Effect of sodium valproate on the open-field behavior of rats.

1. It has been reported that sodium valproate induces a morphine-like withdrawal syndrome in rats. The effects of acute or chronic treatment with sodium valproate on rat behavior was studied in the open-field test. 2. Acute sodium valproate (320 mg/kg, intraperitoneally) decreases the frequency of, and the time spent in grooming even when not modifying locomotion, rearing or defecation (N = 15), either 15 or 60 min after an acute treatment. This effect was not modified (N = 10) by concomitant administration of morphine (2 mg/kg) or naloxone (1 mg/kg). 3. Interruption of prolonged (30 days) valproate treatment with increasing doses of 40 to 320 mg/kg, by gavage, twice daily (N = 10) did not modify rat behavior in the open-field, from the first to the fourteenth day of the test. 4. We conclude that the decreased novelty-induced grooming does not depend on the opioid system and may be related to an anti-anxiety effect of valproate.