Diaphragm motor unit recruitment in rats

We hypothesized that considerable force reserve exists for the diaphragm muscle (DIAm) to generate transdiaphragmatic pressures (Pdi) necessary to sustain ventilation. In rats, we measured Pdi and DIAm EMG activity during different ventilatory (eupnea and hypoxia (10% O₂)–hypercapnia (5% CO₂)) and non-ventilatory (airway occlusion and sneezing induced by intranasal capsaicin) behaviors. Compared to maximum Pdi (Pdi_max generated by bilateral phrenic nerve stimulation), the Pdi generated during eupnea (21 ± 2%) and hypoxia–hypercapnia (28 ± 4%) were significantly less (p < 0.0001) than that generated during airway occlusion (63 ± 4%) and sneezing (94 ± 5%). The Pdi generated during spontaneous sighs was 62 ± 5% of Pdi_max. Relative DIAm EMG activity (root mean square [RMS] amplitude) paralleled the changes in Pdi during different ventilatory and non-ventilatory behaviors (r² = 0.78; p < 0.0001). These results support our hypothesis of a considerable force reserve for the DIAm to accomplish ventilatory behaviors. A model for DIAm motor unit recruitment predicted that ventilatory behaviors would require activation of only fatigue resistant units.     

Novel method for transdiaphragmatic pressure measurements in mice

The diaphragm muscle (DIAm) is responsible for breathing and determines the ability to generate both ventilatory and non-ventilatory behaviors. Size limitations of the mouse make transdiaphragmatic pressure (Pdi) measurement using a dual balloon system untenable. Adult C57BL/6J mice (n = 8) and C57BL/6 × 129 (n = 9), underwent Pdi measurements using solid-state pressure catheters spanning the thoracic and abdominal surfaces of the DIAm. Measurements were conducted during eupnea, hypoxia (10% O₂)–hypercapnia (5% CO₂), chemical airway stimulation (i.e., sneezing), spontaneously occurring deep breaths, sustained tracheal occlusion, and bilateral phrenic nerve stimulation. There was a difference in the Pdi generated across the range of ventilatory and non-ventilatory behaviors (p = 0.001). No difference in Pdi across behaviors was evident between mouse strains (p = 0.161). This study establishes a novel method to determine Pdi across a range of DIAm behaviors in mice that may be useful in evaluating conditions associated with reduced ability to perform expulsive, non-ventilatory behaviors.     

Increased load on the respiratory muscles in obstructive sleep apnea

We wished to quantify, in patients with obstructive sleep apnoea (OSA), the activity of the respiratory muscles in relation to upper airway occlusion and patency in sleep. We hypothesized that particular levels of neuromuscular activation are directly associated with upper airway patency. 21 patients with previously diagnosed OSA and 21 healthy control subjects underwent respiratory muscle testing and polysomnography. Neural respiratory drive, as measured by the electromyogram of the diaphragm (EMG_di) was elevated in the obese OSA patients, awake and supine (13.1(5.6)%max), compared to normal subjects (mean (SD) 8.1(2.3)%max, p < 0.01). During unobstructed breathing in sleep (stage N2) normal subjects had an EMG_di of 7.7(3.9) compared to 22.8(19.2)%max in the OSA group (p < 0.001). Prior to airway occlusion, EMG_{submandibular} and EMG_di dropped markedly, and then, following occlusion, increased progressively to their highest levels at airflow onset. Patients with OSA require specific and increased levels of neural respiratory drive to sustain ventilation in sleep.     

