THE EFFECT OF URETHANE ANESTHESIA ON EVOKED-POTENTIALS IN DENTATE GYRUS

We examined the effect of urethane (1000 mg/kg, followed by 50 mg/kg p er h, i.v.), an anesthetic commonly used by physiologists, on evoked p otentials recorded in dentate gyrus in adult Wistar rats by stimulatin g the ipsilateral perforant path, via chronically implanted electrodes . Urethane decreased paired-pulse inhibition. Under urethane, with pai red-pulse stimulation, the ratio of the second population spike amplit ude to the first increased by 11.1-20.7% at 25-60 ms interstimulus int erval (n = 18, P < 0.05). At 25 ms, the proportion was 3.6 +/- 1.6 whi le awake, and 14.7 +/- 3.5 under urethane. Urethane depressed granule cell excitability and strength of synaptic responses. Under urethane, the ratio of the population spike amplitude obtained at 250 mu A Stimu lation to the maximal response in the same input/output response exami nation decreased by 20%, and the ratio of the excitatory postsynaptic response slopes fell by 10%. These results indicate that urethane affe cts neurotransmission in the hippocampus, and suggest that its effect may be exerted in part on excitatory neurotransmission.