Activation of the mesolimbic dopamine system is known to trigger relapse in animal models of cocaine-seeking behavior. We found that this "priming" effect was selectively induced by D2-like, and not by D1-like, dopamine receptor agonists in rats. Moreover, D1-like receptor agonists prevented cocaine-seeking behavior induced by cocaine itself, whereas D2-like receptor agonists enhanced this behavior. These results demonstrate an important dissociation between D1- and D2-like receptor processes in cocaine-seeking behavior and support further evaluation of D1-like receptor agonists as a possible pharmacotherapy for cocaine addiction.

The purpose of this study was to determine if a balance and strength training program could improve equilibrium and strength in persons with stage I-III Parkinsonism. Subjects were pre-tested on strength and balance (EquiTest) and randomized into either a treatment or a control group. The treatment subjects participated in 10 weeks of lower limb strength training and balance exercises designed to challenge a stable posture and increase limits of stability. Both groups were then posttested on balance, knee flexion, knee extension, and ankle inversion strength. Subjects who received strength and balance training demonstrated significantly improved equilibrium and modest gains in knee flexion and extension strength, while the control group showed no improvement in conditions of destabilizing balance environments and significant declines in strength. Results indicate that 10 weeks of balance and strength training lead to improved equilibrium by producing positive changes in two different control mechanisms. One, training altered the ability to control the motor system when vestibular cues had to be the primary source of reliable feedback; and two, training helped subjects to override faulty proprioceptive feedback and utilize reliable visual or vestibular cues.

The instructional set was effective in improving parameters of gait for at least 4 weeks. These data support the concept that people with Parkinson disease have a potential for motor learning.

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