Relative cerebral glucose metabolism evoked by dental-pulp stimulation in the rat

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✓ Electrical stimulation of dental pulp is widely acknowledged to produce a sensation that is predominantly or exclusively noxious in character. The authors report the pattern of local cerebral glucose utilization evoked by dental-pulp stimulation in the barbiturate-anesthetized rat, using the [14C]2-deoxyglucose method of Sokoloff. Autoradiographs were prepared from cryostat-cut brain sections of animals given an intravenous pulse of [14C]2-deoxyglucose and sacrificed after 45 minutes of continuous bipolar stimulation of the incisor tooth pulp. Areas of high optical density on the autoradiographs identified brain regions where glucose consumption, and hence functional activity, was maximal. Stimulus-related increases in glucose utilization were seen ipsilaterally in an uninterrupted column from the lower levels of trigeminal nucleus caudalis to the rostral extent of the main sensory nucleus. Mandibular incisor pulp stimulation yielded increased deoxyglucose uptake in relatively restricted dorsal portions of the nuclei, while maxillary pulp stimulation produced a more extensive area of uptake ventrally. Elevated deoxyglucose uptake was also seen in the contralateral ventrobasal thalamus and sensory cortex with maxillary, but not mandibular, pulp stimulation. No changes in metabolic activity were detected in extralemniscal or limbic structures. These initial results suggest that the [14C]2-deoxyglucose method may be a useful means of mapping central structures involved in nociception.

Article Information

Address reprint requests to: Andrew G. Shetter, M.D., Neurosurgical Research Laboratory, Barrow Neurological Institute, 350 West Thomas Road, Phoenix, Arizona 85013.

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Figures

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    Autoradiographs demonstrating the stimulus-related increases in optical density seen with mandibular (left) and maxillary (right) dental pulp stimulation at comparable ascending brain-stem levels. Note that optical density is increased over the entire extent of the ipsilateral trigeminal sensory complex (side opposite the labels), and that the mandibular pulp representation is more restricted and more dorsal than that of the maxillary pulp. The high optical densities seen bilaterally in several gray-matter structures (such as the superior and inferior olivary nuclei) represent normal background metabolic activity for the rat,20,26 and are not stimulus-related. The oval defects present on some sections are bubble artifacts. Abbreviations: DC = dorsal columns; D Pyr = pyramidal decussation; IO = inferior olivary nuclear complex; MSN = trigeminal main sensory nucleus; N Caud V = nucleus caudalis of the spinal trigeminal nucleus; N Ip V = nucleus interpolaris; SO = superior olivary nucleus complex; TS V = tract of the spinal trigeminal nucleus; VII = facial nerve.

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    Autoradiographs (left) and their corresponding cresyl violet stains (right) at the level of the obex for maxillary (upper) and mandibular (lower) pulp stimulation. Note that the ipsilateral increases in optical density are uniform across all layers of nucleus caudalis. There is no overlap in the location of the evoked metabolic response for mandibular and maxillary pulp stimulation.

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    Autoradiographs of sections rostral to the brain stem which demonstrate contralateral increases in 2-DG uptake to maxillary pulp stimulation. Left: Layer IV of the main sensory cortex (arrows) and possibly deeper cortical layers as well. The vertically oriented curvilinear stripe in the medial aspect is an artifact produced by tissue folding. Right: Section showing the ventrobasal thalamus (arrow).

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