Abstract
Purpose :
Extracellular matrix (ECM) proteins play an important role in synapse formation and plasticity. Nevertheless, the functional importance of the ECM in the retina is still poorly understood. To investigate the relevance of the ECM in retinal function, we analyzed quadruple knockout (KO) mice lacking the four molecules brevican, neurocan, tenascin-C and tenascin-R.
Methods :
Electroretinogram (ERG) recordings were performed in adult, 14-16 week old quadruple KO and wildtype (WT) mice of either sex (n=8/group). The optokinetic reflex (OKR), a basic mechanism to stabilize moving objects on the retina, was also analyzed (n=6/group). Immunohistochemical stainings were performed and visualized by confocal laser-scanning microscopy (n=7-8/group). Using anti-choline acetyl-transferase (ChAT), cholinergic direction-selective starburst amacrine cells (SACs) were stained and counted on retinal flat-mounts. The number of inhibitory γ-aminobutyric acid receptor type A (GABA-R) positive cells was counted on retinal sections. Also, immunoreactivity of the excitatory vesicular glutamate transporter 1 (VGlut1) was investigated. For statistical analyses the Student`s t-test or Mann-Whitney U test were used.
Results :
ERG recordings revealed significantly reduced a-wave (p<0.05) and b-wave (p<0.001) amplitudes in quadruple KO compared to WT mice. OKR analyses showed a significant reduction in the numbers of saccades in KO animals (p<0.01). A significantly reduced number of SACs could be noted in the ganglion cell layer of KO mice (p=0.01). Additionally, KO mice showed fewer GABA-R+ cells in the ganglion cell layer (WT: 92.5 ± 1.3 cells/mm, KO: 84.5 ± 1.2 cells/mm, p=0.01). Area measurements revealed a significantly increased VGlut1-staining in the inner plexiform (p=0.008) and outer plexiform layer (p=0.0002).
Conclusions :
Quadruple KO mice exhibit reduced a- and b-wave amplitudes, suggesting impaired synaptic integrity. Most interestingly, diminished visual motion processing was evident in these mice, which might be caused by the loss of cholinergic direction-selective SACs. Furthermore, our study implies an impaired balance of inhibitory GABAergic and excitatory glutamatergic neurotransmission in the quadruple KO retina. Collectively, our findings indicate that the lack of four ECM proteins leads to severe impairment of synaptic integrity and visual motion processing.
This is an abstract that was submitted for the 2018 ARVO Annual Meeting, held in Honolulu, Hawaii, April 29 - May 3, 2018.