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 used for the suppression of parkinsonian or essential tremor and for the relief of some types of intractable pain in man. However, the mechanisms by which such stimulations exert their therapeutic effects are essentially unknown. Attempts were made to provide some insight into these mechanisms by measuring the levels of the dopamine metabolites homovanillic acid (HVA) and 3,4-dihydroxyphenylacetic acid (DOPAC), the serotonin metabolite 5-hydroxyindoleacetic acid (5-HIAA) and met-enkephalin-like immunoreactivity in ventricular cerebrospinal fluid (CSF) of patients with Parkinson's disease (PD) or multiple sclerosis (MS) after a 30-minute therapeutic electrical stimulation of the ventralis intermedius nucleus of the thalamus. In nonstimulated control patients, the levels of these compounds did not significantly differ in two CSF samples taken 30 minutes apart. In stimulated patients, a decrease in dopamine metabolite levels associated with a relative increase in met-enkephalin-like immunoreactivity were observed in the CSF sample taken after the 30-minute stimulation as compared to the sample taken immediately before the stimulation. In contrast, the levels of 5-HIAA remained unaffected by the stimulation. These data confirmed the existence of negative interactions between dopaminergic and enkephalinergic systems in man similar to those previously demonstrated in rats. In addition, they suggest that alterations in dopaminergic or enkephalinergic neurotransmission might be involved in the therapeutic action of thalamic electrical stimulation in patients with parkinsonian symptoms and other patients.

Neurological complications of neurofibromatosis type 1 in adulthood

Neurofibromatosis type 1 (NF1) is a genetic disease with a wide range of neurological manifestations. To examine these, and to evaluate neurological morbidity in adulthood of patients with NF1, we studied a hospital-based series of 158 patients that included 138 adult patients aged >18 years and 20 children. NF1 evaluation included a multidisciplinary clinical and a clinically oriented radiological investigation. Neurological events occurring during childhood (in both children and adults of the series) and adulthood were recorded. One or several neurological manifestations have been observed in 55% of patients (adults and children) (n = 87). These included: headache (28 patients); hydrocephalus (7); epilepsy (5); lacunar stroke (1); white matter disease (1); intraspinal neurofibroma (3); facial palsy (1); radiculopathy (5); and polyneuropathy (2). Tumours included: optic pathway tumours (20); meningioma (2); cerebral glioma (3); and malignant peripheral nerve sheath tumours (6). Life-threatening complications were observed in five adults and included four malignant peripheral nerve sheath tumours and one meningioma. Pain was the leading symptom in 11 adults and was related to malignant peripheral nerve sheath tumours, complications of intraspinal neurofibromas, subcutaneous neurofibromas and peripheral nerve neurofibromas. NF1 in adults was not associated with other disabling or life-threatening neurological complications. Symptomatic optic pathway tumours, cerebral gliomas, symptomatic aqueductal stenosis and spinal compression due to intraspinal NF were observed exclusively during childhood. In this series, the predominant neurological features of adults with NF1 were chronic pain and malignant peripheral nerve sheath tumours.

Glial and endothelial cell response to a fetal transplant of purified neurons

Astrocytes, microglia and endothelial cells display very specific phenotypic characteristics in the intact adult CNS, which appear quite versatile when grown in culture without neurons. Indirect evidence from in vitro co-culture studies and analysis of the effects of specific neuronal removal in vivo, does accordingly favour a role of neurons for the phenotypic repression of these cells in the intact brain. In order to provide more direct evidence for such neuronal influence, we attempted to induce, in the rat brain, a reversal of the post-lesional activation of astrocytes, microglia and endothelial cells by transplantation of fetal neurons purified by immunopanning. Host microglial cells which have been activated by the lesion process, penetrated the neuronal graft during the few days after the transplantation. Reactive astrocytes began to appear in the lesioned parenchyma and gathered around the transplant. Thereafter they first sent their processes in the direction of the neuronal graft, before they migrated into the graft a few days later. At this time, which was at the end of the first week post-transplantation, the host endothelial cells sprouted "streamers" of basal lamina within the graft forming small capillaries. During the second week post-transplantation, numerous astrocytes and microglial cells, both displaying a reactive hypertrophied morphology, were observed throughout the grafts. Finally, by the end of the first month, the activated cells differentiated towards a quiescent, resting morphology. At this time the grafts contained a vascular network with morphological characteristics comparable to those observed in the intact brain parenchyma. The results indicate that the interaction of activated astroglia and microglia and endothelial cells with neurons causes the cells to re-differentiate and regain phenotypic features characteristic of intact brain parenchyma, strongly suggesting that neurons play an essential role in the phenotypic restriction of glial and endothelial cells in the adult central nervous system.