Hypnotic effect of tryptophan analog in rats

The effects of DL 2-amino-3-(1-naphthyl) propanoic acid, a tryptophan analog, on sleep and brain chemistry were investigated in rats. Similar to previous findings with tryptophan, the tryptophan analog (30 mg/kg, IP) reduced slow-wave sleep (SWS) latency. The reduction in SWS latency occurred at a time when 5-hydroxytryptamine (5-HT) concentration was reduced in the cortex, pons-medulla and striatum-thalamus with no change in the concentration of 5-hydroxyindoleacetic acid, a major metabolite of 5-HT. At the same time, norepinephrine concentration was reduced in the cortex, hippocampus and striatum-thalamus with a marked reduction (40%) in cortical dopamine (DA). The reduction of cortical DA coincided with a 53% decrease in homovanillic acid, a major metabolite of DA. The behavioral effect of tryptophan analog for six hours, as monitored by the EEG, was an increase in SWS by 25 min and a decrease in waking by 29 min. These data suggest that the effects of the tryptophan analog on sleep may be due to the attenuation of the activity of brain catecholamines and imply that tryptophan may as well produce its hypnotic effect via a similar mechanism.