Background: The effect of inhalational anesthetics on sensory-evoked unit activity in the cerebral cortex has been controversial. Desflurane has desirable properties for in vivo neurophysiologic studies, but its effect on cortical neuronal activity and neuronal responsiveness is not known. The authors studied the effect of desflurane on resting and visual evoked unit activity in rat visual cortex in vivo.
Methods: Desflurane was administered to adult albino rats at steady-state concentrations at 2%, 4%, 6%, and 8%. Flashes from a light emitting diode were delivered to the left eye at 5-s intervals. Extracellular unit activity within the right visual cortex was recorded using a 49-electrode array. Individual units were identified using principal components analysis.
Results: At 2% desflurane, 578 active units were found. Of these, 75% increased their firing rate in response to flash. Most responses contained early (0-100 ms) and late (150-1000 ms) components. With increasing desflurane concentration, the number of units active at baseline decreased (-13%), the number of early-responding units increased (+31%), and number of late-responding units decreased (-15%). Simultaneously, baseline firing rate decreased (-77%), the early response was unchanged, and the late response decreased (-60%).
Conclusions: The results indicate that visual cortex neurons remain responsive to flash stimulation under desflurane anesthesia, but the long-latency component of their response is attenuated in a concentration-dependent manner. Suppression of the long-latency response may be related to a loss of corticocortical feedback and loss of consciousness.