The effects of acute and chronic application of ketamine on the resting spontaneous motility, its development and reactivity was studied in chick embiyos of white Leghorns. 1. Acute application of ketamine (NarcamonR) in a dose of 12.5 mg/kg e.w. partialy depressed spontaneous motility as early as in 11-day old chick embryos . From day 15 of incubation ketamine very effectively blocked spontaneous motility. 2. Ketamine was fully ineffective in spinal preparations (decapitation on day 2 of incubation)of 11- and 13-day-old embryos. It was not until day 15 evoked that it depressed motility as in normal embryos. 3. Chronic continuous supply of ketamine (average dose 6.34 ±0.72 mg/kg e.w./24 h) from day 4 of incubation till day 8, 12, or 16 of incubation reduced the developmental decrease of spontaneous motility by 23.1-6.0 % as compared to the controls. This effect was already observed after the first 4 days of chronic application of ketamine. 4. Chronic application of ketamine significantly diminished the strychnine activation and GABA-mediated depression of spontaneous motility. The depressive effect of the acute application of ketamine itself was hardly affected. The results have shown that ketamine interferes with the development of the endogenous rhythm of intrinsic activity and with the development of reactivity of the generator of embryonic spontaneous motility.
The effect of bcta-carboline (Ji-CCE) on spontaneous motility and its development was studied in chick embryos between the 11th and 19th day of incubation. 1. Acutely administered p-CCE (7.5 mg/kg e.w.) already induced significant activation of motility in 11-day-old embryos. From the 17th day of incubation activation acquired a paroxysmal character. 2. In spinal embryos (decapitated on the second day of incubation) there was no such activating effect, demonstrating that it is associated with supraspinal components of the CNS. 3. In chronic administration from the fourth day of incubation (1.55 ± 0.24 mg/kg e.w./24 h), P-CCE led to reduced development of spontaneous motility. The effect was concentrated in the period between the fourth and eighth day of incubation. The chronic administration of P-CCE augmented the activating effect of metrazol and weakened GABA-inhibition of spontaneous motility. 4. On the basis of their findings, the authors express the hypothesis that the benzodiazepine /1-CCE-scnsitive component of the complex GABA receptor evidently already functions from the beginning of the second half of incubation of chick embryos.