Vibration platform for mice to deliver precise, low intensity mechanical signals to the musculoskeleton.

OBJECTIVE: Low intensity vibration as a therapeutic and training modality has received increased attention despite the lack of clear mechanistic pathways. Thus, to determine mechanisms underpinning vibration-induced musculoskeletal adaptations, a vibration platform for mice was designed, constructed, and validated. METHODS: Critical aspects of the platform include use of off-the-shelf components to (1) tailor individual parameter selection (acceleration and frequency), (2) produce low error across the plate's surface and throughout the range of vibration parameters, and (3) utilize accelerometer feedback to ensure fidelity within and between bouts of vibration. The vibration device is controlled by a centrally-mounted linear actuator on the underside of the platform that is modulated by accelerometer feedback. RESULTS: Triaxial accelerometers confirmed that vibrations were purely vertical and acceleration responses were within 5% of target stimuli for all accelerations (0.2-1.0 g) and frequencies (25-90 Hz). The platform produced acceleration responses with ≤4% error between 25-90 Hz. Vibration modes were not detected indicating that the circular plate produced uniform stimuli across the platform (error ≤1.1%, P≥0.23) and mouse body mass did not affect the platform's performance (P≥0.43). CONCLUSIONS: Our vibration device for mice improves upon existing devices and enables precise, low intensity mechanical signals to be applied with confidence.

Musculoskeletal response of dystrophic mice to short term, low intensity, high frequency vibration.

OBJECTIVES: We aimed to identify parameters of low-intensity vibration that initiate the greatest osteogenic response in dystrophin-deficient mice and determine vibration safety for diseased muscle in three separate studies. METHODS: Study1: Mdx mice were randomized into seven vibration treatments and 14 d later, plasma osteocalcin and tibial osteogenic gene expression were compared among treatments. Study2: Three days of vibration was compared to other modalities known to elicit muscle injury in mdx mice. Study3: Dystrophic mice with more severe phenotypes due to altered utrophin were subjected to 7 d vibration to determine if muscle injury was induced. Muscle torque and genes associated with inflammation and myogenesis were assessed in Studies 2-3. RESULTS: Two sets of parameters (45 Hz 0.6 g and 90 Hz 0.6 g) evoked osteogenic responses. 45 Hz upregulated alkaline phosphatase and tended to upregulate osteoprotegerin without altering RANKL, and 90 Hz simultaneously upregulated osteprotegerin and RANKL. Thus, subsequent muscle studies utilized 45 Hz. Vibration for 3 or 7 d was not injurious to dystrophic muscle as shown by the lack of differences between vibrated and non-vibrated mice in torque and gene expression. CONCLUSIONS: Results indicate that vibration at 45 Hz and 0.6 g is safe for dystrophic muscle and may be a therapeutic modality to improve musculoskeletal health in DMD.

Prednisolone treatment and restricted physical activity further compromise bone of mdx mice.

OBJECTIVES: The purpose of this study was to determine the extent to which prednisolone treatment and restricted physical activity caused deleterious changes in inherently compromised mdx bone. METHODS: Four week-old male mdx mice (n=36) were treated for 8-wk either with or without prednisolone (0.8-1.3 mg/kg/d) and were housed in traditional or small cages (restricted activity). Tibial bone strength, geometry, and intrinsic material properties were assessed at the mid-shaft by three-point bending and micro-computed tomography (µCT). RESULTS: Three-point bending results showed that both prednisolone and restricted activity reduced bone strength (7%), however stiffness was only reduced in restricted-activity mice. µCT analyses showed that cortical bone area and cortical thickness were 13% smaller in restricted-activity mice, and may have accounted for their compromised bone strength. Intrinsic material properties, including volumetric bone mineral density (vBMD) and modulus of elasticity, were not impacted by either treatment, however, vBMD tended to be lower in restricted-activity mice (p=0.06). CONCLUSIONS: These data show that prednisolone treatment and restricted physical activity independently accentuate reductions in the strength and geometry of mdx bone, but do not influence intrinsic material properties.

Conformations of synthetic beta peptides in solid state and in aqueous solution: relation to toxicity in PC12 cells.

