Electrophysiology of sensory and sensorimotor processing in mice under general anesthesia

Like many other complex biological phenomena, sensory processing is starting to be studied at the level of the gene. Whereas the mouse is the standard organism for molecular neurobiology, somatosensation and pain are mainly investigated in the rat. The in-vitro electrophysiological technique is well established in mice. The effect of manipulations of the mouse genome on neuronal systems and networks has to be investigated under in-vivo conditions. Thus, the step from the rat to the smaller mouse seems to be important in terms of progress in molecular neurobiology. So far, there is no published study of sensory processing by electrophysiological means in mice under controlled general anesthesia. In this paper we describe a technique for electrophysiological recordings of sensory and sensorimotor processing in anesthetized mice. The mouse is anesthetized by continuous administration of the short-acting general anesthetic methohexital sodium salt via the jugular vein and artificially ventilated via a tracheotomy. The electrocardiogram and the carotid artery blood pressure are monitored. The sensorimotor jaw-opening reflex and the hindpaw withdrawal reflex are elicited by electric stimulation of the tongue and the sole of the hindpaw, respectively. The jaw-opening reflex is inhibited by deep brain stimulation of the rostral ventromedial medulla. On- and off-cells of the rostral ventromedial medulla and sensory neurons of the spinal trigeminal nucleus are extracellularly recorded by tungsten electrodes. General anesthesia can be reliably induced, maintained and sufficiently controlled in mice. Under this condition, studies can be performed on sensory processing in mice.