CENTRAL CONTROL OF MELANOTROPE CELLS OF XENOPUS-LAEVIS

Our research focusses on the role of brain and hypophysis in the contr ol of background adaptation in the clawed toad, Xenopus laevis. This a daptation is regulated by alpha-melanophorestimulating hormone (alpha- MSH). Previously, it was shown that various neurotransmitters influenc e a-MSH release. Here we report about the origin of these factors. Usi ng retrograde labelling techniques combined with immunocytochemistry, it was found that the inhibitory transmitters dopamine and neuropeptid e Y coexist in neurons in the suprachiasmatic nucleus. These neurons p roject to the pars intermedia and synaptically contact the alpha-MSH-p roducing melanotrope cells. In the synapses also GABA is present. Trac ing of the optic nerve indicated the presence of a direct retinosuprac hiasmatic tract. Furthermore, locus coeruleus neurons project to the p ars intermedia. They contain the inhibitory transmitter noradrenaline. The stimulatory factors corticotropin-releasing hormone and thyrotrop in stimulating hormone originate from the magnocellular nucleus which send its processes to the neural lobe of the hypophysis.