Social interaction attenuates the extent of secondary neuronal damage following closed head injury in mice

Oxytocin neurons in the paraventricular nucleus of the hypothalamus circuit-dependently regulates social behavior, which malfunctions in BTBR mouse model of autism

Oxytocin (OXT) a neuropeptide synthesized in the hypothalamic nuclei has a variety of function including socio-emotional processes in mammals. While the neural circuits and signaling pathways in central OXT converge in the paraventricular nucleus of the hypothalamus (PVN), we illuminate specific function of discrete PVN OXT circuits, which connect to the medial amygdala (MeA) and the bed nucleus of the stria terminalis (BnST) in mouse models. The OXTPVN→BnST projections are innervated from entire portions of the PVN, while those OXTPVN→MeA projections are asymmetrically innervated from the posterior portion of the PVN. Compared with OXT neurons in B6 wild type mice, BTBR mice that are recognized as a behavior-based autism model exhibited defect in the OXTPVN→BnST projection. We demonstrate that chemogenetic activation of OXTPVN→MeA circuit enhances anxiety-like behavior and facilitates social approach behavior, while activation of OXTPVN→BnST circuit suppresses anxiety-like behavior along with inhibiting social approach. This chemogenetic manipulation on the OXTPVN→BnST circuit proves ineffective in BTBR mice. Accordingly, chemogenetic activation of OXTPVN neurons that stimulate both OXT circuits induces OXT receptor expressions in both MeA and BnST as with those by social encounter in B6 mice. The induction of OXT receptor genes in the BnST was not observed in BTBR mice. These data support the hypothesis that OXT circuits serve as a regulator for OXT signaling in PVN to control socio-emotional approach/avoidance behavior, and a defect of OXTPVN→BnST circuit contributes to autism-like social phenotypes in BTBR mice.

The Neurobiological Links between Stress and Traumatic Brain Injury: A Review of Research to Date

Neurological dysfunctions commonly occur after mild or moderate traumatic brain injury (TBI). Although most TBI patients recover from such a dysfunction in a short period of time, some present with persistent neurological deficits. Stress is a potential factor that is involved in recovery from neurological dysfunction after TBI. However, there has been limited research on the effects and mechanisms of stress on neurological dysfunctions due to TBI. In this review, we first investigate the effects of TBI and stress on neurological dysfunctions and different brain regions, such as the prefrontal cortex, hippocampus, amygdala, and hypothalamus. We then explore the neurobiological links and mechanisms between stress and TBI. Finally, we summarize the findings related to stress biomarkers and probe the possible diagnostic and therapeutic significance of stress combined with mild or moderate TBI.

Brain Trauma, Glucocorticoids and Neuroinflammation: Dangerous Liaisons for the Hippocampus

Glucocorticoid-dependent mechanisms of inflammation-mediated distant hippocampal damage are discussed with a focus on the consequences of traumatic brain injury. The effects of glucocorticoids on specific neuronal populations in the hippocampus depend on their concentration, duration of exposure and cell type. Previous stress and elevated level of glucocorticoids prior to pro-inflammatory impact, as well as long-term though moderate elevation of glucocorticoids, may inflate pro-inflammatory effects. Glucocorticoid-mediated long-lasting neuronal circuit changes in the hippocampus after brain trauma are involved in late post-traumatic pathology development, such as epilepsy, depression and cognitive impairment. Complex and diverse actions of the hypothalamic–pituitary–adrenal axis on neuroinflammation may be essential for late post-traumatic pathology. These mechanisms are applicable to remote hippocampal damage occurring after other types of focal brain damage (stroke, epilepsy) or central nervous system diseases without obvious focal injury. Thus, the liaisons of excessive glucocorticoids/dysfunctional hypothalamic–pituitary–adrenal axis with neuroinflammation, dangerous to the hippocampus, may be crucial to distant hippocampal damage in many brain diseases. Taking into account that the hippocampus controls both the cognitive functions and the emotional state, further research on potential links between glucocorticoid signaling and inflammatory processes in the brain and respective mechanisms is vital.

