Can 4-aminopyridine modulate dysfunctional gait networks in Parkinson's disease?

Central Nervous System Stimulants Limit Caffeine Transport at the Blood-Cerebrospinal Fluid Barrier

Caffeine, a common ingredient in energy drinks, crosses the blood-brain barrier easily, but the kinetics of caffeine across the blood-cerebrospinal fluid barrier (BCSFB) has not been investigated. Therefore, 127 autopsy cases (Group A, 30 patients, stimulant-detected group; and Group B, 97 patients, no stimulant detected group) were examined. In addition, a BCSFB model was constructed using human vascular endothelial cells and human choroid plexus epithelial cells separated by a filter, and the kinetics of caffeine in the BCSFB and the effects of 4-aminopyridine (4-AP), a neuroexcitatory agent, were studied. Caffeine concentrations in right heart blood (Rs) and cerebrospinal fluid (CSF) were compared in the autopsy cases: caffeine concentrations were higher in Rs than CSF in Group A compared to Group B. In the BCSFB model, caffeine and 4-AP were added to the upper layer, and the concentration in the lower layer of choroid plexus epithelial cells was measured. The CSF caffeine concentration was suppressed, depending on the 4-AP concentration. Histomorphological examination suggested that choroid plexus epithelial cells were involved in inhibiting the efflux of caffeine to the CSF. Thus, the simultaneous presence of stimulants and caffeine inhibits caffeine transfer across the BCSFB.

Effects of ghrelin on the electrical activities of substantia nigra dopaminergic neurons treated with MPP

Ghrelin, a 28 amino acid brain-gut peptide, has attracted increasing attention for its neuroprotective effect in Parkinson's disease (PD). In view of the pivotal role of excitability of dopaminergic neurons in substantia nigra pars compacta (SNc) in the function of nigrostriatal system, it is of great significance to elucidate the regulation of electrical activity of dopaminergic neurons by ghrelin, especially in PD pathogenesis. In this study, we tackled this issue by probing the effects of ghrelin on the electrophysiological properties of dopaminergic neurons in acute application of Methyl-4-phenylpyridinium (MPP⁺), a potent parkinsonizing agent in primates and rodents, with whole cell patch clamp technique. We first observed that MPP⁺ (10, 20 and 50 μM) inhibited the spontaneous firing activity of dopaminergic neurons with dose-dependent and time-dependent properties. MPP⁺ also hyperpolarized the membrane potential, inhibited the evoked firing activity and reduced the amplitude of the inward rectification characteristic (Sag) in dopaminergic neurons. Importantly, ghrelin (100 nM) could improve the above effects of MPP⁺ on the electrical activities of dopaminergic neurons. The potential mechanism of this phenomenon may be that ghrelin upregulated hyperpolarization-activated cyclic nucleotide-gated channel current (I_h) to antagonize the inhibition of MPP⁺ on I_h, thereby improving the electrical activities of dopaminergic neurons.

Potassium channels and their emerging role in parkinson's disease

Parkinson's disease (PD) is the second most common neurodegenerative disorder, which is associated with a selective loss of dopaminergic neurons in the substantia nigra (SN) and a reduction of dopamine in the striatum. Recently, ion channel dysfunction has been considered a reason for the pathogenesis of PD. Potassium (K⁺) channels are widespread in the central nervous system, and play key roles in modulating cellular excitability, synaptic transmission, and neurotransmitter release. Based on recent studies and data, we propose that K⁺ channels may be new therapeutic targets for PD that slow the progressive loss of dopaminergic neurons and attenuate motor and non-motor symptoms. In this review, we mainly focus on: delayed rectifier, inwardly rectifying, and double-pore K⁺ channels. We summarize the expression and function of these channels in PD-related brain regions. We also discuss the effects of pharmacological blockade or activation of K⁺ channels in the progression and treatment of PD.

Neuronal Voltage Gated Potassium Channels May Modulate Nitric Oxide Synthesis in Corpus Cavernosum

Potassium channels (K⁺Ch) in corpus cavernosum play an important role in the regulation of erection. Nitric oxide (NO) acts through opening of K⁺Ch leading to hyperpolarization and relaxation.

Aim : This study aims to update knowledge about the role of voltage-gated K⁺Ch (K_V) channels in erectile machinery and investigate their role in the control of NO action &/or synthesis in the corpus cavernosum.

