Regression of dark color in subterranean fishes involves multiple mechanisms: response to hormones and neurotransmitters

Organisms with source-populations restricted to the subterranean biotope (troglobites) are excellent models for comparative evolutionary studies, due to their specialization to permanent absence of light. Eye and dark pigment regression are characteristics of most troglobites. In spite of the advance in knowledge on the mechanisms behind eye regression in cave fishes, very little is known about pigmentation changes. Studies were focused on three species of the genus Pimelodella. Exemplars of the troglobitic P. spelaea and P. kronei were compared with the epigean (surface) P. transitoria, putative sister-species of the latter. Melanophore areas and densities are significantly lower in the troglobitic species. Evaluating the in vitro response of these cells to adrenaline, acetylcholine and MCH, we observed a reduced response in both troglobites to adrenaline. The same trend was observed with MCH, but not statistically significant. No response to acetilcholine was detected in all the three. Contrary to expectations, even though eye-regression in P. spelaea was much lower than in P. kronei, pigmentation regression was more advanced. Multiple mechanisms of loss showing a mosaic of traits in troglobitic fishes are discussed here.(AU)

Organismos com populações-fonte restritas ao biótopo subterrâneo (troglóbios) são excelentes modelos para estudos evolutivos comparativos, devido à especialização resultante do isolamento sob um regime seletivo particular, com ênfase na permanente falta de luz. A regressão do olho e da pigmentação são características dos troglobites. Apesar do avanço do conhecimento sobre os mecanismos subjacentes à regressão ocular em peixes de caverna, pouco se sabe sobre mudanças de pigmentação. Os estudos foram focados em três espécies do gênero Pimelodella. Exemplares das espécies troglóbias P. spelaea e P. kronei foram comparados com a epígea P. transitoria, provável espécie-irmã dessa última. As áreas e densidades dos melanóforos são significativamente menores nas espécies troglóbias. Avaliando a resposta in vitro dessas células à adrenalina, acetilcolina e MCH, observamos uma resposta reduzida em ambos os troglóbios à adrenalina. A mesma tendência foi observado com o MCH, mas não estatisticamente. Nenhuma resposta à acetilcolina foi detectada três. Contrariamente às expectativas, embora a regressão ocular em P. spelaea seja bem menor do que em P. kronei, a regressão na pigmentação foi mais acentuada. Múltiplos mecanismos de regressão, mostrando um mosaico de características em peixes troglóbios, são discutidos aqui.(AU)

Does MCH play a role on establishment or maintenance of social hierarchy in Nile tilapia?

Body coloration has a fundamental role in animal communication by signaling sex, age, reproductive behavior, aggression, etc. Nile-tilapia exhibits dominance hierarchy and the dominants are paler than subordinates. During social interactions in these animals, these color changes occur rapidly, and normally the subordinates become dark. In teleosteans, from the great number of hormones and neurotransmitters involved in color changes, melanocyte hormone stimulates (α-MSH) and melanin concentrates hormone (MCH) are the most remarkable. The aim of this project was to investigate the role of MCH in the establishment of hierarchical dominance of the Nile-tilapia. We analyzed the effect of background coloration in the dominance hierarchy. It was then compared to the melanophore sensibility of dominants and subordinates' fishes to MCH; finally, it was checked if the social rank affects the number of these pigment cells in dominants and subordinated fishes. Fishes which have a social hierarchy established and adjusted individually to the background exhibits paler body coloration when a visual contact was possible, independently of previous social rank and background color. Probably, even recognizing each other, fishes could be defending their new territory. Melanophores of the subordinate fishes were more sensible to MCH than dominants. It suggests that dominants fishes, which are paler than subordinates, could be under a chronic effect of MCH, which could be due a desensitization of melanophores to this hormone. The opposite effect seems to be occurring on subordinate fishes. It was not observed a significant change in the number of melanophores when the fishes were exposed to a prolonged period of agonistic interaction. It is possible that the exposure time for this interaction might not have been sufficient to have any change in the number of these cells of dominants and subordinate fishes.

