The effects of 5-hydroxytryptophan and L-tryptophan on wakefulness and sleep patterns in the cat.

Sleep in cats was studied for 24 h after i.p. injections of D,L-5-hydroxytryptophan (5-HTP, 40 mg/kg) or L-tryptophan (200 mg/kg and 300 mg/kg) in two separate experiments. Total sleep, total slow wave sleep or deep slow wave sleep was not changed in any experiment. There was an increase of the awake, drowsy pattern over the whole recording period after both 5-HTP and tryptophan injections. An accentuated drowsy pattern, with high voltage 4 c/sec synchronous waves, but with no sleep spindles, was seen during the first hours after 5-HTP injection. REM sleep was completely absent during the first 6 h after 5-HTP and significantly reduced during the first 3 h after tryptophan. The similarity of the effects of 5-HTP and tryptophan suggests that they both act as serotonin precursors. It is also suggested that the serotonin precursors have a general deactivating effect on the waking state, and that they do not necessarily subserve a specific sleep-inducing or sleep-maintaining function.