Comparative analysis of adrenomedullin-like immunoreactivity in the hypothalamus of amphibians

Adrenomedullin (AM) is a novel neuropeptide with special significance in th e mammalian hypothalamo-hypophysial axis. By using an antiserum specific fo r human AM, we have studied the localization of AM-like immunoreactive (AMi ) cell bodies and fibers in the hypothalamus and hypophysis of the amphibia ns Rana perezi (anuran), Pleurodeles wald (urodele), and Dermophis mexicanu s (gymnophionan). Distinct AMi cell groups were found for each species. In the anuran, six cell groups were localized in the preoptic and infundibular regions, whereas only three and one were found in the urodele and gymnophi onan, respectively. A comparative analysis of AMi cells and cells expressin g arginine vasotocin (AVT), neuropeptide Y (NPY), and tyrosine hydroxylase (TH) revealed strong differences between species. Thus, colocalization of A VT/AM is most likely to occur in the preoptic magnocellular nucleus of urod eles and it is reflected by the intense AIM immunoreactivity in the neural lobe of the hypophysis. Colocalization of NPY/AM seems to be possible in th e suprachiasmatic nucleus of anurans. In the gymnophionan, cells containing AVT and NPY are distinct from AMi cells. Only in anurans, the ventral aspe ct of the suprachiasmatic nucleus possesses a small population of AMi cells that express also TH immunoreactivity and most likely also express NPY. Th e results strongly suggest that AM in amphibians plays an important regulat ory role in the hypothalamo-hypophysial system, as has been demonstrated in mammals. On the other hand, substantial differences have been found betwee n species with respect to the degree of colocalization with other chemical substances. (C) 2001 Wiley-Liss, Inc.