Mechanisms of pigmentation loss in subterranean fishes

Troglobitic (exclusively subterranean) organisms usually present, among their apomorphies related to the subterranean life (troglomorphisms), the regression of eyes and melanic pigmentation. The degree of regression varies among species, from a slight reduction to the complete loss of eyes and dark pigmentation, without a taxonomic correlation. While mechanisms of eye reduction have been intensively investigated in some troglobites such as the Mexican blind tetra characins, genus Astyanax, and the European salamander, Proteus anguinus, few studies have focused on pigmentation. The Brazilian subterranean ichthyofauna distinguishes not only by the species richness (23 troglobitic fishes so far known) but also by the variation in the degree of reduction of eyes and pigmentation. This study focused on Brazilian fishes completely devoid of melanic pigmentation: the characiform Stygichthys typhlops (Characidae) and the siluriforms Ancistrus formoso (Loricariidae), Rhamdiopsis sp.1 (Heptapteridae; from caves in the Chapada Diamantina, Bahia) and Rhamdiopsis sp. 2 (cave in Campo Formoso, Bahia). In order to investigate if such depigmentation is the result of blockage in some step in the melanogenesis, in vitro tests of administration of L-DOPA were done, using caudal-fin fragments extracted from living fish. Except for Rhamdiopsis sp. 2, all the studied species were DOPA(+), i.e., melanin was synthesized after L-DOPA administration. This indicates these fish do have melanophores but they are unable to convert L-tyrosine to L-DOPA. On the other hand, Rhamdiopsis sp. 2, like the albino specimens of Trichomycterus itacarambiensis previously studied (which correspond to one third of the population), are DOPA(-), either because the block of melanin synthesis occurs downstream in melanogenesis, which is probably the case with T. itacarambiensis (monogenic system in view of the phenotypic discontinuity), or because the so-called albinos do no possess...

Organismos exclusivamente subterrâneos (troglóbios) usualmente exibem, entre as apomorfias relacionadas à evolução em isolamento nesse ambiente (troglomorfismos), a redução, até perda total, das estruturas visuais e da pigmentação melânica. Os mecanismos de regressão ocular em troglóbios têm sido intensivamente estudados, sobretudo em peixes como os lambaris cegos mexicanos do gênero Astyanax, e salamandras como Proteus anguinus. Por outro lado, poucos são os trabalhos abordando a perda da pigmentação nesses organismos. A ictiofauna subterrânea brasileira destaca-se não só pela riqueza de espécies (23 conhecidas até o momento) como também pelas diferenças no seu grau de troglomorfismo, sem uma correlação taxonômica. O presente estudo abordou as espécies brasileiras totalmente desprovidas de qualquer traço de pigmentação melânica: o caraciforme Stygichthys typhlops (Characidae) e os siluriformes Ancistrus formoso (Loricariidae), Rhamdiopsis sp.1 (Heptapteridae; cavernas da Chapada Diamantina, Bahia) e Rhamdiopsis sp. 2 (caverna de Campo Formoso, Bahia). Com a finalidade de investigar se essa despigmentação é resultado de bloqueio em algum passo da cadeia de síntese de melanina, foram feitos testes in vitro, utilizando-se fragmentos da nadadeira caudal extraídos de exemplares mantidos vivos, de reação à administração de L-DOPA. Com exceção dos de Rhamdiopsis sp. 2, os exemplares estudados revelaram-se DOPA(+), i.e., houve produção de melanina após a administração de L-DOPA, o que indica que sua despigmentação é devida a uma disfunção da tirosinase, enzima responsável pela transformação de tirosina em L-DOPA nos melanóforos, os quais, portanto, ainda existem nesses peixes. Já os exemplares Rhamdiopsis sp. 2, assim como o terço conspicuamente despigmentado da população de Trichomycterus itacarambiensis, espécie estudada anteriormente sob esse aspecto, são DOPA(-), seja porque o bloqueio na síntese de melanina ocorre em um passo a jusante...

Biological effects of insulin on murine melanoma cells and fish erythrophoroma cells: a comparative study.

Insulin is the hormone that plays an essential role in metabolism and mitosis of normal and tumor cells, exerting its pleiotropic effects through binding to specific membrane receptors and promoting the phosphorylation of tyrosine residues of the receptor itself and of other components of the signaling pathway. The aim of this study was to investigate the effects of insulin on melanogenesis and cell growth in three different cell lines: the goldfish GEM-81 erythrophoroma cells (undifferentiated and differentiated with 1.5% dimethylsulfoxide-DMSO), and the murine B16F10 and Cloudman S91 melanoma cells. Undifferentiated GEM-81 and B16F10 cells responded to insulin with a small increase of cell proliferation, whereas S91 cells responded with a decrease of growth. In the two mammalian cell lines, and in DMSO-differentiated GEM-81 cells, the hormone strongly inhibited melanogenesis, by decreasing tyrosinase activity. In undifferentiated GEM-81 cells, insulin had no effect on tyrosinase activity. An increase in the tyrosine phosphorylation status of pp185 (insulin receptor substrate 1 and 2 -- IRS-1/2) phosphorylation degree was observed in S91 mouse melanoma and in differentiated GEM-81 erythrophoroma cells, suggesting that this specific protein was maintained during transformation process and participates in insulin signaling. Our results imply an ancient and diverse history of the insulin signaling system in vertebrate pigment cells.

