Abstract
Purpose: :
A well characterized naturally occurring mutant, the nob (no b wave) mouse has a defect in synaptic transmission from photoreceptors to depolarizing bipolar cells (DBCs) but no morphological abnormalities are reported (Gregg et al., IOVS 2003; Ball et al., Vis Neurosci 2003). We are examining the inner retina of the nob mouse to determine whether loss of DBC activity affects morphology of their axonal projections.
Methods: :
Affected nob and unaffected nob littermate mice were bred locally. Immunohistochemical analyses were performed on flat mounted retinas with an antibody for PKC (1:1000; Sigma). The inner retina of 3 nob and 3 nob unaffected littermates were viewed on a confocal microscope. Digital images were collected every 1.0 um to obtain 12 images throughout a 12µm thick portion of the IPL. Measurements of label intensity, area of the axonal process, and shape factor were made off line for each optical section using Metamorph image analysis software (Universal Imaging Corp.).
Results: :
The total number of axonal processes visualized by PKC label as well as the average area of each projection throughout a 12 µm thick portion of the IPL was significantly reduced in nob mice as compared to unaffected littermates. Label intensity and shape factor of individual projections in affected nob mice were significantly increased as compared to unaffected littermates (p<0.0001).
Conclusions: :
DBC axonal projections in the inner plexiform layer of nob mice are altered as compared to unaffected littermates. Similar alterations have been noted in mouse models of photoreceptor degeneration. However, these findings suggest that photoreceptor cell loss is not necessary to trigger remodeling in the inner retina.
Keywords: bipolar cells • inner retina dysfunction: hereditary • microscopy: light/fluorescence/immunohistochemistry