Development of the differential effect of oxazepam on spontaneous and activated motility in chick embryos.

Development of the acute depressant effect of oxazepam (in a dose of 10 mg/kg egg weight) on spontaneous and activated motor activity was studied in chick embryos (incubation age 11-19 days). The depressant effect of oxazepam was demonstrated for the first time in 13-day-old embryos. From the 15th day of incubation it led to prolonged depression of embryonic motility. From the 15th day the depressant effect of oxazepam depended on the connections of the central motor output with the prosencephalon. In mesencephalic, rhombencephalic and spinal preparations the effect of oxazepam was insignificant. In 13- and 15-day-old embryos oxazepam blocked the activating effect of strychnine and pentylenetetrazol, but not the picrotoxin-induced activation. The picrotoxin activation of embryonic motility was incompletely blocked for the first time in 17-day-old and completely only in 19-day-old embryos. The results are discussed with reference to heterochronia of development of the various components in the complex GABA receptor.