Rhythmic expression, light entrainment and alpha-MSH modulation of rhodopsin mRNA in a teleost pigment cell line.

To investigate whether teleost fish GEM-81 erythrophoroma cells were photosensitive, the cells were submitted to constant darkness (DD), 14 h of light and 10 h of darkness (14L:10D), and 10 h of light and 14 h of darkness (10L:14L). The doubling times (hours) were: DD 35.33+/-0.05; 14L:10D 67.85+/-0.04; and 10L:14D 49.60+/-0.08. In order to verify whether proliferation was dependent on light phase length, GEM-81 cells were submitted to 7L: 5D. The proliferation curves and doubling times were similar in 14L:10D and 7L:5D (respectively 69.44+/-0.03 and 67.85+/-0.04), suggesting that the cell cycle was regulated by the length of the light phase within 24 h, or by the light/dark ratio. We have also demonstrated the expression of Carassius retinal rhodopsin mRNA in GEM-81 cells, which cycles in a circadian rhythm, entrained by light. In addition, we showed that alpha-melanocyte stimulating hormone (alpha-MSH, 10(-10) to 10(-8) M), a conspicuous hormone that exerts mitogenic and melanogenic activity in most vertebrates, decreased rhodopsin mRNA in the first 3 days; after 4 days the inhibition was reversed, and after 5 days an increase in rhodopsin mRNA level was elicited. This is the first report of rhythmic expression of extra-ocular rhodopsin and its modulation by light and hormones.

Expression of endothelin receptors in frog, chicken, mouse and human pigment cells.

Several reports have shown the participation of vasoactive endothelins (ETs) in the regulation of vertebrate pigment cells. In the present study, we identified ET receptors in pigment cells of vertebrate species by RT-PCR assays, and compared the differential expression of the various subtypes in each species by quantitative PCR. RT-PCR was performed with specific primers for ETC, ETA(X) or ETA in Xenopus laevis melanophores, ETA or ETB(2) in chicken melanocytes, ETA or ETB in murine (B-16, S-91 or Melan-A) or human (SK-Mel 23 or SK-Mel 28) melanoma cells, and the products obtained were confirmed by cloning and sequencing. The results showed the presence of ETA(X), but not ETA mRNA, and confirmed the expression of ETC in X. laevis melanophores. ETA and ETB(2) mRNAs were also demonstrated in chicken melanocytes. ETA and ETB receptor were identified in S-91, B16 and Melan-A murine cells. In human melanoma cells, SK-Mel 23 and SK-Mel 28, we confirmed the presence of ETB mRNA, and also found ETA mRNA. The comparison between the two subtypes present in the pigment cell of each species and among species demonstrated that the expression of ETAs in chicken, mouse, and human melanocytes is negligible, as is the expression of ETA(X) in Xenopus melanophores. The relative expression, as determined by quantitative PCR, was as follows: chicken ETB>SK-Mel 23 ETB>S91 ETB>>>Xenopus ETC, suggesting that the endothelin system plays a major role in avian and mammalian pigment cell regulation, as compared to lower vertebrates. The phylogenetic analysis revealed that subtype A receptors were probably the most primitive ET receptors, directly deriving from the ancestral type; all the other receptors, B subtypes and C, originated from diverse derivative molecules.

Chromatic effects of endothelin family peptides in non-innervated fish, Synbranchus marmoratus, melanophores.

