Muscarinic toxins : characterization of adrenoceptor binding and applicability of membrane anchoring via glycosylphosphatidylinositol tail

Adrenoceptors (ARs), G-protein coupled receptors (GPCRs) at the plasma membrane, respond to endogenous catecholamines noradrenaline and adrenaline. These receptors mediate several important physiological functions being especially important in the cardiovascular system and in the regulation of smooth muscle contraction. Impairments in the function of these receptors can thus lead to severe diseases and disorders such as to cardiovascular diseases and benign prostatic hyperplasia. The Eastern green mamba (Dendroaspis angusticeps) venom has been shown to contain toxins that can antagonize the functions of GPCRs. The most well-known are muscarinic toxins (MTs) targeting muscarinic acetylcholine receptors (mAChRs) with high affinity and selectivity. However, some reports have indicated that these toxins might also act on the α1- and α2-ARs which can be divided into various subtypes; the α1-ARs to α1A-, α1B- and α1D-ARs and α2-ARs to α2A-, α2B- and α2C-ARs. In this thesis, the interaction of four common MTs (MT1, MT3, MT7 and MTα) with the adrenoceptors was characterized. It was also evaluated whether these toxins could be anchored to the plasma membrane via glycosylphosphatidylinositol (GPI) tail. Results of this thesis reveal that muscarinic toxins are targeting several α-adrenoceptor subtypes in addition to their previously identified target receptors, mAChRs. MTα was found to interact with high affinity and selectivity with the α2B-AR whereas MT7 confirmed its selectivity for the M1 mAChR. Unlike MTα and MT7, MT1 and MT3 have a broad range of target receptors among the α-ARs. All the MTs characterized were found to behave as non-competitive antagonists of receptor action. The interaction between MTα and the α2B-AR was studied more closely and it was observed that the second extracellular loop of the receptor functions as a structural entity enabling toxin binding. The binding of MTα to the α2B-AR appears to be rather complex and probably involves dimerized receptor. Anchoring MTs to the plasma membrane did not interfere with their pharmacological profile; all the GPI-anchored toxins created retained their ability to block their target receptors. This thesis shows that muscarinic toxins are able to target several subtypes of α-ARs and mAChRs. These toxins offer thus a possibility to create new subtype specific ligands for the α-AR subtypes. Membrane anchored MTs on the other hand could be used to block α-AR and mAChR actions in disease conditions such as in hypertension and in gastrointestinal and urinary bladder disorders in a cell-specific manner and to study the physiological functions of ARs and mAChRs in vivo in model organisms.

Inhibitory effect of high [Mg2+] on the vasopressin-stimulated hydroosmotic permeability of the isolated perfused cortical collecting duct

High magnesium concentration inhibits the effect of arginine vasopressin (AVP) on smooth muscle contraction and platelet aggregation and also influences hepatocyte AVP receptor binding. The aim of this study was to determine the role of magnesium concentration [Mg2+] in AVP-stimulated water transport in the kidney collecting duct. The effect of low and high peritubular [Mg2+] on the AVP-stimulated osmotic water permeability coefficient (Pf) was evaluated in the isolated perfused rabbit cortical collecting duct (CCD). Control tubules bathed and perfused with standard Ringer bicarbonate solution containing 1 mM Mg2+ presented a Pf of 223.9 ± 27.2 µm/s. When Mg2+ was not added to the bathing solution, an increase in the AVP-stimulated Pf to 363.1 ± 57.2 µm/s (P<0.05) was observed. An elevation of Mg2+ to 5 mM resulted in a decrease in Pf to 202.9 ± 12.6 µm/s (P<0.05). This decrease in the AVP-stimulated Pf at 5 mM Mg2+ persisted when the CCDs were returned to 1 mM Mg2+, Pf = 130.2 ± 20.3 µm/s, and was not normalized by the addition of 8-[4-chlorophenylthio]-adenosine 3',5'-cyclic monophosphate, a cAMP analogue, to the preparation. These data indicate that magnesium may play a modulatory role in the action of AVP on CCD osmotic water permeability, as observed in other tissues.

