抄録
Fast-spiking (FS) interneurons are one of the strong sources of cortical inhibition. In this study, we examined developmental changes in the connections between pyramidal and FS cells in rat primary visual cortex. We simultaneously recorded FS and pyramidal neurons from layer 2/3 with the whole-cell recording method. At postnatal 14-17 days (P14-17), FS cells provided weak inhibitory inputs to many neighboring pyramidal cells, while excitatory connections from the latter to the former neurons were found much less frequently. Although the proportion of pairs with inhibitory connections was considerably high, the proportion of pairs reciprocally connected was quite low. The inhibitory connections were weak irrespective of the presence of the reciprocal connections. At P20-25, the proportion of pairs with inhibitory connections decreased, but the proportion of reciprocally connected pairs increased. In addition, the inhibitory connections in the reciprocally connected pairs were much stronger than those in non-reciprocally connected pairs. The specificity of the connections and the strength of the inhibition at P30-35 were indistinguishable from those at P20-25. Taken together, these results indicate that FS cells provide neighboring pyramidal neurons with weak inputs at an early stage and then inhibitory connections in reciprocally connected pairs survive and strengthen. This age-dependent change in synaptic connections may contribute to the maturation of visual responsiveness of cortical neurons. [J Physiol Sci. 2007;57 Suppl:S38]
