No Orcadian Rhythms of Serotoninergic, Alpha-, Beta-Adrenergic and Imipramine Binding Sites in Rat Brain Regions

Lauro, Andrea Di; Giannini, Clemente Patrizio; Muscettola, Giovanni; Greco, Anna Maria; Franciscis, P De

doi:10.3109/07420528609066356

Cited by 12 publications

(2 citation statements)

References 8 publications

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“…There is no correlation between the regional distri bution and phase position of melatonin receptor rhythms and the rhythms in muscarinic, p-and «2-adrenergic, GABAergic and imipramine-binding sites at discrete areas of the brain [21 ]. The density of WB-4101 -binding sites (cti-and ci2-adrenoceptor ligands) in the hypothalamus shows a diurnal rhythm similar to that of melatonin, with maximal density during the light phase which declines after the be ginning of the dark phase [8], On the other hand, other groups were unable to show significant rhythmicity in the density of ai-binding in the cortex, hypothalamus and brain stem of the rat [3]. Further experimental efforts will be re quired in order to determine precisely the association of melatonin receptors with specific types of neurons in the brain and elucidate the mechanism responsible for the ob served rhythms.…”

Section: Discussionmentioning

confidence: 98%

Melatonin Receptors in Discrete Brain Areas of the Male Rat

Nir²,

1988

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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.

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Section: Discussionmentioning

confidence: 98%

Melatonin Receptors in Discrete Brain Areas of the Male Rat

Nir²,

1988

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“…From the results described here, a lowered level of a2-receptor binding during the dark phase might be predicted; however, this appears not to have been the case in the study of Krauchi et al (1984) where peak binding occurred at dusk. Never¬ theless, it is apparent that there is a large degree of diversity, not only between different strains of rat (Di Lauro, Giannini, Muscettola et al 1986), but also between lines of rat strains (Jenni-Eiermann, von figure 5. Effect of yohimbine (YOH) on the lack of a vasoactive intestinal polypeptide (VIP) response to + during the light phase.…”

Section: Resultsmentioning

confidence: 97%

Diurnal variation in the effect of potassium depolarization on vasoactive intestinal polypeptide release from rat hypothalamus: a possible role for adrenaline

Burns

Brown²,

Dobson³

1988

Journal of Endocrinology

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We have previously reported a lack of effect of a depolarizing concentration of K+ on the release of vasoactive intestinal polypeptide (VIP) from the perifused rat hypothalamus, and suggested that this was due to the presence of an endogenous inhibitor of the release of VIP. In this study we report that the VIP response to K+ was restored if the hypothalami were obtained from animals killed during the dark phase of the light-dark cycle. Adrenaline blocked the K+-stimulated release of VIP when used at a concentration of 0.1 mumol/l; however, at a higher concentration (10 mumol/l) adrenaline stimulated the basal release of VIP. The use of specific receptor antagonists indicated that this dual effect of adrenaline was mediated through two distinct receptors, a stimulatory beta-receptor and an inhibitory alpha 2-receptor. The suggestion that adrenaline might be the endogenous inhibitor of the release of VIP, mediating the diurnal variation in the effect of K+, was supported by studies where 50 mmol K+/l was perifused concomitantly with an alpha 2-antagonist, restoring the VIP response to K+ in light-phase hypothalami. In conclusion, adrenaline has a dual role in the control of VIP release and may function to inhibit the K+-stimulated release of VIP in our system.

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Rhythms in second messenger mechanisms

Witte

1991

Pharmacology & Therapeutics

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No Orcadian Rhythms of Serotoninergic, Alpha-, Beta-Adrenergic and Imipramine Binding Sites in Rat Brain Regions

Cited by 12 publications

References 8 publications

Melatonin Receptors in Discrete Brain Areas of the Male Rat

Melatonin Receptors in Discrete Brain Areas of the Male Rat

Diurnal variation in the effect of potassium depolarization on vasoactive intestinal polypeptide release from rat hypothalamus: a possible role for adrenaline

Rhythms in second messenger mechanisms

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