Traumatic brain injury in a Drosophila upregulates nitric oxide synthase associated with increased acute behavioral deficits and decreased survival time

Abstract

Traumatic brain injury (TBI) is as an outside force causing a modification in brain function and/or structural brain pathology that upregulates brain nitric oxide (NO), where NO activity is implicated in secondary pathology leading to behavioral deficits. In mammals, TBI‐induced NO production activates immune responses and potentiates metabolic crisis through mitochondrial dysfunction coupled with vascular dysregulation; however, the direct influence on pathology is complicated by the activation of numerous secondary cascades and activation of other reactive oxygen species. TBI in Drosophilahave clearly demonstrated key features of mammalian TBI including temporary incapacitation, disorientation, and activation of innate immunity (inflammation) and autophagy responses observed immediately after injury and related to persisting deficits. We propose to evaluate nitric oxide synthase expression in the absence of vascular disruption and the adaptive immune system to begin creating a model that minimizes extraneous variables to study the longitudinal influence of NO signaling on secondary pathology leading to behavioral deficits where highly targeted interventions can be evaluated.We optimized a modified high impact trauma (HIT) device on NOS‐GAL4>UAS2xEGFP flies (Bloomington Stock Center, Bloomington, IN) where upregulation of Drosophila nitric oxide synthase (dNOS) expression is associated with increased GFP levels. Ten‐day old flies received TBI from the HIT device at multiple angles (30, 45, 60, 75 degrees) followed by assessment of acute neurological behavior, locomotor activity, brain dNOS levels, twenty‐four‐hour mortality, and survival. Data indicate an increase in brain GFP expression, where robust reproducible levels of dNOS could be recorded after a 75‐degree HIT associated with increased incident of temporary incapacitation, disorientation, changes in acute climbing activity, increased 24‐hour mortality, and decreased survival. Results also indicate an effect on dNOS expression as a function of HIT angle and sex. Ongoing studies quantify levels of TBI‐induced NO activity in the brains. Future studies will evaluate different forms of brain pathology and more extensive behavioral deficits where genetic and pharmacological manipulation can be used to tease out direct effects of NO signaling. Due to conserved signaling cascades between flies and mammals, improved outcomes from modulating NO activity can translate to improved targeted therapies to be tested in mammals.