Normal thermoregulatory responses to 3‐iodothyronamine,trace amines and amphetamine‐like psychostimulants in trace amine associated receptor 1 knockout mice

3‐Iodothyronamine (T1AM) is a metabolite of thyroid hormone. It is an agonist at trace amine‐associated receptor 1 (TAAR1), a recently identified receptor involved in monoaminergic regulation and a potential novel therapeutic target. Here, T1AM was studied using rhesus monkey TAAR1 and/or human dopamine transporter (DAT) co‐transfected cells, and wild‐type (WT) and TAAR1 knock‐out (KO) mice. The IC₅₀ of T1AM competition for binding of the DAT‐specific radio‐ligand [³H]CFT was highly similar in DAT cells, WT striatal synaptosomes and KO striatal synaptosomes (0.72–0.81 μM). T1AM inhibition of 10 nM [³H]dopamine uptake (IC₅₀: WT, 1.4 ± 0.5 μM; KO, 1.2 ± 0.4 μM) or 50 nM [³H]serotonin uptake (IC₅₀: WT, 4.5 ± 0.6 μM; KO, 4.7 ± 1.1 μM) in WT and KO synaptosomes was also highly similar. Unlike other TAAR1 agonists that are DAT substrates, TAAR1 signaling in response to T1AM was not enhanced in the presence of DAT as determined by CRE‐luciferase assay. In vivo, T1AM induced robust hypothermia in WT and KO mice equivalently and dose dependently (maximum change degrees Celsius: 50 mg/kg at 60 min: WT ?6.0 ± 0.4, KO ?5.6 ± 1.0; and 25 mg/kg at 30 min: WT ?2.7 ± 0.4, KO ?3.0 ± 0.2). Other TAAR1 agonists including beta–phenylethylamine (β‐PEA), MDMA (3,4‐methylenedioxymethamphetamine) and methamphetamine also induced significant, time‐dependent thermoregulatory responses that were alike in WT and KO mice. Therefore, TAAR1 co‐expression does not alter T1AM binding to DAT in vitro nor T1AM inhibition of [³H]monoamine uptake ex vivo, and TAAR1 agonist‐induced thermoregulatory responses are TAAR1‐independent. Accordingly, TAAR1‐directed compounds will likely not affect thermoregulation nor are they likely to be cryogens. © 2010 Wiley‐Liss, Inc.     

Muscular adaptations and insulin‐like growth factor‐1 responses to resistance training are stretch‐mediated

Introduction: Modulation of muscle characteristics was attempted through altering muscle stretch during resistance training. We hypothesized that stretch would enhance muscle responses. Methods: Participants trained for 8 weeks, loading the quadriceps in a shortened (SL, 0–50° knee flexion; n = 10) or lengthened (LL, 40–90°; n = 11) position, followed by 4 weeks of detraining. Controls (CON; n = 10) were untrained. Quadriceps strength, vastus lateralis architecture, anatomical cross‐sectional area (aCSA), and serum insulin‐like growth factor‐1 (IGF‐1) were measured at weeks 0, 8, 10, and 12. Results: Increases in fascicle length (29 ± 4% vs. 14 ± 4%), distal aCSA (53 ± 12% vs. 18 ± 8%), strength (26 ± 6% vs. 7 ± 3%), and IGF‐1 (31 ± 6% vs. 7 ± 6%) were greater in LL compared with SL muscles (P < 0.05). No changes occurred in CON. Detraining decrements in strength and aCSA were greater in SL than LL muscles (P < 0.05). Conclusions: Enhanced muscle in vivo (and somewhat IGF‐1) adaptations to resistance training are concurrent with muscle stretch, which warrants its inclusion within training. Muscle Nerve 49 : 108–119, 2014     

Impaired propulsive motility in the distal but not proximal colon of BK channel β1‐subunit knockout mice

