Acute whisker removal reduces neuronal activity in barrels of mouse SmL cortex

The autoradiographic 2-deoxy-D glucose (2-DG) method has been used to map relative changes in metabolic activity in the CNS during various functional states (Plum et al., '76). Here we describe the application of the 2-DG method to assay regional activity in the posteromedial barrel subfield (PMBSF) region of the mouse SmI cortex after acute removal of mystacial vibrissae. One day prior to isotope injection, various combinations of vibrissae (e.g., all vibrissae, row-C only, rows-B and -D only) were plucked from adult male Swiss Webster mice under anesthetic. The next day, 5 muCi of 14C-2-DG were injected into a tail vein, and the mice were allowed to actively explore an empty cage for 45 minutes. The animals were then sacrificed, the brains quickly removed, frozen, and sectioned either parallel or perpendicular to the pia at 80 mum in a cryostat. The sections were mounted, dried on coverslips, and were used to expose X-ray film, after which the sections were stained with thionin and the X-ray film developed. The tissue sections and matching autoradiograms were compared directly from photomicrographs of each. The autoradiograms showed areas of higher activity in barrels for which corresponding vibrissae were present and lower activity in barrels for which appropriate vibrissae were missing. In tangential sections from animals with all vibrissae intact, the PMBSF was uniformly and consistently higher in activity than in cases with all vibrissae missing. The removal of row-C or rows-B and -D resulted in strips of decreased activity in the corresponding PMBSF rows. The same patterns of increased or decreased activity were also seen in sections normal to the pia, but the changes in activity, while greatest in layer IV, extended through all layers of the cortex. Finally, in a number of the autoradiograms, density patterns could be recognized which later were shown to relate directly to sides of individual barrels. The results indicate: (1) Acute removal of the peripheral vibrissal hairs is sufficient to deprive the related contralateral cortical barrel neurons of normal activity. Thus in the mouse somatosensory system it may be possible to determine the relative importance of sensory deprivation and neonatal peripheral lesions in normal cortical development. (2) The barrels are part of a functional cortical columnar organization similar to that in other sensory systems. And, (3) the 14C-2-DG-X-ray technique is sufficiently sensitive to reveal parts of individual barrels in autoradiograms and thus, with some modification, may be suitable for the study of small populations of neurons.