A technique for chronic extracellular recording of neuronal activity in the dorsal horn of the lumbar spinal cord in drug-free, physiologically intact, cats.

A technique has been developed which allows extracellular recording from single neurons in the spinal cord of physiologically intact, awake, drug-free, restrained cats. The technique involves the surgical placement, under general anesthesia, of a stainless steel recording chamber which has a rectangular opening in its center that is 6 mm wide by 12 mm long. The recording chamber is attached to the vertebral column so that the opening is positioned over a similar opening that has been made in the bone of the vertebral column overlying the lumbar enlargement. Following a two week recovery period, the cats, which have been trained to accept restraint, are placed in a plexiglass restraining box, and a microdrive assembly is attached to the recording chamber. Tungsten microelectrodes (Frederick Haer & Co.) are then advanced through the dura into the dorsal horn of the spinal cord while receptive fields are stimulated. The chamber, when properly positioned, provides access to neurons with receptive fields on both hindlimbs. The stability of the system makes it possible to maintain single cell recordings from neurons in the dorsal horn of the spinal cord in the presence of either experimenter-induced or spontaneous movement of hindlimbs, tail or back musculature or during and after intramuscular, intravenous, spinal and epidural drug injections. Of greatest importance is the fact that the animals remain healthy and normal throughout the period of neuronal recordings.