Morphological classification of parvalbumin-containing retinal ganglion cells in mouse: Single-cell injection after immunocytochemistry

PURPOSE. Matching the neuron's morphology with its expression of a particular protein cannot be easily achieved by immunocytochemistry alone, as many proteins are expressed too weakly. In this study, a newly developed method was adopted to match mouse retinal ganglion cell (RGC) morphology with its expression of parvalbumin. METHODS. Parvalbumin-containing ganglion cells were first identified by immunocytochemistry and then were iontophoretically injected with a lipophilic dye DiI. Then confocal microscopy was used to characterize the morphologic classification of the parvalbumin-immunoreactive (IR) ganglion cells on the basis of the dendritic field size, branching pattern, and stratification within the inner plexiform layer. RESULTS. The results indicate that at least eight different types of ganglion cells express parvalbumin in the mouse retina. They were heterogeneous in morphology: monostratified to bistratified, small-to-large dendritic field size, and sparse-to-dense dendritic arbors. CONCLUSIONS. Single-cell injection, after immunocytochemistry, provided the first means to identify the detailed functional anatomy of parvalbumin-containing RGCs in the mouse retina. The combined approach of cell morphology and the selective expression of parvalbumin will not only provide useful data for further correlation of physiological properties of the RGCs, but it will also provide a useful strategy for matching a neuron's morphology with its expression of a particular protein.