Long-chain n-3 fatty acids and inflammation: potential application in surgical and trauma patients

Lipids used in nutritional support of surgical or critically ill patients have been based on soybean oil, which is rich in the n-6 fatty acid linoleic acid (18:2n-6). Linoleic acid is the precursor of arachidonic acid (20:4n-6). In turn, arachidonic acid in cell membrane phospholipids is the substrate for the synthesis of a range of biologically active compounds (eicosanoids) including prostaglandins, thromboxanes, and leukotrienes. These compounds can act as mediators in their own right and can also act as regulators of other processes, such as platelet aggregation, blood clotting, smooth muscle contraction, leukocyte chemotaxis, inflammatory cytokine production, and immune function. There is a view that an excess of n-6 fatty acids should be avoided since this could contribute to a state where physiological processes become dysregulated. One alternative is the use of fish oil. The rationale of this latter approach is that fish oil contains long chain n-3 fatty acids, such as eicosapentaenoic acid. When fish oil is provided, eicosapentaenoic acid is incorporated into cell membrane phospholipids, partly at the expense of arachidonic acid. Thus, there is less arachidonic acid available for eicosanoid synthesis. Hence, fish oil decreases production of prostaglandins like PGE2 and of leukotrienes like LTB4. Thus, n-3 fatty acids can potentially reduce platelet aggregation, blood clotting, smooth muscle contraction, and leukocyte chemotaxis, and can modulate inflammatory cytokine production and immune function. These effects have been demonstrated in cell culture, animal feeding and healthy volunteer studies. Fish oil decreases the host metabolic response and improves survival to endotoxin in laboratory animals. Recently clinical studies performed in various patient groups have indicated benefit from this approach.

4-Aminopyridine inhibits the neuromuscular effects of nitric oxide and 8-Br-cGMP

The effects induced by nitric oxide (NO) in different tissues depend on direct and/or indirect interactions with K+ channels. The indirect interaction of NO is produced by activation of guanylyl cyclase which increases the intracellular cGMP. Since NO, cGMP and 4-aminopyridine alone induce tetanic fade and increase amplitude of muscular contractions in isolated rat neuromuscular preparations, the present study was undertaken to determine whether or not the neuromuscular effects of NO and 8-Br-cGMP can be modified by 4-aminopyridine. Using the phrenic nerve and diaphragm muscle isolated from male Wistar rats (200-250 g), we observed that L-arginine (4.7 mM) and 8-Br-cGMP (18 µM), in contrast to D-arginine, induced an increase in the amplitude of muscle contraction (10.5 ± 0.7%, N = 10 and 8.0 ± 0.7%, N = 10) and tetanic fade (15 ± 2.0%, N = 8 and 11.6 ± 1.7%, N = 8) at 0.2 and 50 Hz, respectively. N G-nitro-L-arginine (4 mM, N = 8 and 8 mM, N = 8) antagonized the effects of L-arginine. 4-Aminopyridine (1 and 10 µM) caused a dose-dependent increase in the amplitude of muscle contraction (15 ± 1.8%, N = 9 and 40 ± 3.1%, N = 10) and tetanic fade (17.7 ± 3.3%, N = 8 and 37.4 ± 1.3%, N = 8). 4-Aminopyridine (1 µM, N = 8) did not cause any change in muscle contraction amplitude or tetanic fade of preparations previously paralyzed with d-tubocurarine or stimulated directly. The effects induced by 4-aminopyridine alone were similar to those observed when the drug was administered in combination with L-arginine or 8-Br-cGMP. The data suggest that the blockage of K+ channels produced by 4-aminopyridine inhibits the neuromuscular effects induced by NO and 8-Br-cGMP. Therefore, the presynaptic effects induced by NO seem to depend on indirect interactions with K+ channels.

