Abstract
Forskolin activates PKA through stimulation of adenylate cyclase and induces late phase LTP in neurons. We previously reported that repetitive exposure of cultured hippocampal slice to forskolin induced a synaptic enhancement developed slowly and lasted for several weeks (forskolin-RISE). The occurrence of the forskolin-RISE was dependent on the times and interval of forskolin application. The forskolin-RISE, originally detected as an enlarged field excitatory postsynaptic potential, was accompanied by an increase in immunohistochemically-identified synaptic structures. We made here an electron-microscopic observation of cultures under development of the RISE and confirmed that the number of ultrastructurally-identified synapses increased in parallel with the RISE. It is assumed that an ultrastructure called 'perforated synapse' (a synapse with interrupted postsynaptic density) is a transitional form of multiplying synapse. Confirming this assumption, the numbers of perforated synapses and of synapses with short postsynaptic density (presumably representing newly-formed synapses) increased in parallel with the RISE. We recently found that a similar synaptic enhancement occurred in cultured hippocampal slice after repeated exposure to glutamate (Glu-RISE). If perforated synapses and short synapses are indices of synaptogenesis, similar ultrastructural changes are expected to occur in the slices developing Glu-RISE. This expectation was also confirmed by the present study. [Jpn J Physiol 54 Suppl:S152 (2004)]
