( rters. The animals received varying amo...)Genetically altered mice no longer like cocaine

Individual mice were placed in a 5-inch-by-7-inch acrylic box with three compartments ?a middle compartment and two test compartments. On the first day of the experiment, mice were allowed to roam around the box.

During the next several days, mice received injections of saline and then various amounts of cocaine on alternating days. Mice injected with saline were confined in one test compartment, while mice injected with cocaine were confined to the other compartment. Mice were kept in these respective compartments for 30 minutes. On the last day of the experiment, mice were again free to roam the box, and no injections were given. The animals were videotaped while they were in the box.

"The normal mice spent more time in the compartment where they had received the cocaine injections," Gu said. "These animals were seeking more cocaine. However, the mice with the modified transporters showed no preference for either test compartment within the box."

The researchers used the video footage to measure each animal's activity level after a cocaine injection. The normal mice on cocaine covered roughly five times the distance than the control mice injected with saline (6 meters vs. 1 meter). In contrast, the cocaine-injected mice with the modified dopamine receptors covered about half the distance that the saline-only injected mice covered (roughly 1.5 meters vs. 3 meters.)

"After the cocaine injections, the normal mice ran all over the place, sniffing and checking everything out in the box over and over again, until we took them out of the box," Gu said. "But cocaine seemed to calm the modified mice, as they sat in a corner for long periods of time."

"To the modified mice, cocaine appears to be a suppr
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Source:Ohio State University