MODULATION OF CORTICOTROPIN-RELEASING HORMONE-STIMULATED CYCLIC ADENOSINE-MONOPHOSPHATE PRODUCTION BY BRAIN-CELLS

Corticotropin-releasing hormone (CRH) is believed to have a role as an important brain neuroregulator acting through specific receptors coupled to adenylate cyclase in addition to its major role in regulating pituitary adrenocorticotropin synthesis and secretion. To study the potential modulatory effects of various regulators and the central effects of CRH, we studied the effects of phorbol ester myristate acetate (PMA), arginine vasopressin (AVP), corticosterone, dexamethasone, and progesterone on CRH stimulation of cyclic adenosine monophosphate (cAMP) production in extrahypothalamic forebrain cell cultures derived from day 17 gestation fetal rats. These cultures contain CRH receptors with similar characteristics as those in anterior pituitary and brain. CRH (10(-9)-10(-7) M) stimulated cAMP in a dose-dependent fashion and maximal stimulation was clearly seen at 10(-7) M CRH. Incubation of the cells with PMA (10(-7) M), a protein kinase C (PKC) agonist, had no effect on basal cAMP, but potentiated CRH-stimulated cAMP. AVP (10(-8), 10(-7) M) had no effect on basal nor CRH-stimulated cAMP accumulation. Corticosterone (10(-7), 10(-6) M) or dexamethasone (10(-9)-10(-7) M) pre-incubation for 18 h did not diminish basal cAMP levels nor inhibit CRH-induced stimulation of cAMP. However, corticosterone inhibited CRH-induced cAMP production in anterior pituitary cells. Neither did exposure to progesterone (2 x 10(-8) M) modulate basal cAMP, CRH-induced cAMP production nor the potentiation of CRH stimulation by PMA. The data demonstrate that CRH receptors in dissociated fetal extrahypothalamic forebrain cell cultures are coupled to an adenylyl cyclase/cAMP second messenger system similarly as shown in studies with anterior pituitary membranes. The interaction between CRH and other regulators is similar to that in anterior pituitary with regard to synergism by a PKC activator such as PMA, but differs in the lack of glucocorticoid inhibition or AVP potentiation of CRH-stimulated cAMP production. The ability of CRH to stimulate cAMP in fetal brain cells additionally suggests that coupling of the receptor to adenylyl cyclase occurs at an early stage of development.