Effect of serotonin on α-melanocyte-stimulating hormone secretion from perifused frog neurointermediate lobe: evidence for the presence of serotonin-containing cells in the frog pars intermedia

Lamacz, Marek; Tonon, Marie‐Christine; Leboulenger, F.; Héry, F.; Idres, Sarah; Verhofstad, A.; Pelletier, Georges; Vaudry, Hubert

doi:10.1677/joe.0.1220135

Cited by 20 publications

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“…However, there is ample precedent for conservation of the functions of hypothalamic neuropeptides in the vertebrate phylum (37)(38)(39). Various studies have established that pituitary melanotrophs are regulated by multiple factors, including classical neurotransmitters and neuropeptides (12,30,(39)(40)(41)(42)(43). Coexistence of frog melanostatin with aminergic neuromediators and possible cooperation with other inhibitory factors, such as dopamine and y-aminobutyrate, deserve further investigation.…”

Section: Resultsmentioning

confidence: 99%

Characterization of melanotropin-release-inhibiting factor (melanostatin) from frog brain: homology with human neuropeptide Y.

Chartrel¹,

Conlon²,

Danger³

et al. 1991

Proc. Natl. Acad. Sci. U.S.A.

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A polypeptide was purified from frog brain extracts on the basis of its ability to inhibit a-melanotropin release from perifused frog neurointermediate lobes. Based on Edman degradation, amino acid analysis, and peptide mapping, the primary structure of this frog melanotropin-releaseinhibiting factor (melanostatin) was determined to be H-TyrPro-Ser-Lys-Pro-Asp-Asn-Pro-Gly-Glu-Asp-Ala-Pro-Ala-GluAsp-Met-Ala-Lys-Tyr-Tyr-Ser-Ala-Leu-Arg-His-Tyr-Ile-AsnLeu-Ile-Thr-Arg-Gln-Arg-Tyr-NH2. Frog melanostatin belongs to the pancreatic polypeptide/neuropeptide Y/peptide YY family, and the structure of this peptide differs from that of human neuropeptide Y by only one amino acid substitution in position 19. A synthetic replicate of frog melanostatin is coeluted with the native peptide on HPLC and is highly potent in inhibiting a-melanotropin secretion in vitro (IC50 = 60 nM).Both the anterior lobe and the intermediate lobe of the pituitary are regulated by hypophysiotropic factors originating from the hypothalamus (1, 2). Five families of hypothalamic neuropeptides involved in the control of anterior pituitary hormone secretion have now been characterized, namely, thyrotropin-releasing hormone (3, 4), gonadotropinreleasing hormone (5), somatostatin (6), corticotropinreleasing hormone (7), and growth hormone-releasing hormone (8,9 (20)(21)(22). However, many studies failed to demonstrate that these peptides meet the criteria expected of a physiological melanotropin-release-inhibiting factor (melanostatin) (23)(24)(25). We report here the purification, sequence analysis, and total synthesis of a 36-residue peptide that is highly potent in inhibiting the secretion of a-melanotropin from frog neurointermediate lobe in vitro. MATERIALS AND METHODSPurification Procedure. Adult frogs (Rana ridibunda) were obtained from a commercial source (Coudtard, St-Hilaire de Riez, France). The brains from 1200 animals (94.5 g, wet weight) were collected on dry ice and kept frozen. The tissue was boiled for 15 min in 0.5 M acetic acid and homogenized in a Waring blendor. After centrifugation (10,000 x g for 30 min at 40C), the supernatant was pumped at a flow rate of 2 ml/min through ten Sep-Pak C18 cartridges (Waters Associates) connected in series. Bound material was eluted with 70% (vol/vol) acetonitrile in water and lyophilized. The dry extract was dissolved in 10 ml of 1% (vol/vol) trifluoroacetic acid and chromatographed on a 2.5 x 100-cm column of Sephacryl S-100 (Pharmacia-LKB) equilibrated with 1 M acetic acid at a flow rate of 2 ml/min. Fractions (10 ml) were collected and absorbance was measured at 280 nm (Fig. 1A).The fractions exhibiting melanotropin-release-inhibiting activity were pooled and 50% of the total material was analyzed by HPLC.The active fraction was pumped at a flow rate of 2 ml/min onto a 1 x 25-cm Vydac 218 TP510 C18 column (The Separations Group) equilibrated with 0.1% trifluoroacetic acid and eluted at a flow rate of 2 ml/min, using the gradient indicated in Fig. 1B. Absorbance was measured at 214 and 280 ...

