1. From the Departments of Surgery (Dodman) and Medicine (Knowles, Thalhammer), Tufts University School of Veterinary Medicine, North Grafton, MA 01536, Department of Psychology, Tufts University, Medford, MA 02155 (Miczek), and Department of Pharmacology and Experimental Therapeutics, Tufts University School of Medicine, Boston, MA 02111 (Shuster).