Age-Associated Changes in Pineal Serotonin N-Acetyltransferase Activity and Melatonin Content in the Male Gerbil

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Abstract
Pineal serotonin N-acetyltransferase (NAT) activity and melatonin content were measured in 2- and 15-mo.-old male gerbils at various times over a 24 h 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-mo.-old gerbils, suggesting the continued existence of a circadian rhythm in each of these biochemical parameters of pineal secretory function at least until 15-mo. of age. Notable differences in the levels of NAT activity and melantonin content between 2- and 15-mo.-old gerbils included a phase shift in peak NAT activity and melatonin content in 15-mo.-old vs. 2-mo.-old gerbils and a latent decrease in NAT activity in 15-mo.-old gerbils after the onset of the light period relative to that in 2-mo.-old gerbils.