Long-Term Effects of Enriched Environment on Neurofunctional Outcome and CNS Lesion Volume After Traumatic Brain Injury in Rats

Environmental Enrichment for Stroke and Traumatic Brain Injury: Mechanisms and Translational Implications

Acquired brain injuries, such as ischemic stroke, intracerebral hemorrhage (ICH), and traumatic brain injury (TBI), can cause severe neurologic damage and even death. Unfortunately, currently, there are no effective and safe treatments to reduce the high disability and mortality rates associated with these brain injuries. However, environmental enrichment (EE) is an emerging approach to treating and rehabilitating acquired brain injuries by promoting motor, sensory, and social stimulation. Multiple preclinical studies have shown that EE benefits functional recovery, including improved motor and cognitive function and psychological benefits mediated by complex protective signaling pathways. This article provides an overview of the enriched environment protocols used in animal models of ischemic stroke, ICH, and TBI, as well as relevant clinical studies, with a particular focus on ischemic stroke. Additionally, we explored studies of animals with stroke and TBI exposed to EE alone or in combination with multiple drugs and other rehabilitation modalities. Finally, we discuss the potential clinical applications of EE in future brain rehabilitation therapy and the molecular and cellular changes caused by EE in rodents with stroke or TBI. This article aims to advance preclinical and clinical research on EE rehabilitation therapy for acquired brain injury. © 2024 American Physiological Society. Compr Physiol 14:5291-5323, 2024.

Deep cerebellar stimulation enhances cognitive recovery after prefrontal traumatic brain injury in rodent

Functional outcome following traumatic brain injury (TBI) varies greatly, with approximately half of those who survive suffering long-term motor and cognitive deficits despite contemporary rehabilitation efforts. We have previously shown that deep brain stimulation (DBS) of the lateral cerebellar nucleus (LCN) enhances rehabilitation of motor deficits that result from brain injury. The objective of the present study was to evaluate the efficacy of LCN DBS on recovery from rodent TBI that uniquely models the injury location, chronicity and resultant cognitive symptoms observed in most human TBI patients. We used controlled cortical impact (CCI) to produce an injury that targeted the medial prefrontal cortex (mPFC-CCI) bilaterally, resulting in cognitive deficits. Unilateral LCN DBS electrode implantation was performed 6 weeks post-injury. Electrical stimulation started at week eight post-injury and continued for an additional 4 weeks. Cognition was evaluated using baited Y-maze, novel object recognition task and Barnes maze. Post-mortem analyses, including Western Blot and immunohistochemistry, were conducted to elucidate the cellular and molecular mechanisms of recovery. We found that mPFC-CCI produced significant cognitive deficits compared to pre-injury and naïve animals. Moreover, LCN DBS treatment significantly enhanced the long-term memory process and executive functions of applying strategy. Analyses of post-mortem tissues showed significantly greater expression of CaMKIIα, BDNF and p75NTR across perilesional cortex and higher expression of postsynaptic formations in LCN DBS-treated animals compared to untreated. Overall, these data suggest that LCN DBS is an effective treatment of cognitive deficits that result from TBI, possibly by activation of ascending, glutamatergic projections to thalamus and subsequent upregulation of thalamocortical activity that engages neuroplastic mechanisms for facilitation of functional re-organization. These results support a role for cerebellar output neuromodulation as a novel therapeutic approach to enhance rehabilitation for patients with chronic, post-TBI cognitive deficits that are unresponsive to traditional rehabilitative efforts.

