Mechanical impacts to the skulls of rats produce specific deficits in maze performance and weight loss: evidence for apoptosis of cortical neurons and implications for clinical neuropsychology

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.

Role of subconcussion in repetitive mild traumatic brain injury

Research now suggests that head impacts commonly occur during contact sports in which visible signs or symptoms of neurological dysfunction may not develop despite those impacts having the potential for neurological injury. Recent biophysics studies utilizing helmet accelerometers have indicated that athletes at the collegiate and high school levels sustain a surprisingly high number of head impacts ranging from several hundred to well over 1000 during the course of a season. The associated cumulative impact burdens over the course of a career are equally important. Clinical studies have also identified athletes with no readily observable symptoms but who exhibit functional impairment as measured by neuropsychological testing and functional MRI. Such findings have been corroborated by diffusion tensor imaging studies demonstrating axonal injury in asymptomatic athletes at the end of a season. Recent autopsy data have shown that there are subsets of athletes in contact sports who do not have a history of known or identified concussions but nonetheless have neurodegenerative pathology consistent with chronic traumatic encephalopathy. Finally, emerging laboratory data have demonstrated significant axonal injury, blood-brain barrier permeability, and evidence of neuroinflammation, all in the absence of behavioral changes. Such data suggest that subconcussive level impacts can lead to significant neurological alterations, especially if the blows are repetitive. The authors propose “subconcussion” as a significant emerging concept requiring thorough consideration of the potential role it plays in accruing sufficient anatomical and/or physiological damage in athletes and military personnel, such that the effects of these injuries are clinically expressed either contemporaneously or later in life.

Weak, physiologically patterned magnetic fields do not affect maze performance in normal rats, but disrupt seized rats normalized with ketamine: possible support for a neuromatrix concept?

The concept of a neuromatrix as a determinant of behavior proposes that complex neuroelectromagnetic patterns supported by specific spatial configurations of neurons underlie the generation of behaviors. When the pattern of neuronal connectivity is changed, as occurs during limbic epilepsy, neuroelectromagnetic patterns change in parallel to sustain behavioral output. Thus, a testable prediction of the neuromatrix concept is that the "normal" behaviors of animals with markedly reorganized neuroelectromagnetic patterns are vulnerable to specific stimuli that are ineffective when applied to a normal population. Because rats treated with ketamine after being induced to seize with pilocarpine exhibit behaviors indistinguishable from those of control populations despite marked changes in brain structure, they represent an ideal population in which to examine this hypothesis. Ketamine-treated pilocarpine-seized rats and normal rats were exposed continuously either to a complex sequence magnetic field or to control conditions during the acquisition of a radial arm maze task for 8 consecutive days. After 14 days of subsequent exposure to a frequency-modulated field (7-500 nT), during which time there was no training, the rats that had been induced to seize and had been exposed continuously to this magnetic configuration exhibited conspicuously slower response durations per arm than rats that had been induced to seize and exposed to control conditions or normal rats that had been exposed to either magnetic fields or control conditions. Thus, the behaviors of rats who have sustained multiple, discrete injuries throughout the brain may be seriously disrupted by the appropriate pattern of exogenous weak magnetic fields. Our results represent the first empirical support for the concept of the neuromatrix.

Impaired spatial learning in a novel rat model of mild cerebral concussion injury

The aim of the present study was to develop a model of mild traumatic brain injury in the rat that mimics human concussive brain injury suitable to study pathophysiology and potential treatments. 34 male Wistar rats received a closed head trauma (TBI) and 30 animals served as controls (CON). Immediately following trauma, animals lost their muscle tone and righting reflex response, recovering from the latter within 11.4 +/- 8.2 min. Corneal reflex and whisker responses returned within 4.5 +/- 3.0 min and 6.1 +/- 2.9 min, respectively. The impact resulted in a short transient decrease of pO2 (P < 0.001), increase in mean arterial blood pressure (P = 0.026), and a reduction of heart rate (P < 0.01). Serial MRI did not show any abnormalities across the entire cerebrum on diffusion, T1, T2, and T2*-weighted images at all investigated time points. TBI animals needed significantly longer to locate the hidden platform in a Morris water maze and spent less time in the training quadrant than controls. TBI led to a significant neuronal loss in frontal cortex (P < 0.001), as well as hippocampal CA3 (P = 0.017) and CA1 (P = 0.002) at 9 days after the trauma; however, cytoskeletal architecture was preserved as indicated by normal betaAPP- and MAP-2 staining. We present a unique, noninvasive rat model of mild closed head trauma with characteristics of human concussion injury, including brief loss of consciousness, cognitive impairment, and minor brain injury.