The role of norepinephrine in adult rat somatosensory (SmI) cortical metabolism and plasticity.

Stimulation of rat facial vibrissae increases glucose utilization in the corresponding barrels (lamina IV) and associated columns in laminae I-VIa of the contralateral first somatosensory (SmI) cortex as assessed autoradiographically by the uptake of [14C]2-deoxy-glucose (2-DG). Chronic deafferentation (2 months) by bilateral vibrissectomy with sparing of the C3 vibrissa (SC3) in adult Sprague-Dawley rats produced no change in the rate of LCGU but led to an increased areal extent of the metabolic representation of the SC3 barrel (39%, P less than 0.001) and column (31%, P less than 0.003) as compared to rats with fully intact vibrissae. In other rats with intact facial vibrissae, 6-hydroxydopamine lesions of the locus coeruleus (LC) depleted ipsilateral cortical norepinephrine (NE) by more than 90% and, 2 months later, led to an 11% and 21% increase in C3 barrel and column metabolic representations, respectively, as compared to the contralateral SmI cortex with intact NE levels (P less than 0.05). When bilateral vibrissectomy was combined with a unilateral LC lesion, the SC3 barrel and column metabolic representation on the LC-intact side enlarged as expected but no enlargement occurred on the NE-depleted side (20% difference; P less than 0.05). Therefore, the effect of NE on the SmI cortex depends on the status of its afferent input. NE inhibits the spread of metabolic activity beyond the activated barrel and column in the intact cortex, but independently modulates plastic enlargement in the partially deafferented SmI cortex.