Protective effect of N-acetylcysteine against oxygen radical-mediated coronary artery injury

The present study investigated the protective effect of N-acetylcysteine (NAC) against oxygen radical-mediated coronary artery injury. Vascular contraction and relaxation were determined in canine coronary arteries immersed in Kreb's solution (95% O2-5% CO2), incubated or not with NAC (10 mM), and exposed to free radicals (FR) generated by xanthine oxidase (100 mU/ml) plus xanthine (0.1 mM). Rings not exposed to FR or NAC were used as controls. The arteries were contracted with 2.5 µM prostaglandin F2alpha. Subsequently, concentration-response curves for acetylcholine, calcium ionophore and sodium fluoride were obtained in the presence of 20 µM indomethacin. Concentration-response curves for bradykinin, calcium ionophore, sodium nitroprusside, and pinacidil were obtained in the presence of indomethacin plus Nomega-nitro-L-arginine (0.2 mM). The oxidative stress reduced the vascular contraction of arteries not exposed to NAC (3.93 ± 3.42 g), compared to control (8.56 ± 3.16 g) and to NAC group (9.07 ± 4.0 g). Additionally, in arteries not exposed to NAC the endothelium-dependent nitric oxide (NO)-dependent relaxation promoted by acetylcholine (1 nM to 10 µM) was also reduced (maximal relaxation of 52.1 ± 43.2%), compared to control (100%) and NAC group (97.0 ± 4.3%), as well as the NO/cyclooxygenase-independent receptor-dependent relaxation provoked by bradykinin (1 nM to 10 µM; maximal relaxation of 20.0 ± 21.2%), compared to control (100%) and NAC group (70.8 ± 20.0%). The endothelium-independent relaxation elicited by sodium nitroprusside (1 nM to 1 µM) and pinacidil (1 nM to 10 µM) was not affected. In conclusion, the vascular dysfunction caused by the oxidative stress, expressed as reduction of the endothelium-dependent relaxation and of the vascular smooth muscle contraction, was prevented by NAC.

Rat vas deferens SERCA2 is modulated by Ca2+/calmodulin protein kinase II-mediated phosphorylation

Ca2+ pumps are important players in smooth muscle contraction. Nevertheless, little information is available about these pumps in the vas deferens. We have determined which subtype of sarco(endo)plasmic reticulum Ca2+-ATPase isoform (SERCA) is expressed in rat vas deferens (RVD) and its modulation by calmodulin (CaM)-dependent mechanisms. The thapsigargin-sensitive Ca2+-ATPase from a membrane fraction containing the highest SERCA levels in the RVD homogenate has the same molecular mass (∼115 kDa) as that of SERCA2 from the rat cerebellum. It has a very high affinity for Ca2+ (Ca0.5 = 780 nM) and a low sensitivity to vanadate (IC50 = 41 µM). These facts indicate that SERCA2 is present in the RVD. Immunoblotting for CaM and Ca2+/calmodulin-dependent protein kinase II (CaMKII) showed the expression of these two regulatory proteins. Ca2+ and CaM increased serine-phosphorylated residues of the 115-kDa protein, indicating the involvement of CaMKII in the regulatory phosphorylation of SERCA2. Phosphorylation is accompanied by an 8-fold increase of thapsigargin-sensitive Ca2+ accumulation in the lumen of vesicles derived from these membranes. These data establish that SERCA2 in the RVD is modulated by Ca2+ and CaM, possibly via CaMKII, in a process that results in stimulation of Ca2+ pumping activity.

