EFFECTS OF MELATONIN ON MELATONIN RECEPTOR DENSITY IN THE SUPRACHIASMATIC NUCLEUS OF RAT HYPOTHALAMUS UNDER STRESS CONDITIONS

We investigated the possibility that strain-dependent differences in the diurnal pattern of wheel running activity rhythms are also reflected in the melatonin profiles. The inbred rat strains ACI/Ztm, BH/Ztm, and LEW/Ztm. LEW were examined for diurnal [12:12-h light-dark (LD)] wheel running activity, urinary 6-sulphatoxymelatonin (aMT6s) excretion, melatonin concentrations of plasma and pineal glands, and melatonin receptor density in the suprachiasmatic nuclei (SCN). ACI rats displayed unimodal activity patterns with a high level of activity, whereas BH and LEW rats showed multimodal activity patterns with ultradian components and reduced activity levels. In contrast, the individual daily profiles of aMT6s excretion and mean melatonin synthesis followed a unimodal time pattern in all three strains, suggesting that different output pathways of the SCN are responsible for the temporal organization of locomotor activity and pineal melatonin synthesis. In addition, melatonin synthesis at night and SCN melatonin receptor density at day were significantly higher in BH and LEW rats than in ACI rats. These results support the hypothesis of a long-term stimulating effect of melatonin on its own receptor density in the SCN.

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Differential Seasonal Regulation of Melatonin Receptor Density in the Pars Tuberalis and the Suprachiasmatic Nuclei: A Study in the Hedgehog (Erinaceus europaeus, L.)

Journal of Neuroendocrinology ◽

10.1111/j.1365-2826.1993.tb00540.x ◽

1993 ◽

Vol 5 (6) ◽

pp. 685-690 ◽

Cited By ~ 18

Author(s):

François Gauer ◽

Mireille Masson-Pévet ◽

Michel Saboureau ◽

Denise George ◽

Paul Pévet

Keyword(s):

Pars Tuberalis ◽

Receptor Density ◽

Suprachiasmatic Nuclei ◽

Melatonin Receptor ◽

Erinaceus Europaeus ◽

Seasonal Regulation

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Responsiveness to melatonin and its receptor expression in the aging circadian clock of mice

AJP Regulatory Integrative and Comparative Physiology ◽

10.1152/ajpregu.1997.273.6.r1855 ◽

1997 ◽

Vol 273 (6) ◽

pp. R1855-R1860 ◽

Cited By ~ 4

Author(s):

Susan Benloucif ◽

Monica I. Masana ◽

Margarita L. Dubocovich

Keyword(s):

Suprachiasmatic Nucleus ◽

Phase Shifts ◽

Receptor Expression ◽

Circadian Activity ◽

Melatonin Receptor ◽

Activity Rhythms ◽

Age Related ◽

Melatonin Administration ◽

Timing System ◽

Circadian Timing System

This study determined the effect of age on the efficacy of melatonin treatment to phase shift circadian activity rhythms and on melatonin receptor expression in the suprachiasmatic nucleus (SCN) and paraventricular nucleus of the thalamus (PVNT) of C3H/HeN mice. The circadian rhythm of 2-[125I]iodomelatonin binding, assessed at three times of the day [circadian times (CT) 2, 10, and 18], showed a modest age-related decrease in the SCN but not the PVNT of old C3H/HeN mice (24 mo). There was a tendency for age to reduce Mel1a melatonin receptor mRNA expression in the suprachiasmatic nucleus during the day, but not during the night. The magnitude of phase shifts of circadian activity rhythms (advances or delays) induced by administration of melatonin at CT 10 or CT 2 was identical in young and old C3H/HeN mice. Together, these results suggest that the decrease in melatonin receptor expression in the SCN had little effect on melatonin-induced phase shifts of circadian activity rhythms. We conclude that the responsiveness of the circadian timing system to melatonin administration does not decrease with age.

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