Membrane resonance and its ionic mechanisms in rat subthalamic nucleus neurons

The oscillatory activity in the basal ganglia is believed to have an important function, but little is known about its actual mechanisms. We studied the resonance characteristics of subthalamic nucleus (STN) neurons and their ionic mechanisms using whole-cell patch-clamp recordings in rat brain slices. A swept-sine-wave current with constant amplitude and linearly increasing frequency was applied to measure the resonance frequency (f_res) of STN neurons. We also used single-frequency sine wave current to evoke firing. We found that the resonance of STN neurons was temperature- and voltage-dependent. The f_res of STN neurons was about 4 Hz when the temperature was maintained at 38 °C and holding potential was at −70 mV. The f_res increased with more negative holding potentials and decreased with lower temperature. Action potentials fired most readily when the input frequency was near f_res. After application of drug ZD7288 (20 μM), the resonance of STN neurons was blocked and the spikes evoked by both impedance amplitude profile (ZAP) current and single-frequency sine wave current arose readily at the lowest frequencies, indicating that hyperpolarization-activated cation current (I_h) generated the resonance and mediated a preferential coupling at frequencies near f_res between inputs and firing. In conclusion, there is a θ-frequency resonance mediated by I_h in STN neurons. The resonance characteristics are temperature- and voltage-dependent. The resonance mediates a frequency-selective coupling between inputs and firing.     

Modulation of histamine H3 receptor function by monovalent ions

Monovalent ions differently affect ligand binding to G protein-coupled receptors (GPCRs) by as yet poorly defined mechanisms. In particular, NaCl often decreases the affinity of agonists but increases it for antagonists. We examined the effect of various monovalent ions on human histamine H₃ receptor (hH₃R), co-expressed with mammalian G proteins (Gα_i1, Gα_i2, Gα_i3 or Gα_o1, and β₁γ₂ dimers, respectively) in Sf9 insect cell membranes, with respect to agonist binding and G protein activation. NaCl (100 mM) had no effect on affinity of the agonist [³H]N^α-methylhistamine ([³H]NAMH). In steady-state GTPase assays, the endogenous agonist histamine had a lower potency and the inverse agonist thioperamide had a higher potency, when NaCl (100 mM) was present. Monovalent ions reduced H₃R-regulated signalling in the order of efficacy Li⁺ ∼ Na⁺ ∼ K⁺ < Cl⁻ < Br⁻ < I⁻. NaCl had a stronger effect on basal hH3R-signalling when Gα_i3 was co-expressed. Asp80^2.50, a putative interaction site for Na⁺, was mutated to Asn80^2.50 (D2.50N-hH₃R). Strikingly, the mutation was unable to activate Gα_i3 at all. The effects can be explained by a model, where (i) monovalent ions as well as a charge-neutralizing mutation of Asp80^2.50 generally reduce the interaction of hH₃R with G proteins, (ii) monovalent anions increase the affinity of G proteins for GDP and thus, indirectly affect their interaction with hH₃R and, (iii) Asp80^2.50 is a key residue for hH₃R/Gα_i3-protein activation. The latter result suggests that hH₃R/G protein-coupling interfaces may differ even between closely related subunits.     

Effect of ageing on the force development in tetanic contractions of motor units in rat medial gastrocnemius muscle

The purpose of this study was to determine the effect of ageing on the rate of force generation of motor units, and the mechanical efficiency of contraction produced by a doublet discharge. The study was carried out on isolated motor units of rat medial gastrocnemius muscle of young (5-10 mo) and two groups of old (24-25 and 28-30 mo) Wistar rats. Motor units were classified into the fast fatigable (FF), fast resistant (FR) and slow (S) ones. The force output and rate of force development were determined for non-doublet unfused tetanic contractions evoked by a series of a constant-rate trains of pulses and corresponding doublet contractions starting with an initial brief interpulse interval of 5 ms, and for maximal tetanic contraction. In FF motor units the rate of force development and the force produced by the doublet discharge increased transiently at the age of 24-25 mo, while in S and FR motor units this increase was observed at the age of 28-30 mo. Age-related decrease in the rate of force development of skeletal muscle cannot be attributed to a decline in efficiency of force production by functioning motor units.     

Common rostrocaudal gradient of output from human intercostal motoneurones during voluntary and automatic breathing

In voluntary breaths, driven through the motor cortex, the pattern of activation in human inspiratory intercostal muscles is unknown. We measured single motor unit behaviour in the first, third, and fifth parasternal intercostal muscles in 5 subjects for ‘quiet’ and matched ‘voluntary’ inspirations. In voluntary breaths, the average onset, peak and end discharge rate of 264 inspiratory single motor units was greater in the first interspace compared to caudal spaces (p < 0.05). Relative to the onset of inspiratory flow, the time of recruitment of single motor units and the onset of multiunit activity were also earlier in the first compared to the fifth interspace (p < 0.05). For 215 ‘common’ motor units, peak discharge frequencies were ∼20% higher in voluntary compared to quiet breaths (p < 0.05), due in part, to small differences in the pattern of breathing. A rostrocaudal gradient of motor unit activation across parasternal intercostal muscles was preserved in voluntary and involuntary tasks. A common mechanism may mediate this pattern of recruitment.     

