Effects of levodopa On visual evoked potential and visual cortex neuron in monocular deprivation rat

Abstract

Background Nearly over 40 years have elapsed since the original findings of visual cortical plasticity,but none of drug has been found for curing amblyopia effectively. Objective The goal of this study was to investigate the effects of different dose of levodopa on flash visual evoked potential(F-VEP)and morphology of visual cortex cells in monocular deprivation rat and explore the possible mechanism of curing amblyopia.Methods Monocular deprivation model were established by suturing eyelids of 30 2-week-old Sprague Dawley(SD)rats for 4 weeks.The 30 SD rats were then divided into 3 groups randomly and 10 rats for each group.Normal saline.20 ms/kg levodopa,80 ms/kg levodopa were intragastrically administered once per day after modeling respectively for 4 weeks.F-VEP was recorded after establishment of model and administration of drug respectively.The rats were sacrificed and the visual cogex was obtained for histological examination,and TUNEL technique was used to assess the structural change of visual cortex.Results The latency of P1 wave was significantly longer in the deprived eye than the normal eyes(P 0.05).The number and structure of neurons in contralateral visual cortex of non-deprived eye were normal.However,the numbers of neurons in deprived eye were significantly less and presented the signs of para-apoptosis in normal saline group.In 20 mg/kg levodopa groups,the alterations of number and morphology in neurons of rat visual eogex were slight.TUNEL assay revealed that the numbers of positive neurons in contralateral visual codex of non-deprived eye were 2.20±1.23.while those in deprived eye were 53.7±9.36,27.20 4±5.96 and 10.70±3.23 in normal saline group,20 mg/kg and 80 mg/kg levodopa group respectively,showing a significant difference among them(P>0.05).After usage of levodopa,the numbers of positive neurons was negatively correlated with the difference value of P,latent period of VEP(r=-0.815,P=0.000).Conclusion Levodopa has a therapeutic effect on rat deprived eye,and its possible mechanism is inhibiting the para-apoptosis of neurons and participating in the development and plasticity of visual system. Key words: Levodopa; Amblyopia; Visual evoked potential; Visual cortex; Para-apoptosis