A Neuronal Receptor for Botulinum Toxin

Corticospinal tract: a new hope for the treatment of post-stroke spasticity

Stroke is the third leading cause of death and disability worldwide. Post-stroke spasticity (PSS) is the most common complication of stroke but represents only one of the many manifestations of upper motor neuron syndrome. As an upper motor neuron, the corticospinal tract (CST) is the only direct descending motor pathway that innervates the spinal motor neurons and is closely related to the recovery of limb function in patients with PSS. Therefore, promoting axonal remodeling in the CST may help identify new therapeutic strategies for PSS. In this review, we outline the pathological mechanisms of PSS, specifically their relationship with CST, and therapeutic strategies for axonal regeneration of the CST after stroke. We found it to be closely associated with astroglial scarring produced by astrocyte activation and its secretion of neurotrophic factors, mainly after the onset of cerebral ischemia. We hope that this review offers insight into the relationship between CST and PSS and provides a basis for further studies.

Glycan-modified cellular nanosponges for enhanced neutralization of botulinum toxin

Botulinum toxin (BoNT) is a potent neurotoxin that poses a significant threat as a biowarfare weapon and a potential bioterrorist tool. Currently, there is a lack of effective countermeasures to combat BoNT intoxication in the event of a biological attack. Here, we report on a novel solution by combining cell metabolic engineering with cell membrane coating nanotechnology, resulting in the development of glycan-modified cellular nanosponges that serve as a biomimetic and broad-spectrum BoNT detoxification strategy. Specifically, we increase the expression levels of gangliosides on THP-1 cells through metabolic engineering, and then collect the modified THP-1 cell membrane and coat it onto synthetic polymeric cores, creating cellular nanosponges that closely mimic host cells. Our findings demonstrate that higher levels of gangliosides on the cellular nanosponges result in greater binding capacities with BoNT. The glycan-modified cellular nanosponges exhibit superior efficacy in neutralizing BoNT cytotoxicity in vitro when compared to their unmodified counterparts. In a mouse model of BoNT intoxication, the glycan-modified cellular nanosponges show more pronounced survival benefits when administered both as a treatment and a preventative regimen. These results highlight the potential of cellular nanosponges, especially when modified with glycans, as a promising countermeasure platform against BoNT and related clostridial toxins.

Layer-Specific BTX-A Delivery to the Gastric Muscularis Achieves Effective Weight Control and Metabolic Improvement

The rising incidence of health-endangering obesity constantly calls for more effective treatments. Gastric intramural injection of botulinum neurotoxin A (BTX-A) as a new modality carries great promise yet inconsistent therapeutic efficacy. A layer-specific delivery strategy enabled by dissolving microneedles is hence pioneered to investigate the working site of BTX-A and the resulting therapeutic effects. The drug-loaded tips of the layer-specific gastric paralysis microneedles (LGP-MN) rapidly release and achieve uniform distribution of BTX-A within the designated gastric wall layers. In an obesity rat model, the LGP-MNs not only prove safer than conventional injection, but also demonstrate consistently better therapeutic effects with muscular layer delivery, including 16.23% weight loss (3.06-fold enhancement from conventional injection), 55.20% slower gastric emptying rate, improved liver steatosis, lowered blood lipids, and healthier gut microbiota. Further hormonal study reveals that the elevated production of stomach-derived glucagon-like peptide-1 due to the muscularis-targeting LGP-MN treatment is an important contributor to its unique glucose tolerance-improving effect. This study provides clear indication of the gastric muscularis as the most favorable working site of BTX-A for weight loss and metabolic improvement purposes, and meanwhile suggests that the LGP-MNs could serve as a novel clinical approach to treat obesity and metabolic syndromes.

