PITUITARY ADENYLATE CYCLASE-ACTIVATING POLYPEPTIDE TRANSDUCES THROUGHCAMP PKA AND PKC PATHWAYS AND STIMULATES PROOPIOMELANOCORTIN GENE-TRANSCRIPTION IN MOUSE MELANOTROPES/

Pituitary adenylate cyclase-activating polypeptide (PACAP) receptors w ere characterized and their function investigated in mouse pituitary n eurointermediate lobe explants. We show that mouse neurointermediate l obes can be maintained for up to 1 month in defined medium. After 8 da ys in culture, these explants are devoid of any of the original tyrosi ne hydroxylase or glutamate decarboxylase immunoreactive fibers, which in situ innervate the melanotropes. Under these culture conditions, n o mitotic activity is detectable in melanotropes and these cells remai n sensitive to physiological regulation such as dopamine and corticotr opin-releasing hormone. Using in situ hybridization and polymerase cha in reaction, we show that in situ and in neurointermediate lobe explan ts, melanotropes express PACAP receptor type I isoforms that transduce through the cAMP and inositol phosphate pathways. In neurointermediat e lobe explants, PACAP 27 and PACAP 38 (10(-8) M) stimulate cAMP accum ulation whereas PACAP 38 but not PACAP 27 stimulates inositol phosphat e breakdown. However, both ligands are potent stimulators of proopiome lanocortin (POMC)-derived peptides exocytosis and POMC gene transcript ion. In addition, stimulation of POMC gene transcription is mediated b oth by cAMP and by inositol phosphate pathways. Taken together, our da ta suggest that PACAP is a major regulator of melanotrope functions.