Pinealectomy and constant illumination increase the density of melatonin binding sites in the pars tuberalis of rodents

Guilhot, François; Masson-Pe´vet, M.; ́vet, P. Pe

doi:10.1016/0006-8993(92)90419-a

Cited by 55 publications

(35 citation statements)

References 33 publications

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“…Our results are consistent with earlier findings in the Atlantic salmon and goldfish [11,12]. Kj in the 4 species were in the range of 9-13 pmol/1 and considerably lower than the values in the whole brains of several spe cies of fish (K<j = 35-68 pmol/1) [11,12] and birds (Kd = 165-705 pmol/1) [16,[22][23][24][25] and the pars tuberalis of rats (K^ = 58-60 pmol/1) [17]. The number of 2-[125I]iodomelatonin binding sites (fW ) in brain membrane prepa rations from the salmonid species (10-15 fmol/mg protein) tended to be similar to the fish brains (Bmax = 7-14 fmol/mg protein) Time (min) less than 50% inhibition at 10 nmol/1 AS = Atlantic salmon; AC = Arctic charr; RT = rainbow trout; CS = coho salmon; K| = inhibition constant.…”

Section: Discussionsupporting

confidence: 82%

“…1 5-Hydroxy-L-tryptophan; L-epinephrinc; tryptophol; 5-methoxytryptophol, 5-mcthoxyindole-3-acetic acid; 5-methoxy-N,N-dimethyltryptamine; 5-mcthoxytryptamine; serotonin, N-methyltryptamine. [11,12], higher than that seen in the pars tuberalis membranes of rats (Bmax = 3-6 fmol/ mg protein) [ 17,19] but comparable to that of several birds (Bmax = 7-40 fmol/mg protein) [16,[22][23][24][25],…”

Section: Discussionmentioning

confidence: 97%

“…data] and steelhead trout [6,7] are also evident in Arctic charr and Atlantic salmon. In mammals and some birds, there is evidence of a causal relationship be tween the high nocturnal plasma melatonin levels and low density of 2-[125I]iodomelatonin binding sites in brain tissue [17][18][19]. More over, experimental manipulation of plasma melatonin levels brought about by pinealectomy or maintaining animals on an LL photo period to reduce daily melatonin levels or melatonin administration to elevate plasma melatonin levels shows a clear inverse rela tionship between the 2-[125I]iodomelatonin binding capacity and blood melatonin levels [16][17][18][19].…”

Section: Discussionmentioning

confidence: 99%

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2-[125I]Iodomelatonin Binding in the Brains of Four Salmonids

et al. 1994

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[¹²⁵I]-Labelled iodomelatonin binding to brain membrane preparations was examined in adults of 4 species of salmonid fishes; 3 species were of cultured stock (Arctic charr, Atlantic salmon, rainbow trout) and 1 was taken from the wild (coho salmon). The specific binding of 2-[¹²⁵I]iodomelatonin to the brain membrane preparations collected from all 4 species was specific, stable, saturable, reversible and of high affinity. Competitive inhibition studies showed that only melatonin, 2-iodomelatonin, 6-chloromelatonin and N-acetylserotonin showed significant inhibition of radioligand binding. In the 4 species studied, the equilibrium dissociation constant (K_d) ranged from 9.3 ± 0.2 pmol/l in coho salmon to 13.2 ± 0.7 pmol/l in rainbow trout, and those in rainbow trout were significantly higher (p < 0.05) than in the others. The maximum number of binding sites (B_max) of the Atlantic salmon preparations (14.3 ± 0.7 fmol/mg protein) was significantly higher than those of the other 3 species (means rang-ing from 9.9 to 11.6 fmol/mg protein). Hill coefficients of all 4 species were close to unity indicating one class of binding site. The interspecies differences in K_d and B_max could not be correlated with phylogeny or life history of the various species. For the three cultured species, samples were collected at both mid-dark and mid-light to examine for diurnal variations; none were found.