The biological activity of endothelins (ETs) in non-innervated Synbranchus marmoratus melanophores was demonstrated. These peptides induced a dose-dependent pigment aggregation (lightening skin) in these cells. However, they presented EC50's (effective concentration required to produce 50% of response) 26, 106 and 35 times higher than, respectively, the melanin concentrating hormone (MCH) EC50, and exhibited a characteristic temporal and dose-dependent autodessensibilization of the aggregative effect on the melanophores of this fish. The receptor characterization suggested the presence of the ET(B) subtype, since BQ-788 (selective antagonist of ET(B)) but not BQ-485 (selective antagonist of ET(A)) blocked the aggregative effect of the hormones. Confirming these data, sarafotoxin (SRTX) S6c, a toxin selective for ET(B), induced maximal aggregation of pigment granules. S6c presented an EC50 6.8 times higher than the MCH EC50, and 3.9, 15.6 and 5.1 times lower than the EC50's ETs, respectively. The melanotropic effect of SRTX S6b and vasoactive intestinal contractor (VIC) were demonstrated for the first time in this work. SRTX S6b induced a dose-dependent pigment aggregation and presented an EC50 2.54 and 17.2 times higher than the S6c and MCH EC50's, respectively. Compared to the ETs it was 1.53, 6.19 and 2.03 times lower, respectively.

Signalling pathways evoked by alpha1-adrenoceptors in human melanoma cells.

The biological effects of catecholamines in mammalian pigment cells are poorly understood, but in poikilothermic vertebrates they regulate the translocation of pigment granules. We have previously demonstrated in SK-Mel 23-human melanoma cells the presence of low affinity alpha(1)-adrenoceptors, which mediate a decrease in cell proliferation and increase in tyrosinase activity, with no change of tyrosinase expression. In this report, we investigated the signalling pathways involved in these responses. Calcium mobilization in response to phenylephrine (PHE), an alpha(1)-adrenergic agonist, was investigated by confocal microscopy, and no change of fluorescence during the treatment was observed, suggesting that calcium is not involved in the signalling pathway activated by alpha(1)-adrenoceptors in SK-Mel 23 cells. cAMP levels, determined by enzyme-immunoassay, were significantly increased by PHE (10(-5)-10(-4)M), that could be blocked by the alpha(1)-adrenergic antagonist benoxathian (10(-5)-10(-4)M). Several biological assays were then performed with PHE, for 72 h, in the absence or presence of various signalling pathway inhibitors, in an attempt to determine the intracellular messengers involved in the responses of proliferation and tyrosinase activity. Our results suggest the participation of p38 and ERKs in PHE-induced decrease of proliferation, and possibly also of cAMP and protein kinase A. Regarding PHE-induced increase of tyrosinase activity, it is suggested that the following signalling components are involved: cAMP/PKA, PKC, PI3K, p38 and ERKs.

Anti-cancer drugs: molecular mechanisms of action.

Genetic alterations are responsible for all cancers. These mutations produce, in turn, alterations in key proteins of certain signaling pathways. Amongst the best known and studied alterations related to malignant transformations are those which occur in Ras protein and p53. In most cases mutations in Ras and p53 lead to the appearance of practically most malignant transformations. Mutated Ras genes exist in approximately 20 to 30% of all human cancers. Ras proteins are switches that regulate diverse functions such as cell proliferation, differentiation and apoptosis. Normal p53 expression, also known as the "genome guardian", is a key molecule for suppressing cell proliferation. The great importance of these proteins rests on their intimacy with the events leading to cell proliferation or death. The comprehension of the extent of transformation on Ras and p53, and of the diverse biochemical pathways of intracellular signaling, activated by them, is of extreme importance for the understanding of malignant transformation, as well as its control, through the creation, for example, of new drugs which contribute to the elimination of these cells. To clarify the consequences originated by transformed Ras, p53 and their biochemical interlinks in the different intracellular pathways, besides the possible intervening points and pharmacological controls presently used in combating cancer, are the aims of this review.

The endothelin/sarafotoxin-induced increase of the proliferation of undifferentiated and DMSO-differentiated GEM-81 goldfish erythrophoroma cells is mediated by ETB receptors.

