An Automated Double Staining Procedure for Bone and Cartilage

Differential skeletal staining is an important part of developmental toxicologic studies. Traditionally these studies have required time-consuming differentiation of one or both stains used and careful attention to the maceration step to prevent specimen destruction. We present a fully automated protocol which does not require differentiation of either dye and incorporates a controlled maceration step which is highly reproducible. This has resulted in high quality staining that is reproducible, stable, and can be done in volume with minimal personnel time. The process involves the staining of skinned, eviscerated specimens fixed in 95% ethanol. Using an automated tissue processor, the specimen is stained in alcian blue for 24 hr, macerated in 3% potassium hydroxide for 24 hr and stained with murexide for 24 hr. The specimens are cleared and preserved in glycerol. Within three days specimens have red stained bone and blue stained cartilage. The procedure was developed using 20-day-old Sprague-Dawley rat fetuses to evaluate the feasibility of using the procedure for teratology studies involving the fetal skeleton. Evenly stained specimens can be examined within three days and stored for years without loss of staining.