A rat embryo staging scale for the generation of donor tissue for neural transplantation

In rat models of Parkinson's and Huntington's diseases, embryonic neural cells obtained from embryos of specified ages can be implanted into the brain to partially restore both physiology and function. However, in litters produced using overnight mating protocols (often from commercial suppliers), the embryonic age can be difficult to determine precisely. As a result, embryonic size based on crown to rump length (CRL) is usually a more reliable method of embryo staging than the day of mating. This approach is not without difficulty. There are a number of rat staging scales in the literature, none of which deal with donor ages younger than E13, and there are discrepancies between scales at some donor ages. In the present article, we have devised a short mating-period protocol to produce precisely aged embryos. We show that CRL is a highly accurate, reproducible index of donor age and we present an updated embryonic staging scale for Sprague-Dawley (CD) rats that includes donor ages younger than those previously reported.