Ontogenesis of rearing and stereotypy responses to apomorphine in the rat

The ontogenesis of rearing and stereotype behavior in response to apomorphine were investigated in the developing rat. The rearing was rarely observed in 15-day-old rats but distinctly in 18-day-old ones. A subcutaneous injection of apomorphine in dose of 1 mg/kg or 2 mg/kg decreased the frequency of rearing in older animals than day 20. On the other hand, 15-day-old rats were already responsive to apomorphine in stereotypy behavior. There was a reciprocal relationship between rearing and stereotypy responses to apomorphine in rat older than 18 days. Functional relationship between rearing and stereotypy in response to apomorphine were discussed in view of the central dopaminergic mechanisms in developing rats.