Effects of isometric elbow flexion on electromyographic spike analysis

The main objective of this research was to examine the relationship between surface electromyographic (SEMG) spike activity and force. The secondary objective was to determine to what extent subcutaneous tissue impacts the high frequency component of the signal, as well as, examining the relationship between measures of SEMG spike shape and their traditional time and frequency analogues. A total of96 participants (46 males and 50 females) ranging in age (18-35 years), generated three 5-second isometric step contractions at each force level of 40, 60, 80, and 100 percent of maximal voluntary contraction (MVC). The presentation of the contractions was balanced across subjects. The right arm of the subject was positioned in the sagittal plane, with the shoulder and elbow flexed to 90 degrees. The elbow rested on a support in a neutral position (mid pronation/mid supination) and placed within a wrist cuff, fastened below the styloid process. The wrist cuff was attached to a load cell (JR3 Inc., Woodland, CA) recording the force produced. Biceps brachii activity was monitored with a pair of Ag/AgCI recording electrodes (Grass F-E9, Astro-Med Inc., West Warwick, RI) placed in a bipolar configuration, with an interelectrode distance (lED) of 2cm distal to the motor point. Data analysis was performed on a I second window of data in the middle of the 5-second contraction. The results indicated that all spike shape measures exhibited significant (p < 0.01) differences as force increase~ from 40 to 100% MVC. The spike shape measures suggest that increased motor unit (MU) recruitment was responsible for increasing force up to 80% MVC. The results suggested that further increases in force relied on MU III synchronization. The results also revealed that the subcutaneous tissue (skin fold thickness) had no relationship (r = 0.02; P > 0.05) with the mean number of peaks per spike (MNPPS), which was the high frequency component of the signal. Mean spike amplitude (MSA) and mean spike frequency (MSF) were highly correlated with their traditional measures root mean square (RMS) and mean power frequency (MPF), respectively (r = 0.99; r = 0.97; P < 0.01).

The roles of ERK1/2 and PI3K in abnormal vascular functions in angiotensin II-infused hypertensive rats

Background: Ang II plays a major role in cardiovascular regulation. Recently, it has become apparent that vascular superoxide anion may play an important role in hypertension development. Treatment with antisense NAD(P)H oxidase or SOD decreased BP in Ang II-infused rats. Wang et al recently reported mice which lack one of the subunits of NAD(P)H oxidase developed hypertension at a much lower extent when compared to the wild type animals infused with Ang II, indicating that superoxide anion contributes to elevation in BP in the Ang II-infused hypertensive model. In the Ang II-infused hypertensive model, altered reactivity of blood vessels is often associated with the elevation of systolic blood pressure. We have observed abnormal tension development and impaired endothelium-dependent relaxation in the isolated aorta of Ang II-infused and DOCA-salt hypertensive rats. Recently, several other cellular signal molecules, including ERK1I2 and PI3K, have been determined to play important roles in the regulation of smooth muscle contraction and relaxation. ERKl/2 and PI3K pathways are also reported to contribute to Ang II induced cell growth, hypertrophy, remodeling and contraction. Moreover, these signaling pathways have shown ROS-sensitive properties. Therefore, the aim of the present study is to investigate the roles of ERKl12 and PI3K in vascular oxidative stress, spontaneous tone and impaired endothelium relaxation in Ang II-infused hypertensive model. Hypothesis: We hypothesize that the activation of ERKl12 and PI3K are elevated in response to an Ang II infusion for 6 days. The elevated activation of phospho-ERKl/2 and PI3K mediated the increased level of vascular superoxide anion, the abnormal vascular contraction and impaired endothelium-dependent vascular relaxation in Ang II-infused hypertensive rats. Methods: Vascular superoxide anion level is measured by lucigenin chemiluminescence. Spontaneous tone and ACh-induced endothelium-dependent relaxation was measured by isometric tension recording in organ chamber. The activity of ERK pathway will be measured by its Western blot of phosphorylation of ERK. PI3K activity was evaluated indirectly by Western blot of the phosphorylation of PDKl, a downstream protein of PI3K signaling pathway. The role of each pathway was also addressed via comparing the responses to the specific inhibitors. Results: Superoxide anion was markedly increased in the isolated thoracic aorta from Ang II-infused rats. There was spontaneous tone developed in rings from Ang II-induced hypertensive but not sham-operated normotensive rats. ACh-induced endothelium-dependent relaxation function is impaired in Ang II-infused hypertensive rats. Superoxide dismutase and NAD(P)H oxidase inhibitor, apocynin, inhibited the abnormal spontaneous tone and ameliorated impaired endothelium-dependent relaxation. The expression of phopho-ERKII2 was enhanced in Ang II-infused rats, indicating the activity of ERK1I2 could be increased. MEK1I2 inhibitors, PD98059 and U126, but not their inactive analogues, SB203580 and U124, significantly reduced the vascular superoxide anion in aortas from Ang II-infused rats. The MEK1I2 inhibitors reduced the spontaneous tone and improved the impaired endothelium-dependent relaxation in aorta of hypertension. These findings supported the role of ERKII2 signaling pathway in vascular oxidative stress, spontaneous tone and impaired endothelium-dependent relaxation in Ang II-infused hypertensive rats. The amount of phospho-PDK, a downstream protein of PI3K was increased in Ang II rats indicating the activity of PI3K activity was elevated. Strikingly, PI3K significantly inhibited the increase of superoxide anion level, abnormal spontaneous tone and restored endothelium-dependent relaxation in Ang II-infused hypertensive rats. These findings indicated the important role of PI3K in Ang II-infused hypertensive rats. Conclusion: ERKII2 and PI3K signaling pathways are sustained activated in Ang II-infused hypertensive rats. The activated ERKII2 and PI3K mediate the increase of vascular superoxide anion level, vascular abnormal spontaneous tone and impaired endothelium-dependent relaxation.

