Regulation of eye and jaw colouration in three-spined stickleback Gasterosteus aculeatus.

Fish can change their skin and eye colour for background matching and signalling. Males of Gasterosteus aculeatus develop ornamental blue eyes and a red jaw during the reproductive season, colours that are further enhanced during courtship. Here, the effects of different hormones on physiological colour changes in the eyes and jaws of male and female G. aculeatus were investigated in vitro. In an in vivo experiment, G. aculeatus were injected with a receptor blocker of a pivotal hormone (noradrenaline) that controls colour change. In males, noradrenaline had aggregating effects on melanophore and erythrophore pigments resulting in blue eyes and a pale jaw, whereas melanocyte-concentrating hormone (MCH) and melatonin resulted in a pale jaw only. When noradrenalin was combined with melanocyte stimulating hormone (MSH) or prolactin, the jaw became red, while the eyes remained blue. In vivo injection of yohimbine, an alpha-2 adrenoreceptor blocker, resulted in dispersion of melanophore pigment in the eyes and inhibited the blue colouration. Altogether, the data suggest that noradrenalin has a pivotal role in the short-term enhancement of the ornamental colouration of male G. aculeatus, potentially together with MSH or prolactin. This study also found a sex difference in the response to MCH, prolactin and melatonin, which may result from different appearance strategies in males, versus the more cryptic females.

Localization of amylin-like immunoreactivity in melanocyte-stimulating hormone-containing cells of the pars intermedia but not those of the pars distalis in the axolotl (Ambystoma mexicanum) pituitary.

Immunohistochemical techniques were employed to investigate the distribution of amylin-like immunoreactivity in the axolotl (Ambystoma mexicanum) pituitary. Amylin-immunoreactive cells were observed in the pars intermedia, and these cells were found to be immunoreactive for α-melanocyte-stimulating hormone (αMSH) as well. In contrast, αMSH-immunoreactive cells in the pars distalis were immuno-negaitive for amylin. These light microscopic findings were confirmed by immunoelectron microscopy. Amylin-immunoreactive signals were located on the haloes of presumable secretory granules in association with αMSH-immunoreactive signals in the amylin-positive cells. However, in the pars distalis, the αMSH-positive cells did not contain amylin-immunoreactive secretory granules. Western blot analysis of axolotl pituitary extracts revealed the labeling of a protein band at approximately 10.5-kDa by the anti-rat amylin serum, which was not labeled by the anti-αMSH antibody. These findings indicate that amylin secreted from MSH-producing cells in the pars intermedia may modulate MSH secretion in an autocrine fashion and may participate in MSH functions such as fatty homeostasis together with MSH.

Cannabinoid CB1 receptor restrains accentuated activity of hypothalamic corticotropin-releasing factor and brainstem tyrosine hydroxylase neurons in endotoxemia-induced hypophagia in rats.

It is well known that endocannabinoids play an important role in the regulation of food intake and body weight. Endocannabinoids and cannabinoid receptors are found in the hypothalamus and brainstem, which are central areas involved in the control of food intake and energy expenditure. Activation of these areas is related to hypophagia observed during inflammatory stimulus. This study investigated the effects of cannabinoid (CB1) receptor blockade on lipopolysaccharide (LPS)-induced hypophagia. Male Wistar rats were pretreated with rimonabant (10 mg/kg, by gavage) or vehicle; 30 min later they received an injection of either LPS (100 µg/kg, intraperitoneal) or saline. Food intake, body weight, corticosterone response, CRF and CART mRNA expression, Fos-CRF and Fos-α-MSH immunoreactivity in the hypothalamus and Fos-tyrosine hydroxylase (TH) immunoreactivity in the brainstem were evaluated. LPS administration decreased food intake and body weight gain and increased plasma corticosterone levels and CRF mRNA expression in the PVN. We also observed an increase in Fos-CRF and Fos-TH double-labeled neurons after LPS injection in vehicle-pretreated rats, with no changes in CART mRNA or Fos-α-MSH immunoreactive neurons in the ARC. In saline-treated animals, rimonabant pretreatment decreased food intake and body weight gain but did not modify hormone response or Fos expression in the hypothalamus and brainstem compared with vehicle-pretreated rats. Rimonabant pretreatment potentiated LPS-induced hypophagia, body weight loss and Fos-CRF and Fos-TH expressing neurons. Rimonabant did not modify corticosterone, CRF mRNA or Fos-α-MSH responses in rats treated with LPS. These data suggest that the endocannabinoid system, mediated by CB1 receptors, modulates hypothalamic and brainstem circuitry underlying the hypophagic effect during endotoxemia to prevent an exaggerated food intake decrease. This article is part of a Special Issue entitled 'Central Control of Food Intake'.

