Recovery from partial deafferentation increases 2-deoxyglucose uptake in distant spinal segments

2-Deoxy[14C]glucose autoradiography was used to study the responsiveness of the partially deafferented rat spinal cord to electrical stimulation of low-threshold afferent fibers. Unilateral extradural dorsal rhizotomies were carried out at L3 to S2, sparing L5. Postoperative sensory deficits were appropriate to the extent of the lesion. Acute, 7 day, and 14 to 20 day postrhizotomy animals and unoperated controls were anesthetized prior to isotope injection and electrical stimulation of Ia fibers in the L5 root. Quantitative densitometry was carried out on enlarged autoradiographs, subdividing the spinal gray matter into laminar divisions drawn from the corresponding stained sections. Optical densities from stimulated and unstimulated sides were compared using paired t tests for each experimental group at each lumbosacral segment (L1 to S2) and at T13 for the day 14 to 20 animals. This procedure provided an objective basis for statistical comparisons between homologous areas even where the differences in density were small. Unoperated animals showed activation in 11 of 23 dorsal horn zones extending to L2 and never involving the base of the dorsal horn (lamina V). Acute and day 7 groups did not appreciably differ from the control group except for activation of lamina V within the L4 segment. In the most delayed group, 18 dorsal horn regions were activated, extending to L1 with an additional zone in T13 . Lamina V contained significant labeling in three segments. In no group was there increased labeling of the ventral horn. The results are interpreted as showing that stimulus-related, neural activity increases after a 2-week delay in regions of spinal cord distant from the normal zone of significant metabolic change. This increase in neural activity during recovery is discussed in relation to time-dependent electrophysiologic, structural, and metabolic responses to deafferentation. The longitudinal spread of dorsal horn activation by preserved afferent fibers in the spared root may facilitate more effective central transmission of sensory information.