No abstract

Pituitary adenylate cyclase-activating polypeptide (PACAP) is well known to protect delayed neuronal cell death in the brain of rodents. In order to investigate the neuroprotective action of PACAP in the retina, we examined the effects of PACAP on kainic acid (KA)-induced neurotoxicity in the rat retina. Many ganglion cells in the retina died after KA injection in the control group and PACAP treatment significantly promoted cell survival. These findings strongly suggest that PACAP plays very important roles in preventing cell death in the retina.

We have investigated the in vivo effect of PACAP on rat Müller cells that are the predominant glial element in the retina. Müller cells were treated with PACAP38, either alone or in the presence of the PACAP-selective antagonist, PACAP6-38. Cellular proliferation was determined by measuring the incorporation of bromodeoxyuridine, while interleukin-6 (IL-6) levels in the culture medium were examined using a B9 cell bioassay. In cultured rat Müller cells, the expression of PACAP receptor (PAC1-R) was assessed with immunohistochemistry using a PAC1-R-specific antiserum. PACAP stimulated IL-6 production in Müller cells at a concentration as low as 10(-12) M, which was not sufficient to induce cell proliferation. This elevation of IL-6 production was significantly inhibited by PACAP6-38. These data suggest that Müller cells are one of the target cells for PACAP, stimulating the release of IL-6, and providing a mechanism whereby PACAP exerts a significant neuroprotective effect in the retina.