Effects of neonatal administration of 5,7-dihydroxytryptamine on locomotor activity.

Neonatal rats treated on day 3 of life with 50 or 100 micrograms 5,7-dihydroxytryptamine exhibited long-lasting selective depletions of serotonin (5-HT). The 5-HT depletions produced a shift in the peak in locomotor activity from its normal occurrence at 15 days of age to later days of age. The observation that the decreases in activity after the peak were delayed, rather than eliminated, suggests that the inhibition of locomotor activity produced by 5-HT may be of transient importance in the developing rat. The transience of the inhibition may be the result of the continuing development of nonserotonergic systems during this time period that are involved in the regulation of activity.