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
VIII.  Estrogens  

	A. 3 Kinds: E1, E2, E3
	
		1. plus phytoestrogens and environmental estrogens
		   (endocrine disruptors)

	B. Produced by the follicle cells of the ovary
	   (before luteinization) = E2 stimulated by LH

		1. P450aro = aromatase converts T

		2. and by brain and adipose tissue
		
		3. Carried in plasma by SBP and albumin
	
	
	C. Made by the feto-placental unit during pregnancy

		1. P from placenta

			a. converted to DHEA in fetal adrenal cortex
	
			b. DHEA to DHEA-S in the liver

		2. DHEAS to Estriol (E3) in the placenta

			a. maternal estrogen supply during pregnancy


	D. estrone (E1) is the primary estrogen during menopause


	E. Functions of Estrogens


		1. an estrogen is defined as
		   any hormone which will stimulate growth of the uterus

			a. endometrium during each menstrual/estrous cycle

			b. other 2o sex organs

		2. prepare mammary gland for lactogenesis

		3. modulate positive feedback for LH surge at ovulation


		4. modify sexual behavior

			a. stimulates lordosis

			b. converted from T masculinizes brain

				i. also necessary for male sexual behavior


		5. angiogenic and anabolic


	F.  Nuclear receptors E-Ra and E-Rb


		1. two of a superfamily of ligand activated transcription factors

			a. bind to E2, then homodimerize, and together they bind
			   the palindromic ERE (estrogen response element) of DNA
			
				i. ERE in promotor or enhancer regions
				
				ii. stimulate or inhibit estrogen responsive genes
				
					(1) e.g:a1 and M3 receptors
			   		    Oxy and Oxy-R, Enk and d receptors
			   		    GnRH and GnRH-R
				
			b. also neural membrane-bound E-R
			
				i. ERX= ER46- a truncated E-Ra variant

				ii. pER distinct from E-Ra and E-Rb
				
				
		2. E-R up-regulated by E; down-regulated by P or T


		3. E-Ra and E-Rb are  expressed in a similar brain distribution

			a. including: olfactory bulb, cerebral cortex, septum,
			   POA, BNST, amygdala, VMN, thalamus, VTA, substantia nigra,
			   dorsal raphe, locus coeruleus, and cerebellum

			b. E-Ra predominant in hippocampus, POA, and VMN
			
				i. E-Ra in VMN for lordosis
			
			c. E-Rb in cerebral cortex and cerebellum


	G.Positive Feedback


		1. females only (similar response in homosexual males)


			a. Hypothalamic APS = Anterior-Supraoptic
			   -Suprachiasmatic-Center

			b. regulated by positive count of plasma [E2] 

			c. [E2]threshold triggers GnRH release ®+ LH surge ®+ ovulation

				i. triggered via Glu/NE

				ii. timed/inhibited by b-endorphin

				iii. LH surge causes luteinization


	H. Luteinization


		1. LH stimulates changing the primary steroid pathway
		   from estrogen to progesterone production


			a. D5 to D4 pathway

			b. corpus luteum is the remainder of the follicle
							
				i. CL secretes more P than E2


		2. P rises just before ovulation
		
			a. P blocks 5-HT to promote lordosis
			
				i. sexual behavior occurs just prior to 
				   ovulation to ensure that fertilization 
				   occurs in the fallopian tubes