Our general goal is to develop an integrated view of the biochemical processes that govern basal synaptic transmission and LTP in the hippocampal CA1 region.
Aim 1 investigates the functional relationship of the protein kinases, CaMK, PKC and Src, all of which have been implicated in LTP. Internal perfusion of kinase inhibitors and alpha-CaMK knockout mice will be used to test the hypothesis that the primary role of PKC and Src in LTP induction is to modulate the NMDA conductance. Other experiments test the possibility that sustained PKC and CaMK activities are responsible for the maintenance of LTP. A critical issue, whether LTP can be reversed by subsequent addition of kinase inhibitor, will be further explored. The possibility that LTP can be easily reversed only in a brief time window after induction will be tested by laser-induced uncaging of kinase inhibitor just after LTP induction. Recent biochemical work suggests another possibility: that CaMK maintains LTP by forming a structural complex with NMDAR-2B. New inhibitors allow this to be tested.
Aim 2 concerns our finding that LTP maintenance can be reversed by cyclic nucleotide analogs such as Rp-cAMPS. The possibility that this is due to inhibition of persistent PKA will be explored. However, it seems more likely that reversal is due to activation of cyclic nucleotide gated channels (CNGC). It is known that Ca2+ elevation can produce weakening, but the consequences of Ca2+ entry through CNGC has not been explored. We will determine whether local uncaging of cyclic nucleotides can raise Ca2+ and reverse LTP.
Aim 3 builds on our observation that an actin-dependent process is required to maintain basal AMPA-mediated transmission. It appears that cytoskeleton-based vesicle transport systems are required to sustain the rapid turnover of AMPA channels. Consistent with this view, preliminary results indicate that a microtubule-motor system and a vesicle fusion process is required for maintaining AMPA transmission.
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