The polymorphism of Knops blood group system in Korean population and their relationship with HLA system

The main purpose of this report is to provide baseline gene frequencies of Knops blood group in the complement receptor 1 gene (CR1) in Korean population. In addition, possible relationship between the CR1 polymorphism and HLA specificities were studied, because the two systems had principal importance in immunity. CR1, which contains Knops antigens, was investigated by PCR-direct sequencing from 238 cord blood from Koreans. HLA data was archived from the enrolled cord blood units. Among the 7 SNPs, only 4843 (for KCAM antigen) and 4223 (for Yk^a) nucleotide positions showed polymorphism. The genotype frequencies of KCAM were A/A (62.2%), A/G (33.2%), and G/G (4.6%); Yk^a were C/C (29.4%), C/T (50%), and T/T (20.6%). KCAM (A/A) associated with HLA-DRB1^∗13 (p = 0.003, P_c = 0.0513); KCAM (G/G) with HLA-A^∗30 (p < 0.001, P_c = 0.0012). The Knops blood group system in Korean population has no diversity, except SNPs for KCAM and Yk^a, and the genotype of KCAM related with specific HLA alleles.     

Sleep-promoting action of IIK7, a selective MT2 melatonin receptor agonist in the rat

Several novel melatonin receptor agonists, in addition to various formulations of melatonin itself, are either available or in development for the treatment of insomnia. Melatonin is thought to exert its effects principally through two high affinity, G-protein coupled receptors, MT₁ and MT₂, though it is not known which subtype is responsible for the sleep-promoting action. The present study used radiotelemetry to record EEG and EMG in un-restrained freely moving rats to monitor the sleep-wake behaviour and examined the acute sleep-promoting activity of an MT₂ receptor subtype selective melatonin analog, IIK7. IIK7 is a full agonist at the MT₂ receptor subtype but a partial agonist at the MT₁ receptor and has ∼90-fold higher affinity for MT₂ than MT₁. Like melatonin, IIK7 (10 mg/kg i.p.) significantly reduced NREM sleep onset latency and transiently increased the time spent in NREM sleep, but did not alter REM sleep latency or the amount of REM sleep. An analysis of the EEG power spectrum showed no change in delta (1–4 Hz) or theta activity (5–8 Hz) following IIK7 administration. Core body temperature was slightly decreased (∼0.3 °C) by IIK7 compared to vehicle-treated rats. The acute and transient changes in the sleep-wake cycle mimic the changes seen with melatonin and suggest that its sleep-promoting activity is mediated by activation of the MT₂ receptor subtype.     

Activity of single motor units in attention-demanding tasks: firing pattern in the human trapezius muscle

Activity of single motor units in relation to surface electromyography (EMG) was studied in 11 subjects in attention-demanding work tasks with minimal requirement of movement. In 53 verified firing periods, single motor units fired continuously from 30 s to 10 min (duration of the experiment work task) with a stable median firing rate in the range of 8–13 Hz. When the integrated surface EMG were stable, the motor units identified as a rule were continuously active with only small modulations of firing rate corresponding to low-amplitude fluctuations in surface EMG. Marked changes in the surface EMG, either sudden or gradual, were caused by recruitment or derecruitment of motor units, and not by modulations of the motor unit firing rate. Motor unit firing periods (duration 10 s-35 s) in low-level voluntary contractions (approximately 1%–5% EMG_max) performed by the same subjects showed median firing rates (7–12 Hz) similar to the observations in attention-related activation.     

