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

Abstract

The distribution of retrogradely labeled spinothalamic tract (STT) neurons was analyzed in macaque monkeys following variously sized, physiologically guided pressure or iontophoretic injections of cholera toxin subunit B (CTb) in order to determine whether different STT termination sites receive input selectively from different sets of STT cells. This report focuses on posterolateral thalamus, where prior anterograde tracing observations identified the posterior part of the ventromedial nucleus (VMpo) as the major projection target of lamina I STT neurons. Large injections in posterolateral thalamus labeled predominantly STT cells in lamina I throughout the spinal cord. In cases with medium-sized or small injections centered in VMpo, almost all labeled STT cells ( approximately 90%) were lamina I neurons. Small injections revealed a posteroanterior (foot to hand) somatotopographic organization consistent with that observed in prior anterograde tracing work; injections in posterior VMpo labeled primarily lumbosacral lamina I cells, whereas injections placed more anteriorly in VMpo labeled primarily cervical lamina I cells. These findings support the concept that VMpo is a primate lamina I spinothalamocortical relay nucleus important for pain, temperature, itch, muscle ache, sensual touch, and other interoceptive feelings from the body, and they provide strong evidence for the general hypothesis that the STT consists of several functionally and anatomically differentiable components.

Termination Zones of Functionally Characterized Spinothalamic Tract Neurons Within the Primate Posterior Thalamus

“…Each method has confirmed that neurons of the dorsal horn send projections to the posterior thalamus. Craig and colleagues have recently advanced a hypothesis that marginal zone neurons preferentially target VMpo and that VPL receives input from neurons located within the deeper laminae (Craig 2006;Craig and Zhang 2006). The present study confirms that the posterior thalamus receives a relatively high proportion of marginal zone projections.…”

“…The input to the posterior thalamus from the STT has been studied using degeneration (Boivie 1979;Mehler 1969;Mehler et al 1960), retrograde (Craig 2006;Craig and Zhang 2006;Willis et al 2001), and anterograde tracing methods (Apkarian and Hodge 1989;Beggs et al 2003;Craig 2004;Gauriau and Bernard 2004a;Ralston and Ralston 1992;Stepneiwska et al 2003). Each method has confirmed that neurons of the dorsal horn send projections to the posterior thalamus.…”

“…Recent retrograde tract tracing studies have shown that marginal zone STT neurons can be preferentially labeled from the posterior thalamus, whereas neurons located in the deep dorsal horn were preferentially labeled from injections in VP (Craig 2006;Craig and Zhang 2006). Because many marginal zone neurons respond selectively to and encode the intensity of noxious mechanical and thermal stimuli (Christensen and Perl 1970;Craig et al 2001;Ferrington et al 1987;Hylden et al 1986;Zhang et al 2006), the posterior thalamus may play a qualitatively different role in pain sensation from VP.…”

Somatotopic Organization of Gentle Touch Processing in the Posterior Insular Cortex

“…Extensive studies suggest that thinfiber networks mediating pain and temperature connect from the superficial laminae of the dorsal horn via somatotopically arranged projections through the spinothalamic tract (STT) to a specific ventromedial posterior thalamic nuclei (VMPo), terminating in the contra-lateral posterior insular cortex (Craig et al, 1994(Craig et al, , 1999Blomqvist and Craig, 2000;Craig, 2003;Craig and Zhang, 2006) (but see Willis et al, 2002). Consistent with these projections, functional imaging of innocuous cooling as well as painful stimuli have revealed a cortically maintained somatotopic organization of the posterior insula with upper body afferents activating regions anterior to those of the lower body (Brooks et al, 2005;Hua le et al, 2005;Henderson et al, 2007).…”

Peripheral nerve injury induces adult brain neurogenesis and remodelling

“…Electrophysiological evidence suggests that C‐fibre stimulation activates the mossy fibre input from the pontine nuclei 33, and that both A‐fibre and C‐fibre stimulation activates the climbing fibres 34, which transmit information from the inferior olive to the cerebellum. In addition, the zona incerta and the periaqueductal grey, two brain regions that deliver major inputs to the inferior olives, are known to relay both ascending nociceptive information 35, 36, 37, as well as descending cortical signals.…”