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

Abstract

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.

Electrophysiological and Endocrinological Aspects of Aging in the Rat Pineal Gland

“…Melatonin synthesis appears to be de pressed since blood melatonin levels are reduced and the nocturnal peak is low. This agrees with previous studies carried out in rats [28,32], hamsters [27,31,33), gerbils [19] and humans [4, 6, 16, 4 1,42], all of which point to a fall in pineal melatonin synthesis or at least a change in the meta bolic clearance of the hormone. It has not been known whether the age-related decline in melatonin secretion is accompanied by a loss of the gland's electrical activity.…”

“…Ultrastructural changes suggest an age-associated decrease in the secretory processes in the pinealocyte of white-footed mice [20]. Increased signs of morphological degeneration in human pineals as a function of age was detected by means of light microscopy [15], electron microscopy and X-ray microanalysis [I] and computed tomography [46], With regard to secretory activity in the pineal gland of old animals, a decrease of pineal melatonin synthesis has Received: August 29, 1985 Accepted after revision: December 12, 1985 been described for the rat [28,32], the golden hamster [27,31,33], the gerbil [19] and humans [4, 6. 16, 41,42].…”

MT2 Melatonin Receptor Immunoreactivity in Neurons is Very High in the Aged Hippocampal Formation in Gerbils

“…Bar = 100 lm Cell Mol Neurobiol (2010) 30:255-263 261 distinct declines; one at puberty and the other from adulthood to senescence. It has been known that the ability of pineal gland to produce melatonin diminishes between 15 and 19 months of age in the gerbil and hamster (Reiter et al 1980;King et al 1981). In addition, about 50% reduction in the nocturnal rate of melatonin production was found in elderly subjects (Touitou 2001).…”

“…Aging is closely related to the reduction in melatonin concentration (Pierpaoli 1998). In elderly human and animals, day-night differences in melatonin secretion are almost absent (Reiter et al 1980;King et al 1981;Karasek 2004). On the other hand, pinealectomy appears to accelerate the aging process and reduce longevity (Reiter et al 1999;Payão et al 2001).…”

Melatonin in the Control of the Estrous Cycle of the Indian Desert Gerbil <i>(Meriones hurrianae: </i>Jerdon)

“…The hypothesis pro posed for the Syrian hamster is that the morn ing melatonin injections are ineffective in producing a gonadal response because the re ceptors for melatonin possibly are downregulated early in the light phase by their exposure to noctumally elevated levels of endogenous melatonin, and only late in the day do they regain their responsiveness to the hormone [4], This hypothesis may not hold for the Indian gerbil as they respond to melatonin injections at both the times. It is possible that, as in the Mongolian gerbil [23,24], the mela tonin rhythm in the Indian gerbil may be very weak and insufficient to downregulate the receptors. Alternately, it is also possible that a chronic presentation of melatonin daily at 9 a.m. may induce some discontinuity of noc turnal melatonin signal which in turn may be responsible for the varied response.…”