Fig. 3. Effects of two amino acids and combined GABA/5-HTP on (A) sleep onset and (B) duration in caffeine-induced sleepless mice intraperitoneal injected a hypnotic dosage of pentobarbital (42 mg/kg, i.p.).

Values are mean ± SE (n = 50). Different letters indicate significant differences at P < 0.05 by Tukey's test and different symbols indicate significant differences ^**P < 0.01, ^***P < 0.001 by Dunnett's test. GABA, γ-aminobutyric acid; 5-HTP, 5-hydroxytryptophan.