PROTECTIVE EFFECTS OF VASOACTIVE-INTESTINAL-PEPTIDE AGAINST DELAYED GLUTAMATE NEUROTOXICITY IN CULTURED RETINA

The effects of vasoactive intestinal peptide (VIP) on glutamate-induce d delayed death were examined using the primary cultures of rat retina l neurons. Effects of VIP on glutamate-induced neurotoxicity were eval uated by double staining with fluorescein diacetate and propidium iodi de. Glutamate (1 mM) was applied to the culture for 10 min in the pres ence and absence of VIP, and visible cells enumerated 24 h after cultu re in normal medium. Effects of VIP on increase in the intracellular C a2+ concentration and currents induced by glutamate in retinal neurons were investigated using the Ca2+ image analyzing system with fura-2 a nd whole-cell patch-clamp recording, respectively. The cAMP contents i n retinal cultures were measured by radioimmunoassay. VLP (10 nM-1 mu M) dose-dependently protected against gIutamate-induced neurotoxicity in cultured retinal neurons. Protection by VIP (100 nM) against glutam ate (1 mM)-induced neurotoxicity was antagonized by VIP6-28 (1 mu M), a VIP antagonist, and H-89 (100 nM and I mu M), a protein kinase A inh ibitor. However, VIP had no effect on gIutamate-induced inward current s nor glutamate-induced increase in the intracellular Ca2+ concentrati on. A 10-min exposure of VIP (100 nM) with glutamate (1 mM) resulted i n an increase in the cAMP level to 446 +/- 58 from 22 +/- 1 pmol/mg pr otein. These findings suggest that VIP protects against the gIutamate- induced neurotoxicity in retinal cultures by elevating the cAMP level via VIP receptors and thereby activating protein kinase A. (C) 1998 El sevier Science B.V. All rights reserved.