Antinociceptive modulation by the adhesion GPCR CIRL promotes mechanosensory signal discrimination.

Adhesion-type GPCRs (aGPCRs) participate in a vast range of physiological processes. Their frequent association with mechanosensitive functions suggests that processing of mechanical stimuli may be a common feature of this receptor family. Previously, we reported that the Drosophila aGPCR CIRL sensitizes sensory responses to gentle touch and sound by amplifying signal transduction in low-threshold mechanoreceptors (Scholz et al., 2017). Here, we show that Cirl is also expressed in high-threshold mechanical nociceptors where it adjusts nocifensive behaviour under physiological and pathological conditions. Optogenetic in vivo experiments indicate that CIRL lowers cAMP levels in both mechanosensory submodalities. However, contrasting its role in touch-sensitive neurons, CIRL dampens the response of nociceptors to mechanical stimulation. Consistent with this finding, rat nociceptors display decreased Cirl1 expression during allodynia. Thus, cAMP-downregulation by CIRL exerts opposing effects on low-threshold mechanosensors and high-threshold nociceptors. This intriguing bipolar action facilitates the separation of mechanosensory signals carrying different physiological information.

Mechano-dependent signaling by Latrophilin/CIRL quenches cAMP in proprioceptive neurons.

Adhesion-type G protein-coupled receptors (aGPCRs), a large molecule family with over 30 members in humans, operate in organ development, brain function and govern immunological responses. Correspondingly, this receptor family is linked to a multitude of diverse human diseases. aGPCRs have been suggested to possess mechanosensory properties, though their mechanism of action is fully unknown. Here we show that the Drosophila aGPCR Latrophilin/dCIRL acts in mechanosensory neurons by modulating ionotropic receptor currents, the initiating step of cellular mechanosensation. This process depends on the length of the extended ectodomain and the tethered agonist of the receptor, but not on its autoproteolysis, a characteristic biochemical feature of the aGPCR family. Intracellularly, dCIRL quenches cAMP levels upon mechanical activation thereby specifically increasing the mechanosensitivity of neurons. These results provide direct evidence that the aGPCR dCIRL acts as a molecular sensor and signal transducer that detects and converts mechanical stimuli into a metabotropic response.

Pain perception and cardiovascular system response among athletes playing contact sports.

The aim of this study was to determine whether the contact sports change the perception of pain as assessed by the cold pressor test (CPT), and if the test induces the same reaction of the cardiovascular system in contact athletes and non-athletes. The study involved 321 healthy men; 140 contact athletes and 181 students of the University of Szczecin (control). Pain threshold and pain tolerance were evaluated using CPT. Cardiovascular measurements were made during CPT. The contact athletes showed a much higher tolerance to pain than the control group (median time 120 vs. 94 s, respectively, p = 0.0002). The thresholds of pain in both groups did not differ significantly between the groups. Systolic blood pressure measured before and during the test in all three measurements was statistically significantly higher in athletes compared with the control group. Heart rate and diastolic blood pressure did not differ significantly between the studied groups.

High-magnitude whole-body vibration effects on bone resorption in adult rats.

INTRODUCTION: Optimal parameters of whole-body vibration (WBV), effective in increasing bone mass or preventing bone loss, are always being sought. We investigated effects of a 6-mo WBV program, consisting of brief daily vibratory sessions, on the bone mass and bone metabolic markers. METHODS: There were 10 male Wistar rats (3 mo old) that were subjected to the 6-mo WBV (frequency 50 Hz, acceleration 4.92 g, peak-to-peak displacement 2.5 mm) composed of 4 30-s bouts per day, performed 5 d per week. There were 10 not vibrated, age-matched rats that served as controls. RESULTS: After completion of the WBV program the concentrations of C-terminal telopeptide of type I collagen in the WBV treated animals were significantly lower in comparison to the controls. There were no effects of the WBV on areal bone mineral density, osteocalcin, and sRANKL levels. DISCUSSION: High-frequency high-magnitude WBV applied for 6 mo decreases bone resorption, but does not affect bone formation and bone mineral density.

Low-volume whole-body vibration lasting 3 or 6 months does not affect biomarkers in blood serum of rats.

