Optimization and validation of a modified radial-arm water maze protocol using a murine model of mild closed head traumatic brain injury

Glyoxalase 1 overexpression improves neurovascular coupling and limits development of mild cognitive impairment in a mouse model of type 1 diabetes

Diabetes is associated with cognitive impairment, but the underlying mechanism remains unclear. Methylglyoxal (MGO), a precursor to advanced glycation endproducts (AGEs), is elevated in diabetes and linked to microvascular dysfunction. In this study, overexpression of the MGO-detoxifying enzyme glyoxalase 1 (Glo1) was used in a mouse model of diabetes to explore whether MGO accumulation in diabetes causes cognitive impairment. Diabetes was induced with streptozotocin. Fasting blood glucose, cognitive function, cerebral blood flow, neurovascular coupling (NVC), Glo1 activity, MGO and AGEs were assessed. In diabetes, MGO-derived hydroimidazolone-1 increased in the cortex, and was decreased in Glo1-overexpressing mice compared to controls. Visuospatial memory was decreased in diabetes, but not in Glo1/diabetes. NVC response time was slightly increased in diabetes, and normalised in the Glo1-overexpressing group. No impact of diabetes or Glo1 overexpression on blood-brain barrier integrity or vascular density was observed. Diabetes induced a mild visuospatial memory impairment and slightly reduced NVC response speed and these effects were mitigated by Glo1. This study shows a link between MGO-related AGE accumulation and cerebrovascular/cognitive functions in diabetes. Modulation of the MGO-Glo1 pathway may be a novel intervention strategy in patients with diabetes who have cerebrovascular complications. KEY POINTS: Diabetes is associated with an increased risk of stroke, cognitive decline, depression and Alzheimer's disease, but the underlying mechanism remains unclear. Methylglyoxal (MGO), a highly reactive by-product of glycolysis, plays an important role in the development of diabetes-associated microvascular dysfunction in the periphery and is detoxified by the enzyme glyoxalase 1. Diabetes reduced visuospatial memory in mice and slowed the neurovascular coupling response speed, which was improved by overexpression of glyoxalase 1. MGO formation and MGO-derived advanced glycation endproduct (AGE) accumulation in the brain of diabetic mice are associated with a slight reduction in neurovascular coupling and mild cognitive impairment. The endogenous formation of MGO, and the accumulation of MGO-derived AGEs, might be a potential target in reducing the risk of vascular cognitive impairment in people with diabetes.

High-fat diet consumption negatively influences closed-head traumatic brain injury in a pediatric rodent model

Traumatic brain injury (TBI) is one of the most common causes of emergency room visits in children, and it is a leading cause of death in juveniles in the United States. Similarly, a high proportion of this population consumes diets that are high in saturated fats, and millions of children are overweight or obese. The goal of the present study was to assess the relationship between diet and TBI on cognitive and cerebrovascular outcomes in juvenile rats. In the current study, groups of juvenile male Long Evans rats were subjected to either mild TBI via the Closed-Head Injury Model of Engineered Rotational Acceleration (CHIMERA) or underwent sham procedures. The animals were provided with either a combination of high-fat diet and a mixture of high-fructose corn syrup (HFD/HFCS) or a standard chow diet (CH) for 9 days prior to injury. Prior to injury, the animals were trained on the Morris water maze for three consecutive days, and they underwent a post-injury trial on the day of the injury. Immediately after TBI, the animals' righting reflexes were tested. Four days post-injury, the animals were euthanized, and brain samples and blood plasma were collected for qRT-PCR, immunohistochemistry, and triglyceride assays. Additional subsets of animals were used to investigate cerebrovascular perfusion using Laser Speckle and perform immunohistochemistry for endothelial cell marker RECA. Following TBI, the righting reflex was significantly increased in TBI rats, irrespective of diet. The TBI worsened the rats' performance in the post-injury trial of the water maze at 3 h, p(injury) < 0.05, but not at 4 days post-injury. Reduced cerebrovascular blood flow using Laser Speckle was demonstrated in the cerebellum, p(injury) < 0.05, but not foci of the cerebral cortices or superior sagittal sinus. Immunoreactive staining for RECA in the cortex and corpus callosum was significantly reduced in HFD/HFCS TBI rats, p < 0.05. qRT-PCR showed significant increases in APOE, CREB1, FCGR2B, IL1B, and IL6, particularly in the hippocampus. The results from this study offer robust evidence that HFD/HFCS negatively influences TBI outcomes with respect to cognition and cerebrovascular perfusion of relevant brain regions in the juvenile rat.

