Consequences of chronic phenobarbital blockade of spontaneous motility in chick embryos for the development of central motor output activity

The consequences of the chronic continuous administration of Na+-phenobarbital in an average dose of 9.8 mg/kg e.w./24 h were studied in chick embryos. Administration was always started on the 4th day of incubation and lasted 4-12 days. Spontaneous motility was tested in 13- and 17-day-old embryos. The continuous, chronic administration of phenobarbital produced the following significant changes in the embryos' spontaneous motor activity and in the reactivity of their central motor output: 1) In 17-day-old embryos it reduced spontaneous motility in direct correlation to the time of administration. In 13-day-old embryos the effect was not yet significant. 2) It significantly inhibited strychnine, bicuculline and metrazol activation of motor output. 3) It raised the sensitivity to the acute administration of oxazepam (by 18-29.4%), but weakened the inhibitory effect of gamma-aminobutyric acid (by 17.6-33.2%). From the results of these observations it is deduced that spontaneous central motor output activity is not just a developmental epiphenomenon, but that it is an important prerequisite for normal development of the embryonic CNS.