Circadian variations in brain serotonin concentration in the lizard Anolis carolinensis

Whole brain serotonin content and concentration was determined in male and female rats using a modification of the extraction procedure outlined by Quay (1963). The mean concentration in male rats was found to be 0.61 [mu]g/g + 0.222 (S.D.) and in female rats the mean was significantly higher, i.e, O.89 [mu]g/g + 0.228 (S.D.) The mean concentration of 5-HT in the whole brain of male lizards was found to be as follows: 5.01 [mu]g/g + 1.63 at 7:00 AM, 1.57 [mu]g/g ± 0.935 at 12 noon, and 5.06 [mu]g/g + 1.33 at 4:00 PM. This indicates a definite circadian rhythm, with the minimum concentration occurring during the middle of the day.