Behavioral Neuroscience, lecture on gating and learning in Aplysia
USD Department of Biology
Behavioral Neuroscience
Summers
Aplysia Behavior
Sensory Stimulation of Siphon Withdrawl
Motor Output driving Siphon Withdrawal
Gating
Conditioning & Memory
text:Kandel pages 1248-1257
Glu
5-HT
Aplysia and Siphon Withdrawl
Siphon Withdrawl Circuitry
end     Acronyms/Abbreviations     Syllabus
Siphon Withdrawal
VI. Gating 			

	A. Behavioral circuitry is completed, enhanced or limited
	
		1. Via Interneuron neurochemical modification 
		
			a. often with neuromodulators or receptors
			
			b. or hormones
			
		2. sensitization may be required for a circuit to be complete
			
			a. priming
				
				i. gradient vs threshold 
	
			
	B. Output of behavioral circuitry is modified
		
		1. altered, repeated, delayed, sped up
			
			a. may require additional circuitry
				
				i. interneurons
					
				ii. brain/ganglia
	
			b. temporal/spatial summation of sensory/interneuron
			   synaptic potentials
			   
			   	i. cause motor cells to discharge repeatedly
			
		2. Learning
		
			a. synaptic plasticity
			
				i. formation of new synapses
				
				ii. strengthening synaptic connections
				
					(1) unsilencing synapses
					
						(a) adding AMPA to 
						     NMDA-only synapses
						
					(2) increasing(a)/decreasing(b) synaptic current
					
						(a) LTP long-term potentiation 
						    or LTS long-term sensitization
						
						(b) LTD long-term depression
	
	
	C. Elementary forms of learning: 
	    habituation, sensitization, classical conditioning
	   
	   	1. Habituation = simplest form of implicit learning
		
			a. novel stimulus
			
				i. initial response = attention, orientation toward
			
			b. repeated exposure
			
				i. if neither harmful nor beneficial
				
			c. it is ignored = habituation
			
			d. habituation leads to decrease in the stregth of the synaptic 
			    connections between excitatory interneurons and motor neurons
	
		
		2. repeated stimulation of gill or tail results in habituation of Aplysia
		   withdrawal reflexes
		   
		   	a. progressively smaller excitatory synaptic 
			    potentials in interneurons/motor neurons
				
				i. due to a ß number of Glu vesicles released
				   from presynaptic sensory neurons
				   
				   	(1) no D in AMPA or NMDA receptors
					
			b. cellular mechanism for learning short-term memory
			
				i. 1 session = 10 tactile stimuli to siphon
				
				Þ habituation for minutes
				
				ii. naive Aplysia 90% of sensory neurons synapse
				     on gill motor neurons
				
					(1) \ monosynaptic plasticity
			
			c. long-term memory
			
				i. 4 sessions Þ habituation for 3 wks
			
		3. Enhancement of synaptic inhibition could also contribute to habituation
		
			a. inhibitory interneurons
			
				i. with long-term habituation in Aplysia only 30% 
				   of sensory neurons synapse on gill motor neurons
	
		4. Not all synapses are equally adaptable
		
			
	D. Elementary Learning: Sensitization
	
		1. harmful stimulus Þ more vigorous response
		
		2. short term sensitization
		
			a. single shock to Aplysia tail Þ Ý excitatory sensory output
			   lasting minutes
			
			b. heterosynaptic process 
			
				i. 5-HT interneuron increases presynaptic 
				   Glu output of sensory terminal
			
			c. 5-HT Synapse on Sensory boutonheterosynaptic interactionpresynaptic 5-HT
			
				i. action of 5-HT terminal has direct immediate effect 
				    on Glu Sensory-Motor synapse
			
			d. 5-HT binds to 2 kinds of 5-HT receptors
			
				i. 5-HT2-like receptors Þ Ý Gp Þ Ý PLC Þ Ý IP3/DG Þ 
				   Ý PKC + Ca++ 

				ii. 5-HT4/6/7-like receptors Þ Ý Gs Þ Ý AC Þ Ý cAMP Þ 
				     Ý PKA
			
			e. Ý PKA Þ ß K+ channel current
			
				i. Ý Ca++ influx
			
			f. Ý PKA + PKC + Ca++ release Glu vesicles from pool
			
				i. enhance binding at active zones
				
			g. \Ý Glu stimulated postsynaptic current
	
			  
		3. long-term sensitization (LTS is similar to LTP)
		
			a. 5 shocks Þ Ý excitatory current
			   lasting days to weeks
			   
			b. persistent 5-HT4/6/7-like activation of cAMP/PKA
			
				i. PKA activates CREB cAMP Response Element Binding Protein 
				
				ii. CREB binds CRE on DNA
				
				iii. new proteins and long-term memory   
	
			   
	E. Classical Conditioning	
	
		1. learning by associating one type of stimulus with another
		
		2. pairing an non-salient stimulus with salient stimulus
		
			a. salient stimulus directly causes a behavior
			
			b. non-salient stimulus associated with the salient stimulus
			   indirectly elicits behavior

VII. Serotonin (5-HT)

VIII. Classical Conditioning and Long-Term Memory