The effects of repeated administration of diazepam, MK-801 and CGP 37849 on rat behavior in two models of anxiety

The effects of repeated administration of diazepam, MK-801 and CGP 37849 on rat behavior in the Vogel conflict test, and in the open field test of neophobia, were studied in rats. The drugs were given at doses active acutely, for 5 days, the last dose was administered 30 or 60 min prior to testing. It appeared that diazepam and MK-801 treated animals showed clear-cut signs of behavioral tolerance and motor sensitization, respectively. CGP 37849 was characterized by the best pharmacological profile, in that on repeated administration the drug not only retained its anxiolytic-like potency in the Vogel test, but even enhanced rat exploratory behavior in a new environment, independently of changes in animal motor activity. Repeated injections of the examined agents did not cause any significant modifications in monoamine levels and their turnover rates, in the striatum and limbic forebrain. It is concluded that the new class of competitive NMDA receptor antagonists, exemplified by CGP 37849, is the most promising candidate for clinical trials in anxiety disorders.