Desflurane Selectively Suppresses Long-latency Cortical Neuronal Response to Flash in the Rat

Abstract

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. We 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-second 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 (0–100ms) and late (150–1000ms) 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 cortico-cortical feedback and loss of consciousness.

The thalamic dynamic core theory of conscious experience

“…Eight different general anesthetics agents have in common mainly that they suppress metabolism in the thalamus and brainstem reticular formation. Moreover, the sensory cortex has been shown to be responsive to stimuli even under large doses of anesthetics such as desflurane, although sustained responding is impaired, presumably because of interruption of thalamo-cortical and cortico-cortical loops (e.g., Hudetz, Vizuete, & Imas, 2009). Interestingly, and closely related to the role of midline nuclei in vegetative and minimally conscious states, blockade of potassium channels in the central medial thalamic nucleus of rats reverses desflurane anesthesia (Alkire, Asher, Franciscus, & Hahn, 2009).…”

The Role of Dendritic Signaling in the Anesthetic Suppression of Consciousness

“…Indeed, a recent functional magnetic resonance imaging study in humans investigated specifically the effect of propofol administration on functional connectivity in the nonspecific and specific thalamocortical systems and found that, under deep sedation, connectivity was reduced to a significantly greater extent in the nonspecific than in the specific system. 121 Furthermore, although a decrease in thalamic metabolism may be the most consistent regional effect of general anesthetics, the cerebral cortex generally remains responsive to sensory stimulation under anesthesia 12,24,121,122 (see the review article by Hudetz 11 ), suggesting that the metabolic suppression may Kaspar Meyer EDUCATION concern primarily the nonspecific thalamic nuclei, whereas the specific projections that carry perceptual information to the sensory cortices remain functional.…”

“…75,76 As an additional observation, which applies equally to the visual, auditory, and somatosensory modalities, there is an interdependency of the latency of sensory cortex responses and their correlation with conscious experience: although early activity in the sensory areas appears to be strictly stimulus bound, later activity, which reflects top-down signals from higher-order cortices, is correlated more closely with the subject's conscious percept. 24,75,76,79,89,90 Thus, several lines of evidence from neuroanatomy, neurophysiology, and functional neuroimaging suggest that top-down signaling fulfills an indispensable function in conscious perception. Accordingly, if general anesthetics interrupt top-down processing, as suggested by the studies reviewed at the outset of the article, this would be one potential mechanism by virtue of which they may suspend consciousness.…”

“…For instance, anesthesia selectively disrupts the late components of the primary visual cortex' response to flash stimuli, which are assumed to be mediated by top-down processing. 24 Also, anesthesia suppresses figure-ground modulation. 25 Figure-ground modulation refers to the observation that neurons in the primary visual cortex (V1) respond differentially to a certain stimulus depending on whether it is part of the background of an image or, alternatively, part of a circumscribed figure that "pops out.…”

Anosmia and hypogeusia as a complication of general anesthesia

“…General anesthesia suppresses the neuronal signal conduction at various levels of all the sensory pathways, including at the receptor, axon, neurosynapse, and cortex [4,5]. Such an effect on sensory pathways has been shown with somatosensory-evoked potentials, visual-evoked potentials, and auditory-evoked potentials; the effect is transient and completely reversible [6][7][8]. However, the effects of general anesthesia on the sense of smell and taste, and the time courses of their recovery, remain to be determined.…”