Projections of hindlimb dorsal roots to lumbosacral spinal cord of cat

Abstract

Single dorsal roots of spinal nerves that contribute to the cat lumbosacral plexus (L3-S2) were cut to evoke degeneration of centrally projecting axons. Serial sections throughout lumbosacral cord levels were impregnated by the Fink-Heimer method (20) to permit charting of the distribution patterns of segmental dorsal root afferent fibers. Afferent fibers that enter a single dorsal root have an extensive distribution to multiple cord segments; their longitudinal extent varies with entry level and with laminar targets. Afferent projections to the ventral horn reach motor nuclei only in their entry segment and the adjacent segments just above and below their entry. Those afferent fibers projecting to intermediate gray (laminae VI and VII) have the most extensive spinal distribution of any types; they may, from a single dorsal root, reach as many as 13 or 14 cord segments. Dorsal horn projections of single roots are also longitudinally expansive. Small-diameter afferent fibers course rostrally and caudally in Lissauer's tract (LT) for up to 9-10 segments. They appear to terminate in at least laminae I and II in and near their entry segment; their endings are difficult to demonstrate at greater distances where they are probably less dense. Larger caliber axons entering the dorsal horn generate a somatotopically organized projection, especially to laminae III and IV. Collaterals of these fibers appear to course longitudinally within the gray matter and they distribute to as many as six to seven segments.

The Distribution of μ and δ Opioid Binding Sites Belonging to a Single Cervical Dorsal Root in the Superficial Dorsal Horn of the Rat Spinal Cord: A Quantitative Autoradiographic Study

“…However, recent anatomical studies using specific markers of populations of fine-diameter primary afferent fibres have reported that some long-projecting fine-diameter primary afferent fibres were observed in Lissauer's tract and superficial layers of the dorsal horn (Traub er al., 1989;Sugiura er al., 1989;Traub et al, 1990), confirming previous results of Culberson and Brown (1984) in Lissauer's tract. Thus, in the present study, it is probable that the residual percentage of opioid binding observed beyond two segments could be related to the long-projecting fine-diameter primary afferent fibres.…”

Physiological Properties of the Lamina I Spinoparabrachial Neurons in the Rat

“…The superficial laminae of the spinal cord receive heavy and direct input from the thin primary afferents A␦ and C fibers and contain primarily nociceptive neurons some of which being identified as projecting to the thalamus (Besson and Chaouch 1987;Brown and Culberson 1981;Cervero and Connell 1984;Culberson and Brown 1984;Fitzgerald 1984;Light and Perl 1979;Mizumura et al 1993;Sugiura et al 1986Sugiura et al , 1988Sugiura et al , 1989Sugiura et al , 1993Fitzgerald 1983, 1986). More recently, several studies also have demonstrated that a high number of nociceptive neurons in the superficial laminae project to the PB area (Hylden et al 1985(Hylden et al , 1986aLight et al 1987Light et al , 1993; see also McMahon and Wall 1983).…”

Excess target‐derived neurotrophin‐3 alters the segmental innervation of the skin

“…On the thorax, dermatomes are arranged as a series of simple, partially overlapping bands, but on limb‐bearing regions of the body they are more complex in shape (Sherrington, 1893; Kuhn, 1953; Hekmatpanah, 1961; Fletcher & Kitchell, 1966; Pubols & Pubols, 1969; Kow & Pfaff, 1975; Brown & Koerber, 1978; Bailey et al ., 1984). Within the spinal dorsal horn, the organization of primary afferent terminals mirrors their organization in the periphery; afferents from neighbouring dermatomes are largely overlapping, while those from nonadjacent dermatomes are not (Culberson & Brown, 1984; Rivero‐Melián & Grant, 1991; Mirnics & Koerber, 1995a, b). Dermatomal organization and the degree of overlap between adjacent segments is consistent across many different organisms (reviewed in Scott, 1982), suggesting a common mechanism for their formation.…”