Urethane affects the rat visual system at subanesthetic doses

Urethane is an anesthetic which is commonly used in neurophysiological studies because it is presumed to have minimal effects upon neuronal activity. This study investigated the influence of urethane anesthesia upon flash evoked potentials (FEPs) recorded from hooded rats. Subanesthetic dosages (25 g/kg and 0.5 g/kg) and an anesthetic dosage (1.0 g/kg) were administered, and subsequently recorded FEPs were compared to vehicle-injected controls. Urethane produced profound qualitative and quantitative effects upon the FEP. At 0.5 g/kg, the P1 (normal latency = 20 msec) and N1 (normal latency = 30 msec) peaks became unrecognizable. Peak N1 disappeared and peak P1 merged with P2 (normal latency = 45 msec). Peak P2 increased in amplitude by about 100%. The results indicate that in the visual system, urethane has a significant influence upon neuronal activity. Caution should be used in interpreting data obtained from urethane-anesthetized rats.