The secondary structures of peptides beta 25-35 (the active toxic fragment) and beta 35-25 (reverse sequence and non-toxic fragment), as well as of the amidated beta (25-35)-NH2 peptide were investigated in aqueous solution and in the solid state by means of Fourier-transformed infrared spectroscopy and circular dichroism spectroscopy. The conformations of the beta 25-35 and beta 35-25 in solid state were identical and contained mostly beta-sheet structures. In solid state the amidated beta (25-35)-NH2 peptide also contained mostly beta-sheet structures. Freshly prepared aqueous solutions of the beta 25-32 (0.5 - 3.8 mM) contained a mixture of beta-sheet and random coil structures. Within 30-60 min incubation at 37 degrees C in water or in phosphate-buffered saline solution (PBS), beta 25-35 was almost fully converted to a beta-sheet structure. Decreasing the temperature from 37 degrees C to 20 degrees C decreased the rate of conversion from random coil to beta-sheet structures, 1-2 h being required for complete conversion. In contrast beta 35-25 in water or in PBS buffer had mostly a random coil structure and remained so for 6 days. The amidated beta(25-35)-NH2 peptide in water (2.7 mM) was also mostly random coil. However, when this peptide (2-2.7 mM) was dissolved in PBS (pH 7.4) or in 140 mM NaCl, a gel was formed and its conformation was mostly beta-sheet. Decreasing the concentration of beta (25-35)-NH2 peptide in 140 mM NaCl aqueous solution from 2 mM to 1 mM or below favored the conversion from beta-sheet structures to random coil structures. The beta 25-35 was toxic to PC12 cells while beta 35-25 was not. The amidated peptide beta (25-35)-NH2 was at least 500-fold less toxic than beta 25-35. Structural differences between these beta peptides in aqueous solutions may explain the difference in their respective toxicities.

Surgical interventions for pharyngeal pouch.

BACKGROUND: A pharyngeal pouch is an out-pouching or pocket that develops from the posterior wall of the pharynx just above the entrance to the oesophagus (gullet). Pouches may give rise to difficulty in swallowing, sensation of a lump in the throat or of food sticking in the throat and may lead to troublesome regurgitation of food. Food may enter the pouch rather than passing down the oesophagus and this and regurgitation may result in weight loss, hoarseness of voice and/or recurrent chest infections. The management of patients with a pharyngeal pouch may be either conservative or surgical. The surgical management can be further divided into two broad categories: endoscopic and open procedures. In the first half of the twentieth century an open surgical approach to the pouch was most frequently used, and remains common in some parts of the world. In recent decades endoscopic procedures (where the approach is made through the mouth) have become popular. The superiority of one approach over another has yet to be clearly demonstrated. OBJECTIVES: To assess the effectiveness and safety of open and endoscopic surgical procedures for the management of a pharyngeal pouch. SEARCH STRATEGY: We searched the Cochrane Ear, Nose and Throat Disorders Group Specialised Register, the Cochrane Central Register of Controlled Trials (CENTRAL) in The Cochrane Library Issue 3, 2004, MEDLINE (1966 to 2004) and EMBASE (1974 to 2004). Reference lists of all identified trials and previous reviews were searched for additional trials. Further electronic searches for key authors identified were made. There were no language restrictions. The date of the last search was September 2004. SELECTION CRITERIA: We sought to identify all randomised controlled trials (RCTs) comparing two or more interventions. DATA COLLECTION AND ANALYSIS: Three reviewers assessed the eligibility of trials for inclusion in the review, based on pre-determined criteria. MAIN RESULTS: No trials were identified which fulfilled the criteria. AUTHORS' CONCLUSIONS: There is no evidence from high quality randomised controlled trials to demonstrate the effectiveness of endoscopic compared with open procedures for pharyngeal pouch. There is no good evidence to establish whether one endoscopic procedure is superior to another.

Organisation of lateral line and auditory areas in the midbrain of Xenopus laevis.