The role of plasticity in the recovery of consciousness

Disorders of consciousness (DOCs), i.e., coma, vegetative state, and minimally conscious state are the consequences of a severe brain injury that disrupts the brain ability to generate consciousness. Recovery from DOCs requires functional and structural changes in the brain. The sites where these plastic changes take place vary according to the pathophysiology of the DOC. The ascending reticular activating system of the brainstem and its complex connections with the thalamus and cortex are involved in the pathophysiology of coma. Subcortical structures, such as the striatum and globus pallidus, together with thalamocortical and corticothalamic projections, the basal forebrain, and several networks among different cortical areas are probably involved in vegetative and minimally conscious states. Some mechanisms of plasticity that allegedly operate in each of these sites to promote recovery of consciousness will be discussed in this chapter. While some mechanisms of plasticity work at a local level, others produce functional changes in complex neuronal networks, for example by entraining neuronal oscillations. The specific mechanisms of brain plasticity represent potential targets for future treatments aiming to restore consciousness in patients with severe DOCs.

Pathological changes in the central nervous system following exposure to ionizing radiation

Experimental studies in animals provide relevant knowledge about pathogenesis of radiation-induced injury to the central nervous system. Radiation-induced injury can alter neuronal, glial cell population, brain vasculature and may lead to molecular, cellular and functional consequences. Regarding to its fundamental role in the formation of new memories, spatial navigation and adult neurogenesis, the majority of studies have focused on the hippocampus. Most recent findings in cranial radiotherapy revealed that hippocampal avoidance prevents radiation-induced cognitive impairment of patients with brain primary tumors and metastases. However, numerous preclinical studies have shown that this problem is more complex. Regarding the fact, that the radiation-induced cognitive impairment reflects hippocampal and non-hippocampal compartments, it is highly important to investigate molecular, cellular and functional changes in different brain regions and their integration at clinically relevant doses and schedules. Here, we provide a literature review in order support the translation of preclinical findings to clinical practice and improve the physical and mental status of patients with brain tumors.

Enriched Environments as a Potential Treatment for Developmental Disorders: A Critical Assessment

The beneficial effects of enriched environments have been established through a long history of research. Enrichment of the living conditions of captive animals in the form of larger cages, sensory stimulating objects, and opportunities for social interaction and physical exercise, has been shown to reduce emotional reactivity, ameliorate abnormal behaviors, and enhance cognitive functioning. Recently, environmental enrichment research has been extended to humans, in part due to growing interest in its potential therapeutic benefits for children with neurodevelopmental disorders (NDDs). This paper reviews the history of enriched environment research and the use of enriched environments as a developmental intervention in studies of both NDD animal models and children. We argue that while environmental enrichment may sometimes benefit children with NDDs, several methodological factors need to be more closely considered before the efficacy of this approach can be adequately evaluated, including: (i) operationally defining and standardizing enriched environment treatments across studies; (ii) use of control groups and better control over potentially confounding variables; and (iii) a comprehensive theoretical framework capable of predicting when and how environmental enrichment will alter the trajectory of NDDs.

Novel therapies for combating chronic neuropathological sequelae of TBI

Traumatic brain injury (TBI) is a risk factor for development of chronic neurodegenerative disorders later in life. This review summarizes the current knowledge and concepts regarding the connection between long-term consequences of TBI and aging-associated neurodegenerative disorders including Alzheimer's disease (AD), chronic traumatic encephalopathy (CTE), and Parkinsonism, with implications for novel therapy targets. Several aggregation-prone proteins such as the amyloid-beta (Aβ) peptides, tau proteins, and α-synuclein protein are involved in secondary pathogenic cascades initiated by a TBI and are also major building blocks of the hallmark pathological lesions in chronic human neurodegenerative diseases with dementia. Impaired metabolism and degradation pathways of aggregation-prone proteins are discussed as potentially critical links between the long-term aftermath of TBI and chronic neurodegeneration. Utility and limitations of previous and current preclinical TBI models designed to study the link between TBI and chronic neurodegeneration, and promising intervention pharmacotherapies and non-pharmacologic strategies to break this link, are also summarized. Complexity of long-term neuropathological consequences of TBI is discussed, with a goal of guiding future preclinical studies and accelerating implementation of promising therapeutics into clinical trials. This article is part of the Special Issue entitled "Novel Treatments for Traumatic Brain Injury".