Domenicantonio Tropepi

Corticostriatal LTP requires combined mGluR1 and mGluR5 activation

Metabotropic glutamate receptors (mGluRs) have been demonstrated to play a role in synaptic plasticity. It has been recently shown that mGluR1 is involved in corticostriatal long-term depression, by means of pharmacological approach and by using mGluR1-knockout mice. Here, we report that both mGluR1 and mGluR5 are involved in corticostriatal long-term potentiation (LTP). In particular, the mGluR1 antagonist LY 367385, as well as the mGluR5 antagonist MPEP, reduce LTP amplitude. Moreover, blockade of both mGluR1 and mGluR5 by LY 367385 and MPEP co-administration fully suppresses LTP. Accordingly, group II and group III mGluRs antagonists fail to affect LTP induction. Interestingly, LTP amplitude is also significantly reduced in both mGluR1- and mGluR5-knockout mice. The differential function of mGluR1 and mGluR5 in corticostriatal synaptic plasticity may play a role in the modulation of the motor activity mediated by the basal ganglia, thus providing a substrate for the pharmacological treatment of motor disorders involving the striatum.

Neuronal vulnerability following inhibition of mitochondrial complex II: a possible ionic mechanism for Huntington's disease

An impaired complex II (succinate dehydrogenase, SD) striatal mitochondrial activity is one of the prominent metabolic alterations in Huntingtons disease (HD), and intoxication with 3-nitropropionic acid (3-NP), an inhibitor of mitochondrial complex II, mimics the motor abnormalities and the pathology of HD. We found that striatal spiny neurons responded to this toxin with an irreversible membrane depolarization/inward current, while cholinergic interneurons showed a hyperpolarization/outward current. Both these currents were sensitive to intracellular concentration of ATP. The 3-NP-induced depolarization was associated with an increased release of endogenous GABA, while acetylcholine levels were reduced. Moreover, 3-NP induced a higher depolarization in presymptomatic R6/2 HD transgenic mice compared to wild-type (WT) mice, showing an increased susceptibility to SD inhibition. Conversely, the hyperpolarization did not significantly differ from the one recorded in WT mice. The diverse membrane changes induced by SD inhibition may contribute to the cell-type-specific neuronal death in HD.

Correlation between changes in CSF dopamine turnover and development of dyskinesia in Parkinson's disease

To assess possible differences in dopamine metabolism that could parallel disease progression in Parkinsons disease (PD), we measured dopamine (DA) and its metabolites in the cerebrospinal fluid (CSF) in PD patients at different stages of disease: de novo (DEN), advanced not showing dyskinesias (ADV), and advanced with dyskinesias (DYS). DA, homovanillic acid (HVA) and dihydroxyphenylacetic acid (DOPAC) were significantly higher in DEN patients compared with other groups. A negative exponential correlation related DA level and disease duration. The HVA/DA ratio was significantly higher in the ADV and DYS group than that found in DEN group. Our data show that disease progression produces an early large decay of DA levels, followed by a stabilization. On the contrary, a late change in DA turnover (increased HVA/DA ratio) is documented in patients with longer disease duration. Our results suggest that the appearance of dyskinesia may not be related to a further loss of DA terminals but to a different, abnormal, DA turnover.

Bilateral Implantation of Centromedian‐Parafascicularis Complex and GPi: A New Combination of Unconventional Targets for Deep Brain Stimulation in Severe Parkinson Disease

Objectives.  Traditional deep brain stimulation (DBS) at the subthalamic nucleus (STN) has proved to be efficacious on core Parkinsonian symptoms. However, very disabling l‐dopa–induced abnormal involuntary movements (AIMs) and axial signs are slightly affected, suggesting that we target less conventional targets. Our candidates for DBS were the globus pallidus internus (GPi) plus the intralaminar thalamic complex (Pf or CM), given its extensive functional links with basal ganglia nuclei.

Intra-arterial Thrombectomy versus Standard Intravenous Thrombolysis in Patients with Anterior Circulation Stroke Caused by Intracranial Arterial Occlusions: A Single-center Experience

