Animals. Male Sprague-Dawley rats (Crl:CD(SD)IGS BR; Charles River, Portage, MI) weighing 250-370 g were used for in vivo studies. They were fed standard chow (Rodent Chow/Tek 8640; Harlan Teklad, Madison, WI) and allowed access to water ad libitum. Animals were allowed to acclimate for 1 week in a 12-h light/dark cycle prior to experiments. They received humane care according to the criteria in the Guide for the Care and Use of Laboratory Animals.