A combined therapeutic regimen of citalopram and environmental enrichment ameliorates attentional set-shifting performance after brain trauma

Pre-operative environmental enrichment does not yield a prophylactic effect against traumatic brain injury-induced neurobehavioral deficits

The robustness of environmental enrichment (EE) in ameliorating neurobehavioral and cognitive deficits after experimental traumatic brain injury (TBI) is unequivocal. What is equivocal is whether EE can function as a prophylactic to afford resiliency and neuroprotection against TBI. We hypothesized that pre-operative EE would yield a protective effect against TBI-induced motor, cognitive, and coping deficits, and that further improvements would be conferred when EE is provided before and after TBI. To test the hypotheses, adult male rats received either 4 weeks of EE or standard (STD) housing prior to undergoing a controlled cortical impact of moderate severity (2.8 mm deformation at 4 m/s) or sham injury while under anesthesia. After injury, the rats were randomly assigned to post-operative EE or STD housing. Motor ability, spatial learning, and memory retention were assessed by beam-walk and water maze tests, respectively. Active and passive behavioral coping strategies were evaluated with the shock probe defensive burying (SPDB) test. c-Fos and cortical lesion volume were also quantified. The post-TBI enrichment groups (EE + TBI + EE and STD + TBI + EE) did not differ (p > 0.05) and performed better than the post-TBI STD-housed groups (EE + TBI + STD and STD + TBI + STD) on motor and cognition (p < 0.05). The post-TBI STD groups did not differ, regardless of whether in EE or STD living conditions before injury (p > 0.05). Moreover, both post-TBI enrichment groups performed better in the SPDB test relative to the STD + TBI + STD group (p < 0.05). c-Fos + cells were upregulated in the ipsilateral CA1 in both pre-injury EE groups relative to the pre-injury STD groups (p < 0.05). No statistical differences were observed in cortical lesion volume among the groups. Overall, these data do not support the hypothesis as no neuroprotective effect was observed with 4 weeks of pre-operative EE and no additional benefit was achieved in the TBI group receiving both pre-and-post EE relative to the TBI group receiving only post-EE. However, the data do reinforce the consistency of post-TBI EE in producing robust neurobehavioral benefits, which further supports this paradigm as a relevant preclinical model of neurorehabilitation.

Effects of chronic stress on cognitive function - From neurobiology to intervention

Exposure to chronic stress contributes considerably to the development of cognitive impairments in psychiatric disorders such as depression, generalized anxiety disorder (GAD), obsessive-compulsive disorder (OCD), post-traumatic stress disorder (PTSD), and addictive behavior. Unfortunately, unlike mood-related symptoms, cognitive impairments are not effectively treated by available therapies, a situation in part resulting from a still incomplete knowledge of the neurobiological substrates that underly cognitive domains and the difficulty in generating interventions that are both efficacious and safe. In this review, we will present an overview of the cognitive domains affected by stress with a specific focus on cognitive flexibility, behavioral inhibition, and working memory. We will then consider the effects of stress on neuronal correlates of cognitive function and the factors which may modulate the interaction of stress and cognition. Finally, we will discuss intervention strategies for treatment of stress-related disorders and gaps in knowledge with emerging new treatments under development. Understanding how cognitive impairment occurs during exposure to chronic stress is crucial to make progress towards the development of new and effective therapeutic approaches.

Cognition and Behavior in the Aging Brain Following TBI: Surveying the Preclinical Evidence

Elderly individuals (65 years and older) represent the fastest-growing demographic of new clinical traumatic brain injury (TBI) cases, yet there is a paucity of preclinical research in aged animals. The limited preclinical work available aligns with the clinical literature in that there appear to be significant differences in pathophysiology, recovery potential, and response to medications between animals at different points across the age spectrum. The aim of this review is to discuss the limited studies and highlight critical age-related differences in affective, cognitive, and neurobehavioral deficits, to discuss factors that influence functional outcomes, and to identify targets for future research. The consensus is that aged rodents face challenges related to dysregulated inflammation, reduced neuroplasticity, and age-related cellular changes, which hinder their recovery after TBI. The most successful intervention studies in animal models to date, of the limited array available, have explored interventions targeting inflammatory downregulation. Current standards of neuropsychopharmacology for post-TBI neurocognitive recovery have not been investigated in a significant capacity. In addition, currently available animal models do not sufficiently account for important age-related comorbidities, dual insults, or differences in TBI mechanism of injury in elderly individuals. TBI in the aged population is more likely to lead to additional neurodegenerative diseases that further complicate recovery. The findings underscore the need for tailored therapeutic interventions to improve outcomes in both adult and elderly populations.

