CDR, PhD Candidate USUHS Graduate School of Nursing HAGERSTOWN, Maryland
Abstract Text: Rodents produce glucocorticoids (corticosterone [CORT] and progesterone [PROG]) in response to injury and stress. These hormones play key roles in immune responses, metabolism, cognition, and behavior. Low CORT levels may be associated with the development of neuropsychiatric symptoms similar to posttraumatic stress disorder (PTSD) in humans. Additionally, stress hormones can alter synaptic plasticity and PROG may modulate secondary injury pathways in neurological trauma. Latency to righting reflex (LRR), which is the tendency of a rat placed on its back to return to its feet, is the amount of time required for a rat to awaken and become ambulatory post-injury, and is a proxy measure of traumatic brain injury (TBI) severity similar to loss of consciousness in humas. Our lab previously demonstrated increased stress hormone responses following a ketamine infusion in male and female rats without an injury condition. However, the effects of mild TBI (mTBI) on stress hormones during LRR and over time post-injury are not well described. Ketamine is an analgesic and anesthetic drug commonly administered to traumatically injured patients. However, little is known regarding the effects of ketamine , on stress hormones after mTBI. The goal of this study was to examine the effects of mTBI and a ketamine infusion on stress hormones after injury, and to determine the association between LRR and stress hormone levels after mTBI. Adult male Sprague Dawley rats with indwelling jugular venous catheters underwent mTBI using the Closed Head Injury Model of Engineered Rotational Acceleration (CHIMERA) model (sham or 3 impacts x 1.5 J, 5 sec delay). LRR was measured immediately after the injury and blood was sampled 1 hour after CHIMERA, immediately prior to an intravenous ketamine or saline infusion administered over 2 hours (0, 10, or 20 mg/kg). Blood was also sampled at a baseline, 3, 5, and 24 hours post-injury. Plasma CORT and PROG levels were measured via enzyme-linked immunosorbent assay (ELISA). Sham animals underwent the same procedures as CHIMERA mTBI animals except the impacts. Preliminary results demonstrate significant elevation of CORT at 1 hour post-injury among CHIMERA animals. Additionally, CORT levels were positively correlated with LRR. These findings indicate that LRR may be a means to delineate among injury responses and identify animals that are susceptible to poor mTBI outcomes. Moreover, time-dependent changes in stress hormone levels post-injury may serve as potential biomarkers for mTBI. The current results may translate to improved diagnosis and care for wounded patients with mTBI.