Guanidine Affects Differentially the Twitch Response of Diaphragm, Extensor Digitorum Longus and Soleus Nerve-Muscle Preparations of Mice

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Produtos naturais como candidatos a fármacos úteis no tratamento do mal de Alzheimer

Alzheimer's disease (AD) is a progressive neurodegenerative pathology with severe economic and social impact. There is currently no cure, although cholinesterase inhibitors provide effective temporary relief of symptoms in some patients. Nowadays drug research and development are based on the cholinergic hypothesis that supports the cognition improvement by regulation of the synthesis and release of acetylcholine in the brain. There are only four commercial medicines approved for treatment of AD and natural products have played an important role in the research for new acetylcholinesterase inhibitors.

Amplification of neuromuscular transmission by methylprednisolone involves activation of presynaptic facilitatory adenosine A(2A) receptors and redistribution of synaptic vesicles

The mechanisms underlying improvement of neuromuscular transmission deficits by glucocorticoids are still a matter of debate despite these compounds have been used for decades in the treatment of autoimmune myasthenic syndromes. Besides their immunosuppressive action, corticosteroids may directly facilitate transmitter release during high-frequency motor nerve activity. This effect coincides with the predominant adenosine A(2A) receptor tonus, which coordinates the interplay with other receptors (e.g. muscarinic) on motor nerve endings to sustain acetylcholine (ACh) release that is required to overcome tetanic neuromuscular depression in myasthenics. Using myographic recordings, measurements of evoked [H-3]ACh release and real-time video microscopy with the FM4-64 fluorescent dye, results show that tonic activation of facilitatory A(2A) receptors by endogenous adenosine accumulated during 50 Hz bursts delivered to the rat phrenic nerve is essential for methylprednisolone (03 mM)-induced transmitter release facilitation, because its effect was prevented by the A(2A) receptor antagonist, ZM 241385 (10 nM). Concurrent activation of the positive feedback loop operated by pirenzepine-sensitive muscarinic M-1 autoreceptors may also play a role, whereas the corticosteroid action is restrained by the activation of co-expressed inhibitory M-2 and Al receptors blocked by methoctramine (0.1 mu M) and DPCPX (2.5 nM), respectively. Inhibition of FM4-64 loading (endocytosis) by methylprednisolone following a brief tetanic stimulus (50 Hz for 5 s) suggests that it may negatively modulate synaptic vesicle turnover, thus increasing the release probability of newly recycled vesicles. Interestingly, bulk endocytosis was rehabilitated when methylprednisolone was co-applied with ZM241385. Data suggest that amplification of neuromuscular transmission by methylprednisolone may involve activation of presynaptic facilitatory adenosine A(2A) receptors by endogenous adenosine leading to synaptic vesicle redistribution. (C) 2014 Elsevier Ltd. All rights reserved.

Toxina botulínica para la secreción descontrolada de saliva : presentación de un caso

La neurotoxina botulínica es producida por la bacteria anaerobia Clostridium botulinum (NTBo). Bloquea la transmisión neuromuscular por lo cual es utilizada para el tratamiento de enfermedades con hiperactividad muscular, bloqueando la liberación de acetilcolina y así la transmisión sináptica en la unión neuromuscular, lo que lleva al debilitamiento y atrofia de los músculos. Este mecanismo de acción motivó el uso de la toxina botulínica en las enfermedades con elevado tono muscular, como la distonía y la espasticidad, por lo cual también ha revolucionado la opción de tratamiento de los trastornos autónomos de hipersecreción. La sialorrea es un síntoma común en diversas enfermedades neurológicas. Las inyecciones de toxina botulínica, guiadas por ultrasonidos en las glándulas salivales, produce una disminución de la salivación excesiva en niños con deficiencias neurológicas como parálisis cerebral. La utilización de la toxina botulínica tipo A ha sido sugerida como tratamiento de la sialorrea en pacientes con parálisis cerebral (PC). Esta recomendación ha sido hecha por el efecto anticolinérgico de esta sustancia, principalmente por su capacidad para bloquear la liberación de acetilcolina a nivel de las membranas pre-sinápticas Aunque la respuesta al tratamrento es distinta en cada niño, en general se ha observado que cuanto más a menudo se utiliza la toxlna botulínica y más alta es la dosis utilizada, los resultados son mejores. Los expertos consideran conveniente el procedimiento porque muchos de estos pacientes están utilizando la toxina botulínica para sus problemas musculares y las distrntas condiciones pueden ser tratadas al mismo tiempo Se reporta la descripción de la aplicación de toxina botulínica en una paciente niña que concurre al Instituto de Rehabilitación Infantil TELETON de la ciudad de Valparaíso, Chile, con un trastorno motor severo y con salivación incontrolada persistente que provoca enfermedades respiratorias a repetición

