Neuropeptide Y-like immunoreactivity in area 17 of chimpanzee.

The distribution and morphology of neuropeptide Y-like immunoreactive (NPY+) neurons in area 17 were studied in 4 chimpanzees (15 to 56 years old) with the aid of immunocytochemical methods. The NPY+ neurons were not pyramidal, but were either multipolar, bipolar, or bitufted in shape. They occurred most frequently in layer 6 and the subjacent white matter, they were sparser in the supragranular layers, and were few in layer 4. The NPY+ somata in the supragranular layers were significantly smaller than those in the infragranular layers. The axon of NPY cells originated either from the soma or from the primary dendrite. The distribution and morphology of NPY+ neurons were not different between the youngest and the oldest chimpanzee. The oval shape of NPY+ neurons, however, changed slightly with aging to a more circular shape. The density of NPY+ fibers was laminar-dependent. A distinct plexus extended through the upper part of layer 4 and the lowest aspect of layer 3. A thin fiber band was found in the lowest part of layer 4. Some NPY+ axons vertically traversed the cortex between pia and white matter. In the superficial layers, "snarls" of fibers appeared.