The arrangements of vibrissae in guinea pigs and golden hamsters were previously reported to be different from those in mice and rats.
Whereas the mystacial pads in mice and rats include four straddlers and five rows of vibrissae, guinea pigs were described to possess
six rows of irregularly aligned mystacial vibrissae and no straddlers, and golden hamsters to include seven vibrissal rows and also no
straddlers. We found that all of these four species possess similar vibrissal arrangements within the mystacial pad. To demonstrate this
similarity, we developed a new method of sinus hair visualization in flattened and cleared preparations of the mystacial pad. Intrinsic
muscles of the mystacial pad that were revealed in thick histological preparations showed clearly the structural and functional
relationships between straddlers and vibrissal rows. To verify this finding, and to extend the knowledge of vibrissal cortical
representations in guinea pigs and golden hamsters, we have investigated the spatial organization and the functional vibrissal
representations of barrels in the posteromedial barrel subfield (PMBSF) of these rodents. The barrel morphology was clearly
preserved in Nissl-stained sections and sections processed for cytochrome oxidase of flattened cerebral cortices. We demonstrate that
the vibrissal arrangement in the mystacial pad is replicated in the PMBSF of guinea pigs and golden hamsters and that this arrangement
is similar to that found in mice and rats. To facilitate comparative studies, these findings strongly recommend the use, in guinea pigs and
golden hamsters, of the same classifications and nomenclatures that are used in mice and rats to describe mystacial vibrissae and
cortical barrels.