High frequency stimulation (130 Hz) of the subthalamic nucleus has dramatic beneficial motor effects in severe parkinsonian patients. However, the mechanisms underlying these clinical results remain obscure. The objective of the present work was to study the neurochemical changes induced in rats by high frequency stimulation of the subthalamic nucleus by using intracerebral microdialysis within its target structures. Our results show that high frequency stimulation of the subthalamic nucleus induces a significant increase of extracellular glutamate levels in the ipsilateral globus pallidus and substantia nigra while GABA was augmented only in the substantia nigra. These data suggest that functional effects induced by high frequency stimulation of the subthalamic nucleus might imply distal mechanisms involving the synaptic relationships with the subthalamic efferences. They question the current view that the direct inhibition of the subthalamic neurons is induced by high frequency stimulation.
We have previously described impairments of cognitive executive functions in 17 patients with OSAS in comparison with 17 normal controls, as assessed by various frontal-lobe-related tests. In the present study, 10 of these OSAS patients treated with continuous positive airway pressure (CPAP) were reevaluated after 4-6 months of treatment. Neuropsychological tasks explored attention, short-term memory span, learning abilities, planning capacities, categorizing activities, and verbal fluency. Patients were found to have normalized most of their cognitive executive and learning disabilities, but all the short-term memory tests remained unchanged. These findings are discussed in light of the contribution of the frontal-lobe-related systems to short-term memory functions, and the eventual pathogenic role played by sleep fragmentation and nocturnal hypoxemia, which are related to the occurrence of apneic and hypopneic events. In conclusion, short-term memory impairment was persistent in OSAS patients despite CPAP treatment for 4-6 months.
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