Experimental therapeutics of Parkinson's disease

1. The loss of central dopamine, which characterises Parkinson's disease, led to the main pharmacological strategy for treatment, namely levodopa, a dopamine-replacement therapy. Several years after treatment, the majority of patients experience dose-limiting side-effects and loss of symptom control. There is a resurgence of interest in neurosurgery for treating the Parkinson's disease, particularly in new techniques targeting the subthalamic nucleus (STN), which is overactive in Parkinson's disease and contributes to symptom development. 2. We performed unilateral subthalamotomy (lesioning the subthalamic nucleus via the toxin N-methyl-D-aspartate) in marmosets and rats with experimentally induced parkinsonism (induced using the toxin 6-hydroxydopamine). A range of similar behaviours common to both rodents and primates were evaluated before and after each type of surgery. Post-mortem histology was used to confirm the lesions. We also provide details of a case with Parkinson's disease who underwent high-frequency bilateral stimulation of the STN and in whom we analysed the STN post-mortem. 3. Unilateral subthalamotomy improved akinesia in parkinsonian primates. However, both monkeys and rodents showed postural abnormalities. The patient who underwent bilateral high-frequency stimulation showed improvement of akinesia and other disease symptoms and no postural abnormalities. Post-mortem analysis did not demonstrate substantial damage of the STN as a result of the electrodes. 4. Although unilateral subthalamotomy improves some aspects of parkinsonism, it causes postural abnormalities in animal models of Parkinson's disease. Because bilateral high-frequency STN stimulation improves disease symptoms, is reversible and is not reported to induce postural side-effects, it may be a better surgical therapy for Parkinson's disease than lesioning the STN.