| Abstract: | The participation of central monoaminergic systems in the regulation of spontaneous motility in developing chick embryos was tested by systemic administration of several drugs, which affect the different sites of central aminergic systems. Amphetamine (2 mg.kg-1 egg weight) evoked an age-dependent depression of spontaneous motility, which first occurred in a significant fashion on day 13 of incubation. Two thirds of this depression depended upon supraspinal influences. The effect of p-chlorophenylalanine (100 mg.kg-1 e.w.) consisted from day 15 of incubation in a short-lasting depression followed by partial recovery of resting motility. alpha-methyldopa (100 mg.kg-1 e.w.) depressed the spontaneous motility from day 13 of incubation, without any signs of recovery within the first hour after drug administration. The most pronounced depressive effect was evoked by melatonin (25 mg.kg-1 e.w.) even in 11-day-old embryos. Along with the increased depth of depression the recovery of motility declined until full cessation of motility was achieved in 17-day-old embryos. The results were interpreted as constituting further evidence for the involvement of central aminergic systems in the development of supraspinal control over spontaneous motor activity generated by the CNS. |
