Multiple types of neuropeptide Y-containing neurons in primate neocortex

The avidin-biotin-peroxidase method was used at the light and electron microscopic levels to analyze neuropeptide Y (NPY)-containing neurons in the neocortex of six adult macaque monkeys. Regions studied included various sensory, motor, limbic, and association areas, designated as 17, 18, 7, 22, 3, 4, 6, 24, and 9 by Brodmann (Beiträge zur Histologischen Lokalisation der Grosshirnrinde. Leipzig: Barth, '06). Several types of NPY-containing neurons can be distinguished by their laminar location, by the size of their perikarya, and by the size, shape, and pattern of ramification of their processes: 1) layer I small local circuit neurons; 2) layer II granule cells; 3) aspiny stellate cells located in layers II-III and V-VI, with long, slender dendrites; 4) sparsely spiny stellate cells; 5) aspiny stellate cells with long, horizontally oriented dendrites, whose cell body is situated in layer VI; 6) Martinotti cells in areas 9, 7, and 24; and 7) multipolar neurons situated in the white matter subjacent to the cortical gray. The possibility of additional neuronal types containing NPY is suggested by labeled densely spinous dendrites in area 6 and recurving axons and axonal loops in the supragranular layers in areas 7 and 9. No NPY-containing neurons were found in layer IV of any area, except layers IVA and B of the visual cortex. Likewise, nonneuronal elements were not labeled. The regional differences in the distribution of some NPY-containing neuron types may reflect adaptations of local neuronal circuits for specialized functions.