BackgroundTraumatic injury to the central nervous system (CNS) triggers a robust inflammatory response that leads to axonal damage and secondary degeneration of spared tissue. In contrast, some immune responses have neuroprotective effects. However, detailed information regarding the dynamics of immune responses after traumatic CNS injury is still unavailable.MethodsIn the present study, changes in the immune cells present in the injured brain, spleen, and cervical lymph nodes (CLNs), which are draining lymphatic organs from the CNS, were analyzed after controlled cortical impact (CCI) by flow cytometry and immunohistochemistry.ResultsThe number of neutrophils and macrophages that infiltrated the injured brain immediately increased 1 d post-injury and declined rapidly thereafter. In the injured brain, resident microglia showed a bimodal increase during the first week and in the chronic phase (≥3 weeks) after injury. Increase in the Iba-1+ microglia/macrophages was observed around the injured site. Morphologic analysis showed that Iba-1+ cells were round at 1 week, whereas those at 3 weeks were more ramified. Furthermore, CD86+/CD11b+ M1-like microglia increased at 4 weeks after CCI, whereas CD206+/CD11b+ M2-like microglia increased at 1 week. These results suggest that different subsets of microglia increased in the acute and chronic phases after CCI. Dendritic cells and T cells increased transiently within 1 week in the injured brain. In the CLNs and the spleen, T cells showed dynamic changes after CCI. In particular, the alteration in the number of T cells in the CLNs showed a similar pattern, with a 1-week delay, to that of microglia in the injured brain.ConclusionThe data from this study provide useful information on the dynamics of immune cells in CNS injuries.

Sleep is characterized by unique patterns of cortical activity alternating between the stages of slow-wave sleep (SWS) and rapid-eye movement (REM) sleep. How these patterns relate to the balanced activity of excitatory pyramidal cells and inhibitory interneurons in cortical circuits is unknown. We investigated cortical network activity during wakefulness, SWS, and REM sleep globally and locally using in vivo calcium imaging in mice. Wide-field imaging revealed a reduction in pyramidal cell activity during SWS compared with wakefulness and, unexpectedly, a further profound reduction in activity during REM sleep. Two-photon imaging on local circuits showed that this suppression of activity during REM sleep was accompanied by activation of parvalbumin (PV)+ interneurons, but not of somatostatin (SOM)+ interneurons. PV+ interneurons most active during wakefulness were also most active during REM sleep. Our results reveal a sleep-stage-specific regulation of the cortical excitation/inhibition balance, with PV+ interneurons conveying maximum inhibition during REM sleep, which might help shape memories in these networks.

Cortical computation is distributed across multiple areas of the cortex by networks of reciprocal connectivity. However, how such connectivity contributes to the communication between the connected areas is not clear. In this study, we examine the communication between sensory and motor cortices. We develop an eye movement task in mice and combine it with optogenetic suppression and two-photon calcium imaging techniques. We identify a small region in the secondary motor cortex (MOs) that controls eye movements and reciprocally connects with a rostrolateral part of the higher visual areas (VRL/A/AL). These two regions encode both motor signals and visual information; however, the information flow between the regions depends on the direction of the connectivity: motor information is conveyed preferentially from the MOs to the VRL/A/AL, and sensory information is transferred primarily in the opposite direction. We propose that reciprocal connectivity streamlines information flow, enhancing the computational capacity of a distributed network.

