Anxiolytic effect in the elevated plus-maze of the NMDA receptor antagonist AP7 microinjected into the dorsal periaqueductal grey.

In order to localise the often reported anxiolytic action of N-methyl-D-aspartate (NMDA) receptor antagonists, 2-amino-7-phosphonoheptanoic acid (AP7) was injected into the dorsal periaqueductal grey (DPAG) of rats exposed to the elevated plus-maze model of anxiety. Doses of 0.2, 2 and 20 nmol AP7 caused a dose-dependent increase in the percentage of open arm entries, the effect of the last two doses being significantly different from control. A non-significant tendency to increase the percentage of time spent on the open arms of the maze was also noticed. In contrast, the total number of entries into either the open or enclosed arms was not affected. Injections of AP7 localized outside the DPAG were ineffective. Therefore, microinjection of AP7 into the DPAG caused a selective anxiolytic effect in the elevated plus-maze. It may be suggested that the DPAG is a site of the anxiolytic action of NMDA antagonists reported following systemic administration.