Abstract
Abstract: :
Purpose: In the mouse retina, calretinin–immunoreactive neurons situate in the inner margin of the INL and in the GCL whereas their three narrow strata of immunoreactive processes are present in the IPL (Haverkamp and Wassle, 2000). Cholinergic neurons in INL and GCL are immunoreactive for calretinin and their two distinct narrow bands of processes overlap with the outer and inner strata of calretinin–IR processes in the IPL. Here we find that Type 2 catecholaminergic amacrine cells, marked by a TH::RFP reporter in a transgenic mouse model, are also immunoreactive for calretinin but surprisingly they provide a single primary dendrite contributing to the middle stratum of calretinin–IR processes in the IPL. Methods: Transgenic mice hemizygous for tyrosine hydroxylase (TH)–driven red fluorescent protein (RFP) were used in these experiments. Immunocytochemistry for dsRed and calretinin was performed on either vertical slices or wholemount retinas. Rabbit polyclonal anti–dsRed and mouse monoclonal anti–calretinin were used as primary antibodies. Fluorescent specimens were viewed by using a confocal microscope. Results: In retinal vertical sections, antibody against calretinin labeled amacrine cells in the inner nuclear layer and displaced amacrine cells/ganglion cells in ganglion cell layer. Three calretinin–IR strata were found in the IPL and one of them is in the middle of IPL. Type 2 catecholaminergic amacrine cells that were immunoactive for dsRed were predominantly distributed in the INL while a few cells were also seen in the GCL. They had a single primary process that radially ran into the IPL from the somas either in the INL or GCL and arborized with a narrow band in the middle of the IPL. Double labeling for dsRed and calretinin showed that dsRed–positive neurons were also immunoreactive for calretinin and dsRed/calretinin–IR cell processes formed a narrow stratum in the IPL. No calretinin immunoreactivity was found in type 1 catecholaminergic amacrine cells (DA cells). In 3 retinal wholemounts, all type 2 catecholaminergic amacrine cells, which were labeled with an antibody against dsRed in both INL and GCL, were also revealed by calretinin. Conclusions: TH::RFP transgenic mice provides an opportunity to investigate the morphological and physiological properties of type 2 catecholaminergic amacrince cells in the mouse retina. In addition to inner and outer strata of calretinin–IR processes in the IPL represent cholinergic strata, the middle stratum of calretinin–IR processes serves, at least partially, as the dendritic band of type 2 catecholaminergic amacrine cells in the IPL.
Keywords: retina: proximal (bipolar, amacrine, and ganglion cells) • immunohistochemistry • amacrine cells