PLASTICITY OF CEREBRAL METABOLIC WHISKER MAPS IN ADULT MICE AFTER WHISKER FOLLICLE REMOVAL -II - MODIFICATIONS IN THE SUBCORTICAL SOMATOSENSORY SYSTEM

The follicles of whiskers C1-3 were removed from the left side of the snout of adult mice. Adjacent whiskers B1-3 and D1-3 were stimulated w hile local rates of glucose utilization were measured with the [C-14]2 -deoxyglucose method two, four, eight, 64, 160 and similar to 250 days after follicle removal. Local metabolic activity in the trigeminal se nsory brainstem and somatosensory thalamus was compared with that of u noperated mice with the same stimulation and of mice with the same les ion that had all whiskers clipped. Actual rates of glucose utilization were measured in brainstem subnuclei caudalis and interpolaris wherea s metabolic activation was only assessable by colour-coded imaging in brainstem nucleus principalis and in the thalamic ventrobasal complex. Whisker stimulation activated the somatotopically appropriate loci in brainstem and thalamus. In addition, the territory deprived by follic le removal was metabolically activated in subnuclei caudalis and inter polaris at all time intervals examined. The activation was statistical ly significant in subnucleus interpolaris at two days, indicating that the metabolic representations of whiskers neighbouring the lesion rap idly expanded into the deprived territory. Nucleus principalis showed a broad metabolic activation at two and four days that was absent at t he longer time intervals examined. Instead, at similar to 250 days the metabolic representations of the whiskers adjacent to the lesion were enlarged into the deprived territory as in the subnuclei. Since metab olic whisker representation in the ventrobasal complex appeared to hav e changed in the same fashion, follicle removal apparently resulted in congruent modifications of the whisker map in the three nuclei of ter mination as well as in the thalamic relay at the longest time interval examined. Since metabolic responsiveness of the deprived barrels in b arrel cortex of the same animals increased statistically significantly only several months after follicle removal, the novel neural response s in the brainstem were not effectively transmitted to barrel cortex i mmediately and the slowly evolving cortical modifications are more lik ely to be associated with regrowth of the connectivity of primary neur ons.(28) By contrast, unmasking of hitherto suppressed inputs may unde rlie the early expansion of metabolic whisker representation in the br ainstem. (C) 1997 IBRO. Published by Elsevier Science Ltd.