Electrically-evoked Contractions Research Articles

Characterization of rat gastric myogenic contractions and modulation by oxytocin and arginine-vasopressin

BackgroundInterstitial cells of Cajal generate slow wave gastric electrical activity, initiating spontaneous muscle contractions. This becomes dysrhythmic during nausea when [Arg8]-vasopressin (AVP) is also released. In human stomach AVP increased spontaneous contraction activity and muscle tone, not neuronally-mediated contractions. Rodents cannot vomit, releasing the related hormone, oxytocin (OT) instead. We hypothesised that rat stomach would behave differently. Experimental approachSpontaneous and electrically-evoked (EFS) contractions were measured in rat forestomach and antrum circular muscle. Custom software defined spontaneous contractions by analysing eight motility parameters. ResultsThe forestomach was quiescent. Irregular antrum contractions became regular adjacent to the pylorus (1.7 ± 0.4 mN; 1.2 ± 0.1 contractions/min, n = 12). These were unaffected by tetrodotoxin (10−6 M), atropine (10−6 M) and L-NAME (3 × 10−4 M). In both regions, AVP (pEC50∼9.0) and OT (∼0.5 log10-unit less potent) caused contraction (greater in antrum), competitively antagonized by, respectively, SR49059 (pKB∼9.5) and L371257 (pKB∼9.0), reduced by tetrodotoxin but unaffected by atropine. In the antrum, AVP and OT (∼2 log10-units less potent/efficacious) regularized and increased spontaneous contraction amplitude, frequency, rates of contraction/decay. In both regions, EFS-evoked contractions, abolished by atropine/tetrodotoxin, were reduced by AVP and OT, with AVP more potent and efficacious, particularly in forestomach. ConclusionIrregular spontaneous contractions of gastric antrum suggest variable ICC-muscle coupling. AVP and less potently, OT, enhanced frequency and force of contractions via V1A and OT receptors. Compared with human, differences in contraction regularity, potency and ability of AVP/OT to affect neuronal function suggests caution when using rat stomach to model ICC functions and nauseagenic stimuli.

A passive increase in muscle temperature enhances rapid force production and neuromuscular function in healthy adults

ObjectiveTo test the effects of hot-water immersion on the rapid force production and parameters of neuromuscular function in healthy adults. DesignCross-sectional study. MethodsFifteen healthy adults (24.9±5.6 years; 178±11.4cm; 72.8±16.2kg) performed neuromuscular assessments before, after and ∼15min after either 90min of 42°C (hot) or 36°C (sham-condition) water immersion (lower body). Knee extensors rate of torque development (RTD) was measured during explosive voluntary contraction in the interval of 0−50ms (RTDV50) and 0−150ms (RTDV150) and during electrically-evoked contractions by single twitches (RTDtwitch) and low- and high-frequencies doublets (RTD20Hz and 100Hz). Rate of EMG rise (RER) was calculated for voluntary contractions and half-relaxation time (HRT) and electromechanical delay (EMD) was measured during single twitches. ResultsAfter the hot-water immersion (when rectal and muscle temperature were elevated [↑1°C and ↑2.4°C, respectively]), RTDV50, RTD20Hz and RTD100Hz significantly increased and HRT decreased when compared to baseline and sham-condition (p<0.05). Approximately 15min after the hot-water immersion (when muscle temperature was still higher [↑1.4°C], but rectal temperature at baseline level), RTDV50 remained higher and RTDtwitch presented higher values than baseline and sham-condition. The RTD20Hz and RTD100Hz showed further increases compared to post hot-water immersion trials. HRT showed no changes compared to post water immersion, but the EMD presented lower values than baseline and sham-condition. No changes were observed for RTDV150 and RER at any moment. ConclusionIncreased muscle temperature provoked by 42°C hot-water immersion increases the early phase of the RTD (<70ms) (voluntary and evoked) and decreases HRT and EMD of the knee extensors.

