Background: Cognitive functions including sensory processing, consciousness, and memory are disrupted by anesthetics. General anesthesia is thought to be a state of suppressed net cortical activity characterized by decreased activity of excitatory pyramidal neurons and enhanced GABAergic inhibitory activity. In cortical circuits, pyramidal neuron activity is sculpted by inhibitory interneurons, which in the cortex express three, non­overlapping markers: 5HT3a­receptor (5HT3aR), parvalbumin (PV), and somatostatin (SST). Although interneurons play an important role in regulation of cortical function, the effect of general anesthetics on interneuron activity remains unknown. In this study, we aimed to characterize cortical interneuron activity in the living mouse brain under general anesthesia.

Methods: We expressed the ultrasensitive genetically encoded calcium indicator, GCaMP6, in layer 2/3 pyramidal cells and interneurons using transgenic (Thy1­GCaMP6) and knock­in (PV­Cre, SST­ Cre, 5HT3a­Cre) mice with adeno­associated virus encoding GCaMP6. Mice expressing GCaMP6 were anesthetized with either sevoflurane or ketamine­xylazine (KX). We used two­photon calcium imaging to record the neuronal activities of pyramidal neurons and interneurons in the primary somatosensory, motor, and visual cortices during awake, anesthetized, and recovery states. We measured the fluorescent signals of each soma over time, calculating the ΔF/F0, where F0 is the baseline fluorescent signal. Image analysis was performed in NIH ImageJ and data was evaluated with Student's t­-test in GraphPad Prism.

Results: We found that sevoflurane and ketamine­xylazine anesthesia significantly decreased the average and peak F/F0 of both pyramidal cells and all interneurons classes (5HT3aR, PV, and SST) as compared to awake animals. At the subcellular level, calcium activities of dendritic branches and dendritic spines were also reduced compared to awake state. Decreased neuronal activities under anesthesia occurred across all observed cortical areas. Moreover, suppressed neuronal activities continue into the recovery period as compared to awake state.
Conclusion: Our results suggest that general anesthesia results in not only the suppression of excitatory pyramidal cell activity, but also decreased GABAergic inhibition from interneurons. Neuronal activities continue to be suppressed into the recovery period, suggesting a persistent effect on cortical dynamics in the perioperative period.

General anesthesia induces a reduction of cortical inhibitory interneuron activity in vivo