New clue to cocaine addicts' odd behaviors

PITTSBURGH, Jul 20, 2005 (United Press International via COMTEX) -- Scientists are trying to find the brain circuitry involved in the impulsive behavior seen in users of cocaine and other psychostimulant drugs.

The same circuitry has been implicated in such disorders as schizophrenia, depression and post-traumatic stress disorder.

University of Pittsburgh researchers Yukiori Goto and Anthony Grace sought to understand the effects of cocaine sensitization on connections between two higher brain regions -- the prefrontal cortex and the hippocampus -- as well as the nucleus accumbens, the limbic system area that processes reward behavior.

Electrophysiological studies of the effects of cocaine on that circuitry demonstrated the drug disrupts the normal plasticity.

They also performed behavioral studies in which cocaine-sensitized rats were placed in a plus-shaped maze and taught that in response to a visual cue they should turn left or right to obtain a piece of cereal. Goto and Grace found while the rats learned the correct response strategy faster than normal rats, they were significantly less able to change strategies when required to ignore cues and always turn left or right to receive the reward.

The study appears in the journal Neuron.