[Effect of asiaticoside on systolic blood pressure and relaxation of isolated thoracic aorta of rats].

OBJECTIVE: To investigate the effect of asiaticoside on blood pressure and relaxation of thoracic aorta in rats and explore the underlying mechanism. METHODS: SD rats treated with 50 and 100 mg/kg asiaticoside by daily gavage for 2 weeks were monitored for systolic blood pressure changes, and histological changes of the thoracic aorta were evaluated using HE staining. In isolated rat endothelium-intact and endothelium-denuded thoracic aorta rings, the effects of asiaticoside on relaxation of the aortic rings were tested at baseline and following norepinephrine (NE)- and KCl-induced constriction. The vascular relaxation effect of asiaticoside was further observed in NE-stimulated endothelium-intact rat aortic rings pretreated with L-nitroarginine methyl ester, indomethacin, zinc protoporphyrin Ⅸ, tetraethyl ammonium chloride, glibenclamide, barium chloride, Iberiotoxin, 4-aminopyridine, or TASK-1-IN-1. The aortic rings were treated with KCl and NE followed by increasing concentrations of CaCl2 to investigate the effect of asiaticoside on vasoconstriction induced by external calcium influx and internal calcium release. RESULTS: Asiaticoside at 50 and 100 mg/kg significantly lowered systolic blood pressure in rats without affecting the thoracic aorta histomorphology. While not obviously affecting resting aortic rings with intact endothelium, asiaticoside at 100 mg/kg induced significant relaxation of the rings constricted by KCl and NE, but its effects differed between endothelium-intact and endothelium-denuded rings. In endothelium-intact aortic rings pretreated with indomethacin, ZnPP Ⅸ, barium chloride, glyburide, TASK-1-IN-1 and 4-aminopyridine, asiaticoside did not produce significant effect on NE-induced vasoconstriction, and tetraethylammonium, Iberiotoxin and L-nitroarginine methyl ester all inhibited the relaxation effect of asiaticoside. In KCland NE-treated rings, asiaticoside obviously inhibited CaCl2-induced vascular contraction. CONCLUSION: Asiaticoside induces thoracic aorta relaxation by mediating high-conductance calcium-activated potassium channel opening, promoting nitric oxide release from endothelial cells and regulating Ca2+ influx and outflow, thereby reducing systolic blood pressure in rats.

Alarin potentiates ongoing epileptiform activity in rat brain slices: an in vitro electrophysiological study.

Alarin is a newly discovered neuropeptide that belongs to the galanin peptide family with a wide range of bioactivity in the nervous system. Its function in the brain's autonomic areas has been studied, and it has been reported that alarin is involved in the regulation of excitability in hypothalamic neurons. Its role in the regulation of excitability in the hippocampus, however, is unknown. In this study, we investigated if alarin induced any synchronous discharges or epileptiform activity, and if it had any effect on already initiated epileptiform discharges. We used thick acute horizontal hippocampal slices obtained from 30­ to 35­day­old rats. Extracellular field potential recordings were evaluated in the CA1 region of the hippocampus. Our data demonstrated that, alarin application did not result in any epileptiform activity or abnormal discharges. 4­aminopyridine was applied to induce epileptiform activity in the slices. We found that alarin increased the frequency of interictal­like events and the mean power of local field potentials in the CA1 region of the hippocampus, which was induced by 4­aminopyridine. These results demonstrated for the first time that alarin has a modulatory effect on synchronized neuronal discharges and showed the contribution of the neuropeptide alarin to epilepsy­like conditions.

4-aminopyridine improves evoked potentials and ambulation in the taiep rat: A model of hypomyelination with atrophy of basal ganglia and cerebellum.

