Investigations of amitraz neurotoxicity in rats. II. Effects on visual evoked potentials. Boyes, W.K. and Moser, V.C. (1986) Fundam. Appl. Toxicol. 00,000-000. As a part of a series of studies investigating the possible neurotoxicity of amitraz (AMZ), a formamidine pesticide, visual evoked potentials were recorded from Long-Evans rats following acute and short-term repeated exposure to AMZ. The first of three experiments examined the relationship between a single i.p. injection of AMZ (0, 50 and 100 mg/kg) and the latency and peak-to-peak amplitude of pattern-reversal (PREP) and flash-evoked potentials (FEP). The effects of another formamidine, cholordimeform (CDM; 40 mg/kg) were also studied for comparison purposes. Two hours after treatment, AMZ exposure produced large, dose-related increases in PREP amplitudes. Exposure to CDM produced similar changes. Neither compound changed FEP amplitudes. In summary, AMZ produced two phases of change in visual evoked potentials. The first phase was characterized by large increases in PREP amplitudes without increasing FEP amplitudes in the same rats. The second phase was characterized by suppression of PREP P2N3 amplitude. Short-term repeated exposure produced signs of accumulating intoxication including progressive loss of body weight, lowered body temperature and prolonged duration of evoked potential changes.