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
XI. Sensitized Leech Shortening 			back to Neuromuscular Function

	A. Reflex Motor Shortening Circuit
	
		1. T/P/N sensory neurons È Glu release
			
			a. locally direct to L, VE, DE motor neurons
			
				i. AMPA/NMDA
		
		2. UI interneuron(s): AMPA/NMDA
			
			a. chain or long axon
				
		3. L, VE, DE motor neurons È ACh
				
		4. longitudinal, oblique, circumferential muscles
		
			a. Nicotinic Receptors
			
			b. whole body contraction
			
				i. requires UI chain/long axon

				
	B. Sensitized Motor Shortening Circuit
	
		1. Strong/Noxious stimulus
			
		2. TPN È Glu release
		
		3. S cell chain: AMPA/NMDA
		
			a. FCS electrical synapses Ü S cells in all ganlia
		
		4. S È Glu Ü AMPA/NMDA È R
		
			a. S È myomodulin È R
		
		5. P-cells polysynaptic on R-cells
		
			a.  mechanism of S È R-cell modulation
		
		6. di-synaptic link between S-cell and R-cell
		
			a.  first synapse = electrical junction with C-interneurons (coupling)	
			
				i.  high fidelity
				
			b.  second synapse = glutamatergic CÜR link
			
				i.  CNQX sensitive (6-cyano-7-nitroquinoxaline-2,3-dione)
				
					a.  AMPA/Kainate antagonist

					
		7.  R-cells È 5-HT Ü 5-HT7 back Ü S-cell 
			
			a.  GsÈACÈcAMPÈPKA
			
				i. PKA + Ca++ gated K+ ion channel
				
				ii. ò  S-cell AHP / Ê threshold / È firing rate
				
					(1) modulation of AHP È learning in vertebrates
					    and invertebrates
					
					(2) AHP dysfunction ó learning/memory deficits 

						(a) aging / age-related disease
						   (i.e. Alzheimer's)
				
				iii. 5-HT has negative feedback effect on R-cells: 5-HT1A?
	
				
			b. R È 5-HT Ü 5-HT7 TPN:UI synapse
	
			
			c. á S-cell activity  
				
				i. propagated down the S chain
				
				ii. propagated back to C and R cells  
	
					
		8.  Positive feedback loop
		
			a. Ý S   ó Ý R
		
			b. critical for full sensitization of shortening
			
				i. maintains ñ 5-HT levels

					
		9.  Ý excitability of L, VE, DE
		
			a. S È L/VE/DE
			
			b. R È TPN:UI È L/VE/DE
	
	
	C. Reactivated Sensitized Shortening
	
		1. lengthened leech ñ neutral / weak stimulus
		
			a. TPN È S   ó Ý R È TPN:UI È L/VE/DE
			
				i. S È L/VE/DE
		
			b. leech rapidly shortened
			
		2. S ablation Ê sensitization
		
			a. but... leech axons regenerate 
			
				i. sensitization returns 
				
				ii. recovery from neuronal injury 
				
					(1) in which a form of learning is lost
					    and then regained