BARBITURATE SENSITIVE COMPONENTS OF VISUAL ERPS IN A REPTILE

THE selective effects of methohexital anesthesia were used to differentiate components of visual event-related brain potentials (ERPs) in pond turtles (Pseudemys scripta). Tectal and forebrain omitted stimulus potentials (OSPs) were found to be particularly sensitive to the barbiturate; they are reversibly abolished while the large early wave of the forebrain flash visual evoked potential (VEP; 110-120 ms) is reduced by only 27 +/- 11% and that of the tectal VEP (55-65 ms) is increased by 40 +/- 12%. Concurrent with the decline of the OSP is the loss of late slow wave components (ca. > 125 ms) of forebrain and tectal VEPs and the appearance of irregularities in the responses of 5 Hz repetitive flashing. The barbiturate effects on the VEP and recovery cycles are remarkably similar to those reported in mammals.