title: Co-localization of mesotocin and opsin immunoreactivity in the hypothalamic preoptic nucleus of Xenopus laevis.
abstract: The purpose of the present investigation was to provide a detailed description of the encephalic photoreceptors of Xenopus laevis at the light microscopic level and to determine their relationship with the neurosecretory cells of the hypothalamus in order to further our understanding of photoperiodic regulation of seasonal rhythms. Numerous opsin-positive neurons were found in the hypothalamic magnocellular preoptic nucleus and their axonal processes were seen to run laterally towards the basal regions of the brain, reaching the neural lobe of the hypophysis. Analysis of labelling with different antisera in adjacent sections, as well as double-immunolabelling carried out on the same section, revealed that mesotocin immunoreactivity was present in most of the opsin-positive neurons; however, no evidence for opsin and vasotocin coexpression was found in any of the sections analysed. The close localization of LHRH and opsin/mesotocin fibers in some regions of the brain, such as the median eminence, suggests that some interaction between these two systems might exist. In conclusion, in this study we provide the first strong evidence that the hypothalamic mesotocinergic neurons, which have been proved to be connected to the GnRH system in other species, are directly involved in photoreception in Xenopus laevis. These findings represent a novel contribution to our understanding of how light influences the seasonal reproductive cycles in lower vertebrates.
authors.affiliation: Department of Morphology and Cellular Biology, University of Oviedo, Oviedo, Spain.
authors.forename: María
authors.initials: M
authors.lastname: Alvarez-Viejo
authors.forename: Rafael
authors.initials: R
authors.lastname: Cernuda-Cernuda
authors.forename: Willem J
authors.initials: WJ
authors.lastname: DeGrip
authors.forename: Carmen
authors.initials: C
authors.lastname: Alvarez-López
authors.forename: José M
authors.initials: JM
authors.lastname: García-Fernández
mesh_terms: D000818:Animals; D001683:Biological Clocks / Q000502:physiology; D005260:Female; D007987:Gonadotropin-Releasing Hormone / Q000378:metabolism; D007150:Immunohistochemistry; D009434:Neural Pathways / Q000166:cytology / Q000378:metabolism; D009474:Neurons / Q000166:cytology / Q000378:metabolism; D010121:Oxytocin / Q000031:analogs & derivatives* / Q000378:metabolism*; D020419:Photoreceptor Cells, Vertebrate / Q000166:cytology*; D011301:Preoptic Area / Q000166:cytology* / Q000378:metabolism; D017299:Rod Opsins / Q000378:metabolism*; D014982:Xenopus laevis / Q000033:anatomy & histology*
chemical_list: D017299:Rod Opsins; D007987:Gonadotropin-Releasing Hormone; C001713:mesotocin; D010121:Oxytocin