The whiskers on the face of mice project through several synapses to anatomically distinct cortical structures called barrels. In this study, the activities of six energy-related enzymes in isolated barrels in layer IV in the somatosensory cortex of adult mice were determined using quantitative histochemical techniques. Data from control barrels and from barrels for which the corresponding whiskers had been damaged were obtained. The analyses were made on freeze-dried cryostat sections. Individual barrels were identified in unstained sections and subsequently, portions of them were dissected out and weighed on a quartz fiber balance. Micromethods for histochemistry, including the use of oil wells and enzymatic cycling amplification, were used. Because only small samples were needed (25 to 40 ng), the levels of several enzymes in the same barrel or the distribution of an enzyme within parts of a single barrel could be determined. The following enzyme levels (given in moles per kg dry weight per hr ± SE) were observed in controls: citrate synthase, 5.3 ± 0.15; malate dehydrogenase, 20.8 ± 0.90; hexokinase, 5.2 ± 0.25; lactate dehydrogenase, 10.6 ± 0.20; glycogen phosphorylase, 0.374 ± 0.031; and glucose-6-phosphate dehydrogenase, 0.638 ± 0.012. In single barrels, the mitochondrial enzyme, citrate synthase, had a higher activity within the barrel hollow - which is richer in mitochondria - (7.2 ± 0.12) as compared to the barrel side - which is poorer in mitochondria - (4.4 ± 0.22). The activities of these six enzymes were determined in particular barrels following cauterization of the related groups of whiskers in adult mice. For example, 60 days after whisker damage, activities expressed as a percentage of control were: citrate synthase, 69%; malate dehydrogenase, 61%; hexokinase, 79% lactate dehydrogenase, 92%; glycogen phosphorylase, 132%; and glucose-6-phosphate dehydrogenase, 112%. These significant enzymatic changes occurred in the adult mouse brain in spite of the fact that the injury to peripheral tactile organs was three synapses away. Moreover, no anatomical changes in the barrels have been reported after similar damage to the periphery. We interpret the changes in enzyme levels as a manifestation of adaptive 'plasticity' in the sense that the metabolic machinery of a neural system is matched to its metabolic need, which, in this case, is reduced as a consequence or reduced neuronal activity.
|Original language||English (US)|
|Number of pages||7|
|Journal||Journal of Neuroscience|
|State||Published - 1981|
ASJC Scopus subject areas