Aplysia Learning 2010

Aplysia Learning 2010 - Defini,on of learning Innate...

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Unformatted text preview: 4/5/10 Defini,on of learning Innate Behavior is gene,cally encoded, not requiring learning. Permanent, unmodifiable. Learned Behavior is either acquired de novo by experience, or modified by experience. N. Tinbergen Defini,on of learning LEARNING A change in animal behavior as a consequence of behavioral experience MEMORY The informa,on that is stored during learning. It can either be conscious (can be recalled) or nonconscious (can’t be recalled, but contributes to altera,ons in future behavior Memory can also be categorized by its dura,on. In humans, short ­term memory lasts minutes ­hours. Long ­term memory lasts days ­weeks ­life,me. 1 4/5/10 Learning in the Aplysia gill withdrawal reflex Eric Kandel Nobel Prize 2000 Learning in the Aplysia gill withdrawal reflex Gill withdrawal reflex 2 4/5/10 Learning in the Aplysia gill withdrawal reflex [email protected] Ubiquitous form of learning involving gradual reduc,on and cessa,on of s,mulus ­evoked reflex response with repeated s,mulus presenta,on [email protected]@on Enhancement of s,mulus ­evoked reflex response aWer the animal is startled by some other strong s,mulus Both can have either short, intermediate, and long [email protected], determined by number and spacing of [email protected] Learning in the Aplysia gill withdrawal reflex [email protected] Ubiquitous form of learning involving gradual reduc,on and cessa,on of s,mulus ­evoked reflex response with repeated s,mulus presenta,on [email protected]@on Enhancement of s,mulus ­evoked reflex response aWer the animal is startled by some other strong s,mulus short ­term habitua,on and recovery intermediate ­ or long ­term habitua,on Both can have either long, intermediate, and short [email protected], determined by number and spacing of [email protected] 3 4/5/10 Neural basis for short ­term habitua,on Short ­term habitua,on occurs because of [email protected] depression (a reduc,on in synapse strength) at the sensory neuron motor neuron synapse Neural basis for short ­term habitua,on Short ­term habitua,on mechanism: decrease in presynap,c vesicle release Covalent modifica,on of exis,ng proteins (phospho ­ ryla,on) Long ­term habitua,on: structural remodeling and synapse removal Degrada,on and synthesis of proteins; protein transla,on is required Bailey & Chen, 1984 4 4/5/10 Neural basis for short ­term habitua,on Intermediate ­ and long ­term habitua,on also involve a dis,nct postsynap,c weakening process Long ­term poten,a,on (LTP) Long ­term depression (LTD) Ezzeddine & Glanzman 2003 Neural basis for sensi,za,on Sensi,za,on is due to [email protected] [email protected] at the sensory neuron ­motor neuron synapse. 5 4/5/10 Neural basis for sensi,za,on Serotonin (5 ­HT), released by facilitatory interneurons, is the key trigger for sensi,za,on Applica,on of 5 ­HT in a reduced prepara,on mimics sensi,za,on. Neural basis for sensi,za,on Short ­term [email protected]@on occurs when 5 ­HT receptors ac,vate cAMP ­dependent kinase (PKA), which phosphorylates K+ channels. This closes channels and increases excitability of the sensory neuron presynap,c terminal. Covalent modifica,on of exis,ng proteins (by phosphoryla,on) 6 4/5/10 Neural basis for sensi,za,on Long ­term [email protected]@on occurs when mul,ple pulses of 5 ­HT cause sustained PKA ac,va,on. PKA migrates to the nucleus, where it ac,vates CREB. CREB drives gene transcrip,on that leads to synapse growth and structural change. CREB transcrip,on factors regulate gene expression for long ­term plas,city Neural basis for sensi,za,on Long ­term [email protected]@on occurs when mul,ple pulses of 5 ­HT cause sustained PKA ac,va,on. PKA migrates to the nucleus, where it ac,vates CREB. CREB drives gene transcrip,on that leads to synapse growth and structural change. 7 4/5/10 Neural basis for sensi,za,on Intermediate ­and long ­ term [email protected]@on also involve postsynap,c strengthening, triggered by postsynap,c calcium. This includes inser,on of new AMPA receptors. Mul,ple neural mechanisms for sensi,za,on Covalent modif ­ ica,on of pre ­ synap,c proteins Protein trafficking, local protein synthesis New gene transcrip,on, major structural changes 8 4/5/10 Synap,c plas,city and learning [email protected] Modifiability or changeability of in the func,on or structure of a system in response to external input [email protected] [email protected] Altera,on of synapse func,on by use or learning Molecular logic of learning Evolu,on places ac,vity ­dependent signaling pathways at specific synapses. These provide a capacity for plas,city. In individual animals, sensory experience can then change synapse or cellular func,on. These cellular changes mediate learned changes in behavior. 5HT receptors cAMP PKA CREB postsynap,c calcium Are there conserved signaling pathways for plas,city and learning? Olfactory Learning in Drosophila Classical [email protected]—a type of learning in which an innocuous sensory s,mulus, which ini,ally produces no behavioral response, is presented along with a second s,mulus that naturally evokes a reflex response. AWer pairing the two s,muli, the innocuous s,mulus will, by itself, elicit the response. (e.g. Pavlov) Tully & Quinn’s olfactory condi,oning maze Measure the % of flies in the control tube aWer training 9 4/5/10 Are there conserved signaling pathways for plas,city and learning? Normal flies learn the odor that is paired with the shock. Random mutagenesis resulted in several mutants with altered learning & reten,on. Tully & Quinn Are there conserved signaling pathways for plas,city and learning? Identification of genes in learning mutants ! dunce gene mutated: cAMP phosphodiesterase ! normal role of protein: breaks down cAMP ! problem in mutant: cAMP overload in neurons ! amnesiac ! gene mutated: PACAP ! normal role of protein: peptide that activates adenylyl cyclase in neurons ! problem in mutant: too little cAMP in target neurons ! rutabaga ! gene mutated: adenylate cyclase ! normal role of protein: produces cAMP in neurons ! problem in mutant: little or no cAMP produced other mutants identified in similar experiments: ! CREB mutants! problem in mutant: failure to form long-term memory. Short-term memory was ok.! Conclusion These mutations all interfere with cAMP/PKA/CREB pathway. This is a conserved signaling pathway for plasticity and learning across species. Other genes with conserved plasticity functions include NMDA receptors, CaMKinase, and genes related to AMPA receptor insertion. 10 ...
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