Activation of the proopiomelanocortin gene with ketoconazole as a treatment for Parkinson's disease: a new hypothesis.

Parkinson's disease is a neurodegenerative process characterized by progressive degeneration of the substantia nigra and concurrent loss of neuromelanin in these structures. The present hypothesis suggests that progression of Parkinson's disease may be reduced by enhancing the regional levels of neuroprotective factors derived from proopiomelanocortin (POMC). One practical means to accomplish this goal may be administration of ketoconazole or other inhibitors of corticosteroid synthesis at doses sufficient to stimulate hypophyseal secretion of POMC. The POMC constituents adrenocorticotropic hormone (ACTH) and melanocycle-stimulating hormone (MSH), which mobilize neuromelanin generation and lipotropins, those motivating lipid components of neuromelanin and endorphin, which then together stimulate and protect neural components of the substantia nigra.

Effects of Coccoloba uvifera L. on UV-stimulated melanocytes.

BACKGROUND: Exposure to ultraviolet (UV) radiation induces generation of reactive oxygen species, production of proinflammatory cytokines and melanocyte-stimulating hormone (MSH) as well as increase in tyrosinase activity. The potential photoprotective effects of Coccoloba uvifera extract (CUE) were evaluated in UV-stimulated melanocytes. METHODS: Human epidermal melanocytes were used as an in vitro model to evaluate the effects of CUE on the production interleukin-1alpha (IL-1alpha), tumor necrosis factor alpha (TNF-alpha), and alpha-MSH under basal and UV-stimulated conditions. Antioxidant and anti-tyrosinase activities were also evaluated in membrane lipid peroxidation and mushroom tyrosinase assay, respectively. RESULTS: Coccoloba uvifera L. showed antioxidant and anti-tyrosinase activities and also inhibited the production of IL-1alpha, TNF-alpha and alpha-MSH in melanocytes subjected to UV radiation (P<0.01). Moreover, CUE inhibited the activity of tyrosine kinase in cell culture under basal and UV radiation conditions (P<0.001), corroborating the findings of the mushroom tyrosinase assay. CONCLUSION: This study supports the photoprotective potential of CUE.

Involvement of somatolactin in background adaptation of the cichlid fish Cichlasoma dimerus.

Somatolactin (SL) is a pituitary hormone present exclusively in fish that is involved in different physiological processes. The role of SL was evaluated in Cichlasoma dimerus (Teleostei, Perciformes) exposed for 10 days to a black and white background (BB and WB). Changes in alpha-melanophore stimulating hormone (alphaMSH) and melanin concentrating hormone (MCH) cells were also analyzed for comparison with SL. A melanin dispersing effect was observed in fish exposed to a BB, while a concentrating one was observed in those exposed to a WB. By Western blot, three SL-immunoreactive (ir) bands (32, 28 and 23.5 kD) were evidenced. Pituitary SL-ir levels were 2.66- and 2.67-fold greater in the 32 Kd and 28 kD bands, respectively, in BB fish compared with those of WB fish. The SL-ir 23.5 Kd band was not included in the analysis because of its unknown identity. In addition, SL-ir cell number and area were significantly higher in the BB condition (BB 22.73+/-1.46, WB 7.37+/-0.54 and BB 27.39+/-1.00 microm2; WB: 16.61+/-0.65 microm2). No significant differences were observed in the number of the hypothalamic MCH-ir neurons. However, a significant difference was observed in their nuclear area (BB 11.61+/-0.42 microm2, WB 17.80+/-0.84 microm2). alphaMSH-ir cells showed a marked increased in number (BB 35.96+/-1.22, WB 24.36+/-1.04), but no significant differences were observed in the cell area. In conclusion, this study presented clear evidence towards a possible involvement of SL in the adaptation to background colors in teleost together with alphaMSH and MCH.

