It is now clear that electrical coupling via gap junctions isprevalent across the retina, expressed by each of the fivemain neuronal types. With the introduction of mutants inwhich selective gap junction connexins are deleted, themouse has recently become an important model for studyingthe function of coupling between retinal neurons. In thisstudy we examined the tracer-coupling pattern of ganglioncells by injecting them with the gap junction-permanenttracer Neurobiotin to provide, for the first time, a comprehensivesurvey of ganglion cell coupling in the wildtypemouse retina. Murine ganglion cells were differentiated into22 morphologically distinct subtypes based on somadendriticparameters. Most (16/22) ganglion cell subtypes were tracer-coupled to neighboring ganglion and/or amacrinecells. The amacrine cells coupled to ganglion cellsdisplayed either polyaxonal or wide-field morphologies withextensive arbors. We found that different subtypes of ganglioncells were never coupled to one another, indicatingthat they subserved independent electrical networks. Finally, we found that the tracer-coupling patterns of the 22ganglion cell populations were largely stereotypic acrossthe 71 retinas studied. Our results indicate that electricalcoupling is extensive in the inner retina of the mouse, suggestingthat gap junctions play essential roles in visual information processing.

We report a series of three cases of unusual locations of chronic osteochondral fragments arising from the posterolateral aspect of the lateral femoral condyle, presenting acutely in young adults, in which the unstable fragment contained the origin of the popliteus tendon, with MRI and arthroscopic correlation. Although atypical, we hypothesize that these cases represent adult osteochondritis dissecans with extension to a popliteus tendon origin. Preoperative diagnosis of popliteus tendon involvement may influence clinical management in patients with an unstable osteochondral fragment in this location.