Despite tremendous research effort in the field, our current understanding of the molecular mechanisms underlying neuropathic pain is still incomplete. In the present study, our objective was to elucidate the involvement of the Wnt/β-catenin signaling pathway in the development of neuropathic pain. We showed that Wnt/β-catenin signaling is activated in the spinal cord dorsal horn after partial sciatic nerve ligation (PSL). Expression of Wnt3a, a prototypic Wnt ligand that activates the Wnt/β-catenin pathway, was also upregulated in the dorsal horn. We then tested the effect of intrathecal administration of XAV939, a Wnt/β-catenin signaling inhibitor, and found that this treatment effectively attenuated the induction of neuropathic pain. Conversely, intrathecal administration of Wnt3a to the lumbar spinal cord of naïve animals triggered the development of allodynia. These results suggest a critical involvement of the Wnt/β-catenin pathway in the development of neuropathic pain. Moreover, we also found that PSL-induced microglial activation was significantly suppressed by intrathecal administration of XAV939 treatment. Because it was revealed that Wnt3a treatment triggered brain-derived neurotrophic factor (BDNF) release from microglial cells in vitro, it is possible that Wnt3a upregulation in the dorsal horn leads to the activation of microglial cells, then triggers BDNF secretion that is responsible for the establishment of neuropathic pain. Further studies will be needed for the comprehensive understanding of the roles of Wnt/β-catenin signaling in the development of neuropathic pain.

Prepared movements are more efficient than those that are not prepared for. Although changes in cortical activity have been observed prior to a forthcoming action, the circuits involved in motor preparation remain unclear. Here, we use in vivo two-photon calcium imaging to uncover changes in the motor cortex during variable waiting periods prior to a forepaw reaching task in mice. Consistent with previous reports, we observed a subset of neurons with increased activity during the waiting period; however, these neurons did not account for the degree of preparation as defined by reaction time (RT). Instead, the suppression of activity of distinct neurons in the same cortical area better accounts for RT. This suppression of neural activity resulted in a distinct and reproducible pattern when mice were well prepared. Thus, the selective suppression of network activity in the motor cortex may be a key feature of prepared movements.

Secondary progressive multiple sclerosis (SPMS) is an autoimmune disease of the central nervous system (CNS) characterized by progressive motor dysfunction, sensory deficits, and visual problems. The pathological mechanism of SPMS remains poorly understood. In this study, we investigated the role of microglia, immune cells in the CNS, in a secondary progressive form of experimental autoimmune encephalomyelitis (EAE), the mouse model of SPMS. We induced EAE in nonobese diabetic mice and treated the EAE mice with PLX3397, an antagonist of colony stimulating factor‐1 receptor, during secondary progression in order to deplete microglia. The results showed that PLX3397 treatment significantly exacerbated secondary progression of EAE and increased mortality rates. Additionally, histological analysis showed that PLX3397 treatment significantly promoted inflammation, demyelination, and axonal degeneration. Moreover, the number of CD4+ T cells in the spinal cord of EAE mice was expanded due to PLX3397‐mediated proliferation. These results suggest that microglia suppressed secondary progression of EAE by inhibiting the proliferation of CD4+ T cells in the CNS.

Synopsis: Arid5a is a key molecule in inflammatory and autoimmune diseases, yet its role in cancer progression is unknown. Arid5a expression is shown to increase in mesenchymal tumors and augment immune evasion by promoting tryptophan catabolism and chemokine expression.

Traumatic brain injury (TBI) results in severe motor function impairment, and subsequent recovery is often incomplete. Rehabilitative training is considered to promote restoration of the injured neural network, thus facilitating functional recovery. However, no studies have assessed the effect of such trainings in the context of neural rewiring. Here, we investigated the effects of two types of rehabilitative training on corticospinal tract (CST) plasticity and motor recovery in mice. We injured the unilateral motor cortex with contusion, which induced hemiparesis on the contralesional side. After the injury, mice performed either a single pellet-reaching task (simple repetitive training) or a rotarod task (bilateral movement training). Multiple behavioral tests were then used to assess forelimb motor function recovery: staircase, ladder walk, capellini handling, single pellet, and rotarod tests. The TBI+rotarod group performed most forelimb motor tasks (staircase, ladder walk, and capellini handling tests) better than the TBI-only group did. In contrast, the TBI+reaching group did not perform better except in the single pellet test. After the injury, the contralateral CST, labeled by biotinylated dextran amine, formed sprouting fibers into the denervated side of the cervical spinal cord. The number of these fibers was significantly higher in the TBI+rotarod group, whereas it did not increase in the TBI+reaching group. These results indicate that bilateral movement training effectively promotes axonal rewiring and motor function recovery, whereas the effect of simple repetitive training is limited.