A cryogenic device for reversibly blocking transmission through small regions of the spinal cord white matter.

A simple cryogenic device is described. This device is capable of cooling neural tissue in contact with the probe and maintaining the tissue at the desired temperature for extended periods of time. The cold probe can thereby reversibly block neural transmission through small portions of the spinal cord white matter. Interruption of axonal transmission is achieved by placing the tip of the device in contact with the exposed surface of the spinal cord and cooling the tip of the probe to -1 to +2 degrees C. The investigator monitors the tip temperature and adjusts the pump rate to maintain a constant tip temperature. The cross-sectional area under the probe where effective transmission block is achieved is about 1.5 mm2 which approximates the size of a single funiculus in the cat thoracic spinal cord. The cryogenic device was constructed for less than $700. The properties of this device were studied in physiologic experiments in cats. This device reversibly, selectively and repeatedly blocked the ascending mass action potential in the dorsolateral funiculus, transmission through ascending spinal axons in the dorsal columns, transmission through axons of spinal dorsal horn cells, the descending inhibitory input to the dorsal horn and the activity of thalamic nociceptive neurons. The reversible cold block effects on single units were observed for the duration of the experiments (up to 18 h) with no detectable damage to the underlying tissue. The physiologic effects of the cold block were usually reversed a few minutes after rewarming, although in some cases it took up to 40 min for the complete reversal of the cold block. This cryogenic device is useful for studying spinal cord pathways.