SCH 23390: D-1 modulation of oral dyskinesias induced in snakes by Xenopus skin mucus.

The granular gland skin secretion of Xenopus laevis induces seven involuntary oral dyskinesias and climbing behavior in the water snake Nerodia sipedon. In a previous study the D-2 receptor antagonist, haloperidol (HAL), selectively potentiated mucus-induced yawning and chewing but attenuated fixed gaping; other oral behaviors were unaffected; HAL alone induced no dyskinesias and failed to modify mucus-induced decreases in tongue flicking, cage climbing and activity. As skin compounds have neuroleptic properties known to induce human and animal dyskinesias, we hypothesized that D-1 receptor antagonism may modulate the four of seven mucus-induced dyskinesias and the climbing not altered by HAL. We found that, like HAL, SCH 23390 (SCH) potentiated mucus-induced yawning, attenuated fixed gaping and had no effect on climbing. Unlike HAL's potentiation of chewing, SCH attenuated chewing and potentiated writhing tongue movements. SCH alone, like skin mucus, attenuated tongue flicking and activity but, given with mucus, SCH increased tongue flicking and activity to control levels. Compared to the HAL study, results suggest that mucus-induced yawning and fixed gaping are similarly modulated by both HAL and SCH, while these drugs have opposite effects on writhing tongue and chewing. SCH given alone or with frog mucus had unique effects on activity and normal tongue flicking.