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NEURAL CONTROL OF SALIVARY SECRETION PARASYMPATHETIC CONTROL SYMPATHETIC CONTROL EXCITATION SECRETION COUPLING SALIVARY REFLEXES BUFFERING ACTION OF SALIVA
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2 0 10203040 0 20 40 60 80 100 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)
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Afferent (sensory fiber) CNSPNS Efferent (secretomotor fiber) Label HRP
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RAT HORIZONTAL BRAINSTEM SECTION CAUDAL ROSTRAL MIDLINE TERMINATION OF GLOSSOPHARYNGE AL NERVE FIBERS CELL BODIES OF INFERIOR SALIVATORY NUCLEUS
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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
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Sympathetic nervous system Parasympathetic nervous system
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Effect of autonomic nervous system stimulation on salivary secretion
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EpilemmalHypolemmal
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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
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Muscarinergic acetyl cholin receptor mAChR (93% type 3)
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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
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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.
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A CELL Na + (150) Cl - (130) K + (3) K + (140) Na + (30) Cl - (8) K+K+ Na + 0 + - V = -60 to -75 mV MEMBRANE POTENTIAL
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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
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G-PROTEIN COUPLED ION CHANNEL
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Stimulus-response coupling NEUROTRANSMITTER MEMBRANE RECEPTOR G PROTEIN ADENYLATE CYCLASE
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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.
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BASOLATERAL APICAL TIGHT JUNCTION
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0.00.51.01.52.0 5.6 5.8 6.0 6.2 6.4 6.6 6.8 7.0 7.2 7.4 7.6 7.8 Salivary pH Flow rate of parotid saliva (ml/min)
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0.25 M Tartaric acid 2 M NaCl 0.5 M NH4Cl 0.5 M CaCl 2 0.5 M MgCl 2 0.5 M KCl 1 M NaCl 0.1 M Tartaric acid 0.5 M NaCl 0.05 M Quinine 1 M Sucrose 02468 1012 Flow rate of saliva Different taste qualities induce different flow rates of saliva
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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"
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Neurotrophic Factors Neurotrophic Factors are endogenous, soluble proteins regulating survival, growth, morphological plastisity, or synthesis of proteins for different functions in neurons
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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.
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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
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The neurotrophic hypothesis
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Predictions of the neurotrophic hypothesis Target ablation / null mutation Increased target / overexpression
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synaptic plasticity Kang & Schuman (1995) Science 26, 1658-1662 differentiation controlGDNF Biological activities of neurotrophic factors neuron survival no factor GDNF neurite outgrowth no factor NGF
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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
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Specificity and promiscuity in the neurotrophin family TrkA TrkB TrkC p75 NTR NGF NT-4 BDNFNT-3
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GDNF RET GFR Specificity and promiscuity in the GDNF family NTN GFR -2 ART GFR -3 PSP GFR -4
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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
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