Neurofilament protein distribution in the macaque monkey dorsolateral premotor cortex

Regional and laminar distribution patterns of neurofilament proteins in the dorsolateral premotor cortex (PMd) were studied with monoclonal antibody S MI-32 in five adult macaque monkeys and compared with the cytoarchitectonic al features of the PMd. Our goal was to reveal whether the increasing funct ional diversity of the PMd which electrophysiological studies have unravell ed over the last years is reflected on a structural level by differences in the neurochemical phenotype. Differences in size, shape and packing densit y of immunopositive layer III and V pyramidal cells define areas much more clearly than do differences in cytoarchitecture. The PMd can be subdivided into a rostral and a caudal part at a level slightly anterior to the genu o f the arcuate sulcus. The extent of these two areas matches the two cytoarc hitectonically defined areas F7 and F2, respectively. Within area F2, diffe rences in layer V immunoreactive neurons define a dorsal (F2d) and a ventra l (F2v) region. The border between areas F2d and F2v lies at the superior p recentral dimple and cannot be detected cytoarchitectonically in Nissl-stai ned sections. Neurofilament proteins are involved in the stabilization of t he cytoskeleton of the axon and have been correlated with axonal size and c onduction velocity of nerve fibres. This regional variability in the neuroc hemical phenotype of layer V within the caudal PMd may reflect a differenti al organization of the descending output from this part of the premotor cor tex. It might also be related to differences in the motor control of volunt ary arm and leg movements.