Social isolation reinforces aging-related behavioral inflexibility by promoting neuronal necroptosis in basolateral amygdala

Aging is characterized with a progressive decline in many cognitive functions, including behavioral flexibility, an important ability to respond appropriately to changing environmental contingencies. However, the underlying mechanisms of impaired behavioral flexibility in aging are not clear. In this study, we reported that necroptosis-induced reduction of neuronal activity in the basolateral amygdala (BLA) plays an important role in behavioral inflexibility in 5-month-old mice of the senescence-accelerated mice prone-8 (SAMP8) line, a well-established model with age-related phenotypes. Application of Nec-1s, a specific inhibitor of necroptosis, reversed the impairment of behavioral flexibility in SAMP8 mice. We further observed that the loss of glycogen synthase kinase 3α (GSK-3α) was strongly correlated with necroptosis in the BLA of aged mice and the amygdala of aged cynomolgus monkeys (Macaca fascicularis). Moreover, genetic deletion or knockdown of GSK-3α led to the activation of necroptosis and impaired behavioral flexibility in wild-type mice, while the restoration of GSK-3α expression in the BLA arrested necroptosis and behavioral inflexibility in aged mice. We further observed that GSK-3α loss resulted in the activation of mTORC1 signaling to promote RIPK3-dependent necroptosis. Importantly, we discovered that social isolation, a prevalent phenomenon in aged people, facilitated necroptosis and behavioral inflexibility in 4-month-old SAMP8 mice. Overall, our study not only revealed the molecular mechanisms of the dysfunction of behavioral flexibility in aged people but also identified a critical lifestyle risk factor and a possible intervention strategy.

A Systematic Review of Closed Head Injury Models of Mild Traumatic Brain Injury in Mice and Rats

Mild TBI (mTBI) is a significant health concern. Animal models of mTBI are essential for understanding mechanisms, and pathological outcomes, as well as to test therapeutic interventions. A variety of closed head models of mTBI that incorporate different aspects (i.e., biomechanics) of the mTBI have been reported. The aim of the current review was to compile a comprehensive list of the closed head mTBI rodent models, along with the common data elements, and outcomes, with the goal to summarize the current state of the field. Publications were identified from a search of PubMed and Web of Science and screened for eligibility following PRISMA guidelines. Articles were included that were closed head injuries in which the authors classified the injury as mild in rats or mice. Injury model and animal-specific common data elements, as well as behavioral and histological outcomes, were collected and compiled from a total of 402 articles. Our results outline the wide variety of methods used to model mTBI. We also discovered that female rodents and both young and aged animals are under-represented in experimental mTBI studies. Our findings will aid in providing context comparing the injury models and provide a starting point for the selection of the most appropriate model of mTBI to address a specific hypothesis. We believe this review will be a useful starting place for determining what has been done and what knowledge is missing in the field to reduce the burden of mTBI.

The Inflammatory Continuum of Traumatic Brain Injury and Alzheimer's Disease

The post-injury inflammatory response is a key mediator in long-term recovery from traumatic brain injury (TBI). Moreover, the immune response to TBI, mediated by microglia and macrophages, is influenced by existing brain pathology and by secondary immune challenges. For example, recent evidence shows that the presence of beta-amyloid and phosphorylated tau protein, two hallmark features of AD that increase during normal aging, substantially alter the macrophage response to TBI. Additional data demonstrate that post-injury microglia are “primed” and become hyper-reactive following a subsequent acute immune challenge thereby worsening recovery. These alterations may increase the incidence of neuropsychiatric complications after TBI and may also increase the frequency of neurodegenerative pathology. Therefore, the purpose of this review is to summarize experimental studies examining the relationship between TBI and development of AD-like pathology with an emphasis on the acute and chronic microglial and macrophage response following injury. Furthermore, studies will be highlighted that examine the degree to which beta-amyloid and tau accumulation as well as pre- and post-injury immune stressors influence outcome after TBI. Collectively, the studies described in this review suggest that the brain’s immune response to injury is a key mediator in recovery, and if compromised by previous, coincident, or subsequent immune stressors, post-injury pathology and behavioral recovery will be altered.

While I Still Remember: 30 Years of Alzheimer's Disease Research

Turns out I have been a major contributor to the Journal of Alzheimer's Disease over its 20-year history. As such, I was invited to provide a review of my work over the years. What follows is a retrospective of how the Alzheimer-related research of a Ph.D. (i.e., not an M.D.) transitioned from basic to clinical, and moved from bench to bedside and back again.I have included some of the more humorous and poignant twists along the way that some older players may find familiar and I hope might inspire some younger players to hang in there.