Neurosteroids: Deficient cognitive performance in aged rats depends on low pregnenolone sulfate levels in the hippocampus

Pregnenolone sulfate (PREG S) is synthesized in the nervous system and is a major neurosteroid in the rat brain. Its concentrations were measured in the hippocampus and other brain areas of single adult and aged (22–24 month-old) male Sprague–Dawley rats. Significantly lower levels were found in aged rats, although the values were widely scattered and reached, in about half the animals, the same range as those of young ones. The spatial memory performances of aged rats were investigated in two different spatial memory tasks, the Morris water maze and Y-maze. Performances in both tests were significantly correlated and, accompanied by appropriate controls, likely evaluated genuine memory function. Importantly, individual hippocampal PREG S and distance to reach the platform in the water maze were linked by a significant correlation, i.e., those rats with lower memory deficit had the highest PREG S levels, whereas no relationship was found with the PREG S content in other brain areas (amygdala, prefrontal cortex, parietal cortex, striatum). Moreover, the memory deficit of cognitively impaired aged rats was transiently corrected after either intraperitoneal or bilateral intrahippocampal injection of PREG S. PREG S is both a γ-aminobutyric acid antagonist and a positive allosteric modulator at the N-methyl-d-aspartate receptor, and may reinforce neurotransmitter system(s) that decline with age. Indeed, intracerebroventricular injection of PREG S was shown to stimulate acetylcholine release in the adult rat hippocampus. In conclusion, it is proposed that the hippocampal content of PREG S plays a physiological role in preserving and/or enhancing cognitive abilities in old animals, possibly via an interaction with central cholinergic systems. Thus, neurosteroids should be further studied in the context of prevention and/or treatment of age-related memory disorders.

Galantamine: Effect on nicotinic receptor binding, acetylcholinesterase inhibition, and learning

Classical eyeblink conditioning is a well-characterized model paradigm that engages the septohippocampal cholinergic system. This form of associative learning is impaired in normal aging and severely disrupted in Alzheimer's disease (AD). Some nicotinic cholinergic receptor subtypes are lost in AD, making the use of nicotinic allosterically potentiating ligands a promising therapeutic strategy. The allosterically potentiating ligand galantamine (Gal) modulates nicotinic cholinergic receptors to increase acetylcholine release as well as acting as an acetylcholinesterase (AChE) inhibitor. Gal was tested in two preclinical experiments. In Experiment 1 with 16 young and 16 older rabbits, Gal (3.0 mg/kg) was administered for 15 days during conditioning, and the drug significantly improved learning, reduced AChE levels, and increased nicotinic receptor binding. In Experiment 2, 53 retired breeder rabbits were tested over a 15-wk period in four conditions. Groups of rabbits received 0.0 (vehicle), 1.0, or 3.0 mg/kg Gal for the entire 15-wk period or 3.0 mg/kg Gal for 15 days and vehicle for the remainder of the experiment. Fifteen daily conditioning sessions and subsequent retention and relearning assessments were spaced at 1-month intervals. The dose of 3.0 mg/kg Gal ameliorated learning deficits significantly during acquisition and retention in the group receiving 3.0 mg/kg Gal continuously. Nicotinic receptor binding was significantly increased in rabbits treated for 15 days with 3.0 mg/kg Gal, and all Gal-treated rabbits had lower levels of brain AChE. The efficacy of Gal in a learning paradigm severely impaired in AD is consistent with outcomes in clinical studies.

A genetic selection for Caenorhabditis elegans synaptic transmission mutants.

We have isolated 165 Caenorhabditis elegans mutants, representing 21 genes, that are resistant to inhibitors of cholinesterase (Ric mutants). Since mutations in 20 of the genes appear not to affect acetylcholine reception, we suggest that reduced acetylcholine release contributes to the Ric phenotype of most Ric mutants. Mutations in 15 of the genes lead to defects in a gamma-aminobutyric acid-dependent behavior; these genes are likely to encode proteins with general, rather than cholinergic-specific, roles in synaptic transmission. Ten of the genes have been cloned. Seven encode homologs of proteins that function in the synaptic vesicle cycle: two encode cholinergic-specific proteins, while five encode general presynaptic proteins. Two other Ric genes encode homologs of G-protein signaling molecules. Our assessment of synaptic function in Ric mutants, combined with the homologies of some Ric mutants to presynaptic proteins, suggests that the analysis of Ric genes will continue to yield insights into the regulation and functioning of synapses.

