Immunohistochemical localization of atrial natriuretic factor and autoradiographic distribution of atrial natriuretic factor-binding sites in the brain of the cave salamander Hydromantes genei (Amphibia, Plethodontidae)

The distribution of atrial natriuretic factor (ANF)-like immunoreactivity i n the central nervous system of the cave salamander Hydromantes genei (Amph ibia, Plethodontidae) was investigated by using antisera raised against rat and human ANF(1-28). Concurrently, the location of ANF-binding sites was d etermined by autoradiography, using radioiodinated human ANF(1-28) as a tra cer. In several regions of the brain, including the olfactory bulb, the pre optic area, the ventral thalamus, the tectum of the mesencephalon, and the choroid plexuses inside the ventricles, a good correlation was observed bet ween the distribution of ANF-immunoreactive elements and the location of AN F-binding sites. Mismatching was found in the habenular nucleus, the commis sura habenularis, the fasciculum retroflexus, and the interpeduncular nucle us, which contained high levels of binding sites but were devoid of ANF-imm unoreactive structures. In contrast, a few other regions, such as the pinea l gland and the subcommissural organ, showed a high concentration of ANF-li ke immunoreactivity but did not contain ANF-binding sites. This study provi des the first localization of ANF-like immunoreactivity and ANF-binding sit es in the brain of an urodele amphibian. The results show that the ANF pept idergic system in the cave salamander has an organization more simple than the organizations described for the brain of frog or other vertebrates. Thi s feature is probably related to the expression of highly pedomorphic chara cters in plethodontids. The anatomical distribution of ANF-immunoreactive e lements and ANF-binding sites suggests that ANF-related peptides may act as hypophysiotropic hormones as well as neurotransmitters and/or neuromodulat ors in the salamander brain. (C) 2001 Wiley-Liss, Inc.