Sustained attention performance deficits in the three-choice serial reaction time task in male and female rats after experimental brain trauma

Impaired attention is central to the cognitive deficits associated with long-term sequelae for many traumatic brain injury (TBI) survivors. Assessing complex sustained attention post-TBI is clinically-relevant and may provide reliable avenues towards developing therapeutic and rehabilitation targets in both males and females. We hypothesized that rats subjected to a moderate TBI will exhibit attentional deficits seen as reduced accuracy and increased distractibility in an operant 3-choice serial reaction time task (3-CSRT), designed as an analogue of the clinical continuous performance test. Upon reaching baseline of 70% accuracy at the 300 ms cue, adult male and female Sprague-Dawley rats were subjected to a controlled cortical impact (2.8 mm deformation at 4 m/s) or sham injury over the right parietal cortex. After two weeks of recovery, they were retested on the 3-CSRT for ten days. Dependent measures include percent accuracy (overall and for each of the three cue ports), percent omissions, as well as latency to instrumental poke and retrieve reward. Results demonstrate that both males and females displayed reduced percent accuracy and increased omissions when re-tested post-TBI on 3-CSRT compared to Sham rats and to their own pre-insult baseline (p's < 0.05). Performance accuracy was impaired consistently throughout the ten days of post-surgery re-testing, suggesting pronounced and long-lasting dysfunction in sustained attention processes. Deficits were specifically more pronounced when the cue was pseudorandomly presented in the left-side cue port (p < 0.05), mirroring clinical hemispatial neglect. These data demonstrate significant and persistent complex attention impairments in both sexes after TBI, rendering identifying efficient therapies for cognitive recovery as pivotal.

Enriching adult male rats prior to traumatic brain injury does not attenuate neurobehavioral or histological deficits

Environmental enrichment (EE) confers significant increases in neurobehavioral and cognitive recovery and decreases histological damage in various models of traumatic brain injury (TBI). However, despite EE's pervasiveness, little is known regarding its prophylactic potential. Thus, the goal of the current study was to determine whether enriching rats prior to a controlled cortical impact exerts protection as evidenced by attenuated injury-induced neurobehavioral and histological deficits relative to rats without prior EE. The hypothesis was that enrichment prior to TBI would be protective. After two weeks of EE or standard (STD) housing, anesthetized adult male rats received either a controlled cortical impact (2.8 mm deformation at 4 m/s) or sham injury and then were placed in EE or STD conditions. Motor (beam-walk) and cognitive (spatial learning) performance were assessed on post-operative days 1-5 and 14-18, respectively. Cortical lesion volume was quantified on day 21. The group that was housed in STD conditions before TBI and received post-injury EE performed significantly better in motor, cognitive, and histological outcomes vs. both groups in STD conditions regardless of whether having received pre-injury EE or not (p < 0.05). That no differences in any endpoint were revealed between the two STD-housed groups after TBI suggests that enriching rats prior to TBI does not attenuate neurobehavioral or histological deficits and therefore does not support the hypothesis.

Multi-Mechanistic Approaches to the Treatment of Traumatic Brain Injury: A Review

Traumatic brain injury (TBI) is a leading cause of death and disability worldwide. Despite extensive research efforts, the majority of trialed monotherapies to date have failed to demonstrate significant benefit. It has been suggested that this is due to the complex pathophysiology of TBI, which may possibly be addressed by a combination of therapeutic interventions. In this article, we have reviewed combinations of different pharmacologic treatments, combinations of non-pharmacologic interventions, and combined pharmacologic and non-pharmacologic interventions for TBI. Both preclinical and clinical studies have been included. While promising results have been found in animal models, clinical trials of combination therapies have not yet shown clear benefit. This may possibly be due to their application without consideration of the evolving pathophysiology of TBI. Improvements of this paradigm may come from novel interventions guided by multimodal neuromonitoring and multimodal imaging techniques, as well as the application of multi-targeted non-pharmacologic and endogenous therapies. There also needs to be a greater representation of female subjects in preclinical and clinical studies.

Milnacipran Ameliorates Executive Function Impairments following Frontal Lobe Traumatic Brain Injury in Male Rats: A Multimodal Behavioral Assessment

Traumatic brain injuries (TBIs) affect more than 10 million patients annually worldwide, causing long-term cognitive and psychosocial impairments. Frontal lobe TBIs commonly impair executive function, but laboratory models typically focus primarily on spatial learning and declarative memory. We implemented a multi-modal approach for clinically relevant cognitive-behavioral assessments of frontal lobe function in rats with TBI and assessed treatment benefits of the serotonin-norepinephrine reuptake inhibitor, milnacipran (MLN). Two attentional set-shifting tasks (AST) evaluated cognitive flexibility via the rats' ability to locate food-based rewards by learning, unlearning, and relearning sequential rule sets with shifting salient cues. Adult male rats reached stable pre-injury operant AST (oAST) performance in 3-4 weeks, then were isoflurane-anesthetized, subjected to a unilateral frontal lobe controlled cortical impact (2.4 mm depth, 4 m/sec velocity) or Sham injury, and randomized to treatment conditions. Milnacipran (30 mg/kg/day) or vehicle (VEH; 10% ethanol in saline) was administered intraperitoneally via implanted osmotic minipumps (continuous infusions post-surgery, 60 μL/h). Rats had a 10-day recovery post-TBI/Sham before performing light/location-based oAST for 10 days and, subsequently, odor/media-based digging AST (dAST) on the last test day (26-27 days post-injury) before sacrifice. Both AST tests revealed significant deficits in TBI+VEH rats, seen as elevated total trials and errors (p < 0.05), which generally normalized in MLN-treated rats (p < 0.05). This first simultaneous dual AST assessment demonstrates oAST and dAST are sufficiently sensitive and robust to detect subtle attentional and cognitive flexibility executive impairments after frontal lobe TBI in rats. Chronic MLN administration shows promise for attenuation of post-TBI executive function deficits, thus meriting further investigation.