Optical analysis of developmental changes in synaptic potentiation in the neonatal rat corticostriatal projection

We applied voltage-sensitive dye imaging to neonatal rat cortical slice preparations and analyzed developmental changes in synaptic plasticity, long-term potentiation (LTP), in the corticostriatal projection. Coronal slice preparations were dissected from postnatal 1- to 21-day (P1-P21) rats, and the transmembrane voltage-related optical signals evoked by cortical stimulation were recorded using a 464ch optical recording system with the voltage-sensitive absorption dye. In the striatum, the optical signal was composed of a fast spike-like signal followed by a slow signal, which corresponded to an action potential and an excitatory postsynaptic potential (EPSP), respectively. The slow signal could be detected at the P1 stage, suggesting that the EPSP is already expressed in the corticostriatal projection at least at early stages after birth. On the other hand, the slow signal was potentiated with a single shot of tetanic stimulation and the potentiation lasted at least 1 h, which is considered to correspond to long-term potentiation. With ontogenetic examinations, we found that (1) the EPSP could be potentiated with tetanic stimulation from the P9 stage and that (2) after the LTP induction, the potentiation was maintained for a longer time in the postnatal 3W stage than in the 2W stage. These results suggest that characteristics of LTP change dynamically during postnatal development.