Search for the optimal monosodium glutamate treatment schedule to study the neuroprotective effects of PACAP in the retina.

We have previously shown the protective effects of pituitary adenylate cyclaseactivating polypeptide (PACAP) in monosodium glutamate (MSG)-induced retinal degeneration. In the present article, we have investigated the optimal model for examining this neuroprotective effect. One MSG treatment on postnatal (P) days 1 or 5, in spite of leading to same ultrastructural changes, does not cause enough damage to study neuroprotection. When retinas were treated three times with MSG, the entire inner retina degenerated. Neuroprotection with PACAP was achieved with at least two treatments. Evidence suggests that PACAP provides protection against excitotoxicity, therefore, it may be a useful agent in reducing excitotoxic damage in the retina.