Dynamic changes of touch- and laser heat-evoked field potentials of primary somatosensory cortex in awake and pentobarbital-anesthetized rats

In this investigation, changes of mechanical- (MEP) and laser-evoked potent ials (LEP) in rat primary somatosensory cortex during the course of pentoba rbital (PB) anesthesia were examined. Temporal analysis of changes in the m agnitude and latency of MEP and LEP, EEG activity, gross motor behaviors, a nd the tail flick response following laser stimulation before, during, and after PB administration (50 mg/kg, i.p.) was performed and correlated in ch ronically implanted rats. During the wakeful condition, there were two majo r cortical components each following mechanical stimulation (MEP1 and MEP2, n=17) and laser stimulation (LEP1 and LEP2, n=10), respectively. After PB administration, the positive peak in MEP1 was enhanced, and all other compo nents disappeared. These components returned with different time courses. T wo hours after PB administration, when the rat had spontaneous movements an d flexor reflexes, LEP2 showed reversed polarity. MEP2 returned gradually 3 h after PB administration when the rat regained its ability to execute coo rdinated movements. After 4 h, LEP1 began to reappear and LEP2 returned to its negative polarity. We found that PB facilitated A beta fiber-related co rtical evoked potential (MEP1), while differentially inhibited A delta and C fiber-related components (MEP2, LEP1 and LEP2). Characterization of these anesthesia-induced changes in cortical output may be useful in studying th e neural basis of tactile and pain sensations. (C) 2001 Elsevier Science B. V. All rights reserved.