The Effect of Lowering the Serotonin Content of the Rat Brain on Spontaneous Locomotor Activity

Abstract

Electrothermic lesions of the midbrain of rats were made in the region of the median or median plus dorsal raphe nuclei through an unipolar electrode. Concentration of serotonin (5HT) in the telencephalon decreased variously among rats and locomotor activity increased following lesions. No close correlation was obtained between locomotor activity and the 5HT concentration in the telencephalon 7 to 14 days after the lesion. The effect of p-chlorophenylalanine (PCPA, a total dose of 400 mg/kg, i.p.) was also investigated on locomotor activity, and on 5HT and 5-hydroxyindoleacetic acid (5HIAA) levels in the telencephalon of the rat. PCPA lowered the 5HT content to less than 35% of the control in the telencephalon, but did not significantly alter locomotor activity. Only an excess mounting behavior was observed. These results suggest that an increase in locomotor activity due to raphe lesion has no primary connection with lowering the 5HT content of the rat brain.