Brain oscillatory 4–35 Hz EEG responses during an n-back task with complex visual stimuli

Brain oscillatory responses of 4–35 Hz EEG frequencies elicited during performance of a visual n-back task with complex visual stimuli were assessed in 20 adult volunteers. Spectral power changes were assessed separately for target and non-target stimuli in four different memory load conditions (0, 1, 2, and 3-back). The presentation of both target and non-target stimuli elicited long-lasting ∼4–8 Hz power increases, which were more prominent at the beginning of stimulus onset during presentation of target stimuli, as compared to non-target stimuli, in the 0-back memory load condition. ∼8–25 Hz power decreases appeared at stimulus onset. These power decreases were more prominent during the presentation of target stimuli, as compared to non-target stimuli, and their duration increased as a function of memory load between the 0-, 1-, and 2-back, but not the 3-back, memory load conditions. The current results provide further evidence in support of the notion of a complex interplay between both ∼4–8 Hz power increases and ∼8–25 Hz power decreases during cognitive memory task performance.     

The aerobic-anaerobic transition: re-examination of the threshold concept including an electromyographic approach

Summary The surface electromyogram (EMG) from the vastus lateralis muscle and the metabolic and respiratory parameters were studied simultaneously during an incremental exercise in order to identify EMG signal modifications during the aerobic-anaerobic transition. Subjects performed an incremental test on the bicycle ergometer from an initial work load of 175 W to exhaustion by steps of 25 W. Ventilatory flow ( _E), oxygen uptake ( ) and carbon dioxide flow ( ) were recorded continuously. For lactate concentration determination, venous blood samples were collected during the final 30 s of each step. EMG signals were stored on magnetic tape. They were then converted into successive spectra to allow the study of EMG total power (PEMG) and mean power frequency (MPF) evolutions. A non linear increase in blood lactate reflected by a breaking point at 250 W was observed. A change in ratio occured at 275 W. PEMG value showed a non linear increase reflected by a breaking point at 275 W. MPF value increased from the first to the seventh step with a tendency to decrease at the last step. A great interindividual variance of EMG data was observed indicating the difficulty of correlating mean values of EMG parameters with mean values of blood lactate in order to explain sudden lactate increase by fast twitch fibre recruitment. However, comparison of individual EMG data suggests a progressive recruitment of fast twitch fibres as work load increases.     

Persisting changes in basolateral amygdala mRNAs after chronic ethanol consumption

Adolescent alcohol use is common and evidence suggests that early use may lead to an increased risk of later dependence. Persisting neuroadaptions in the amygdala as a result of chronic alcohol use have been associated with negative emotional states that may lead to increased alcohol intake. This study assessed the long-term impact of ethanol consumption on levels of several basolateral amygdala mRNAs in rats that consumed ethanol in adolescence or adulthood. Male Long-Evans rats were allowed restricted access to ethanol or water during adolescence (P28, n = 11, controls = 11) or adulthood (P80, n = 8, controls = 10) for 18 days. After a sixty day abstinent period, the brain was removed and sections containing the basolateral amygdala were taken. In situ hybridization was performed for GABA_A α₁, glutamic acid decarboxylase (GAD₆₇), corticotropin releasing factor (CRF), and N-methyl-d-aspartate (NMDA) NR2A mRNAs. A significant decrease was observed in GABA_A α₁, GAD₆₇, and CRF, but not NR2A, mRNAs in adult rats that consumed ethanol in comparison to controls. No significant changes were seen in adolescent consumers of ethanol for any of the probes tested. A separate analysis for each probe in the piriform cortex ascertained that the changes after ethanol consumption were specific to the basolateral amygdala. These results indicate that chronic ethanol consumption induces age-dependent alterations in basolateral amygdala neurochemistry.     

Antioxidant N-acetylcysteine inhibits the activation of JNK3 mediated by the GluR6–PSD95–MLK3 signaling module during cerebral ischemia in rat hippocampus

