Bertrand Degos

Striatal Medium-Sized Spiny Neurons: Identification by Nuclear Staining and Study of Neuronal Subpopulations in BAC Transgenic Mice

Precise identification of neuronal populations is a major challenge in neuroscience. In the striatum, more than 95% of neurons are GABAergic medium-sized spiny neurons (MSNs), which form two intermingled populations distinguished by their projections and protein content. Those expressing dopamine D1-receptors (D1Rs) project preferentially to the substantia nigra pars reticulata (SNr), whereas those expressing dopamine D2- receptors (D2Rs) project preferentially to the lateral part of the globus pallidus (LGP). The degree of segregation of these populations has been a continuous subject of debate, and the recent introduction of bacterial artificial chromosome (BAC) transgenic mice expressing fluorescent proteins driven by specific promoters was a major progress to facilitate striatal neuron identification. However, the fraction of MSNs labeled in these mice has been recently called into question, casting doubt on the generality of results obtained with such approaches. Here, we performed an in-depth quantitative analysis of striatal neurons in drd1a-EGFP and drd2-EGFP mice. We first quantified neuronal and non-neuronal populations in the striatum, based on nuclear staining with TO-PRO-3, and immunolabeling for NeuN, DARPP-32 (dopamine- and cAMP-regulated phosphoprotein Mr∼32,000), and various markers for interneurons. TO-PRO-3 staining was sufficient to identify MSNs by their typical nuclear morphology and, with a good probability, interneuron populations. In drd1a-EGFP/drd2-EGFP double transgenic mice all MSNs expressed EGFP, which was driven in about half of them by drd1a promoter. Retrograde labeling showed that all MSNs projecting to the SNr expressed D1R and very few D2R (<1%). In contrast, our results were compatible with the existence of some D1R-EGFP-expressing fibers giving off terminals in the LGP. Thus, our study shows that nuclear staining is a simple method for identifying MSNs and other striatal neurons. It also unambiguously confirms the degree of segregation of MSNs in the mouse striatum and allows the full exploitation of results obtained with BAC-transgenic mice.

Neuroleptic-Induced Catalepsy: Electrophysiological Mechanisms of Functional Recovery Induced by High-Frequency Stimulation of the Subthalamic Nucleus

High-frequency stimulation (HFS) of the subthalamic nucleus (STN) remarkably alleviates motor disorders in parkinsonian patients. The mechanisms by which STN HFS exerts its beneficial effects were investigated in anesthetized rats, using a model of acute interruption of dopaminergic transmission. Combined systemic injections of SCH-23390 [R(+)-7-chloro-8-hydroxy-3-methyl-1-phenyl-2,3,4,5,-tetrahydro-1H-3-benzazepine] and raclopride, antagonists of the D1 and D2 classes of dopaminergic receptors, respectively, were performed, and the parameters of STN HFS that reversed the neuroleptic-induced catalepsy were determined in freely moving animals. The effects of neuroleptics and the impact of STN HFS applied at parameters alleviating neuroleptic-induced catalepsy were analyzed in the substantia nigra pars reticulata (SNR), a major basal ganglia output structure, by recording the neuronal firing pattern and the responses evoked by cortical stimulation. Neuroleptic injection altered the tonic and regular mode of discharge of SNR neurons, most of them becoming irregular with bursts of spikes and pauses. The inhibitory component of the cortically evoked response, which is attributable to the activation of the direct striatonigral circuit, was decreased, whereas the late excitatory response resulting from the indirect striato-pallido-subthalamo-nigral circuit was reinforced. During STN HFS, the spontaneous firing of SNR cells was either increased or decreased with a global enhancement of the firing rate in the overall population of SNR cells recorded. However, in all of the cases, SNR firing pattern was regularized, and the bias between the trans-striatal and trans-subthalamic circuits was reversed. By these effects, STN HFS restores the functional properties of the circuits by which basal ganglia contribute to motor activity.

Biotin-responsive basal ganglia disease in ethnic Europeans with novel SLC19A3 mutations.