Copeptin, a surrogate marker of arginine8 vasopressin, has no ability to modulate human and mouse gastric motility

Copeptin, a glycosylated peptide fragment derived from the C-terminal region of the precursor of arginine8 vasopressin (AVP), is co-secreted with AVP in equimolar amounts. Elevated plasma AVP modulates gastric motility so we investigated whether copeptin had a similar effect.Copeptin (10-9-10-7M), and AVP (10-12-10-5M), were evaluated for their ability to modulate spontaneous and electrically-evoked (EFS) contractions of human proximal and distal gastric circular muscle in vitro. Similar experiments were performed on the mouse stomach and we re-examined the published effect of copeptin on the mouse aorta.In the presence of tetrodotoxin (10-6M), atropine (10-6M) and L-NAME (3 × 10-4M), human proximal and distal stomach muscle contracted spontaneously and rhythmically as did mouse distal stomach.Copeptin (10-9-10-7M), had no effect on baseline muscle tone or myogenic spontaneous contractions of either human or mouse stomach. However, AVP concentration-dependently increased tone, amplitude and frequency of contractions in both regions of human stomach with similar potency (pEC50 9.0-9.5; n = 4) and threshold concentration (10-11-10-10M). AVP was similarly active in the mouse stomach. EFS-evoked cholinergic contractions (human and mouse) were unaffected by both peptides EFS-evoked relaxations of mouse stomach were unaffected by copeptin.In sub-maximally contracted mouse aorta the elevated tone was unaffected by copeptin (10-7M) (cf. previously published study) but was reduced by carbachol (10-6M) and sodium nitroprusside (10-3M).We conclude that in contrast to AVP, copeptin over a concentration range reported in the plasma has no direct ability to modulate the motility of the human and mouse stomach.

Attenuated activation of knee extensor muscles during fast contractions in older men and women.

Reduced physical function and increased risk of falls in older adults are accompanied by age-related reductions in torque development of leg muscles, although the mechanisms and potential sex differences are not understood. To determine the mechanistic origins (neural vs. muscular) for the age-related reduction in torque development, we compared the peak rates of torque development (RTD) during electrically-evoked and fast voluntary contractions of the knee extensors between young and older men and women. Sets of single- and double-pulse electrical stimulations evoked contractions of the knee extensor muscles in 20 young (23.0 ± 0.8years; 10 women) and 20 older adults (78.2 ± 1.5years; 10 women), followed by voluntary isometric knee extension contractions with torque development as fast as possible that matched the torque during electrically-evoked contraction (10-40% maximal torque). Peak RTD during fast-voluntary contractions was 41% less than electrically-evoked contractions (p < 0.001), but more so for older adults (44%) than young (38%, p = 0.04), with no sex differences. Peak RTD during fast-voluntary contractions was more variable between contractions for the older than young adults (77%MVC s-1 vs. 47%MVCs-1, p < 0.001). Additionally, older women exhibited greater variability than older men (81%MVCs-1 vs. 72%MVCs-1, p = 0.04) with no sex-related differences within the young adults. Older adults had slower and more variable RTD during voluntary contractions than young adults, particularly older women. The limited age-related differences in electrically-evoked RTD suggest the primary mechanism for the slower torque development of the knee extensor muscles in older men and women involve reduced neural activation.

Fatigue Etiology At Exhaustion When Cycling Above Vs At Or Below Maximal Lactate Steady-state Threshold.