Old Age Exacerbates White Matter Neuroinflammation and Cognitive Deficits Following Closed-Head Injury, Particularly in Female Mice

The increasing incidence of traumatic brain injury (TBI) among older adults, particularly mild injuries from falls, underscores the need to investigate age-related outcomes and potential sex differences in response to TBI. Although previous research has defined an aging-TBI signature (heightened glial responses and cognitive impairment) in open-skull moderate-to-severe TBI models, it is unknown whether this signature is also present in mild closed-head injuries (CHIs). This study explores the influences of age and sex on recovery in a mouse CHI model induced by an electromagnetic impactor device in 4-month-old and 18-month-old C57BL/6 mice. We assessed the righting reflex, body weight, behavior (radial arm water maze and active avoidance), and inflammation (GFAP, IBA1, CD45) in the neocortex, corpus callosum, and hippocampus. We observed that aged female mice exhibited more severe TBI-induced cognitive deficits. In addition, a more pronounced reactive neuroinflammatory response with age was noted within white matter regions. Conversely, gray matter regions in aged animals either showed no enhanced pathological changes in response to injury or the aged mice displayed hyporesponsive glia and signs of dystrophic glial degeneration that were not evident in their younger counterparts following CHI. These findings suggest that aging influences CHI outcomes, partially reflecting the aging-TBI signature seen in more severe injuries in white matter, while a distinct aging and mild-TBI signature was identified in gray matter. The heightened vulnerability of females to the combined effects of age and mild CHI establishes a foundation for further investigation into the mechanisms underlying the sexually dimorphic response in aging females.

A Gad2 specific Slc6a8 deletion recapitulates the contextual and cued freezing deficits seen in Slc6a8-/y mice

The creatine (Cr)-phosphocreatine shuttle is essential for ATP homeostasis. In humans, the absence of brain Cr causes significant intellectual disability, epilepsy, and language delay. Mutations of the creatine transporter (SLC6A8) are the most common cause of Cr deficiency. In rodents, Slc6a8 deletion causes deficits in spatial learning, novel object recognition (NOR), as well as in contextual and cued freezing. The mechanisms that underlie these cognitive deficits are not known. Due to the heterogeneous nature of the brain, it is important to determine which systems are affected by a loss of Cr. In this study, we generated mice lacking Slc6a8 in GABAergic neurons by crossing Slc6a8FL mice with Gad2-Cre mice. These Gad2-specific Slc6a8 knockout (cKO) mice, along with the ubiquitous Slc6a8 KO (Slc6a8-/y), Gad2-Cre+, and wild-type (WT) mice were tested in the Morris water maze, NOR, conditioned freezing, and the radial water maze. Similar to the Slc6a8-/y mice, cKO mice had reduced contextual and cued freezing compared with WT mice. The cKO mice had a mild spatial learning deficit during the reversal phase of the MWM, however they were not as pronounced as in Slc6a8-/y mice. In NOR, the Gad2-Cre mice spent less time with the novel object, similar to the reduced novel time in the cKO mice. There were no changes in radial water maze performance. Slc6a8 deletion in GABAergic neurons is sufficient to recapitulate the conditioned freezing deficits seen in Slc6a8-/y mice.

Multilevel meta-analysis and dose-response analysis for bisphenol A (BPA) exposure on metabolic and neurobehavioral effects

Evidence suggests that oral exposure to bisphenol A (BPA) may result in adverse metabolic and neurobehavioral effects. The aim of the present meta-analysis is to examine this association based on systematically selected laboratory rodent studies published from 2012 to 2021 and sourced from Scopus, Web of Science, EmBase, and PubMed. Articles satisfying eligibility and inclusion criteria were included for the calculation of the summary standardised mean difference (SMD). Subgroup analysis and subsequent dose-response analysis were conducted if applicable. In total, 32 studies were analysed for 6 metabolic endpoints (cholesterol, triglycerides, insulin, glucose, leptin, and adiponectin) and 6 neurobehavioral endpoints (locomotor activity, exploratory, anxiety, depression, spatial learning and memory, non-spatial learning and memory). Summary SMDs implied that no significant effects were observed in endpoints considered. The dose was not determined as a significant moderator with regards to medium or high heterogeneity; however, there was significant impairment of spatial learning and memory at health-based guidance value ('HBGV') (0.05-9 mg (kg bw)-1 day-1) and 'High' (>9 mg (kg bw)-1 day-1) dose group. As a result, an indicative toxicological reference dose value of 0.034 mg (kg bw)-1 day-1 was proposed due to large variability. Potential harm to spatial learning and memory from BPA exposure requires further investigation. This study has provided some additional information on potential adverse metabolic and neurobehavioral effects of BPA from the perspective of meta-analysis which can inform the public, regulatory authorities, and policymakers.

