Behavioral Neuroscience, lecture on Leech and its behavior
USD Department of Biology
Behavioral Neuroscience
Leech Shortening
Sensory Stimulation of Shortening
S&R Sensitization
Motor Efferents
Neuromuscular Function
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  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  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  Glu release
		3. S cell chain: AMPA/NMDA
			a. FCS electrical synapses  S cells in all ganlia
		4. S  Glu  AMPA/NMDA  R
			a. S  myomodulin  R
		5. P-cells polysynaptic on R-cells
			a.  mechanism of S  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 CR link
				i.  CNQX sensitive (6-cyano-7-nitroquinoxaline-2,3-dione)
					a.  AMPA/Kainate antagonist

		7.  R-cells  5-HT  5-HT7 back  S-cell 
			a.  GsACcAMPPKA
				i. PKA + Ca++ gated K+ ion channel
				ii.   S-cell AHP /  threshold /  firing rate
					(1) modulation of AHP  learning in vertebrates
					    and invertebrates
					(2) AHP dysfunction  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  5-HT  5-HT7 TPN:UI synapse
			c.  S-cell activity  
				i. propagated down the S chain
				ii. propagated back to C and R cells  
		8.  Positive feedback loop
			a.  S     R
			b. critical for full sensitization of shortening
				i. maintains  5-HT levels

		9.   excitability of L, VE, DE
			a. S  L/VE/DE
			b. R  TPN:UI  L/VE/DE
	C. Reactivated Sensitized Shortening
		1. lengthened leech  neutral / weak stimulus
			a. TPN  S     R  TPN:UI  L/VE/DE
				i. S  L/VE/DE
			b. leech rapidly shortened
		2. S ablation  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