Abstract

Age of onset of ability to tremor and latency, duration of action and tremoring frequencies, measured by spectral analysis, were determined in adult and developing rats for each of six tremorigenic drugs. Tremoring could first be elicited at 6 to 8 days of age by administration of 1,1,1-trichloro-2,2-bis(p-Chlorophenyl)ethane (DDT) and veratramine, but did not develop until 9 days of age in response to tremorine and oxotremorine injection and not until 13 days of age after injection of harmine and harmaline. In general, the ontogenesis of drug-induced tremor corresponded with the ages at which the neural structures proposed as the sites of action for each drug are believed to mature. DDT is believed to exert its tremorigenic action at the spinal cord level, tremorine and oxotremorine at the midbrain tegmental level and harmine and harmaline at the cortical-striatal level. The present findings suggest that veratramine may also exert its tremorigenic effects at the spinal level. Spectral analysis revealed that tremorine tremor shares certain characteristics with DDT tremor and therefore may act at both the midbrain and spinal levels. In the adult the mean tremoring frequency was 10 to 12 cps for all drugs, except DDT, which caused tremoring at the rate of 22 cps. The tremoring frequency increased 1 to 2 cps from age of onset to adulthood for all drugs except DDT. The mean frequency of DDT tremor increased from 10 to 22 cps during development. The results suggest that drug-induced tremor may be useful for studying the developing nervous system, as well as for elucidating the mechanisms involved in tremor phenomena.