Compromised trigemino-coerulean coupling in migraine sensitization can be prevented by blocking beta-receptors in the locus coeruleus.

BACKGROUND: Migraine is a disabling neurological disorder, characterized by recurrent headaches. During migraine attacks, individuals often experience sensory symptoms such as cutaneous allodynia which indicates the presence of central sensitization. This sensitization is prevented by oral administration of propranolol, a common first-line medication for migraine prophylaxis, that also normalized the activation of the locus coeruleus (LC), considered as the main origin of descending noradrenergic pain controls. We hypothesized that the basal modulation of trigeminal sensory processing by the locus coeruleus is shifted towards more facilitation in migraineurs and that prophylactic action of propranolol may be attributed to a direct action in LC through beta-adrenergic receptors. METHODS: We used simultaneous in vivo extracellular recordings from the trigeminocervical complex (TCC) and LC of male Sprague-Dawley rats to characterize the relationship between these two areas following repeated meningeal inflammatory soup infusions. Von Frey Hairs and air-puff were used to test periorbital mechanical allodynia. RNAscope and patch-clamp recordings allowed us to examine the action mechanism of propranolol. RESULTS: We found a strong synchronization between TCC and LC spontaneous activities, with a precession of the LC, suggesting the LC drives TCC excitability. Following repeated dural-evoked trigeminal activations, we observed a disruption in coupling of activity within LC and TCC. This suggested an involvement of the two regions' interactions in the development of sensitization. Furthermore, we showed the co-expression of alpha-2A and beta-2 adrenergic receptors within LC neurons. Finally propranolol microinjections into the LC prevented trigeminal sensitization by desynchronizing and decreasing LC neuronal activity. CONCLUSIONS: Altogether these results suggest that trigemino-coerulean coupling plays a pivotal role in migraine progression, and that propranolol's prophylactic effects involve, to some extent, the modulation of LC activity through beta-2 adrenergic receptors. This insight reveals new mechanistic aspects of LC control over sensory processing.

Postnatal development of inner lamina II interneurons of the rat medullary dorsal horn.

ABSTRACT: Pain processing in young mammals is immature. Despite the central role of the medullary dorsal horn (MDH) in processing orofacial sensory information, the maturation of the neurons within the MDH has been largely overlooked. Combining in vitro electrophysiological recordings and 3D morphological analysis over the first postnatal month in rats, we investigated the age-dependent development of the neurons within the inner lamina II (IIi) of the MDH. We show the lamina IIi neuronal population transition into a more hyperpolarized state, with modification of the action potential waveform, and a shift from single spiking, at early postnatal ages, to tonic firing and initial bursting at later stages. These physiological changes are associated with a strong structural remodelling of the neuronal morphology with most of the modifications occurring after the third postnatal week. Among the lamina IIi neuronal population, the subpopulation of interneurons expressing the γ isoform of the protein kinase C (PKCγ+) are key elements for the circuits underlying facial mechanical allodynia. How do they develop from the rest of the lamina IIi constitute an important question that remained to be addressed. Here, we show that PKCγ+ interneurons display electrophysiological changes over time comparable with the PKCγ- population. However, they show a distinctive increase of the soma volume and primary branches length, as opposed to the PKCγ- population. Together, our data demonstrate a novel pattern of late postnatal maturation of lamina IIi interneurons, with a spotlight on PKCγ+ interneurons, that may be relevant for the development of orofacial sensitivity.

Effect of marital satisfaction on self-regulation efforts in couples: Value of heart rate variability measurements.

This study explored self-regulatory efforts during the viewing of couple interactions and their association with relationship satisfaction. High-frequency heart rate variability (HF-HRV) was measured for each participant during a video recall of a recent couple interaction to quantify the self-regulatory processes governed by parasympathetic activity. Among 30 couples, HF-HRV was measured continuously during three specific periods to explore its change over time using a video-recall procedure: (1) resting state; (2) viewing of couple interactions (expressing daily life situations and conflictual interactions); and (3) recovery. Results of multilevel models revealed a u-shaped pattern of HF-HRV responses for men and women across the three periods with a nadir at the midway through the process. This pattern of physiological change (vagal suppression) reflects a flexible response to a stressful situation. Nevertheless, the pattern of physiological responses varied according to the level of relationship satisfaction. Men who were more satisfied in their couple relationship presented greater vagal suppression than dissatisfied men. In contrast, no significant HF-HRV changes were found in women over the different periods of the video-recall procedure and no moderating effect of relationship satisfaction. We discuss the different patterns of physiological responses observed both for men and women in terms of interindividual variability according to the level of their relationship satisfaction. The present study highlights the important role of relationship satisfaction in regulatory processes.

Ultrasonographic quantification of architectural response in tibialis anterior to neuromuscular electrical stimulation.

While muscle contraction in voluntary efforts has been widely investigated, little is known about contraction during neuromuscular electrical stimulation (NMES). The aim of this study was to quantify in vivo muscle architecture of agonist and antagonist muscles at the ankle joint during NMES. Muscle fascicle lengths and pennation angles of the tibialis anterior (TA) and lateral gastrocnemius muscles were assessed via ultrasonography in 8 healthy young males. Measures were obtained during maximal NMES and torque-matched voluntary dorsiflexion contractions. In the TA, NMES induced a shorter fascicle length (67.2±8.1mmvs 74.6±11.4mm; p=0.04) and a greater pennation angle (11.0±2.4° vs 9.3±2.5°; p=0.03) compared with voluntary torque-matched dorsiflexion contractions. Architectural responses in the antagonist lateral gastrocnemius muscle did not significantly differ from rest or between voluntary and electrically induced contractions (p>0.05). Contraction of the antagonist muscle was not a contributing factor to a greater fascicle shortening and increased pennation angle in the TA during NMES. TA architectural response during NMES likely arose from the contribution of muscle synergists during voluntary contractions coupled with a potentially localized contractile activity under the stimulation electrodes during NMES induced contractions.