Background Large‐conductance Ca²⁺‐activated K⁺ (BK) channels regulate smooth muscle tone. The BK channel β1‐subunit increases Ca²⁺ sensitivity of the α‐subunit in smooth muscle. We studied β1‐subunit knockout (KO) mice to determine if gastrointestinal (GI) motility was altered. Methods Colonic and intestinal longitudinal muscle reactivity to bethanechol and colonic migrating motor complexes (CMMCs) were measured in vitro. Gastric emptying and small intestinal transit were measured in vivo. Colonic motility was assessed in vivo by measuring fecal output and glass bead expulsion time. Myoelectric activity of distal colon smooth muscle was measured in vitro using intracellular microelectrodes. Key Results Bethanechol‐induced contractions were larger in the distal colon of β1‐subunit KO compared to wild type (WT) mice; there were no differences in bethanechol reactivity in the duodenum, ileum, or proximal colon of WT vsβ1‐subunit KO mice. There were more retrogradely propagated CMMCs in the distal colon of β1‐subunit KO compared to WT mice. Gastrointestinal transit was unaffected by β1‐subunit KO. Fecal output was decreased and glass bead expulsion times were increased in β1‐subunit KO mice. Membrane potential of distal colon smooth muscle cells from β1‐subunit KO mice was depolarized with higher action potential frequency compared to WT mice. Paxilline (BK channel blocker) depolarized smooth muscle cells and increased action potential frequency in WT distal colon. Conclusions & Inferences BK channels play a prominent role in smooth muscle function only in the distal colon of mice. Defects in smooth muscle BK channel function disrupt colonic motility causing constipation.     

Soleus and lateral gastrocnemius H‐reflexes during standing with unstable footwear

Introduction: Unstable footwear has been shown to increase lower extremity muscle activity, but the reflex response to perturbations induced by this intervention is unknown. Methods: Twenty healthy subjects stood in stable and unstable footwear conditions (presented randomly) while H‐reflex amplitude and background muscle activity were measured in the soleus and lateral gastrocnemius (LG) muscles. Results: Wearing unstable footwear resulted in larger H‐reflexes (normalized to the maximal M‐wave) for the LG (+12%; P = 0.025), but not for the soleus (+4%; P > 0.05). Background activity of both muscles was significantly higher in the unstable condition. Conclusions: The H‐reflex facilitation observed with unstable footwear was unexpected, as challenging postural conditions usually result in reflex depression. Increased muscle activity, decreased presynaptic inhibition, and/or more forward postural position may have (over‐)compensated the expected reflex depression. Differences between LG and soleus H‐reflex modulation may be due to diverging motor unit recruitment thresholds. Muscle Nerve 51 :764–766, 2015     

Actin sliding velocity on pure myosin isoforms from dystrophic mouse muscles

Duchenne muscular dystrophy (DMD) is a genetic disease characterized by skeletal muscle wasting and atrophy. Recent evidence suggests that the impaired skeletal muscle performance in DMD is not solely dependent on a loss of contractile muscle mass. In this study the myosin motor function of mdx and control (wildtype, WT) mice was compared using pure myosin isoforms in an “in vitro motility assay” (IVMA). Actin sliding velocity (Vf) on myosin 2B extracted from single muscle fibers of gastrocnemius muscles was significantly lower in mdx mice (3.48 ± 0.13 μm/s, n = 18) than in WT mice (4.02 ± 0.19 μm/s, n = 10). No difference in Vf was found between myosin 1 extracted from soleus muscles of mdx (0.84 ± 0.04 μm/s, n = 13) and of WT (0.89 ± 0.04 μm/s, n = 10). The results suggest that the dystrophic process alters myosin molecular function, and this contributes to the functional impairment in dystrophic muscles. Muscle Nerve 40: 249–256, 2009     

Effects of exercise and muscle type on BDNF,NT‐4/5, and TrKB expression in skeletal muscle

Muscle‐derived neurotrophins are thought to contribute to the adaptation of skeletal muscle to exercise, but the effects of brief exercise interventions on BDNF, NT‐4/5, and trkB are not understood. RNA was extracted for RT‐PCR from soleus and medial gastrocnemius of Sprague‐Dawley rats exercised on a treadmill at speeds up to 20 m/min at 5% incline for 5 or 10 days. BDNF expression was elevated in soleus following 5 days (184%, P < 0.001) but not 10 days of exercise. NT‐4/5 and trkB were not affected at either time‐point. BDNF mRNA was significantly higher in soleus at rest when compared with medial gastrocnemius (193%, P < 0.05). No significant effects of muscle type were detected for NT‐4/5 and trkB. Our results indicate differential control of BDNF expression between soleus and medial gastrocnemius following 5 days of exercise. BDNF may be a protein with an uncharacterized contribution to the acute adaptation of skeletal muscle to exercise, whereas NT‐4/5 shows no response. Muscle Nerve, 2009     