The taiep rat is a tubulin mutant with an early hypomyelination followed by progressive demyelination of the central nervous system due to a point mutation in the Tubb4a gene. It shows clinical, radiological, and pathological signs like those of the human leukodystrophy hypomyelination with atrophy of the basal ganglia and cerebellum (H-ABC). Taiep rats had tremor, ataxia, immobility episodes, epilepsy, and paralysis; the acronym of these signs given the name to this autosomal recessive trait. The aim of this study was to analyze the characteristics of somatosensory evoked potentials (SSEPs) and motor evoked potentials (MEPs) in adult taiep rats and in a patient suffering from H-ABC. Additionally, we evaluated the effects of 4-aminopyridine (4-AP) on sensory responses and locomotion and finally, we compared myelin loss in the spinal cord of adult taiep and wild type (WT) rats using immunostaining. Our results showed delayed SSEPs in the upper and the absence of them in the lower extremities in a human patient. In taiep rats SSEPs had a delayed second negative evoked responses and were more susceptible to delayed responses with iterative stimulation with respect to WT. MEPs were produced by bipolar stimulation of the primary motor cortex generating a direct wave in WT rats followed by several indirect waves, but taiep rats had fused MEPs. Importantly, taiep SSEPs improved after systemic administration of 4-AP, a potassium channel blocker, and this drug induced an increase in the horizontal displacement measured in a novelty-induced locomotor test. In taiep subjects have a significant decrease in the immunostaining of myelin in the anterior and ventral funiculi of the lumbar spinal cord with respect to WT rats. In conclusion, evoked potentials are useful to evaluate myelin alterations in a leukodystrophy, which improved after systemic administration of 4-AP. Our results have a translational value because our findings have implications in future medical trials for H-ABC patients or with other leukodystrophies.

Comparative analysis of hippocampal extracellular space uncovers widely altered peptidome upon epileptic seizure in urethane-anaesthetized rats.

BACKGROUND: The brain extracellular fluid (ECF), composed of secreted neurotransmitters, metabolites, peptides, and proteins, may reflect brain processes. Analysis of brain ECF may provide new potential markers for synaptic activity or brain damage and reveal additional information on pathological alterations. Epileptic seizure induction is an acute and harsh intervention in brain functions, and it can activate extra- and intracellular proteases, which implies an altered brain secretome. Thus, we applied a 4-aminopyridine (4-AP) epilepsy model to study the hippocampal ECF peptidome alterations upon treatment in rats. METHODS: We performed in vivo microdialysis in the hippocampus for 3-3 h of control and 4-AP treatment phase in parallel with electrophysiology measurement. Then, we analyzed the microdialysate peptidome of control and treated samples from the same subject by liquid chromatography-coupled tandem mass spectrometry. We analyzed electrophysiological and peptidomic alterations upon epileptic seizure induction by two-tailed, paired t-test. RESULTS: We detected 2540 peptides in microdialysate samples by mass spectrometry analysis; and 866 peptides-derived from 229 proteins-were found in more than half of the samples. In addition, the abundance of 322 peptides significantly altered upon epileptic seizure induction. Several proteins of significantly altered peptides are neuropeptides (Chgb) or have synapse- or brain-related functions such as the regulation of synaptic vesicle cycle (Atp6v1a, Napa), astrocyte morphology (Vim), and glutamate homeostasis (Slc3a2). CONCLUSIONS: We have detected several consequences of epileptic seizures at the peptidomic level, as altered peptide abundances of proteins that regulate epilepsy-related cellular processes. Thus, our results indicate that analyzing brain ECF by in vivo microdialysis and omics techniques is useful for monitoring brain processes, and it can be an alternative method in the discovery and analysis of CNS disease markers besides peripheral fluid analysis.

Ursolic acid inhibits the synaptic release of glutamate and prevents glutamate excitotoxicity in rats.

The present study evaluated the effect of ursolic acid, a natural pentacyclic triterpenoid, on glutamate release in rat cortical nerve terminals (synaptosomes) and its neuroprotection in a kainic acid-induced excitotoxicity rat model. In cortical synaptosomes, ursolic acid produced a concentration-dependent inhibition of evoked glutamate release with a half-maximum inhibition of release value of 9.5 µM, and calcium-free medium and the P/Q -type Ca2+ channel blocker, ω-agatoxin IVA, but not ω-conotoxin GVIA, an N-type Ca2+ channel blocker, prevented the ursoloic acid effect. The molecular docking study indicated that ursolic acid interacted with P/Q-type Ca2+ channels. Ursolic acid also significantly decreased the depolarization-induced activation of Ca2+/calmodulin-dependent protein kinase II (CaMKII) and the subsequent phosphorylation of synapsin I, and the ursolic acid effect on evoked glutamate release was inhibited by the CaMKII inhibitor KN 62 in synaptosomes. In addition, in rats that were intraperitoneally injected with ursolic acid 30 min before kainic acid intraperitoneal injection, cortical neuronal degeneration was attenuated. This effect of ursolic acid in the improvement of kainic acid-induced neuronal damage was associated with the reduction of kainic acid-induced glutamate increase in the cortex of rats; this was characterized by the reduction of glutamate and glutaminase levels and elevation of glutamate dehydrogenase, glutamate transporter 1, glutamate-aspartate transporter, and glutamine synthetase protein levels. These results suggest that ursolic acid inhibits glutamate release from cortical synaptosomes by decreasing P/Q-type Ca2+ channel activity and subsequently suppressing CaMKII and exerts a preventive effect against glutamate neurotoxicity by controlling glutamate levels.

