Behavioral Neuroscience, lecture on GABA inhibition
USD Department of Biology
Behavioral Neuroscience
Rusty Crayfish 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
Crayfish figures
Crayfish Escape Neurocircuitry
end     Acronyms/Abbreviations
Escape - Crayfish
IX. g-aminobutyric Acid (GABA) 	

	A. NH2-CH2-CH2-CH2-COOH GABA the inhibitory transmitter

		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

X. Non-Giants and Parallel Advantage