Changes in soleus H‐reflex during walking in middle‐aged,healthy subjects

Introduction: To assess the effect of aging on stretch reflex modulation during walking, soleus H‐reflexes obtained in 15 middle‐aged (mean age 56.4 ± 6.9 years) and 15 young (mean age 23.7 ± 3.9 years) subjects were compared. Methods: The H‐reflex amplitude, muscle activity (EMG) of the soleus and tibialis anterior muscles, and EMG/H‐reflex gain were measured during 4‐km/h treadmill walking. Results: The normalized H‐reflex amplitude was lower in the swing phase for the middle‐aged group, and there was no difference in muscle activity. EMG/H‐reflex gain did not differ between groups. Conclusions: H‐reflex amplitude during walking was affected by aging, and changes during the swing phase could be seen in the middle‐aged subjects. Subdividing the 2 age groups into groups of facilitated or suppressed swing‐phase H‐reflex revealed that the H‐reflex amplitude modulation pattern in the group with facilitated swing‐phase H‐reflex may be influenced by aging. Muscle Nerve 51: 419–425, 2015     

Phrenic nerve involvement and respiratory muscle weakness in patients with Charcot‐Marie‐Tooth disease 1A

Diaphragm weakness in Charcot‐Marie‐Tooth disease 1A (CMT1A) is usually associated with severe disease manifestation. This study comprehensively investigated phrenic nerve conductivity, inspiratory and expiratory muscle function in ambulatory CMT1A patients. Nineteen adults with CMT1A (13 females, 47 ± 12 years) underwent spiromanometry, diaphragm ultrasound, and magnetic stimulation of the phrenic nerves and the lower thoracic nerve roots, with recording of diaphragm compound muscle action potentials (dCMAP, n = 15), transdiaphragmatic and gastric pressures (twPdi and twPgas, n = 12). Diaphragm motor evoked potentials (dMEP, n = 15) were recorded following cortical magnetic stimulation. Patients had not been selected for respiratory complaints. Disease severity was assessed using the CMT Neuropathy Scale version 2 (CMT‐NSv2). Healthy control subjects were matched for age, sex, and body mass index. The following parameters were significantly lower in CMT1A patients than in controls (all P < .05): forced vital capacity (91 ± 16 vs 110 ± 15% predicted), maximum inspiratory pressure (68 ± 22 vs 88 ± 29 cmH₂O), maximum expiratory pressure (91 ± 23 vs 123 ± 24 cmH₂O), and peak cough flow (377 ± 135 vs 492 ± 130 L/min). In CMT1A patients, dMEP and dCMAP were delayed. Patients vs controls showed lower diaphragm excursion (5 ± 2 vs 8 ± 2 cm), diaphragm thickening ratio (DTR, 1.9 [1.6‐2.2] vs 2.5 [2.1‐3.1]), and twPdi (8 ± 6 vs 19 ± 7 cmH₂O; all P < .05). DTR inversely correlated with the CMT‐NSv2 score (r = ?.59, P = .02). There was no group difference in twPgas following abdominal muscle stimulation. Ambulatory CMT1A patients may show phrenic nerve involvement and reduced respiratory muscle strength. Respiratory muscle weakness can be attributed to diaphragm dysfunction alone. It relates to neurological impairment and likely reflects a disease continuum.     

Apigenin inhibits sciatic nerve denervation–induced muscle atrophy

Introduction: Apigenin (AP) has been reported to elicit anti‐inflammatory effects. In this study, we investigated the effect of AP on sciatic nerve denervation–induced muscle atrophy. Methods: Sciatic nerve–denervated mice were fed a 0.1% AP‐containing diet for 2 weeks. Muscle weight and cross‐sectional area (CSA), and the expression of atrophic genes and inflammatory cytokines in the gastrocnemius were analyzed. Results: Denervation significantly induced muscle atrophy. However, values for muscle weight and CSA were greater in the denervated muscle of the AP mice than the controls. AP suppressed the expression of MuRF1, but upregulated both myosin heavy chain (MHC) and MHC type IIb. AP also significantly suppressed expression of tumor necrosis‐alpha in the gastrocnemius and soleus muscles, and interleukin‐6 expression in the soleus muscle. Discussion: AP appears to inhibit denervation‐induced muscle atrophy, which may be due in part to its inhibitory effect on inflammatory processes within muscle. Muscle Nerve 58 : 314–318, 2018     