Rhein exhibits antioxidative effects similar to Rhubarb in a rat model of traumatic brain injury

Background

The brain is secondarily harmed by pathological, physiological, and biological reactions that are caused by traumatic brain injury (TBI). Rhein, a significant composition of Rhubarb, is a well-known traditional Chinese treatment method and has a strong oxidation-resisting characteristic, but Rhein’s mechanism remains unclear.

Methods

This study aimed to identify Rhein in the brain tissues of TBI model of rats, and confirm whether Rhein induced an antioxidative effect similar to its parent medicine, Rhubarb. First, the ultra performance liquid chromatography-tandem mass spectrometry (UPLC-MS/MS) method was applied to identify Rhein in the brain tissue of the controlled cortical impact (CCI) rats after intra-gastric administration of Rhubarb. Further, for the purpose of calculating the oxidant stress of the CCI rats, the malondialdehyde (MDA), catalase (CAT), superoxide dismutase (SOD), and glutathione disulfide (GSSG), as well as the proportion of glutathione (GSH)/GSSG were measured in the brain tissues.

Results

The results showed that Rhein was absorbed in the brain tissues of CCI rats. Rhubarb and rhein elevated the SOD, CAT activities, GSH level, and GSH/GSSG ratio, and diminished the MDA and GSSG levels.

Conclusion

The data demonstrated that Rhubarb and Rhein had the potential to be used as a neuroprotective drug for TBI, and that Rhein induced an antioxidative effect similar to its parent medicine, Rhubarb.

Novel GLP-1R/GIPR co-agonist "twincretin" is neuroprotective in cell and rodent models of mild traumatic brain injury

Several single incretin receptor agonists that are approved for the treatment of type 2 diabetes mellitus (T2DM) have been shown to be neuroprotective in cell and animal models of neurodegeneration. Recently, a synthetic dual incretin receptor agonist, nicknamed "twincretin," was shown to improve upon the metabolic benefits of single receptor agonists in mouse and monkey models of T2DM. In the current study, the neuroprotective effects of twincretin are probed in cell and mouse models of mild traumatic brain injury (mTBI), a prevalent cause of neurodegeneration in toddlers, teenagers and the elderly. Twincretin is herein shown to have activity at two different receptors, dose-dependently increase levels of intermediates in the neurotrophic CREB pathway and enhance viability of human neuroblastoma cells exposed to toxic concentrations of glutamate and hydrogen peroxide, insults mimicking the inflammatory conditions in the brain post-mTBI. Additionally, twincretin is shown to improve upon the neurotrophic effects of single incretin receptor agonists in these same cells. Finally, a clinically translatable dose of twincretin, when administered post-mTBI, is shown to fully restore the visual and spatial memory deficits induced by mTBI, as evaluated in a mouse model of weight drop close head injury. These results establish twincretin as a novel neuroprotective agent and suggest that it may improve upon the effects of the single incretin receptor agonists via dual agonism.

A Clinically Relevant Closed-Head Model of Single and Repeat Concussive Injury in the Adult Rat Using a Controlled Cortical Impact Device

Repeat concussions (RC) can result in significant long-term neurological consequences and increased risk for neurodegenerative disease compared with single concussion (SC). Mechanisms underlying this difference are poorly understood and best elucidated using an animal model. To the best of our knowledge, there is no closed-head model in the adult rat using a commercially available device. We developed a novel and clinically relevant closed-head injury (CHI) model of both SC and RC in the adult rat using a controlled cortical impact (CCI) device. Adult rats received either a single or repeat CHI (three injuries, 48 h apart), and acute deficits in sensorimotor and locomotor function (foot fault; open field), memory (novel object), and anxiety (open field; corticosterone [CORT]) were measured. Assessment of cellular pathology was also conducted. Within the first week post-CHI, rats with SC or RC showed similar deficits in motor coordination, decreased locomotion, and higher resting CORT levels. Rats with an SC had memory deficits post-injury day (PID) 3 that recovered to sham levels by PID 7; however, rats with RC continued to show memory deficits. No obvious gross pathology was observed on the cortical surface or in coronal sections. Further examination showed thinning of the cortex and corpus callosum in RC animals compared with shams and increased axonal pathology in the corpus callosum of both SC and RC animals. Our data present a model of CHI that results in clinically relevant markers of concussion and an early differentiation between SC and RC.