Exercising above maximal lactate steady state (MLSS) has detrimental effects compared to exercising at MLSS. However, neuromuscular fatigue (NMF) to exercise above MLSS is unknown. PURPOSE: To evaluate NMF during exercise slightly below, at and above MLSS. METHODS: Nine men (24±3 yrs.; 76±7 kg; V̇O2max, 3.55±0.19 L·min-1) exercised to exhaustion at MLSS, 10 W below (-10W) and above (+10W) MLSS. NMF was evaluated before (B), at min 10 (10’), 30 (30’) and at exhaustion, by maximal voluntary contractions (MVC). Voluntary activation (VA) and contractile function of knee extensors [peak twitch torque (TwPt)] were tested using electrically-evoked contractions. Oxygen uptake (V̇O2) and blood lactate concentration ([Lac]) were measured. RESULTS: Time to exhaustion (TTE) for -10W (66±14 min) and +10W (44±8 min) were longer and shorter than MLSS (53±9 min) (p<0.05). V̇O2 was stable for -10W (10’, 2.9±0.19; 30’, 2.9±0.28; TTE, 2.9±0.25 L·min-1) and MLSS (10’, 3.0±0.21; 30’, 3.0±0.29; TTE, 3.1±0.23 L·min-1) (p>0.05), but increased at +10W (10’, 3.0±0.21; 30’, 3.2±0.32; TTE, 3.3±0.39 L·min-1; p<0.05). [Lac] was stable for -10W (10’, 4.1±1.1; 30’, 4.4±1.2; TTE, 4.0±1.0 mM; p>0.05). MLSS showed an increase at TTE (10’, 5.3±1.4; 30’, 5.8±1.4; TTE, 6.1±1.8 mM; p<0.05). +10W showed a constant increase (10’, 5.3±1.2; 30’, 8.0±1.6; TTE, 8.6±1.6 mM; p<0.05). MVC dropped from baseline for -10W (B, 561±178; 10’, 436±128; 30’, 420±131; TTE, 395±120 N; p<0.05), MLSS (B, 518±130; 10’, 405±96; 30’, 361±75; TTE, 344±73 N; p<0.05) and +10W (B, 517±172; 10’, 392±124; 30’, 384±146; TTE, 349±88 N; p<0.05), and was not different amongst conditions. VA dropped from baseline for -10W (B, 98±2; 10’, 90±6; 30’, 89±6; TTE, 89±6 %; p<0.05), MLSS (B, 97±2; 10’, 91±5; 30’, 91±5; TTE, 88±5 N; p<0.05) and +10W (B, 98±2; 10’, 94±5; 30’, 90±7; TTE, 87±7 %; p<0.05), and was not different amongst conditions. TwPt dropped from baseline for -10W (B, 173±30; 10’, 129±22; 30’, 119±17; TTE, 112±17 N; p<0.05), MLSS (B, 172±31; 10’, 129±28; 30’, 119±24; TTE, 111±22 N; p<0.05) and +10W (B, 167±33; 10’, 113±25; 30’, 103±27; TTE, 97±26 N; p<0.05). +10W showed greater decline throughout the bout compared to the other conditions. CONCLUSION: Despite different TTE amongst conditions, peripheral NMF was only different exercising slightly above MLSS compared to the other conditions.

Muscle alterations induced by electrostimulation are lower at short quadriceps femoris length

This study aimed at determining through MRI investigations, force and soreness assessments whether the modulation of muscle length is a relevant strategy for minimising neuromuscular electrical stimulation (NMES)-induced muscle damage in young healthy participants. Comparison of 2 NMES sessions (40 isometric electrically-evoked contractions of the knee extensors) was randomly performed on 1 knee flexed at 50° (short muscle length) and the contralateral at 100° (long muscle length) in a single group of healthy participants. Indirect markers of muscle damage including changes in maximal voluntary isometriccontraction (MVC) force, muscle volume and transverse relaxation time (T2) were measured before, 2days (D2), 4days (D4) and 7days (D7) after the NMES sessions in each limb of the ten participants. Although stimulation intensity was similar during the NMES session on both limbs, significantly lower force production was recorded at long muscle length (peak at 30 ± 5% MVC force) as compared to short muscle length (peak at 61 ± 12% MVC force). In the following days, MVC force at long muscle length was decreased from D2 to D7, whereas no significant changeoccurred at short muscle length. Increases in muscle volume and T2 were found at each time point in stimulated muscles at long muscle length, whereas no change was found at short muscle length. For the same stimulation intensity, NMES-induced isometric contractions generate higher knee extension force output and result in lower muscle tissues alterations that could be related to a lower intramuscular shear strain when exercise is performed at short muscle length.

UBC-Nepal expedition: peripheral fatigue recovers faster in Sherpa than lowlanders at high altitude.

