Immunocytochemical distribution of PTH immunoreactivity in vertebrate brains

Immunoreactive (IR) cell bodies, reacting with an antiserum specific for the 48-64 region of bovine parathyroid hormone (PTH), were detected in the brains of primitive vertebrates (hagfish), bullfrogs, and higher vertebrates (mice). In each species the IR perikarya were located in the preoptic region, although the precise location and abundance of IR perikarya differed among species. Fiber tracts from these IR perikarya were traced to the neurohypophysis in the hagfish but only to the median eminence in the bullfrog and mouse, where the axonal terminals were in close proximity to hypophyseal portal blood vessels. These results suggest that a novel PTH-like peptidergic system, similar to those secreting hypophysiotropic-releasing factors, is present in the vertebrate brain.