Light microscope differentiation of two populations of rat olfactory bulb granule cells.

Examination of glycolmethacrylate embedded olfactory bulbs of normal rats revealed that the granule cells of the accessory olfactory bulb were dissimilar from the majority of main olfactory bulb granule cells. Cells from these structures can be discriminated on the basis of spherical form. nuclear diameter, nucleoplasm staining, basal dendritic arborizations, and susceptibility to loss after neonatal X-irradiation. Based on their staining qualities, we have called these cells light and dark granule cells. In the normal rat the dark granules make up about 85% of granule cells in the main olfactory bulb and is the cell type preferentially killed by neonatal X-irradiation. Timing of postnatal X-irradiation and consequent differential loss of the dark type of main olfactory bulb granule cell suggests that the light type is largely prenatally formed.