Behavioral Neuroscience Summers

Rhythmicity & Behavior Sensory input for Rhythmicity Afferent path to the SCN Circadian Rhythms

Efferent SCN output Integration of Rhythms into Behavior Glu

VIP AVP GABA 5-HT

Figures of Rhythmicity Retina-RGC-SCN Molecular SCN end  Acronyms/Abbreviations   Syllabus

BIOLOGICAL RHYTHMS
XI. Efferent Circadian Output 			

			
	A. 3 Major paths for SCN efferents 
	
		1. Within SCN: between core and shell
		
			a. VIPcore® AVPshell; AVPshell ® VIPcore
		
		2. To and Through the SPVZ
		
			a. Anterior Hypothalamic Subparaventritcular Zone
		
			b. SPVZ is dorsal & caudal to SCN
			
				i. SCN shell projects to medial SPVZ
				
				ii. SCN core projects to lateral SPVZ
			
		3. To and Through the RCA
		
			a. Anterior Hypothalamic Retrochiasmatic Area
			
			b. RCA is dorsal & rostral to SCN
			
				i. reciprocal innervation
	
	B. Reciprocal innervation of SCN core and shell establishes the biological clock
	
	C. SPVZ
	
		1. Shell Fibers
		
			a. extend caudally to DMH
			
				i.part of sleep/wake regulatory centers
				
				ii. secrete clock gene controlled neuropeptides 
			   	(their receptors also clock gene controlled)
				
					1)VIP, cardiotrophin-like cytokine and prokineticin 2
			
			b. AVP projections to the PVN
		   
		   		i. confer circadian electrical activity in PVN
				
					1) Glu & GABA connections also important
			
				ii. PVN regulates Neuroendocrine and Autonomic Functions
				
					1) also Tob, behavioral state, and Pineal Melatonin
						
			c. two paths to the Habenula and Pineal Gland  

				i. via Hypothalamus/Habenula & Pineal
				
				ii. via median forebrain bundle ® NST ® Spinal Cord Lateral Horn (sympathetic)
				     NST ® SCLH ® superior cervical ganglion; SCG ® Pineal
					
					1) LH ® ACh Nicotinic-R on SCG
					
					2) SCG ® NE b2-R on Pineal

				iii. mammalian pineal has intrinsic rhythms, 
					 also clearly driven by SCN

				iv. pineal produces melatonin from 5-HT during darkness 
			   	    to regulate organismal rhythms and facilitate sleep

					1) melatonin phase-shifts SCN = feedback

					2) may coordinate rhythms longer than 1 day

						a) e.g. estrous/menstrual and
					    	circannual reproductive cycles

				iii. parietal eye (sharks, frogs, lizards) connects to
				     pineal, and photoreceptive pineal (birds):
				     Link pineal to environment

					1) Pineal is the primary clock in some animals 
	
			d. to BNST (bed nucleus of the stria terminalis) - anxiety and reproduction
			
			e. to Paraventricular Thalamus

				i. PVT projects rostrally to septum, amygdala, 
		   		   hippocampus, and cingulate cortex
		   
		   			1) circadian influence on memory, 
			   		   autonomic function, and affective tone

			   
				ii. PVT also projects to the Nucleus Accumbens
		
					1) applies circadian influence on motor integration 
			   		    and reinforcement/reward mechanisms
			
		2. Core projections
		
			a. to ventral tuberal area (between VMN & ARC), 
			
			b. PH
			
			c. lateral septum
			
			d. Periacqueductal Gray (PAG; MCG)
		
	D. RCA
	
		1. Shell projections
		
			a. small group of fibers anterior to AH and mPOA
		
				i. POA also part of sleep/wake regulatory centers
			
				ii. clock controlled VIP, 
				    cardiotrophin-like cytokine and prokineticin 2
		 			
		2. Core projections
		
			a. to Basal Forebrain
			
				i. integrates circadian information with Behavioral State
				   & Neocortical function
				
			b. to hypothalamus
			
			c. IGL
			
				i. indirectly (via RCA) innervates IGL
			
			d. brainstem, spinal cord
				
				ii. SCN/RCA/brainstem - circadian autonomic regulation
				
				iii. SCN/RCA/spinal cord - circadian sensorimotor integration
			
			e. projections overlap with those through SPVZ
				
	E. Projects both Stimulatory and Inhibitory output
		
		1. Excitatory signals produced by Glu binding AMPA and NMDA receptors
			
			a. Also AVP (V1A) and VIP (VPAC2) outputs
			
		2. Inhibition via GABA through GABAA receptors
		
	F. IGL 
	
		1. Optic nerve projections to the Lateral Geniculate Nucleus
		
			a. SCN ® RCA ® IGL
	   
		2. IGL has projections to  midline thalamus, zona incerta,
		   pretectal area / superior colliculus or optic tetum and back to SCN

			a. SCN/IGL/midline thalamic nuclei - influence circadian
			   regulation of behavioral state

			b. SCN/IGL/subthalamic zona incerta - regulates circadian
			   motor integration
			   
			c. SCN/IGL/tectal zones - circadian visual functioning
			
		3. IGL also innevates the median/dorsal raphé
		   (d. raphé innervates LGN)

			a. mRaphé innervates SCN - 5-HT phase shifts rhythm

	G. Redundancy
	
		1. Multiple and Feedback inputs to control circadian rhythmicity
		   in various functions

		2. Rhythms of Autonomic Output through SCN/hypothalamus,
		   SCN/PVT/limbic and SCN/RCA/brainstem projections
		   
		3. Motor rhythyms integrated via SCN/PVT/NAcc, SCN/RCA/spinal cord
		   and SCN/RCA/IGL/zona incerta projections
		   
		4. Wake/Sleep/Activity Rhythms synergistically 
		   influenced by at least 3 systems:
		   
		   	a. SCN through SPVZ to Hypothalamus
			
			b. SCN to RCA to Basal Forebrain
			
			c. SCN to IGL to midline thalamus