Dihydropyridine-sensitive calcium channels are involved in the induction of N-methyl-D-aspartate receptor-independent long-term potentiation in visual cortex of adult rats.

It was recently shown that induction of long-term potentiation (LTP) in the visual cortex of adult rats does not require suppression of inhibition or N-methyl-D-aspartate (NMDA) receptor activation. In the present study we examined the role of dihydropyridine-sensitive Ca2+ channels in the induction of this form of LTP. In visual cortical slices from 60 to 90-day-old rats tetanic stimulation (100 Hz 0.2 s, every 5 s for 10 min) of the white matter in the control medium or in the presence of D,L-2-amino-5-phosphonovalerate (100-200 microM) induced LTP of the field potential in layer III. Tetanic stimulation in the presence of nifedipine (50-100 microM) or nimodipine (10 microM) prevented induction of LTP in most of the slices. It appears that the known reduction of NMDA receptor activity in the mature neocortex is accompanied by a diminished role of NMDA receptors and an increased importance of voltage-gated Ca2+ channels in maintaining synaptic plasticity.