Akiva Cohen, Ph.D. - US grants

DESCRIPTION (provided by applicant): In the United States, traumatic brain injury (TBI) occurs every 21 seconds, afflicts up to two million people annually, and is the primary cause of death and disability in young adults and children. The initial TBI lesion is now known to propagate long-lasting secondary heterogeneous pathologies, which underlie long term morbidities. The hippocampus, a brain structure crucial for learning and memory and also a frequent site of seizure initiation, is often damaged during TBI. It is still unknown however, how injury-induced changes in cellular metabolism, neurotransmitter function, and synaptic plasticity lead to the altered regional hippocampal excitability that contributes to post traumatic cognitive impairment and seizures. Our laboratory has elucidated novel connections between metabolic and electrophysiological alterations in the injured hippocampus. We have previously established that diminshed inhibitory efficacy compromises dentate gyrus function. Moreover, we have identified several molecular and metabolic adaptations in hippocampal function that may underlie reduced dentate gyrus filtering efficiency of afferent input and suppression of hippocampal long-term potentiation, including reduced expression of the chloride transporter KCC2, reduced NMDA receptor mediated calcium influx, and disruption of essential amino acid metabolism. Our long-range goal is to develop effective and well-tolerated strategies for ameliorating pathologies associated with TBI. The objective of this application is to understand the causes and consequences of injury-induced alterations in hippocampal excitability and metabolism. Our preliminary data led to the formulation of the following CENTRAL HYPOTHESIS: TBI-induced alteration in neuronal amino acid metabolism causes regional changes in hippocampal excitability, which together with disruptions in chloride transport and calcium mediated signaling, results in increased susceptibility to seizures and cognitive deficit. To test this hypothesis, a multi-disciplinary approach focused on elucidating basic mechanisms will examine excitatory and inhibitory function, as well as neuronal metabolism in hippocampal subregions. A thorough comprehension of these mechanisms will provide insight for directing the development of potential therapies to ameliorate cognitive dysfunction and seizures in TBI patients. PUBLIC HEALTH RELEVANCE: Traumatic brain injury (TBI) is a major public health issue, which has a significant impact upon our healthcare system. Economic analyses of the annual cost of TBI-related disabilities range from $4.5 billion in direct expenditure (medical care and services) to $20.6 billion in injury-related work loss and disability. Our long-range goal is to develop effective and well-tolerated clinical management strategies for reducing or ameliorating cognitive dysfunction and seizures in TBI patients.

DESCRIPTION (provided by applicant): Traumatic brain injury (TBI) is the primary cause of death and disability in young adults and children. It occurs every 21 seconds and afflicts up to two million people annually in the United States. TBI is a heterogeneous insult that precipitates a cascade of ripples that propagate severe long-lasting pathologies. The limbic hippocampus, a brain structure crucial for learning and memory is often damaged in TBI. It is still unknown how regional changes in cellular metabolism and neurotransmitter function contribute to cognitive impairment associated with TBI. However, our preliminary data suggest that post-traumatic regional shifts in hippocampal excitability are due in part to a change in metabolic priorities. Our key observation is that specific amino acids normally employed for neurotransmitter synthesis are potentially diverted to protein synthesis and catabolism for energy thus disturbing the necessary balance between excitation and inhibition. Significantly, dietary administration of branched chain amino acids (BCAAs) after injury results in comprehensive cognitive restoration. We have thus formulated the following CENTRAL HYPOTHESIS: Dietary intervention with branched chain amino acids restores posttraumatic cognitive deficit by ameliorating regional shifts in hippocampal excitability. To test this hypothesis, cellular metabolism, as well as excitatory and inhibitory function in hippocampal subregions will be studied from the molecular to the systemic level in a mouse model of TBI. Better understanding the temporal window and mechanism(s) contributing to our successful dietary intervention will enable the specific formulation of the most efficacious future intervention to alleviate this devastating (i.e. cognitive impairment) pathology. PUBLIC HEALTH RELEVANCE: Traumatic brain injury (TBI) is a major public health issue, which has a significant impact upon our healthcare system. Economic analyses of the annual cost of TBI-related disabilities range from $4.5 billion in direct expenditure (medical care and services) to $20.6 billion in injury-related work loss and disability. Our long-range goal is to continue to formulate an efficacious, safe and well- tolerated dietary intervention that can be rapidly translated from the bench to the clinic to ameliorate cognitive dysfunction in TBI patients.