Coat colour changes associated with cabergoline administration in bitches.

Cabergoline or bromocriptine were administered orally to 60 bitches at doses of 5 microg/kg and 15 microg/kg daily, respectively, for two to 45 days for the treatment of pseudopregnancy or for oestrus induction. Seven of the dogs which received cabergoline for more than 14 days developed coat colour changes from the second week of administration to the next coat shedding. Of these, fawn-coloured bitches developed a yellowish coat colour while Argentine boar hounds became black spotted, mainly on their extremities. In previous untreated oestrous periods, these bitches had shown no coat colour changes. It is concluded that a colour shift in certain haircoats of particular breeds could be mediated through the inhibition of the secretion of melanocyte-stimulating hormone by the administration of the dopaminergic agonist cabergoline for more than two weeks. Transient coat colour changes should be considered a possible side effect when planning long-term treatment with dopaminergic agonists in dogs.

Postnatal decrease of sodium current density in rat pituitary melanotropes following the onset of dopaminergic innervation.

Peptide secretion from rat melanotropes is tonically inhibited by a dopaminergic synaptic input that develops after birth and acts through D2 dopamine receptors. In this study, whole-cell Na(+) currents were recorded from melanotropes that were isolated from rat pituitary intermediate lobes at postnatal days 1-20 (P1-P20) and maintained in culture for 5-24 h. Coincident with the development of innervation, melanotropes exhibited a progressive decrease in peak Na(+) current density from P3 to P14. The decrease involved a 50% reduction in maximal Na(+) conductance with no detectable changes in channel gating. Subcutaneous injections of the D2 antagonist sulpiride, applied from P11 to P13, restored melanotrope Na(+) channel activity to pre-innervation levels. Thus, the activation of D2 receptors by the dopaminergic input reduces the functional expression of Na(+) channels in melanotropes.

Fluorescence study of conformational properties of melanotropins labeled with aminobenzoic acid.

The native hormone alpha-melanocyte-stimulating hormone (alpha-MSH) and its more potent analog [Nle(4),D-Phe(7)]alpha-MSH (NDP-alpha MSH), labeled at the amino terminal with the fluorescent aminobenzoic acid (Abz) isomers, were examined by fluorescence methods. We observed energy transfer between the tryptophan(9) residue acting as donor and Abz as acceptor, the transfer being more pronounced to the ortho-form of the acceptor. Within the hypothesis that different peptide conformations coexist in equilibrium during the fluorescence decay, we supposed that the intensity decay was modulated by an acceptor-donor distance distribution function f(r). From the time-resolved fluorescence experimental data, we recovered the distance distribution between Abz and Trp(9), using the CONTIN program, within the framework of the Förster resonance energy transfer model. The methodology proved to be useful to provide quantitative information about conformational dynamics of melanotropins and its dependency on the solvent. In aqueous medium, alpha-MSH has a broad Abz-Trp(9) distance distribution, reflecting the structural flexibility of the peptide. Three different distance populations could be identified in the labeled analog NDP-alpha MSH in water, indicating distinct conformational states for the synthetic peptide, compared with the native hormone. Measurements in trifluoroethanol resulted in the recovery of two Abz-Trp(9) distance populations, both for the native and the analog hormones, reflecting the decrease, induced by the solvent, of the conformational states available to the peptides.

In vitro expression of tyrosine hydroxylase by a subpopulation of rat melanotrophs is down-regulated by dopamine.

