Behavioral Neuroscience Summers

Leech Shortening Sensory Stimulation of Shortening S&R Sensitization Learning Motor Efferents Neuromuscular Function Integration

Glu 5-HT ACh Leech figures Shortening Neurocircuitry end     Acronyms/Abbreviations

Sensitization - Leech
VIII. Motor Stimulation of Shortening 			back to  S-R Sensitization
	
	A. Motor Neurons
	
		1. 34 neurons in the ganglion that are recognized as motor neurons
		
			a. 28 (14 pairs) excitatory motor neurons
			
				i. Cholinergic = secrete acetylcholine (ACh)
				
					(1) binds to Nicotinic receptors
			
			b. 6 (3 pairs) of inhibitory motor neurons
			
				i. GABAergic? Glycine?
				
			c. 30/34 motor neurons located on dorsal ganglion surface 
			
				i. AE and HE on ventral surface
				
					(1) each ganglion
			
		2. Innervate 5 groups of muscle 
		    in each segment responsible for leech movement
			
			a. Body wall muscle: 3 layers
			
				i. outermost: circumferential
				 
				ii. middle layer: oblique
				
				iii. innermost = longitudinal: thickest
			
			b. 4th group: erection of the skin of each annulus
			
			c. Flattener muscles = 5th group
			
			d. connective nerve sheath contains muscle fibers
			
		3. ventral annulus erector (AE) neurons innervate 4th muscle group
		
			a. Mechanical skin stimulation à erects skin ring 
			
				i. monosynaptic pathway: TPN à AE neurons
				
				ii. each segment is made up of 5 annuli (rings) 
				
		4. Flattener motor neurons 
		
			a. innervate dorsoventral 5th muscle group
			
			b. flatten the leech when contracted
			
		5. ventral Heart Excitor (HE) cells
				
			a. each ganglion
				
			b. Innervate muscles of the heart tube
			
		6. L, VE, DE
				
			a. L cells are important motor neurons   
				
				i. for longitudinal muscle
				
					a. discrete bands of fibers 
					   separated by connective tissue
			
			b. VE = ventral excitatory; DE = dorsal excitatory neurons
			
				i. labeled as numbers in ganglion map
				
				ii. stimulate muscle contraction during shortening
			
			c. Numerous motor neurons elicit the longitudinal muscle layer
			     to induce swimming
			
			d. Shortening is a reflex
					
				i. Monosynaptic pathway exists
	
			
	B. Simplest Motor Circuit = monosynaptic
	
		1. T/P/N à L/VE/DE
		
			a. Glu à AMPA/NMDA
			
			b. direct local circuit
			
				i. mechanosensory neurons to motor neurons
				
					(1) no interneurons
			
			c. only localized shortening
			
				 i. not a full defensive shortening response
				 
				 	(1) not the entire body			
	
	C. Full Shortening Simple Motor Circuit
	
		1. T/P/N à interneuron
		
			a. this interneuron is Unknown (UI)
			
			b. still must be Glu à AMPA/NMDA
		
		2. UI necessary for full body shortening
		
			a. might be:
			
				i. one cell with long axons
				
				ii. chain of UI cells
				
					(1) 1/ganglion
					
					(2) unlikely to be electrical synapses
					
						(a) es: unmodifiable response 
		
		3. UI È L/VE/DE motor neurons
		
			a. L È longitudinal muscle contraction
			
				i. L È ACh release È Nicotinic R Èmuscle contraction
				
				ii. intersegmental interneuron pathways 
				   ensure whole-body shortening
			
			b. L/VE/DE motor neurons control the shortening tension
		
		4. \Sensory neuronsÈ interneuronal pathways È motor neurons à
		      È longitudinal muscles È shortening reflex
		
			a. S cell ativity unnecessary for normal whole-body shortening 
			
				i. but S cell corresponds with L motor neuron output
				
					(1) during Sensitization