? DESCRIPTION (provided by applicant): Traumatic brain injury (TBI) is the primary cause of death and disability in children and young adults. TBI afflicts approximately two million people annually in the United States and no effective therapy exists. The neurological impairments associated with TBI include learning and memory deficits and increased risk of seizures. The hippocampus is critically involved in both of these phenomena and highly susceptible to damage by traumatic brain injury. Normal hippocampus-dependent cognition requires normal hippocampal output. TBI both diminishes hippocampal output and impairs hippocampus-dependent cognition. In area CA1 of the hippocampus the reduction in output after injury is due primarily to an increase in inhibition. In particular, inhibition from a subset of inhibitory neuros, the cholecystokinin (CCK) positive interneurons, was recently shown to increase after injury. CCK basket cell interneurons provide perisomatic inhibition and are instrumental in regulating action potential firing in CA1 pyramidal neurons, the output cells of the hippocampus. Stimulus-evoked action potentials in pyramidal neurons are significantly reduced after injury, and suppressing inhibition from CCK interneurons with the cannabinoid WIN55,212-2 was recently shown to restore normal stimulus-evoked action potentials in CA1 pyramidal neurons. The current proposal is designed to test the following CENTRAL HYPOTHESIS: Traumatic brain injury causes augmented inhibition from CCK interneurons in hippocampal area CA1. This increased inhibition diminishes hippocampal output and contributes to cognitive impairment. Selectively suppressing CCK interneurons in CA1 will restore normal hippocampal output and mitigate injury- induced cognitive impairment. We will test this hypothesis by measuring hippocampal output both in vitro and in vivo before and after activating the chemogenetic neuronal silencer hM4Di in CCK interneurons.. The development of effective therapeutic strategies for TBI will require a clear understanding of which cell types are affected, and a way to correct their underlying dysfunction. The current proposal is designed to meet these objectives, and will lay the groundwork for translational methods to target and repair TBI damaged neurons.

DESCRIPTION (provided by applicant): Traumatic brain injury (TBI) is the primary cause of death and disability in children and young adults. TBI occurs every 21 sec and afflicts approximately two million people annually in the United States. TBI is a heterogeneous insult that precipitates molecular and physiological cascades that culminate in severe long-lasting neuropathologies. The hippocampus and the medial prefrontal cortex (mPFC), brain structures crucial for higher cognitive function, are often damaged in TBI. Optimal brain function requires the delicate balance between excitatory and inhibitory neurotransmission (E/I balance) in these brain regions. Furthermore, E/I balance is essential for the induction and maintenance of neural oscillations, which underlie cognitive and executive function. In TBI, E/I balance is disrupted and restoring this network balance is critical to recovering normal cognitive function. Our preliminary data demonstrate that injury- induced E/I imbalance in area CA1 is predominately mediated by alterations in inhibitory synaptic transmission and that brain injury diminishes mPFC network excitability. Furthermore, distinct components of inhibitory neuronal circuitry contribute to E/I imbalances following TBI and also underlie the pharmacologic re-establishment of E/I balance which brings about comprehensive cognitive restoration in brain injured animals. Based on these results, we hypothesize that inhibitory circuits-crucial for the induction and maintenance of hippocampal and cortical theta and gamma rhythms-are selectively altered by TBI, thus causing cognitive and working memory impairments. Moreover, branched chain amino acids (BCAAs), administered in vivo following TBI, rescue normal cognitive functions by restoring hippocampal and cortical E/I balance and normal oscillations. To test this hypothesis, in vivo recordings as well as assays of excitatory and inhibitory function in hippocampal and cortical subregions will be studied at the systemic to molecular level in a well-established mouse model of TBI. Network excitability, as a measure of E/I balance, will be recorded extracellularly with field recording techniques and voltage sensitive dyes. Determining the specific inhibitory circuitry that causes regional hippocampal and cortical E/I imbalances and identifying the distinctive elements of altered inhibitory circuitry responsive to BCAA intervention will enable development of targeted therapeutic interventions to alleviate cognitive impairments caused by TBI.