Segmental and laminar organization of the spinothalamic neurons in cat: Evidence for at least five separate clusters

Abstract

The spinothalamic tract (STT), well known for its role in the relay of information about noxe, temperature, and crude touch, is usually associated with projections from lamina I, but spinothalamic neurons in other laminae have also been reported. In cat, no complete overview exists of the precise location and number of spinal cells that project to the thalamus. In the present study the laminar distribution of retrogradely labeled cells in all spinal segments (C1-Coc2) was investigated after large WGA-HRP injections in the thalamus. The results show that this distribution of STT cells differed greatly between the different spinal segments. Quantitative analysis showed that there exist at least five separate clusters of spinothalamic neurons. Lamina I neurons in cluster A and lamina V neurons in cluster B are mainly found contralaterally throughout the length of the spinal cord. Cluster C neurons are located bilaterally in the ventrolateral part of laminae VI-VII and lamina VIII of the C1-C3 spinal cord. Cluster D neurons were found contralaterally in lamina VI in the C1-C2 segments, and cluster E neurons were located mainly contralaterally in the medial part of laminae VI-VII and lamina VIII of the lumbosacral cord. Most spinothalamic neurons are not located in the enlargements and most spinothalamic neurons are not located in lamina I, as suggested by several other authors. The location of the spinothalamic neurons shows remarkable similarities, but also differences, with the location of spino-periaqueductal gray neurons.

Retrograde analyses of spinothalamic projections in the macaque monkey: Input to posterolateral thalamus

“…Two studies differentiated STT cells that project to medial versus lateral thalamus (Giesler et al, 1979;Craig et al, 1989), albeit with large injections; one study examined input to Pf in the cat (Comans and Snow, 1981), and two others selectively identified cells that project to the nucleus submedius (Craig and Burton, 1981;Dado and Giesler, 1990). A recent retrograde labeling study in cat using massive injections discriminated five different groups of STT cells based on their location and longitudinal distribution in the spinal cord (Klop et al, 2005a). All of these studies add evidence directly supporting the hypothesis that the mammalian STT consists of several differentiable components.…”

“…Prior studies in rat, cat, monkey, and human using bulk tracing methods indicated that the STT distributes projections to several thalamic nuclei that each have different anatomical and functional associations and, conversely, that the STT originates in several different cell groups that each have different anatomical and functional characteristics (Le Gros Clark, 1936;Mehler et al, 1960;Boivie, 1979;Willis et al, 1979;Burton and Craig, 1983;Mantyh, 1983;Albe-Fessard et al, 1985;Apkarian and Hodge, 1989;Craig et al, 1989). These observations clearly suggest the hypothesis that the STT comprises several distinct components that each convey ascending activity selectively associated with different spinal functions (Craig et al, 1989;Stepniewska et al, 2003;Truitt et al, 2003;Klop et al, 2005a). However, direct evidence addressing the hypothesis that the STT consists of distinct components has been lacking, and thus some investigators assert that all STT neurons have a direct role in pain processing (e.g., Willis and Westlund 1997;but cf.…”

“…In order to address the overall hypothesis that the primate STT contains several functionally and anatomically distinct components, subsequent contributions from the present series of retrograde labeling experiments will provide analyses of the sources of STT input to other major STT termination sites. In addition to the STT input to VPL, examples of major STT projections that need to be distinguished include: the STT inputs to VPI, VL, and MDvc (Ganchrow, 1978;Boivie, 1979;Burton and Craig, 1983;Stepniewska et al, 2001;Craig, 2004); the physiologically distinct population of lamina VII STT cells that project to CL (Giesler et al, 1981); the anatomically and physiologically unique group of STT cells that are bilaterally distributed in the ventral horn and intermediate zone of C2 (Carstens and Trevino, 1978b;Apkarian and Hodge, 1989;Klop et al, 2005a); and the population of lateral sacral neurons that were labeled by a large injection in this series, which are potentially related to specialized pelvic parasympathetic functions (see Truitt et al, 2003;cf. Klop et al, 2005b).…”

Retrograde analyses of spinothalamic projections in the macaque monkey: Input to ventral posterior nuclei

“…Thus, a likely hypothesis is that the STT comprises several distinct components that each convey ascending activity selectively involved in different spinal functions (Craig et al, 1989;Stepniewska et al, 2003;Truitt et al, 2003;Klop et al, 2005). However, direct evidence for this hypothesis has been lacking, allowing some investigators to assert that all STT neurons have a direct role in pain (e.g., Willis and Westlund, 1997) and other investigators to assert that STT neurons do not have a direct role in motor function (e.g., Greenan and Strick, 1986).…”

Retrograde analyses of spinothalamic projections in the macaque monkey: Input to the ventral lateral nucleus

“…Thus, some investigators consider it likely that the STT comprises several distinct components that each convey ascending activity from particular cell groups to particular nuclei and each of which is selectively involved in particular spinal functions (Craig et al, 1989;Stepniewska et al, 2003;Truitt et al, 2003;Klop et al, 2005). However, direct evidence for this hypothesis has been lacking, allowing other investigators to assert that all STT neurons have a direct role in pain (e.g., Willis and Westlund 1997) or to assert that STT neurons do not have a direct role in motor function (e.g., Greenan and Strick 1986).…”