Long-term potentiation (LTP) and its dependence upon NMDA receptor-mediated Ca[2+] entry has been widely studied as the presumptive mechanism underlying learning and memory. Numerous proteins have been implicated in the induction, maintenance, and modulation of LTP expression. This proposal adds a novel contributor, the Ca[2+]/calmodulin kinase II (CaMKII) gated Cl[-] channel ClC-3, to the regulation of LTP that is unique in its ability to modulate synaptic responses and LTP in an activity- and developmentally-dependent manner. Although ClC-3 is broadly expressed throughout the brain, the ClC-3 knockout mouse shows complete, selective postnatal neurodegeneration of the hippocampus. In fact, multiple lines of ClC-3 knockout mice exhibit similar hippocampal degeneration, suggesting a novel role of this channel in maintaining normal brain function. In support, recent preliminary studies show seizure-like activity in ClC-3 knockout mice;a role for Cl[-] channels, specifically ClC-3, in regulating excitability in the adult brain has not been studied. Prior work has demonstrated that ClC-3 is spatially and functionally linked to the NMDA receptor: NMDA receptordependent Ca[2+] entry, activation of CaMKII, and subsequent phosphorylation/gating of ClC-3 by CaMKII links the two channels via a Ca[2+]-mediated feedback loop. As a result of the shift in the Cl[-] gradient during development, we hypothesize that ClC-3 facilitates excitation and Ca[2+] influx early in development when the equilibrium potential for Cl[-] is depolarizing;conversely, ClC-3 gating suppresses excitation and Ca[2+] influx, thereby restraining the expression of LTP in adulthood when Cl[-] flux is hyperpolarizing. Thus ClC-3 is ideally suited to differentially influence synaptic plasticity as a function of Ca[2+] influx and internal [Cl[-]]. The goal of this application is to characterize the impact of ClC-3 gating on NMDA receptor currents and expression of LTP as a function of the developmentally-regulated Cl[-] gradient. The ClC-3 knockout model allows us to explore the delicate interaction between neuronal development, plasticity, excitation-inhibition balance, and long-term survival ? a unifying mechanism likely to be applicable in multiple contexts beyond chloride channels.
Synaptic development and plasticity are integral to our understanding of neuronal function and disease, so understanding the events that underlie these processes is of fundamental significance. We have found that ClC-3 chloride channels localize to the post-synaptic plasma membranes of hippocampal neurons where they are both spatially and functionally linked to excitatory glutamatergic receptors. This proposal identifies ClC-3 as a novel regulator of synaptic transmission in the hippocampus, unique in its ability to modulate synaptic events and plasticity in an activity- and developmentally-dependent manner.
|Farmer, Laurel M; Le, Brandy N; Nelson, Deborah J (2013) CLC-3 chloride channels moderate long-term potentiation at Schaffer collateral-CA1 synapses. J Physiol 591:1001-15|