Abstract
In the stable culture of hippocampal slice, repeated inductions (≥3 times) of LTP by exposures to glutamate (Glu) at regular intervals (3-24h) lead to a slowly-developing (requiring ∼1w to develop) long-lasting (lasting ≥3w) enhancement of synaptic transmission efficiency coupled with an increase in the number of synapses. We call this phenomenon RISE (Repetitive-LTP Induced Synaptic Enhancement) to discriminate it from conventional single LTP. Electron microscope (EM) examination shows that the number of synapses with small postsynaptic density (PSD) increases transiently during the developing phase of RISE, indicating ongoing synaptogenesis. Recently we reported that field EPSP in the culture after repeated Glu-exposures contained a component susceptible to Joro-Spider Toxin (JSTX), a selective blocker of Ca2+-permeable AMPAR (CaP-AMPAR) in this period. Here we report that the appearance of CaP-AMPAR is not only a result of RISE but also a cause of its establishment. When we applied JSTX for a limited period (24h) during the developing phase of RISE (4d after the 1st Glu-application), RISE was not established, when examined 14d later. When we examined the culture treated with JSTX after the repeated Glu-exposures by EM, the increase in the number of small-PSD synapses was abolished, although other morphological features including the occurrence of perforated synapses were unaffected. These results suggest that Ca2+-influx through CaP-AMPAR is required for the growth and maintenance of new synapses. [J Physiol Sci. 2007;57 Suppl:S151]
