Organization of Neuropeptide Y-Immunoreactive Cells in the Mongolian gerbil (Meriones unguiculatus) Visual Cortex

Neuropeptide Y (NPY) is found throughout the central nervous system where it appears to be involved in the regulation of a wide range of physiological effects. The Mongolian gerbil, a member of the rodent family Muridae, is a diurnal animal and has been widely used in various aspects of biomedical research. This study was conducted to investigate the organization of NPY-immunoreactive (IR) neurons in the gerbil visual cortex using NPY immunocytochemistry. The highest density of NPY-IR neurons was located in layer V (50.58%). The major type of NPY-IR neuron was a multipolar round/oval cell type (44.57%). Double-color immunofluorescence revealed that 89.55% and 89.95% of NPY-IR neurons contained gamma-aminobutyric acid (GABA) or somatostatin, respectively. Several processes of the NPY-IR neurons surrounded GABAergic interneurons. Although 30.81% of the NPY-IR neurons contained calretinin, NPY and calbindin-D28K-IR neurons were co-expressed rarely (3.75%) and NPY did not co-express parvalbumin. Triple-color immunofluorescence with anti-GluR2 or CaMKII antibodies suggested that some non-GABAergic NPY-IR neurons may make excitatory synaptic contacts. This study indicates that NPY-IR neurons have a notable architecture and are unique subpopulations of the interneurons of the gerbil visual cortex, which could provide additional valuable data for elucidating the role of NPY in the visual process in diurnal animals.