Effects of oral administration of L-methionine on activity/rest rhythm

We describe a chronobiological study of the effects of the oral administration of the essential amino acid L-methionine to common quail (Coturnix coturnix). This amino acid is a precursor of the neurotransmitter acetylcholine which is responsible for controlling and maintaining wakefulness through the ventrolateral pre-optic area of the hypothalamus and controlling the REM sleep in the nucleus reticularis pontinus oralis (NRPO). The quail model was chosen as these birds are monophasic and active by day, as are humans. The animals were kept under a constant 12h:12h light/dark cycle, fed ad libitum and housed in separate cages equipped for activity recording. Methionine was administered daily (1 h before lights off) for 1 week (chronic treatment), with the birds divided into 4 groups: a capsule with 15 mg of L-methionine (Met15 treatment group); a capsule with 30 mg of L-methionine (Met30 treatment group); a capsule with methylcellulose as excipient (control group); no capsule (basal group). In addition, we compared the first day of treatment (acute experiment) with the basal and control results. Actimetry (DAS24 (c)) was used to quantify the activity data, and the sleep/wake rhythm was analyzed using the Ritme (c) software package. The statistical analysis of the activity data was descriptive (+/- SD) and inferential (Tukey test). The data showed increased (p<0.05) mean diurnal activity pulses in the Met30 group versus the other groups in both the acute and the chronic experiments. No changes were found in nocturnal activity. The chronobiological analysis showed a significant increase in the MESOR parameter of the Met30 group in both chronic and acute experiments versus the other groups. The acrophase showed no significant changes, in all groups being at around 13: 45 h. In conclusion, the oral administration of L-methionine increased diurnal activity; probably due to the stimulating neuromodulatory action of acetylcholine.