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Previous issue date: 2008-03-28 === Coordena??o de Aperfei?oamento de Pessoal de N?vel Superior === The light, besides the vision stimuli, controls other process completely independent of image formation, such as the synchronization of the organismic circadian rhythms to the enviromental light/dark cycle. In mammals, this adjust occurs through the retinohypothalamic tract, a direct retinal projection to the suprachiasmatic nucleus, considered to be the major circadian pacemaker. Early studies have identified only the suprachiasmatic nucleus as a retinal target in the hypothalamus. However, using more sensitive neuroanatomic tracers, other retinorecipient hypothalamic regions outside to suprachiasmatic nucleus were pointed in a great number of mammalian species. In this study, the retinohypothalamic tract was shown in the rock cavy (Kerodon rupestris), an endemic rodent of the semiarid region of the Brazilian Northeast, using unilateral intravitreal injections of cholera toxin subunit b as a neuronal tracer. The results reveal that in the rock cavy, besides the suprachiasmatic nucleus, several hypothalamic regions receive direct retinal projection, such as the ventrolateral preoptic nucleus, medial and lateral preoptic areas, the supraoptic nucleus and bordering areas, anterior, lateral and rectrochiasmatic hypothalamic areas, and the subparaventricular zone. The results are discussed by comparing with those of the literature, into a functional context === A luz, al?m de ser o est?mulo para a vis?o, tamb?m controla processos que s?o completamente independentes da forma??o de imagem, como o ajuste dos ritmos circadianos do organismo ao ciclo claro/escuro ambiental. Em mam?feros, este ajuste ocorre atrav?s do trato retino-hipotal?mico, uma proje??o direta da retina para o n?cleo supraquiasm?tico, o principal marcapasso circadiano. Os trabalhos pioneiros mostraram a proje??o retino-hipotal?mica exclusivamente para o n?cleo supraquiasm?tico. Entretanto, atrav?s do uso de tra?adores neurais mais sens?veis, outras ?reas hipotal?micas retino-recipientes foram apontadas em um amplo n?mero de esp?cies de mam?feros. Neste
trabalho o trato retino-hipotal?mico no moc? (Kerodon rupestris), um roedor end?mico da caatinga brasileira, foi demonstrado atrav?s de inje??o intra-ocular unilateral da subunidade b da toxina col?rica como tra?ador neuronal e revela??o imuno-histoqu?mica. Os nossos resultados mostram que, no moc?, al?m do n?cleo supraquiasm?tico, v?rias
outras ?reas hipotal?micas recebem proje??o direta da retina, tais como o n?cleo pr?-?ptico ventrolateral, as ?reas pr?-?pticas medial e lateral, o n?cleo supra-?ptico e adjac?ncias, as ?reas hipotal?micas anterior, lateral e retroquiasm?tica e a zona subparaventricular. Os resultados s?o discutidos ? luz dos dados da literatura, dentro de um contexto funcional
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