Is there a catecholamine-serotonin interaction in the control of locomotor activity?

Previous studies have reported that rats given either midbrain raphe lesions or the serotonin synthesis inhibitor, p-chlorophenylalanine, show an increase above controls in their locomotor response to various doses of (+)-amphetamine. These data have been taken to be indicative of a catecholamine-serotonin interaction. The present data demonstrate that this increased response to amphetamine was obtained following lesions specific to the median raphe nucleus, whereas lesions of the dorsal raphe nucleus were without effect. These results also question the validity and generality of the catecholamine-serotonin interaction hypothesis by demonstrating: (1) that when the data are plotted as a per cent of baseline activity, the interaction disappears; and (2) that a very similar effects is observed when amphetamine injections are replaced by scopolamine injections.