Inhibition of Acute mGluR5-Dependent Depression in Hippocampal CA1 by High-Frequency Magnetic Stimulation.

High-frequency magnetic stimulation (HFMS) applied directly to the hippocampal slice preparation in vitro induces activity-dependent synaptic plasticity and metaplasticity. In addition, changes in synaptic transmission following HFMS involve the activation of N-methyl-D-aspartate and metabotropic glutamate receptors (mGluR). Here, we asked whether a short period of HFMS (5 × 10 delta-burst trains, duration of ~1 min) could alter mGluR5-mediated depression at Schaffer collateral-CA1 synapses in the acute brain slice preparation at 30 min after HFMS. To this end, we obtained field excitatory postsynaptic potential (fEPSP) slopes from Schaffer collateral-CA1 synapses after HFMS or control. First, we demonstrated that activity-dependent plasticity following HFMS depends on the slice orientation towards the magnetic coil indicating specific ion fluxes induced by magnetic fields. Second, we found that the mGluR5-specific agonist (RS)-2-chloro-5-hydroxyphenylglycine reduced the field excitatory postsynaptic potential (fEPSP) slopes in control slices but rather enhanced them in HFMS-treated slices. In contrast, the compound (S)-3,5-dihydroxyphenylglycine acting at both mGluR1 and mGluR5 reduced fEPSP slopes in both control and HFMS-treated slices. Importantly, the mGluR-dependent effects were independent from the slice-to-coil orientation indicating that asynchronous glutamate release could play a role. We conclude that a short period of HFMS inhibits subsequently evoked mGluR5-dependent depression at Schaffer collateral-CA1 synapses. This could be relevant for repetitive transcranial magnetic stimulation in psychiatric disorders such as major depression.

Hinge screw or no hinge stabilization provides decreased stability compared to hinge plate in a biomechanical evaluation of distal femoral derotational osteotomies.

PURPOSE: Derotational distal femoral osteotomy (DFO) is the causal treatment for patients with femoral torsional deformity. The fixation is achieved by a unilateral angle-stable plate. Delayed- or non-unions are one of the main risks of the procedure. An additional contralateral fixation may benefit the outcome. Therefore, we hypothesize that primary stability in DFO can be improved by an additional fixation with a hinge screw or an internal plate. METHODS: Derotational DFO was performed in 15 knees and fixed either with an angle-stable plate only (group 'None'), with an additional lateral screw (group 'Screw') or with an additional lateral plate (group 'Plate'). Biomechanical evaluation was carried out under axial loading of 150 N (partial weight bearing) and 800 N (full weight bearing), followed by internal and external rotation. After linear axial loading in step 1, a cyclic torsional load of 5 Nm was applied under constant axial load in step 2. In step 3, the specimens were unloaded. Micromovements between the distal and proximal parts of the osteotomy were recorded at each step for all specimens. RESULTS: In step 1, the extent of micromovements was highest in group 'None' and lowest in group 'Plate' without being significantly different. In step 2, group 'Plate' showed significantly higher stability, reflected by less rotation and lower micromovements. Increasing the axial load from 150 to 800 N at step 2 resulted in increased stability in all groups but only reached significance in group 'None'. CONCLUSION: An additional contralateral plate significantly increased stability in derotational DFO compared to the unilateral angle-stable plate only. Contrary, a contralateral hinge screw did not provide improved stability. STUDY DESIGN: Experimental study. LEVEL OF EVIDENCE: IV.

Comparison between dedicated MRI and symphyseal fluoroscopic guided contrast agent injection in the diagnosis of cleft sign in athletic groin pain and association with pelvic ring instability.

OBJECTIVE: To compare dedicated MRI with targeted fluoroscopic guided symphyseal contrast agent injection regarding the assessment of symphyseal cleft signs in men with athletic groin pain and assessment of radiographic pelvic ring instability. METHODS: Sixty-six athletic men were prospectively included after an initial clinical examination by an experienced surgeon using a standardized procedure. Diagnostic fluoroscopic symphyseal injection of a contrast agent was performed. Additionally, standing single-leg stance radiography and dedicated 3-Tesla MRI protocol were employed. The presence of cleft injuries (superior, secondary, combined, atypical) and osteitis pubis was recorded. RESULTS: Symphyseal bone marrow edema (BME) was present in 50 patients, bilaterally in 41 patients and in 28 with an asymmetrical distribution. Comparison of MRI and symphysography was as followed: no clefts: 14 cases (MRI) vs. 24 cases (symphysography), isolated superior cleft sign: 13 vs. 10, isolated secondary cleft sign: 15 vs. 21 cases and combined injuries: 18 vs. 11 cases. In 7 cases a combined cleft sign was observed in MRI but only an isolated secondary cleft sign was visible in symphysography. Anterior pelvic ring instability was observed in 25 patients and was linked to a cleft sign in 23 cases (7 superior cleft sign, 8 secondary cleft signs, 6 combined clefts, 2 atypical cleft injuries). Additional BME could be diagnosed in 18 of those 23. CONCLUSION: Dedicated 3-Tesla MRI outmatches symphysography for purely diagnostic purposes of cleft injuries. Microtearing at the prepubic aponeurotic complex and the presence of BME is a prerequisite for the development of anterior pelvic ring instability. CLINICAL RELEVANCE STATEMENT: For diagnostic of symphyseal cleft injuries dedicated 3-T MRI protocols outmatch fluoroscopic symphysography. Prior specific clinical examination is highly beneficial and additional flamingo view x-rays are recommended for assessment of pelvic ring instability in these patients. KEY POINTS: • Assessment of symphyseal cleft injuries is more accurate by use of dedicated MRI as compared to fluoroscopic symphysography. • Additional fluoroscopy may be important for therapeutic injections. • The presence of cleft injury might be a prerequisite for the development of pelvic ring instability.

