Lumbar cerebrospinal fluid (CSF) gamma-aminobutyric acid (GABA) levels determined by fluorometric assay in four seizure patients were found to be significantly lower during bilateral, continuous cerebellar stimulation than those determined after a 7-day period without stimulation. The CSF GABA concentrations during chronic unilateral, alternating cerebellar stimulation were reduced in three seizure patients but unchanged in a fourth patient. The percentage decrease in CSF GABA appeared to be independent of cerebellar stimulation frequency. These findings suggest that GABA-mediated neuronal transmission is depressed during cerebellar surface stimulation and this evoked reduction in GABA activity may compromise the efficacy of cerebellar stimulation in the treatment of epilepsy. Lumbar CSF cyclic guanosine monophosphate levels determined by radioimmunoassay were not significantly altered by either mode or frequency of cerebellar stimulation.

Lumbar cerebrospinal fluid (CSF) norepinephrine (NE) concentrations were preoperatively determined in five patients using a radioenzymatic assay technique. Stereotaxic thalamotomy was performed using depth coagulating electrodes with stimulating points at 5.0-mm intervals along the shaft. No significant alterations in prestimulation lumbar CSF NE levels were noted 12 days after electrode installation. Stimulating points within the caudate nucleus were anatomically localized using ventricular landmarks and stimulation-induced neurophysiological responses were recorded. Twelve hours after intermittent electrical stimulation of the caudate nucleus, lumbar CSF NE concentrations were significantly decreased. Our data suggest the presence of noradrenergic pathways in man that are inhibited by caudate nucleus stimulation.

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