Some rat melanotrophs express in vivo tyrosine hydroxylase mRNA. In this report we show, by Western-blotting, that cultures of adult rat melanotrophs, but not adenohypophyseal cells, express tyrosine hydroxylase. Immunocytochemical analyses confirmed the existence of a subpopulation of melanotrophs expressing tyrosine hydroxylase. Bromocryptine (2.5 x 10(-7) M), a D2 dopamine agonist, down-regulated melanotroph tyrosine hydroxylase expression in a time-dependent manner; initial effect was detected at 15 h and maximum at 3 days treatment (reduction to about 40% of control values). Down-regulation at 3 days was dose-dependent (ED(50) around 2 x 10(-9) M). This decrease was reversed by sulpiride, a D2 dopamine antagonist. The cell number was slightly increased by bromocryptine treatment. These data suggest tyrosine hydroxylase expression in melanotrophs being under tonic inhibitory control by dopamine innervation in vivo.

The distribution of melanin-concentrating hormone in the monkey brain (Cebus apella).

Melanin-concentrating hormone was identified in the brain of Cebus monkey using immunohistochemical and in situ hybridization. MCH-immunoreactive neurons were found in the lateral hypothalamus and dorsolateral zona incerta. MCH-ir fibers were seen in the medial mammillary nucleus, and in the median eminence, and very few fibers in the globus pallidus. This is the first report describing the MCH-ir cell and fiber distribution in the monkey brain.

Structure-activity correlations of melanotropin peptides in model lipids by tryptophan fluorescence studies.

Steady-state and time-resolved fluorescence spectroscopy were employed in the study of the structure and interactions of alpha-MSH (alpha-melanocyte-stimulating hormone) and its analogs, [Nle4,D-Phe7]-alpha-MSH (MSH-I) and Ac-[Nle4,Asp5,D-Phe7,Lys10]-alpha-MSH(4-10)-NH2 (MSH-II). In aqueous buffer, the fluorescence parameters of the single tryptophan of alpha-MSH and MSH-I were similar and did not allow any distinction between these molecules. On the other hand, the tryptophan fluorescence of MSH-II was notably different, reflecting its cyclic lactam turn structure. In the presence of acidic lipid vesicles, the fluorescence properties of the peptides were different, indicating structural changes on incorporation of the peptide into the liquid-crystalline phase of the lipid. No evidence of interaction was observed in the presence of the neutral lipid dimyristoylphosphatidylcholine (DMPC). The association constants for lipid-peptide interactions were compared for binding isotherms which either neglected or accounted for electrostatic effects through Gouy-Chapman potential functions. The relative order of association constants in either treatment was MSH-II > MSH-I > alpha-MSH. These results parallel the reported biological activities that show increased potencies and prolongation of response for the analogs, MSH-II and MSH-I, as compared to the native hormone, alpha-MSH. Time-resolved fluorescence results showed that the fluorescence decay of melanotropins is best described by triple-exponential kinetics. In the lipid-peptide complex, there was a change in the relative concentrations of the components, with the intermediate-lifetime component predominating compared to those in solution.(ABSTRACT TRUNCATED AT 250 WORDS)

Cytological differences in the localization of glucocorticoid receptor-like immunoreactivity in the normal and transplanted pituitary pars intermedia.

Glucocorticoid receptor-like immunoreactivity (GCRI) was found in the normal pituitary pars intermedia (PI) when immunohistochemistry was used. Since in previous studies we described two kinds of cells in the denervated (grafted) PI, i.e., "light cells" (overactive cells which do not contain detectable melanocyte-stimulating hormone) and "dark cells" (hypoactive cells which contain the hormone), it was decided to investigate whether different patterns of distribution of the receptors could be detected in the grafted gland when compared with the intact PI. Intact glands showed the receptors located in the nucleus. In transplanted glands, it was observed that light cells showed receptors in both the nuclei and the cytoplasm; on the other hand, dark cells displayed them in the nuclei only, as is the case in all cells of the normal PI. We had previously interpreted dark cells as dopamine-indifferent, whereas light cells were considered dopamine-sensitive. The changes in the distribution of GCR after denervation by grafting, which only affected the light cells, support the view of other authors that GCR of the pars intermedia are under the influence of dopamine and reinforce our opinion that dark cells are dopamine-indifferent.

