Melatonin Receptors in Discrete Brain Areas of the Male Rat

Abstract

The distribution of melatonin receptors in six discrete brain areas of mature (3–4 months old) and aged (>24 months old) male rats was recorded every 4 h during a 24-hour light: dark cycle (L:D 14:10 h). ^I25I-melatonin was used as a melatonin receptor probe. In the mature animals, specific binding of ¹²⁵I-melatonin was found in all brain areas investigated, i.e. hypothalamus, medulla pons, hippocampus, cerebellum, parietal cortex and striatum. The density of ¹²⁵I-melatonin-binding sites in the hypothalamus, medulla pons and hippocampus exhibited clear diurnal rhythms with different patterns and phases. No such rhythm was evident in the cerebellum, parietal cortex and striatum. The apparent affinity of the binding sites was similar in all the brain regions and did not change at any of the times recorded. In the old male rats, the density of ¹²⁵I-melatonin binding sites in the hypothalamus was only 10% of that in the mature animals at 13 h after the onset of light and was vanishingly small throughout the 24-hour period. The 24-hour mean of the binding site density in the parietal cortex, hippocampus and medulla pons was significantly lower than in mature rats with no apparent diurnal variations. The age-related decrease in the density of melatonin-binding sites was less pronounced in the cerebellum and striatum. In all brain areas tested, apart from the hypothalamus, the decrease in receptor densities was not accompanied by changes in the apparent affinity towards the ligand. Serum concentrations of melatonin measured by radioimmunoassay exhibited a significant nocturnal rise in the rats, but in the aged this rise was about one third of that in the mature animals. The results clearly indicate diurnal rhythms in ¹²⁵I-melatonin binding in the hypothalamus, medulla pons and hippocampus of mature rats, vanishing in the aged animals despite persistence of rhythm in circulating melatonin. In addition, a definite age-related decline in melatonin receptors is evident, particularly in the hypothalamus and hippocampus.

Melatonin Nocturnal Surge Modulates Nicotinic Receptors and Nicotine-Induced [3H]Glutamate Release in Rat Cerebellum Slices

“…Antioxidative stress activity in cerebellar tissue and granular cerebellum cells (Mason et al, 1999) and inhibition of granule cells apoptosis (Persengiev, 2001) were demonstrated. Melatonin membrane receptors were identified in rat and human cerebellum by binding techniques (Laudon et al, 1988;Al-Ghoul et al, 1998); however, melatonin function on cerebellar neurons is still poorly understood.…”

Melatonin Receptor (Mt1 and Mt2) Proteins Expression in Thyroid Gland and Level of Thyroxin (T4), Thyrotropin (Tsh) Hormone During Progression of Age in Male Swiss Albino Mice

“…The reduced expression of MT2 melatonin receptor in hippocampal region of Alzheimer's patients was also mentioned 52 . Further age-related lowering in the density of melatonin binding sites was reported in discrete hypothalamic and hippocampal region of rat brain 33 . Declining expression of melatonin receptors with age in caudal artery of hypertensive rats was also reported 53 .…”

“…Melatonin also helps to inhibited lipid peroxidation stimulated by fenton in the thyroid gland 28 . An age-related decline in melatonin receptor binding sites in several tissues of different species including the rat, Syrian hamster and mice supra chiasmatic nucleus (SCN), rat brain [32][33][34] suggested declined melatonin activity in those tissues during aging. In thyroid gland melatonin receptors binding sites were also reported but till date age related patterns of melatonin receptor proteins expression was unknown.…”

Melatonin and the Aging Brain

“…Dax and Sugden [9] reported that reduced serum melatonin level and pineal melatonin level in the rat refl ected a decreased ability of the pineal gland to synthesize melatonin. There was also an age-related reduction in density of melatonin-binding sites in the parietal cortex, hippocampus and medulla pons and a less conspicuous decrease in cerebellum and striatum [10] . Sharma et al [11] reported that plasma melatonin level declined with aging in humans.…”