Circadian rhythms and influence of light on serotonin, norepinephrine, and epinephrine contents in the pineal-paraphyseal complex of soft-shelled turtles (Lissemys punctata punctata).

The aims of the current investigation were to examine the circadian rhythms in the pineal-paraphyseal amines and indoleamine in juvenile turtles. An attempt was also made to study the influence of photoperiod on pineal activities in adult turtles. Serotonin, norepinephrine, and epinephrine levels were studied at four different time intervals (0600, 1200, 1800, and 2400 hr) of a 24-hr period. Increased serotonin level was observed during day and trough values during night, but the norepinephrine and epinephrine levels showed reverse changes. Continuous light (24L:0D) or long photoperiod (22L:2D) resulted in an elevation of serotonin level and diminution of norepinephrine level, but continuous darkness (0L:24D) or short photoperiod (2L:22D) showed reverse changes. Epinephrine level altered in parallel to that of norepinephrine with long (22L:2D) or short (2L:22D) photoperiod, but remained unaltered with continuous light (24L:0D) or continuous darkness (0L:24D). It is suggested that circadian rhythms exist in pineal-paraphyseal amines and indoleamine in juvenile turtles like that of adult turtles. It is also suggested that light greatly modulates serotonin, norepinephrine, and epinephrine contents in the pineal-paraphyseal complex of the soft-shelled turtle.