Transplantation of the pituitary pars distalis induces the corticotrophs to store melanocyte-stimulating hormone, an effect reversed by the administration of corticotropin-releasing factor.

Corticotrophs of the pituitary pars distalis do not contain immunohistochemically detectable alpha-melanocyte-stimulating hormone (MSH). After grafting the glands beneath the renal capsule for 25 days, this hormone could be demonstrated in corticotrophs, coexisting with corticotropin. The administration of corticotropin-releasing factor deprived these cells of the content of MSH but did not apparently affect the presence of adrenocorticotropin (ACTH). It is suggested that the histological appearance of MSH in the corticotrophs may be due to a diminished rate of corticotropin release, which may provide time for splitting the former hormone in amounts larger than the negligible ones normally present in the pars distalis, or to the hypothetical fact that some hypothalamic factor may inhibit the cleavage of ACTH into MSH.

Secretion of melanocyte-stimulating hormone and adrenocorticotropin from transplanted pituitary pars intermedia in stressed and nonstressed rats.

Rats bearing kidney grafts of the pituitary pars intermedia were divided into three groups: unstressed, acutely stressed, and chronically stressed. Corresponding sham-operated rats were used for comparisons. Twenty days after grafting, the rats were sacrificed and alpha-melanocyte-stimulating hormone (alpha-MSH), adrenocorticotropin (ACTH), and corticosterone were estimated in plasma. The adrenal/body weight ratio and DNA content of the glands were also investigated. The following results were obtained: MSH was found not to be increased in unstressed rats, but it was in grafted animals subjected to acute and chronic swimming stress. ACTH and corticosterone rose in all three groups. Adrenal/body weight ratio and DNA content increased only in grafted chronically stressed rats. Moreover, plasma corticosterone was found higher in grafted hypophysectomized rats than in non-grafted hypophysectomized animals. Administration of ergocryptine to nonstressed grafted rats induced a decrease in the blood content of ACTH and MSH, indicating that the grafts were the source of a part of the circulating ACTH. On the other hand, the fall in MSH levels could show the effect of the drug upon the pars intermedia. Comparison of the ratios of both hormones released in incubations showed that grafts secreted more ACTH than MSH; on the other hand, when intact neurointermediate lobes were incubated, MSH predominated over ACTH. For the first time it is demonstrated that the pars intermedia can secrete ACTH in vivo. Nevertheless, the ability to secrete this hormone is not a property of normal intact pars intermedia, but it manifests in the transplantations probably due to the overactivity of light cells induced by chronic stoppage of dopaminergic inhibition.

Melanotropin structure-activity studies on melanocytes of the teleost fish, Synbranchus marmoratus.

The minimal sequence of alpha-MSH required for full agonism on fish (Synbranchus marmoratus) melanocytes was determined to be Ac-alpha-MSH5-10-NH2 since Ac-alpha-MSH6-10-NH2 and Ac-alpha-MSH6-9-NH2 were inactive. The N-terminal tripeptide sequence, Ser-Tyr-Ser, lacked any contribution to potency since the 4-13 (Ac-[Nle4]-alpha-MSH4-13-NH2) sequence was equipotent to alpha-MSH. The important potentiating amino acids were found to be Met at position 4 of the amino terminus and Val at position 13 of the carboxy terminus of the hormone, since Ac-alpha-MSH4-10-NH2 was about 100 times more potent than the Ac-alpha-MSH5-10-NH2 sequence, and Ac-[Nle4]-alpha-MSH4-13-NH2 was about 10 times more active than Ac-[Nle4]-alpha-MSH4-12-NH2. The minimal sequence for equipotency to alpha-MSH was demonstrated to be Ac-[Nle4]-alpha-MSH4-13-NH2. [Nle4, D-Phe7]-alpha-MSH was about 10 times more active than alpha-MSH. Unexpectingly, several conformationally restricted cyclic melanotropins were either partial agonists ([Cys4, Cys10]-alpha-MSH) or totally inactive (Ac[Cys4, Cys10]-alpha-MSH4-10-NH2) on fish melanocytes. These results point out some rather remarkable differences between S. marmoratus and tetrapod melanophores relative to structural requirements for MSH receptor recognition and signal transduction.

