Involvement of Calcium in Pineal Gland Function

Abstract

he pineal gland functions as a neurohumoral transducer, accepting photic information from T the retinae and converting this neural message into chemical mediators, the best documented of which is melatonin (N-acetyl-5-methoxytryptamine) ( 1). The onset of darkness causes information to travel from the suprachiasmatic nuclei of the hypothalamus via the superior cervical ganglia to postganglionic sympathetic nerves that end in the pineal, where they release norepinephrine. The resultant stimulation of B-adrenergic receptors, possibly augmented by a-adrenergic stimulation, leads to an increased activity of N-acetyltransferase (NAT) (2), the rate-limiting enzyme involved in synthesis of melatonin ( 3 ) . Serotonin, derived from dietary tryptophan taken up by pinealocytes from the blood, is N-acetylated by NAT, which is subsequently 0-methylated by hydroxyindole-0-methyltransferase (HIOMT) to form melatonin, which is then released into the general circulation. Being a small lipophilic molecule, melatonin is generally considered to be released rapidly and passively following synthesis, although there is some evidence that short-term storage of melatonin by the pineal gland might occur (4).Melatonin's lipophilicity also ensures that it distributes widely to target tissues, which, therefore, receive photoperiodic information and can subsequently act with appropriate physiological responses ( 5 ) .The multiplicity of extracellular and intracellular ' Fullbright Fellow on leave from Department of Preclinical Veterinary Studies,

IMPORTANCE OF LIGHT IN TEMPORAL ORGANIZATION OF PHOTORECEPTOR PROTEINS AND MELATONIN-PRODUCING SYSTEM IN THE PINEAL OF CARPCATLA CATLA

“…Many aspects of pinealocyte activity, including a number of cellular processes within the pineal photoreceptors, are under the control of serum calcium (Ca ++ ), and therefore pineal functions are often related directly or indirectly to calcium metabolism (Morton & Reiter, 1991). In our study, the serum as well as intra-pineal Ca ++ levels in each carp group, by exhibiting significant negative correlation with the band intensities of pineal rod-like opsin and α-TD, suggest that the synthesis of photoreceptor proteins in the presence of light might be stimulated by the low levels of intra-pineal and serum Ca ++ .…”

Calbindin‐D28k, calretinin, and S‐100 immunoreactivities in rat pineal gland during postnatal development

“…The aim of our study was first to examine the distribution of these calcium-binding proteins during pineal postnatal development where calcium seems to play, at least in adult, an important role [Chik and Ho, 1989;Morton and Reiter, 1991;White and Klein, 19931, hoping to get insights into the ontogeny of calcium homeostasis; second we wanted to follow cellular morphological changes as well as modifications in cell distribution during this crucial period.…”

Thermotrophic Effect of Melatonin in Adrenalectomized and Thyroidectomized Rats

“…Involvement of calcium in pineal gland function, including synthesis of melatonin, is documented [21]. Whether the calcium lac tate given in drinking water to both the shamoperated controls and the TX rats in the 2nd experiment had an effect on endogenous mel atonin production remains to be studied.…”