Abstract
Purpose: :
During a recent study of Enhanced Green Fluorescent Protein (EGFP)–expressing cells in transgenic mice, we found a line in which EGFP is expressed in a subset of amacrine cells in the inner nuclear layer (INL), and in some cells in the ganglion cell layer (GCL). The purpose of this study was to characterize the EGFP–labeled cells based on general morphology and pattern of stratification, using known immunological markers.
Methods: :
Transgenic mice were generated by injecting a construct consisting of 1.2 kb CD44 promoter linked to the EGFP gene. Mice were initially screened by PCR and transgenic animals were examined by confocal microscopy. Retinal whole mounts were used to estimate the density of EGFP–positive cells. We also injected Lucifer yellow or Neurobiotin into somas in a number of different retinas. Double label immunohistochemistry was done on 10µm frozen sections to enable the stratification pattern of the EGFP–labeled terminals to be examined.
Results: :
A population of amacrine cells was found to express EGFP in the retinas from a line of CD44 –EGFP transgenic mice. The labeled cells had a density of 1978± 19.8 cells per mm2. The cells extended their axon arbors into stratum 3 of the retina, which lies between the two bands of ChAT–positive amacrine cell processes. The EGFP expressing cells were positive for GAD immunoreactivity suggesting that they were GABAergic. The GCL was dominated by two types, one bright and one of intermediate brightness. Similarly, somas that were bright or of intermediate brightness could be found in the INL, although there were also many more types of dimmer brightness. There was no evidence of coupling among the EGFP–labeled cells.
Conclusions: :
The present study describes a population of GABAergic amacrine cells in mouse retina that stratifies in sublamina 3. Based on morphological considerations, the brightest cells in the GCL might be a typeB1 or possibly A2.
Keywords: amacrine cells • retina: proximal (bipolar, amacrine, and ganglion cells) • retinal connections, networks, circuitry