Botulinum toxin A injection in the treatment of chronic pelvic pain with hypertonic pelvic floor in women: Treatment techniques and results

Chronic pelvic pain (CPP) is an extremely bothersome condition which leads to major effects in women's everyday life. In addition to visceral sources of pain, pelvic floor dysfunction including myofascial pain and spasm on the pelvic floor muscles causing hypertonicity are causes often overlooked. Injecting botulinum toxin type A (BoNT-A) into hypertonic pelvic floor muscles may aid the relaxation of pelvic floor musculature. The muscles that are injected in CPP treatment include the obturator internus, levator ani (pubococcygeus, iliococcygeus, and puborectalis), and coccygeus. Generally, injections can be performed tolerably with safety under conscious sedation combined with local anesthesia. Most practitioners perform BoNT-A injection of pelvic floor muscles using anatomical landmarks identified by manual palpation only. For the precise location of injection sites, some needle guidance techniques were proposed, including electromyography, electrical stimulation, ultrasound, fluoroscopy, and/or computed tomography. Side effects of BoNT-A injection in CPP are rare and self-limiting. Because of the reversible nature of BoNT-A, reinjection appears to be necessary. Increasing proof points out that BoNT-A is a promising treatment option for CPP in women. We conducted a review of published literature in Pubmed, using chronic pelvic pain in women, hypertonic pelvic floor, and botulinum toxin as the keywords. This article aims to summarize the treatment techniques and results of BoNT-A injection for hypertonic pelvic floor in women with chronic pelvic pain.

Protective Effect of Botulinum Toxin against Ultraviolet-Induced Skin Pigmentation

BACKGROUND

Hyperpigmentation following ultraviolet irradiation has cosmetic concerns. Botulinum toxin type A can favorably affect skin pigmentation. However, the mechanism of skin pigmentation is unclear.

METHODS

In vitro, human epidermal melanocytes were co-cultured with human keratinocytes. After cells were treated with botulinum toxin type A, cell morphology, proliferation, and dendricity were analyzed, and immunofluorescence, tyrosinase activity, and melanin contents were determined. To evaluate the effect of botulinum toxin type A on ultraviolet B-irradiated mouse skin, ultraviolet B alone was applied to one side of the back of each mouse as a control, whereas ultraviolet B plus injection of botulinum toxin type A was applied to the contralateral side. Skin pigmentation, histology, and the number of dihydroxyphenylalanine-positive melanocytes were evaluated. The L* colorimeter value was measured. Enzyme-linked immunosorbent assay determinations of basic fibroblast growth factor, interleukin-1 alpha, and prostaglandin E2 were performed.

RESULTS

Immunohistochemical staining revealed botulinum toxin type A in the cytoplasm of melanocytes and in the positive control. In vitro, melanocyte dendricity and melanin contents were decreased slightly but significantly (p < 0.05) after botulinum toxin type A treatment. In vivo, botulinum toxin type A suppressed skin pigmentation. The number of dihydroxyphenylalanine-positive melanocytes was also significantly lower than in the control side. Tyrosinase activity and melanin content were also significantly reduced (p < 0.05). Botulinum toxin type A also significantly reduced the amounts of basic fibroblast growth factor, interleukin-1 alpha, and prostaglandin E2 (all p < 0.05).

CONCLUSION

Botulinum toxin type A can suppress epidermal melanogenesis through both direct and indirect mechanisms.

Innervation zone distribution of the biceps brachii muscle examined using voluntary and electrically-evoked high-density surface EMG

BACKGROUND

High density surface electromyography (EMG) can be used to estimate muscle innervation zones (IZ). The objective of this study was to compare the differences in the distribution of the biceps brachii (BB) IZ derived from voluntary contractions (VC) and electrical stimulation (ES) of the musculocutaneous nerve.

METHODS

Surface EMG signals were recorded from the medial and lateral BB with two 64-channel high density electrode matrices in eight healthy men. The surface EMG was recorded at different percentages of the maximal voluntary contraction (MVC) force (20-100% MVC) and at different percentages of the current needed to elicit a maximal M-wave (20-100% Imax). The IZs of the medial and lateral BB were identified from the EMG signals and expressed as a row number within a given medial-lateral column.