Differential expression of calcium channels in sympathetic and parasympathetic preganglionic inputs to neurons in paracervical ganglia of guinea-pigs

Neurons in pelvic ganglia receive nicotinic excitatory post-synaptic potentials (EPSPs) from sacral preganglionic neurons via the pelvic nerve, lumbar preganglionic neurons via the hypogastric nerve or both. We tested the effect of a range of calcium channel antagonists on EPSPs evoked in paracervical ganglia of female guinea-pigs after pelvic or hypogastric nerve stimulation. omega-Conotoxin GVIA (CTX GVIA, 100 nM) or the novel N-type calcium channel antagonist, CTX CVID (100 nM) reduced the amplitude of EPSPs evoked after pelvic nerve stimulation by 50-75% but had no effect on EPSPs evoked by hypogastric nerve stimulation. Combined addition of CTX GVIA and CTX CVID was no more effective than either antagonist alone. EPSPs evoked by stimulating either nerve trunk were not inhibited by the P/Q calcium channel antagonist, omega-agatoxin IVA (100 nM), nor the L-type calcium channel antagonist, nifedipine (30 muM). SNX 482 (300 nM), an antagonist at some R-type calcium channels, inhibited EPSPs after hypogastric nerve stimulation by 20% but had little effect on EPSPs after pelvic nerve stimulation. Amiloride (100 muM) inhibited EPSPs after stimulation of either trunk by 40%, while nickel (100 muM) was ineffective. CTX GVIA or CTX CVID (100 nM) also slowed the rate of action potential repolarization and reduced afterhyperpolarization amplitude in paracervical neurons. Thus, release of transmitter from the terminals of sacral preganglionic neurons is largely dependent on calcium influx through N-type calcium channels, although an unknown calcium channel which is resistant to selective antagonists also contributes to release. Release of transmitter from lumbar preganglionic neurons does not require calcium entry through either conventional N-type calcium channels or the variant CTX CVID-sensitive N-type calcium channel and seems to be mediated largely by a novel calcium channel. (C) 2004 IBRO. Published by Elsevier Ltd. All rights reserved.

Evidencia sobre la eficacia de cannabinoides en el dolor neuropático oncológico

Contexto: La eficacia de los cannabinoides en el dolor neuropático es desconocida. El control del dolor es determinante en los pacientes ya que genera un impacto negativo en la calidad de vida de los pacientes. Objetivo: El presente trabajo pretende demostrar la evidencia sobre la eficacia de los medicamentos cannabinoides en el control del dolor neuropático oncológico, mediante la evaluación de la literatura disponible. Metodología: Se realizó una revisión sistemática de literatura incluyendo estudios experimentales, observacionales y revisiones sistemáticas en un periodo de 15 años. Se incluyeron todos los estudios desde el años 2000 con evidencia IB según la escala de evidencia de Oxford. Resultados: Cuatro estudios cumplieron criterios para su inclusión, sin embargo la evidencia es baja y no permite recomendar o descartar los cannabinoides como terapia coadyuvante en control del dolor neuropático oncológico. La combinación de THC/CDB (Sativex®) parece ser un medicamento seguro pues no se reportaron muertes asociadas a su uso, sin embargo la presentación de eventos adversos a nivel gastrointestinal y neurológico podría aumentar el riesgo de interacciones medicamentosas y tener un impacto negativo en la calidad de vida de los pacientes oncológicos. Conclusiones: No hay suficiente literatura y la evidencia no es suficiente para recomendar o descartar el uso de los cannabinoides en dolor neuropático oncológico. Futuros estudios deben realizarse para analizar el beneficio de estos medicamentos. Aunque ética y socialmente hay resistencia para el uso de los cannabinoides, actualmente hay una gran discusión política en el mundo y en Colombia para su aceptación como terapia en el control del dolor.