Decreased motor unit firing rate in the potentiated tibialis anterior in humans

With repeated activity, force production, rate of force production, and relaxation time are impaired. These are characteristics ofa fatigued muscle (Vandenboom, 2004). However, brief bouts of near maximal to maximal activity results in the increased ability of the muscle to generate force, termed post activation potentiation (P AP)(V andervoort et aI., 1983). The purpose of the present study was to characterize motor unit firing rate (MUFR) in the unfatigued, potentiated tibialis anterior (TA). Using a quadrifilar needle electrode, MUFR was measured during a 5s 50% MVC in which the TA was either potentiated or unpotentiated; monopolar electrodes measured surface parameters. A lOs MVC was used to potentiate the muscle. Firing rate decreased significantly from 20.15±2.9Opps to 18.27±2.99pps, while mean power frequency decreased significantly from 60. 13±7.75 Hz to 53.62±8.56 Hz. No change in root mean square (RMS) was observed. Therefore, in the present study, MUFR decreases in response to a potentiated TA.

Contribution des isoformes de la myosine à l'obstruction respiratoire dans le souffle chez le cheval

La myosine est une protéine motrice impliquée dans la contraction du muscle lisse. Un de ces isoformes, appelé (+)insert lui procure une vélocité accrue. L’objectif de cette étude était d’évaluer la contribution de cet isoforme au bronchospasme observé chez les chevaux atteints de souffle, un modèle d’asthme humain. Nous avons procédé à l’analyse de l’expression génique de l’isoforme (+)insert dans les voies respiratoires de chevaux issus de 3 cohortes afin d’évaluer 1) la présence de cet isoforme chez les chevaux atteints de souffle ; 2) la réversibilité de son expression avec 2 traitements usuels (corticostéroïdes inhalés et retrait antigénique); et 3) la cinétique de réapparition de l’isoforme suite à une période de rémission de la maladie. Les résultats révèlent 1) une expression augmentée de l’isoforme (+)insert dans l’ensemble de l’arbre bronchique des chevaux atteints de souffle en exacerbation comparée aux contrôles et aux chevaux en rémission ; 2) les deux traitements conduisent à une réduction de l’expression de l’isoforme, mais l’administration de corticostéroïdes mène à une diminution plus rapide que celle induite par le retrait antigénique; et 3) une période de 30 jours ou plus d'exposition antigénique est nécessaire pour la réapparition de l’isoforme (+)insert dans l’arbre bronchique des chevaux atteints de souffle. Cette étude montre pour la première fois une modulation et une réversibilité de l’expression de l'isoforme (+)insert de la myosine en fonction du statut médical du sujet. Les données suggèrent que cet isoforme pourrait faire partie d’un mécanisme protecteur activé en réponse à une exposition antigénique prolongée.

