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Integration of neural plasticity

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  1. Integration of neural plasticity • Multiple mechanisms per synapse • Multiple synapses per cell • Multiple cells per function • Examples • Tritonia escape response • Aplysia gill withdrawal reflex • Leech central pattern generator • Autonomic control of hypertrophy

  2. Tritonia/Aplysia flight • Stereotypical swim response • Phasic, fixed duration • Simple pattern generator • Individually identified neurons • Simple connectivity Getting, 1980

  3. Metabotropic Neuromodulation • DSI stimulation triggers fast and slow depolarization • Slow depolarization is GTP dependent • Blocked by non-hydrolyzable GDP-b-S Recording Stimulation

  4. Recording Stimulation Tritonia Metabotropic Neuromodulation • DSI stimulation triggers fast and slow depolarization • Slow depolarization is GTP dependent • Blocked by non-hydrolysable GDP-b-S Fast Ionotropic depolarization Slow metabotropic depolarization Blocks metabotropic process

  5. Neuromodulation • Multiple receptor types at a single synapse induce divergent actions • Fast/slow • Excitatory/inhibitory • Multiple substance release at a single synapse induce multiple actions • Multiple neurotransmitters • Serotonin/norepinepherine/dopamine • Neuromodulatory peptides • Somatostatin, substance P, vasopressin • Accommodation/facilitation over sec - min

  6. UTMB Magazine Aplysia gill withdrawal • Gill & siphon normally exposed for metabolite exchange • Tactile/nocioceptive stimulation triggers withdrawal • Similar pathways in all species Gill Mantle Siphon Tail Leonard & Edstrom, 2004

  7. Neural Circuit • Sensory neurons (SN) • Motorneurons (L7, LDg1, LDg2…) • Interneurons (ex: L16, L25) SN L25 L16 INin INin L7 LDG1 LDG2 Leonard & Edstrom, 2004

  8. Habituation • EPSP amplitude declines during habituation • Quantal • SN goes from releasing 3 NT vesicles to 0 Est # vesicle release Record post-synaptic EPSP amplitude in response to sensory nerve stimulus, construct a histogram, and look for discrete quanta Number observed EPSP Amplitude (uV) Castellucci & Kandel, 1974

  9. Habituation • Presynaptic neurotransmitter vesicles separate from the cell membrane • Depletion • Ca2+ dose-dependent untethering (calpain), channel inactivation (CaV), recruitment of SV (PKC) (?) Naïve sensory terminal Habituated sensory terminal Note: greater distance between vesicles and membrane. Bailey & Chen, 1988

  10. Sensitization • EPSP amplitude is potentiated by prior stimulation of separate pathway Siphon Tail SN SN L25 L29 L16 L7 LDG1 LDG2 Leonard & Edstrom, 2004

  11. Sensitization • Tail interneuronal collaterals synapse with siphon interneurons • Facilitating interneuron L29 • Serotonergic + SCP • Presynaptic • Serotonin • GaSACPKA--|KIRKIR--|CaVNT release • SCP Sensory neuron recordings PSP and spike width show habituation Until L29 is briefly tetanized Hawkins, 1981

  12. Sensitization • Amplification within sensitization • Single stimulus  hours of increased gain • Multiple stim  days • Rate/dose decoding • PKA: fast acting, slow transport • Local K/Ca channels • Distributed K/Ca channels • Nuclear import, CREB

  13. Long term sensitization • CREB induces new synapse formation by formation of sensory collaterals. Stimulation of cultured neuron results in rapid development of a new dendritic spine Goldin, et al., 2001