Glial response in early stages of traumatic brain injury

Supplementary Pharmacotherapy for the Behavioral Abnormalities Caused by Stressors in Humans, Focused on Post-Traumatic Stress Disorder (PTSD)

Used as a supplement to psychotherapy, pharmacotherapy that addresses all of the known metabolic and genetic contributions to the pathogenesis of psychiatric conditions caused by stressors would require an inordinate number of drugs. Far simpler is to address the abnormalities caused by those metabolic and genetic changes in the cell types of the brain that mediate the behavioral abnormality. Relevant data regarding the changed brain cell types are described in this article and are derived from subjects with the paradigmatic behavioral abnormality of PTSD and from subjects with traumatic brain injury or chronic traumatic encephalopathy. If this analysis is correct, then therapy is required that benefits all of the affected brain cell types; those are astrocytes, oligodendrocytes, synapses and neurons, endothelial cells, and microglia (the pro-inflammatory (M1) subtype requires switching to the anti-inflammatory (M2) subtype). Combinations are advocated using several drugs, erythropoietin, fluoxetine, lithium, and pioglitazone, that benefit all of the five cell types, and that should be used to form a two-drug combination, suggested as pioglitazone with either fluoxetine or lithium. Clemastine, fingolimod, and memantine benefit four of the cell types, and one chosen from those could be added to the two-drug combination to form a three-drug combination. Using low doses of chosen drugs will limit both toxicity and drug-drug interactions. A clinical trial is required to validate both the advocated concept and the choice of drugs.

Anesthesia and analgesia for experimental craniotomy in mice and rats: a systematic scoping review comparing the years 2009 and 2019

Experimental craniotomies are a common surgical procedure in neuroscience. Because inadequate analgesia appears to be a problem in animal-based research, we conducted this review and collected information on management of craniotomy-associated pain in laboratory mice and rats. A comprehensive search and screening resulted in the identification of 2235 studies, published in 2009 and 2019, describing craniotomy in mice and/or rats. While key features were extracted from all studies, detailed information was extracted from a random subset of 100 studies/year. Reporting of perioperative analgesia increased from 2009 to 2019. However, the majority of studies from both years did not report pharmacologic pain management. Moreover, reporting of multimodal treatments remained at a low level, and monotherapeutic approaches were more common. Among drug groups, reporting of pre- and postoperative administration of non-steroidal anti-inflammatory drugs, opioids, and local anesthetics in 2019 exceeded that of 2009. In summary, these results suggest that inadequate analgesia and oligoanalgesia are persistent issues associated with experimental intracranial surgery. This underscores the need for intensified training of those working with laboratory rodents subjected to craniotomies.

Systematic review registration

https://osf.io/7d4qe.

Tackling Neuroinflammation After Traumatic Brain Injury: Complement Inhibition as a Therapy for Secondary Injury

Traumatic brain injury (TBI) is a leading cause of mortality, sensorimotor morbidity, and neurocognitive disability. Neuroinflammation is one of the key drivers causing secondary brain injury after TBI. Therefore, attenuation of the inflammatory response is a potential therapeutic goal. This review summarizes the most important neuroinflammatory pathophysiology resulting from TBI and the clinical trials performed to attenuate neuroinflammation. Studies show that non-selective attenuation of the inflammatory response, in the early phase after TBI, might be detrimental and that there is a gap in the literature regarding pharmacological trials targeting specific pathways. The complement system and its crosstalk with the coagulation system play an important role in the pathophysiology of secondary brain injury after TBI. Therefore, regaining control over the complement cascades by inhibiting overshooting activation might constitute useful therapy. Activation of the complement cascade is an early component of neuroinflammation, making it a potential target to mitigate neuroinflammation in TBI. Therefore, we have described pathophysiological aspects of complement inhibition and summarized animal studies targeting the complement system in TBI. We also present the first clinical trial aimed at inhibition of complement activation in the early days after brain injury to reduce the risk of morbidity and mortality following severe TBI.

NMDA receptor-dependent prostaglandin-endoperoxide synthase 2 induction in neurons promotes glial proliferation during brain development and injury

Astrocytes play critical roles in brain development and disease, but the mechanisms that regulate astrocyte proliferation are poorly understood. We report that astrocyte proliferation is bi-directionally regulated by neuronal activity via NMDA receptor (NMDAR) signaling in neurons. Prolonged treatment with an NMDAR antagonist reduced expression of cell-cycle-related genes in astrocytes in hippocampal cultures and suppressed astrocyte proliferation in vitro and in vivo, whereas neuronal activation promoted astrocyte proliferation, dependent on neuronal NMDARs. Expression of prostaglandin-endoperoxide synthase 2 (Ptgs2) is induced specifically in neurons by NMDAR activation and is required for activity-dependent astrocyte proliferation through its product, prostaglandin E₂ (PGE₂). NMDAR inhibition or Ptgs2 genetic ablation in mice reduced the proliferation of astrocytes and microglia induced by mild traumatic brain injury in the absence of secondary excitotoxicity-induced neuronal death. Our study defines an NMDAR-mediated signaling mechanism that allows trans-cellular control of glial proliferation by neurons in brain development and injury.