Altérations synaptiques à la jonction neuromusculaire dans un modèle murin de sclérose latérale amyotrophique

La sclérose latérale amyotrophique est une maladie neurodégénérative fatale caractérisée par la dégénérescence progressive des neurones moteurs centraux et périphériques. L’un des premiers signes de la maladie est la dénervation de la jonction neuromusculaire (JNM). Les diverses unités motrices (UM) ne présentent toutefois pas la même vulnérabilité à la dénervation dans la SLA: les UM rapide fatigables sont en fait les plus vulnérables et les UM lentes sont les plus résistantes. Alors que des études précédentes ont démontré dans plusieurs modèles animaux de la SLA de nombreuses variations synaptiques, les découvertes ont été contradictoires. Par ailleurs, le type d’UM n’a pas été tenu en compte dans ces divers travaux. Nous avons donc émis l’hypothèse que la présence de la mutation SOD1 pourrait affecter différemment la transmission synaptique des UM, en accord avec leur vulnérabilité sélective. En effectuant des enregistrements électrophysiologiques et de l’immunohistochimie, nous avons étudié la transmission synaptique des différents types d’UM du muscle à contraction rapide Extensor Digitorum Longus (EDL; rapide fatigable (FF) MU) et du muscle à contraction lente Soleus (SOL; lente (S) and rapide fatigue-résistante (FR) MU) de la souris SOD1G37R et leur congénères WT. Pour identifier le type d’UM, un marquage par immunohistochimie des chaînes de myosine a été effectué. Un triple marquage de la JNM a également été effectué pour vérifier son intégrité aux différents stades de la maladie. À P160, dans la période asymptomatique de la maladie, alors qu’aucune altération morphologique n’était présente, l’activité évoquée était déjà altérée différemment en fonction des UM. Les JNMs FF mutantes ont démontré une diminution de l’amplitude des potentiels de plaque motrice (PPM) et du contenu quantique, alors que les JNMs lentes démontraient pratiquement le contraire. Les JNMs FR montraient quant à elles une force synaptique semblable au WT. À P380, dans la période présymtomatique, de nombreuses altérations morphologiques ont été observées dans le muscle EDL, incluant la dénervation complète, l’innervation partielle et les extensions du nerf. La transmission synaptique évoquée des UM FF étaient toujours réduites, de même que la fréquence des potentiels de plaque motrice miniatures. À P425, à l’apparition des premiers symptômes, l’activité synaptique des JNMs S était redevenue normale alors que les JNMs FR ont montré à ce moment une diminution du contenu quantique par rapport au contrôle. De manière surprenante, aucun changement du ratio de facilitation n’a été observé malgré les changements flagrants de la force synaptique. Ces résultats révèlent que la fonction de la JNM est modifiée différemment en fonction de la susceptibilité des UM dans l’ALS. Cette étude fournit des pistes pour une meilleure compréhension de la physiologie de la JNM durant la pathologie qui est cruciale au développement d’une thérapie adéquate ciblant la JNM dans la SLA.

A novel spectral representation of electromyographic signals

Time/frequency and temporal analyses have been widely used in biomedical signal processing. These methods represent important characteristics of a signal in both time and frequency domain. In this way, essential features of the signal can be viewed and analysed in order to understand or model the physiological system. Historically, Fourier spectral analyses have provided a general method for examining the global energy/frequency distributions. However, an assumption inherent to these methods is the stationarity of the signal. As a result, Fourier methods are not generally an appropriate approach in the investigation of signals with transient components. This work presents the application of a new signal processing technique, empirical mode decomposition and the Hilbert spectrum, in the analysis of electromyographic signals. The results show that this method may provide not only an increase in the spectral resolution but also an insight into the underlying process of the muscle contraction.

