml/min)

Afferent (sensory fiber)

CNSPNS

Efferent (secretomotor fiber)

LabelHRP

RAT HORIZONTAL BRAINSTEM SECTION

CAUDALROSTRAL

MIDLINE

TERMINATION OF GLOSSOPHARYNGEAL NERVE FIBERS

CELL BODIES OF INFERIOR SALIVATORY

NUCLEUS

CNS PNS Target

Sympathetic trunc

1st order neuron2nd order neuron

Sym

pat

het

icn

ervo

us

syst

em

neurotransmitterneurotransmitterAcetylcholine (ACh)

Noradrenalin/norepinephrin (NA)

1st order neuron

2nd order neuron

neurotransmitter

neurotransmitterAcetylcholine (ACh)Acetylcholine (ACh)P

aras

ymp

ath

etic

ner

vou

s sy

stem

Sympathetic nervous system

Parasympathetic nervous system

Effect of autonomic nervous system stimulation on salivary secretion

Stimulation Duration(min)

Flow(ml/30min)

Amylase(mg/ml)

Degranulation

Sympathetic10/sec

30 0.065 30.63 ++++

Parasymapathetic10/sec

30 0.85 0.043 ?

Epilemmal Hypolemmal

ALL SALIVARY GLANDS ARE INNERVATED BY PARASYMPATHETIC NERVE FIBERS

SYMPATHETIC INNERVATION IS VARIABLE - NOT ALL GLANDS ARE INNERVATED AND THE RELATIVE VOLUMES OF SALIVA PRODUCED BY SYMPATHETIC STIMULATION AND THE TYPES OF ADRENORECEPTORS ON THE BASOLATERAL MEMBRANE ARE VARIABLE

Relative volumes of fluid secreted by sympathetic stimulation

Dog Cat Rabbit Rat SheepParotid - + + ++ +Submandibular ++ +++ (+) ++ (+)Sublingual (+) ++

Types of adrenoreceptors responsible for fluidsecretion

Parotid (β) β(α) α(β) αβ βSubmandibular β α(β) (β) αβSublingual ? α(β)

Muscarinergic acetyl cholin receptor mAChR (93% type 3)

NEUROTRANSMITTERS INVOLVED IN SALIVARY SECRETION

NOREPINEPHRINE binds to either α or β adrenergic receptors

ACETYLCHOLINE binds to muscarinic cholinergic receptors

VASOACTIVE INTESTINAL PEPTIDE binds to vasoactive intestinal receptors

SUBSTANCE P binds to substance P receptors

These neurotransmitters bind to receptors on the basolateral membrane of the acinar cells.

The receptors belong to a large family of membrane receptors that transduce their signals via a guanine neucleotide regulatory protein (G-protein).

Activation of the G-protein results in the formation of cyclic AMP and eventually protein exocytosis.

Alternatively activation of the G-protein leads to the formation of IP3, which leads to Ca2+ mobilization and, subsequently, fluid secretion.

Stimulus-response couplingNEUROTRANSMITTER

MEMBRANE RECEPTOR

G PROTEIN

ADENYLATECYCLASE

Na+Cl-

K+

Ca2+

K+K+

Ca2+

Ca2+

Na+

Na+ATP

ATP

ATP

ATP

Ca2+IP3

Gp

PIP2

PLCDAGC.Kinase

PEPTMUSCVIP

Gs

A. Cyclase

cAMPA. Kinase

PROTEINH2O

Cl-

BASOLATERAL

APICAL

TIGHT JUNCTION

0.00.0 0.50.5 1.01.0 1.51.5 2.02.05.65.6

5.85.8

6.06.0

6.26.2

6.46.4

6.66.6

6.86.8

7.07.0

7.27.2

7.47.4

7.67.6

7.87.8S

aliv

ary

pHS

aliv

ary

pH

Flow rate of parotid saliva (ml/min)Flow rate of parotid saliva (ml/min)

0 5 10 15 205.0

5.5

6.0

6.5

Plaque pH

Minutes after sucrose rinse

0.25 M Tartaric acid

2 M NaCl

0.5 M NH4Cl

0.5 M CaCl2

0.5 M MgCl2

0.5 M KCl

1 M NaCl

0.1 M Tartaric acid

0.5 M NaCl0.05 M Quinine

1 M Sucrose

0 2 4 6 8 10 12Flow rate of saliva

Different taste qualities induce different flow rates of saliva

Stanley CohenUSA

Vanderbilt UniversitySchool of MedicineNashville, TN, USA

Rita Levi-MontalciniItaly and USAInstitute of Cell

Biology of the C.N.R. Rome, Italy

The Nobel Prize in Physiology or Medicine 1986The Nobel Prize in Physiology or Medicine 1986

"for their discoveries of growth factors""for their discoveries of growth factors"

Neurotrophic FactorsNeurotrophic Factors are endogenous, soluble proteins regulating survival, growth, morphological plastisity, or

synthesis of proteins for different functions in neurons

Proteins initially characterized as Proteins initially characterized as neurotrophic factors:neurotrophic factors:Neurotrophins Neurotrophins (NGF, BDNF, NT-3, NT-4, (NGF, BDNF, NT-3, NT-4,

NT-6)NT-6)GDNF-familyGDNF-family GDNF, NrTN, PSP, ARTGDNF, NrTN, PSP, ARTCNTFCNTFetc.etc.

Proteins Proteins notnot initially characterized as initially characterized as neurotrophic factors:neurotrophic factors:FGF-familyFGF-family aFGF, bFGFaFGF, bFGFIGFIGFEGFEGFTGFTGFαα and and ββInterleukin 1, 3, 6Interleukin 1, 3, 6etc.etc.

The Neurotrophic Theory

Neurons are produced in excess during development

They send out neurites and compete over neurotrophic factors in “target” areas,

Those that reach target survive

Classical

The neurotrophic hypothesis

Predictions of the neurotrophic hypothesis

Target ablation / null mutation

Increased target / overexpression

synaptic plasticity

Kang & Schuman (1995) Science 26, 1658-1662

differentiation

control GDNF

Biological activities of neurotrophic factors

neuron survivalno factor GDNF

neurite outgrowthno factor NGF

Neurotrophins NGF

Families of neurotrophic factors

GDNF family GDNF

Neurokine family CNTF

Transforming growth factor βs TGFβ-1, TGFβ-2, TGFβ-3

Insulin-like growth factors IGF-1, IGF-2

Fibroblast growth factors FGF-1, FGF-2, FGF-5

Hepatocyte growth factor HGF

, BDNF, NT-3, NT-4

, NTN, PSP, ART

, CT-1, LIF

Specificity and promiscuity in the neurotrophin family

TrkA

TrkB

TrkC

p75 NTR

NGF

NT-4

BDNF

NT-3

GDNF

RET

GFRα-1

Specificity and promiscuity in the GDNF family

NTN

GFRα-2

ARTGFRα-3

PSP GFRα-4

A. A ballot used in Florida to elect the president.

B. Evander Holyfield losing world championship title

C. A scientist’s attempt to use common names for biological experiments

What is a knockout

NGF knockouts Development of the sympatheticnervous system is impared

GDNF knockouts Development of the kidneys and theenteric nervous system is impaired,as well as some parasympatheticganglia

NrTN knockouts Development of the enteric nervoussystem and parasympatheticganglia innervating salivary glandsare impaired