Lateral line areas in the midbrain of Xenopus laevis were identified by recording evoked potentials and neural activity elicited by stimulating anterior and posterior lateral line nerves. Spike activity was found in the lateral half of the optic tectum, ventrolateral tectum, and torus semicircularis. Contra- and ipsilateral lateral line pathways to these regions were identified. Spike discharge was associated with an evoked potential (EP) consisting of a large negative-positive wave sometimes preceded by a small positive-negative deflection. EP depth profiles varied according to electrode position within the lateral line midbrain projection field. In the middle of the field a dramatic increase in EP growth occurred as the electrode passed through the torus semicircularis, with peak amplitudes being achieved 900-1,100 micron from the surface within nucleus principalis and magnocellularis. Tracks at the lateral edge of the field showed a steady growth of EP, with peak amplitudes around 600 micron as the electrode passed through ventrolateral tectum. Auditory responses to tone pips were found in the nucleus laminaris and principalis in caudomedial regions of the torus semicircularis, in areas lying medial to the main centers of lateral line evoked activity; this is a similar organisation to that found in teleost fish. The results indicate the torus semicircularis and deep layers of the lateral tectum to be involved in lateral line processing Some topographic separation of the representation of anterior and posterior lateral line systems is indicated. The possible involvement of these areas in lateral line stimulus localisation is discussed.

Single-unit study of lateral line cells in the optic tectum of Xenopus laevis: evidence for bimodal lateral line/optic units.

Responses of single units in the Xenopus tectum to stimulation of the contralateral anterior lateral line nerve (cALLN) and optic nerve were studied. Cells responded to cALLN stimulation with a phasic burst of spikes that was repeatable between trials; latencies ranged from 4 to 23 msec. The most excitable cells were located in layer 6 of the ventrolateral tectum. Cells responding to stimulation of the ipsilateral ALLN were far less numerous and robust, and showed latencies 3-10 msec greater than those of contralateral responses. Tectal cell responses to cALLN nerve stimulation grew progressively to saturation with stimulus voltage and paralleled the growth of the ALLN compound action potential; cells responded to stimulation of either supra- or infraorbital branches of cALLN. These observations indicate convergence of primary lateral line afferents in the medulla and/or tectum. Lateral line tectal cells showed strong habituation at interstimulus times less than 8-20 seconds. Experiments on bimodal cells revealed facilitatory and inhibitory interactions between optic and lateral line inputs. Some cells responded to stimulation of either lateral line or optic nerves, with combined stimulation producing responses exceeding the sum of responses to separate nerve stimulation. In other cells the response to optic nerve stimulation was markedly increased by lateral line nerve stimulation, despite the absence of response to lateral line nerve stimulation alone. Facilitation was also evident in cells that responded only to combined stimulation of lateral line and optic nerves. Some cells exhibited an early (5-10 msec) and late (20-40 msec) response to optic nerve stimulation; lateral line nerve stimulation, despite eliciting no response itself, produced strong facilitation of the early but almost complete suppression of the late optic nerve response.

Biphenyl-derivatives of 2-amino-7-phosphonoheptanoic acid, a novel class of potent competitive N-methyl-D-aspartate receptor antagonist--I. Pharmacological characterization in vitro.

Omega-Phosphono-substituted alpha-amino acids have long been known to be antagonists at the N-methyl-D-aspartate (NMDA) receptor. D-2-Amino-5-phosphonopentanoic (D-AP5) and D-2-amino-7-phosphonoheptanoic (D-AP7) acids are the "prototype" compounds of this kind. Insertion of a biphenyl-moiety in the middle of the AP7 chain results in increased affinity and reverses the enantioselectivity from a D- to an L-form preference (Müller et al., (1992) Helv. Chim. Acta 75: 855-864). We describe here a series of substituted biphenyl-AP7-derivatives, the most potent of which have affinities (in a [3H]CGP-39653 binding assay using native and recombinant receptors) and potencies (antagonism of NMDA-induced depolarizations in a cortical wedge preparation; inhibition of glutamate-stimulated [3H]MK-801 binding under non-equilibrium conditions) in the low nanomolar range. Structure-activity relationships show that hydroxy-substitution at the C5-atom in the AP7-chain as well as substitution in the second phenyl ring with space filling (such as chloro-)groups in the para- and especially the ortho-position (extending the torsion angle of the two rings) increase affinity and potency of these compounds. They have no relevant affinities for the strychnine-insensitive glycine co-agonist site or the MK-801/PCP channel blocking site on the NMDA receptor complex. AMPA- and kainate-induced responses were not affected by biphenyl-analogues. These compounds also do not interact with a number of other neurotransmitter receptor sites, and they do not inhibit the uptake of [3H] glutamate in rat brain synaptosomes. However, they display affinities in the (sub)micromolar range for a non-NMDA, non-AMPA, non-kainate binding site for [3H]glutamate, measured in the presence of calcium chloride, the functional correlate of which has not yet been elucidated.

