Antidepressant-like effects of NMDA-receptor antagonist injected into the dorsal hippocampus of rats.

Exposure to uncontrollable stressors causes behavioral changes that have been related to depressive states in humans. Poststress intrahippocampal administration of amino-7-phosphonoheptanoic acid (AP-7), a glutamate NMDA-receptor antagonist, attenuated the restraint-induced decreased exploration of an elevated plus maze 24 h later. The objective of the study was to test if this treatment would also attenuate the increased immobility seem in the forced swim test (FST) due to preexposition to this stressful situation. Male Wistar rats with cannulae aimed at the dorsal hippocampus were submitted to 15 min of forced swimming and tested 24 h later. They received bilateral intrahippocampal injections of AP-7 (10 nmol) either before or after the pretest swimming session or before the test. Poststress treatment increased latency to display the first episode of immobility and tended to reduce total immobility time. The drug was ineffective when given before stress or before test and in nonstressed animals. This suggests that glutamate NMDA receptors located in the dorsal hippocampus are involved in the behavioral changes observed in the FST.