Functional specialization of central projections from identified primary afferent fibers

1. Somata of primary afferent fibers were impaled in the L7 or S1 dorsal root ganglion in cats anesthetized with alpha-chloralose. Individual cells (n = 182) were characterized according to receptive field (RF) and by the peripheral mechanoreceptor they innervated. They were then stimulated intracellularly while recording the evoked cord dorsum potentials (CDPs) simultaneously at four sites. CDPs were recorded in response to single fiber stimulation while varying both the frequency and the numbers of action potentials (APs) evoked per trial. Stimulus parameters included: 1) single APs evoked at both high (18 Hz) and low (0.67 Hz) frequencies, 2) pairs of APs (50-ms ISI) delivered at 0.67 Hz, and 3) trains of four APs (20-ms ISI) also delivered at 0.67 Hz. The properties of the CDPs and their relationship to receptor type innervated by the fiber were determined. 2. CDPs evoked by 18-Hz stimulation consisted of an axon fiber spike followed at a short latency [600 +/- 9.9 (SEM) microseconds] by the onset of ...