OBJECTIVE To report the first 2 European cases of biotin-responsive basal ganglia disease and novel SLC19A3 mutations. DESIGN Case reports. SETTING University hospital. Patients A 33-year-old man and his 29-year-old sister, both of Portuguese ancestry, presented with recurrent episodes of encephalopathy. Between episodes patients exhibited generalized dystonia, epilepsy, and bilateral hyperintensities of the caudate and putamen. MAIN OUTCOME MEASURES Clinical and radiologic findings. RESULTS Administration of high doses of biotin or of a combination of biotin and thiamine during encephalopathies resulted in spectacular clinical and radiologic improvement in both patients. Sequencing of the SLC19A3 disclosed 2 novel mutations, both of which created premature stop codons in the protein sequence of hTHTR2. CONCLUSION This study demonstrates that biotin-responsive basal ganglia disease is a panethnic condition. A therapeutic trial with high doses of biotin and thiamine seems mandatory in every unexplained encephalopathy with bilateral lesions of putamen and caudate nuclei.

Transcranial magnetic stimulation as an efficient treatment for psychogenic movement disorders

Background Management of psychogenic movement disorders (PMDs) is challenging for neurologists and, to date, there is no consensus about their treatment. Recent studies suggested a possible therapeutic effect of repeated transcranial magnetic stimulation (TMS) in psychogenic paralysis and tremor. Objective To document the clinical impact of TMS in PMDs. Methods We blindly video scored symptoms of consecutive patients with PMD who were recorded before and after TMS. TMS was delivered at low frequency (0.25 Hz) over the motor cortex contralateral to symptoms. Results Twenty-four patients were included. They presented with dystonia, myoclonus, tremor, Parkinsonism or stereotypies. The median duration of symptoms before TMS was 2.8 years (6 months to 30 years). The overall score of 75% of patients improved by >50% and, furthermore, the clinical benefits were sustained upon protracted follow-up (median 19.8 months). There was no correlation between improvement and duration of symptoms before TMS. Conclusions TMS is a therapeutic option for PMDs, including chronic PMDs.

Subthalamic nucleus high‐frequency stimulation generates a concomitant synaptic excitation–inhibition in substantia nigra pars reticulata

Non‐technical summary  Parkinsons disease, a neurodegenerative pathology, causes motor and cognitive impairments such as tremor at rest, muscle rigidity and depression. An efficient surgical therapy, deep brain stimulation, allows treatment of most symptoms of Parkinsons disease. The principle of deep brain stimulation is to stimulate electrically, at high frequency and low intensity, the subthalamic nucleus. However, how deep brain stimulation works is still not fully elucidated. We investigated the mechanism of deep brain stimulation of the subthalamic nucleus by recording the activity of neurons that are directly under the control of subthalamic nucleus neurons. We demonstrate that deep brain stimulation of the subthalamic nucleus activates local subthalamic glutamatergic neurons as well as GABAergic fibres travelling through this structure inducing a synaptic excitation–inhibition balance in the output structure. Thus, we conclude that deep brain stimulation restores the activity of the pathological brain network by providing a proper excitation–inhibition balance.

The pleiotropic movement disorders phenotype of adult ataxia-telangiectasia

Objective: To assess the clinical spectrum of ataxia-telangiectasia (A-T) in adults, with a focus on movement disorders. Methods: A total of 14 consecutive adults with A-T were included at 2 tertiary adult movement disorders centers and compared to 53 typical patients with A-T. Clinical evaluation, neurophysiologic and video-oculographic recording, imaging, laboratory investigations, and ATM analysis were performed. Results: In comparison with typical A-T cases, our patients demonstrated later mean age at onset (6.1 vs 2.5 years, p < 0.0001), later loss of walking ability (p = 0.003), and longer survival (p = 0.0039). The presenting feature was ataxia in 71% and dysarthria and dystonia in 14% each. All patients displayed movement disorders, among which dystonia and subcortical myoclonus were the most common (86%), followed by tremor (43%). Video-oculographic recordings revealed mostly dysmetric saccades and 46% of patients had normal latencies (i.e., no oculomotor apraxia) and velocities. The α-fetoprotein (AFP) level was normal in 7%, chromosomal instability was found in 29% (vs 100% of typical patients, p = 0.0006), and immunoglobulin deficiency was found in 29% (vs 69%, p = 0.057). All patients exhibited 2 ATM mutations, including at least 1 missense mutation in 79% of them (vs 36%, p = 0.0067). Conclusion: There is great variability of phenotype and severity in A-T, including a wide spectrum of movement disorders. Karyotype and repeated AFP level assessments should be performed in adults with unexplained movement disorders as valuable clues towards the diagnosis. In case of a compatible phenotype, A-T should be considered even if age at onset is late and progression is slow.

