Distribution of vasotocin- and mesotocin-like immunoreactivities in the brain of typhlonectes compressicauda (Amphibia, gymnophiona): further assessment of primitive and derived traits of amphibian neuropeptidergic systems.

To further assess primitive and derived conditions, we have studied the vasotocinergic (AVT) and mesotocinergic (MST) systems by immmunohistochemistry in the brain of Typhlonectes compressicauda. This species belongs to a separate order of amphibians which differs in several morphological and behavioral aspects from anurans and urodeles which have been studied previously. Nevertheless, the vasotocinergic and mesotocinergic systems of T. compressicauda are largely comparable to those of other amphibians. Apart from a well-developed hypothalamo-hypophyseal system, extrahypothalamic AVT-and MST-immunoreactive groups of cells and extensive networks of fibers were found. A major difference, however, is that neuropeptidergic cells in the caudal hypothalamus and the midbrain tegmentum of T. compressicauda contain MST, whereas those in corresponding locations contain AVT in anurans and urodeles. This suggests that certain neuropeptidergic cell groups in the gymnophionan brain have switched from AVT to MST gene expression, and, thereby, offers a new view on the functional significance of these neuropeptidergic systems.