Vasotocin and mesotocin in the brains of amphibians: State of the art

Immunohistochemical studies during the last decade have revealed elaborate systems of vasotocinergic (AVT) and mesotocinergic (MST) neuronal elements in the brain of a variety of amphibians including anurans, urodeles, and gy mnophionans. Apart from a well-developed hypothalamo-hypophysial system, th e antibodies demonstrated the existence of extrahypothalamic AVT- and MST-i mmunoreactive cell groups as well as extensive extrahypothalamic networks o f immunoreactive fibers. The wide distribution of AVT- and MST-immunoreacti ve fibers throughout the brains of amphibians suggests that the two neurope ptidergic systems are involved not only in hypothalamo-hypophysial interact ions, but also in a variety of other brain functions. Moreover, there is no w evidence that sex-related differences occur in amphibians as previously s hown for amniotes. It should be noted, however, that substantial variation occurs in the relative densities of AVT- and MST-immunoreactive fibers and number of cells between species, even within a single order of amphibians. Similar observations have been made in other classes of vertebrates and pro mpt us, therefore, to critically evaluate conclusions with respect to speci fic functions of AVT and MST in the central nervous system of vertebrates. (C) 2001 Wiley-Liss, Inc.