DEMONSTRATION OF PARATHYROID HORMONE-RELATED PROTEIN IN MENINGES AND ITS RECEPTOR IN ASTROCYTES - EVIDENCE FOR A PARACRINE MENINGO ASTROCYTIC

In contrast to the nervous and glial tissue of the adult rat brain the meninges are immunoreactive for parathyroid hormone-related protein ( PTHrP), a hormone that binds with high affinity to the recently cloned PTH/PTHrP receptor. Accordingly immunoreactivity is found in cultured meningeal cells but not in astrocytes. In contrast, astrocytes but no t meningeal cells synthesize the mRNA for the PTHrP receptor shown by reverse transcription of total RNA preparations and subsequent polymer ase chain reaction with primers specific for the PTHrP receptor. The e xpression of the PTH/PTHrP receptor was confirmed by the dose-dependen t activation of the adenylate cyclase in astrocytes and the rapid deve lopment of cellular processes following on incubation with PTHrP. We c onclude that PTHrP secreted by meninges forms a paracrine meningo-astr ocytic loop and may cause astrocytic differentiation, possibly involve d in the formation of the glial limiting membrane.