High frequency discharges in sensory nerves following ischemia

The effects of ischemia and recovery from ischemia on afferent discharges recorded from dorsal root filaments were assessed in anesthesized cats. During ischemia produced by cross-clamping the lumbar aorta, some of the hindlimb afferents originating in muscle spindles exhibited a sustained high frequency discharge of 120--160 Hz, the so-called "explosion." During recovery from ischemia, nerve discharges appeared in previously inactive dorsal root afferent nerve fibers not of muscle spindle origin. The post-ischemic high frequency discharges appeared in bursts of action potentials at frequencies of 200--500 per second, with 6--32 spikes per burst; the bursts recurred at intervals of 120--600 msec. The nerve fibers exhibiting post-ischemic bursts could not be activated by muscle stretch, muscle tension, palpation, or tactile skin stimulation prior to or during the ischemia. No post-ischemic burst discharges could be detected in analogous experiments with the sural nerve. Intermediate size fibers from normal cutaneous and muscle mechanoreceptors were eliminated as possible origins of the post-ischemia activity. Possible sources include dorsal root ganglion cells or fibers whose sensory endings lie in deep structures such as the walls of the larger blood vessels.