D-2 receptor-mediated inhibition by a substituted quinolinone derivative, 7-[3-(4-(2,3-dimethylphenyl)piperazinyl)propoxy]-2(1H)-quinolinone (OPC-4392), of dopaminergic neurons in the ventral tegmental area.

A microiontophoretic study was performed to investigate the effects of a newly synthesized quinolinone derivative, 7-[3-(4-(2,3-dimethylphenyl) piperazinyl) propoxy] 2-(1H)-quinolinone (OPC-4392), on neuronal activities of the ventral tegmental area (VTA) of rats anesthetized with chloral hydrate. The VTA neurons, which were identified by antidromic stimulation of the nucleus accumbens (Acc), were classified into type I and type II neurons according to the responses to Acc stimulation: type I neurons had a long spike latency of over 7 msec (9.63 +/- 0.25 msec), and the type II, a short latency of less than 7 msec (2.98 +/- 0.27 msec) upon Acc stimulation. In all of 11 type I neurons, iontophoretically applied OPC-4392 and dopamine inhibited the antidromic spikes elicited by Acc stimulation. This inhibition was antagonized by simultaneous application of domperidone (dopamine D-2 antagonist). However, in 16 out of 19 type II neurons the antidromic spikes were not affected by either OPC-4392 or dopamine. When the effects of iontophoretically applied OPC-4392 and dopamine on spontaneous firings were tested in 32 VTA neurons identified by Acc stimulation (including type I and type II neurons), there was a relationship between the effects of these two drugs. These results suggest that OPC-4392 acts on dopamine D-2 receptors of the dopaminergic neurons in the VTA, thereby inhibiting neuronal activity.