The reduced oxygen tension of high altitude compromises performance in lowlanders. In this environment, Sherpa display superior performance, but little is known on this issue. Sherpa present unique genotypic and phenotypic characteristics at the muscular level, which may enhance resistance to peripheral fatigue at high altitude compared to lowlanders. We studied the impact of gradual ascent and exposure to high altitude (5050m) on peripheral fatigue in age-matched lowlanders and Sherpa, using intermittent electrically-evoked contractions of the knee extensors. Peripheral fatigue (force loss) was lower in Sherpa during the first part of the protocol. Post-protocol, the rate of force development and contractile impulse recovered faster in Sherpa than in lowlanders. At any time, indices of muscle oxygenation were not different between groups. Muscle contractile properties in Sherpa, independent of muscle oxygenation, were less perturbed by non-volitional fatigue. Hence, elements within the contractile machinery contribute to the superior physical performance of Sherpa at high altitude. Altitude-related acclimatisation is characterised by marked muscular adaptations. Lowlanders and Sherpa differ in their muscular genotypic and phenotypic characteristics, which may influence peripheral fatigability at altitude. After gradual ascent to 5050m, 12 lowlanders and 10 age-matched Sherpa (32± 10vs. 31± 11years, respectively) underwent three bouts (separated by 15s rest) of 75 intermittent electrically-evoked contractions (12 pulses at 15Hz, 1.6s between train onsets) of the dominant leg quadriceps, at the intensity which initially evoked 30% of maximal voluntary force. Trains were also delivered at minutes 1, 2 and 3 after the protocol to measure recovery. Tissue oxygenation index (TOI) and total haemoglobin (tHb) were quantified by a near-infrared spectroscopy probe secured over rectus femoris. Superficial femoral artery blood flow was recorded using ultrasonography, and delivery of oxygen was estimated (eDO2 ). At the end of bout 1, peak force was greater in Sherpa than in lowlanders (91.5%vs. 84.5% baseline, respectively; P< 0.05). Peak rate of force development (pRFD), the first 200 ms of the contractile impulse (CI200 ), and half-relaxation time (HRT) recovered faster in Sherpa than in lowlanders (percentage of baseline at 1min: pRFD: 89%vs. 74%; CI200 : 91%vs. 80%; HRT: 113%vs. 123%, respectively; P< 0.05). Vascular measures were pooled for lowlanders and Sherpa as they did not differ during fatigue or recovery (P< 0.05). Mid bout 3, TOI was decreased (90% baseline) whereas tHb was increased (109% baseline). After bout 3, eDO2 was markedly increased (1266% baseline). The skeletal muscle of Sherpa seemingly favours repeated force production at altitude for similar oxygen delivery compared to lowlanders.

Effect of reflexive activation of motor units on torque development during electrically-evoked contractions of the triceps surae muscle.

The aim of the study was to identify stimulation conditions permitting the occurrence of extra torque (ET) and to examine their impact on spinal and corticospinal excitabilities. Twelve subjects received stimulation trains over the tibial nerve (20 s duration, 1 ms pulse duration) that were delivered at 3 stimulation frequencies (20, 50, and 100 Hz) and at 5 intensities (110%, 120%, 130%, 140%, and 150% of the motor threshold). Torque-time integral (TTI) of each stimulation train was calculated. Spinal [maximum H-reflex (Hmax)/maximal M-wave (Mmax)] and corticospinal [maximal motor evoked potential amplitude (MEPmax)/Mmax] excitabilities were assessed at rest before and after each stimulation train by tibial nerve stimulation and by transcranial magnetic stimulation, respectively. Moreover, a twitch at each stimulation intensity was delivered before and after each stimulation train. The EMG activity associated with this twitch was analyzed to identify the initial motor unit (MU) recruitment pathway before each stimulation train and discriminate trials to H-trials (indirect recruitment) and M-trials (direct recruitment). TTI was higher for H-trials compared with M-trials for all tested frequencies. There was a decrease in Hmax/Mmax for the 20 Hz-H trials and an increase for the 100 Hz-H trials, whereas MEPmax/Mmax remained unchanged at post measurements. Present results demonstrate that the initial MU recruitment pattern plays a main role in the ET occurrence, with the indirect recruitment via the afferent volley being substantial for its development. The modulations of Hmax/Mmax without changes in MEPmax/Mmax suggest that the ET development affects spinal excitability and that these changes are frequency dependent. NEW & NOTEWORTHY This study brings new insights into the stimulation conditions permitting the development of extra torque. An initial indirect recruitment of motor units, inducing reflex activation of spinal neurons through Ia afferent solicitation, appears a prerequisite for extra torque development. Under these conditions, spinal excitability modulations were frequency dependent.

Utilizing Physiological Principles of Motor Unit Recruitment to Reduce Fatigability of Electrically-Evoked Contractions: A Narrative Review

Neuromuscular electrical stimulation (NMES) is used to produce contractions to restore movement and reduce secondary complications for individuals experiencing motor impairment. NMES is conventionally delivered through a single pair of electrodes over a muscle belly or nerve trunk using short pulse durations and frequencies between 20 and 40Hz (conventional NMES). Unfortunately, the benefits and widespread use of conventional NMES are limited by contraction fatigability, which is in large part because of the nonphysiological way that contractions are generated. This review provides a summary of approaches designed to reduce fatigability during NMES, by using physiological principles that help minimize fatigability of voluntary contractions. First, relevant principles of the recruitment and discharge of motor units (MUs) inherent to voluntary contractions and conventional NMES are introduced, and the main mechanisms of fatigability for each contraction type are briefly discussed. A variety of NMES approaches are then described that were designed to reduce fatigability by generating contractions that more closely mimic voluntary contractions. These approaches include altering stimulation parameters, to recruit MUs in their physiological order, and stimulating through multiple electrodes, to reduce MU discharge rates. Although each approach has unique advantages and disadvantages, approaches that minimize MU discharge rates hold the most promise for imminent translation into rehabilitation practice. The way that NMES is currently delivered limits its utility as a rehabilitative tool. Reducing fatigability by delivering NMES in ways that better mimic voluntary contractions holds promise for optimizing the benefits and widespread use of NMES-based programs.

