Facilitation of opiate- and enkephalin-induced motor activity in the mouse by phenytoin sodium and carbamazepine.

In the first experiment, adult male Swiss-Webster mice were systemically injected with a standard dose of morphine. Compared to the influence of vehicle, the motor activity of morphine-injected mice was increased. Neither phenytoin sodium nor carbamazepine alone facilitated motor activity, but pretreatment with both drugs further facilitated the increased motor activity produced by morphine. In a second experiment, mice were injected centrally with a long-acting analog of leu-enkephalin. It also increased motor activity in comparison with vehicle. Again, both phenytoin sodium and carbamazepine further facilitated this response. Both experiments suggest a facilitatory interaction between some aspects of these anticonvulsants and opiate-induced motor activity.