The regulation of the corticomelanotropic cell activity in aves. III--Effect of various peptides on the release of MSH from dispersed, perfused duck pituitary cells. Cosecretion of ACTH with MSH.

1. The melanotropin-releasing activity of arginine-vasopressin (AVP), arginine-vasotocin (AVT), oxitocin (OT), mesotocin (MT) and corticotropin-releasing factor (CRF) was studied in the duck using dispersed, perfused pituitary cells and a specific alpha-MSH RIA. 2. Log dose-response curves were obtained for all the peptides ranging from 5 to 100 ng/ml. All peptides behaved as partial agonists compared to duck median eminence extracts (DME). 3. AVT and MT displayed an alpha-MSH releasing capacity of 60% relative to DME whereas all other peptides behaved as weak agonists with less than 15% capacity relative to DME. 4. AVT and CRF when perfused together acted synergistically on alpha-MSH release yielding a dose response line whose slope approximated that of DME. 5. ACTH was cosecreted together with alpha-MSH in all situations studied with an ACTH to alpha-MSH molar ratio of about 10. 6. It is concluded that CRF and neurohypophyseal peptides may be physiological stimulators of both alpha-MSH and ACTH release in aves.

Modifications in alpha-MSH concentrations in different hypothalamic areas during the estrous cycle in the rat.

The present experiments were undertaken to examine the pattern of alpha-MSH during the estrous cycle in different hypothalamic areas and assess if during the whole estrous cycle the MSH which arises from proopiomelanocortin (POMC) has the same concentrations pattern as MSH from the dorso-lateral hypothalamus. MSH concentration of the mediobasal hypothalamus (MBH), preoptic area (POA) and dorso-lateral hypothalamus (DLH) was measured using a specific radioimmunoassay. The rats were sacrificed every four hours by perfusion. It is possible to observe a circadian rhythm in all the areas studied except in MBH during estrus. The MSH concentration in MBH was high during the light period, inversely, in POA the concentration remained low. In general, when MSH is high in MBH, it is low in POA and vice versa. The pattern of MSH in DLH is very similar to that observed for the peptide in POA.

Modifications in alfa-MSH concentrations in different hypothalamic areas during the estrous cycle in the rat

Este trabajo fue realizado con el fin de 1) examinar las variaciones en la concentración de alfa-MSH en áreas hipolámicas a lo largo del ciclo estrual y 2) analizar si durante el ciclo el alfa-MSH que deriva de la proopiomelanocortina (POMC) tiene las mismas variaciones de concentración que el alfa-MSH que deriva del hipotálamo dorso lateral (HDL). La concentración de alfa-MSH en el hipotálamo mediobasal (HMB), área preóptica (APO) y HDL fue medida utilizando un radioinmunoensayo específico. Las ratas fueron sacrificadas cada cuatro horas mediante perfusión intracardíaca de solución fisiológica. Se observa un ritmo circadiano en todas las áreas estudiadas, excepto en HMB durante el estro. La concentración de alfa-MSH en HMB se mantuvo alta durante el período de luz a la inversa de lo que se observaba en el APO. En general cuando los niveles de alfa-MSH se encuentran elevados en HMB, se mantienen bajos en APO y viceversa. El perfil hallado en HDL es muy semejante al de APO. La acumulación de alfa-MSH en los cuerpos neuronales del sistema de la POMC, y su disminución en las fibras que provienen de dicho sistema durante la tarde del proestro, podrían relacionarse con la caracteristica liberación de LH y PRL que ocurre en ese momento