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Chandramohan Wakade, Sangeetha Sukumari-Ramesh, Melissa D. Laird, Krishnan M. Dhandapani and John R. Vender

Object

Traumatic brain injury (TBI) induces significant neurological damage, including deficits in learning and memory, which contribute to a poor clinical prognosis. Treatment options to limit cognitive decline and promote neurological recovery are lacking, in part due to a poor understanding of the secondary or delayed processes that contribute to brain injury. In the present study, the authors characterized the temporal and spatial changes in the expression of postsynaptic density protein-95 (PSD-95), a key scaffolding protein implicated in excitatory synaptic signaling, after controlled cortical impacts in mice. Neurological injury, as assessed by the open-field activity test and the novel object recognition test, was compared with changes in PSD-95 expression.

Methods

Adult male CD-1 mice were subjected to controlled cortical impacts to simulate moderate TBI in humans. The spatial and temporal expression of PSD-95 was analyzed in the cerebral cortex and hippocampus at various time points following injury and sham operations. Neurological assessments were performed to compare changes in PSD-95 with cognitive deficits.

Results

A significant decrease in PSD-95 expression was observed in the ipsilateral hippocampus beginning on Day 7 postinjury. The loss of PSD-95 corresponded with a concomitant reduction in immunoreactivity for NeuN (neuronal nuclei), a neuron-specific marker. Aside from the contused cortex, a significant loss of PSD-95 immunoreactivity was not observed in the cerebral cortex. The delayed loss of hippocampal PSD-95 directly correlated with the onset of behavioral deficits, suggesting a possible causative role for PSD-95 in behavioral abnormalities following head trauma.

Conclusions

A delayed loss of hippocampal synapses was observed following head trauma in mice. These data may suggest a cellular mechanism to explain the delayed learning and memory deficits in humans after TBI and provide a potential framework for further testing to implicate PSD-95 as a clinically relevant therapeutic target.

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Melanie D. King, Melissa D. Laird, Sangeetha Sukumari Ramesh, Patrick Youssef, Basheer Shakir, John R. Vender, Cargill H. Alleyne Jr. and Krishnan M. Dhandapani

Subarachnoid hemorrhage (SAH) is a devastating neurological injury associated with significant patient morbidity and death. Since the first demonstration of cerebral vasospasm nearly 60 years ago, the preponderance of research has focused on strategies to limit arterial narrowing and delayed cerebral ischemia following SAH. However, recent clinical and preclinical data indicate a functional dissociation between cerebral vasospasm and neurological outcome, signaling the need for a paradigm shift in the study of brain injury following SAH. Early brain injury may contribute to poor outcome and early death following SAH. However, elucidation of the complex cellular mechanisms underlying early brain injury remains a major challenge. The advent of modern neuroproteomics has rapidly advanced scientific discovery by allowing proteome-wide screening in an objective, nonbiased manner, providing novel mechanisms of brain physiology and injury. In the context of neurosurgery, proteomic analysis of patient-derived CSF will permit the identification of biomarkers and/or novel drug targets that may not be intuitively linked with any particular disease. In the present report, the authors discuss the utility of neuroproteomics with a focus on the roles for this technology in understanding SAH. The authors also provide data from our laboratory that identifies high-mobility group box protein-1 as a potential biomarker of neurological outcome following SAH in humans.