Effect of Peptidase Inhibitors on Dynorphin A (1-17) or (1-13)-Induced Antinociception and Toxicity at Spinal Level

Our group has earlier demonstrated that three enzymes sensitive to peptidase inhibitors (PIs), amastatin (A)-, captopril (C)-, and phosphoramidon (P), played an important role in inactivation of enkephalins at the spinal level. Dynorphin-converting enzyme (DCE) hydrolyzes dynorphin (Dyn) A (1-17) or Dyn A (1-13) mainly at the Arg6-Arg7 bond. Dynorphin A and its derived peptides interact with opioid and glutamate receptors at their N- and C-terminals, respectively. The purpose of the present study was to evaluate the antinociceptive potency and toxicity of intrathecal administered Dyn A (1-17), Dyn A (1-13), or Dyn A (1-6) under pretreatment with ACP and/or the DCE inhibitor p-hydroxymercuribenzoate (PHMB). The effect of these PIs on Dyn A (1-17)-induced inhibition of electrically-evoked contractions in mouse vas deferens was also investigated. The inhibitory potency of Dyn A (1-17) on electrically-evoked contractions in mouse vas deferens under pretreatment with ACP was higher than that with AC, AP, or CP. Pretreatment with ACP augmented Dyn A (1-17) or (1-13)-induced antinociception by approximately 50- or 30-fold with no sign of allodynia when administered intrathecally at low doses. Pretreatment with ACP and PHMB induced neuropathy. These findings showed that intrathecal administration of low-dose Dyn A (1-17) or DynA (1-13) increased antinociception under pretreatment with ACP, but without signs of allodynia in rat.

Contributions of Central Command and Muscle Feedback to Sympathetic Nerve Activity in Contracting Human Skeletal Muscle

During voluntary contractions, muscle sympathetic nerve activity (MSNA) to contracting muscles increases in proportion to force but the underlying mechanisms are not clear. To shed light on these mechanisms, particularly the influences of central command and muscle afferent feedback, the present study tested the hypothesis that MSNA is greater during voluntary compared with electrically-evoked contractions. Seven male subjects performed a series of 1-min isometric dorsiflexion contractions (left leg) separated by 2-min rest periods, alternating between voluntary and electrically-evoked contractions at similar forces (5–10% of maximum). MSNA was recorded continuously (microneurography) from the left peroneal nerve and quantified from cardiac-synchronized, negative-going spikes in the neurogram. Compared with pre-contraction values, MSNA increased by 51 ± 34% (P < 0.01) during voluntary contractions but did not change significantly during electrically-evoked contractions (−8 ± 12%, P > 0.05). MSNA analyzed at 15-s intervals revealed that this effect of voluntary contraction appeared 15–30 s after contraction onset (P < 0.01), remained elevated until the end of contraction, and disappeared within 15 s after contraction. These findings suggest that central command, and not feedback from contracting muscle, is the primary mechanism responsible for the increase in MSNA to contracting muscle. The time-course of MSNA suggests that there is a longer delay in the onset of this effect compared with its cessation after contraction.

