Pineal indoleamine metabolism in the cotton rat, Sigmodon hispidus: studies on norepinephrine, serotonin, N-acetyltransferase activity and melatonin.

The purpose of this study was to examine the levels of norepinephrine (NE), serotonin, melatonin and N-acetyltransferase (NAT) activity in the cotton rat pineal gland in relationship to environmental lighting. In each of two experiments cotton rats were collected from the wild and housed indoors in a 14:10 light:dark (LD) cycle (lights on at 0600) for a period of at least two weeks. Pineal glands were removed from animals in groups of eight at 0800, 1200, 1600, 2000, 2400, 0200 and 0400 hours over a 24 hour period for each experiment. Collection was done under a dim red light during the nighttime hours. In the first experiment pineal melatonin production showed a striking circadian rhythm with nighttime levels 20 times greater than that of daytime levels. In the second experiment pineal NE, serotonin and NAT activity were measured in aliquots from the same gland. NE showed no circadian rhythm whereas serotonin values were significantly depressed at night. The nighttime NAT activity rose to 10 times that of the daytime level. The NAT peak was concurrent with the melatonin peak. These data indicate that the neural and the biochemical control of the cotton rat pineal may be similar to that of other mammalian species.