Ontogenetic development of ketamine-induced sleeping time and electrocorticographic changes in rats.

Latency to the loss of righting reflex and sleeping time after ketamine were measured in 261 rats aged 7, 12, 18, 25 and 90 days. The sensitivity to ketamine was highest in 7-day-old animals and decreased with age. In the youngest group rats slept after the 20-mg/kg dose whereas not all adult animals lost their righting ability after a dose of 160 mg/kg. Electrocorticographic (ECoG) study demonstrated an age dependence of changes induced by ketamine. The youngest group exhibited only suppression of the originally discontinuous ECoG whereas signs of slow-wave sleep or depression appeared in older rats.