The calcium antagonistic effects of cyproheptadine on contraction, membrane electrical events and calcium influx in the guinea-pig taenia coli.

1 The ability of cyproheptadine (Cph) to inhibit membrane translocation of calcium in smooth muscle was investigated by studying the drug's action on contraction, electrical activity and calcium influx in the guinea-pig taenia coli.2 Cph >/= 10(-6)M reduced the amplitude of normal spontaneous contractions and concurrently decreased the number of action potentials occurring with each slow-wave of depolarization (sucrose-gap recordings). These inhibitory effects of Cph were antagonized by increasing the medium [Ca] three fold to 7.68 mM.3 Intracellular recordings showed that Cph >/= 2 x 10(-6)M decreased the amplitude and extended the duration of the action potential. These effects were only partially reversible in normal medium whereas large overshooting action potentials were again seen in 7.68 mM Ca medium.4 High frequency mechanical activity was produced by inclusion of veratridine 5 x 10(-6)M in the perfusate. Low concentrations of Cph (>/= 10(-7)M) reduced the amplitude of such contractions at a faster rate than they did normal spontaneous contractions.5 At concentrations between 10(-7) and 10(-6)M, Cph fully reduced the tonic component of contractions elicited in 112 mM isotonic KCl whilst having little or no effect on either (i) the initial phasic KCl contraction or (ii) the ;repolarization contracture' normally produced on wash-out of the KCl or (iii) the spontaneous contractions before and after KCl treatment. In contrast, at Cph 2 x 10(-6)M, the repolarization contracture, as well as the isotonic KCl contraction, was totally blocked whereas spontaneous contractions were still unaffected. Progressively higher Cph concentrations inhibited all components of this contractile cycle.6 Dose-response curves for the rate of drug-induced relaxation of tonic contractures produced in hypertonic 42.7 mM high-potassium medium, showed the calcium antagonistic potency of Cph to be intermediate between that of chlorpromazine and D600. The minimum Cph concentration for effect lay between 1 and 5 x 10(-7)M, and the effects of Cph 2 x 10(-6)M (approximately the ID(50)) were totally antagonized by 12.8 mM Ca.7 By means of a lanthanum wash procedure, Cph >/= 2 x 10(-6)M was found to decrease the (45)Ca uptake occurring into strips of taenia coli in normal medium, although the maximum effect (at Cph 10(-5)M) amounted to only 25% inhibition of the uptake occurring into control strips (also found with D600). The increased uptake occurring in hypertonic 44.7 mM high-potassium medium was inhibited in a dose-dependent manner by Cph 1 x 10(-7)M.8 The results are consistent with an action of Cph in reducing the flow of Ca(2+) through voltage-dependent Ca channels in the smooth muscle cell membrane. It is suggested that the interaction of Cph molecules with such sites is dependent upon membrane potential as well as drug concentration.

Mechanism by which cyproheptadine inhibits insulin secretion.

1 Isolated islets of Langerhans from the rat have been used in studies designed to elucidate the mechanism by which cyproheptadine inhibits insulin secretion. 2 D-Glucose and tolbutamide, both of which require extracellular Ca2+ to produce insulin release, failed to evoke a secretory response from islets pretreated with cyproheptadine. Conversely veratridine, the calcium ionophore A23187 and theophylline, all of which are capable of mobilizing sufficient intracellular Ca2+ to evoke insulin secretion in the absence of extracellular Ca2+, produced similar responses from cyproheptadine pretreated and control islets. 3 Cyproheptadine completely inhibited Ca2+ uptake induced by D-glucose and high Ko+, two agents which depolarize the islet beta-cell membrane, whilst Ca2+ uptake elicited by removal of extracellular Na+ (i.e. Na+-Ca2+ counter transport) was only slightly reduced. 4 A significant increase in Na+ uptake produced by veratridine was sensitive to tetrodoxin but only partially reduced by cyproheptadine. 5 These results suggest that cyproheptadine inhibits depolarization-dependent calcium entry into pancreatic beta-cells.

