Electrophysiological study of the topography of the vibrissae projections to the tactile thalamus and cerebral cortex in mutant mice with hair defects

Projections of the mystacial vibrissae to the tactile thalamus and somatosensory neocortex were studied in mutant mice with hair defects, of the Mottled ($\text{Mo}\text{Mo}$), Hairless ($\text{hr}\text{hr}$), and Nude ($\text{Nu}\text{Nu}$) types. Results show that Mottled mice have projections of the same kind as normal mice. In Hairless mice there are silent zones between the projections of intact vibrissae. In Nude mice which lack hairs since birth, the most important change is that the vibrissae project to regions of the thalamus and the SI cerebral cortex ordinarily innervated from the common fur of the muzzle. Thus Nude mice seem to compensate for the absence of hairs of the common fur. We hypothesize that this change represents the counterpart of changes observed in normal mice whose vibrissae follicles were destroyed at birth. Nude mice lack hairs since birth and their vibrissae project to the fur regions. In normal mice whose vibrissae were destroyed at birth, common hairs of the mystacial pad project to the vibrissa region.