Circadian variations in melatonin‐binding sites in discrete areas of the male rat brain

Abstract

The binding of lZSI-melatonin to synaptosomes prepared from whole brains of male rats of the CD strain and from the brain, hypothalamus and striatum of male rats of the Sabra-Wistar strain was assessed throughout a 24 h period. The animals were maintained under a daily schedule of 14 h light (05:0&19:00 h) and 10 h darkness. In whole brain preparations the density of binding sites at 1890 h was higher by about 70% than at 02%~ h with no variations in apparent affinity of the binding sites throughout the daily period. Specific binding of iZSI-melatonin was found in both hypothalamus and striatum of the male rat with a distinct diurnal variation in binding site density in the hypothalamus only. The density of 12sI-melatonin-binding sites in the hypothalamus was maximal between 1O:OO and 18:00 h and dropped sharply after the lights went off. The apparent lZSI-melatonin-binding affinities in these regions were constant and very similar to those in whole brain preparations. The daily variations in densities of '251-melatonin-binding sites in discrete brain areas may represent a diurnal rhythmicity in the responsiveness of the neuroendocrine axis to melatonin.

Circadian actions of melatonin at the suprachiasmatic nucleus

“…2-[~25I]-Iodomelatonin binding within the SCN has been reported to change over the circadian cycle of rats reared in a 12-h light 12-h dark cycle [8,17,38,41]. The pattern of 2-[~zsI]-iodomelatonin binding, measured either by quantitative autoradiography or radioreceptor binding, oscillated with a circadian rhythm; highest binding appeared during the period surrounding the day-to-night transition [8,38,41] (however, see [17]).…”

“…The pattern of 2-[~zsI]-iodomelatonin binding, measured either by quantitative autoradiography or radioreceptor binding, oscillated with a circadian rhythm; highest binding appeared during the period surrounding the day-to-night transition [8,38,41] (however, see [17]). Whether sensitivity to 2-[~2sI]-iodomelatonin binding is regulated by the light-dark cycle or the circadian clock could not be determined from these studies.…”

Weak Magnetic Fields as a Novel Therapeutic Modality in Parkinson's Disease

“…The mechanisms underlying this phenomenon remain unexplained; changes in dopamine receptor sensitivity or postreceptor events are unlikely to explain the diurnal fluctuations in symptoms (Gancher & Nutt, 1987). However, the observations that melatonin secretion and melatonin binding sites undergo diurnal variations Chan & Ebadi, 1980;Zisapel et al, 1988) as well as the findings of circadian variations in the inhibition of dopamine release by melatonin (Zisapel et al, 1985), suggest a temporal relationship between fluctuations in Parkinsonian motor symptoms and diurnal variations in melatonin functions.…”

Antipsychotic-like effect of agomelatine in a rodent model

“…Some evidences suggest that melatonin modulates the striatal and limbic activity (26). Melatonin-binding sites have been found in some brain areas such as the striatum and the limbic system, which have rich dopamine content (26). It has also been hypothesized that melatonin inhibits the limbic dopaminergic activity, thus mesolimbic and mesocortical dopamine tone may increase when the melatonin secretion decreases (15,27).…”

“…Theoretically, the anti-psychotic effect is mediated by means of antidopaminergic activity in certain regions of the central nervous system. Some evidences suggest that melatonin modulates the striatal and limbic activity (26). Melatonin-binding sites have been found in some brain areas such as the striatum and the limbic system, which have rich dopamine content (26).…”