RESULTS

ES current intensity had no significant effect on the group mean IZ location (p > 0.05). However, The IZ during VC was located more proximally with increasing force (p < 0.05), likely due to muscle shortening. The position of the IZ varied slightly (by up to ~ 8 mm) in a medial-lateral direction under both contraction types, but this spatial effect was not significant. The IZ during ES and weak VC (20, 40% MVC) was similar (p > 0.05), but was more proximal in the latter than the former during 60-100% MVC (p < 0.05).

CONCLUSION

ES can be used to detect spatial differences in IZ location free of the confounding effects of muscle shortening and recruitment order of different sized motor units. The method may prove beneficial for locating the IZ in patients who lack voluntary control of their musculature.

Effectiveness of Robot-Assisted Upper Limb Training on Spasticity, Function and Muscle Activity in Chronic Stroke Patients Treated With Botulinum Toxin: A Randomized Single-Blinded Controlled Trial

Background: The combined use of Robot-assisted UL training and Botulinum toxin (BoNT) appear to be a promising therapeutic synergism to improve UL function in chronic stroke patients.

Objective: To evaluate the effects of Robot-assisted UL training on UL spasticity, function, muscle strength and the electromyographic UL muscles activity in chronic stroke patients treated with Botulinum toxin.

Methods: This single-blind, randomized, controlled trial involved 32 chronic stroke outpatients with UL spastic hemiparesis. The experimental group (n = 16) received robot-assisted UL training and BoNT treatment. The control group (n = 16) received conventional treatment combined with BoNT treatment. Training protocols lasted for 5 weeks (45 min/session, two sessions/week). Before and after rehabilitation, a blinded rater evaluated patients. The primary outcome was the Modified Ashworth Scale (MAS). Secondary outcomes were the Fugl-Meyer Assessment Scale (FMA) and the Medical Research Council Scale (MRC). The electromyographic activity of 5 UL muscles during the “hand-to-mouth” task was explored only in the experimental group and 14 healthy age-matched controls using a surface Electromyography (EMGs).

Results: No significant between-group differences on the MAS and FMA were measured. The experimental group reported significantly greater improvements on UL muscle strength (p = 0.004; Cohen's d = 0.49), shoulder abduction (p = 0.039; Cohen's d = 0.42), external rotation (p = 0.019; Cohen's d = 0.72), and elbow flexion (p = 0.043; Cohen's d = 1.15) than the control group. Preliminary observation of muscular activity showed a different enhancement of the biceps brachii activation after the robot-assisted training.

Conclusions: Robot-assisted training is as effective as conventional training on muscle tone reduction when combined with Botulinum toxin in chronic stroke patients with UL spasticity. However, only the robot-assisted UL training contributed to improving muscle strength. The single-group analysis and the qualitative inspection of sEMG data performed in the experimental group showed improvement in the agonist muscles activity during the hand-to-mouth task.

Clinical Trial Registration:www.ClinicalTrials.gov, identifier: NCT03590314

[Function of synaptic vesicle protein 2A (SV2A) as a novel therapeutic target for epilepsy]

Epilepsy is a chronic neurologic disease characterized by recurrent seizures, affecting nearly 1% of the population. Synaptic vesicle protein 2A (SV2A) is a membrane protein specifically expressed in synaptic vesicles and is now implicated in the pathogenesis of epileptic disorders. This is because 1) Sv2a-knockout mice exhibit severe seizures, 2) SV2A serves as a specific binding site for certain antiepileptics (e.g., levetiracetam and its analogues) and 3) the SV2A expression changes under various epileptic conditions both in animals (e.g., kindling) and humans (e.g., intractable temporal lobe epilepsy and focal cortical dysplasia). Furthermore, it has been shown that a missense mutation in the SV2A gene caused intractable epilepsy, involuntary movements and developmental retardation, indicating a causative role of SV2A dysfunction in epilepsy. In order to explore the mechanism of SV2A in modulating development of epileptogenesis, we recently developed a novel rat model (Sv2a^L174Q rat) carrying a missense mutation (Leu174Gln) in the Sv2a gene. These rats were highly susceptible to the kindling development associated with repeated pentylenetetrazole treatments or electrical stimulations of the amygdala. In addition, the Sv2a^L174Q mutation specifically impaired depolarization-induced GABA, but not glutamate, release in the hippocampus and amygdala. All this evidence indicates that the SV2A-GABAergic system plays a crucial role in modulating epileptogenesis and encourages discovery research into the novel antiepileptic agents which enhance the function of the SV2A-GABA system.

