Gill withdrawal reflex using Aplysia californica sea slug: -A mantle-covered gill is used for breathing -A siphon is used for expelling seawater and waste -Gill withdrawal occurs when the siphon is touched -Defensive mechanism used by Aplysia

Habituation leads to decreased neurotransmitter release and reduced gill withdrawal

Habituation vs. sensitization to repeated stimulus mild stimulus noxious stimulus Sensitization:

Repetitive shocks for 4 days induces shock memory for 2-3 weeks = LTM In left panel, control is touched w/ brush every 30 min; “one shock” animals receive a shock after 3rd brush touch [remember for 1h] In right panel, “4 single shocks” received 4 shocks/day & remembers for 2-3d; animals receiving 4 per day x 4d remember for 2-3 weeks= LTM! [START WITH THIS SLIDE ON 4/6/16!]

Short-term facilitation targets K+ channels, NT vesicles, & Ca2+ channels

Catalytic subunits of PKA translocate from the cytoplasm to the nucleus

RNA polymerase needs direct contact w/ enhancer binding proteins to activate transcription DNA in promoter & regulatory regions is thought to loop around to bring activating proteins in contact w/ polymerase

CREB-2 represses transcription; CREB-1 displaces it to activate CREB: cAMP response element binding protein; becomes phosphorylated by PKA then binds CRE; CBP then binds CREB to co-activate txn (CREB-CBP can also repress) CREB: basic Leu zipper protein complexing Mg2+ *PKA kinase

Long-term sensitization (4-5 shocks) lasts for days and requires lasting changes in synaptic connectivity stimulating the tail then the siphon increased response in gill with drawal requires interneuron release of 5HT  increased cAMP  increased PKA  enhanced NT release Fig. 63-5 Kandel: Sensitization causes increased synaptic potentials & heightened behavioral responses to stimulus

Long-term sensitization: MAPK, CREB; short-term sensitization: 5HT, cAMP activate PKA, closing K+ channels NT release see Kandel p.1015 Fig. 65-5: short-term response to tail stimulation: 5HT interneuron activated AdCyc  increase cAMP  PKA activity  shut off K+ channel, more Ca2+ for vesicle/NT release long-term response to tail stimulation: CREB binds to CREs & upreg transcription for synaptic stabilization, growth

Learning to pair stimulus with reward: classical conditioning

US/CS: unconditional/conditional stimulus Classical conditioning in Aplysia: pairing tail shock with water jet on the siphon; output= gill withdrawal reflex US CS US/CS: unconditional/conditional stimulus Mechanism: activation of interneurons via CS increases Ca2+ to enhance response to stimulus (activation of Ca2+-dep AdCyc)

Training and neuronal circuits in learning in Aplysia 5HT neuron (tail) siphon Conditioned stimulus: learned response (water on siphon) US: shock The animal learns to withdraw siphon for an interval

Conditioning vs. sensitization: preceding activity activates calmodulin, AdCyc Sensory neuron

In classical conditioning, presynaptic depolarization increases Glu release to amplify EPSP response

Classical conditioning employs coincidence detectors AdCyc (SN) & NMDAR (MN) Figure 21-53. Intracellular signaling pathways during sensitization and classical conditioning in the Aplysia gill-withdrawal reflex arc. Sensitization occurs when the facilitator neuron is triggered by the unconditioned stimulus (US) in the absence of the conditioned stimulus (CS) to the siphon sensory neuron (see Figure 21-52). Classical conditioning occurs when the CS is applied 1 – 2 seconds before the US, and involves coincidence detectors in both the presynaptic siphon sensory neuron and the motor neuron. In the sensory neuron, the detector is an adenylate cyclase that is activated by both Ca2+-calmodulin and by Gsα· GTP (see Figure 21-42). In the motor neuron, the detectors are NMDA glutamate receptors (see Figure 21-40). Partial depolarization of the motor neuron induced by an unconditioned stimulus (via an unknown transmitter) from interneurons activated by the tail sensory neuron enhances the response to glutamate released by the siphon sensory neuron.

Conditioning in Drosophila to evaluate short-term memory

Genetic mutants in Drosophila that identified memory pathways amnesiac: enhances AdCyc; dPACAP= pituitary AdCyc activating peptide Ddc: Dopamine decarboxylase rutabaga: defective Ca2+-calmod dep. AdCyc dunce: PDE mutation

Declarative (explicit) memory: recall of facts or events Nondeclarative (implicit) memory: unconscious memory for procedural or motor skills (includes associative learned tasks) *Removal of either the ventromed prefrontal cortex (medial temporal lobe) or the perirhinal cortex impairs DNMS performance **HM: epileptic patient who had bilateral medial temporal lobotomy; developed profound anterograde amnesia

Declarative memory formation requires the prefrontal & perirhinal cortexes

The delayed nonmatch-to-sample (DNMS) test: -Measures declarative (explicit) learning and memory -Requires subject to compare a presented object with a previously-presented comparison object -Selection of a novel object is encouraged by an edible reward -After novel object rule is learned, the delay period in object presentation is increased from 10 to 120 sec -Number of displayed objects requiring recollection increases -Model for human anterograde amnesia

Medial temporal lesions mimic human amnesia (declarative only)

Spatial learning & memory requires NMDARs in the hippocampus (the Morris water maze test)

Explicit memory storage in vertebrate medial temporal system: the hippocampus DG to CA3: mossy fiber pathway (nonassociative LTP) CA3 to CA1: Schaffer collateral pathway (associative LTP) EC to DG: perforant pathway (associative LTP)

Long-term potentiation: functional model for explicit memory HFS: 100 Hz (brief) LFS: <0.1 Hz *increased EPSP amplitude maintained for >60 min

Long-term potentiation in CA1 is highly afferent-specific

LTP in the Schaffer collateral pathway requires: Cooperativity: activation of multiple afferents (NMDAR-dep) Synapse selectivity: only the active afferents will be potentiated Associative: requires simultaneous pre/post activity to depolarize postsynaptic cell

Spaced stimuli give larger sustained EPSP amplitude (LTP) vs Spaced stimuli give larger sustained EPSP amplitude (LTP) vs. one tetanic stimulation

Hippocampal neuron LTP requires simultaneous afferent activity and postsynaptic depolarization

Postsynaptic depolarization activates CamKII & leads to greater numbers of AMPARs in postsynaptic membrane CamKII

CaMKII activity is regulated by Ca2+-calmodulin binding to release regulatory “hinge”

LTP may not rely solely upon new AMPAR insertion, but also enhanced NT release probability

The number of NT release events increases after LTP induction

Multiple spaced trains, or stimuli, leads to late-phase LTP; one train evokes smaller increase in EPSP for less time

Genetic blockade of PKA eliminates late-phase LTP

Early-phase LTP does not require CREB activation, synapse growth

Synaptic structural changes in L-LTP include new AZs, PSDs