Whole-body vibration training (WBV) has been reported to improve both, bone strength and neuromuscular performance. Although changes in hormonal and immunological parameters following vibration exercises were reported, there are still few studies concerning the immune response with respect to different duration of WBV. In our study, we aimed to establish whether three and six months of specific, short-lasting WBV (four bouts lasting 30 s, 1 min rest intervals) influences blood cell counts as well as some immunological parameters in rats. Adult male Wistar rats were assigned randomly to two groups trained for three (WBV3mo) or six (WBV6mo) months and results were compared to the age matched control group (C). After the training period, red and white blood cells, lymphocytes, monocytes, granulocytes, hemoglobin, and hematocrit, as well as interleukin-1b, interleukin-10, interleukin-6, and vascular endothelial growth factor levels were determined. No significant differences between WBV3mo, WBV6mo, and C groups in complete blood counts or in immunological parameters were found, indicating that the whole-body vibration training used in this study did not disturb the balance of examined indices, directly or indirectly involved in inflammatory processes.

Field hockey players have different values of ulnar and tibial motor nerve conduction velocity than soccer and tennis players.

The aim of this study was to describe motor nerve conduction velocity in upper and lower extremities in sportsmen. Fifteen high-level field hockey players, seventeen soccer players and ten tennis players were recruited from the Polish National Field Hockey League, Polish Soccer League Clubs, and Polish Tennis Association clubs,respectively. The control group comprised of seventeen healthy, non-active young men. Nerve conduction velocities of ulnar and tibial nerve were assessed with NeuroScreen electromyograph (Toennies, Germany) equipped with standard techniques of supramaximal percutaneus stimulation with constant current and surface electrodes. No significant differences in motor nerve conduction velocities were found between dominant and non-dominant limbs in each studied group. Ulnar nerve conduction velocity measured from above elbow to below elbow was significantly lower only in the field hockey players' dominant limb. Tibial conduction velocity of the field hockey players' non-dominant lower limb was higher in comparison to the tennis players and the control group. There was no significant correlation between body mass and NCV as well as between height of subjects and NCV in both athletes or non-athletes. A slight trend towards a lower TCV values in athletes with longer duration of practicing sport was found. It was most pronounced in the non-dominant lower extremity of field hockey players.

Complex myograph allows the examination of complex muscle contractions for the assessment of muscle force, shortening, velocity, and work in vivo.

BACKGROUND: The devices used for in vivo examination of muscle contractions assess only pure force contractions and the so-called isokinetic contractions. In isokinetic experiments, the extremity and its muscle are artificially moved with constant velocity by the measuring device, while a tetanic contraction is induced in the muscle, either by electrical stimulation or by maximal voluntary activation. With these systems, experiments cannot be performed at pre-defined, constant muscle length, single contractions cannot be evaluated individually and the separate examination of the isometric and the isotonic components of single contractions is not possible. METHODS: The myograph presented in our study has two newly developed technical units, i.e. a). a counterforce unit which can load the muscle with an adjustable, but constant force and b). a length-adjusting unit which allows for both the stretching and the contraction length to be infinitely adjustable independently of one another. The two units support the examination of complex types of contraction and store the counterforce and length-adjusting settings, so that these conditions may be accurately reapplied in later sessions. RESULTS: The measurement examples presented show that the muscle can be brought to every possible pre-stretching length and that single isotonic or complex isometric-isotonic contractions may be performed at every length. The applied forces act during different phases of contraction, resulting into different pre- and after-loads that can be kept constant - uninfluenced by the contraction. Maximal values for force, shortening, velocity and work may be obtained for individual muscles. This offers the possibility to obtain information on the muscle status and to monitor its changes under non-invasive measurement conditions. CONCLUSION: With the Complex Myograph, the whole spectrum of a muscle's mechanical characteristics may be assessed.

Assessment of precision and reproducibility of a new myograph.

BACKGROUND: The physiological characteristics of muscle activity and the assessment of muscle strength represent important diagnostic information. There are many devices that measure muscle force in humans, but some require voluntary contractions, which are difficult to assess in weak or unconscious patients who are unable to complete a full range of voluntary force assessment tasks. Other devices, which obtain standard muscle contractions by electric stimulations, do not have the technology required to induce and measure reproducible valid contractions at the optimum muscle length. METHODS: In our study we used a newly developed diagnostic device which measures accurately the reproducibility and time-changed-variability of the muscle force in an individual muscle. A total of 500 in-vivo measurements of supra-maximal isometric single twitch contractions were carried out on the musculus adductor pollicis of 5 test subjects over 10 sessions, with ten repetitions per session. The same protocol was performed on 405 test subjects with two repetitions each to determine a reference-interval on healthy subjects. RESULTS: Using our test setting, we found a high reproducibility of the muscle contractions of each test subject. The precision of the measurements performed with our device was 98.74%. Only two consecutive measurements are needed in order to assess a real, representative individual value of muscle force. The mean value of the force of contraction was 9.51 N and the 95% reference interval was 4.77-14.25 N. CONCLUSION: The new myograph is a highly reliable measuring device with which the adductor pollicis can be investigated at the optimum length. It has the potential to become a reliable and valid tool for diagnostic in the clinical setting and for monitoring neuromuscular diseases.

