Sleep-inducing effects of three hypnotics in a new model of insomnia in rats.

Sleep-inducing effects of hypnotic drugs are difficult to demonstrate in rats because of high baseline sleep times. Most increases in slow wave sleep (SWS) following the administration of hypnotics have been found to be at the expense of REM sleep rather than waking. In the first experiment we found that rats chronically implanted with electrodes for recording ECoG and EMG slept significantly less during the first two hours of the dark period when housed under 16-hr light 8-hr dark (16L/8D) than when housed under 12L/12D conditions. The second experiment examined the effects of flurazepam, phenobarbital and thalidomide administered orally at the onset of the two-hour period of increased waking resulting from the 16L/8D lighting. All three drugs caused dose-dependent reductions in waking and increases in SWS with no alterations in REM% of total sleep time. Sleep onset latency was also significantly was also significantly reduced by all three drugs. As in man, flurazepam was the most potent, and thalidomide was the least potent of the hypnotics in rats.