Age-associated changes in pineal serotonin N-acetyltransferase activity and melatonin content in the male gerbil

Pineal serotonin N-acetyltransferase (NAT) activity and melatonin content were measured in 2- and 15-month old male gerbils at various times over a 24h light:dark cycle (LD 14:10). A nocturnal increase over the low daytime values in NAT activity and melatonin content was noted in both 2- and 15-month old gerbils, suggesting the continued existence of a circadian rhythm in each of these biochemical parameters of pineal secretory function at least until 15-months of age. Notable differences in the levels of NAT activity and melatonin content between 2- and 15-month old gerbils included (1) a phase shift in peak NAT activity and melatonin content in 15-month old versus 2-month old gerbils and (2) a latent decrease in NAT activity in 15-month old gerbils after the onset of the light period relative to that in 2-month old gerbils.