S. Ogle1,2,3, H. G. May2,4, P. Adelson1,2, J. Lifshitz2,3, T. Currier Thomas2,3, S. B. Johnson1 1Banner University Medical Center- Phoenix,Surgery,Phoenix, AZ, USA 2University Of Arizona,College Of Medicine, Child Health,Phoenix, AZ, USA 3Barrow Neurological Institute At Phoenix Children’s Hospital,Phoenix, AZ, USA 4University Of Bath,Bath, UK, United Kingdom
Introduction: Traumatic brain injury (TBI) disrupts neuronal processes and connections (circuits), which initiate reparative events to rebuild damaged circuits (synaptogenesis). Aberrant synaptogenesis, however, can lead to circuit reorganization which is thought to manifest as persistent neurological dysfunction. In rodents, circuit reorganization in the thalamocortical circuit leads to the development of late-onset sensory sensitivity to whisker stimulation; similar to light/sound hypersensitivity in TBI survivors. Developmental synaptogenesis is, in part, stimulated by astrocyte-secreted thrombospondin-1 and 2 (TSP) via interaction with the α2δ-1 subunit on neuronal voltage-gated calcium channels (α2δ-1). TSP levels are high during development, but diminish with age. After focal trauma in rodent models, TSP levels increase and experimental TSP antagonism decreases epileptiform activity. We, therefore, hypothesize that TBI-induced TSP expression will coincide with circuit reorganization in the thalamocortical circuit.
Methods: Adult male Sprague-Dawley rats underwent sham or moderate midline fluid percussion brain injury. At multiple time points over 2-months post-injury, expression of TSPs and synaptic markers were quantified from thalamocortical circuit biopsies using qPCR and automated capillary westerns, respectively. Tissue sections were stained for glial acidic fibrillary protein and processed using silver and Golgi staining. GFAP and silver pixel density were quantified over time in cortical and thalamic regions. Golgi stained neurons were 3D reconstructed and analyzed for neuronal process length, number and surface area with Neurolucida software.
Results: In the thalamus, TSP-1 gene and protein expression significantly increases 7 days post-injury (DPI). Gene and protein expression of α2δ-1, pre- and post-synaptic markers also significantly change over time. In the cortex, TSP-1 gene expression increases at 7 DPI which coincides with significant changes of expression of α2δ-1, pre- and post-synaptic markers. Protein analysis of the cortex is still on going. Histologically, there is increasing neuronal pathology and astrocytosis at 7 DPI. Neuronal process length, number, and complexity also differ significantly from shams in both relays over time.
Conclusion: Changes in synaptogenic and synaptic marker expression, pathology and neuronal morphology coincide with the development of late-onset of symptoms. This supports post-TBI reparative events leading to aberrant synaptogenesis and circuit reorganization resulting in neurological dysfunction. Persistent astrocytosis after TBI provides a source of the increased expression of TSP, which likely mediates synaptogenesis and ongoing events. Understanding the unique time course and mechanism of chronic neurological dysfunction after TBI is critical to development of treatment strategies.