EEG µ rhythm in virtual reality reveals that motor coding of visual objects in peripersonal space is task dependent.

Previous fMRI studies have shown that the visual perception of manipulable objects spontaneously involves the sensorimotor system, especially when the objects are located in peripersonal space. However, it has also been suggested that the motor coding of manipulable objects perceived in peripersonal space depends on an anticipation to interact with them. The present study aims at clarifying this issue by analyzing healthy adults' EEG activity on the centro-parietal region while perceptually judging intrinsic (prototypical or distorted shape) or extrinsic (reachable or not reachable location) properties of visual objects. In both the object identification and reachability judgment tasks, time-frequency decomposition of EEG signals was performed across the first 1000 ms following object presentation for trials on which no post-stimulus response was required (90% of the trials). Event-Related-(De)Synchronization (ERD/S) of µ rhythm was computed using the 150 ms pre-stimulus period as baseline. In the reachability judgment task, EEG analysis showed a desynchronization of µ rhythm starting 300 ms after object presentation, but only when the objects were presented with a prototypical shape in peripersonal space. For those objects, desynchronization of µ rhythm diminished progressively from peripersonal to extrapersonal space. By contrast, no such gradient was observed in the object identification task. On the whole, these data indicate that motor coding of visual objects expressed in the µ rhythm depends on an object's shape and location in space, but also on the goal of the perceptual task.

Bilateral Strength Deficit Is Not Neural in Origin; Rather Due to Dynamometer Mechanical Configuration.

During maximal contractions, the sum of forces exerted by homonymous muscles unilaterally is typically higher than the sum of forces exerted by the same muscles bilaterally. However, the underlying mechanism(s) of this phenomenon, which is known as the bilateral strength deficit, remain equivocal. One potential factor that has received minimal attention is the contribution of body adjustments to bilateral and unilateral force production. The purpose of this study was to evaluate the plantar-flexors in an innovative dynamometer that permitted the influence of torque from body adjustments to be adapted. Participants were identically positioned between two setup configurations where torques generated from body adjustments were included within the net ankle torque (locked-unit) or independent of the ankle (open-unit). Twenty healthy adult males performed unilateral and bilateral maximal voluntary isometric plantar-flexion contractions using the dynamometer in the open and locked-unit mechanical configurations. While there was a significant bilateral strength deficit in the locked-unit (p = 0.01), it was not evident in the open-unit (p = 0.07). In the locked-unit, unilateral torque was greater than in the open-unit (p<0.001) and this was due to an additional torque from the body since the electromyographic activity of the agonist muscles did not differ between the two setups (p>0.05). This study revealed that the mechanical configuration of the dynamometer and then the body adjustments caused the observation of a bilateral strength deficit.

How we perceive our own hands: Effects of attention, aging, and sex.

This study investigates whether both the perception of somesthetic sensations arising spontaneously on the hand and their modulation by attention are subject to change with advancing age and sex. Participants aged between 50 and 68 (N = 24), and younger (19-27; N = 24), with an equal sex ratio in each group, described the spontaneous sensations they felt on one of their hands. Two 10-s tests were carried out with participants either seeing their tested hand (gaze towards the visible hand) or not (contralateral gaze, hidden hand). Within the age range covered by our participants, aging had an effect on the spatial distribution of sensations, insofar as the older participants reported feeling more sensations in their palm whereas the younger participants had more sensitive fingers. Age also influenced the number, nature, intensity, and duration of sensations in interaction with gaze and/or sex. The most frequent pattern was a benefit of ipsilateral relative to contralateral gazing in young women. Attentional modulation was seldom observed in men and was absent among older participants.

Inter and intra-individual differences in steering wheel hand positions during a simulated driving task.

This paper describes an experimental study focusing onto the way drivers use the steering wheel while performing a 2D tracking task. The stimulus during this task was a steering wheel angle signal recorded in real situations involving turns and straight lines performed at about 30 km/h. The hand positions of 20 volunteers were recorded in 6 steering scenarios involving 7 road geometries using a 3D motion capture system. The hand movement data were analysed via a descriptive/inferential procedure: each hand was considered using nine indicators - eight membership value averages linked to eight fuzzy angle windows and a frequency value related to the off steering wheel position - while the indicators were investigated using multiple correspondence analysis and non-parametric global and post-hoc tests. Results showed that inter-individual differences were larger than intra-individual differences. Considering 2 × 9 = 18 windows, the inter-individual differences mainly appeared during two main kinds of steering hand strategies: with versus without crossing hands, the latter being the most often used (17 among 20 participants). The intra-individual data showed that some drivers maintained a nearly identical strategy for all road geometries, while other drivers changed their hand position with the direction and/or maximum angle value of the turn. Practitioner Summary: Understanding hand position strategy could be used to design steering wheel assistance in relation to a driver's physical resources with a view to adapting the steering wheel to disabled drivers.