Distribution of tyrosine hydroxylase immunoreactivity in the brain of Typhlonectes compressicauda (Amphibia, Gymnophiona): further assessment of primitive and derived traits of amphibian catecholamine systems.

Until now, catecholamine systems are well studied in the brains of anurans and urodeles, but such data are almost completely lacking for the third order of amphibians, i.e. the limbless Gymnophiona or Apoda. To further assess general and derived features of the catecholamine systems in this class of vertebrates, the distribution of tyrosine hydroxylase immunoreactive (THi) cell bodies and fibers was studied in the brain of the gymnophionan Typhlonectes compressicauda. The distribution of THi cell groups in the brain of gymnophionans largely resembles that found in anurans and urodeles. However, in gymnophionans additional THi cells were found in the reticular formation and in the prevagal part of the solitary tract nucleus. Other differences with anurans and urodeles concern the relatively larger number of THi cells in the midbrain tegmentum and in the hypothalamus, where the cells are mainly of the liquor-contacting type. The distribution of THi fibers in some brain regions of gymnophionans, e.g. pallial and basal forebrain areas, shows a greater resemblance with that of urodeles than with that of anurans. A peculiar feature of Typhlonectes are the pericellular baskets of THi varicosities in the lateral septal region. Such baskets were never observed in other amphibians, but do occur in the septal region of amniotes. Finally, the data obtained in this study support the suggestion that catecholamines play a role in the processing of sensory modalities such as olfactory, visual, auditory, vestibular, and mechanoreceptive lateral line information, but not in electroreception.