Processing of splanchnic and somatic input in thoracic spinal cord of the rat

Abstract

To better understand the spinal transmission of visceral afferent information, we conducted neurophysiological studies of single spinal neurons that receive input from the greater splanchnic nerve (GSN). Extracellular single-neuron recordings were made in the thoracic spinal cord of chloralose-anesthetized, paralyzed, and artificially ventilated rats, some of which had undergone acute spinal transection at C1. Neurons were divided into four classes according to their responses to GSN stimulation: one-burst excitatory, two-burst excitatory, biphasic, and inhibited. We then studied the characteristics of the convergent somatic input to each class of neurons using either natural somatic stimuli or electrical stimulation of the iliohypogastric nerve (IHN). Most splanchnic input was mediated by unmyelinated fibers, whereas somatic input was mediated by both unmyelinated and small myelinated fibers. Most of the neurons exhibited somatic receptive fields, and the majority responded to both innocuous and noxious somatic stimuli. However, a small number could be excited only by GSN stimulation. Although a careful analysis of response characteristics indicated that there was a tendency for neurons to exhibit similar responses to electrical stimulation of the GSN and the IHN, we observed many combinations of somatic and visceral responses. We suggest that visceral afferent activity, in addition to being processed via convergent somatovisceral pathways, may be processed by neurons that convey only visceral information or by neurons in which visceral and somatic information is differentially coded.

Immobilization stress sensitizes rat dorsal horn neurons having input from the low back

“…Probably, the neurons of our study had even more connections with other sources, e.g. joints (Schaible et al., ) and viscera (Akeyson and Schramm, ), but this possibility was not tested.…”

Bilaterally evoked monosynaptic EPSPs, NMDA receptors and potentiation in rat sympathetic preganglionic neurones in vitro

“…These sources include neurones originating in the lateral funiculi of the white matter itself, that also bilaterally project towards SPNs (Jansen & Loewy, 1997), and propriospinal and ascending inputs, likely to be recruited when stimulating the iLF (e.g. see Akeyson & Schramm, 1994). Polysynaptic inputs were apparent when stimulating the iLF, cIML and cLF, suggesting we were activating segmental circuits involving interneurones, presumably located in laminae I, IV, V, VII or IX (Strack et al 1989;Craig, 1993;Cabot et al 1994), in addition to pathways directly innervating SPNs.…”

Monosynaptic convergence of somatic and visceral C-fiber afferents on projection and local circuit neurons in lamina I

“…41 , 47 In agreement with this, unit responses of dorsal horn neurons to stimulation of both visceral and somatic afferents have been reported in a number of in vivo studies. 1 , 2 , 4 , 6 , 9 , 16 , 32 However, little is known about the detailed organization of the neuronal network underlying somatovisceral integration in the superficial dorsal horn or whether both types of afferents directly contact any specific class of neurons.…”