Visual Function Test in Beagle with Electro-physiological Methods (ERG and VEP)-Second Report-

Abstract

In order to establish a novel method for examining the electro-physiological visual functions in a toxicity test, we investigated changes in the wave patterns of the electroretinograms (ERG) and visual evoked potentials (VEP) when Ethambutol (EB), a visual toxicant, was administered to Beagle dogs. Among six male beagle dogs (about 10 months of age, body weight: 8∼11kg) used, three dogs were assigned to the EB group and three to the control group. To investigate the drug effects on visual function under the condition where no general health problems other than those relating to visual function were observed in the dogs, the dosage of EB began to be gradually reduced as soon as the remaining of the food was observed, from 1,000mg/kg/day to 200mg/kg/day. The oral administration had been continued for three months under the above-mentioned conditions. The wave patterns of ERG (a-wave, b-wave and oscillatory potentials) and VEP (flash visual evoked potential: F-VEP, and pattern reversal-visual evoked potential: P-VEP) were recorded before and after the administration. As for the post-administration, the recordings were carried out at week 1, 2, 3, 4, 8 and 13 of the administration, as well as one month after the drug withdrawal (one dog had additional test two months after withdrawal, becouse the dog showed no recovery in one month). P-VEP exhibited the following changes in wave patterns due to the EB administration; an elongation of peak latency, and obscured waves. Recoveries of both of these changes were observed after drug withdrawal. On the other hand, F-VEP exhibited no clear effects of EB administration, because the reproducibility on the changed patterns was poor. The ERG showed no effects of the EB administration.

These findings suggest that the toxic effect of EB on visual functions may be detected by recording the wave patterns of P-VEP in Beagle dogs.