Behavioral Neuroscience, lecture on Leech and its behavior
USD Department of Biology
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
III. Sensory Stimulation of Shortening 			back to  Leeches and Behavior


	A. Sensory Neurons - all Somatosensory
	
		1. Respond specifically and selectively to mechanical stimuli
		
			a. clearly defined receptive fields 
			
				i. circumscribed region of skin responds only to stimuli  
		
			b. T/P/N - Touch, Pressure and Pain cells have similar morphological features
			
				i. Single process arises from cell body
			
					(1) large 1o branches pass through neuropil
				
						(a) leave the ganglion in peripheral nerve roots

					(1) 2o processes different among T/P/N
	
			
		2. Touch = T cell
		
			a. mechanosensory/stretch resceptors
			
				i. T/P not activated by temperature, acidity, or osmotic pressure
					
			b. responds to light or heavier touch
			
			c. simplest branching pattern
			
				i. short 2o branches 
				
				ii. don't cross midline of ganglion
			
			d. small - brief action potential
			
			e. glutamatergic = secrretes glutamate (Glu)
		
				i. AMPA and NMDA receptors (ionotropic)
				
		3. Pressure = P cell
		
			a. mechanosensory/stretch resceptors
			
			b. responds to heavier pressure
			
				i. not light touch
				
			c. intermediate branching
			
			d. bigger - longer action potentials
			
				i. than T
			
			e. Glu
			
				i. AMPA & NMDA
				
				ii. metabotropic (mGluR)
		
			
		4. Nociceptive (pain) neurons = N cell
			
			a. noxious mechanical stimulation of the skin
			
				i. require stronger mechanical stimuli
				
			b. elaborate branching
			
				i. several 2o branches 
				
				ii. extending on both sides of the ganglion
			
			c. larger longer action potentials (than T)
				
				i. large after hyperpolarization (undershoot)

			d. Glu
	
			
	B. Sensory pathway to Shortening Reflex
		
					
		1. Mechanosensory stimuli activates T/P/N 
		
			a. graded responses: T < P < N 
			
			
		2. T/P/N  S-cell
		
			a. T/P/N release  Glu
			
				i. Glu binds to S-cell AMPA and NMDA receptors
			
			b. S cell = interneuron
		
			
			c. + 2nd (unknown) intersegmental neural pathway
		
			
			d. these 2 intersegmental neural pathways extend 
			   from head ganglion along entire nerve 
	
			
		3. S  R
		
			a. R = Retzius cells are serotonergic cells
			
				i. serotonin = 5-HT 
				
					(1) monoamine transmitter
					
				ii. R = largest neurons in leech NS
				 
		4. S-cells  motor neurons (e.g. L-cells)
	

IV. Glutamate (Glu)

V. Serotonin (5-HT)

VI. S & R Sensitization