Mangiferin depresses vesicular glutamate release in synaptosomes from the rat cerebral cortex by decreasing synapsin I phosphorylation.

Mangiferin is a glucosyl xanthone that has been shown to be a neuroprotective agent against brain disorders involving excess glutamate. However, the effect of mangiferin on the function of the glutamatergic system has not been investigated. In this study, we used synaptosomes from the rat cerebral cortex to investigate the effect of mangiferin on glutamate release and identify the possible underlying mechanism. We observed that mangiferin produced a concentration-dependent reduction in the release of glutamate elicited by 4-aminopyridine with an IC50 value of 25 µM. Inhibition of glutamate release was blocked by removing extracellular calcium and by treatment with the vacuolar-type H+-ATPase inhibitor bafilomycin A1, which prevents the uptake and storage of glutamate in vesicles. Moreover, we showed that mangiferin decreased the 4-aminopyridine-elicited FM1-43 release and synaptotagmin 1 luminal domain antibody (syt1-L ab) uptake from synaptosomes, which correlated with decreased synaptic vesicle exocytosis. Transmission electron microscopy in synaptosomes also showed that mangiferin attenuated the 4-aminopyridine-elicited decrease in the number of synaptic vesicles. In addition, antagonism of Ca2+/calmodulin-dependent kinase II (CaMKII) and protein kinase A (PKA) counteracted mangiferin's effect on glutamate release. Mangiferin also decreased the phosphorylation of CaMKII, PKA, and synapsin I elicited by 4-aminopyridine treatment. Our data suggest that mangiferin reduces PKA and CaMKII activation and synapsin I phosphorylation, which could decrease synaptic vesicle availability and lead to a subsequent reduction in vesicular glutamate release from synaptosomes.

Cynarin, a caffeoylquinic acid derivative in artichoke, inhibits exocytotic glutamate release from rat cortical nerve terminals (synaptosomes).

The purpose of this study was to evaluate the effect of cynarin, a caffeoylquinic acid derivative in artichoke, on glutamate release elicited by 4-aminopyridine (4-AP) in rat cortical nerve terminals (synaptosomes). We observed that cynarin decreased 4-aminopyridine-elicited glutamate release, which was prevented by the removal of external free Ca2+ with ethylene glycol bis (ß-aminoethyl ether)-N,N,N,N-tetraacetic acid (EGTA) or the blockade of P/Q-type calcium channels with ω-agatoxin IVA. Molecular docking also revealed that cynarin formed a hydrogen bond with the P/Q-type Ca2+ channel, indicating a mechanism of action involving Ca2+ influx inhibition. Additionally, the inhibitory effect of cynarin on glutamate release is associated with a change in the available synaptic vesicles, as cynarin decreased 4-AP-elicited FM1-43 release or hypertonic sucrose-evoked glutamate release from synaptosomes. Furthermore, the suppression of protein kinase A (PKA) prevented the effect of cynarin on 4-AP-elicited glutamate release. 4-AP-elicited PKA and synapsin I or synaptosomal-associated protein of 25 kDa (SNAP-25) phosphorylation at PKA-specific residues were also attenuated by cynarin. Our data indicate that cynarin, through the suppression of P/Q-type Ca2+ channels, inhibits PKA activation and attenuates synapsin I and SNAP-25 phosphorylation at PKA-specific residues, thus decreasing synaptic vesicle availability and contributing to glutamate release inhibition in cerebral cortex terminals.

Fampridine for gait imbalance in patients with multiple sclerosis (MS): a systematic review and meta-analysis.

