Behavioral Neuroscience Summers

Crayfish Escape Behavior Crayfish Neuroanatomy Fundamentals of Neurocircuitry Sensory Afferent input for Tail Flip

Gating the Full Flip Gating the Tail Flip for Upward Thrust Parallel Gating of Crayfish Escape Motor Neuron output for Crayfish Escape Integration: Crayfish Escape

Acetylcholine ACh GABA 5-HT

Crayfish figures Crayfish Escape Neurocircuitry end     Acronyms/Abbreviations

Escape - Crayfish
IX. g-aminobutyric Acid (GABA) 	

	A. NH2-CH2-CH2-CH2-COOH 

		1. formed from Glu by L-glutamic acid decarboxylase (GAD) 

			a. GABA shunt: bypass from Kreb's to provide glutamate 

			b. GABA catabolized by GABA-T
			  (GABA transaminase = a-ketoglutarate aminotransferase) 
			  
				i. NH3 to glutamate synthesis 

		2. inhibitory amino acid transmitter = inhibits firing of neurons 

	B. Receptors - 2 major types   

 		1. GABAA = ligand-gated Cl- channel 

			a. postsynaptic inhibition: hyperpolarizing
			   postsynaptic membrane
					
				i. influx of Cl- 

			b. GABAA on GABA neurons is functionally
			   presynaptic inhibition  

			c. 5 subunits - 2a + 2b + 1g  (usually) 

				i. a binds benzodiazepines (valium) 

				ii. b binds GABA

				iii. other sites near membrane bind barbiturates, anesthetics,
				     alcohols and H2O, neuroactive steroids; and
				     inside bind convulsants and picrotoxin 

				iv. extraordinary structural diversity: a1-6, b1-4, g1-3, d, e, q, r1-2 

					(1) yields functional diversity 

				v. superfamily of ligand gated channels including
				   nicotinic, 5-HT3, NMDA, AMPA, KA & glycine-R 

			b. GABAB 	(fewer) 

				i. often presynaptic

					1) G K+ ® open K+ or close Ca++ channels

						(a) autoreceptors inhibit GABA neurons
						    by hyperpolarization
						
					2) also Gi® X AC

				ii. sometimes postsynaptic 
				
					1) ­ phospholipase A2 ® ­ cAMP 


			c. GABAC in retina
	
				i. more sensitive Cl- channel


			d. GABA transporter (GABAT)


	C. GABA projections in vertebrates   

		1.  GABA interneurons in many brain regions
		   
			a. intrinsic neurons in cortex, hippocampus, cerebellum,
			   suprachiasmatic nucleus (SCN), olfactory bulb and retina... 

		2. projections from hypothalamus to cerebral cortex

			a. direct pathway for limbic, emotional, and visceral 
			   information to reach the cortex 

			b. IGL to SCN shell neurons colocalize NPY

		3. projections of striatum to substantia nigra

			a. regulate coordination of movement

	D. Crayfish GABA projections

		1. MGs, LGs, and SIs have GABA terminals
        
			a. regulate coordination of movement                

				i. through recurrent, Sensory, SI, MoG, and FF inihibition