[Spasticity: from pathophysiology to treatment]

The article presents modern views on the pathophysiology of spasticity, which is a frequent disabling consequence to the upper motor neuron (UMN) damage. Morphological and functional system of motion organization and the changes after the UMN damage is considered. The authors analyze existing definitions of spasticity. Stages of spasticity development are described in the context of neuroplasticity as well as in the framework of pathogenesis and sanogenesis. Existing ideas of its pathogenesis are compared with the typical clinical symptoms. The occurring pathological processes in muscles, tendons and joints that can aggravate the development of spasticity and complicate the diagnosis are considered. In addition, the main pathological spasticity patterns are described and the current development of diagnostic techniques is estimated. A review of main methods of spasticity treatment is presented. Special attention is paid to the botulinum neurotoxin type A (BoNT) preparations and central action muscle relaxants. The pathophysiological basement for complex treatment of spasticity as a part of the general rehabilitation process is given, so that the BoNT can be considered as the obligatory element of standard rehabilitation programs.

Post-stroke Hemiplegic Gait: New Perspective and Insights

Walking dysfunction occurs at a very high prevalence in stroke survivors. Human walking is a phenomenon often taken for granted, but it is mediated by complicated neural control mechanisms. The automatic process includes the brainstem descending pathways (RST and VST) and the intraspinal locomotor network. It is known that leg muscles are organized into modules to serve subtasks for body support, posture and locomotion. Major kinematic mechanisms are recognized to minimize the center of gravity (COG) displacement. Stroke leads to damage to motor cortices and their descending corticospinal tracts and subsequent muscle weakness. On the other hand, brainstem descending pathways and the intraspinal motor network are disinhibited and become hyperexcitable. Recent advances suggest that they mediate post-stroke spasticity and diffuse spastic synergistic activation. As a result of such changes, existing modules are simplified and merged, thus leading to poor body support and walking performance. The wide range and hierarchy of post-stroke hemiplegic gait impairments is a reflection of mechanical consequences of muscle weakness, spasticity, abnormal synergistic activation and their interactions. Given the role of brainstem descending pathways in body support and locomotion and post-stroke spasticity, a new perspective of understanding post-stroke hemiplegic gait is proposed. Its clinical implications for management of hemiplegic gait are discussed. Two cases are presented as clinical application examples.

A simulation study on the relation between the motor unit depth and action potential from multi-channel surface electromyography recordings

To investigate the spatial information of individual motor unit (MUs) using multi-channel surface electromyography (EMG) decomposition. The K-means clustering convolution kernel compensation (KmCKC) approach was employed to detect the innervation pulse trains (IPTs) from the simulated surface EMG signals, and the motor unit action potentials (MUAPs) were evaluated using the spike-triggered average (STA) technique. The relationships between the features of MUAP and MU depth were determinated with a least square fitting method. The errors of peak-to-peak (PTP) amplitude of reconstructed MUAPs were less than 5.73%, even with 0 dB signal-to-noise (SNR). The fitting errors with nonlinear model were less than 5.55% for SNRs higher than 20 dB. The results show that it is possible to provide a useful method for estimating MU depth from surface EMG recordings. It is expected to extend the applicability of surface EMG technique to more challenging clinical applications.

