Electrocortical activity patterns during chloral hydrate induced sleep in developing rats.

Abstract

The neocortical EEG was quantified during sleep, while under light chloral hydrate anaesthesia, in rats ranging from 9 to 20 days of postnatal age. Continuous amplitude modulation at 0.5-1.0 min per cycle, synchronously over all frequency bands, was observed in 9- and in 10-day-old pups. By day 13, the mean amplitude had risen considerably in each of the frequency bands, and a slow fluctuation in delta-wave activity began to be discernible. Sodium glutamate injections induced EEG changes at 10 days which mimicked certain aspects of normal maturation (viz., large stereotyped potentials at irregular intervals, along with a selective increase in delta-wave activity). Natural as well as experimentally induced EEG changes were paralleled by a rise in neocortical amino acid concentrations, including glutamic acid and GABA. Delta wave amplitudes during quiet sleep increased still further between 13 and 14 days, while beta activity remained at a constant level. Between days 14 and 15 a precipitous decline in delta-wave activity was found, attributable to greater inhibition of slow waves during active sleep. No further developmental changes were noted, except for a gradual rise in the time spent in quiet sleep relative to active sleep.