Clozapine promotes approach-oriented behavior in male mice.

Clozapine, an atypical antipsychotic agent, exerts ameliorative effects upon negative symptoms, but to date, its mechanism of action is poorly understood. We employed ethological methods to study the effects of clozapine, given 1 hour beforehand, on the social responses of (1) an individually housed male mouse exposed to an equally "matched" aggressive male opponent and (2) a group-housed "intruder" mouse exposed to an isolated, aggressive male. Encounters lasted 6 minutes. In matched pairs, mice given clozapine (0.01, 0.03, or 0.1 mg/kg s.c.) showed a significant increase in aggression without signs of stimulation. When given to intruder mice, clozapine (0.03, 0.1, or 0.3 mg/kg p.o.) markedly reduced defensive behavior and reinstated their investigative and sexual activities. The results suggest that low, nonsedating doses of clozapine counteract social withdrawal by selectively increasing "situationally appropriate" approach behavior.

The pharmacology of SDZ EAA 494, a competitive NMDA antagonist.

SDZ EAA 494 (D-CPPene) was characterized as a competitive NMDA antagonist, having a pA2 value against NMDA depolarizations in frog spinal cord and rat neocortex of 6.7-6.8 and a pKi of 7.5 in a [3H]CGP39653 binding assay, with no action on other receptors or amine reuptake. The compound was orally active in rodent maximal electroshock models with an ED50 of around 16 mg/kg, was protective in rats even 24 hours after oral application and had an oral therapeutic index of around 8. Muscle relaxation, ataxia, flattened body posture and reduced acquisition of a passive avoidance task, suggesting potential effects on memory formation, occurred at supra-anticonvulsant doses in rodents, with PCP-like stimulatory effects produced only by high i.p. doses or constant i.v. infusions. This favourable profile is discussed in relation to the negative outcome of a recent trial of the compound in patients with intractable epilepsy. The conclusion is drawn that standard models for screening new anticonvulsants are inappropriate to seeking drugs active in patients with a protracted convulsive history. The anti-ischaemic action of SDZ EAA 494 encourages further testing in brain trauma, in which the anticonvulsant action of the compound may be an added benefit.

Glyceraldehyde-3-phosphate dehydrogenase varies with age in glycolytic muscles of rats.

Glyceraldehyde-3-phosphate dehydrogenase (GAPDH) mRNA, protein, and enzyme activity levels in hindlimb muscles of adult and senescent Fischer 344 x Brown Norway rats were investigated. Soleus muscles from adult and senescent rats had similar levels of GAPDH. In contrast, muscles containing a large proportion of glycolytic fibers had lower GAPDH levels in senescent rats relative to these muscles in adult rats; this was observed at both the mRNA and protein levels. These data indicate that skeletal muscle glycolytic capacity of fast muscles is diminished with age and that it may be caused by changes at the level of transcription. Also, because GAPDH mRNA levels change with age in several rat muscles, GAPDH mRNA is not always a proper internal control for mRNA analyses of aging skeletal muscle.

Effects of a metabotropic glutamate agonist, trans-ACPD, on cortical epileptiform activity.

The effect of the metabotropic glutamate receptor agonist trans-1-amino-1,3,cyclopentanedicarboxylic acid (trans-ACPD) on epileptiform activity induced in rat neocortical slices by exposure to Mg(2+)-free medium was examined. Trans-ACPD dose dependently (10-200 microM) decreased the frequency of spontaneous epileptiform events whilst increasing both the duration of afterpotentials and the number of afterbursts associated with single events. This effect on afterpotentials and afterbursting was particularly pronounced in 14-17 day-old rats and was blocked by the sigma ligand ditolyguanidine (DTG) 10 microM. The putative metabotropic glutamate receptor antagonist L-AP3 did not antagonise the actions of trans-ACPD. The results suggest a role for metabotropic glutamate receptors in epilepsy, possibly in the transition from interictal to ictal activity.