Mechanisms implicated in the contralateral effect in the central nervous system after unilateral injury: focus on the visual system

The retina, as part of the central nervous system is an ideal model to study the response of neurons to injury and disease and to test new treatments. During the last decade is becoming clear that unilateral lesions in bilateral areas of the central nervous system trigger an inflammatory response in the contralateral uninjured site. This effect has been better studied in the visual system where, as a rule, one retina is used as experimental and the other as control. Contralateral retinas in unilateral models of retinal injury show neuronal degeneration and glial activation. The mechanisms by which this adverse response in the central nervous system occurs are discussed in this review, focusing primarily on the visual system.

Pathophysiological Responses and Roles of Astrocytes in Traumatic Brain Injury

Traumatic brain injury (TBI) is immediate damage caused by a blow to the head resulting from traffic accidents, falls, and sporting activity, which causes death or serious disabilities in survivors. TBI induces multiple secondary injuries, including neuroinflammation, disruption of the blood–brain barrier (BBB), and brain edema. Despite these emergent conditions, current therapies for TBI are limited or insufficient in some cases. Although several candidate drugs exerted beneficial effects in TBI animal models, most of them failed to show significant effects in clinical trials. Multiple studies have suggested that astrocytes play a key role in the pathogenesis of TBI. Increased reactive astrocytes and astrocyte-derived factors are commonly observed in both TBI patients and experimental animal models. Astrocytes have beneficial and detrimental effects on TBI, including promotion and restriction of neurogenesis and synaptogenesis, acceleration and suppression of neuroinflammation, and disruption and repair of the BBB via multiple bioactive factors. Additionally, astrocytic aquaporin-4 is involved in the formation of cytotoxic edema. Thus, astrocytes are attractive targets for novel therapeutic drugs for TBI, although astrocyte-targeting drugs have not yet been developed. This article reviews recent observations of the roles of astrocytes and expected astrocyte-targeting drugs in TBI.

Cell Proliferation in the Piriform Cortex of Rats with Motor Cortex Ablation Treated with Growth Hormone and Rehabilitation

Traumatic brain injury represents one of the main health problems in developed countries. Growth hormone (GH) and rehabilitation have been claimed to significantly contribute to the recovery of lost motor function after acquired brain injury, but the mechanisms by which this occurs are not well understood. In this work, we have investigated cell proliferation in the piriform cortex (PC) of adult rats with ablation of the frontal motor cortex treated with GH and rehabilitation, in order to evaluate if this region of the brain, related to the sense of smell, could be involved in benefits of GH treatment. Male rats were either ablated the frontal motor cortex in the dominant hemisphere or sham-operated and treated with GH or vehicle at 35 days post-injury (dpi) for five days. At 36 dpi, all rats received daily injections of bromodeoxyuridine (BrdU) for four days. We assessed motor function through the paw-reaching-for-food task. GH treatment and rehabilitation at 35 dpi significantly improved the motor deficit caused by the injury and promoted an increase of cell proliferation in the PC ipsilateral to the injury, which could be involved in the improvement observed. Cortical ablation promoted a greater number of BrdU+ cells in the piriform cortex that was maintained long-term, which could be involved in the compensatory mechanisms of the brain after injury.

MCC950 Inhibits NLRP3 Inflammasome and Alleviates Axonal Injures in Early Stages of Diffuse Axonal Injury in Rats

Increasing evidence has revealed that neuroinflammation plays a pivotal role in axonal injures. Nucleotide oligomerization domain (NOD)-like receptor protein (NLRP3) inflammasome is reported to be widely involved with the pathology of central nervous system disorders. But the role of NLRP3 in diffuse axonal injury (DAI) are rarely reported. The purpose of this study was to investigate the expression of NLRP3 after diffuse axonal injury and the role of NLRP3 in axonal injures. The lateral head rotation device was used to establish DAI model of rats. Immunohistochemical staining for β-amyloid precursor protein and Bielschowsky silver staining were used to assess axonal injures and axonal loss. Terminal Deoxynucleotidyl Transferase-Mediated Digoxigenin-dUTP-Biotin Nick-End Labelling Assay was used to detect cell apoptosis. Brain water content was used to assess cerebral edema and the modified Neurologic Severity Score was used to assess the neurological deficits. Components of NLRP3 inflammasome, such as NLRP3, apoptosis-associated speck-like (ASC) adapter protein and caspase-1, and pro-inflammatory cytokines, for example IL-18 and IL-1β, were over-expressed in early stages of DAI. MCC950, a selective small-molecule inhibitor of NLRP3 inflammasome, inhibited the over-expression of NLRP3 inflammasome and pro-inflammatory cytokines after DAI. MCC950 alleviated axonal injures and cell apoptosis. MCC950 also decreased brain water content and alleviated neurologic deficits 1 day and 3 days after DAI but not 7 days after DAI. These results suggest that MCC950 treatment in the early stages of DAI has a time limiting effect in preventing from axonal injuries and neurological deficits, and that NLRP3 inflammasome plays an important role in axonal injures and may be a potential candidate for axonal injures following DAI.