Cerebral ischemia induces kainate receptor glutamate receptor 6 (GluR6) binding to the postsynaptic density protein 95 (PSD95), which in turn anchors mixed lineage kinase 3 (MLK3) via SH3 domain in rat brain. MLK3 subsequently activates c-Jun NH₂-terminal kinase (JNK) via MAP kinase kinases (MKKs). In this study, we investigated the association of PSD95 with GluR6 and MLK3, the autophosphorylation of MLK3, the combination of MLK3 with JNK3, and the phosphorylation of JNK3 during cerebral ischemia in rat hippocampus CA1. Our results indicate that the GluR6–PSD95–MLK3 complex quickly enhanced at 5 min of ischemia and peaked at 10 min of ischemia, and then gradually reduced with the prolonged time of ischemia. Interestingly, the combination of MLK3 and JNK3 gradually increased from 5 min to 30 min of ischemia. JNK3 phosphorylation first increased and then attenuated in cytosol, suggesting the translocation of activated JNK3 to nucleus during ischemia. To further investigate the possible mechanism of JNK3 activation, antioxidant N-acetylcysteine (NAC) was given to the rats 20 min prior to ischemia. Results indicate that NAC distinctly inhibited the association of PSD95 with GluR6 and MLK3, the autophosphorylation of MLK3, the combination of MLK3 with JNK3 and JNK3 activation. Taken together, these finding indicate that ischemic stimulation results in JNK3 activation through the GluR6–PSD95–MLK3 signaling module, and that the activation of JNK3 is closely related to oxidative stress.     

Negative crosstalk between M1 and M2 muscarinic autoreceptors involves endogenous adenosine activating A1 receptors at the rat motor endplate

At the rat motor nerve terminals, activation of muscarinic M₁ receptors negatively modulates the activity of inhibitory muscarinic M₂ receptors. The present work was designed to investigate if the negative crosstalk between muscarinic M₁ and M₂ autoreceptors involved endogenous adenosine tonically activating A₁ receptors on phrenic motor nerve terminals. The experiments were performed on rat phrenic nerve-hemidiaphragm preparations loaded with [³H]-choline (2.5 μCi/ml). Selective activation of muscarinic M₁ and adenosine A₁ receptors with 4-(N-[3-clorophenyl]-carbamoyloxy)-2-butyryltrimethylammonium (McN-A-343, 3 μM) and R-N⁶-phenylisopropyladenosine (R-PIA, 100 nM), respectively, significantly attenuated inhibition of evoked [³H]-ACh release induced by muscarinic M₂ receptor activation with oxotremorine (10 μM). Attenuation of the inhibitory effect of oxotremorine (10 μM) by R-PIA (100 nM) was detected even in the presence of pirenzepine (1 nM) blocking M₁ autoreceptors, suggesting that suppression of M₂-inhibiton by A₁ receptor activation is independent on muscarinic M₁ receptor activity. Conversely, the negative crosstalk between M₁ and M₂ autoreceptors seems to involve endogenous adenosine tonically activating A₁ receptors. This was suggested, since attenuation of the inhibitory effect of oxotremorine (10 μM) by McN-A-343 (3 μM) was suppressed by the A₁ receptor antagonist, 1,3-dipropyl-8-cyclopentylxanthine (2.5 nM), and by reducing extracellular adenosine with adenosine deaminase (0.5 U/mL) or with the adenosine transport blocker, S-(p-nitrobenzyl)-6-thioinosine (NBTI, 10 μM). The results suggest that the negative crosstalk between muscarinic M₁ and M₂ autoreceptors involves endogenous adenosine outflow via NBTI-sensitive (es) nucleoside transport system channelling to the activation of presynaptic inhibitory A₁ receptors at the rat motor endplate.     

Effects of incremental exercise on cerebral oxygenation measured by near-infrared spectroscopy: A systematic review

