Techniques for identification of the young obese Zucker rat and some observations on brown adipose tissue morphology and histochemistry in the young obese Zucker rat.

Several techniques for the identification of the young obese Zucker rat were developed and tested. A procedure utilizing biopsies of hypodermal adipocytes was successful in identifying the obese phenotype in large litters of 7-d and older rats. This technique involves sizing and counting fat cells in esterase stained cryostat sections of skin biopsies. Another procedure involved measuring times to cessation of spontaneous activity upon acute exposure to a cold environment. As early as 3 d, obese rats become inactive (in the cold) in a significantly shorter time when compared to the lean rat. This technique was not a discriminating test for the identification of the obese genotype at 3 d of age. A preliminary analysis of brown fat histology and histochemistry indicated larger and more lipid filled brown adipocytes in the obese animal when compared to lean animals at 10 and 14 d of age. Brown fat from young obese animals was histochemically similar to brown fat in lean rats.