Muscle function and protein metabolism after initiation of eccentric contraction-induced injury.

This study was designed to determine the relationship between skeletal muscle function and protein metabolism after initiation of eccentric contraction-induced injury. Mouse anterior crural muscles were injured in vivo, and then either immediately or 3, 6, 24, 48, 72, 120, or 336 h after injury muscles were isolated and studied for indexes of muscle function, injury, phagocyte infiltration, and protein metabolism. A group of mice were administered anti-polymorphonuclear cell and anti-macrophage antisera in an attempt to reduce phagocytic infiltration into injured muscle. Force production in extensor digitorum longus muscles was reduced 55% immediately after injury induction and did not recover significantly until 120 h postinjury (28% below baseline). However, rates of protein degradation were not elevated until 48 h postinjury (60% above normal) and were not correlated with the changes in force production (r = -0.37; P = 0.24). Phagocytic infiltration was evident 24-120 h postinjury and was correlated with the elevated protein degradation rates (r = 0.75; P < 0.01). Protein synthesis rates began to increase approximately 48 h after injury was induced and were elevated by 83% 5 days postinjury. Fourteen days after injury, muscle protein degradation and synthesis rates had returned to normal, as well as specific force production, and phagocytic infiltration was not detected. However, muscle mass, protein content, and absolute force production were lower than normal. Antisera-treated mice were rendered neutropenic, but there was no difference in any variable measured between muscles from these mice and muscles from normal mice.

Eccentric contraction-induced injury in normal and hindlimb-suspended mouse soleus and EDL muscles.

The primary objective of this study was to compare the magnitude of injury in mouse extensor digitorum longus (EDL) and soleus muscles induced by high-force eccentric contractions. A second objective was to study the effect of altering the daily loading of the muscles through hindlimb suspension (HS) on the injury. One of two protocols was performed in vitro: 1) 15 eccentric contractions (n = 20: 10 EDL and 10 soleus muscles) or 2) 15 isometric contractions (n = 20: 10 EDL and 10 soleus muscles). After the protocol, the decrements in contractile performance and lactate dehydrogenase (LDH) release were measured at 15-min intervals over 1 h. Immediately after the eccentric contraction protocol, markedly greater decrements in maximal isometric tetanic force (Po) occurred in the normal EDL than in the normal soleus muscles (60.7 +/- 4.2 vs. 7.6 +/- 2.1%, P < or = 0.0001). LDH release immediately after the eccentric contraction protocol was 2.7-fold greater in the normal EDL than in the normal soleus muscles. To investigate the role of recent loading of the muscles in the injury, EDL (n = 9) and soleus (n = 10) muscles from mice subjected to HS for 14 days performed the eccentric contraction protocol. HS resulted in greater decrements in contractile performance for the soleus muscles (decreases in Po immediately after the protocol for HS and normal soleus muscles were 31.0 +/- 1.8 and 7.6 +/- 2.1%, respectively; P < or = 0.0001) but not for the EDL muscles.(ABSTRACT TRUNCATED AT 250 WORDS)

Eccentric contraction-induced injury of mouse soleus muscle: effect of varying [Ca2+]o.

The objective of this study was to determine the effect of varying extracellular Ca2+ concentration ([Ca2+]o) on eccentric contraction-induced muscle injury. Isolated mouse soleus muscles (n = 64) performed either 20 eccentric or 20 isometric contractions over a 40-min period in a Krebs buffer containing 0.5, 1.25, or 5.0 mM Ca2+. Measurements of contractile function and lactate dehydrogenase accumulation in the buffer were then made every 15 min for 2 h. Prostaglandin E2, leukotriene B4, and tyrosine accumulation in the incubation medium and total muscle [Ca2+] were measured at the end of the experiment. Reductions in maximal isometric tetanic force for muscles immediately after performance of 20 eccentric and 20 isometric contractions were 21.1 +/- 1.4 and 1.2 +/- 0.7%, respectively. Total muscle [Ca2+] was 28-37% higher in muscles that performed eccentric contractions than in those that performed isometric contractions. However, estimates made with a confocal laser scanning microscope and fluo 3 do not indicate that there was a difference in free cytosolic [Ca2+] between fibers from injured and control muscles. Also, leukotriene B4, prostaglandin E2, and tyrosine accumulation in the buffer from muscles that performed eccentric contractions was not elevated over that from muscles that performed isometric contractions. Furthermore, lactate dehydrogenase accumulation and reductions of contractile function over the 2-h incubation period were not enhanced by higher [Ca2+]o or influenced by the type of contraction. These findings suggest that muscles that were injured by eccentric contractions were able to buffer the increased influx of extracellular Ca2+, maintain a normal free cytosolic [Ca2+], and avoid activation of Ca(2+)-sensitive degradative pathways.