Spasticity, Motor Recovery, and Neural Plasticity after Stroke

Spasticity and weakness (spastic paresis) are the primary motor impairments after stroke and impose significant challenges for treatment and patient care. Spasticity emerges and disappears in the course of complete motor recovery. Spasticity and motor recovery are both related to neural plasticity after stroke. However, the relation between the two remains poorly understood among clinicians and researchers. Recovery of strength and motor function is mainly attributed to cortical plastic reorganization in the early recovery phase, while reticulospinal (RS) hyperexcitability as a result of maladaptive plasticity, is the most plausible mechanism for poststroke spasticity. It is important to differentiate and understand that motor recovery and spasticity have different underlying mechanisms. Facilitation and modulation of neural plasticity through rehabilitative strategies, such as early interventions with repetitive goal-oriented intensive therapy, appropriate non-invasive brain stimulation, and pharmacological agents, are the keys to promote motor recovery. Individualized rehabilitation protocols could be developed to utilize or avoid the maladaptive plasticity, such as RS hyperexcitability, in the course of motor recovery. Aggressive and appropriate spasticity management with botulinum toxin therapy is an example of how to create a transient plastic state of the neuromotor system that allows motor re-learning and recovery in chronic stages.

Imaging three-dimensional innervation zone distribution in muscles from M-wave recordings

OBJECTIVE

To localize neuromuscular junctions in skeletal muscles in vivo which is of great importance in understanding, diagnosing and managing of neuromuscular disorders.

APPROACH

A three-dimensional global innervation zone imaging technique was developed to characterize the global distribution of innervation zones, as an indication of the location and features of neuromuscular junctions, using electrically evoked high-density surface electromyogram recordings.

MAIN RESULTS

The performance of the technique was evaluated in the biceps brachii of six intact human subjects. The geometric centers of the distributions of the reconstructed innervation zones were determined with a mean distance of 9.4  ±  1.4 cm from the reference plane, situated at the medial epicondyle of the humerus. A mean depth was calculated as 1.5  ±  0.3 cm from the geometric centers to the closed points over the skin. The results are consistent with those reported in previous histology studies. It was also found that the volumes and distributions of the reconstructed innervation zones changed as the stimulation intensities increased until the supramaximal muscle response was achieved.

SIGNIFICANCE

Results have demonstrated the high performance of the proposed imaging technique in noninvasively imaging global distributions of the innervation zones in the three-dimensional muscle space in vivo, and the feasibility of its clinical applications, such as guiding botulinum toxin injections in spasticity management, or in early diagnosis of neurodegenerative progression of amyotrophic lateral sclerosis.

Three-Dimensional Innervation Zone Imaging from Multi-Channel Surface EMG Recordings

There is an unmet need to accurately identify the locations of innervation zones (IZs) of spastic muscles, so as to guide botulinum toxin (BTX) injections for the best clinical outcome. A novel 3D IZ imaging (3DIZI) approach was developed by combining the bioelectrical source imaging and surface electromyogram (EMG) decomposition methods to image the 3D distribution of IZs in the target muscles. Surface IZ locations of motor units (MUs), identified from the bipolar map of their MU action potentials (MUAPs) were employed as a prior knowledge in the 3DIZI approach to improve its imaging accuracy. The performance of the 3DIZI approach was first optimized and evaluated via a series of designed computer simulations, and then validated with the intramuscular EMG data, together with simultaneously recorded 128-channel surface EMG data from the biceps of two subjects. Both simulation and experimental validation results demonstrate the high performance of the 3DIZI approach in accurately reconstructing the distributions of IZs and the dynamic propagation of internal muscle activities in the biceps from high-density surface EMG recordings.

Safety and Efficacy of Botulinum Toxin to Preserve Gland Function after Radiotherapy in Patients with Head and Neck Cancer: A Prospective, Randomized, Placebo-Controlled, Double-Blinded Phase I Clinical Trial

This prospective, randomized, placebo-controlled, double-blinded phase I clinical trial investigates safety and efficacy of botulinum toxin (BoNT) to preserve gland function after radiotherapy in patients with head and neck cancer. Twelve patients with advanced head and neck cancer were injected with BoNT into the submandibular glands prior to primary radiochemotherapy. Six patients received BoNT/A and 6 patients BoNT/A and B, half of each subgroup into their left and the other half into their right gland. As an internal control, sodium chloride was injected into the respective contralateral gland (placebo). For the evaluation of the salivary gland function, technetium pertechnetate salivary gland scintigraphy was performed before and after the end of radiotherapy. BoNT/A and B were well tolerated. Analysis of the scintigraphic data revealed no statistically significant difference between BoNT and placebo regarding the scintigraphic uptake difference (pBoNT/A = 0.84 and pBoNT/A-B = 0.56 for BoNT/A vs. placebo and BoNT/A-B vs. placebo, respectively). We also found no significant difference in treatment between BoNT and placebo in terms of salivary excretion fraction (pBoNT/A = 0.44; pBoNT/A-B = 0.44). This study demonstrates that BoNT can be safely combined with radiochemotherapy. Dosing and timing of BoNT injection should be further investigated for efficacy analysis.