The effect of age on coordination of stabilization during changing environmental dynamics.

Coordination as part of the stabilization process of joints is compromised in older adults. We addressed changes in neuromuscular control and force output during a ballistic force production task influenced by different environmental dynamics. Aged participants (AP) and young participants (YP) were asked to perform a unilateral maximal leg extension against a movable sled in a reaction-time task. The task was performed in a sitting posture and involved a stable (1 degree of freedom; DoF) or an unstable (3 DoF) condition of the sled. Electromyographic and dynamometric recordings were made and analyzed using the cross-correlation-function, assessment of peak EMG-activity and peak force. Initial motor strategies (i.e. motor system adjustments in order to meet the demands of the particular task while respecting individual constraints) were assessed by analyzing total reaction times (TRT), premotor time (PMT) and electromechanical delay (EMD). The AP group showed motor control strategies governed by prolonged TRT in both conditions. However, the change of mechanical interactions (i.e. the interaction between the participant and the sled in its particular mechanical state) caused group specific motor system adjustments in PMT and EMD. Force measures showed reduced peak forces in AP accompanied by less loss of force between conditions compared to YP. Inter- and intramuscular coordination strategies differed between YP and AP reflected in changes in CCF and peak EMG values. We conclude that change in environmental dynamics is associated with specific adjustments of control properties of the motor system. These adjustments were sensitive to age and mechanical condition (1 or 3 DoF) and might contribute to declines in motor output seen in AP. However, due to the nature of the task, our results do not allow a direct transfer to situations involving whole body balance.

Neural control of joint stability during a ballistic force production task.

Changes in transmission in Ia afferent and corticospinal pathways have been reported to depend on various factors including task complexity and the phase of movement. Here, we test whether a unilateral voluntary force production task leads to specific changes in both Ia afferent (by the use of the H-reflex technique) and corticospinal (by the use of transcranial magnetic stimulation, TMS) pathways in response to different mechanical conditions. The participants were exposed to either one or three mechanical degrees of freedom (DoF) of an external object while performing a unilateral knee extension movement in a sitting posture. The amplitudes of the m. soleus (SOL) EMG to either type of stimulation were normalized to amplitudes obtained during voluntary tonic contractions at matched background EMG in order to assess movement-related alterations. The results at two phases during movement (initial phase and during task execution) were analyzed. The unstable 1 DoF condition led to elevated co-contraction of SOL and the tibialis anterior muscle. Phase- and movement-related modulations of muscle responses to both types of stimulation were present in both mechanical conditions. However, the stable 1 DoF condition caused a significant facilitation of normalized H-reflexes in the initial phase of movement as compared to 3 DoF (1 DoF: 206%, 3 DoF: 96%, P < 0.001). Conversely, larger normalized amplitudes in response to TMS were found in the initial phase of the 3 DoF condition as compared to 1 DoF (1 DoF: 107%, 3 DoF 160%, P < 0.001). Additionally, during task execution the normalized amplitudes of TMS and H-Reflex testing revealed a relative decrease when compared to the initial phase of movement. It is suggested that presynaptic mechanisms caused the changes in the normalized H-reflexes (and thus in Ia afferent transmission) and that altered normalized responses to TMS reflect changes in corticospinal transmission. Consequently, we reason that the transmission in both pathways is sensitive to the nature of the mechanical interaction and thus to biomechanical task demands. Finally, the voluntary nature of the task might have caused a decisive influence of anticipatory control mechanisms triggered by advance information about the modality of environmental dynamics.

High-frequency magnetic stimulation induces long-term potentiation in rat hippocampal slices.

Recent reports indicate that the exposure of brain tissues to transcranial magnetic stimulation induces persistent changes in neuronal activity and influences hippocampal synaptic plasticity. However, the modulation of synaptic efficiency by magnetic stimulation in vitro is still unclear. In the present study, we investigated whether high-frequency magnetic stimulation (HFMS) can induce long-term potentiation (LTP) in rat hippocampal slices in vitro. During baseline recording and after HFMS, field excitatory postsynaptic potentials (fEPSPs) were recorded within the CA1 stratum radiatum in response to electrical stimulation of the Schaffer collateral inputs. For LTP induction, HFMS was delivered through a circular coil positioned closely above the slices using two different paradigms (A: 10 trains of 20 pulses at 100 Hz with 1s intervals, 5 repetitions with 10s intervals; B: 3 trains of 100 pulses at 100 Hz with 20s intervals). The intensity of the magnetic stimulus was adjusted to 60-75 A/micros. After application of HFMS, electrically evoked CA1 fEPSPs were enhanced showing significant levels of LTP by both paradigms (A: 142+/-9% of baseline, n=6; B: 129+/-7%, n=8). Furthermore, HFMS-induced LTP induced by paradigm A was prevented by the presence of the selective N-methyl-D-aspartate receptor (NMDAR) blocker D-AP5 (50 microM) in the bath solution (95+/-6% of the baseline, n=6; p<0.01 compared to control condition without D-AP5). Further, the lack of changes in paired-pulse ratio and the afferent fiber volleys exclude presynaptic involvement in HFMS-induced LTP. In summary, we have demonstrated that HFMS can induce NMDAR-dependent LTP in the CA1 region in vitro.