Even if anesthetics are widely used in the medical practice, there are still many unresolved issues relating to their mechanism(s) of action on neuronal circuits. Since their action is likely to be synaptic, these compounds could act either presynaptically, with a modification of neurotransmitter release and/or reuptake machineries, or postsynaptically, with alterations of the number and/or sensitivity of post-synaptic receptors. Despite the complexity of these molecular targets, all general anesthetics induce a profound inhibition of cortical EEG activity while sparing evoked cortical responses. Based on these considerations, we began the investigation of the electrophysiological action of various classes of general anesthetics on the activity of the rat visual system to identify potential targets and uncover specific features of their action. We compared the effects of three states of anesthesia induced by two different anesthetic molecules (sevoflurane and propofol). During experiments, adult rats were kept at 37°C, curarized, mechanically ventilated and oxygen and CO2 levels were continuously monitored. Rats were exposed to monocular light pulses of different durations and intensities and EEG activity and evoked potentials, both ON and OFF responses, were recorded using implanted superficial electrodes. While basal cortical activity is reduced in a comparable manner by both classes of anesthetics, throughout the three states of anesthesia, the effect on visual evoked activity exhibit clear differences, suggesting the presence of two very distinct circuital mechanisms of action. In future, the analysis on the response of visual cortex, might provide important informations on the mode of action of general anesthetics.
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