Impaired saccadic adaptation in DYT11 dystonia

Background Recent neuroimaging studies point to a possible pathophysiological role of cerebellar dysfunction in dystonia. The authors investigated the association between sensorimotor adaptation, cerebellar dysfunction and the myoclonus–dystonia phenotype. Methods The authors prospectively analysed reactive saccade adaptation in a genetically homogeneous group of 14 patients with DYT11 dystonia owing to a mutation of the SGCE gene. The authors used a backward reactive saccade adaptation task, a well-characterised experimental oculomotor paradigm involving the cerebellum. The principle of this paradigm is to simulate a spatial error in saccade generation by systematically shifting a visual target during saccade execution. Repetition of this systematic error induces a gradual decrease in the initial saccade amplitude, reflecting an adaptive phenomenon. Results Saccade adaptation was significantly lower in the DYT11 patients than in healthy controls (mean value: 8.9%±4.5% vs 21.6%±4.5%; p=8.3×10−6). The time course of adaptation also differed between the patients and controls (p=0.002), reflecting the slower saccadic adaptation in the patients. Conclusions This study provides the first neurophysiological evidence of cerebellar dysfunction in DYT11 dystonia and supports a role of cerebellar dysfunction in the myoclonus–dystonia phenotype.

The long-term outcome of orthostatic tremor

Objectives Orthostatic tremor is a rare condition characterised by high-frequency tremor that appears on standing. Although the essential clinical features of orthostatic tremor are well established, little is known about the natural progression of the disorder. We report the long-term outcome based on the largest multicentre cohort of patients with orthostatic tremor. Methods Clinical information of 68 patients with clinical and electrophysiological diagnosis of orthostatic tremor and a minimum follow-up of 5 years is presented. Results There was a clear female preponderance (76.5%) with a mean age of onset at 54 years. Median follow-up was 6 years (range 5–25). On diagnosis, 86.8% of patients presented with isolated orthostatic tremor and 13.2% had additional neurological features. At follow-up, seven patients who initially had isolated orthostatic tremor later developed further neurological signs. A total 79.4% of patients reported worsening of orthostatic tremor symptoms. These patients had significantly longer symptom duration than those without reported worsening (median 15.5 vs 10.5 years, respectively; p=0.005). There was no change in orthostatic tremor frequency over time. Structural imaging was largely unremarkable and dopaminergic neuroimaging (DaTSCAN) was normal in 18/19 cases. Pharmacological treatments were disappointing. Two patients were treated surgically and showed improvement. Conclusions Orthostatic tremor is a progressive disorder with increased disability although tremor frequency is unchanged over time. In most cases, orthostatic tremor represents an isolated syndrome. Drug treatments are unsatisfactory but surgery may hold promise.

NDRG1-linked Charcot-Marie-Tooth disease (CMT4D) with central nervous system involvement.

Charcot-Marie-Tooth disease type 4D (CMT4D) is an autosomal recessive demyelinating polyneuropathy, associated with deafness exclusively found in Gypsies and resulting from a homozygous R148X mutation in the N-myc downstream-regulated gene 1 (NDRG1). We report the detailed phenotypic study of a family without Gypsy ancestry, who presented with severe demyelinating polyneuropathy, deafness, subcortical white matter abnormalities on brain magnetic resonance imaging studies, and the R148X mutation in NDRG1. For the first time, central nervous system white matter lesions are demonstrated in CMT4D. This report extends the clinical knowledge of CMT4D and indicates that the role of the R148X mutation in NDRG1 in the central nervous system should be further studied.

C2orf37 mutational spectrum in Woodhouse–Sakati syndrome patients

Alazami AM, Schneider SA, Bonneau D, Pasquier L, Carecchio M, Kojovic M, Steindl K, de Kerdanet M, Nezarati MM, Bhatia KP, Degos B, Goh E, Alkuraya FS. C2orf37 mutational spectrum in Woodhouse–Sakati syndrome patients.