Pituitary adenylate cyclase-activating peptide induces neurite outgrowth in cultured monkey trigeminal ganglion cells: Involvement of receptor PAC1

Purpose: Our previous studies in the rabbit trigeminal nerve (TgN) showed that pituitary adenylate cyclase-activating peptide (PACAP) accelerated the extension of neuronal processes and recovery of corneal sensitivity. The purposes of the present study were 1) develop a procedure to culture trigeminal nerve (TgN) cells from monkeys, 2) test whether PACAP induces sprouting and elongation of axons in our culture system, 3) investigate the signaling mechanisms producing axon elongation induced by PACAP, and 4) test the action of PACAP on tear protein secretion by monkey lacrimal acinar cells. Methods: Primary cultures of TgN cells were established from rhesus monkeys. Cellular distribution of the PACAP receptor, PAC1, was determined with immunostaining. Axonal length in cultured TgN ganglion cells was evaluated with staining by antibody for neurofilament. mRNA expression was determined with quantitative real-time polymerase chain reaction (qPCR). Secretion of tear protein from cultured acinar cells was measured with immunoblotting. Results: Our results showed that dissociated, cultured TgN cells contained neuronal ganglion and Schwann cells, and the PAC1 receptor was expressed in both cell types. PACAP-27 significantly induced neurite outgrowth, which was inhibited by PACAP 6-27. Inhibitors for adenylate cyclase and phospholipase C also inhibited neurite outgrowth. Follistatin was upregulated by PACAP-27 during the culture period. PACAP enhanced secretion of tear proteins. Conclusions: Our data suggested PAC1 activation is involved in TgN neurite outgrowth.