Botulinum Toxin Injection for Spastic Scapular Dyskinesia After Stroke: Case Series

Spastic scapular dyskinesia after stroke is rare, which causes impaired shoulder active range of motion (ROM). To date, there has been no report about botulinum toxin injection to spastic periscapular muscles. This study presents botulinum toxin A injection for management of spastic periscapular muscles after stroke in 2 cases.This is a retrospective study of 2 cases of spastic scapular dyskinesia after stroke. Spasticity of periscapular muscles including rhomboid and lower trapezius was diagnosed by physical examination and needle electromyographic study. Botulinum toxin was injected into the spastic periscapular muscles under ultrasound imaging guidance.During the 3-week follow-up visit after injection, both patients showed increased shoulder active ROM, without any sign of scapular destabilization.The results suggest that botulinum toxin injection to spastic periscapular muscles can increase shoulder active ROM without causing scapular destabilization in patients with poststroke spastic scapular dyskinesia.

Down-regulation of TGF-b1, TGF-b receptor 2, and TGF-b-associated microRNAs, miR-20a and miR-21, in skin lesions of sulfur mustard-exposed Iranian war veterans

Sulfur mustard (SM) affects divergent cellular pathways including cell cycle, apoptosis, necrosis, and inflammatory responses. SM-induced lesions in skin include late-onset hyper-pigmentation, xerosis, and atrophy. It seems that TGF-b signaling pathway is a major player for SM pathogenesis. Here, we have employed a real-time polymerase chain reaction (PCR) approach to evaluate the expression alterations of all TGF-b variants and their receptors in skin biopsies obtained from 10 Iran-Iraq war veterans. Using specific LNA primers, the expression alteration of a TGF-bR2 regulator, miR-20a, and TGF-b downstream target, miR-21, was also assessed in the same samples Our real-time PCR data revealed a significant down-regulation of TGF-b1 and TGF-bR2, the major mediators of TGF-b signaling pathway, in skin biopsies of SM-exposed patients (p = 0.0015 and p = 0.0115, respectively). Down-regulation of TGF-b signaling pathway seems to contribute in severe inflammation observed in SM-exposed patients' tissues. MiR-20a and miR-21, as two important TGF-b associated microRNAs (miRNAs), were also down-regulated in SM-exposed skin lesions, compared to those of control group (p = 0.0003). Based on our findings, these miRNAs could be directly or indirectly involve in the pathogenesis of SM. Altogether, our data suggest the suitability of TGF-b1, TGF-bR2, as well as miR-20a and miR-21 as potential biomarkers for diagnosis and treatment of SM-exposed patients.

Fusion proteins and select lipids cooperate as membrane receptors for the soluble N-ethylmaleimide-sensitive factor attachment protein receptor (SNARE) Vam7p

Vam7p, the vacuolar soluble Qc-SNARE, is essential for yeast vacuole fusion. The large tethering complex, homotypic fusion and vacuole protein sorting complex (HOPS), and phosphoinositides, which interact with the Vam7p PX domain, have each been proposed to serve as its membrane receptors. Studies with the isolated organelle cannot determine whether these receptor elements suffice and whether ligands or mutations act directly or indirectly on Vam7p binding to the membrane. Using pure components that are active in reconstituted vacuolar fusion, we now find that Vam7p binds to membranes through its combined affinities for several vacuolar membrane constituents: HOPS, phosphatidylinositol 3-phosphate, SNAREs, and acidic phospholipids. Acidic lipids allow low concentrations of Vam7p to suffice for fusion; without acidic lipids, the block to fusion is partially bypassed by high concentrations of Vam7p.

