Abstract
In the central nervous system, synaptic efficiency is modifiable in activity-dependent manners. Homer1a/Vesl-1S, an activity-dependently inducible member of the scaffold protein family Homer/Vesl, has been implicated in long-term up-regulation of synaptic efficiency (various forms of LTP), as well as in short-term modification of AMPA receptors (arguably, both up- and down-regulation). It is not clear, however, whether Homer 1a takes part in induction of LTD (long-term depression). The present experiments examined roles of Homer 1a in inducing LTD at a variety of corticocortical synapses in rat visual cortex slices by using whole-cell patch clamp. Homer 1a was injected by diffusion from patch pipettes. With or Without Homer 1a injected, LTD induction was attempted by pairing 1 Hz stimulation with post-synaptic depolarization for 10 min. Without Homer 1a, LTD was induced at synapses between layer IV axons onto layer II/III pyramidal cells, those between layer II/III axons onto layer V pyramidal cells and those between layer II/III axons onto layer VI pyramidal cells. However, at synapses between layer IV axons onto layer VI pyramidal cells, LTD induction was failed. With Homer 1a protein injected, on the other hand, LTD induction was reduced in magnitude at layer II/III-to-layer VI pyramidal cell synapses, but not at the other synapses examined, suggesting a synapse-specific effect of Homer 1a. [J Physiol Sci. 2006;56 Suppl:S168]