Endothelins (ETs) and sarafotoxins (SRTXs) have been reported to exert ET(B)-mediated effects on vertebrate pigment cells. GEM-81 cell line, a red pigment cell-derived cutaneous tumor of the teleost Carassius auratus, expresses ET(B) receptors and can be differentiated with 1.5% DMSO treatment, thus constituting an useful model to investigate ET and SRTX effects on cultured fish pigment cells. Our aim was to characterize the pharmacology and biological effects mediated by ET receptors in DMSO-differentiated and undifferentiated cells. ET subtype receptors and their respective Ki values in both cell types were determined by competitive binding assays using (125)I ET-1 and BQ-485 (an ET(A) antagonist) or BQ-788 (an ET(B) antagonist). BQ-788, but not BQ-485, significantly reduced (125)I-ET-1 binding in both cell types, with similar low (Ki > nM) affinities. To determine the proliferation effects of ETs/SRTXs, cells were treated for 72 h with the hormones, and counted in a hemocytometer. The proliferation assays were repeated for SRTX S6c in the presence or absence of BQ-788. The results demonstrated that, with the exception of ET-1 (biphasic effect) and ET-3 (no significant effect) in undifferentiated GEM-81 cells, all the tested hormones induced increases in the proliferation of both types of cells. The hormones were equipotent in DMSO-differentiated cells, which exhibited increased sensitivity to ETs, but not to SRTXs, as compared with undifferentiated cells. The BQ-788 antagonistic effect was also exerted on the proliferation responses to SRTX S6c. These results corroborate the long and important evolutionary history of the ET/SRTX receptor system in vertebrate pigment cells.

Catecholamine effects on human melanoma cells evoked by alpha1-adrenoceptors.

The biological effects of catecholamines in mammalian pigment cells are poorly understood. Our previous results showed the presence of alpha(1)-adrenoceptors in SK-Mel 23 human melanoma cells. The aims of this work were to (1) characterize catecholamine effects on proliferation, tyrosinase activity and expression, (2) identify the alpha(1)-adrenoceptor subtypes, and (3) verify whether chronic norepinephrine (NE) treatment modified the types and/or pharmacological characteristics of adrenoceptors present in SK-Mel 23 human melanoma cells. Cells treated with the alpha(1)-adrenergic agonist, phenylephrine (PHE, 10(-5) or 10(-4) M), for 24-72 h, exhibited decreased cell proliferation and enhanced tyrosinase activity, but unaltered tyrosinase expression as compared with the control. The proliferation and tyrosinase activity responses were inhibited by the alpha(1)-adrenergic antagonist prazosin, suggesting they were evoked by alpha(1)-adrenoceptors. The presence of actinomycin D, a transcription inhibitor, did not diminish PHE-induced effects. RT-PCR assays, followed by cloning and sequencing, demonstrated the presence of alpha(1A)- and alpha(1B)-adrenoceptor subtypes. NE-treated cells (24 or 72 h) were used in competition assays, and showed no significant change in the competition curves of alpha(1)-adrenoceptors as compared with control curves. Other adrenoceptor subtypes were not identified in these cells, and NE pretreatment did not induce their expression. In conclusion, the activation of SK-Mel 23 human melanoma alpha(1)-adrenoceptors elicit biological effects, such as proliferation decrease and tyrosinase activity increase. Desensitization or expression of other adrenoceptor subtypes after chronic NE treatment were not observed.

Mechanisms of action of melanin-concentrating hormone in the teleost fish erythrophoroma cell line (GEM-81).

Melanin-concentrating hormone (MCH) evokes an increase of GEM-81 cell proliferation. This action of 10(-6)M MCH was inhibited in the presence of the following blockers: U-73122 (phospholipase C), Ro-31-8220 (PKC) or KN-93 (Ca(2+)/calmodulin-dependent kinase). The more selective PKC inhibitors, HBDDE and Go-6983, which block, respectively, PKC alpha/gamma isoform and beta1 isoform, were used. HBDDE was ineffective whereas Go-6983 reversed the proliferative response promoted by MCH. Flow cytometry assays demonstrated that MCH induces a slow and long-lasting rise in intracellular calcium, which can be blocked by U-73122. Our results also show a cAMP increase evoked by MCH. Our data support the assumption that MCH exerts its effect on GEM-81 erythrophoroma cells through activation of phosholipase C, beta1 PKC, and Ca(2+)/calmodulin-dependent PKC, and eliciting a slow, long-lasting rise in calcium, which may trigger the proliferative signal.

Identification of protein kinase C (PKC) isoforms in teleostean, amphibian and avian pigment cells.