BACKGROUND: Gait imbalance is one of the frequent complications in subjects with multiple sclerosis (MS). Fampridine (4-aminopyridine) is a potassium-channel blocker that is administered for gait imbalance in MS. Different studies showed the effects of fampridine on gait status based on various tests in subjects with MS. Some showed significant improvement after treatment, and others did not. So, we designed this systematic review, and meta-analysis to estimate the pooled effects of fampridine on gait status in patients with MS. METHODS: The main goal is the evaluation of times of different gait test pre and post fampridine treatment. Two independent expert researchers conducted a systematic and comprehensive search in PubMed, Scopus, EMBASE, Web of Science, and Google Scholar and also gray literature, including references of the references and conference abstracts. The search was done on September 16, 2022. Before-after studies trials reporting scores of the walking tests. We extracted data regarding the total number of participants, first author, publication year, country of origin, mean age, Expanded Disability Status Scale (EDSS), and the results of walking tests. RESULTS: The literature search revealed 1963 studies; after deleting duplicates, 1098 studies remained. Seventy-seven full texts were evaluated. Finally, 18 studies were included for meta-analysis, while most of them were not placebo-controlled trials. The most frequent country of origin was Germany, and the mean age and EDSS ranged between 44 and 56 years and 4 and 6, respectively. The studies were published between 2013 and 2019. The pooled standardized mean difference (SMD) (after-before) of the MS Walking Scale (MSWS-12) was - 1.97 (95%CI: - 1.7, - 1.03) (I2 = 93.1%, P < 0.001). The pooled SMD (after-before) of the six-minute walk test (6MWT) was 0.49 (95%CI: 0.22, - 0.76) (I2 = 0%, P = 0.7). The pooled SMD (after-before) of T Timed 25-Foot Walk (T25FW) was - 0.99(95%CI: - 1.52, - 0.47) (I2 = 97.5%, P < 0.001). CONCLUSION: This systematic review and meta-analysis show that fampridine improves gait imbalance in patients with MS.

Elabela relaxes rat pulmonary artery and trachea via BKCa, KV, and KATP channels.

OBJECTIVE: Elabela is a newly discovered peptide hormone. This study aimed to determine the functional effects and mechanisms of action of elabela in rat pulmonary artery and trachea. MATERIALS AND METHODS: Vascular rings isolated from the pulmonary arteries of male Wistar Albino rats were placed in chambers in the isolated tissue bath system. The resting tension was set to 1 g. After the equilibration period, the pulmonary artery rings were contracted with 10-6 M phenylephrine. Once a stable contraction was achieved, elabela was applied cumulatively (10-10-10-6 M) to the vascular rings. To determine the vasoactive effect mechanisms of elabela, the specified experimental protocol was repeated after the incubation of signaling pathway inhibitors and potassium channel blockers. The effect and mechanisms of action of elabela on tracheal smooth muscle were also determined by a similar protocol. RESULTS: Elabela exhibited a concentration-dependent relaxation in the precontracted rat pulmonary artery rings (p < .001). Maximal relaxation level was 83% (pEC50: 7.947 CI95(7.824-8.069)). Removal of the endothelium, indomethacin incubation, and dideoxyadenosine incubation significantly decreased the vasorelaxant effect levels of elabela (p < .001). Elabela-induced vasorelaxation levels were significantly reduced after iberiotoxin, glyburide, and 4-Aminopyridine administrations (p < .001). L-NAME, methylene blue, apamin, TRAM-34, anandamide, and BaCl2 administrations did not cause a significant change in the vasorelaxant effect level of elabela (p = 1.000). Elabela showed a relaxing effect on precontracted tracheal rings (p < .001). Maximal relaxation level was 73% (pEC50: 6.978 CI95(6.791-7.153)). The relaxant effect of elabela on tracheal smooth muscle was decreased significantly after indomethacin, dideoxyadenosine, iberiotoxin, glyburide, and 4-Aminopyridine incubations (p < .001). CONCLUSIONS: Elabela exerted a prominent relaxant effect in the rat pulmonary artery and trachea. Intact endothelium, prostaglandins, cAMP signaling pathway, and potassium channels (BKCa, KV, and KATP channels) are involved in the vasorelaxant effect of elabela. Prostaglandins, cAMP signaling pathway, BKCa channels, KV channels, and KATP channels also contribute to elabela-induced tracheal smooth muscle relaxant effect.

Inhibitory effect of sulfur dioxide inhalation on Hering-Breuer inflation reflex in mice: role of voltage-gated potassium channels.