Varenicline decreases ethanol intake and increases dopamine release via neuronal nicotinic acetylcholine receptors in the nucleus accumbens

BACKGROUND AND PURPOSE Varenicline, a neuronal nicotinic acetylcholine receptor (nAChR) modulator, decreases ethanol consumption in rodents and humans. The proposed mechanism of action for varenicline to reduce ethanol consumption has been through modulation of dopamine (DA) release in the nucleus accumbens (NAc) via α4*-containing nAChRs in the ventral tegmental area (VTA). However, presynaptic nAChRs on dopaminergic terminals in the NAc have been shown to directly modulate dopaminergic signalling independently of neuronal activity from the VTA. In this study, we determined whether nAChRs in the NAc play a role in varenicline’s effects on ethanol consumption. EXPERIMENTAL APPROACH Rats were trained to consume ethanol using the intermittent-access two-bottle choice protocol for 10 weeks. Ethanol intake was measured after varenicline or vehicle was microinfused into the NAc (core, shell or core-shell border) or the VTA (anterior or posterior). The effect of varenicline treatment on DA release in the NAc was measured using both in vivo microdialysis and in vitro fast-scan cyclic voltammetry (FSCV). KEY RESULTS Microinfusion of varenicline into the NAc core and core-shell border, but not into the NAc shell or VTA, reduced ethanol intake following long-term ethanol consumption. During microdialysis, a significant enhancement in accumbal DA release occurred following systemic administration of varenicline and FSCV showed that varenicline also altered the evoked release of DA in the NAc. CONCLUSION AND IMPLICATIONS Following long-term ethanol consumption, varenicline in the NAc reduces ethanol intake, suggesting that presynaptic nAChRs in the NAc are important for mediating varenicline’s effects on ethanol consumption.

Upregulation and Functionality of Neuronal Nicotinic Acetylcholine Receptors

Cigarette smoking is, in developed countries, the leading cause of premature death. In tobacco smoke, the main addictive compound is nicotine, which in the brain binds to neuronal nicotinic acetylcholine receptors (neuronal nAChRs). These have been implicated in addiction, but also in several neurological disorders including Alzheimer's and Parkinson's diseases, Tourette's syndrome, attention-deficit hyperactivity disorder (ADHD), schizophrenia, pain, depression, and autosomal-dominant noctural frontal lobe epilepsy; all of which makes nAChRs an intriguing target of study. Chronic treatment with nicotine leads to an increase in the number of nAChRs (upregulation) in the brain and changes their functionality. Changes in the properties of nAChRs are likely to occur in smokers as well, since they are exposed to nicotine for long periods of time. Several nAChR subtypes likely play a role in the formation of nicotine addiction by participating in the release of dopamine in the striatum. The aim of this study was to clarify at cellular level the changes in nAChR characteristics resulting from chronic nicotine treatment. SH-SY5Y cells, endogenously several nAChR-expressing, and SH-EP1-h-alfa7 cells, transfected with the alfa 7 nAChR subunit gene were treated chronically with nicotine. The localisation of alfa 7 and beta2 subunits was studied with confocal and electron microscopy. Functionality of nAChRs was studied with calcium fluorometry. Effects of long-term treatment with opioid compounds on nAChRs were studied by means of ligand binding. Confocal microscopy showed that in SH-SY5Y cells, alfa7 and beta2 subunits formed clusters, unlike the case in SH-EP1-h alfa7 cells, where alfa7 nAChRs were distributed more diffusely. The majority of nAChR subunits localised on endoplasmic reticulum (ER). The isomers of methadone acted as agonists at alfa7 nAChRs. Acute morphine challenge also stimulated nAChRs. Chronic treatment with methadone or morphine led to an increased number of nAChRs. In animal studies, mice received nicotine for 7 weeks. Electron microscopical analysis of the localisation of nAChRs showed in the striatum that alfa7 and beta2 nAChR subunits localised synaptically, extrasynaptically, and intracellularly, with the majority localising extrasynaptically. Chronic nicotine treatment caused an increase in the number of nAChR subunits at all studied locations. These results suggest that the alfa7 nAChR and beta2 subunit-containing nAChRs respond to chronic nicotine treatment differently. This may indicate that the functional balance of various nAChR subtypes in control of the release of dopamine is altered as a result of chronic nicotine treatment. Compounds binding both to opioid and nACh receptors may be of clinical importance.

