Behavioral Neuroscience Summers

text:The Basis of Neuropharmacology 8th Edition - Cooper, Bloom, Roth:read Rhythmicity & Behavior Sensory input for Rhythmicity Afferent path to the SCN Circadian Rhythms Efferent SCN output Integration of Rhythms into Behavior end     Acronyms/Abbreviations     Syllabus

Glu VIP AVP GABA 5-HT Figures of Rhythmicity Retina-RGC-SCN Molecular SCN

BIOLOGICAL RHYTHMS
IV. Afferent Path to the SCN 			

	A. Rods and Cones of the Retina become hyperpolarized by light
	    
		1. light ® unbending (11th C cis®trans) retinal in rhodopsin
	   
		2. transrhodopsin àñPDE àò cGMP
		
		3. 5'-GMP cannot bind to cyclic nucleotide-gated Na+ channels
		
		4. ò normal Na+ influx à hyperpolarization
		
		5. hyperpolar action potential stimulates retinal ganglia cells
	
	   
	B. Photosensitive Melanopsin and Crypotchrome in RGC also
	   stimulated by light 	    

		1. both retinal and RGC signals required
	
	
	C. a small bundle of fibers from RGC in the optic nerve innervates
	     ventrolateral region (core) of SCN

		1. retinohypothalamic tract
		
			a. first branch from optic nerve
		
		2. RHT terminals release Glu and PACAP
		
			a. ñCa++ àñCAM Kinase
			
			b. ñPKA àñpCREB

				i. ñkinases stimulate mPER1&2

				
	D. optic nerve also projects to the Intergeniculate Leaflet (IGL) of the
	   Lateral Geniculate Nucleus of the thalamus and superior colliculus
	   or optic tectum (homologues)

	   			
V. Suprachiasmatic Nucleus (SCN)

	A. 10,000 neurons in rat; 50,000 in humans
	
		1. small cells (8-12 mm)
		
		2. sparse dendritic arbors - remain mostly within SCN


	B. anterior border of the hypothalamus (just above the optic chiasm)

		1. core - ventrolateral - larger cells
		
			a. located directly above the optic chiasm

			b. receives 1o and 2o visual afferents

			c. contains neurons producing VIP and GRP
			
				i. colocalized with GABA

			d. optic nerve to IGL to SCN

				i. geniculohypothalamic tract (GHT)
				   returns information to SCN

					(1) GABA/NPY neurons

				ii. IGL/GHT integrates photic & nonphotic information

				iii. LGN also innevates the median/dorsal raphé
			  	     (d raphé innervates LGN)
				
				iv. paraventricular thalamus (PVT; also to shell)
				
			e. median raphé innervates SCN core

				i. secretes 5-HT binds 5-HT7

		2. shell- dorsomedial - smaller cells surround core
		
			a. receives input from nonvisual sources
			
				i. hypothalamus
				
				ii. retrochiasmatic area
				
				iii. limbic structures
				
				iv. brainstem and PVT

			b. SCN shell contains neurons secreting AVP and calretinin
			
				i. colocalized with GABA


		3. SCN efferent projections are topographically
		   organized by core and shell


	C. SCN cells are autogenic - spontaneous neural firing in vitro

		1. very low resting potentials (near threshold)

		2. cyclic firing activity

			a. single cell fires at 24h periodicity

			b. high (8-10 Hz) during the day, low (2-4 Hz) at night

				i. intracellular [Cl-] ñ during the day, ¯ at night

				ii. inhibitory and excitatory GABA