The application of the Hilbert spectrum to the analysis of electromyographic signals

This paper investigates the application of the Hilbert spectrum (HS), which is a recent tool for the analysis of nonlinear and nonstationary time-series, to the study of electromyographic (EMG) signals. The HS allows for the visualization of the energy of signals through a joint time-frequency representation. In this work we illustrate the use of the HS in two distinct applications. The first is for feature extraction from EMG signals. Our results showed that the instantaneous mean frequency (IMNF) estimated from the HS is a relevant feature to clinical practice. We found that the median of the IMNF reduces when the force level of the muscle contraction increases. In the second application we investigated the use of the HS for detection of motor unit action potentials (MUAPs). The detection of MUAPs is a basic step in EMG decomposition tools, which provide relevant information about the neuromuscular system through the morphology and firing time of MUAPs. We compared, visually, how MUAP activity is perceived on the HS with visualizations provided by some traditional (e.g. scalogram, spectrogram, Wigner-Ville) time-frequency distributions. Furthermore, an alternative visualization to the HS, for detection of MUAPs, is proposed and compared to a similar approach based on the continuous wavelet transform (CWT). Our results showed that both the proposed technique and the CWT allowed for a clear visualization of MUAP activity on the time-frequency distributions, whereas results obtained with the HS were the most difficult to interpret as they were extremely affected by spurious energy activity. (c) 2008 Elsevier Inc. All rights reserved.

Cannabinoids and tremor induced by motor-related disorders: friend or foe?

Tremor arises from an involuntary, rhythmic muscle contraction/relaxation cycle and is a common disabling symptom of many motor-related diseases such as Parkinson disease, multiple sclerosis, Huntington disease, and forms of ataxia. In the wake of anecdotal, largely uncontrolled, observations claiming the amelioration of some symptoms among cannabis smokers, and the high density of cannabinoid receptors in the areas responsible for motor function, including basal ganglia and cerebellum, many researchers have pursued the question of whether cannabinoid-based compounds could be used therapeutically to alleviate tremor associated with central nervous system diseases. In this review, we focus on possible effects of cannabinoid-based medicines, in particular on Parkinsonian and multiple sclerosis-related tremors and the common probable molecular mechanisms. While, at present, inconclusive results have been obtained, future investigations should extend preclinical studies with different cannabinoids to controlled clinical trials to determine potential benefits in tremor.

Single Synapse Information Coding in Intraburst Spike Patterns of Central Pattern Generator Motor Neurons

Burst firing is ubiquitous in nervous systems and has been intensively studied in central pattern generators (CPGs). Previous works have described subtle intraburst spike patterns (IBSPs) that, despite being traditionally neglected for their lack of relation to CPG motor function, were shown to be cell-type specific and sensitive to CPG connectivity. Here we address this matter by investigating how a bursting motor neuron expresses information about other neurons in the network. We performed experiments on the crustacean stomatogastric pyloric CPG, both in control conditions and interacting in real-time with computer model neurons. The sensitivity of postsynaptic to presynaptic IBSPs was inferred by computing their average mutual information along each neuron burst. We found that details of input patterns are nonlinearly and inhomogeneously coded through a single synapse into the fine IBSPs structure of the postsynaptic neuron following burst. In this way, motor neurons are able to use different time scales to convey two types of information simultaneously: muscle contraction (related to bursting rhythm) and the behavior of other CPG neurons (at a much shorter timescale by using IBSPs as information carriers). Moreover, the analysis revealed that the coding mechanism described takes part in a previously unsuspected information pathway from a CPG motor neuron to a nerve that projects to sensory brain areas, thus providing evidence of the general physiological role of information coding through IBSPs in the regulation of neuronal firing patterns in remote circuits by the CNS.