Chlordimeform produces profound, selective, and transient changes in visual evoked potentials of hooded rats

Rat visual function was tested after acute exposure to chlordimeform (CDM), a formamidine insecticide/acaricide. Adult male Long-Evans rats were surgically implanted with epidural recording electrodes overlying visual cortex and tested 1 week later. Pattern reversal-evoked potentials (PREPs), flash-evoked potentials (FEPs), and FEP recovery ratios were measured after acute CDM administration. Averaged recordings obtained during 200 reversals of a black-and-white square wave grating comprised the PREPs, and those obtained during 128 paired strobe lamp flashes comprised the FEPs. In the first study, which examined dose-response relationships, i.p. injections of 0 (saline), 5, 15, or 40 mg/kg CDM-HCl were administered 30 min prior to testing. The PREP amplitudes showed large dose-related changes in the CDM-treated rats. PREP N1P1 and P1N3 peak-to-peak amplitudes increased more than 200% in the 40 mg/kg group. In contrast, FEP amplitudes and FEP recovery ratios were unchanged by CDM. Both PREP and FEP peak latencies were increased by CDM in dose-related fashions. In the second study, which examined the time course of CDM action, PREPs and paired-pulse FEPs were recorded 3, 6, and 24 h after dosage with either 0 or 40 mg/kg CDM. All evoked potential changes were large at 3 and 6 h, but had returned to control values by 24 h. In summary, acute exposure to CDM temporarily increased both the amplitude and latency of PREPs, but only the latency of FEPs.