Segmental regulation pattern of body surface temperature in the rat hindlimb

Abstract

Body surface zones or ‘thermatomes’, whose temperature is regulated by a single spinal segment, were investigated by thermography in the rat hindlimb. First, the spatial relation between the dermatome delineated by dye extravasation and the corresponding thermatome was investigated in rats pretreated with intravenous application of Evans blue. Electrical stimulation of the spinal nerves and sympathetic trunk segments at L3 and L5 induced a distal dominant temperature decrease. In contrast, Evans blue extravasation appeared in the medial (in L3) and lateral (in L5) paw only by electrical stimulation of the spinal nerves. Second, thermatomes L1–L5 were determined in other rats. Electrical stimulation of the sympathetic trunk segments L1–L6 produced a temperature decrease in the abdomen, hindlimb, and tail. However, the hindlimb temperature was regulated mainly by L2–L5 levels, particularly by L4 and L5. The abdomen was regulated uniformly by L1–L6, and the tail by L6. It was demonstrated that thermatomes are manifested differently from the corresponding dermatomes in the rat hindlimb.

Introduction

Thermography is used clinically to evaluate lumbar radiculopathy [8], [13], [23], [24] and for neurogenic painful disease such as peripheral neuropathy [2], [9], and complex regional pain syndrome [3], [7], [15]. Thermography is also used to examine experimental rat models of neuropathic pain [1], [18] and axon reflex [14], [20].

It has been hypothesized that body surface temperature is regulated in segmental units identical to sensory dermatomes [12], [17]. However, it has been reported that the areas of temperature change are not directly correlated with the dermatome of the impaired spinal nerve root [13], [23]. Based on these findings indicating that areas with a temperature change do not precisely follow dermatomes, some investigators are skeptical about the diagnostic value of thermography for lumbar radiculopathy [4], [12], [17]. However, body surface areas (currently designated as ‘thermatomes’) in which temperature is regulated by a spinal nerve or a single segment of the sympathetic trunk, have not been carefully investigated and clarified to date. The diagnostic value of thermography for painful neuropathies would be enhanced if thermatomes are confirmed.

The purpose of the present study was to investigate the spatial correspondence between thermatomes and dermatomes and to clarify the distribution of lumbar thermatomes in rats.