Neuroscience
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Several brain structures including the brainstem, the cerebellum and the frontal cortico-basal ganglia network, with the primary and premotor areas have been shown to participate in the functional organization of gait initiation and postural control in humans, but their respective roles remain poorly understood. The aim of this study was to better understand the role of the supplementary motor area (SMA) and posterior cerebellum in the gait initiation process. Gait initiation parameters were recorded in 22 controls both before and after continuous theta burst transcranial stimulation (cTBS) of the SMA and cerebellum, and were compared to sham stimulation, using a randomized double-blind design study. ⋯ Functional inhibition of the SMA led to a shortened APA phase duration with advanced and increased muscle activity; during execution, it also advanced muscle co-activation and decreased the duration of stance soleus activity. Cerebellar functional inhibition did not influence the APA phase duration and amplitude but increased muscle co-activation, it decreased execution duration and showed a trend to increase velocity, with increased swing soleus muscle duration and activity. The results suggest that the SMA contributes to both the timing and amplitude of the APAs with no influence on step execution and the posterior cerebellum in the coupling between the APAs and execution phases and leg muscle activity pattern during gait initiation.
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The periodontal ligament (PDL) includes several types of nerve endings, such as Aβ-, Aδ-, and C-fibers, which play critical roles in detecting the strength and direction of occlusal force. Previous studies have demonstrated that electrical stimulation of the PDL activates the somatosensory and insular cortices. However, the profile of cortical excitation in response to mechanical PDL stimulation mostly remains unknown. ⋯ A paired-pulse protocol of mechanical stimulation revealed that the amplitude of the second response was smaller than the first response, in accordance with the shorter interstimulus interval. Systemic application of morphine, a potent blocker of nociception, reduced the amplitude of the maximum excitation, particularly in S2/IOR compared to S1. These results suggest that S1 and S2/IOR are principally excited by mechanical and electrical stimulation, respectively, and that S2/IOR is involved in nociception processing.
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The insular cortex is a critical brain region involved in nicotine addiction. However, its specific cellular and synaptic mechanisms underlying nicotine addiction remains largely unknown. In the present study, we examined how nicotine modulates synaptic transmission and plasticity in layer V pyramidal neurons of the mouse insular cortex. ⋯ Blockade of GABAA receptors or β2-containing nAChRs prevented the effects of nicotine on synaptic potentiation. Taken together, these results suggest that in layer V pyramidal neurons of the insular cortex, activation of β2-containing nAChRs expressed in non-FS interneurons suppresses synaptic potentiation through enhancing GABAergic synaptic transmission. These findings provide important insights into the cellular and synaptic mechanisms of insular cortical changes in nicotine addiction.
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Muscle pain is an important health issue and frequently related to static force exertion. The aim of this study is to evaluate whether peripheral inflammatory mechanisms are involved with static contraction-induced muscle pain in rats. To this end, we developed a model of muscle pain induced by static contraction performed by applying electrical pulses through electrodes inserted into muscle. ⋯ Furthermore, an increased hyperalgesic response was observed when the selective bradykinin B1 agonist des-Arg9-bradykinin was injected into the previously stimulated muscle. Together, these findings demonstrate that static contraction induced mechanical muscle hyperalgesia in gastrocnemius muscle of rats is modulated through peripheral inflammatory mechanisms that are dependent on neutrophil migration, bradykinin, sympathetic amines and prostanoids. Considering the clinical relevance of muscle pain, we propose the present model of static contraction-induced mechanical muscle hyperalgesia as a useful tool for the study of mechanisms underlying static contraction-induced muscle pain.
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Recent evidence suggests that ischemia/reperfusion (I/R) in an organ may have distance effect on the brain. In this study, the effects of renal I/R, limb I/R or both together on the structural and function of hippocampus were evaluated and compared. Hence, rats were subjected to 2-h bilateral lower limb ischemia, 45-min bilateral renal ischemia, or combined limb and renal ischemia followed by 1-day reperfusion. ⋯ In the rats with combined limb and renal I/R, the hippocampal neuronal loss and impaired synaptic plasticity were the same as those with limb I/R, but basal synaptic transmission was lowered. In conclusion, the 2-h lower limb ischemia compared to 45-min renal ischemia induced more injurious distant effects on the hippocampus after 1-day reperfusion. The combination of renal and limb I/R did not add or potentiate hippocampal neuronal loss and synaptic plasticity impairment, whereas it decreased the basal synaptic transmission with respect to each one alone.