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.
KeywordsParathyroid Hormone PTH2R Receptor Ligand Tuberoinfundibular Peptide TIP39 Neuropeptide Hypothalamus Distribution Immunoreactivity Fluorescent Amplification Immunocytochemistry Immunolabeling Secretion Somatostatin Growth hormone releasing hormone Gonadotropin releasing hormone Corticotropin releasing hormone Arginine vasopressin Anatomical Double-labeling Release Fiber terminals Vesicular glutamate transporter Excitatory Median eminence Paraventricular Periventricular Arcuate Nucleus Preoptic Pituitary
We gratefully acknowledge Carolyn Smith and the NINDS Light Imaging Facility for help with confocal microscopy. We thank Dr. H. Gainer, NINDS, NIH and Dr. R. Edwards, UCSF for generously providing the anti-arginine-vasopressin-neurophysin and the anti-vesicular glutamate transporter-2 antibodies, respectively. Support was provided by a NARSAD Young Investigator Award for Arpád Dobolyi and by the National Institute of Mental Health Intramural Research Program for Ted B. Usdin.