We conducted a systematic review and meta-regression analysis to quantify effects of exercise on brain hemodynamics measured by near-infrared spectroscopy (NIRS). The results indicate that acute incremental exercise (categorized relative to aerobic capacity (VO₂peak) as low – <30% VO₂peak; moderate – ≥30% VO₂peak to <60% VO₂peak; hard – ≥60% VO₂peak to <VO₂peak; and very hard – ≥VO₂peak intensities) performed by 291 healthy people in 21 studies is accompanied by moderate-to-large increases (mean effect, dz ± 95% CI) in the prefrontal cortex of oxygenated hemoglobin (O₂Hb) or other measures of oxygen level (O₂Hbdiff) or saturation (SCO₂) (0.92 ± 0.67, 1.17), deoxygenated hemoglobin (dHb) (0.87 ± 0.56, 1.19), and blood volume estimated by total hemoglobin (tHb) (1.21 ± 0.84, 1.59). After peaking at hard intensities, cerebral oxygen levels dropped during very hard intensities. People who were aerobically trained attained higher levels of cortical oxygen, dHb, and tHb than untrained people during very hard intensities. Among untrained people, a marked drop in oxygen levels and a small increase in dHb at very hard intensities accompanied declines in tHb, implying reduced blood flow. In 6 studies of 222 patients with heart or lung conditions, oxygenation and dHb were lowered or unchanged during exercise compared to baseline. In conclusion, prefrontal oxygenation measured with NIRS in healthy people showed a quadratic response to incremental exercise, rising between moderate and hard intensities, then falling at very hard intensities. Training status influenced the responses. While methodological improvements in measures of brain oxygen are forthcoming, these results extend the evidence relevant to existing models of central limitations to maximal exercise.     

Whole-blood culture is a valid low-cost method to measure monocytic cytokines — A comparison of cytokine production in cultures of human whole-blood, mononuclear cells and monocytes

Whole-blood and peripheral blood mononuclear cell (PBMC) cultures are used as non-validated surrogate measures of monocytic cytokine production. The aim of this investigation was to compare ex vivo cytokine production from human whole-blood and PBMC with that from isolated monocytes. We also assessed the intra- and inter-individual variation in cytokine production. In 64 healthy men (age 19-40 years) IL-6, TNF and IL-10 were measured by enzyme-linked immunosorbent assay in supernatants from whole-blood, PBMC and monocytes cultured 24 h with lipopolysaccharide (LPS) or UV-killed L. acidophilus. Cytokines produced from whole-blood was found to be more strongly correlated with monocytic cytokines than cytokines from PBMC, particularly after LPS-stimulation: r = 0.57, P < 0.001 versus r = 0.33, P = 0.01 for IL-6 and r = 0.43, P < 0.001 versus r = 0.30, P = 0.02 for TNF-α. Adjustment for a preceding 8-week dietary fatty acid-intervention did not change any of the associations. Based on measurements at three time-points 8 weeks apart the intra-individual variation was ≥ 50% smaller than the inter-individual variation (P < 0.05) in most whole-blood cytokine responses and LPS-stimulated IL-6 from PBMC. We conclude that whole-blood cultures are well-suited low-cost proxy-measures of monocytic cytokine production. Moreover, large inter-individual variation in cytokine production was demonstrated whereas the individual responses in whole-blood were reproducible even over long time-periods.     

Low tidal volume with PEEP and recruitment expedite the recovery of pulmonary function

The potentially harmful effects of short-term mechanical ventilation during surgery have been examined in recent years. An optimal strategy for mechanical ventilation of patients during non-laparoscopic abdominal surgery must be devised. A total of 63 patients undergoing elective open abdominal surgery with more than 2 h of ventilation time were selected for this randomized, open-label, clinical study. They were divided into three ventilation groups: high volume of 9 ml/kg IBW (ideal body weight) with ZEEP (zero end-expiratory pressure); low volume of 7 ml/kg IBW with 8 cm H₂O PEEP (positive end expiratory pressure); and low volume of 7 ml/kg IBW with 8 cm H₂O PEEP and recruitment. Intraoperative PaO₂/FiO₂ ratio and pulmonary compliance and postoperative pulmonary function were measured. There were no significant differences in intraoperative PaO₂/FiO₂ ratio among the three groups (P=0.31). The pulmonary compliance of three groups showed different changes over time (group effect over time P=0.0006). There were no significant differences in FEV1 or FVC among the three groups (P=0.32 and 0.09, respectively), but both of these measurements showed different changes over time (group effect over time P<0.001). On the first postoperative day, the low volume with high PEEP and recruitment group had significantly higher FEV1 than the other two groups (mean ± SD): 1.52±0.37 versus 0.95±0.38 (P<0.001) and 1.52±0.37 versus 0.95±0.34 (P<0.001), respectively. Low tidal volume with PEEP and recruitment showed advantages in maintaining the pulmonary compliance and expediting the recovery of the 1^st postoperative day’s pulmonary function in patients undergoing non-laparoscopic abdominal surgery.