Expression and distribution of tuberoinfundibular peptide of 39 residues in the rat central nervous system.

Tuberoinfundibular peptide of 39 residues (TIP39) has been recently purified and identified as a selective ligand for the parathyroid hormone 2 receptor. As a next step toward understanding its functions, we report the expression and distribution of TIP39 in the rat central nervous system. In situ hybridization histochemistry and immunocytochemistry revealed TIP39-containing cell bodies in three distinct areas. The major one comprises the subparafascicular area posterior through the intralaminar nucleus of the thalamus; a second is the medial paralemniscal nucleus at the pontomesencephalic junction; and a third is in the dorsal and dorsolateral hypothalamic areas, which contained a few, scattered cell bodies. We found, in contrast to the highly restricted localization of TIP39-containing cell bodies, a much more widespread localization of TIP39-containing fibers. The highest density of fibers was observed in limbic areas such as the septum, the amygdala, and the bed nucleus of the stria terminalis; in areas involved in endocrine regulation, such as the hypothalamic dorsomedial, paraventricular, periventricular, and arcuate nuclei; in auditory areas, such as the ectorhinal and temporal cortices, inferior colliculus, medial geniculate body, and some of the nuclei of the superior olivary complex; and in the dorsolateral funiculus of the spinal cord. The localization of TIP39-containing nuclei and fibers provides an anatomical basis for previously demonstrated endocrine and nociceptive effects of TIP39 and suggests additional functions for TIP39, one apparent candidate being the regulation of auditory information processing.