Protective effects of betaxolol in eyes with kainic acid-induced neuronal death

In the present study, we investigated whether betaxolol, a selective β1-adrenoceptor antagonist, has neuroprotective effect on kainic acid (KA)-induced retinal damage. Neurotoxicities were induced in adult male rats by intravitreal injection of KA (total amount, 6 nmol). To examine the neuroprotective effects of betaxolol, rats were pretreated with betaxolol topically 60 min before KA injection to the rat eyes and twice daily for 1, 3, and 7 days after KA injection. The neuroprotective effects of betaxolol were estimated by measuring the thickness of the various retinal layers, and by counting the number of choline acetyltransferase (ChAT)- and tyrosine hydroxylase (TH)-positive cells in each retinal layer. The retina is highly vulnerable to KA-induced neuronal damage. Morphometric analysis of retinal damage in KA injected eyes, the thickness of the retinal layers decreased markedly after KA injection period of both 3 and 7 days. Furthermore, the numbers of ChAT- and TH-positive cells were significantly reduced by intravitreal injection of KA. However, when two drops of betaxolol, once before KA injection and twice daily for 7 days after KA injection, were continuously administered, the reductions in the retinal thickness and the retinal ChAT- and TH-positive cells were significantly attenuated. The present study suggests that topically applied betaxolol has neuroprotective effect on the retinal cell damage due to KA-induced neurotoxicity.