The Effects and mechanism different experimental stress models on visual evoked potentials

ABSTRACT Early researches have put forward that NO and lipid peroxidation were increased during stress. However, it is not clear whether NO and lipid peroxidation have roles on visual system changes possibly occurred in stress. To investigate this topic, 120 albino rats were used in this study. Experimental animals were divided equally into 12 groups as follows; Control group (C), L- NAME+control group (CL), Vitamin E+control group (CE), cold stress group (CS), immobilization stress group (IS), cold+ immobilization stress group (CIS), L-NAME+stress groups (CSL, ISL, CISL), Vit E+stress groups (CSE, ISE, CISE). Chemical agents, L-NAME and Vitamin E, were administrated 10 mg/kg/day i.p. and 30 mg/kg/day i.m. respectively throughout 15 days experimental period. Physiological solution was injected to the control groups during the experimental period. Visual evoked potentials (VEPs) were recorded from animals at the end of the experimental period. Afterwards, blood, retina and brain of rats were taken in order to measure biochemical parameters. Plasma corticosteron levels were increased according to the control group. L-NAME increased corticosteron level only in LCS group with respect to its control group, while Vitamin E decreased corticosteron levels in all stress groups compared with their respective control groups. Brain and retina TBARS levels were significantly increased in all stress groups compared with the control group. L-NAME decreased lipid peroxidation in all stress groups, but increased only in CL group according to their corresponding control groups. Although, Vitamin E decreased significantly TBARS levels in all stress groups with respect to C group. Compared with the control group, significant increases were observed in brain nitrit levels of all groups and in retina nitrit levels of IS group. It was observed that L-NAME and Vitamin E decreased the nitrit levels in both retina and brain of all stress groups with respect to their control groups. It was observed that GSH-Px activities were affected by stress. On the other hand, effects of L-NAME was found to depend on the stress models All VEP components were prolonged in all stress groups compared with their control groups. L-NAME prolonged all VEP components in CL group with respect to C group. However, L-NAME and Vit E reduced VEP latencies in all stress groups respective to their control groups. Among the peak-to-peak amplitudes of VEPs only P2N2 amplitude was decreased in LC and in all stress groups respect to control group.