LOCAL CEREBRAL GLUCOSE-UTILIZATION IN STIMULATED RATS SEDATED WITH THIOPENTAL

Background: Recent studies have suggested that supraspinal structures are involved in barbiturate-induced enhancement of nociceptive process ing, The goal of the study was to determine whether cortical and subco rtical regions involved in nociception were relatively activated or de pressed by noxious stimulation during infusion of small doses of thiop ental. Methods: Local cerebral glucose utilization (LCGU) was measured with the C-14-2-deoxyglucose radioautographic technique in 14 rats, D uring the LCGU experiment, pressure was applied to the tail every 2 mi n, and the somatic motor response threshold was recorded, Seven animal s received thiopental infusions to produce a steady-state plasma conce ntration (target concentrations of 10 mu g/ml), and seven untreated an imals served as controls. Results: A steady-state plasma thiopental co ncentration (11.1 +/- 1.8 to 13.0 +/- 2.1 mu g/ml) was accompanied by a decrease in the somatic motor response threshold from 277 +/- 32 g ( before thiopental) to 215 +/- 41 g (P < 0.001), The somatic motor resp onse threshold remained unchanged in the control group, Average LCGU w as 29% less in the thiopental-treated animals than in the untreated co ntrols (Pi 0.001), In cortical regions associated with nociception, LC GU was relatively increased (+3% +/- 14%) during the thiopental infusi on in comparison to the visual and auditory cortices (-18% +/- 13%; P < 0.001), Individual structures that showed relative changes during th iopental infusion Included the nucleus accumbens (+17%, P < 0.05) and the habenula (-17%, P < 0.05), Heterogenous relative changes (P < 0.05 ) In LCGU were observed in the auditory system: auditory cortex (-22%) , medial geniculate (-16%), lateral lemniscus (+26%), superior olive ( +38%). Conclusions: Noxious stimulation during low-dose thiopental inf usions relatively increased LCGU in cortical regions postulated to be responsible for processing of noxious stimuli. Nuclei in the descendin g pain modulating system were not relatively depressed.