Authors#

Jinrong Li, Ph.D., Md Sams Sazzad Ali, Ph.D., and Christian H. Lemon, Ph.D. Department of Biology, University of Oklahoma, Norman, OK 73019 corresponding author email: lemon@ou.edu

Jinrong Li is a Research Associate while Md Ali is a Post-Doctoral Fellow in Chris Lemon’s lab in the Department of Biology at the University of Oklahoma. They study neural circuit and molecular mechanisms of taste and somatosensory processing in the mouse brain.

Background#

Acute anesthetized preparations in mice that support neural recording and stimulation in stereotaxic coordinates are useful for real-time functional mapping of the projections of active sensory neurons in the brain using electrophysiological methods, imaging, and optogenetics. A single recording session in studies of this type can last for extended periods of up to several hours, requiring robust control over anesthetic depth and level in mice – a model species used in many areas of neuroscience albeit one that displays low tolerance for vagaries in physiological condition. To address this challenge in our acute mouse neurophysiological studies on orofacial sensory processing, we developed a method for gas anesthesia for mice where animals freely respire an isoflurane/ oxygen mixture through a tracheostomy tube. To achieve this, the distal end of this tube is loosely connected to custom concentric gas exchange tubing that delivers the isoflurane mixture and scavenges exhaled gas/excess isoflurane. Under this method, mice respire under their own power, without the aid of mechanical ventilator, and can remain successfully anesthetized for hours with fast control and adjustment of anesthetic level. What is more, this preparation does not involve the use of a nose cone, which frees access to the oral cavity and whisker pad for stimulus delivery in oral sensory and somatosensory studies. Here we describe this method of anesthesia, which our group has successfully used in several publications on gustatory and trigeminal neurophysiology in mouse models (e.g., Wilson and Lemon 2014, Lemon, Kang et al. 2016, Li and Lemon 2019). In brief, under procedures described here a tracheostomy tube is surgically secured following initial induction of mice by a shortlasting injectable anesthetic. Mice are then placed in a stereotaxic device and transferred to gas anesthesia respired through the tracheostomy tube. Importantly, these methods are for acute preparations only, where mice are not allowed to recover from anesthesia and are sacrificed at the end of the experimental session. Our procedure could be adapted for use with rat models through, in part, increasing the dimensions of the tracheostomy tube and gas exchange tubing. Prior to using these methods, investigators must consult with and receive approval from their local Institutional Animal Care and Use Committee (IACUC).

Materials#

Anesthetics and chemicals (some may require a license for purchase and research use)#

• ketamine
• xylazine
• atropine
• eye ointment
• isoflurane

Apparatus and supplies#

• surgical tools suitable for mice
• oxygen cylinder and regulator
• various tubing and supplies, as below
• stainless steel wire, 0.011” diameter (A-M Systems, Cat No. 792100)
• vacuum system with regulator and safe exhaust discharge
• single channel isoflurane vaporizer
• Stereotaxic Alignment System (Kopf model 930)
• pulse oximeter and heart rate monitor (e.g., MouseSTAT® Jr., Kent Scientific Corporation)
• feedback controlled heating pad for mice
• acrylic mouse induction chamber