Receptive fields of unmyelinated ventral root afferent fibres in the cat.

Abstract

The receptive fields were determined for 118 afferent fibers in the S2, S3 and Ca (caudal) 1 ventral roots of the cat. Of these fibers, 93 were unmyelinated, another 11 were probably unmyelinated, and 14 were myelinated, according to estimates of their conduction velocities. Confirmation that the recordings were from ventral root filaments came from EM of 10 of the filaments from which recordings of the activity of unmyelinated afferents were made. Receptive fields were demonstrated for 12 unmyelinated afferent fibers in the distal stumps of the S2 and S3 ventral roots which were sectioned 3 wk previously, indicating that the cell bodies giving rise to these fibers were not in the spinal cord. The action potentials of some of the unmyelinated ventral root afferent fibers were complex, suggesting branching of the afferents within the ventral root. Of the unmyelinated ventral root afferents 1/3 had receptive fields in somatic structures: the skin and deep tissues. Of the unmyelinated ventral root afferents, 2/3 had receptive fields in the viscera of the pelvis: the bladder, urethra, vagina, and lower bowel. Many of the unmyelinated afferents in the ventral roots, especially those with cutaneous receptive fields, had high thresholds and may participate in nociception. The cat ventral root apparently contains a major sensory component, and the Law of Bell and Magendie may not be an accurate description of the organization of the ventral root in this animal.