Slowly adapting receptors (SARs), vagal mechanosensitive receptors located in the lung, play an important role in regulating the breathing pattern and Hering-Breuer inflation reflex (HBIR). Inhalation of high concentration of sulfur dioxide (SO2), a common environmental and occupational air pollutant, has been shown to selectively block the SAR activity in rabbits, but the mechanism underlying this inhibitory effect remained a mystery. We carried out this study to determine if inhalation of SO2 can inhibit the HBIR and change the eupneic breathing pattern, and to investigate further a possible involvement of voltage-gated K+ channels in the inhibitory effect of SO2 on these vagal reflex-mediated responses. Our results showed 1) inhalation of SO2 (600 ppm; 8 min) consistently abolished both the phasic activity of SARs and their response to lung inflation in anesthetized, artificially ventilated mice, 2) inhalation of SO2 generated a distinct inhibitory effect on the HBIR and induced slow deep breathing in anesthetized, spontaneously breathing mice, and these effects were reversible and reproducible in the same animals, 3) This inhibitory effect of SO2 was blocked by pretreatment with 4-aminopyridine (4-AP), a nonselective blocker of voltage-gated K+ channel, and unaffected by pretreatment with its vehicle. In conclusion, this study suggests that this inhibitory effect on the baseline breathing pattern and the HBIR response was primarily mediated through the SO2-induced activation of voltage-gated K+ channels located in the vagal bronchopulmonary SAR neurons.NEW & NOTEWORTHY This study demonstrated that inhaled sulfur dioxide completely and reversibly abolished the activity of vagal bronchopulmonary slowly adapting receptors, significantly inhibited the apneic response to lung inflation, and induced slow deep breathing in anesthetized mice. More importantly, our results further suggested that this inhibitory effect was mediated through an action of sulfur dioxide and its derivatives on the voltage-gated potassium channels expressed in the slowly adapting receptor sensory neurons innervating the lung.

Potassium channels at the crossroads of neuroinflammation and myelination in experimental models of multiple sclerosis.

Multiple sclerosis (MS) is a chronic demyelinating disease of the central nervous system (CNS), characterized by the presence of localized demyelinating lesions accompanied by an inflammatory reaction, evidently leading to neurodegeneration. A number of ion channels have been implicated in the progression of MS, most notably in cell types involved in the immune response. In the present study, we investigated the implication of two ion channel isoforms, Kv1.1 and Kv1.3, in experimental models of neuroinflammation and demyelination. Immunohistochemical staining of brain sections from the mouse cuprizone model displayed high levels Kv1.3 expression. In an astroglial cellular model of inflammation, stimulation with LPS resulted also in a higher expression of Kv1.1 and Kv1.3, while the introduction of 4-Aminopyridine (4-AP) exacerbated the release of pro-inflammatory chemokine CXCL10. In the oligodendroglial cellular model of demyelination, the alteration in expression levels of Kv1.1 and Kv1.3 may be correlated with that of MBP levels. Indirect co-culture was attempted to further understand the communication between astrocytes and oligodendrocytes, The addition of reactive astrocytes' secretome significantly inhibited the production of MBP, this inhibition was accompanied by an alteration in the expression of Kv1.1 and Kv1.3. The addition of 4-AP in this case did not alleviate the decrease in MBP production. In conclusion, the use of 4-AP generated controversial results, suggesting 4-AP may be used in the early stages of the disease or in the remission phases to stimulate myelination, yet in induced toxic inflammatory environment, 4-AP exacerbated this effect.

KCNA1 gain-of-function epileptic encephalopathy treated with 4-aminopyridine.

Precision medicine for Mendelian epilepsy is rapidly developing. We describe an early infant with severely pharmacoresistant multifocal epilepsy. Exome sequencing revealed the de novo variant p.(Leu296Phe) in the gene KCNA1, encoding the voltage-gated K+ channel subunit KV 1.1. So far, loss-of-function variants in KCNA1 have been associated with episodic ataxia type 1 or epilepsy. Functional studies of the mutated subunit in oocytes revealed a gain-of-function caused by a hyperpolarizing shift of voltage dependence. Leu296Phe channels are sensitive to block by 4-aminopyridine. Clinical use of 4-aminopyridine was associated with reduced seizure burden, enabled simplification of co-medication and prevented rehospitalization.

