Sodium leak channels in the central amygdala modulate the analgesic potency of volatile anaesthetics in mice

Background

Analgesia is an important effect of volatile anaesthetics, for which the spinal cord is a critical neural target. However, how supraspinal mechanisms modulate analgesic potency of volatile anaesthetics is not clear. We investigated the contribution of the central amygdala (CeA) to the analgesic effects of isoflurane and sevoflurane.

Methods

Analgesic potencies of volatile anaesthetics were tested during optogenetic and chemogenetic inhibition of CeA neurones. In vivo calcium imaging was used to measure neuronal activities of CeA neuronal subtypes under volatile anaesthesia. Contributions of the sodium leak channel (NALCN) in GABAergic CeA (CeA^GABA) neurones to analgesic effects of volatile anaesthetics were explored by specific NALCN knockdown. Electrophysiological recordings on acute brain slices were applied to measure volatile anaesthetic modulation of CeA neuronal activity by NALCN.

Results

Optogenetic or chemogenetic silencing CeA neurones reduced the analgesic effects of isoflurane or sevoflurane in vivo. The calcium signals of CeA^GABA neurones increased during exposure to isoflurane or sevoflurane at analgesic concentrations. Knockdown of NALCN in CeA^GABA neurones attenuated antinociceptive effects of isoflurane, sevoflurane, or both. For example, mean concentrations of isoflurane, sevoflurane, or both that induced immobility to tail-flick stimuli were significantly increased (isoflurane: 1.17 [0.05] vol% vs 1.24 [0.04] vol%, P=0.01; sevoflurane: 2.65 [0.07] vol% vs 2.81 [0.07] vol%; P<0.001). In brain slices, isoflurane, sevoflurane, or both at clinical concentrations increased NALCN-mediated holding currents and conductance in CeA^GABA neurones, which increased excitability of CeA^GABA neurones in an NALCN-dependent manner.

Conclusions

The analgesic potencies of volatile anaesthetics are partially mediated by modulation of NALCN in CeA^GABA neurones.