Somatic afferent fibers which continuously discharge after being isolated from their receptors

A previous study in our laboratory has shown that some afferent axons produce prolonged discharges after the axons have been completely isolated. We have attempted to identify the type of afferent fibers displaying such activity. Single unit activity was recorded from a filament dissected from the distal stump of the cut sural or plantar nerve of an anesthetized rat. After thorough identification of the receptor type, the nerve was cut at a site between the recording electrode and the receptive field, completely isolating the fiber being recorded. Unit activity was recorded up to 1 h after sectioning the nerve. Upon sectioning the nerve, most units showed brief injury discharges lasting only a few seconds. However, 21 of 70 units exhibited prolonged discharges lasting at least 30 min after having been isolated from their receptors. These 21 units included 8 slowly adapting type II cutaneous mechanoreceptors, 3 Pacinian corpuscles and 10 muscle spindle afferent units. These results suggest that prolonged injury discharges can be produced in the axons of the slowly adapting type II cutaneous mechanoreceptors, Pacinian corpuscles, and muscle spindle afferents. This phenomenon may have important clinical and experimental consequences.