Sciatic nerve injury regeneration in adult male rats using gelatin methacrylate (GelMA)/poly(2-ethy-2-oxazoline) (PEtOx) hydrogel containing 4-aminopyridine (4-AP).

One of the most important parts of the body is the peripheral nervous system, and any injuries in this system may result in potentially lethal consequences or severe side effects. The peripheral nervous system may not rehabilitate the harmed regions following disabling disorders, which reduce the quality of life of patients. Fortunately, in recent years, hydrogels have been proposed as exogenous alternatives to bridge damaged nerve stumps to create a useful microenvironment for advancing nerve recovery. However, hydrogel-based medicine in the therapy of peripheral nerve injury still needs a lot of improvement. In this study, GelMA/PEtOx hydrogel was used for the first time to deliver 4-Aminopyridine (4-AP) small molecules. 4-AP is a broad-spectrum potassium channel blocker, which has been demonstrated to increase neuromuscular function in patients with various demyelinating disorders. The prepared hydrogel showed a porosity of 92.2 ± 2.6% after 20 min, swelling ratio of 456.01 ± 2.0% after 180 min, weight loss of 81.7 ± 3.1% after 2 weeks, and good blood compatibility as well as sustainable drug release. MTT analysis was performed to assess the cell viability of the hydrogel and proved that the hydrogel is an appropriate substrate for the survival of cells. In vivo studies were performed for functional analysis and the sciatic functional index (SFI) as well as hot plate latency results showed that the use of GelMA/PEtOx+4-AP hydrogel enhances the regeneration compared to the GelMA/PEtOx hydrogel and the control group.

Plantainoside D Reduces Depolarization-Evoked Glutamate Release from Rat Cerebral Cortical Synaptosomes.

Inhibiting the excessive release of glutamate in the brain is emerging as a promising therapeutic option and is efficient for treating neurodegenerative disorders. The aim of this study is to investigate the effect and mechanism of plantainoside D (PD), a phenylenthanoid glycoside isolated from Plantago asiatica L., on glutamate release in rat cerebral cortical nerve terminals (synaptosomes). We observed that PD inhibited the potassium channel blocker 4-aminopyridine (4-AP)-evoked release of glutamate and elevated concentration of cytosolic Ca2+. Using bafilomycin A1 to block glutamate uptake into synaptic vesicles and EDTA to chelate extracellular Ca2+, the inhibitory effect of PD on 4-AP-evoked glutamate release was prevented. In contrast, the action of PD on the 4-AP-evoked release of glutamate in the presence of dl-TBOA, a potent nontransportable inhibitor of glutamate transporters, was unaffected. PD does not alter the 4-AP-mediated depolarization of the synaptosomal membrane potential, suggesting that the inhibitory effect of PD on glutamate release is associated with voltage-dependent Ca2+ channels (VDCCs) but not the modulation of plasma membrane potential. Pretreatment with the Ca2+ channel blocker (N-type) ω-conotoxin GVIA abolished the inhibitory effect of PD on the evoked glutamate release, as did pretreatment with the protein kinase C inhibitor GF109203x. However, the PD-mediated inhibition of glutamate release was eliminated by applying the mitochondrial Na+/Ca2+ exchanger inhibitor CGP37157 or dantrolene, which inhibits Ca2+ release through ryanodine receptor channels. These data suggest that PD mediates the inhibition of evoked glutamate release from synaptosomes primarily by reducing the influx of Ca2+ through N-type Ca2+ channels, subsequently reducing the protein kinase C cascade.

4-Aminopyridine Protects Nigral Dopaminergic Neurons in the MPTP Mouse Model of Parkinson's Disease.