Biphasic cardiovascular and respiratory effects induced by β-citronellol

β-Citronellol is a monoterpene found in the essential oil of various plants with antihypertensive properties. In fact, β-citronellol possesses hypotensive actions due to its vasodilator abilities. Here we aimed to show that β-citronellol recruits airway sensory neural circuitry to evoke cardiorespiratory effects. In anesthetized rats, intravenous injection of β-citronellol caused biphasic hypotension, bradycardia and apnea. Bilateral vagotomy, perivagal capsaicin treatment or injection into the left ventricle abolished first rapid phase (named P1) but not delayed phase P2 of the β-citronellol effects. P1 persisted after pretreatment with capsazepine, ondansetron, HC-030031 or suramin. Suramin abolished P2 of apnea. In awake rats, β-citronellol induced biphasic hypotension and bradycardia being P1 abolished by methylatropine. In vitro, β-citronellol inhibited spontaneous or electrically-evoked contractions of rat isolated right or left atrium, respectively, and fully relaxed sustained contractions of phenylephrine in mesenteric artery rings. In conclusion, chemosensitive pulmonary vagal afferent fibers appear to mediate the cardiovascular and respiratory effects of β-citronellol. The transduction mechanism in P1 seems not to involve the activation of transient receptor potential vanilloid subtype 1 (TRPV1), transient receptor potential ankyrin subtype 1 (TRPA1), purinergic (P2X) or 5-HT3 receptors located on airways sensory nerves. P2 of hypotension and bradycardia seems resulting from a cardioinhibitory and vasodilatory effect of β-citronellol and the apnea from a purinergic signaling.

Guinea-pig ileum as ex vivo model useful to characterize ligands displaying Imidazoline I2 and Adrenergic alpha2 mixed activity: a preliminary study

The lack of an effective analgesic treatment makes pain a clinical challenge and the need of a novel approach to identify new agents is urgent. In this scenario I2-ligands can be considered an alternative strategy in pain therapy. The development of an &lt;em&gt;ex vivo&lt;/em&gt; model useful for the evaluation of functional activities at both a2 and I2-IBs (imidazoline binding sites) is an important task in pharmacological sciences since several I2 ligands display activity also towards a receptors. The present study aims to develop an &lt;em&gt;ex vivo&lt;/em&gt; model for estimating the activity of I2-IBs ligands in a biological sample where a1 and a2 adrenergic receptors are present. For this purpose the imidalzoline endogenous ligand, harmane, reference compounds, 2BFI and BU224, and imidazoline derivatives 1-3 have been selected taking into account their in vitro activity towards IBs and adrenergic receptors. All compounds have been tested &lt;em&gt;ex vivo&lt;/em&gt; in guinea pig-ileum where a2A-ARs are prejunctionally and I2-IBS postjunctionally localized. Adrenergic component has been identified by the studying the interference of compounds on the electrically-evoked contraction while I2-IBs activity by testing the ability of compounds to inhibit the carbachol-evoked contractions in the presence of prazosin to mask the a1 adrenoceptors. Compounds 1 and 2 were found I2-IBs antago nists (pIC50=4.2 and 4.0, respectively) whereas compound 3 was I2-IBs agonist (EC50=0.38 mM); All ligands were a2 adrenergic agonists. This paper suggests guinea-pig ileum as the first &lt;em&gt;ex vivo&lt;/em&gt; approach for establishing both the intrinsic activity of I2-IBs ligands and the physiological correlation between IBs and adrenergic system.

Inhibiting fatty acid amide hydrolase normalizes endotoxin‐induced enhanced gastrointestinal motility in mice

Gastrointestinal (GI) motility is regulated in part by fatty acid ethanolamides (FAEs), including the endocannabinoid (EC) anandamide (AEA). The actions of FAEs are terminated by fatty acid amide hydrolase (FAAH). We investigated the actions of the novel FAAH inhibitor AM3506 on normal and enhanced GI motility. We examined the effect of AM3506 on electrically-evoked contractility in vitro and GI transit and colonic faecal output in vivo, in normal and FAAH-deficient mice treated with saline or LPS (100 µg·kg(-1), i.p.), in the presence and absence of cannabinoid (CB) receptor antagonists. mRNA expression was measured by quantitative real time-PCR, EC levels by liquid chromatography-MS and FAAH activity by the conversion of [(3)H]-AEA to [(3)H]-ethanolamine in intestinal extracts. FAAH expression was examined by immunohistochemistry. FAAH was dominantly expressed in the enteric nervous system; its mRNA levels were higher in the ileum than the colon. LPS enhanced ileal contractility in the absence of overt inflammation. AM3506 reversed the enhanced electrically-evoked contractions of the ileum through CB(1) and CB(2) receptors. LPS increased the rate of upper GI transit and faecal output. AM3506 normalized the enhanced GI transit through CB(1) and CB(2) receptors and faecal output through CB(1) receptors. LPS did not increase GI transit in FAAH-deficient mice. Inhibiting FAAH normalizes various parameters of GI dysmotility in intestinal pathophysiology. Inhibition of FAAH represents a new approach to the treatment of disordered intestinal motility.

