Responses of spinal cord dorsal horn neurones to non-noxious and noxious cutaneous temperature changes in the spinal rat

Abstract

(1) Lumbar dorsal horn units characterized by their mechanical cutaneous sensitivities were tested for their responses to temperature changes of the skin in the decerebrate spinal rats. (a) Class 1 units (i.e. driven by non-noxious mechanical stimuli) were rarely thermally sensitive. (b) Nearly all class 2 units (i.e. driven by both non-noxious and noxious mechanical stimuli) and 4 of the 5 class 3 units (i.e. driven by noxious mechanical stimuli) were sensitive to temperature changes. (2) According to their thermal response threshold and their response range, these units were divided into 3 groups. (a) Warming units whose response threshold and maximum response were below 42.5 degrees C. Such units were rarely encountered. (b) Warming/noxious heat units whose response threshold was below 42.5 degrees C but with a maximum response above this temperature. They represented approximatively one-third of the radiant heat-sensitive units. (c) Noxious heat units whose response threshold was above 42.5 degrees C and maximum discharge several degrees above it. Approximately 50% of units activated by radiant heat belonged to this group. (3) Responses to radiant heat stimulation were frequently affected by a first noxious heat application. It consisted: --in a threshold decrease and/or an increase of their cellular discharge for a same temperature range. Only observed for warming/noxious heat units and noxious heat units, this sensitization phenomenon predminantly affected noxious heat units. --in a decrease of cellular discharge for a same temperature range. This desensitization phenomenon was observed for the 3 groups of units driven by radiant heat but mainly for warming units. (4) Supramaximal transcutaneous electrical stimulation revealed that nearly all the thermally sensitive units received A delta and/or C inputs. These units were largely distributed throughout the dorsal horn (laminae I, IV and V). Ten of the 12 lamina I units responded to noxious thermal stimuli. (5) These data indicate that an increase in skin temperature is coded at the level of the rat spinal cord dorsal horn by both an increase in discharge of low threshold temperature sensitive units and a progressive recruitment of high threshold units.

An ionophoretic study of the responses of rat caudal trigeminal nucleus neurones to non‐noxious mechanical sensory stimuli.

“…Similarities with the dorsal horn of the rat spinal cord are also apparent (Menetrey, Giesler & Besson, 1977), with the magnocellular part of n. caudalis corresponding to laminae III and IV of the dorsal 74 SENSORY RESPONSES IN RAT CAUDAL TRIGEMINAL horn (Rexed, 1954), and the adjacent reticular areas to laminae V and VI. This conclusion would be in agreement with the morphological observations of Gobel et al (1977).…”

Windup in Dorsal Horn Neurons Is Modulated by Endogenous Spinal μ-Opioid Mechanisms

“…Audible tones generated by the DAPSYS software provided cues for accurate manual delivery of the mechanical stimuli. Neurons were classified functionally according to their responses evoked by graded intensities of mechanical stimuli applied to the receptive field (Menetrey et al, 1977;Li et al, 1999;Weng et al, 2001). Specifically, neurons that responded in a graded manner with increasing firing rates to the stimulus range from non-noxious to noxious intensity were classified as WDR cells.…”

Diminished Inflammation and Nociceptive Pain with Preservation of Neuropathic Pain in Mice with a Targeted Mutation of the Type I Regulatory Subunit of cAMP-Dependent Protein Kinase

“…The decreased Fos immunoreactivity was observed in laminae I-II and V-VI of the dorsal horn (Figs. 2, 3), which are areas that contain the majority of nociresponsive neurons in the dorsal horn (Menétrey et al, 1977).…”