Lynx1 Modulation of Nicotinic Acetylcholine Receptors

Nicotinic receptors are the target of nicotine in the brain. They are pentameric ion channels. The pentamer structure allows many combinations of receptors to be formed. These various subtypes exhibit specific properties determined by their subunit composition. Each brain region contains a fixed complement of nicotinic receptor subunits. The midbrain region is of particular interest because the dopaminergic neurons of the midbrain express several subtypes of nicotinic receptors, and these dopaminergic neurons are important for the rewarding effects of nicotine. The α6 nicotinic receptor subunit has garnered intense interest because it is present in dopaminergic neurons but very few other brain regions. With its specific and limited presence in the brain, targeting this subtype of nicotinic receptor may prove advantageous as a method for smoking cessation. However, we do not fully understand the trafficking and membrane localization of this receptor or its effects on dopamine release in the striatum. We hypothesized that lynx1, a known modulator of other nicotinic receptor subtypes, is important for the proper function of α6 nicotinic receptors. lynx1 has been found to act upon several classes of nicotinic receptors, such as α4β2 and α7, the two most common subtypes in the brain. To determine whether lynx1 affects α6 containing nicotinic receptors we used biochemistry, patch clamp electrophysiology, fast scan cyclic voltammetry, and mouse behavior. We found that lynx1 has effects on α6 containing nicotinic receptors, but the effects were subtle. This thesis will detail the observed effects of lynx1 on α6 nicotinic receptors.

Mechanism of acetylcholine-induced calcium signaling during neuronal differentiation of P19 embryonal carcinoma cells in vitro

Muscarinic (mAChRs) and nicotinic acetylcholine receptors (nAChRs) are involved in various physiological processes, including neuronal development. We provide evidence for expression of functional nicotinic and muscarinic receptors during differentiation of P19 carcinoma embryonic cells, as an in vitro model of early neurogenesis. We have detected expression and activity alpha(2)-alpha(7), beta(2), beta(4) nAChR and M1-M5 mAChR subtypes during neuronal differentiation. Nicotinic alpha(3) and beta(2) mRNA transcription was induced by addition of retinoic acid to P19 cells. Gene expression Of alpha(2), alpha(4)-alpha(7), beta(4) nAChR subunits decreased during initial differentiation and increased again when P19 cells underwent final maturation. Receptor response in terms of nicotinic agonist-evoked Ca2+, flux was observed in embryonic and neuronal-differentiated cells. Muscarinic receptor response, merely present in undifferentiated P19 cells, increased during neuronal differentiation. The nAChR-induced elevation of intracellular calcium ([Ca2+](i)) response in undifferentiated cells was due to Ca2+ influx. In differentiated P19 neurons the nAChR-induced [Ca2+](i) response was reduced following pretreatment with ryanodine, while the mAChR-induced response was unaffected indicating the contribution of Ca2+ release from ryanodine-sensitive stores to nAChR- but not mAChR-mediated Ca2+ responses. The presence of functional nAChRs in embryonic cells suggests that these receptors are involved in triggering Ca2+ waves during initial neuronal differentiation. (C) 2007 Elsevier Ltd. All rights reserved.

Alpha7 Nicotinic Acetylcholine Receptor Expression and Activity During Neuronal Differentiation of PC12 Pheochromocytoma Cells

Nicotinic acetylcholine receptors (nAChR) exert pivotal roles in synaptic transmission, neuroprotection and differentiation. Particularly, homomeric alpha 7 receptors participate in neurite outgrowth, presynaptic control of neurotransmitter release and Ca(2+) influx. However, the study of recombinant alpha 7 nAChRs in transfected cell lines is difficult due to low expression of functional receptor channels. We show that PC12 pheochromocytoma cells induced to differentiation into neurons are an adequate model for studying differential nAChR gene expression and receptor activity. Whole-cell current recording indicated that receptor responses increased during the course of differentiation. Transcription of mRNAs coding for alpha 3, alpha 5, alpha 7, beta 2 and beta 4 subunits was present during the course of differentiation, while mRNAs coding for alpha 2, alpha 4 and beta 3 subunits were not expressed in PC12 cells. alpha 7 subunit expression was highest following 1 day of induction to differentiation. Activity of alpha 7 nAChRs, however, was most elevated on day 2 as revealed by inhibition experiments in the presence of 10 nM methyllycaconitine, rapid current decay and receptor responsiveness to the alpha 7 agonist choline. Increased alpha 7 receptor activity was noted when PC12 were induced to differentiation in the presence of choline, confirming that chronic agonist treatment augments nAChR activity. In summary, PC12 cells are an adequate model to study the role and pharmacological properties of this receptor during neuronal differentiation.