Military personnel deployed to the wars in Afghanistan (Operation Enduring Freedom; OEF) and Iraq (Operation Iraqi Freedom; OIF) are at high risk of sustaining a traumatic brain injury (TBI) from exposures to a blast (i.e., blast waves from explosions) and other types of head injuries (12,52). While early interventions are important to blunt secondary injury and maximize functional outcome, chronic interventions are also needed by veterans to aid recovery of persistent debilitating symptoms resulting from TBI. While motor functions tend to improve significantly, residual cognitive disturbance remains the most significant concern of persons with all severities of TBI. Normal brain cognitive function depends on synaptic communication via neurotransmitter release. We have previously shown that experimental TBI can produce persistent deficits in evoked neurotransmitter release, but the mechanisms are unknown. Neurotransmitter release at the synapse requires fusion of synaptic vesicles with the presynaptic plasma membrane. A crucial step in this process involves the assembly of a soluble N-ethylmaleimide-sensitive factor attachment protein receptor (SNARE) complex, a highly stable, parallel four-helix bundle formed between the synaptic vesicle SNARE synaptobrevin 2 (SYB2) and the plasma membrane SNAREs syntaxin 1 and synaptosome-associated protein of 25 kDa (SNAP-25). The pathology of SNARE proteins may play an important role in TBI, especially concerning neurotransmission and subsequent cognitive disturbances. Cysteine string protein alpha (CSP) promotes SNARE-complex assembly by chaperoning SNAP-25 during synaptic activity. It has recently been discovered that lithium, at therapeutically relevant concentrations, can enhance the expression of CSP. This represents a novel mechanism by which lithium may restore neurotransmitter release deficits after TBI. We have preliminary evidence showing a decrease in both CSP expression and SNARE-complex assembly after TBI that is attenuated by lithium treatment. It is well known that lithium has multiple actions. We will also contrast the chronic effects of lithium treatment on SNARE proteins to GSK3b and BDNF levels which represent traditional mechanisms of action of lithium. The goal of this proposal is to determine the effects of chronic TBI on key SNARE-complex mechanisms of neurotransmission. The overall hypothesis is that chronic cognitive deficits following TBI may be, at least partially, attributable to impairment in synaptic SNARE-complex formation and subsequent neurotransmitter release deficits.
Specific Aim 1 will examine the effects of TBI on individual SNARE proteins, SNARE-complex assembly, and CSP, a key regulator of SNARE-complex assembly.
Specific Aim 2 will determine if increasing the expression of CSP by lithium is associated with a restoration of SNARE-complex assembly, cognitive function, and histopathology.
Specific Aim 3 will determine if lithium, at doses that attenuate SNARE complex loss, can attenuate evoked neurotransmitter release deficits after TBI. Lithium treatment is initiated at chronic intervals that are relevant to Veteran's exposed to TBI-inducing physical forces. Successful completion of this project may provide evidence that SNARE-complexes and cognitive function are chronically diminished after TBI and can be restored, at least partially, by lithium therapy.
Traumatic Brain Injury (TBI) is the 'signature injury' in the recent conflicts in Iraq and Afghanistan, with blast events accounting for nearly 70% of injuries in wounded service members. TBI is a major cause of cognitive deficits and can result in both short-term and long-term physiological and psychological disorders in returning combat veterans. Neurotransmitter release from neurons is required for normal brain function. TBI can produce diminished neurotransmitter release, but the causes are unknown. Pharmacotherapies are needed to restore this vital neuronal function to aid Veterans seeking assistance in VA clinics for TBI- related symptoms.
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