Behavioral Neuroscience Summers

Sexual Behavior Reflexes Sensory Reception - Tactile Receptors Spinal Synapses Afferent Spinal Pathways

Hypothalamic Gating Efferent Motor Cascade Neuromuscular Production of Lordosis Integrated Story of Lordosis VIP Substance P Estrogens

5-HT GnRH ACh Lordosis figures   Sensory Receptors Spinal Cord   Lordosis Circuitry end     Acronyms/Abbreviations

LORDOSIS
XI.  Hypothalamic Gating    

	A. Activating the ventromedial nucleus of the Hypothalamus (VMN)
	
	
		1. necessary for behavior
					
			a. = Gating
			
			
				i. active VMN allows the response
				
				
				ii. inhibited VMN blocks lordosis
		
		
		2. switches on the efferent circuit
		
		
		3. modified by input from other systems (upstream)
		

	B. E2 primes neurons of the  hypothalamus = VMN to MCG/PAG

		1. binds to ERa and stimulates
		   transcription via the ERE (estrogen response element)

			a. induces P receptors
			
				i. longer priming is better
				
				ii. 2 or more pulses of E2 is equivalent
				    to longer priming

			b. also upregulates a1 and M3 receptors
			   OT and OT-R, Enk and opioid d receptors
			   ñ axon terminal [GnRH] and [GnRH-R]

			c. mPOA, CeA, hippocampus and midbrain central gray
			   also concentrate E2


		2. raises the level of tonic activity

			a. threshold facilitation necessary


	C. E2 is followed by a short burst of P prior to lordosis


		1. P: fast response - intracellular and membranal receptors
		
			a. temporal order and pulsatile P is critical
			
			b. synchronizes lordosis behavior with ovulation
			
				i. shows the same E2+P combinatorial effects
				
				ii. E2 primes pituitary for LH release
				
				iii. P stimulates LH release

				
			c. E2 followed by long-term P inhibits lordosis
			
				i. also inhibits LH release
				
				ii. as during pregnancy

			
		2. P inhibits 5-HT

			a. 5-HT tonically inhibits behavior
			
				i. 5-HT from median raphé

			b. P disinhibits system


	D. 4 kinds of cells in VMH signal MCG
	
		1. large excitatory input from VMH to MCG
		
			a. 2 routes
		
		2. sweeping route through supraoptic commissure
		
			a. SP binding NK1-R
			
			b. PrL
			
			c. HIP 70 or EI70

		3. GnRH neurons from VMH inntervate MCG via
		   a medial periventricular route
		   
		4. potentiate neurons of the MCG 

			a. threshold facilitation necessary


	E. 7 kinds of neurons modulate activity of
	   excitatory VMH signals to MCG
	   
	   	1. Inhibition is 1o and must be overcome 
		   for Lordosis to take place
		   
		   	a. 5-HT
			
				i. 5-HT1A: Gi
				
				ii. 5-HT2A/C stimulate lordosis
				
					(1) acting in POA (rather than VMN)
				
				iii. 5-HT inhibited by GABA
			
			b. b-End
			
				i. m opioid R: Gi

			
		2. Stimulatory input functions following E2 priming
		   of excitatory output neurons
		
			a. NE
			
				i. a1b receptors
				
					(1) Gp(q)àñPLCàñIP3 ÈCa++ & DG È PKC
					
					(2) Ca++ influx produces potentiation
			
			b. ACh
			
				i. muscarinic M3 R Gp(q)àñPLCàñIP3 ÈCa++ & DG/PKC
			
			c. OT
			
				i. OT-R Gp(q)àñPLCàñIP3 ÈCa++ & DG/PKC

			d. Enk
			
				i. d opioid R: Gi, K+ channel?

			e. GABA via inhibiting 5-HT
			
				i. GABAA Cl- channels

				ii. GABAB Ca++ channel blocker
				    regulates GABA release in VMN


	F. accessory olfactory (vomeronasal) information potentiates E2/P effects


		1. olfactory/accessory olfactory neurons secrete GnRH


			a. hypothalamic GnRH develops ontogenetically from olfactory tissue 


		2. visual input, e.g. presence of the male, also facilitates response 


	G. Sensory information is integrated by the limbic system


		1. modular sensory information from association cortices to amygdala

			a. olfactory & cortex « corticomedial amygdala ®  BNST ® VMN

				i. recognize male scent and respond


			b. CeA ® VMN

				i. CeA has ERa

				ii. CeA mediates action of behavioral response

					(1) stress ® corticosterone (B) È 5-HT release

						(a) 5-HT inhibits behavior
						
						(b) CRF or ACTH will also inhibit behavior


					(2) P + B È 5-HT


						(a) stronger inhibition timed for the short period when
						    P normally disinhibits behavior


		2. integrated sensory information from association corticies to hippocampus


			a. CA1-4 ® learning appropriate environmental
			   context for sexual behavior


				i. appropriate context stimulates behavior

				ii. inappropriate context should block behavior


		3. temporal lobe analyzes sexual goal objects
		
		4. prefrontal cortex is important for performance of sexual patterns
		
			a. pacing

		
	H. Preoptic Area
	
		1. medial portion = mPOA facilitates lordosis
		
			a. also E2 sensitive
		
		2. POA enhances E2 production
		
			a. contains GnRH cells
		
		3. foster locomotion, approach and courtship behaviors
		
			a. lordosis requires the sudden cessation of
			   rapid POA-dependent locomotion
			   
			b. POA innervates ventral tegmental area (VTA)
			
				i. VTA disrupts lordosis
				
					(1) not a dopamine (DA) effect
					
					(2) VTA innervates MCG (ventral part)
					    and disruption occurs through this
						connection

				ii. POA ®VTA
				    disrupts lordosis

				iii. ACh fibers from septum pass through POA
			
			c. E2 diminishes excitability of POA
			
			d. Another disinhibition, this time by 
			   E2 on POA and VTA
		

	I. VMH stimulates MCG which stimulates medullary reticular formation