Crossed and uncrossed projections to cat sacrocaudal spinal cord: I. Axons from cutaneous receptors

Abstract

Intra-axonal recording and horseradish peroxidase staining techniques were used to map terminal fields of primary afferent fibers from cutaneous receptors within the cat sacrocaudal spinal cord. It was hypothesized that projection patterns of cutaneous afferent fibers mirror the known somatotopic organization of sacrocaudal dorsal horn cells. Forty-three primary afferent fibers, innervating either slowly adapting type I receptors, hair follicles, or slowly adapting type II receptors, all on the tail, were recovered. All collaterals (N = 372) branched from parent axons in the dorsal columns. Most collaterals coursed rostromedially to the ipsilateral gray matter, penetrated the medial dorsal horn, and arborized within laminae III, IV, and to a lesser extent, V. Ipsilateral projections to dorsal horn were as follows: axons with dorsal or dorsolateral receptive fields (RFs; n = 20) to the lateral portion, axons with lateral RFs (n = 4) to the central portion, and axons with ventral or ventro-lateral RFs (n = 19) to the medial portion. Most axons (16 of 20) with dorsal or dorsolateral RFs also had contralateral projections to lateral dorsal horn and most axons (15 of 19) with ventral or ventrolateral RFs also had contralateral projections to medial dorsal horn. No axons with lateral RFs had crossed projections. These data represent the first complete mapping of the somatotopic organization of primary afferent fiber projection patterns to a spinal cord level. The findings demonstrate that ipsilateral projection patterns of sacrocaudal primary afferent fibers are in register with the somatotopic organization of the dorsal horn. Our earlier suggestion that crossed projections of primary afferent fibers give rise to crossed components of dorsal horn RFs spanning the midline is supported by these results.

Commissural propriospinal connections between the lateral aspects of laminae III–IV in the lumbar spinal cord of rats

“…Second, although crossed primary afferents that terminate in laminae III-V of the contralateral dorsal horn have been reported at the level of cervical, thoracic, and sacral spinal segments (Light and Perl, 1979;Ritz et al, 1989Ritz et al, , 1991, almost none of them was found at the level of lumbar segments where our studies were carried out. Third, when we previously studied the course and termination pattern of rubrospinal, raphe-spinal, and cerulospinal fibers that descend in the dorsal aspect of the lateral funiculus and enter the gray matter by passing the areas of the dorsal horn where our tracer injections were located, we as well as other independent laboratories demonstrated that the number of descending axons that traverse the dorsal horn, cross the midline in the posterior commissure, and terminate in the lateral aspect of the dorsal horn is negligible (Brown, 1974;Holstege, 1987;Shieh et al, 1983;Antal et al, 1992Antal et al, , 1996.…”

Central anatomy of individual rapidly adapting low‐threshold mechanoreceptors innervating the “hairy” skin of newborn mice: Early maturation of hair follicle afferents

“…6C). A bilateral representation of the axial midline has been detailed previously (Smith, 1986;Ritz et al, 1989), but it is noteworthy that a midline receptive field was neither sufficient (Fig. 9A) nor a prerequisite (Fig.…”

“…Thresholds and CVs were 5.6 mN, 0.7 m/sec (A) and 0.07 mN, 0.9 m/sec (B). Scale bar ϭ 100 m. the cord across diverse species (for review see Woodbury and Scott, 1991; for single fiber somatotopy, see Ritz et al, 1989;Shortland et al, 1989;Brown et al, 1991;Shortland and Woolf, 1993a).…”

Crossed and uncrossed projections to the cat sacrocaudal spinal cord: III. Axons expressing calcitonin gene‐related peptide immunoreactivity

“…We have previously demonstrated a bilateral termination of large-diameter primary afferent fibers projecting to the cat sacrocaudal spinal cord, originating from cutaneous receptors or from muscle spindle primary endings (Ritz et al, 1989. Small-diameter primary afferent fibers also project to the ipsilateral and contralateral spinal gray (Light and Perl, 1979b;Sugiura et al, 1989).…”

“…A goal of spinal cord neurobiologists is to understand this distribution of information within the spinal cord gray matter. Our laboratory has deployed a multi-faceted approach to understanding the structural-functional organization of the cat sacrocaudal spinal cord (S3-Ca7), that portion of the neuraxis that innervates the tail (Ritz and Greenspan, 1985;Ritz et al, , 1989Ritz et al, , 1991Ritz et al, , 1992aMasson et al, 1991;Gladfelter et al, 1993). The cat sacrocaudal spinal cord is attractive for the study of spinal cord organization and plasticity following injury (Ritz et al, 1992b;Walker et al, 1998;Friedman et al, 2000; see also Bennett et al, 1999) because: 1) complete caudal transection produces a clear-cut, reproducible behavioral effect; 2) underlying anatomical and physiological alterations are accessible to analyses; and 3) lesions to this spinal cord region, caudal to S3, produce minimal complications to locomotor and eliminatory systems.…”