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Section: Resultsmentioning

confidence: 99%

Characterization of melanotropin-release-inhibiting factor (melanostatin) from frog brain: homology with human neuropeptide Y.

Chartrel¹,

Conlon²,

Danger³

et al. 1991

Proc. Natl. Acad. Sci. U.S.A.

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“…Immunocytochemical studies have shown that nerve terminals reaching melanotrope cells contain, in addition to dopamine [10, 13]and TRH [14, 15, 16, 17], the classical neurotransmitters γ-aminobutyric acid (GABA) [18, 19, 20]and serotonin [21, 22], as well as the neuropeptides mesotocin [17, 23], corticotropin-releasing factor [24, 25]and neuropeptide Y (NPY) [13, 20, 26, 27, 28, 29]. Double-labeling experiments also revealed that a single neuron may contain more than one factor.…”

Section: Introductionmentioning

confidence: 99%

Amphibian Melanotrope Subpopulations Respond Differentially to Hypothalamic Secreto-Inhibitors

et al. 2001

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The melanotrope population of the frog intermediate lobe consists of two subtypes of cells, referred to as high-(HD) and low-density (LD) melanotrope cells, which differ markedly in their basal morphofunctional features as well as their in vitro response to hypothalamic factors, such as the stimulator thyrotropin-releasing hormone (TRH) and the inhibitor dopamine. In this study, we have investigated whether other major hypothalamic regulators of the release of α-melanocyte-stimulating hormone (α-MSH), such as γ-aminobutyric acid (GABA) and neuropeptide Y (NPY), also differentially regulate frog melanotrope subpopulations. Our results show that in LD cells, both factors markedly inhibited proopiomelanocortin (POMC) mRNA accumulation and α-MSH secretion. In contrast, the secretory and biosynthetic activity of HD cells was not modified by GABA. NPY inhibited POMC transcript accumulation and tended to reduce α-MSH secretion in HD cells, yet these effects were less pronounced than those evoked in LD cells. In addition, GABA and NPY inhibited the KCl-induced rise in cytosolic free calcium levels in both subpopulations. Taken together, these results further indicate that frog melanotrope subpopulations are differentially regulated by the hypothalamus and strongly suggest that the intensity of such regulation is directly related to the activity of the cell subset. Thus, the LD subpopulation represents a highly responsive cell subset which is regulated by multiple neuroendocrine factors (TRH, dopamine, GABA and NPY), whereas the hormone storage HD subpopulation shows a moderate response to single stimulatory (TRH) and inhibitory (NPY) inputs.

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“…To obtain a high resolution of the multi- 24 Valentijn/Vaudry/Cazin Adrenaline-Activated Potassium Channels …”

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Adrenaline Induces Hyperpolarization in Frog Pituitary Melanotrophs through Activation of Potassium Channels

Valentijn

Vaudry²,

Cazin³

1994

Neuroendocrinology

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A patch-clamp study was conducted on cultured frog pituitary melanotrophs, in order to investigate the effects of adrenaline on the electrical activity of these cells. In the whole-cell configuration, adrenaline (1 µM) caused hyperpolarization that was accompanied by a fall in membrane input resistance and a blockage of spontaneous action potentials. Under voltage clamp, adrenaline elicited a net-outward current. The hyperpolarization became undetectable at a command voltage of –100 mV which corresponded to the equilibrium potential of potassium ions. The effect of adrenaline on membrane potential and spontaneous activity was blocked by the α₂-adrenergic receptor antagonist yohimbine (1-10 µM) but could not be mimicked by the α₂-adrenergic agonist clonidine (1–10 µM). In the cell-attached configuration, exposure of the extra-patch membrane to adrenaline increased the occurrence of single-channel currents with a slope conductance of 100 pS. The deduced reversal potential of these currents corresponded to the equilibrium potential of potassium ions. These results suggest that frog melanotrophs display an α₂-adrenergic receptor subtype coupled to potassium channels involved in hyperpolarization.

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Effect of serotonin on α-melanocyte-stimulating hormone secretion from perifused frog neurointermediate lobe: evidence for the presence of serotonin-containing cells in the frog pars intermedia

Cited by 20 publications

References 0 publications

Characterization of melanotropin-release-inhibiting factor (melanostatin) from frog brain: homology with human neuropeptide Y.

Characterization of melanotropin-release-inhibiting factor (melanostatin) from frog brain: homology with human neuropeptide Y.

Amphibian Melanotrope Subpopulations Respond Differentially to Hypothalamic Secreto-Inhibitors

Adrenaline Induces Hyperpolarization in Frog Pituitary Melanotrophs through Activation of Potassium Channels

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