General anesthesia triggers immediate early gene expression and low-threshold spike bursting in the mouse paraventricular thalamus

Position du problème et objectif(s) de l’étude

Despite massive use of general anesthetic agents, our understanding of brain functioning under general anesthesia is currently limited. Even though recent effort using state-of-the-art neuroscience methods, such as intracerebral electrophysiology and optogenetics in animal models, has undertaken to identify key nuclei for loss and recovery of consciousness, no comprehensive model yet allow to predict brain dynamics from pharmacologically induced clinical changes, much less describe intracellular events including neuronal plasticity. In this context, we propose, in a mouse model, whole-brain mapping of the brain activity-related « immediate early gene » cFos expression, and targeted multi-unit extracellular electrophysiological recording in the paraventricular thalamus (PVT).

Matériel et méthodes

Experiments were conducted in adult mice, the anesthetic agent used was sevoflurane. Whole-brain histology was performed using the iDisco+ tissue clearing method, immunolabelling of the cFos protein, and a single-plane illumination fluorescence microscope. Expression of the immediate early gene cFos was mapped on a 3D anatomical atlas. Automated quantification of cFos-positive cells was done with a custom-made software. Electrophysiological recordings in the PVT used 32-channels silicon probes, implanted either acutely or chronically, and were performed under « light », « deep », or no anesthesia. Extracellular spikes were sorted as single-spikes or low-threshold-spike bursts (LTS).

Résultats & Discussion

Whole-brain mapping of cFos expression showed increased labelling in various cortical and deep brain regions, including the lateral hypothalamus, the central lateral amygdala, the amygdalopiriform transition, the piriforme cortex, the supramammilary nucleus , and the PVT. In particular, cFos-positive cells were doubled in the PVT. This midline thalamic nucleus can display LTS in conditions of hyperpolarization, including during physiological sleep. Such electrophysiological activity may alter neocortical computation, and could through calcium signaling induce cFos expression. Electrophysiological recording in the PVT showed that twice as many neurons displayed LTS under general anesthesia as compared to the awake state. Other electrophysiological features seemed unchanged. These results are consistent with sevoflurane-induced hyperpolarization, for instance through K2P channels, allowing LTS via T-type low-voltage activated calcium channels deinactivation, leading to increased intracellular calcium ion concentration, and downstream signaling eventually triggering cFos expression. This electrophysiological activity may be self-maintained, and participate in postoperative delirium. Besides, cFos expression can be involved in neuronal plasticity, that would be in this case inappropriate, and as such may participate in postoperative cognitive dysfunction. Future work will include formal mathematical modelling in order to build pharmacologically testable dynamical models of brain states under general anesthesia.

Conclusion

General anesthesia triggers the expression of the immediate early gene cFos in the PVT, which displays during anesthesia LTS in an increased number of neurons compared to what can be measured during waking. These features may lead to prolonged electrophysiological dynamics and pharmacologically induced plasticity, that could relate to postoperative delirium and cognitive dysfunction

Auteurs

Julie AREIAS (1), Julie PERROY (1), Vivien SZABO (2) - (1)Igf, Univ. Montpellier, Cnrs, Inserm, Montpellier, France, (2)Sar Gui De Chauliac, Chu Montpellier, Igf, Univ. Montpellier, Cnrs, Inserm, Montpellier, France

Orateur(s)

Vivien SZABO (Montpellier)