BACKGROUND Severely impaired patients with persisting intracranial occlusion despite standard treatment with intravenous (IV) administration of recombinant tissue plasminogen activator (rtPA) or presenting beyond the therapeutic window for IV rtPA may be candidates for interventional neurothrombectomy (NT). The safety and efficacy of NT by the Penumbra System (PS) were compared with standard IV rtPA treatment in patients with severe acute ischemic stroke (AIS) caused by large intracranial vessel occlusion in the anterior circulation. METHODS Consecutive AIS patients underwent a predefined treatment algorithm based on arrival time, stroke severity as measured by the National Institutes of Health Stroke Scale (NIHSS) score, and site of arterial occlusion on computed tomographic angiography (CTA). NT was performed either after a standard dose of IV rtPA (bridging therapy [BT]) or as single treatment (stand-alone NT [SAT]). Rates of recanalization, symptomatic intracranial bleeding (SIB), mortality, and functional outcome in NT patients were compared with a historical cohort of IV rtPA treated patients (i.e., controls). Three-month favourable outcome was defined as a modified Rankin Scale (mRS) score ≤2. RESULTS Forty-six AIS patients were treated with NT and 51 with IV rtPA. The 2 groups did not differ with regard to demographics, onset NIHSS score (18.5±4 v 17±5; P=.06), or site of intracranial occlusion. Onset-to-treatment time in the NT and IV rtPA groups was 230 minutes (±78) and 176.5 (±44) minutes, respectively (P=.001). NT patients had significantly higher percentages of major improvement (≥8 points NIHSS score change at 24 hours; 26% v 10%; P=.03) and partial/complete recanalization (93.5% v 45%; P<.0001) compared to controls. Treatment by either SAT or BT similarly improved the chance of early recanalization and early clinical improvement. No significant differences were observed in the rate of SIB (11% v 6%), 3-month mortality (24% v 25%), or favorable outcome (40% v 35%) between NT and IV rtPA patients. CONCLUSIONS Despite significantly delayed time of intervention, NT patients had higher rates of recanalization and early major improvement, with no differences in symptomatic intracranial hemorrhages. Early NIHSS score improvement did not translate into better 3-month mortality or outcome. NT seems a safe and effective adjuvant treatment strategy for selected patients with severe AIS secondary to large intracranial vessel occlusion in the anterior circulation.

Induction of corticostriatal LTP by 3-nitropropionic acid requires the activation of mGluR1/PKC pathway.

Huntingtons disease (HD) is an autosomal dominant neurodegenerative disorder typically affecting individuals in midlife. HD is characterized by the selective loss of striatal spiny neurons, while large cholinergic interneurons are spared. An impaired mitochondrial complex II (succinate dehydrogenase, SD) activity is known as a prominent metabolic alteration in HD. Accordingly, chronic treatment with 3-nitropropionic acid (3-NP), an irreversible SD inhibitor, mimics motor abnormalities and pathology of HD in several animal models. We have previously shown that in vitro application of 3-NP induces a long-term potentiation (LTP) of corticostriatal synaptic transmission through NMDA glutamate receptor. Since this 3-NP-induced LTP (3-NP-LTP) is shown by striatal spiny neurons, but not by cholinergic interneurons, it might play a role in the regional and cell type-specific neuronal death observed in HD. Here we investigate the role of group I metabotropic glutamate receptors (mGluRs) in the induction of 3-NP-LTP. We report that selectively blocking mGluR1, but not mGluR5, suppresses 3-NP-LTP induction. Moreover, we show that a PKC-mediated mechanism is involved in the formation of 3-NP-LTP. Characterizing the cellular mechanisms underlying 3-NP-LTP may provide new insights to better understand the processes leading to the selective neuronal loss observed in HD.

Drugs and clinical trials in neurodegenerative diseases

Neurodegenerative diseases are disabling conditions continuously increasing due to aging of population. A disease modifying therapy that slows or stops disease progression is therefore a major unmet medical need. Unfortunately, research for effective treatments is hampered by lack of knowledge on the pathologic processes underpinning these diseases and of reliable biomarkers. Clinical trials are difficult, as they require large populations that need to be followed for very long periods to capture possible effects on disease progression. These difficulties produce frequent failures and waste of human and economic resources. Since research has to continue in this area, until comprehensive knowledge of basic pathologic processes is obtained, alternative study designs can be considered to identify disease modifiers and to reduce costs of clinical studies.

Tissue plasminogen activator is required for striatal post-ischemic synaptic potentiation.

Recent experimental observations indicate that tPA plays a key role in the development of neuronal damage that follows cerebral ischemia and excitotoxicity. In an attempt to clarify how tPA favors ischemia-induced neuronal damage, we performed in vitro electrophysiological experiments in striatal slices by using mice selectively lacking this serine protease. We found that tPA ablation did not affect the membrane depolarization of striatal neurons exposed to combined oxygen and glucose deprivation but fully prevented the induction of NMDA-dependent post-ischemic long-term synaptic potentiation. The absence of striatal post-ischemic potentiation observed in tPA-lacking mice may account for the significant neuroprotection observed in these animals after the occlusion of middle cerebral artery.