Effects of moderate‐ and high‐intensity chronic exercise on brain‐derived neurotrophic factor expression in fast and slow muscles

Introduction: Brain‐derived neurotrophic factor (BDNF) protein expression is sensitive to cellular activity. In the sedentary state, BDNF expression is affected by the muscle phenotype. Methods: Eighteen Wistar rats were divided into the following 3 groups: sedentary (S); moderate‐intensity training (MIT); and high‐intensity training (HIT). The training protocol lasted 8 weeks. Forty‐eight hours after training, total RNA and protein levels in the soleus and plantaris muscles were obtained. Results: In the plantaris, the BDNF protein level was lower in the HIT than in the S group (P < 0.05). A similar effect was found in the soleus (without significant difference). In the soleus, higher Bdnf mRNA levels were found in the HIT group (P < 0.001 vs. S and MIT groups). In the plantaris muscle, similar Bdnf mRNA levels were found in all groups. Conclusions: These results indicate that high‐intensity chronic exercise reduces BDNF protein level in fast muscles and increases Bdnf mRNA levels in slow muscles. Muscle Nerve 53: 446–451, 2016     

Upregulation of axon guidance molecules in the adult central nervous system of Nogo‐A knockout mice restricts neuronal growth and regeneration

Adult central nervous system axons show restricted growth and regeneration properties after injury. One of the underlying mechanisms is the activation of the Nogo‐A/Nogo receptor (NgR1) signaling pathway. Nogo‐A knockout (KO) mice show enhanced regenerative growth in vivo, even though it is less pronounced than after acute antibody‐mediated neutralization of Nogo‐A. Residual inhibition may involve a compensatory component. By mRNA expression profiling and immunoblots we show increased expression of several members of the Ephrin/Eph and Semaphorin/Plexin families of axon guidance molecules, e.g. EphrinA3 and EphA4, in the intact spinal cord of adult Nogo‐A KO vs. wild‐type (WT) mice. EphrinA3 inhibits neurite outgrowth of EphA4‐positive neurons in vitro. In addition, EphrinA3 KO myelin extracts are less growth‐inhibitory than WT but more than Nogo‐A KO myelin extracts. EphA4 KO cortical neurons show decreased growth inhibition on Nogo‐A KO myelin as compared with WT neurons, supporting increased EphA4‐mediated growth inhibition in Nogo‐A KO mice. Consistently, in vivo, Nogo‐A/EphA4 double KO mice show increased axonal sprouting and regeneration after spinal cord injury as compared with EphA4 KO mice. Our results reveal the upregulation of developmental axon guidance cues following constitutive Nogo‐A deletion, e.g. the EphrinA3/EphA4 ligand/receptor pair, and support their role in restricting neurite outgrowth in the absence of Nogo‐A.     

Cell autonomous and noncell‐autonomous role of NF‐κB p50 in astrocyte‐mediated fate specification of adult neural progenitor cells

In previous work, we demonstrated that NF‐κB p50 acts as crucial regulator of adult hippocampal neural progenitor cells (ahNPC). Indeed, NF‐κB p50 knockout (KO) mice are characterized by remarkably reduced hippocampal neurogenesis. As a follow up to that work, herein we show that when cultured in vitro, ahNPC from wild type (WT) and p50KO mice are not significantly different in their neurogenic potential. This observation prompted us to investigate cell‐autonomous and noncell‐autonomous consequences of p50 absence on neuronal fate specification of ahNPC. In particular, we focused our attention on astrocytes, known to provide soluble proneurogenic signals, and investigated the influence of WT and p50KO astrocyte conditioned media (ACM) on WT and p50KO ahNPC differentiation. Interestingly, while WT ACM promoted both neuronal and astroglial differentiations, p50KO ACM only supported astroglial differentiation of WT ahNPC. By using a LC–MS/MS approach, we identified some proteins, which are significantly upregulated in p50KO compared with WT astrocytes. Among them, lipocalin‐2 (LCN‐2) was recognized as a novel astroglial‐derived signal regulating neuronal fate specification of ahNPC. Interestingly, LCN‐2 proneurogenic effect was greatly reduced in p50KO NPC, where LCN‐2 receptor gene expression appeared downregulated. In addition to that, we demonstrated p50KO NPC unresponsiveness to both neuronal and astroglial fate specification signals from WT and p50KO ACM, and we identified a reduced expression of α2δ1, a thrombospondin‐1 receptor, as another phenotypic change occurring in ahNPC in the absence of p50. Altogether, our data suggest that dysregulated NPC‐astrocyte communication may contribute to a reduced hippocampal neurogenesis in p50KO mice in vivo. GLIA 2016 GLIA 2017;65:169–181     