Various pharmacological blockers targeting K+ channel have been identified to be related to the treatment of Parkinson's disease (PD). Previous studies showed that 4-Aminopyridine (4-AP), a wide-spectrum K+ channel blocker, was able to attenuate apomorphine-induced rotation in parkinsonism rats, indicating the possible beneficial effects in attenuation of PD motor symptoms. However, it is unclear whether 4-AP exhibits neuroprotective effects against the neurodegeneration of substantia nigra (SN)-striatum system in PD. In this study, the 1-Methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP)-treated mouse model was employed to evaluate the neuroprotective effects of 4-AP. Results showed that 4-AP inhibited MPTP-induced dopaminergic neuronal loss in the SN as well as dopamine depletion in the striatum. Behavior indexes of open field test and rotarod test confirmed that 4-AP attenuated MPTP-induced motor deficits. We also showed that 4-AP treatment could significantly attenuate the MPTP-induced increase in malonaldehyde (MDA) levels and decrease in superoxide dismutase (SOD) levels. Additionally, MPTP significantly reduced the Bcl-2 expression and promoted the Caspase-3 activation; 4-AP protected dopaminergic neurons against MPTP-induced neurotoxicity by reversing these changes. These results indicate that 4-AP exerts a neuroprotective effect on dopaminergic neurons against MPTP by decreasing oxidative stress and apoptosis. This provides a promising therapeutic target for the treatment of PD.

Cell-specific switch for epileptiform activity: critical role of interneurons in the mouse subicular network.

During epileptic seizures, neuronal network activity is hyper synchronized whereby GABAergic parvalbumin-interneurons may have a key role. Previous studies have mostly utilized 4-aminopyridine to induce epileptiform discharges in brain slices from healthy animals. However, it is not clear if the seizure-triggering ability of parvalbumin-interneurons also holds true without the use of external convulsive agents. Here, we investigate whether synchronized activation of parvalbumin-interneurons or principal cells can elicit epileptiform discharges in subiculum slices of epileptic mice. We found that selective synchronized activation of parvalbumin-interneurons or principal cells with optogenetics do not result in light-induced epileptiform discharges (LIEDs) neither in epileptic nor in normal brain slices. Adding 4-aminopyridine to slices, activation of parvalbumin-interneurons still failed to trigger LIEDs. In contrast, such activation of principal neurons readily generated LIEDs with features resembling afterdischarges. When GABAA receptor blocker was added to the perfusion medium, the LIEDs were abolished. These results demonstrate that in subiculum, selective synchronized activation of principal excitatory neurons can trigger epileptiform discharges by recruiting a large pool of downstream interneurons. This study also suggests region-specific role of principal neurons and interneurons in ictogenesis, opening towards differential targeting of specific brain areas for future treatment strategies tailored for individual patients with epilepsy.

Effects of 4-Aminopyridine on Combined Nerve and Muscle Injury and Bone Loss.

PURPOSE: Musculoskeletal injuries are common, and peripheral nerve injury (PNI) causes significant muscle and bone loss within weeks. After PNI, 4-aminopyridine (4-AP) improves functional recovery and muscle atrophy. However, it is unknown whether 4-AP has any effect on isolated traumatic muscle injury and PNI-induced bone loss. METHODS: A standardized crush injury was performed on the sciatic nerve and muscles in mice, and the mice were assigned to receive normal saline or 4-AP treatment daily for 21 days. The postinjury motor and sensory function recovery was assessed, injured muscles were processed for histomorphometry, and the tibial bone was scanned for bone density. RESULTS: 4-Aminopyridine significantly accelerated the postinjury motor and sensory function recovery, improved muscle histomorphometry, increased muscle satellite cell numbers, and shifted muscle fiber types after combined nerve and muscle injury. Importantly, the 4-AP treatment significantly reduced PNI-induced bone loss. In contrast, in the case of isolated muscle injury, 4-AP had no effect on functional recovery and bone density, but it improved muscle-specific histomorphometry to a limited extent. CONCLUSIONS: These findings demonstrate the potential beneficial effects of 4-AP on the recovery of muscle morphology and bone density after combined muscle and nerve injury. CLINICAL RELEVANCE: Nerve injuries frequently involve muscle and result in rapid muscle and bone atrophy. In this scenario, 4-AP, in addition to accelerating nerve functional recovery, might work as an adjunctive agent to improve the recovery of injured muscle and attenuate PNI-induced bone loss.

Inhibition of Synaptic Glutamate Exocytosis and Prevention of Glutamate Neurotoxicity by Eupatilin from Artemisia argyi in the Rat Cortex.

