Confocal images were acquired with a Nikon PCM 2000 (Nikon Inc. Mellville, NY, USA) using the Argon (488) and the green Helium-Neon (543) lasers. Serial optical sectioning was performed with Simple 32, C-imaging computer software (Compix Inc, Cranberry Township, PA, USA). Z series sections were collected at 0.5 mm using a 606 PlanApo objective and a scan zoom of 26. Images were processed in NIH Image J (National Institutes of Health, Springfield, VA, USA).