Methods : Tension studies using isolated rabbit corpus cavernosum (CC) strips and rat anococcygeus muscle were conducted. Results are expressed as mean ± SEM.

Results : Electric field stimulation (EFS, 2–16 Hz) evoked frequency-dependent relaxations of the PE (phenylephrine)-precontracted CC strips. At 2 Hz, EFS-induced relaxation amounted to 73.17 ± 2.55% in presence 4-AP (10⁻³ M) compared to 41.98 ± 1.45% as control. None of the other selective K⁺Ch blockers tested inhibited EFS-induced relaxation. 4-AP (10⁻³M) significantly attenuated ACh-induced relaxation of rabbit CC where dose-response curve was clearly shifted upward, and attenuated SNP- induced relaxation, for example, to 49.28 ± 4.52% compared to 65.53 ± 3.01% as control at 10⁻⁶ M SNP. The potentiatory effect of 4-AP on EFS was abolished or reversed in presence of N^G-nitro-L-arginine (L-NNA, non-selective nitric oxide synthase inhibitor, 10⁻⁵M, and 2 × 10⁻⁴M). Same results were observed in rat anococcygeus muscle which is a part of the erectile machinery in rats.

Conclusion : This study provides evidence for the presence of prejunctional voltage-gated K⁺Ch in CC, the blockade of which may increase the neuronal synthesis of NO.

Dalfampridine in Parkinson's disease related gait dysfunction: A randomized double blind trial

BACKGROUND

Disease-related gait dysfunction causes extensive disability for persons with Parkinson's disease (PD), with no effective therapies currently available. The potassium channel blocker dalfampridine has been used in multiple neurological conditions and improves walking in persons with multiple sclerosis.

OBJECTIVES

We aimed to evaluate the effect of dalfampridine extended release (D-ER) 10mg tablets twice daily on different domains of walking in participants with PD.

METHODS

Twenty-two participants with PD and gait dysfunction were randomized to receive D-ER 10mg twice daily or placebo for 4weeks in a crossover design with a 2-week washout period. The primary outcomes were change in the gait velocity and stride length.

RESULTS

At 4weeks, gait velocity was not significantly different between D-ER (0.89m/s±0.33) and placebo (0.93m/s±0.27) conditions. The stride length was also similar between conditions: 0.96m±0.38 for D-ER versus 1.06m±0.33 for placebo. D-ER was generally well tolerated with the most frequent side effects being dizziness, nausea and balance problems.

CONCLUSIONS

D-ER is well tolerated in PD patients, however it did not show significant benefit for gait impairment.

Pharmacological Alternatives for the Treatment of Neurodegenerative Disorders: Wasp and Bee Venoms and Their Components as New Neuroactive Tools

Neurodegenerative diseases are relentlessly progressive, severely impacting affected patients, families and society as a whole. Increased life expectancy has made these diseases more common worldwide. Unfortunately, available drugs have insufficient therapeutic effects on many subtypes of these intractable diseases, and adverse effects hamper continued treatment. Wasp and bee venoms and their components are potential means of managing or reducing these effects and provide new alternatives for the control of neurodegenerative diseases. These venoms and their components are well-known and irrefutable sources of neuroprotectors or neuromodulators. In this respect, the present study reviews our current understanding of the mechanisms of action and future prospects regarding the use of new drugs derived from wasp and bee venom in the treatment of major neurodegenerative disorders, including Alzheimer’s Disease, Parkinson’s Disease, Epilepsy, Multiple Sclerosis and Amyotrophic Lateral Sclerosis.

What are the priorities in Parkinson's disease clinical research? A focus on motor complications, gait and cognition

Motor complications, gait and balance disturbance, and cognitive impairment are problems frequently faced by patients with Parkinson's disease and by their treating physicians, and become more common as the disease progresses. Motor complications may be prevented or at least delayed by judicious use of levodopa, with other dopaminergic agents used for their levodopa-sparing effect. Increasingly, research has concentrated on nondopaminergic neurotransmitter systems, which may also have applicability in the management of gait and balance, and also in cognitive impairment in Parkinson's disease. This review, therefore, tackles these issues and discusses possible future treatments that may be available for the management of these challenging comorbidities.