Behavioral effects in the elevated plus maze of an NMDA antagonist injected into the dorsal hippocampus: influence of restraint stress

The objective of the study was to investigate the influence of restraint st ress on the effects of 2-amino-7-phosphonoheptanoic acid (AP7), an NMDA rec eptor antagonist, injected into the hippocampus of rats submitted to the el evated plus maze (EPM). Male Wistar rats with cannulas aimed to the dorsal hippocampus were forced immobilized for 2 h. Twenty four hours later they r eceived bilateral injections of saline or AP7 (10 nmol/0.5 mul), and were t ested in the EPM. In another experiment the animals received the treatment immediately before or after the restraint period, and were tested in the EP M 24 h later. AP7 had no effect in any anxiety measure in non-stressed rats . In stressed animals the drug increased the percentage of open arm entries when injected before the test in the EPM. When administered immediately af ter the restraint period, AP7 increased the percentage of time spent in the open arms and tended to do the same with the percentage of entries in thes e same arms. The results suggest that interference with hippocampal NMDA re ceptors modify the anxiogenic effect of restraint stress in an EPM. (C) 200 0 Elsevier Science Inc. All rights reserved.