Role of benzodiazepine receptors located in the dorsal periaqueductal grey of rats in anxiety.

Studies with electrical brain stimulation suggest that the dorsal periaqueductal grey matter (DPAG) is related to anxiety and to the anti-aversive effects of benzodiazepines (BZD) compounds. However, direct stimulation of the brain may prevent conclusions about the role of specific regions in the control of normal behaviour. In the present study we employed the elevated plus-maze, an ethologically based model of anxiety, to investigate the role of BZD receptors located in the DPAG in anxiety and in the anxiolytic effect of systemically injected BZD. The results showed that midazolam (20-80 nmol), a BZD agonist, dose-dependently increased the percentage of entries and time spent in open arms when microinjected into the DPAG. The effect of midazolam (80 nmol) was antagonized by flumazenil (80 nmol), a BZD antagonist, microinjected into the DPAG 10 min before the agonist. FG 7142 (20-80 nmol), a BZD partial inverse agonist, decreased time spent in open arms at the dose of 40 nmol and the number of open arms entries at all doses when microinjected into the DPAG. The microinjection of flumazenil (80 nmol) into the DPAG failed to antagonize the anxiolytic effect of systemically injected diazepam (2.5 mg/kg). These results strengthen the idea of an involvement of BZD receptors located in the DPAG with anxiety. They also suggest that the DPAG is not the only structure responsible for the anxiolytic effects of systemically injected BZD.