Page 145 - NNS 2014 Program & Abstract Book

The exact role of neuron-microglia communication through CX3CL1-
CX3CR1 signaling in neurodegenerative disorders remains elusive as
recent studies targeting this pathway have shown both neuroprotective
and neurotoxic properties. Traumatic brain injury (TBI) initiates a ro-
bust activation of microglia, which has been shown to persist for years
following the initial event, and can ultimately result in neurodegen-
eration. In the current study we examined the effect of CX3CR1 de-
letion (CX3CR1GFP/GFP) upon multiple pathways underlying TBI-
induced neurotoxic responses both at acute (24 hrs) and chronic (3
months) time points after injury. TBI or sham surgery was induced by
controlled cortical impact in CX3CR1GFP/GFP mice (KO) and wild type
(WT) animals. 24 hrs following TBI, KO animals had a reduced neu-
roinflammatory response compared to WT mice. Specifically, KO mice
had significantly decreased expression of the pro-inflammatory medi-
ators IL-1b, TNFa, NOS2, and IL6 compared to WT-TBI mice. We next
examined the effect of CX3CR1 deletion upon TBI-induced hippo-
campal-dependent cognitive funciton 3 months after injury using the
radial arm water maze (RAWM). Although KO mice had a higher
baseline for errors during day one of RAWM, they had a significantly
ameliorated response (decreased errors) compared to WT-TBI mice.
Isolated hippocampi from these animals were analyzed for multiple
markers associated with synaptic function by Western blot analyses.
Our results demonstrate that TBI alters post-synaptic NMDAr, as the
NR2b- but not the NR2a subunit was significantly increased in WT-TBI
mice, however this effect was abrogated in KO-TBI mice. Furthermore,
TBI induced a significant increase in the Src-like kinase Fyn as well as
the phosphorylation of p44/42 MAP kinase in WT mice, which again
was abrogated in KO-TBI mice. Interestingly, we did observe a strong
trend for increased PSD-95 in WT-TBI mice compared to sham, which
was blunted in KO-TBI mice. Taken together, these data indicate that
CX3CR1 deletion prevents the TBI-induced pro-inflammatory and
neurotoxic response acutely, which may in part underlie the amelio-
rated response of TBI-induced synaptic dysfunction chronically.
Key words
behavior, CX3CR1, hippocampus, NMDAR
D2-01
HETEROGENEOUS TBI MODELS REVEAL DIVERGENT
EFFECTS IN NEURONAL AND OLIGODENDROGLIAL
PROGENITORS
Mierzwa, M.J.1 , Sullivan, G.M.1, Beer, L.A.1 , Ahn, S.2, Armstrong,
R.C.1
1CNRM/Uniformed Services University of the Health Sciences, Be-
thesda, MD, USA
2National Institutes of Health, Bethesda, MD, USA
The regenerative capacity of the CNS must be optimized to promote
repair following traumatic brain injury (TBI). Sonic hedgehog (Shh)
maintains neural stem cell niches and promotes oligodendrogenesis.
Accordingly, we examined whether Shh signaling contributes to neu-
ronal (DCX +) or oligodendrocyte (NG2 +) progenitor responses in two
distinct models of TBI. Shh-responsive cells were heritably labeled in
vivo using Gli1CreERT2 transgenic mice crossed to R26-YFP or R26-
IAP reporter lines. Reporter expression was induced by tamoxifen ad-
ministration on 2-3 d post-TBI. Controlled cortical impact (CCI) onto
the dura produced injury to the cerebral cortex. Following CCI: a)
reporter labeled cells decreased in the ipsilateral cortex, b) DCX + cells
were not found in the lesion penumbra, and c) YFP + and DCX +
YFP + cells increased in the subventricular zone (SVZ). In the alter-
native TBI model, impact onto the skull produced traumatic axonal
injury (TAI) in the corpus callosum. Following TAI: a) YFP + cells
within the SVZ decreased at 2wks and recovered by 6wks, b) NG2 +
cells were increased in the cerebral cortex, and showed a similar trend
in the corpus callosum, and c) In all regions, NG2 + cells were rarely
labeled with YFP. Overall, YFP + cells were extremely rare in the
corpus callosum of non-injured mice and after either TAI or CCI, or
even after microinjection of a Smo agonist (SAG) into the corpus
callosum. After SAG microinjection, YFP + cells and NG2 + cells in-
creased in the SVZ but were not double-labeled, indicating an effect of
Smo signaling without Gli1 transcriptional activation in NG2 cells. Our
findings show roles for Shh signaling in both neuronal and oligoden-
droglial progenitor responses, with differential downstream effectors of
the pathway. Importantly, cortical versus white matter damage from
TBI resulted in opposite responses of Shh-activated neural stem cells
within the SVZ. Supported by the NMSS and the DoD in the Center for
Neuroscience and Regenerative Medicine (CNRM).
Key words
neural stem cell, oligodendrocyte progenitor, sonic hedgehog, sub-
ventricular zone
D2-02
CHARACTERIZATION OF BLAST-INDUCED VESTIBULAR
INJURY IN RATS
Wang, Y., Wei, Y., Tong, L.C., Arun, P., Edwares, A.A., Oguntagyo,
S.A., Gist, I.D., Long, J.B.
Walter Reed Army Institute of Research, Silver Spring, MD, USA
Blast exposure is the most common cause of traumatic brain injury
(TBI) in warfighters. Nearly 60% of blast TBI victims exhibit hearing
loss, tinnitus, dizziness and balance disorders. To date, the etiologies of
these injuries are largely undefined. A high fidelity animal model is
critical to define the mechanism(s) of injury and develop therapeutic
strategies for blast-induced neurobehavioral deficits. In this study, we
used an air-driven shock tube to simulate primary blast and investigated
the pathological effects of blast exposures on central and peripheral
auditory/vestibular systems. Anesthetized rats (Sprague Dawley, male,
350 g) were tautly secured in a transverse prone position 2.5 ft within
the mouth of a 1 ft diameter shock tube with the right side facing the
oncoming shockwave. Rats were exposed to two closely coupled
shockwaves (peak total pressures of 5, 12 or 19 psi) separated by 30 sec.
Rats were euthanized at varied intervals (6 h, 24 h, 7 d and 14 d) post
injury and tissues underwent histological and RNA analyses. All rats
received rotarod training prior to and testing after blast exposures for
evaluation of motor coordination and balance. Compared to a single
blast insult, repeated blast exposures significantly impaired motor co-
ordination. Intensity-dependent blast-induced damage to middle and
inner ears was evident with no significant differences between left and
right ears. Labyrinthine hemorrhage was prominent at 24 h up to 14
days after blast exposure. Repeated blast exposures caused significant
axonal degeneration and glial cell proliferation in the central vestibular
signal processing regions of the brain, and also triggered multiple gene
expression changes that are associated with DNA repair, neural growth,
inflammation and pain. These findings indicate that both peripheral and
central vestibular systems are vulnerable to blast injuries, and are
particularly disrupted by closely coupled repeated blasts. Neuroin-
flammation, which occurred during the early phase post injury, could be
a major factor leading to secondary neuronal damage.
Key words
blast TBI, inflammation, motor coordination, pathology, vestibular
system
A-113