The Delayed Neuroprotective Effect of Methylene Blue in Experimental Rat Brain Trauma

After traumatic brain injury (TBI), an increase in dysfunction of the limbs contralateral to injury focus was observed. Using different behavioral tests, we found that a single intravenous injection of methylene blue (MB, 1 mg/kg) 30 min after the injury reduced the impairment of the motor functions of the limbs from 7 to 120 days after TBI. Administration of methylene blue 30 min after the injury and then monthly (six injections in total) was the most effective both in terms of preservation of limb function and duration of therapeutic action. This therapeutic effect was clearly manifested from the seventh day and continued until the end of the experiment-by the 180th day after TBI. MB is known to possess antioxidant properties; it has a protective effect against TBI by promoting autophagy and minimizing lesion volume in the first two weeks after TBI. Studies of the brains on the 180th day after TBI demonstrated that the monthly treatment of animals with MB statistically significantly prevented an increase in the density of microglial cells in the ipsilateral hemisphere and a decrease in the thickness of the corpus callosum in the contralateral hemisphere in comparison with untreated animals. However, on the 180th day after TBI, the magnetic resonance imaging scan of the animal brains did not show a significant reduction in the volume of the lesion in MB-treated animals. These findings are important for understanding the development of the long-term effects of TBI and expand the required therapeutic window for targeted neuroprotective interventions.

TSPO Modulates IL-4-Induced Microglia/Macrophage M2 Polarization via PPAR-γ Pathway

Microglia activation has been reported to be associated with pathogenesis of neuroinflammation, central nervous system damage, and degeneration diseases. With various damage-associated molecules released, M1 polarization of microglia emerges early after injury and followed by M2 polarization. In this study, we demonstrate using a primary microglia polarization model that, during the M2 polarization of microglia, the protein expression of translocator protein (TSPO) was decreased and peroxisome proliferator-activated receptor (PPAR-γ) activation was observed. In addition, we found TSPO antagonist PK11195 treatment enhanced PPAR-γ expression in M2-polarized microglia, while TSPO agonist FGIN-1-27 and TSPO overexpression in microglia significantly suppressed PPAR-γ expression in both the cytoplasm and nucleus. Then, real-time quantitative PCR was used to detect the expression of M2 polarization markers in microglia after TSPO ligand treatment, the data showed that PK11195 promoted the expression of CD206, Arg-1, YM-1, and FIZZ-1 induced by interleukin-4 (IL-4), and FGIN-1-27 and TSPO overexpression inhibited the expression of these molecules. Furthermore, the release of BDNF, CNTF-1, IGF-1, and NGF-1 from microglia was determined by enzyme-linked immunosorbent assay; these trophic factors showed similar trends with expression of M2 polarization markers. Levels of BDNF, CNTF-1, IGF-1, and NGF-1 were obviously upregulated by PK11195 and downregulated by FGIN-1-27 and TSPO overexpression. We propose that IL-4 in the hypoxic ischemia brain site induces the M2 polarization of microglia, and TSPO inhibits the M2 polarization and trophic factor release through PPAR-γ pathway.

Role of Astrocytes in Post-traumatic Epilepsy

Traumatic brain injury, a common cause of acquired epilepsy, is typical to find necrotic cell death within the injury core. The dynamic changes in astrocytes surrounding the injury core contribute to epileptic seizures associated with intense neuronal firing. However, little is known about the molecular mechanisms that activate astrocytes during traumatic brain injury or the effect of functional changes of astrocytes on seizures. In this comprehensive review, we present our cumulated understanding of the complex neurological affection in astrocytes after traumatic brain injury. We approached the problem through describing the changes of cell morphology, neurotransmitters, biochemistry, and cytokines in astrocytes during post-traumatic epilepsy. In addition, we also discussed the relationship between dynamic changes in astrocytes and seizures and the current pharmacologic agents used for treatment. Hopefully, this review will provide a more detailed knowledge from which better therapeutic strategies can be developed to treat post-traumatic epilepsy.