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Section: Discussionsupporting

confidence: 82%

Section: Discussionmentioning

confidence: 97%

Section: Discussionmentioning

confidence: 99%

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2-[125I]Iodomelatonin Binding in the Brains of Four Salmonids

et al. 1994

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“…It has, indeed, been shown that constant light exposure or short photoperiod modulates melatonin binding in the pars tuberalis of rodents [104,105], spleen of guinea pigs [106] and testis of quails [107]. The effect of constant light on melatonin binding sites is probably mediated via lightinduced decrease in serum melatonin with consequent up-regulation of the tissue receptors for melatonin.…”

Section: Hormonal Regulation Of Melatonin Receptor Bindingmentioning

confidence: 99%

Biological Basis and Possible Physiological Implications of Melatonin Receptor- Mediated Signaling in the Rat Epididymis

Shiu¹,

Li²,

Siu³

et al. 2000

Neurosignals

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The mammalian epididymis plays an important role in sperm maturation, an important process of male reproduction. Specific high-affinity 2-[¹²⁵I]iodomelatonin binding sites, satisfying the pharmacokinetic properties of specific receptors, have been found in the rat corpus epididymis, suggesting a direct melatonin action on epididymal physiology. Subsequent molecular and cell biology studies have identified these 2-[¹²⁵I]iodomelatonin binding sites to be mt₁ (MEL_1A) and MT₂ (MEL_1B) melatonin receptor subtypes. Changes in the binding characteristics of these receptors in the rat corpus epididymis in response to castration and steroid hormones like testosterone and hydrocortisone indicated that these membrane melatonin receptors are biologically functional receptors, whose activities are differentially regulated by testosterone and hydrocortisone. These melatonin receptors are coupled to pertussis toxin (PTX)-sensitive G_i protein and probably participate in androgenic and adrenergic regulation of rat corpus epididymal epithelial cell functions. Furthermore, rat corpus epididymal epithelial cell proliferation was stimulated by melatonin, whose action was dependent on the concentration and duration of exposure to the hormone. Interestingly, an MT₂ receptor ligand (4-phenyl-2-propionamidotetraline, 4-P-PDOT) induced a stimulatory effect on epididymal epithelial cell proliferation similar to that produced by melatonin. In contrast, a nuclear melatonin receptor agonist (1-[3-allyl-4-oxo-thiazolidine-2-ylidene]-4-methyl-thiosemi-carbazone, CGP52608) and 8-bromo-cAMP inhibited epididymal epithelial cell proliferation. Taken together, our data lead us to postulate that one of the possible physiological functions of melatonin on the rat epididymis is the stimulation of mt₁ and MT₂ melatonin receptors resulting in the inhibition of cAMP signaling and an increase in epithelial cell proliferation.

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“…Autoradiographic binding procedure was performed as previously described [41]. Sections were preincubated at 4°C for 15 min in Tris buffer (100 m M , pH 7.4) containing 4 m M CaCl 2 , and then incubated in the same buffer containing 100 p M 125 I-melatonin (Dupont NEN, France) with or without an excess of cold melatonin (1 µ M ) for 60 min at room temperature.…”

Section: Methodsmentioning

confidence: 99%

Melatonin Receptors in the Pituitary of a Teleost Fish: mRNA Expression, 2-[125I]Iodomelatonin Binding and Cyclic AMP Response

Gaildrat

Falcón²

2000

Neuroendocrinology

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Melatonin has for a long time been involved in the photoperiodic control of fish physiology (growth, reproduction) and behavior (locomotor activity); but its mechanisms of action are not understood. We show here that 2-[¹²⁵I]iodomelatonin binds specifically to membrane preparations from Pike (Esox lucius, L.) pituitaries (K_D: 556 pM; B_max: 2.8 fmol/mg proteins). Radioautography indicated that the binding was restricted to a part of the pituitary only. Using polymerase chain reaction from pike genomic DNA, we subcloned two partial cDNAs encoding the P1.4 (Mel_1a) and the P2.6 (Mel_1b) melatonin receptor subtypes. The two corresponding transcripts were expressed in the pituitary as revealed by RT-PCR assay and Southern blot hybridization. In culture, melatonin inhibited in a time- and dose-dependent manner cyclic AMP levels in pituitaries cultured in the presence of forskolin, an adenylyl cyclase activator. This is the first evidence for the expression of melatonin receptors and binding sites, and for the modulation of a second messenger by melatonin in the pituitary of a nonmammalian species. We suggest that in fish, the melatonin-mediated photoperiodic control of neuroendocrine functions involves, at least, a direct effect on the pituitary.

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Pinealectomy and constant illumination increase the density of melatonin binding sites in the pars tuberalis of rodents

Cited by 55 publications

References 33 publications

2-[<sup>125</sup>I]Iodomelatonin Binding in the Brains of Four Salmonids

2-[<sup>125</sup>I]Iodomelatonin Binding in the Brains of Four Salmonids

Biological Basis and Possible Physiological Implications of Melatonin Receptor- Mediated Signaling in the Rat Epididymis

Melatonin Receptors in the Pituitary of a Teleost Fish: mRNA Expression, 2-[<sup>125</sup>I]Iodomelatonin Binding and Cyclic AMP Response

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