NEURAL CONTROL OF SALIVARY SECRETION PARASYMPATHETIC CONTROL SYMPATHETIC CONTROL EXCITATION SECRETION COUPLING SALIVARY REFLEXES BUFFERING ACTION OF SALIVA

K Cl HCO 3 Na Concentration (mEq/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) Label HRP

RAT HORIZONTAL BRAINSTEM SECTION CAUDAL ROSTRAL MIDLINE TERMINATION OF GLOSSOPHARYNGE AL NERVE FIBERS CELL BODIES OF INFERIOR SALIVATORY NUCLEUS

CNSPNS Target Sympathetic trunc 1st order neuron 2nd order neuron Sympathetic nervous system neurotransmitter Acetylcholine (ACh) Noradrenalin/ norepinephrin (NA) 1st order neuron 2nd order neuron neurotransmitter Acetylcholine (ACh) Parasympathetic nervous system

Sympathetic nervous system Parasympathetic nervous system

Effect of autonomic nervous system stimulation on salivary secretion

EpilemmalHypolemmal

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

Muscarinergic acetyl cholin receptor mAChR (93% type 3)

NEUROTRANSMITTERS INVOLVED IN SALIVARY SECRETION NOREPINEPHRINE binds to either  or  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 IP 3, which leads to Ca 2+ mobilization and, subsequently, fluid secretion.

A CELL Na + (150) Cl - (130) K + (3) K + (140) Na + (30) Cl - (8) K+K+ Na V = -60 to -75 mV MEMBRANE POTENTIAL

BASIC ION CHANNEL ION CHANNELS ARE PORES THROUGH THE CELL MEMBRANE THAT ALLOW SELECTIVE PASSAGE OF IONS THROUGH THE MEMBRANE. THERE ARE SEVERAL TYPES OF ION CHANNEL

G-PROTEIN COUPLED ION CHANNEL

Stimulus-response coupling NEUROTRANSMITTER MEMBRANE RECEPTOR G PROTEIN ADENYLATE CYCLASE

SIGNAL TRANSDUCTION PROCESSES IN SALIVARY GLANDS 1. Generation of cAMP following  -adrenergic receptor stimulation, which leads to protein exocytosis. 2. Formation of 1,4,5-inositol triphosphate (IP 3 ) after muscarinic acetylcholine receptor stimulation, which leads to Ca 2+ mobilization and fluid secretion.

BASOLATERAL APICAL TIGHT JUNCTION

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

0.25 M Tartaric acid 2 M NaCl 0.5 M NH4Cl 0.5 M CaCl M MgCl M KCl 1 M NaCl 0.1 M Tartaric acid 0.5 M NaCl 0.05 M Quinine 1 M Sucrose Flow rate of saliva Different taste qualities induce different flow rates of saliva

Stanley Cohen USA Vanderbilt University School of Medicine Nashville, TN, USA Rita Levi-Montalcini Italy and USA Institute of Cell Biology of the C.N.R. Rome, Italy The Nobel Prize in Physiology or Medicine 1986 "for their discoveries of growth factors"

Neurotrophic Factors Neurotrophic Factors are endogenous, soluble proteins regulating survival, growth, morphological plastisity, or synthesis of proteins for different functions in neurons

Proteins initially characterized as neurotrophic factors: Neurotrophins (NGF, BDNF, NT-3, NT-4, NT-6) GDNF-familyGDNF, NrTN, PSP, ART CNTFetc. Proteins not initially characterized as neurotrophic factors: FGF-familyaFGF, bFGF IGFEGF TGF  and  Interleukin 1, 3, 6 etc.

The Neurotrophic Theory uNeurons are produced in excess during development uThey send out neurites and compete over neurotrophic factors in “target” areas, uThose 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, differentiation controlGDNF Biological activities of neurotrophic factors neuron survival no factor GDNF neurite outgrowth no factor NGF

NeurotrophinsNGF Families of neurotrophic factors GDNF family GDNF Neurokine familyCNTF Transforming growth factor  sTGF  -1, TGF  -2, TGF  -3 Insulin-like growth factorsIGF-1, IGF-2 Fibroblast growth factorsFGF-1, FGF-2, FGF-5 Hepatocyte growth factorHGF, 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 BDNFNT-3

GDNF RET GFR  Specificity and promiscuity in the GDNF family NTN GFR  -2 ART GFR  -3 PSP GFR  -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