Summers

Neurobiology Spring 2000 click here for text only acronyms

text: Fundamental Neuroscience - Zigmond, et al.,: Read pages 1256-1257, 1331-1333, 1379-1381, 1434-1437, 1465-1473 for this lecture end

XXXII. Limbic System and Hypothalamus (limbus = border)			back to XXXI. Reflexes
 

	A. Limbic system has multiple, distinct circuits


		1. separate, but overlapping functions


		2. limbic system plays a role processing olfactory information


			a. much emotional behavior, e.g. fear or sexual behavior, is strongly
			   affected by olfactory cues or pheromones


		3. limbic input in primates is dominated by connections with cortical
		   association areas


	B. circuits of the Hippocampal formation (subiculum, Ammon's horn [CA1-4],
	   dentate gyrus)


		1. input:


			a. limbic association corticies (cingulate, parahippocampal,
			     medial orbital [frontal] & temporal pole gyri): 


				i. PTO assoc + prefrontal assoc + 1o sensory ® limbic
				   association ® entorhinal cortex (part of parahippocampal
				   gyrus) ® hippocampal form.


					(1) integrated sensory information (multiple sensory modes)


						(a) complex (e.g. spatial) environmental features


							(i) learning setting  and/or  context


						(b) sensory modality preserved in amygdalar input 


			b. all major regulatory tranmitter systems project to hippocampus


				i. DA: from VTA via mesolimbic pathway 


				ii. NE: from LC 


				iii. 5-HT: from median raphe via median forebrain bundle


				iv. ACh: from basal and medial septal nuclei


			c. steroid input


				i. E2 important for learning


					(1) Glu/NMDA/Ca++/NOS/NO induced LTP is evident
					      in all hippocampal circuits


					(2) 5-HT can stimulate LTP,  E2 enhances 5-HT activity


				ii. B/F bind to G-R to cause negative feedback on PVN CRH secretion


		2. efferent pathway is the fornix


			a. pyramidal cells in CA + subiculum


				i. 2 output systems


					(1) both involved in cognitive aspects of learning and memory


			b. subiculum axons synapse in mammillary bodies of hypothalamus
			     + nucleus accumbens


				i. bidirectional connections

											               ­
				ii. subiculum ® mammillary ® thalamus ® cingulate « entorhinal « hippocampus
											               ¯

				iii. important role in memory


			c. CA1-4 axons synapse in septal nuclei (ACh and GABA)


				i. CA ® fornix ® septal nuclei ® fornix ® CA


					(1) consummatory behavior: e.g. reproduction, feeding


				ii. CA ® fornix ® septal n. + bed n. stria terminalis ®- PVN ® ¯ CRH


			d. dentate projects only within hippocampus


		3. consolidating short-term into long-term memory


			a. including spatial memory


		4. considerable overlap with amygdalar circuits


	C. Amygdalar circuits


		1. input: limbic association corticies & ACh, 5-HT, DA, NE systems


			a. sensory information is not integrated


				i. individual sensory information about  objects


			b. direct input from olfactory bulb


			c. amygdala (basolateral, central, corticomedial) uses objective
			   sensory information to organize responses


				i. preferentially involved in emotions & their behavioral expression


					(1) e.g. rage


		2. output pathways


			a. stria terminalis; bed nucleus of the stria terminalis


				i. corticomedial amygdala ® VMN hypothalamus


					(1) VMN mediates diverse appetitive behavior: eating, sex


					(2) corticomedial n. reciprocally connected to olfactory


						(a) involved in behavior stimulated by olfactory stimuli


			b. ventral amygdalofugal pathway


				i. basolateral amygdala ®amygdalofugal ® thalamic relay n ® cortex


					(1) basolateral largest; attach emotional significance to stimulus


						(a) 4 outputs: cortex (cingulate, temporal pole, m. orbitofrontal,
						      prefrontal, hippocampus), basal n. (of Meynert), 
							 thalamus, central nucleus of the amygdala (CeA)


				ii. CeA ® amygdalofugal ® NST/parabrachial/vagal (autonomic control)


					(1) CeA is key to mediating behavioral responses to emotion


					(2) CeA ® hypothalamus


			c. CeA CRF ® CeA GABA ® BNST & VMN


				i. amygdala stimulates PVN CRH secretion  

XXXIII. Neuroendocrine Modulation

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