The influence of subchronic administration of the neurosteroid allopregnanolone on sleep in the rat.

The endogenous neurosteroid allopregnanolone has recently been demonstrated to have somnogenic properties that are very similar to those of other agonistic modulators of GABA(A) receptors, especially of short-acting benzodiazepines. Short-acting benzodiazepines are established to rapidly lose their hypnotic effect upon repeated administration. To investigate the tolerance potential of allopregnanolone, we assessed sleep-wake behavior in rats during subchronic treatment (once daily for five days) with placebo or 15 mg/kg allopregnanolone (n = 8 each). The sleep patterns of the placebo and allopregnanolone group did not differ significantly before and after treatment. Throughout the entire treatment period the allopregnanolone group exhibited shorter non-rapid eye movement sleep (non-REMS) latencies, prolonged REMS latencies, longer non-REMS episodes, more pre-REMS and less low-frequency, but higher spindle activity in the electroencephalogram (EEG) within non-REMS than the placebo group. The lack of tolerance effects suggests that allopregnanolone may be an efficacious modulator of sleep-wake behavior over longer time periods than most drugs targeting the benzodiazepine binding site of the GABA(A) receptor.