Distribution of SV2C mRNA and protein expression in the mouse brain with a particular emphasis on the basal ganglia system

Synaptic vesicle 2 proteins (SV2), SV2A, SV2B and SV2C, are integral proteins localized on the surface of synaptic vesicles in all neurons. SV2 proteins appear to play an important, but not yet fully understood role in synaptic vesicle exocytosis and neurotransmitter release. Moreover, SV2 seems to be the receptor of the botulinum neurotoxin A. In the present study, using single and double-labeling fluorescent immunohistochemistry and in situ hybridization we have identified the brain pattern of SV2C mRNA and protein expression in mice. Our results indicated that SV2C protein was expressed in a small subset of brain regions including the olfactory bulb, olfactory tubercle, nucleus accumbens, caudate-putamen, ventral pallidum, globus pallidus, substantia nigra and the ventral tegmental area. These results were confirmed by means of in situ hybridization, except for the globus pallidus and the substantia nigra pars reticulata, in which no labeling was found, suggesting that SV2C-positive fibers in these areas are terminals of striatal projecting neurons. In the striatum, we found that, in addition to its presence in the projection neurons, SV2C was densely expressed in a fraction (around 45%) of cholinergic interneurons. In addition, our data also showed that SV2C was densely expressed in most dopaminergic neurons in the substantia nigra pars compacta and the ventral tegmental area (more than 70% of the dopaminergic neurons analyzed were SV2C-positive). Altogether, our results suggest that SV2C may contribute to the regulation of neurotransmitter release and synaptic transmission in the basal ganglia including cholinergic striatal interneurons and nigro-striatal/mesolimbic dopamine neurons.

Evaluation of the heterogeneous reactivity of the syntaxin molecules on the inner leaflet of the plasma membrane

The soluble N-ethylmaleimide-sensitive fusion (NSF) attachment protein (SNAP) receptor (SNARE) protein syntaxin 1A forms nano-sized clusters (membrane rafts) on the plasma membrane (PM) that are in equilibrium with freely diffusing syntaxin molecules. SNARE-complex formation between syntaxin 1A and SNAP-25 (synaptosome-associated protein of 25 kDa) on the PM and synaptobrevin 2 on the vesicles (trans-SNAREs) is crucial for vesicle priming and fusion. This process might be impeded by the spontaneous accumulation of non-fusogenic cis-SNARE complexes formed when all three SNARE proteins reside on the PM. We investigated the kinetics of cis-SNARE complex assembly and disassembly and both exhibited biphasic behavior. The experimental measurements were analyzed through integration of differential rate equations pertinent to the reaction mechanism and through the application of a heuristic search for time constants and concentrations using a genetic algorithm. Reconstruction of the measurements necessitated the partitioning of syntaxin into two phases that might represent the syntaxin clusters and free syntaxin outside the clusters. The analysis suggests that most of the syntaxin in the clusters is concentrated in a nonreactive form. Consequently, cis-SNARE complex assembly in the clusters is substantially slower than outside the rafts. Interestingly, the clusters also mediate efficient disassembly of cis-SNARE complexes possibly attributable to the high local concentration of complexes in the clusters area that allows efficient disassembly by the enzymatic reaction of NSF.

Levetiracetam has a time- and stimulation-dependent effect on synaptic transmission

We recently reported that rodent hippocampal slices incubated with levetiracetam for 3h had altered responses to repetitive stimulation and reduced neurotransmitter release. However, our experiments failed to determine the actual time course of diminished transmission in individual slices followed over time. We have now been able to record from the same slices for up to 3h to determine the latency of the levetiracetam effect after the onset of exposure. Within 30 min of levetiracetam exposure, the later field potentials of a burst were reduced. Between 60 and 180 min the relative size of later field potentials remained stable. Similar time-dependent reductions were not seen in control slices or in slices exposed to the inactive levetiracetam isomer UCB L060. These new results establish a clear time dependence of the levetiracetam effect, even in vitro, and are best explained by levetiracetam acting within neurons to alter synaptic vesicle release.