Selective Activation of the Muscles of Micturition Using Intrafascicular Stimulation of the Pudendal Nerve

We investigate the hypothesis that intrafascicular stimulation of the pudendal nerve (PN) can be used to selectively activate the detrusor bladder muscle and the external urethral sphincter (EUS). Nine anesthetized male canines were used in this study. Muscle activations were measured via bladder catheter pressure transducers and EUS electromyography (EMG) wires. The PNs were exposed via dissection of the ischioanal fossa and implanted with Utah Slanted Electrode Arrays (USEAs). USEAs consist of 100, 0.5–1.5 mm long microelectrodes that project out from a 4 $\,\times\,$ 4 mm substrate. Intrafascicular stimulation was delivered via individual USEA microelectrodes in order to map the ability of each electrode to selectively or nonselectively evoke detrusor and/or EUS contractions. We were able to selectively activate the detrusor using 33 Hz stimulation of PN axons with an average of $4.57 \pm 3.82$ ( ${\rm mean }\pm {\rm sd}$ ) USEA electrodes per animal tested. Electrically-evoked and distention-evoked bladder contractions had similar kinetics. Sustained bladder contractions were evoked via 60 s of intrafascicular stimulation. The EUS was activated using 33 Hz stimulation via an average of $26.14 \pm 19.45$ electrodes per animal tested. High frequency ( $> {2}~{\rm kHz}$ ) stimulation delivered via EUS selective electrodes produced nonselective block of PN axons. Examples of how this selective axonal access could be used to restore continence and activate micturition were demonstrated in two animals. We report herein the first study demonstrating selective detrusor and EUS activation via microelectrodes implanted intrafascicularly in the PN. Such selective activation enables new therapeutic possibilities for controlling the muscles of micturition.

Three different ways in which 5-hydroxytryptamine can affect cholinergic activity in guinea-pig isolated ileum.

The effects of 5-hydroxytryptamine (5-HT) have been studied on electrically-evoked contractions mediated by cholinergic nerves in guinea-pig isolated ileum. Low concentrations of 5-HT (0.0001-0.01 microgram ml-1) caused a sustained increase in submaximal, electrically-evoked contractions. Higher concentrations of 5-HT (0.1-10 micrograms ml-1) initially evoked a fast, rapidly-fading contraction of the muscle. Subsequently, 5-HT 0.1-10 micrograms ml-1 caused a sustained reduction in the height of the electrically-evoked contractions. The effects of 5-HT 0.01 and 0.1 microgram ml-1 on the electrically-evoked contractions were not blocked by methysergide 0.1 microgram ml-1 or by hexamethonium 10 micrograms ml-1, and may be due to changes in neuronal acetylcholine (ACh) release, since contractions evoked by exogenous ACh were unaffected by 5-HT. The results therefore imply that 5-HT can affect gut cholinergic activity in at least three different ways, two of which may modulate evoked ACh release by mechanisms which may be insensitive to tachyphylaxis.

Effect of Crude Extracts from Leonotis nepetaefolia (Labiatae) on Rat and Guinea-pig Smooth Muscle and Rat Cardiac Muscle

The actions of hydroalcoholic and tea extracts of stems of Leonotis nepetaefolia on agonist-induced and electrically-evoked contractions have been analysed in-vitro in rat uterus and left atrium and in guinea-pig ileum and trachea. The tea extract (500-2000 micrograms mL-1) caused parallel and graded rightward shifts of concentration-response curves to bradykinin and BaCl2 in the rat isolated uterus, but antagonized responses to prostaglandin F2 alpha in a typically non-competitive manner. The hydroalcoholic extract also caused rightward displacements of the curves to bradykinin, acetylcholine (ACh), angiotensin II, oxytocin and BaCl2 and reduced their maximal contractile effects. Both extracts (30-3000 micrograms mL-1) relaxed uterine preparations precontracted with KCl (80 mM), the hydroalcoholic extract being about 2-fold more potent than the tea extract. The relaxant response to the former was unaffected by propranolol (1 microM) or forskolin (10 nM), but was potentiated 2-fold by 3-isobutyl-1-methylxanthine (10 microM). In the guinea-pig ileum the hydroalcoholic extract shifted the ACh- and bradykinin-induced contractile curves to the right and markedly inhibited their maximal effects, whereas the tea extract caused a typical non-competitive antagonism of ACh-induced contractile responses. In field-stimulated ileal strips, both extracts (3-3000 micrograms mL-1) caused contractions and inhibited twitch responses. Guinea-pig tracheal rings precontracted with carbachol (0.3 microM) were relaxed only by concentrations of either extract in excess of 1000 micrograms mL-1, an action that was unaffected by propranolol (0.1 microM) or by offomethacin (1 microM).(ABSTRACT TRUNCATED AT 250 WORDS)

Characterization of the prejunctional adenosine receptors in the rat anococcygeus muscle.