Differential effects of anesthetics on in vivo skeletal muscle contractile function in the mouse.

The purpose of this study was to evaluate the effects of four anesthetic regimens on in vivo contractile function of mouse ankle dorsiflexor muscles. The torque-frequency and torque-velocity relationships were determined for the following anesthetics: fentanyl-droperidol and diazepam (F-d/d); ketamine and xylazine (K/x); pentobarbital sodium (Ps); and methoxyflurane (Mf). Mf, Ps, and F-d/d regimens resulted in comparable contractile responses at low doses, whereas K/x produced a relative depression in isometric contractile function as shown by a decrease in the torque-time integral at the 300-Hz stimulation frequency (-13.9%; P < 0.05). Moreover, K/x caused a shift to the left in the torque-frequency curve as indicated by increases in torque-time integrals at 25 and 50 Hz. Both Ps and F-d/d regimens exhibited dose-dependent effects during the isovelocity contractions. Ps significantly reduced work (-28.7%) and average power (-28.9%) at 800 degrees/s at the high dose. In contrast, F-d/d anesthesia resulted in increases in peak torque (16-20%) and work (15-18%) output at all eccentric contraction velocities at the high dose, whereas average power was increased only at -800 (17%) and -1,000 degrees/s (17%). In conclusion, commonly used anesthetic regimens can affect the contractile response in vivo; K/x and Ps yield smaller torque outputs, whereas Mf and F-d/d consistently produce larger contractile responses. Mf and F-d/d are recommended for use in studying skeletal muscle function in mice in vivo.

Estradiol effect on anterior crural muscles-tibial bone relationship and susceptibility to injury.

The study's objective was to determine whether estradiol (E2) deficiency alters the functional relationship of muscle to bone and causes a differential increase in injury susceptibility. Ovariectomized 6-wk-old mice were administered E2 (40 micrograms. day-1. kg-1; n = 8) or the oil vehicle (n = 8) for 21 days. The anterior crural muscles of the left hindlimb were then stimulated to produce 150 maximal in vivo eccentric contractions. In vitro functional measurements were then made on the extensor digitorum longus (EDL) muscle and tibia from both the exercised and unexercised legs. The maximal isometric torque produced by the anterior crural muscles before the eccentric contraction protocol and the unexercised EDL maximal isometric tetanic force (P(0)) were higher in E2-treated mice by 18 and 14%, respectively (P < or = 0.03). Both ultimate load and stiffness for the unexercised tibia were higher by 16% in E2-treated mice (P < or = 0.03). The muscle-to-bone relationship of these measurements was unaffected by E2 status (P > or = 0.59). No evidence for increased injury susceptibility was found in either tissue from E2-deficient mice. In fact, the decrement in P(0) was only 36.9 +/- 3.8% in exercised EDL muscles from E2-deficient mice compared with 50.6 +/- 4.2% in exercised muscles from E2-treated mice (P = 0.03). Tibia stiffness was 3.9% higher in bones from exercised legs than in bones from unexercised legs (72.64 +/- 2.77 vs. 69.95 +/- 2.66 N/mm; P = 0.05) with ultimate load showing a similar trend (P = 0.07); no effect of E2 status was observed on these differences (P > or = 0.53). In conclusion, the functional relationship of bone to muscle and the susceptibility to injury in bone are not altered by the presence of E2 in ovariectomized mice; however, E2 does increase injury susceptibility in the EDL muscle.