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
VIII. Conditioning & Memory 			

	A. Classical/Pavlovian Conditioning	
	
		1. salient stimulus (US = unconditioned stimulus) 
		    elicits behavior (UR = unconditioned response)
		
			a. bring food (US) to dog Þ salivation (UR)
			
			b. shock (US) to aplysia tail Þ gill retraction (UR)

		
		2. pairing with a non-salient stimulus (CS = conditioned stimulus)
		    results in associative learning
		   
			a. conditioning is more complex than sensitization
			
				i. association of 2 stimuli
		   
			b. repeatedly ring a bell (CS) just before bringing food US
		   
				i. bell (CS) alone will elicit salivation (CR = conditioned response)
	
		   
			c. touch siphon or mantle shelf with tail shock
			
				i. US alone = shock causes strong gill retraction 
				
				ii. CS alone = touching siphon causes weak gill retraction
	
				
				iii. training = CS + US (shock + touching siphon)
				
				iv. following pairing:
				    CS alone = touching siphon causes strong gill retraction
		   

		3. Timing is critical 
		
			a. CS must precede the US
			
				i. within an interval of 0.5 s

			
			b. CS precedes but slightly overlaps US = delay conditioning
	
			
			c. CS first, time gap, then US = trace conditioning
			
			
		4. US activates facilitating interneurons
		
			a. with delay training the modulatory interneurons
			    are engaged immediately after the CS
			
			b. activity dependent - facilitation during CS + US pairing Þ
			   Þ facilitation with CS alone
	
					
				i. presynaptic mechanisms - synergy at Adenylate Cyclase (AC)
				
					(1) activity in CS Glu neuron causes Ca++ influx
				
					(2) Ca++ + calmodulin binds to AC
					
					(3) potentiates 5-HT4,6,7-like production of cAMP
					
						(a) Tail shock (US) stimlates 5-HT interneurons
						    that impinge on CS siphon/mantle neurons
	
					
					(4) stimulation of siphon/mantle now reactivate
					     5-HT modulation on siphon/mantle sensory output
					
						(a) AC = coincidence detector
						
							(i) responds to both CS and US 
	
				
				ii. postsynaptic - retrograde signal
				
					(1) during sensitization Glu binds AMPA-R on motor neuron
					
						(a) not enough depolarization
						    to remove Mg++ from NMDA-R
					
					(2) paired CS + US Ý depolarization Þ
					     Þ expels Mg++ Þ Ca++ influx
		
		 			(3) train of action potenitals in the motor neuron
					
					(4) Ca++ Þ Ý retrograde signal
					
						(a) Aplysia have synthetic/degradative pathways
						    for NO (nitric oxide)
						
						(b) Ca++ Þ Ý NOS (NO synthase)
						
						(c) NOS coverts Arg Þ Cit:  NO given off
						
						(d) NO is a gas \ a retrograde signaler
						
						(e) NO binds heme group of GC activates cGMP
						
							(i) cGMP facilitates both transmitter release
							     and learning
							
							(ii) is NO the retrograde signal?
	
						
	B. Operant-Reward Conditioning
	
		1. similar to classical conditioning except
		
			a. a behavior replaces the CS
			
				i. e.g. dog steps on pedal to get food
				
					(1) both pedal or bell would stimulate salivation
					
					 	(a) also called instrumental conditioning 
		
		2. Aplysia operant behavior is biting
		
			a. esophageal nerve activated when random biting 
			    and swallowing seaweed are successful
			
				i.reward signal = dopamine (DA)
				
					(1) DA is also the salient neurotransmitter in the
					     nucleus accumbens vertebrate reward system
			
			b. no esophageal nerve signal on "empty" bite
		
		3. Virtual reward = stimulation of esophageal nerve
		
			a. operant training = virtural reward paired with random biting
			
		4. CR = increased spontaneous biting
	
	
	C. Long-Term Memory
	
		1. Übung macth den Meister (Practice makes perfect)
		
			a. repeated experience consolidates memory
			
				i. converting short-term into longer term memory
				
				ii. independent but overlapping processes

				
		2. First: Sensitization, via 5-HT, enhances release of transmitter (Glu)
		
			a. through 5-HT4,6,7 receptors activtate cAMP + PKA
	
			
		3. Then: Consolidation involves: 
		
			a. gene expression
			
			b. new protein synthesis
			
			c. growth or pruning of synaptic connections
			
		4. 5-HT4,6,7 Þ Ý PKA Þ Ý MAP Kinase 

			a. PKA + MAP K Þ nucleus
			
			b. PKA phosphoylates CREB1 (transcription factor)
			
				i. MAP K removes CREB2 inhibition from CREB1
	
			
			c. CREB1 binds to CRE (cAMP response element)
			
				i. CRE in promotor or enhancer of cAMP inducible genes
	
			
			d. CREB/CRE stimulates ubiquitin carboxythermal hydrolyase gene
			
			e. ubiquitin hydrolyase cleaves the inhibitory regulatory subunit of PKA
			
				i. \ persisent PKA activity
				
				ii. \ persistent sensitization
	
				
			f. CREB/CRE also stimulates another important transcription factor
			    via the C/EBP gene
			
				i. C/EBP binds to the CAAT box at the promotor/gene junction
				    of many genes associated with growth
				
					(1) transcription of growth-related proteins
				
				ii. new synapses ar formed
	
			
	D. \ LTS and Conditioning in Aplysia 
	      are reinforced / consolidated by
	
		1. presynaptic synergy at AC
		
			a. greater effect of 5-HT
			
				i. more Glu release
		
		2. postsynaptic recruitment of NMDA-R current
		    and retrograde messenger release
		
		3. retrograde facilitation of presynaptic release
		
			a. more Glu release
		
		4. repeated 5-HT (interval important) stimulates gene expression
		
			a. persistent PKA
			
				i. greater effect of 5-HT
				
					(1) more Glu release
		
			b. new growth proteins
		
		5. growth proteins Þ new synapses
		
			a. more sites for Glu release

Syllabus