Abstract
High-frequency stimulation produces long-term potentiation (LTP) at inhibitory synapses of layer 5 cells in developing rat visual cortex. Induction of this LTP was prevented by inhibition of postsynaptic G proteins, phospholipase C, inositol trisphosphate receptors, or Ca2+ increase, indicating that postsynaptic Ca2+ elevation is necessary for induction. On the other hand, the maintenance of LTP requires the activity of presynaptic, but not postsynaptic, cells, albeit at a low frequency. Our analysis has demonstrated that LTP maintenance is mediated by presynaptic Ca2+ entries through multiple (P, N and L) types of high-threshold Ca2+ channels, which activate Ca2+-dependent reactions different from those triggering transmitter release, suggesting that this LTP is expressed and maintained presynaptically. Analysis of the expression site of LTP, using paired-pulse stimulation and coefficient of variation, was consistent with this view. These observations strongly suggest that the production of LTP requires retrograde signals from postsynaptic cells to presynaptic terminals. I will describe the experimental data used to test the involvement of retrograde messenger candidates in the production of LTP at visual cortical inhibitory synapses. [Jpn J Physiol 54 Suppl:S33 (2004)]