Importance of Control Groups for Evaluating Long-Term Behavioral and Cognitive Outcomes of Controlled Cortical Impact in Immature Rats

Therapies are limited for pediatric traumatic brain injury (TBI), especially for the very young who can experience long-term consequences to learning, memory, and social behavior. Animal models of pediatric TBI have yielded mechanistic insights, but demonstration of clinically relevant long-term behavioral and/or cognitive deficits has been challenging. We characterized short- and long-term outcomes in a controlled cortical impact (CCI) model of pediatric TBI using a panel of tests between 2 weeks and ∼4 months after injury. Male rats with CCI at postnatal Day (PND) 10 were compared with three control groups: Naïve, Anesthesia, and Craniotomy. Motor testing (PND 25-33), novel object recognition (NOR; PND 40-50), and multiple tasks in water maze (WM; PND 65-100) were followed by social interaction tests (PND 120-140). Anesthesia rats performed the same as Naïve rats in all tasks. TBI rats, when compared with Naïve controls, had functional impairments across most tests studied. The most sensitive cognitive processes affected by TBI included those that required fast one-trial learning (NOR, WM), flexibility of acquired memory traces (reversals in WM), response strategies (WM), or recognition memory in the setting of reciprocal social interactions. Both TBI and Craniotomy groups demonstrated increased rates of decision making across several WM tasks, suggesting disinhibition of motor responses. When the TBI group was compared with the Craniotomy group, however, deficits were detected in a limited number of outcomes. The latter included learning speed (WM), cognitive flexibility (WM), and social recognition memory. Notably, effects of craniotomy, when compared with Naïve controls, spanned across multiple tasks, and in some tasks, could reach the effect sizes observed in TBI. These results highlight the importance of appropriate control groups in pediatric CCI models. In addition, the study demonstrates the high sensitivity of comprehensive cognitive testing to detect long-term effects of early-age craniotomy and TBI and provides a template for future testing of experimental therapies.

Electromagnetic Controlled Closed-Head Model of Mild Traumatic Brain Injury in Mice

Highly reproducible animal models of traumatic brain injury (TBI), with well-defined pathologies, are needed for testing therapeutic interventions and understanding the mechanisms of how a TBI alters brain function. The availability of multiple animal models of TBI is necessary to model the different aspects and severities of TBI seen in people. This manuscript describes the use of a midline closed head injury (CHI) to develop a mouse model of mild TBI. The model is considered mild because it does not produce structural brain lesions based on neuroimaging or gross neuronal loss. However, a single impact creates enough pathology that cognitive impairment is measurable at least 1 month after injury. A step-by-step protocol to induce a CHI in mice using a stereotaxically guided electromagnetic impactor is defined in the paper. The benefits of the mild midline CHI model include the reproducibility of the injury-induced changes with low mortality. The model has been temporally characterized up to 1 year after the injury for neuroimaging, neurochemical, neuropathological, and behavioral changes. The model is complementary to open skull models of controlled cortical impact using the same impactor device. Thus, labs can model both mild diffuse TBI and focal moderate-to-severe TBI with the same impactor.

Roadbumps at the Crossroads of Integrating Behavioral and In Vitro Approaches for Neurotoxicity Assessment

With the appreciation that behavior represents the integration and complexity of the nervous system, neurobehavioral phenotyping and assessment has seen a renaissance over the last couple of decades, resulting in a robust database on rodent performance within various testing paradigms, possible associations with human disorders, and therapeutic interventions. The interchange of data across behavior and other test modalities and multiple model systems has advanced our understanding of fundamental biology and mechanisms associated with normal functions and alterations in the nervous system. While there is a demonstrated value and power of neurobehavioral assessments for examining alterations due to genetic manipulations, maternal factors, early development environment, the applied use of behavior to assess environmental neurotoxicity continues to come under question as to whether behavior represents a sensitive endpoint for assessment. Why is rodent behavior a sensitive tool to the neuroscientist and yet, not when used in pre-clinical or chemical neurotoxicity studies? Applying new paradigms and evidence on the biological basis of behavior to neurobehavioral testing requires expertise and refinement of how such experiments are conducted to minimize variability and maximize information. This review presents relevant issues of methods used to conduct such test, sources of variability, experimental design, data analysis, interpretation, and reporting. It presents beneficial and critical limitations as they translate to the in vivo environment and considers the need to integrate across disciplines for the best value. It proposes that a refinement of behavioral assessments and understanding of subtle pronounced differences will facilitate the integration of data obtained across multiple approaches and to address issues of translation.