In vivo myograph measurement of muscle contraction at optimal length.

BACKGROUND: Current devices for measuring muscle contraction in vivo have limited accuracy in establishing and re-establishing the optimum muscle length. They are variable in the reproducibility to determine the muscle contraction at this length, and often do not maintain precise conditions during the examination. Consequently, for clinical testing only semi-quantitative methods have been used. METHODS: We present a newly developed myograph, an accurate measuring device for muscle contraction, consisting of three elements. Firstly, an element for adjusting the axle of the device and the physiological axis of muscle contraction; secondly, an element to accurately position and reposition the extremity of the muscle; and thirdly, an element for the progressive pre-stretching and isometric locking of the target muscle. Thus it is possible to examine individual in vivo muscles in every pre-stretched, specified position, to maintain constant muscle-length conditions, and to accurately re-establish the conditions of the measurement process at later sessions. RESULTS: In a sequence of experiments the force of contraction of the muscle at differing stretching lengths were recorded and the forces determined. The optimum muscle length for maximal force of contraction was established. In a following sequence of experiments with smaller graduations around this optimal stretching length an increasingly accurate optimum muscle length for maximal force of contraction was determined. This optimum length was also accurately re-established at later sessions. CONCLUSION: We have introduced a new technical solution for valid, reproducible in vivo force measurements on every possible point of the stretching curve. Thus it should be possible to study the muscle contraction in vivo to the same level of accuracy as is achieved in tests with in vitro organ preparations.

Octreotide, a somatostatin analogue, attenuates movement evoked discharges of fine afferent units from inflamed knee joints of rats.

This electrophysiological study examined whether octreotide, a stable analogue of somatostatin (SOM), reduces the mechanosensitivity of fine primary afferents from inflamed knee joints of rats similarly to SOM itself (Pain 73 (1997) 377). Close intra-arterial application of 200 microl of octreotide (10(-6)-10(-3) M) dose-dependently diminished the responses to passive non-noxious and noxious rotations of the joint in most of the units tested. The inhibitory effects of octreotide required a higher concentration (10(-3) M) compared to SOM to successfully decrease the number of recorded spikes. Application of cyclo-somatostatin, a SOM antagonist, before the octreotide injection prevented the reduction of the movement evoked discharges. These data indicate that octreotide is able to successfully decrease the responses of mechanosensitive fine afferent units innervating the inflamed knee joint of the rat and may, therefore, be useful in the treatment of articular pain of peripheral origin.

Effects of different molecular weight elastoviscous hyaluronan solutions on articular nociceptive afferents.

OBJECTIVE: To compare 3 different hyaluronan (HA) preparations used as therapeutic agents for osteoarthritis pain in humans in order to establish the degree to which a single application affects the sensitivity of nociceptors in both the normal and the acutely inflamed rat joint. METHODS: In anesthetized rats, single-unit recordings were performed from the medial articular nerve of the right knee joint under normal conditions and during an acute experimental arthritis. Fifty fine afferent units (conduction velocities 0.8-15.3 meters/second) responded to passive movements of the knee joint. They were exposed to a torque meter-controlled, standardized stimulus protocol consisting of innocuous and noxious inward and outward rotations of the joint. This stimulus protocol of 50 seconds' duration was repeated every 5 minutes for 2-3 hours. Three commercially available HA preparations and a buffer solution, the solvent of these preparations, were injected intraarticularly after discharges resulting from 6 stimulus protocols were averaged and used as controls. RESULTS: Both in normal and in inflamed joints, the injection of Hyalgan did not reduce nerve impulse frequency of the evoked discharges. The injections of Orthovisc had no effect in normal joints, but produced a transient frequency reduction of the evoked discharge in inflamed joints. Synvisc significantly reduced (by an average of 50%) the impulse discharge in both normal and inflamed joints 50 minutes after injection, and this level of impulse discharge continued until the end of the recording period (120-130 minutes after injection). The buffer, which had elastoviscous properties substantially different from those of Hyalgan, Orthovisc, and Synvisc, had no such effect. CONCLUSION: We conclude that the elastoviscous properties of HA solutions are determining factors in reducing pain-eliciting nerve activity both in normal and in inflamed rat joints.

