New technique for drug application to the spinal cord of walking mice.

With the increasing availability of mutant mice that allow the conditional silencing of specific classes of interneurons in the spinal cord by drug application, a method for easily delivering drugs locally on spinal cord segments in adult animals has the potential for providing insights into the functioning of neuronal networks controlling walking. Here we describe a simple technique for this purpose. The drug is applied in high concentrations in a bath created with Vaseline walls around one to three segments of the spinal cord exposed under general anesthetic (isoflurane) combined with a strong, long-lasting analgesic (buprenorphine). After 20min of drug application the Vaseline and the drug is removed and skin closed. We first document that the surgery and analgesic have no obvious influences on the kinematics of hind leg movements after recovery from the anesthetic, and that the analgesic enhanced locomotor activity. We then describe the influence of applying a glycine-receptor antagonist onto the lumbar segments of the spinal cord to demonstrate that the method is effective in modifying the functioning of neuronal systems in the spinal cord. Combining this method with kinematic and electromyographic recording techniques allows the detailed investigation of the effects of drugs on the walking behavior in adult mice.