Development of spontaneous motility in chick embryos. Interaction of reserpine and apomorphine

The effect of apomorphine (1 mg/kg egg weight) on a base of the pre-administration of reserpine (2.5 mg/kg e.w.) 30 min or 2 or 4 hours previously was studied in chick embryos from the 13th to 19th day of incubation. Only the depressant effect of apomorphine was manifested in 13-day embryos. In 15-day embryos summation of the depressant effect of both drugs was recorded for the first time. In 17-day and especially 19-day embryos apomorphine raised the frequency of spontaneous movements high above the level of reserpine-induced depression of motor activity. This activating effect of apomorphine depended upon the supraspinal parts of the CNS, as it disappeared in 17-day embryos after decentralization of the spinal cord (particularly after chronic decapitation). We consider these findings to be further experimental evidence of the participation of catecholaminergic (in particular dopaminergic) central systems in supraspinal control of embryonic motor activity.