Assessment of musculo‐articular and muscle stiffness in young and older men

Introduction: The aim of this cross‐sectional study was to concurrently assess musculo‐articular stiffness (MAS) and muscle stiffness (MS) of the knee extensors in younger and older individuals. Methods: Fourteen young (22.1 ± 3.0 years old) and 12 older (65.4 ± 5.7 years old) men were tested for maximal voluntary contraction (MVC), rate of torque development (RTD), muscle thickness, MAS, and MS of knee extensors. Results: MVC, RTD, and muscle thickness were higher in the younger group (288.6 vs. 194.3 Nm, 1319.5 vs. 787.0 Nm s^?1, 23.1 vs. 17.7 mm, respectively, P < 0.05). MAS normalized to the load supported (30% of MVC) was not different between groups (87.9 vs. 88.5 Nm^?1kg^?1), whereas the older group exhibited a higher level of normalized MS (23.2 vs. 18.6 Nm^?1kg^?1, P < 0.05). Conclusions: Determinants of MS have been highlighted along with their role in elevated MS. The unaltered level of MAS, which is functionally important in an aging population, might be achieved through a decrease in tendon stiffness. Muscle Nerve 46: 559–565, 2012     

Inflammatory response during slow‐ and fast‐twitch muscle regeneration

Introduction: Skeletal muscles are characterized by their unique ability to regenerate. Injury of a so‐called fast‐twitch muscle, extensor digitorum longus (EDL), results in efficient regeneration and reconstruction of the functional tissue. In contrast, slow‐twitch muscle (soleus) fails to properly reconstruct and develops fibrosis. This study focuses on soleus and EDL muscle regeneration and associated inflammation. Methods: We determined differences in the activity of neutrophils and M1 and M2 macrophages using flow cytometry and differences in the levels of proinflammatory cytokines using Western blotting and immunolocalization at different times after muscle injury. Results: Soleus muscle repair is accompanied by increased and prolonged inflammation, as compared to EDL. The proinflammatory cytokine profile is different in the soleus and ED muscles. Conclusions: Muscle repair efficiency differs by muscle fiber type. The inflammatory response affects the repair efficiency of slow‐ and fast‐twitch muscles. Muscle Nerve 55 : 400–409, 2017     

Locally acting ACE‐083 increases muscle volume in healthy volunteers

Introduction: ACE‐083 is a locally acting follistatin‐based therapeutic that binds myostatin and other muscle regulators and has been shown to increase muscle mass and force in neuromuscular disease mouse models. This first‐in‐human study examined these effects. Methods: In this phase 1, randomized, double‐blind, placebo‐controlled, dose‐ranging study in healthy postmenopausal women, ACE‐083 (50–200 mg) or placebo was administered unilaterally into rectus femoris (RF) or tibialis anterior (TA) muscles as 1 or 2 doses 3 weeks apart. Results: Fifty‐eight postmenopausal women were enrolled, 42 ACE‐083 and 16 placebo. No serious adverse events (AE), dose‐limiting toxicities, or discontinuations resulting from AEs occurred. Maximum (mean ± SD) increases in RF and TA muscle volume were 14.5% ± 4.5% and 8.9% ± 4.7%, respectively. No significant changes in mean muscle strength were observed. Discussion: ACE‐083 was well tolerated and resulted in significant targeted muscle growth. ACE‐083 may have the potential to increase muscle mass in a wide range of neuromuscular disorders. Muscle Nerve 57 : 921–926, 2018     

