Opposite changes in dopamine metabolites and met-enkephalin levels in the ventricular CSF of patients subjected to thalamic electrical stimulation

High-frequency electrical stimulations of thalamic nuclei are currently use d for the suppression of parkinsonian or essential tremor and for the relie f of some types of intractable pain in man. However, the mechanisms by whic h such stimulations exert their therapeutic effects are essentially unknown . Attempts were made to provide some insight into these mechanisms by measu ring the levels of the dopamine metabolites homovanillic acid (HVA) and 3,4 -dihydroxyphenylacetic acid (DOPAC), the serotonin metabolite 5-hydroxyindo leacetic acid (5-HIAA) and met-enkephalin-like immunoreactivity in ventricu lar cerebrospinal fluid (CSF) of patients with Parkinson's disease (PD) or multiple sclerosis (MS) after a 30-minute therapeutic electrical stimulatio n of the ventralis intermedius nucleus of the thalamus. In nonstimulated co ntrol patients, the levels of these compounds did not significantly differ in two CSF samples taken 30 minutes apart. In stimulated patients, a decrea se in dopamine metabolite levels associated with a relative increase in met -enkephalin-like immunoreactivity were observed in the CSF sample taken aft er the 30-minute stimulation as compared to the sample taken immediately be fore the stimulation. In contrast, the levels of 5-HIAA remained unaffected by the stimulation. These data confirmed the existence of negative interac tions between dopaminergic and enkephalinergic systems in man similar to th ose previously demonstrated in rats. In addition, they suggest that alterat ions in dopaminergic or enkephalinergic neurotransmission might be involved in the therapeutic action of thalamic electrical stimulation in patients w ith parkinsonian symptoms and other patients.