Adenosine receptor agonists inhibited electrically-evoked contractions of the rat isolated anococcygeus muscle. The compounds tested were: N6-cyclopentyladenosine (CPA), N((S, trans)-2-hydroxycyclopentyl)adenosine (GR79236), the R- and S-isomers of phenylisopropyladenosine (PIA), 5'-N-ethylcarboxamidoadenosine (NECA), ((2-(4-(2-carboxyethyl)phenyl)ethyl)amino)-N-ethylcarbox-amidoa denosine (CGS 21680) and N-((2-methylphenyl)methyl)adenosine (metrifudil). The rank order of agonist potency was: CPA = R-PIA = GR79236 = NECA >> S-PIA > metrifudil > CGS 21680, which is consistent with an effect mediated by adenosine A1 receptors. A similar rank order of potency was obtained for inhibition of electrically-evoked contractions of the guinea-pig ileum. However, there may be a lower receptor reserve in rat anococcygeus compared with the guinea-pig ileum, since higher concentrations of agonists were necessary to produce effects in the anococcygeus than in the guinea-pig ileum and S-PIA behaved as a partial agonist. The effect of NECA was antagonized in rat anococcygeus and guinea-pig ileum by the mixed A1/A2 receptor antagonist, 8-phenyltheophylline (pA2 values of 6.8 and 6.9, respectively). The selective A1-receptor antagonist, 8-cyclopentyl-1,3- dipropylxanthine (DPCPX), also blocked the inhibitory response to NECA in both tissues. Here, however, the pA2 values (9.6 and 8.6, respectively) were slightly but significantly different. These values confirm that the prejunctional adenosine receptors of the rat anococcygeus are of the A1 type, and suggest that they are similar but not necessarily identical to those of the guinea-pig ileum. The differing potencies of DPCPX as an antagonist of NECA between the preparations may reflect a tissue-dependent variation in sensitivity to this antagonist.

Can the effects of meptazinol on the guinea-pig isolated ileum be explained by inhibition of acetylcholinesterase?

It has previously been shown that there is a cholinergic component in the antinociceptive action of the opioid analgesic drug meptazinol. In the present study meptazinol was shown to be an inhibitor of acetylcholinesterase in-vitro with a potency one hundredth that of physostigmine. This activity was found to reside only in the (-)-enantiomer of meptazinol. The anticholinesterase activity of meptazinol may explain the increase in the size of the electrically-evoked contraction of the guinea-pig isolated ileum preparation since by using a long pulse width (5 ms) it was found that the (-)-enantiomer of meptazinol modified only the component of the response due to neuronally released acetylcholine and had no direct effect on the smooth muscle. This property of meptazinol may also be responsible for the cholinergic effects of the drug in-vivo.

Effects of the calcium antagonists diltiazem, verapamil and nitrendipine on the contractile responses of guinea-pig isolated ileum to electrical stimulation or carbachol.

The effects of the organic Ca2+ antagonists nitrendipine, verapamil and diltiazem on the cholinergic contractile responses induced by field electrical stimulation or carbachol (0.1 microM) and on contractions evoked by high concentration KCl (30 mM) were studied in isolated preparations from the guinea-pig ileum. The three Ca2+ antagonists dose-dependently suppressed the contractile responses showing the same order of potency (nitrendipine greater than verapamil greater than diltiazem) with the three different types of stimulation. Comparison of the IC50 values of the Ca2+ antagonists for carbachol-, KCl- and electrically-evoked contractions demonstrated that the carbachol-evoked contractions were most sensitive to the inhibitory action of the antagonists tested. The presynaptic inhibitory effect of (Met)enkephalin (10 nM) on the electrically-evoked cholinergic contractions was only slightly potentiated by high concentrations (1 or 10 microM) of nitrendipine and diltiazem and remained unchanged by verapamil. The results suggest that the Ca2+ antagonists tested block mainly the carbachol-activated L-type Ca2+ channels on the smooth muscle cells, while the effects on the N-type Ca2+ channels are insignificant, except for the high concentrations of nitrendipine and diltiazem.