Post‐activation potentiation: The neural effects of post—activation depression

Introduction: Our knowledge of the neurophysiology of post‐activation potentiation (PAP) is limited. The purpose of this study was to examine the effect of PAP on twitch torque and H‐reflex amplitude after a 10‐s maximal voluntary contraction (MVC). Methods: PAP measurements were assessed with the plantarflexors in a relaxed state and during a tonic contraction at 10% MVC. Results: The H‐reflex/maximum M‐wave ratio (H/M) decreased significantly (P < 0.05) and returned to baseline levels after 1 min. The decrement in H/M was depressed when the plantarflexors were active at 10% MVC, and the depression was more obvious in the lateral gastrocnemius than in the soleus muscle. Conclusions: The inhibition induced immediately after contraction could be attributed to post‐activation depression. We conclude that PAP after a 10‐s MVC cannot be attributed to increased motor neuron excitability through the reflex pathway as assessed by the H‐reflex technique. Muscle Nerve 52 : 252–259, 2015     

Ingestion of transient receptor potential channel agonists attenuates exercise‐induced muscle cramps

Introduction: Exercise‐associated muscle cramping (EAMC) is a poorly understood problem that is neuromuscular in origin. Ingestion of transient receptor potential (TRP) channel agonists has been efficacious in attenuating electrically induced muscle cramps. This study examines the effect of TRP agonist ingestion on voluntarily induced EAMC and motor function. Methods: Study 1: Thirty‐nine participants completed 2 trials after ingesting TRP agonist‐containing active treatment (A), or vehicle (V) control. Cramping in the triceps surae muscle was induced via voluntary isometric contraction. Study 2: After ingesting A or V, 31 participants performed kinematic and psychomotor tests of manual dexterity. Results: A increased precramp contraction duration (A, 36.9 ± 4.1 s; V, 27.8 ± 3.1 s), decreased cramp EMG area under the curve (A, 37.3 ± 7.7 %EMG_max·s; V, 77.2 ± 17.7 %EMG_max·s), increased contraction force to produce the cramp (A, 13.8 ± 1.8 kg; V, 9.9 ± 1.6 kg), and decreased postcramp soreness (A, 4.1 ± 0.3 arbitrary units (a.u.); V, 4.7 ± 0.3 a.u.). Kinematic and psychomotor tests were not affected. Discussion: TRP agonist ingestion attenuated EAMC characteristics without affecting motor function. Muscle Nerve 56 : 379–385, 2017     

Vastus lateralis NA+‐K+‐ATpase activity,protein, and isoform distribution in chronic obstructive pulmonary disease

In this study we investigate the hypothesis that protein abundance, isoform distribution, and maximal catalytic activity of sodium–potassium–adenosine triphosphatase (Na⁺‐K⁺‐ATPase) would be altered in muscle of patients with moderate to severe chronic obstructive pulmonary disease (COPD). Tissue samples were obtained from the vastus lateralis of 10 patients with COPD (mean ± SE: age = 67 ± 2.9 years; FEV₁ = 39 ± 5.5%) and 10 healthy, matched controls (CON: age = 68 ± 2 years; FEV₁ = 114 ± 4.2%). The samples were assessed for maximal catalytic activity (V_max) of the enzyme using the K⁺‐stimulated 3‐O‐methylfluorescein‐phosphatase (3‐O‐MFPase) assay, enzyme abundance using the [³H]‐ouabain assay, and isoform content of both α (α₁, α₂, α₃) and β (β₁, β₂, β₃) using Western blot techniques. A 19.4% lower (P < 0.05) V_max was observed in COPD compared with CON (90.7 ± 6.7 vs. 73.1 ± 4.7 nmol · mg protein^?1 h^?1). No differences between groups were observed for pump concentration (259 ± 15 vs. 243 ± 17 pmol · g wet weight). For the isoforms, α₁ was decreased by 28% (P < 0.05), and α₂ was increased by 12% (P < 0.05) in COPD compared with CON. No differences between groups were observed for α₃ or for the β isoforms. We conclude that moderate COPD compromises V_max, which occurs in the absence of changes in pump abundance. The reduction in V_max could be due to a shift in isoform expression (α₁, α₂), alterations in intrinsic regulation, or to structural changes in the enzyme. The changes observed in the catalytic activity of the pump could have major effects on membrane excitability and fatigability, which are typically compromised in COPD. Muscle Nerve, 2009