The pineal gland of poikilothermic vertebrates originates as an evagination from the diencephalic roof between the habenular and the posterior commissures, and associates with a parapineal organ to form the so-called pineal complex. The pinealocytes may be photosensitive, secretory or intermediate cells between both. Melatonin, the indoleamine secreted by the pineal, exhibits a circadian secretory rhythm that conveys environmental information to the organism. The peak melatonin secretion occurs during the night, although there are a few examples of an increase in indoleamine secretion during the day. Melatonin is also synthesized in other sites such as the retina, and it has been found in many invertebrates and unicellular organisms. The rhythmic secretory pattern of melatonin is responsible for many biological rhythms exhibited by lower vertebrates. These rhythms are abolished by pinealectomy in some species, but not in others, suggesting the existence of an extra-pineal pacemaker. The photoperiod and the temperature (especially in reptiles) are the main environmental factors affecting the secretory rhythm of melatonin. Poikilothermic vertebrates exhibit a circadian rhythmic color change, with nocturnal blanching, usually related to melatonin secretion. In amphibians, melatonin exhibits a potent skin lightening activity. However, in fishes and reptiles the melatonin effects vary with the species, the developmental stage, and the pigment cell location. Melatonin also exerts inhibitory or excitatory activity on the amphibian reproductive system, regulation of circadian locomotory activity in reptiles, and modulation of the amphibian metamorphosis. Melatonin has also a modulatory effect on the response of target cells to different hormones and high concentrations or prolonged exposure to the indoleamine may cause autodesensitization in various tissues. Binding sites of melatonin have been detected in the central nervous system and peripheral tissues of various vertebrates. The relative potencies of melatonin analogues demonstrated two subtypes of melatonin receptors (ML-1 and ML-2). A transmembrane melatonin receptor has been cloned from Xenopus laevis melanophores; it belongs to the family of the G protein-coupled receptors and exhibits 85% homology with the mammalian nervous system receptor. Melatonin binding sites in the nucleus of many cell types and its potent intracellular anti-oxidant action suggest mechanisms of action other than through the G-protein coupled receptor.

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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.

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.

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.

RESUMOO projeto visa ampliar a formação cidadã de jovens e consiste no planejamento, aplicação e avaliação de aulas (teóricas e práticas), abrangendo seis diferentes temas, todos estimulando o conhecimento e cuidado com o corpo humano (autocuidado). Estão entre eles: funções básicas do corpo humano, puberdade e Doenças Sexualmente Transmissíveis (DSTs), distúrbios alimentares, consumo de drogas, transtornos de humor, etc. Essas aulas são ministradas no Centro Alvorecer Ação Social e Educacional (CAASE), que tem como objetivo facilitar o acesso de jovens carentes ao mercado de trabalho, através de um Programa de Aprendizagem. Nosso projeto visa não somente contribuir para a formação dos jovens, mas também ampliar a formação das acadêmicas do curso de Enfermagem envolvidas, que participam do planejamento, confecção e aplicação das aulas. A capacitação dos funcionários-docentes do CAASE também entra como objetivo do projeto, uma vez que eles deverão poder continuar parte das atividades quando não for possível a participação dos docentes e alunos da Universidade Federal do Paraná (UFPR). Finalmente, a obtenção de dados sobre a avaliação do projeto feita pelos adolescentes, funcionários do CAASE e acadêmicas da UFPR, bem como sobre a situação de empregabilidade dos adolescentes vinculados soma-se a este artigo com o objetivo de ampliar a compreensão do alcance geral desta ação. Palavras-chave: educação; fisiologia; adolescentes; cidadania; saúde. ABSTRACTThis project aims at fostering the sense of citizenship of teenagers. It consists of the planning, implementation and evaluation of theoretical and practical classes, including six different themes that stimulate the knowledge and care with the human body (selfcare). The treated themes were: The human body basic functions, puberty and Sexually Transmitted Diseases (STDs), eating disorders, use of drugs, mood disorders and others. The lessons were given at the Centro Alvorecer Ação Social e Educacional (CAASE) that intends to increase access of unprivileged teenagers to the job market through a learning program. Our project helps in the teenagers' education, but also aims at enriching the general formation of Nursery 1 Agradecimentos: à Profa. Dra. Carolina A. O. Freire pela revisão do resumo em inglês e à Laísa Souza pela tradução do resumo para espanhol.

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