The Distribution and Neurochemistry of the Parathyroid Hormone 2 Receptor in the Rat Hypothalamus

This study reports the distribution of parathyroid hormone 2 receptor (PTH2R)-immunoreactive fibers in the hypothalamus using fluorescent amplification immunocytochemistry. The pattern of immunolabeling is strikingly similar to that of tuberoinfundibular peptide of 39 residues (TIP39), a peptide recently purified from bovine hypothalamus and proposed to be a ligand of the PTH2R based on pharmacological data. To investigate the anatomical basis of suggestions that TIP39 affects the secretion of several hypophysiotropic hormones we performed double-labeling studies and found that only somatostatin fibers contain PTH2R in the median eminence, which suggests that somatostatin release could be directly regulated via the PTH2R. However, several hypothalamic nuclei projecting to the median eminence contain a high density of both TIP39 and PTH2R fibers and terminals. We report here, that the PTH2R terminals also contain vesicular glutamate transporter−2, and suggest that TIP39 terminals are ideally positioned to modulate glutamatergic influences on hypophysiotropic neurons.