Impact of exogenous melatonin on postnatal teratogenic changes of the optic nerve due to acute prenatal ethanol administration

In this study the impacts of melatonin, known for its antioxidant and neuro-protective characteristics against alcohol, known for its toxic effect on the optic nerve due to acute use and its teratogenic effects on young animals of pregnant rats are investigated experimentally. 24 Wistar albino female adult rats were used in the study and the subjects were assessed in three trimesters. Each trimester was divided into 4 groups and 6 young animals for each group, 24 for each trimester and altogether 72 young animals were included into the study. 1 ml/kg serum physiologic was administered i.p. to the 1st control group, single dose 2 gr/kg ethanol to the 2nd group, single dose 2 gr/kg ethanol + 10 mg/kg melatonin to the 3rd group, and single dose 10 mg/kg melatonin i.p. to the 4th group on day G7, G15, and G21, respectively. Each young rat was included into the VFP study after a period of two postnatal weeks (P14) following anesthesia with i.p. ketamine (60-100 mg/kg) + xylazine (5-10 mg/kg). After VFP, intra-cardiac perfusion with 150 ml fluid of 2% formaldehyde + glutaraldehyde mixture buffered by 0.1 M phosphate was performed on the animals following anesthesia with i.p. ketamine (60-100 mg/kg) + xylazine (5-10 mg/kg). Afterwards, the optic nerve was dissected. The right optic nerve was examined using light- and electron microscope, the left optic nerve was examined biochemically. The electrophysiological examination revealed a significant extension of latents in all 3 trimesters exposed to ethanol; however, a decrease was observed in the amplitude only in the 1st trimester. A significant extension of latents was observed in all 3 trimesters exposed to ethanol + melatonin; however, an increase was observed in the amplitude in the 1st and 2nd trimesters. Biochemical tissue MDA study revealed that compared to the control group (p=0.040) and melatonin group MDA was increased (p=0.000) only in the 1st trimester. Significant decrease was observed in the MDA value of the ethanol+melatonin group compared to ethanol group (p=0.008). MAD values showed no statistically meaningful differences in the 2nd and 3rd trimesters. Biochemical tissue SOD level study revealed statistically increased SOD activity (p=0.043) in the ethanol+melatonin group compared to the ethanol group for the 1st trimester. No statistically meaningful differences were observed in the 2nd and 3rd trimesters. Compared to the control group, qualitative assessment based on light microscope images showed slimming in myelin sheaths and decrease in axon diameter of myelinated axons in the optic nerves in the ethanol group of all three trimesters, whereas an increase was observed in the number and size of glial cells. Number of dense cells dying due to the cytotoxic effect of ethanol was more significant in the first two trimesters. Compared to the ethanol group, increase in myelin thickness and axon diameter was observed in all three trimesters in the ethanol+melatonin group. Myelinated axon thickness and axon diameter of the optic nerve in the melatonin group was similar to the control group. Quantitative assessment of stereological analyses results based on electron microscope images showed that ethanol decreased myelin thickness, axon area, and axon diameter in all three trimesters; in the ethanol+melatonin group, however, increase was observed in myelin thickness, axon area, and axon diameter in the 1st trimester, increase in myelin thickness and axon area, but no change in axon diameter in the 3rd trimester, and no impact was observed in the 2nd trimester. Myelin sheath thickness of myelinated axons, axon area, and axon diameter of the optic nerve in the melatonin group was similar to the control group. In conclusion, although the teratogenic effect of ethanol particularly in the 1st trimester, the antioxidant and neuro-protective effect of melatonin was shown in electrophysiological, biochemical and histological investigations. Keywords: Alcohol (ethanol), melatonin, VEP, optic nerve, MDA, SOD