The beta isoform of protein kinase C (PKC) has been described as the main isoform involved in the stimulation of melanogenesis in mammalian skin melanocytes. Little is known about PKC isoforms in non-mammalian pigment cells. In neopterigian fish (holostei and teleostei), PKC is associated with pigment granule aggregation within the pigment cells (skin lightening), whereas in elasmobranchs and tetrapods, the activation of PKC leads to pigment granule dispersion (skin darkening). In an attempt to a better understanding of this distinct functional behavior upon PKC activation, we decided to investigate the PKC isoforms expressed in pigment cell lines of teleost fish, amphibians and birds, using RT-PCR followed by cloning and sequencing. Our results demonstrate the presence of messenger RNA (mRNA) for the following PKC isoforms: beta 1, lambda and iota in GEM-81 cells (Carassius auratus erythrophoroma), beta 1, beta 2 and zeta in Xenopus laevis (amphibian) melanophores; beta 1 and lambda in Gallus gallus (chicken) primary melanocytes. Beta 1 PKC seems to be conserved throughout phylogeny, but the diversity of the other isoforms in the different groups may account for the functional differences after PKC activation, which are observed between teleost and tetrapod pigment cells.

Melatonin biological activity and binding sites in human melanoma cells.

The effects of melatonin, N-acetylserotonin and serotonin on the growth and tyrosinase activity of SK-Mel 23 and SK-Mel 28 human melanoma cell lines were investigated. Binding assays were also performed to establish the nature of the binding site. SK-Mel 28 cells were responsive to melatonin and its precursors, exhibiting a decrease in growth and an increase in tyrosinase activity after a 72 hr treatment. N-acetylserotonin was as potent as melatonin, the minimal effective concentration (MEC, which is defined as the smallest concentration that elicits a measurable biological response, significantly different from control) being 10-8 m. Serotonin was the least potent (MEC = 10-6 m). Both melatonin antagonists, prazosin and luzindole, exhibited no effect per se and reversed both responses to melatonin. SK-Mel 23 cells, however, showed no significant responses to the indoleamines. Competition binding assays in SK-Mel 28 cells demonstrated the presence of binding sites to 2-[125 I]-iodomelatonin, which was displaced by the unlabelled hormone, by both antagonists, and by N-acetylserotonin. The curve adjustment of the displacement values with melatonin suggests the existence of two binding sites, with the following Ki values: 1.0 x 10-10 m and 6.5 x 10-6 m. Ki values for acetylserotonin, prazosin and luzindole were, respectively, 3.8 x 10-8 m, 1.2 x 10-8 m, and 8.3 x 10-6 m. Surprisingly, in SK-Mel 23 cells, melatonin and luzindole were able to compete with the radioligand, with Ki values of 3.1 x 10-8 and 2.4 x 10-8 m, respectively. Our data suggest that SK-Mel 28 cells probably possess high affinity binding sites to melatonin and, in addition, MT3 low affinity binding sites, because N-acetylserotonin was as effective as the native hormone, and prazosin effectively blocked the actions of melatonin. Both sites are functional as demonstrated by the blockade promoted by both luzindole and prazosin on the proliferative and melanogenic responses. Although growth and tyrosinase activity of SK-Mel 23 cells were not affected by melatonin or its precursors, this cell line possesses high affinity binding sites, which may be non-functional, or trigger responses other than the ones herein investigated.

Adrenoceptors in avian and fish pigment cells.

Very little is known about the neurohumoral control of avian pigmentation and about adrenergic subtypes mediating catecholaminergic-controlled color change in nonmelanophore pigment cells of poikilothermic vertebrates. To determine the adrenoceptor subtypes in avian melanocytes and fish GEM-81 competitive binding assays were performed with the following radioactive ligands and their cold ligand counterparts: [3H]prazosin and benoxathian or unlabeled prazosin; [3H]rauwolscine and idazoxan or yohimbine; [3H]propranolol and metoprolol or ICI 118,551 and [125I]iodocyanopindolol and ICI 118,551. Our results suggest that: alpha(1)-adrenoceptors [K(i)=1.38 micro M; maximum displacement (md)=80%, benoxathian), alpha(2)-adrenoceptors (K(i)=0.21 micro M; md=82%, idazoxan), and beta(2)-adrenoceptors (K(i)=7.3 micro M; md=73%, ICI 118,551) are expressed in avian melanocytes, and that alpha(2)-adrenoceptors (K(i)=1.24 nM, idazoxan, K(i)=59 nM, yohimbine, md=65%, idazoxan and yohimbine; K(i)=0.19 nM, md=69%, prazosin), beta(1)-adrenoceptors (K(i)=22.2 micro M, md=75%, metoprolol), and beta(2)-adrenoceptors (K(i)=32.2 micro M, md=92%, ICI 118,551) are expressed in GEM-81 erythrophoroma cells. This may be the first study to show the presence of adrenoceptors in avian melanocytes and one of a few characterizing adrenoceptor subtypes in teleost nonmelanophore pigment cells.