Gabapentin reduces the mechanosensitivity of fine afferent nerve fibres in normal and inflamed rat knee joints.

The antiepileptic drug gabapentin has been shown to have an antihyperalgesic effect following central administration. This electrophysiological investigation examined whether peripherally administered gabapentin could modulate the mechanosensitivity of primary afferents innervating normal and kaolin/carrageenan inflamed rat knee joints. Close intraarterial injection of gabapentin (0.01, 1 and 100mg/kg) dose-dependently reduced afferent firing rate in both normal and acutely inflamed rat knees in response to normal and hyper-rotation of the joint. Thus, in addition to its central mode of action, peripheral administration of gabapentin reduces nociception locally and this may prove to be beneficial in the treatment of various pain syndromes including inflammatory arthritis.

The neurokinin-2 receptor is not involved in the sensitization of primary afferents of the rat knee joint.

Using electrophysiological methods, we aimed in the present study to determine whether the NK(2) receptor is involved in the sensitization of articular afferents of the rat. Impulse activity from 27 single fine nerve fibres innervating knee joints was recorded during non-noxious and noxious joint rotations. Close intraarterial application of the NK(2) receptor agonist [beta-Ala(8)]NKA(4-10) at doses of 0.2-200 nmol did not sensitize the afferents from normal knee joints to mechanical stimuli whereas the application of substance P (20 nmol) increased their mechanosensitivity. These data further support the hypothesis that the NK(2) receptor is not involved in the sensitization of primary afferents in normal knee joints to mechanical stimuli.

Inhibitory effect of somatostatin on the mechanosensitivity of articular afferents in normal and inflamed knee joints of the rat.

The effect of somatostatin on the sensory activity of primary afferents was studied in normal and acutely inflamed rat knee joints. Fine afferent nerve fibers with conduction velocities of 0.9-18.0 m/s were recorded as single units. All nerve fibers tested responded to local mechanical stimulation, movements of the joint and i.a. injections of KCl (10(-4) mol, 0.1 ml) close to the joint. Somatostatin (10(-4) mol, 0.2 ml) caused no direct response of the units. In normal joints, somatostatin did not change the discharges evoked by non-noxious movements but decreased the responses to noxious movements significantly to about 63% of the responses before the application. In acutely inflamed joints, somatostatin reduced the discharges of non-noxious and of noxious movements to about 55% and 52%, respectively. Injections of somatostatin with lower concentrations (10(-6) mol, 10(-8) mol) i.a. close to inflamed joints revealed shorter and less pronounced reductions of the responses to noxious movements. In a proportion of afferents, substance P (10(-4) mol) and bradykinin (10(-4) mol) were able to increase these responses again. These data indicate that the mechanosensitivity of articular afferents in normal joints may also be regulated by several neuropeptides based on a balance of pro-inflammatory peptides such as substance P, and anti-inflammatory peptides such as somatostatin. In an inflamed joint, pro-inflammatory peptides seem to predominate resulting in a sensitization of the peripheral nerve fibers. In this case, an application of somatostatin or its analogues could be used clinically to compensate this effect.

Responsiveness of slowly conducting articular afferents to bradykinin: effects of an experimental arthritis.

Bradykinin (BK), an important inflammatory mediator and potent algogenic substance, is supposed to contribute to the generation of arthritic hyperalgesia and pain. The present study was undertaken to examine if an experimental kaolin/carrageenan arthritis sensitizes articular afferents to BK in the cat's knee joint using two different approaches. First, the proportion of afferent units activated by BK was assessed in fully inflamed joints and compared with corresponding data of normal knee joints. BK (injected i.a. as a bolus close to the joint) at the dose of 2.6 micrograms activated 60% of the units of groups II-IV in the inflamed state, compared to 71% in normal joints. The proportions of low- and high-threshold afferents activated by BK were similar, but more spontaneously active units than units without ongoing activity responded to BK both in inflamed and normal knee joints. Second, the responsiveness of individual afferent units to BK was examined during the development of inflammation. Units not activated by BK remained unresponsive after inflammation. From 11 units activated by BK, 3 units lost their responsiveness and in 4 other units the response to BK was reduced within 2-6 h after the onset of inflammation. Only in 4 units was the BK response increased in the inflamed joint. It is concluded that desensitizing rather than sensitizing processes are involved to change the response behavior of articular afferents to BK during acute experimental inflammation.