The inhibition of synaptic glutamate release to maintain glutamate homeostasis contributes to the alleviation of neuronal cell injury, and accumulating evidence suggests that natural products can repress glutamate levels and associated excitotoxicity. In this study, we investigated whether eupatilin, a constituent of Artemisia argyi, affected glutamate release in rat cortical nerve terminals (synaptosomes). Additionally, we evaluated the effect of eupatilin in an animal model of kainic acid (KA) excitotoxicity, particularly on the levels of glutamate and N-methyl-D-aspartate (NMDA) receptor subunits (GluN2A and GluN2B). We found that eupatilin decreased depolarization-evoked glutamate release from rat cortical synaptosomes and that this effect was accompanied by a reduction in cytosolic Ca2+ elevation, inhibition of P/Q-type Ca2+ channels, decreased synapsin I Ca2+-dependent phosphorylation and no detectable effect on the membrane potential. In a KA-induced glutamate excitotoxicity rat model, the administration of eupatilin before KA administration prevented neuronal cell degeneration, glutamate elevation, glutamate-generating enzyme glutaminase increase, excitatory amino acid transporter (EAAT) decrease, GluN2A protein decrease and GluN2B protein increase in the rat cortex. Taken together, the results suggest that eupatilin depresses glutamate exocytosis from cerebrocortical synaptosomes by decreasing P/Q-type Ca2+ channels and synapsin I phosphorylation and alleviates glutamate excitotoxicity caused by KA by preventing glutamatergic alterations in the rat cortex. Thus, this study suggests that eupatilin can be considered a potential therapeutic agent in the treatment of brain impairment associated with glutamate excitotoxicity.

Mechanism of 4-aminopyridine inhibition of the lysosomal channel TMEM175.

Transmembrane protein 175 (TMEM175) is an evolutionarily distinct lysosomal cation channel whose mutation is associated with the development of Parkinson's disease. Here, we present a cryoelectron microscopy structure and molecular simulations of TMEM175 bound to 4-aminopyridine (4-AP), the only known small-molecule inhibitor of TMEM175 and a broad K+ channel inhibitor, as well as a drug approved by the Food and Drug Administration against multiple sclerosis. The structure shows that 4-AP, whose mode of action had not been previously visualized, binds near the center of the ion conduction pathway, in the open state of the channel. Molecular dynamics simulations reveal that this binding site is near the middle of the transmembrane potential gradient, providing a rationale for the voltage-dependent dissociation of 4-AP from TMEM175. Interestingly, bound 4-AP rapidly switches between three predominant binding poses, stabilized by alternate interaction patterns dictated by the twofold symmetry of the channel. Despite this highly dynamic binding mode, bound 4-AP prevents not only ion permeation but also water flow. Together, these studies provide a framework for the rational design of novel small-molecule inhibitors of TMEM175 that might reveal the role of this channel in human lysosomal physiology both in health and disease.

Pharmacological evidence that potassium channels mediate hydrogen sulfide-induced inhibition of the vasopressor sympathetic outflow in pithed rats.

Hydrogen sulfide (H2S) is a gasotransmitter that modulates neurotransmission. Indeed, it has been recently demonstrated that H2S inhibits the sympathetic outflow in male rats, although the mechanisms remain elusive. Thus, this study evaluated the role of potassium channels on NaHS-induced sympathoinhibition. For this purpose, male and female Wistar rats were anesthetized, pithed, and cannulated. After that, animals received selective electrical stimulation of the vasopressor sympathetic outflow (T7-T9). Prior to 310 µg/kg·min NaHS i.v. continuous infusion animals received: (1) bidistilled water (tetraethylammonium, TEA; 4-aminopyridine, 4-AP; and barium chloride, BaCl2; vehicle; 1 ml/kg); (2) TEA (non-selective K+ channels blocker; 16.5 mg/kg); (3) 4-AP (non-selective voltage-dependent K+ channels blocker; 5 mg/kg); (4) BaCl2 (inward rectifier K+ channels blocker; 65 µg/kg); (5) DMF 5%, glucose 10% and NaOH 0.1 N (glibenclamide vehicle; 1 ml/kg); (6) glibenclamide (ATP-dependent K+ channels blocker; 10 mg/kg); (7) DMSO 4% (paxilline vehicle; 1 ml/kg); and (8) paxilline (large-conductance voltage- and Ca2+-activated K+ channel blocker; 90 µg/kg). The NaHS-induced sympathoinhibition was: (1) equally observed in male and female rats; (2) unaffected by vehicles; (3) reversed by the potassium channel blockers. Taken together, our results suggest that NaHS-induced sympathoinhibition does not depend on sex and it is mediated by the activation of several potassium channels.