PROJECTIONS FROM THE PELVIC NERVE TO THE PERIPHERY OF THE CATS THALAMIC VENTRAL POSTEROLATERAL NUCLEUS AND ADJACENT REGIONS OF THE POSTERIOR COMPLEX

1. Mapping experiments were performed in the region of the ventral pos terolateral nucleus of the lateral thalamus in pentobarbitone-anesthet ized cats with the aim to locate foci with input from the electrically stimulated pelvic nerve. The locations of the recording sites were ve rified in Nissl-stained histological sections with reference to electr olytic lesions. 2. Of the 68 visceroceptive thalamic neurons identifie d, 63% were located in the periphery of the ventral posterolateral nuc leus (VPL(p)) and 34% in the dorsal, lateral, and medial aspects of th e posterior complex (POd, POl, and POm, respectively) directly adjacen t to VPL(p). The region surrounding the middle and caudal part of the ventral posterolateral nucleus (VPL) received a much denser input from the pelvic nerve than that around the rostral pole of VPL. 3. The res ponse latencies of the thalamic neurons to pelvic nerve stimulation ra nged from 10 to 65 ms(median: 16 ms; interquartile distance: 12-20 ms) indicating a transmission of information from the pelvic space via sm all and large diameter myelinated fibers. 4. Seventy-nine percent of t he visceroceptive neurons tested (n = 58), in addition, had low thresh old somatic receptive fields that were located in 67% of the cases in regions of the lower back, the thigh, the tail and/or the heel and in 26% of the cases on the hindfoot. None of the 40 visceroceptive neuron s tested with noxious mechanical stimulation of the skin responded to this kind of stimulus. 5. It is concluded that the lateral thalamic re gion around, but not within, VPL proper contains neurons that play a r ole in the processing of visceral information from pelvic organs in th e cat.