Behavioral Neuroscience, lecture on Acetylcholine
USD Department of Biology
Behavioral Neuroscience
Summers
C-Start Behavior
Fundamentals of Neurocircuitry
Senstory Stimulus for Startle
Mauthner Cells - Response Gating
Mauthner Efferent output
Neuromuscular Function
Integration of C-Start Circuitry and Behavior
Glu
DA
ACh
Transmitter Figures
Figures of C-Start Behavior
C-Start Circuitry
Acronyms/Abbreviations
end
Fish Escape Behavior
IX.  Acetylcholine (ACh)  
                                   O
		        I I
(CH3)3N+-CH2-CH2-O-C-CH3
	A. substrates: choline and acetyl CoA
	                 (diet)     (Glycolysis and Kreb's)
		        
		1. synthetic enzyme: choline acetyltransferase (CAT)

			a. cytosolic   (most is synaptic)

			b. CoA left over


		2. degradative enzyme: acetylcholine esterase (AChE)

			a. membrane protein

			b. catabolites = choline and acetate
			
				i. reuptake of choline

			c. turnover = 150ms	or	5,000 ACh molecules/s

			
	B. Muscarinic and Nicotinic Receptors 	(membrane proteins)


		1. muscarinic M1 - M5    7tm

			a. slow response time (100 - 250 ms)

			
			b. act directly on ion channels 	

				i. open or close K+, Ca++, or Cl- channels

					(1) may lead to depolarization 
					   or hyperpolarization

					   
			c. and activate 2nd messenger system (via G proteins)
							     DAGPKC
				i. M1,3,5 Gp(q)PLCPIP2IP3 & Ca++

				ii. M2,4 GiACcAMP  PKA


		2. Nicotinic

			a. made up of 5 subunits, from these a, b, g, d, e
            
				i. four glycosylated peptide chains a, b, g, d in muscle
	
				ii. neuronal only a & b

			
			b. ACh binds to the a subunit

				i. binding causes conformational change

					1) allows cations, not anions, to pass
                    
						a) Na+ pases first, 
							depolarizing muscle cell membrane

					2) deporlarization  Ca++ release
						from SR stimulates contraction of
						trunk, fin, oculomotor, jaw & opercular musculature
						 
	C. Central ACh Distribution in vertebrates: Involved in Learning
	
		1. ACh is produced in the nucleus basalis 

			a. projections to the cerebral cortex and many parts of the brain

			b. these cells degenerate during Alzheimer's disease

			
		2. ACh is in 2 specific populations in the limbic system

			a. septum to hippocampus  & habenulo-endopeduncular projections

			b. short axon striatal cells
	
	D. Autonomic NS
	
		1. all sympathetic and parasympathetic preganglionic neurons

		2. parasympathetic postganglionic neurons

	
	
	E. ACh as a transmitter for motor actions and coordination
	
		1. motor neurons 
		\ all skeletal neuromuscular junctions
		
			a. Invertebrate motor neurons
			
			b. Vertebrate motoneurons of spinal cord & cranial nerves (I-XII)
			
				i. abducens (VI) innervation of the eye
                
				ii. trigeminal (V) innervation of the operculum
			
		2. Cells in the caudate-putamen nucleus involved in motor coordination 
		
		3. PPT (pedunculopontine tegmental nucleus) and LDT (laterodorsal tegmental nucleus)
			innervation of substantia nigra

X. Neuromuscular Function