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Visual cortex flash evoked potentials (FEPs), pattern reversal evoked potentials (PREPs), and body temperature were measured in hooded rats following IP injections on separate days of saline, and of 15 and 30 mg pentobarbital/kg body weight. Two experiments were performed, differentiated by standard (23 degrees C) and warm (31 degrees C) room temperatures. The 30 mg/kg dose produced hypothermia of 2.6 degrees C in the standard environment, but not in the warm environment. Early components of FEPs were generally increased in amplitude by the 15 mg/kg dose, and decreased by the 30 mg/kg dose at 23 degrees C. At 31 degrees C, the 30 mg/kg dose did not decrease early component amplitude, suggesting that hypothermia can potentiate some effects of pentobarbital. Amplitudes of late FEP components were depressed at both ambient temperatures. The main PREP components N1P1 and P1N3 were increased in amplitude by the 15 mg/kg dose, but returned to near baseline levels at 30 mg/kg, at both temperatures. PREP component N2P2 was reduced in amplitude by the 30 mg/kg dose only at 23 degrees C. Treatment with 30 mg/kg pentobarbital increased FEP and PREP latencies at both ambient temperatures, but the magnitudes of the increases at 31 degrees C were typically less than half those observed at 23 degrees C. These results indicate that hypothermia contributes to some pentobarbital-induced changes in both FEPs and PREPs, but that pentobarbital also produces effects independent of hypothermia.

The effects of ketamine on photic evoked potentials, recorded from the superior colliculus, were determined in hooded rats. Animals were given intraperitoneal injections of saline, or of 1, 10, 50 or 100 mg ketamine/kg body weight on separate days. Evoked potentials were recorded at 5, 20, 40 and 60 min following injection. Individual components in an early positive complex were augmented by the 100 mg/kg dose. Following administration of the 50 and 100 mg/kg doses, a positive spike (latency of 53 msec) emerged from the middle of a negative wave. A second positive spike (latency of 65 msec) also became prominent at these doses. Late oscillatory potentials were slightly augmented by the 100 mg/kg dose of ketamine. The relationship between these effects of ketamine on photic evoked potentials, and the postanaesthetic psychological manifestations of ketamine, is yet to be determined.