Abstract
Thalamocortical connections undergo remarkable plasticity during critical period, and accumulating evidence demonstrated that an activation of silent synapses at postsynaptic site is an important underlying mechanism in this process. In contrast, relatively little is known about the nature of presynaptic property at this connection, especially in relation to the development and plasticity. We studied developmental changes of release probability at thalamocortical synapses on a layer IV neuron in the developing mouse barrel cortex using progressive block of EPSCs by MK-801, an open channel blocker of N-methyl-D-aspartate type of glutamate receptor, in combination with the conventional paired pulse ratio method. We found that there were two classes of terminals with high and low probability of release throughout the development, and only the higher one was further higher during the critical period. Furthermore, our analysis indicated a possibility that such higher probability was found selectively at terminals synapsing onto postsynaptic silent synapses. Our results suggest that presynaptic sites may also have an active role in plasticity, by working concomitantly with postsynaptic silent synapses during critical period. [Jpn J Physiol 54 Suppl:S146 (2004)]