A review of behavioral methods for the evaluation of cognitive performance in animal models: Current techniques and links to human cognition

INTRODUCTION

Memory is defined as the ability to store, maintain and retrieve information. Learning is the acquisition of information that changes behavior and memory. Stress, dementia, head trauma, amnesia, Alzheimer's, Huntington, Parkinson's, Wernicke-Korsakoff syndrome (WKS) may be mentioned among the diseases in which memory and learning are affected. The task of understanding deficits in memory and learning in humans is daunting due to the complexity of neural and cognitive mechanisms in the nervous system. This job is made more difficult for clinicians and researchers by the fact that many techniques used to research memory are not ethically acceptable or technically feasible for use in humans. Thus, animal models have been necessary alternative for studying normal and disordered learning and memory. This review attempts to bridge these domains to allow biomedical researchers to have a firm grasp of "memory" and "learning" as constructs in humans whereby they may then select the proper animal cognitive test.

RESULTS AND CONCLUSION

Various tests (open field habituation test, Y-maze test, passive avoidance test, step-down inhibitory avoidance test, active avoidance test, 8-arms radial maze test, Morris water maze test, radial arm water maze, novel object recognition test and gait function test) have been designed to evaluate different kinds of memory. Each of these tests has their strengths and limits. Abnormal results obtained using these tasks in non-human animals indicate malfunctions in memory which may be due to several physiological and psychological diseases of nervous system. Further studies by using the discussed tests can be very beneficial for achieving a therapeutic answer to these diseases.

Morris water maze: a versatile and pertinent tool for assessing spatial learning and memory

Since its development about 40 years ago (1981–2021), Morris water maze has turned into a very popular tool for assessing spatial learning and memory. Its many advantages have ensured its pertinence to date. These include its effectiveness in evaluating hippocampal-dependent learning and memory, exemption from motivational differences across diverse experimental manipulations, reliability in various cross-species studies, and adaptability to many experimental conditions with various test protocols. Nonetheless, throughout its establishment, several experimental and analysis loopholes have galvanized researchers to assess ways in which it could be improved and adapted to fill this gap. Therefore, in this review, we briefly summarize these developments since the early years of its establishment through to the most recent advancements in computerized analysis, offering more comprehensive analysis paradigms. In addition, we discuss the adaptability of the Morris water maze across different test versions and analysis paradigms, providing suggestions with regard to the best paradigms for particular experimental conditions. Hence, the proper selection of the experimental protocols, analysis paradigms, and consideration of the assay’s limitations should be carefully considered. Given that appropriate measures are taken, with various adaptations made, the Morris water maze will likely remain a relevant tool to assess the mechanisms of spatial learning and memory.

The interaction of the circadian and immune system: Desynchrony as a pathological outcome to traumatic brain injury

Traumatic brain injury (TBI) is a complex and costly worldwide phenomenon that can lead to many negative health outcomes including disrupted circadian function. There is a bidirectional relationship between the immune system and the circadian system, with mammalian coordination of physiological activities being controlled by the primary circadian pacemaker in the suprachiasmatic nucleus (SCN) of the hypothalamus. The SCN receives light information from the external environment and in turn synchronizes rhythms throughout the brain and body. The SCN is capable of endogenous self-sustained oscillatory activity through an intricate clock gene negative feedback loop. Following TBI, the response of the immune system can become prolonged and pathophysiological. This detrimental response not only occurs in the brain, but also within the periphery, where a leaky blood brain barrier can permit further infiltration of immune and inflammatory factors. The prolonged and pathological immune response that follows TBI can have deleterious effects on clock gene cycling and circadian function not only in the SCN, but also in other rhythmic areas throughout the body. This could bring about a state of circadian desynchrony where different rhythmic structures are no longer working together to promote optimal physiological function. There are many parallels between the negative symptomology associated with circadian desynchrony and TBI. This review discusses the significant contributions of an immune-disrupted circadian system on the negative symptomology following TBI. The implications of TBI symptomology as a disorder of circadian desynchrony are discussed.