Evans Blue and Fluorescein Isothiocyanate-Dextran Double Labeling Reveals Precise Sequence of Vascular Leakage and Glial Responses after Exposure to Mild-Level Blast-Associated Shock Waves

Augmentation of psychiatric symptom onset vulnerability in male mice due to mild traumatic brain injury

Mild traumatic brain injury (mTBI) can induce psychiatric symptoms, including anxiety, depression, and diminished interest. These symptoms can manifest shortly after injury or exhibit delayed onset months or years later, often worsening in severity. Therefore, early intervention and effective treatment are crucial. However, mTBI lacks clear diagnostic markers, making the underlying pathophysiological mechanisms elusive. Additionally, there is a dearth of suitable animal models and a limited understanding of the biochemical changes in the brain that contribute to post-mTBI psychological symptoms. In this study, we hypothesized that mTBI can trigger brain vulnerability mechanisms, which eventually lead to symptom manifestation in response to subsequent stressors. Using a mouse model, we induced very mild blast-induced mTBI without overt trauma or behavioral changes and subsequently subjected the mice to psychological stress. We analyzed the behavioral alterations and gene expression changes in the brain, focusing on microglial and astrocytic markers involved in the immune system and immune responses. The mice exposed to both blast and defeat stress exhibited significantly lower preference scores in the social interaction test than the mice subjected to blast exposure alone, defeat stress alone, or the control condition. Gene expression analysis revealed a distinct set of genes associated with blast exposure during the development of psychiatric symptoms and genes associated with social defeat stress. The results revealed that neither blast exposure nor defeat stress alone significantly affected mouse social behavior; however, their combined influence resulted in noticeable aberrations in social interactions and/or interest. The findings of the present study provide critical insights into the complex interplay between mTBI and psychological stress. Additionally, they provide a novel mouse model for future research aimed at elucidating the pathophysiological mechanisms underlying the psychiatric symptoms associated with mTBI. Ultimately, this knowledge may enhance early intervention and therapeutic strategies for individuals with mTBI-related psychiatric disorders.

The Neurovascular Unit as a Locus of Injury in Low-Level Blast-Induced Neurotrauma

Blast-induced neurotrauma has received much attention over the past decade. Vascular injury occurs early following blast exposure. Indeed, in animal models that approximate human mild traumatic brain injury or subclinical blast exposure, vascular pathology can occur in the presence of a normal neuropil, suggesting that the vasculature is particularly vulnerable. Brain endothelial cells and their supporting glial and neuronal elements constitute a neurovascular unit (NVU). Blast injury disrupts gliovascular and neurovascular connections in addition to damaging endothelial cells, basal laminae, smooth muscle cells, and pericytes as well as causing extracellular matrix reorganization. Perivascular pathology becomes associated with phospho-tau accumulation and chronic perivascular inflammation. Disruption of the NVU should impact activity-dependent regulation of cerebral blood flow, blood-brain barrier permeability, and glymphatic flow. Here, we review work in an animal model of low-level blast injury that we have been studying for over a decade. We review work supporting the NVU as a locus of low-level blast injury. We integrate our findings with those from other laboratories studying similar models that collectively suggest that damage to astrocytes and other perivascular cells as well as chronic immune activation play a role in the persistent neurobehavioral changes that follow blast injury.