[1] Univ Colorado, Dept Pharmacol, Hlth Sci Ctr, Aurora, CO 80045 USA
[2] Univ Colorado, Dept Prevent Med & Biometr, Hlth Sci Ctr, Aurora, CO 80045 USA
[3] Univ London Imperial Coll Sci Technol & Med, Fac Med, MRC, Ctr Clin Sci, London W12 0NN, England
[4] US Dept Vet Affairs, Med Ctr, Portland, OR 97239 USA
[5] Univ Tennessee, Ctr Hlth Sci, Dept Anat & Neurobiol, Memphis, TN 38163 USA