ABSTRACT
Background The excitotoxicity to retinal neurons caused by abnormal elevation of glutamate in retina is a common pathology concomitant with major blind-causing eye diseases.However,an effective approach to protect retinal neurons from glutamate-induced excitotoxicity is still lack.Intraperitoneal administration of α-melanocyte stimulating hormone(α-MSH)has been shown to protect hippocampal neurons from glutamate-induced excitotoxicity.Objective This study was to investigate the protective effect of α-MSH on glutamate-induced excitotoxicity in a chicken embryonic retinal explant culture system.Methods The retinas were isolated from chick embryos at embryonic day 9(E9) and cultured as explants.The explants at 3,5 and 7 days in vitro and the retinas at corresponding embryonic day 12,14 and 16(E12,E14,E16)were collected.The morphology of explant cultures was examined by hematoxylin and eosin staining,and the expression of melanocortin receptors (MCRs)was analyzed by real-time PCR.In the experiment of glutamate-induced excitotoxicity,the retinal explants at 4 days in vitro were treated with glutamate for 48 hours,α-MSH was incubated with the explants 30 minutes before and during the glutamate treatment period.Then the apoptotic cells were detected by TUNEL staining and quantified.The glutamate alone treated-explants and those treated with culture media were included as controls.The expression of glial fibrillary acidic protein(GFAP) at 48 hours after treatment in all retinal explants was analyzed by real-time PCR.Results Hematoxylin and eosin staining showed that the retinal explants exhibited similar morphology to those observed in the retinas from chick embryos at the corresponding developmental stages.The real-time PCR analyses of chick retinas showed that MC1R mRNA level at E9,E12,E14 and E16 was significantly lower than that in post-hatch day 1 (all P=0.000) ;whereas the transcript level of MC5R was significantly increased from E9 to E12 and E14 (both P =0.000),and then gradually decreased from E14 to P1.The expression of these genes showed similar temporal patterns in the retinal explant cultures.TUNEL staining revealed that treatment of the retinal explant cultures with α-MSH substantially and significantly reduced number of apoptotic cells induced by glutamate (P =0.000),which was accompanied by significant suppression of glutamate-induced GFAP up-regulation (P =0.000).Conclusions Application of α-MSH dramatically ameliorated glutamate-induced cell death in retinal explant cultures.This protective effect may be due to α-MSH-mediated suppression of astrogliosis caused by abnormal elevation of glutamate.