Long-Lasting Suppression of Acoustic Startle Response after Mild Traumatic Brain Injury

Abstract

Acoustic startle response (ASR) is a defensive reflex that is largely ignored unless greatly exaggerated. ASR is suppressed after moderate and severe traumatic brain injury (TBI), but the effect of mild TBI (mTBI) on ASR has not been investigated. Because the neural circuitry for ASR resides in the pons in all mammals, ASR may be a good measure of brainstem function after mTBI. The present study assessed ASR in Sprague-Dawley rats after mTBI using lateral fluid percussion and compared these effects to those on spatial working memory. mTBI caused a profound, long-lasting suppression of ASR. Both probability of emitting a startle and startle amplitude were diminished. ASR suppression was observed as soon as 1 day after injury and remained suppressed for the duration of the study (21 days after injury). No indication of recovery was observed. mTBI also impaired spatial working memory. In contrast to the suppression of ASR, working memory impairment was transient; memory was impaired 1 and 7 days after injury, but recovered by 21 days. The long-lasting suppression of ASR suggests long-term dysfunction of brainstem neural circuits at a time when forebrain neural circuits responsible for spatial working memory have recovered. These results have important implications for return-to-activity decisions because recovery of cognitive impairments plays an important role in these decisions.

Toll-like receptor 4 enhancement of non-NMDA synaptic currents increases dentate excitability after brain injury

“…1–2, based on n=2 sham and n=3 FPI rats). However, contralateral hippocampal neuronal degeneration has been reported at later time points after FPI and cortical impact (Colicos et al, 1996; Neese et al, 2007; Pang et al, 2014), possibly due to secondary neuronal injury. Since neuronal injury and death can activate the innate immune responses, we used Western blot analysis to quantify hippocampal TLR4 protein levels at various time points after FPI.…”

Traumatic brain injury impairs sensorimotor function in mice

“…Recent studies have shown that sensorimotor coordination measured as the ASR is altered in a rodent models of TBI but only one has utilized a mouse model 8, 11, 12 . To take advantage of the powerful tools provided by genetic engineering, many investigators in the field of neurotrauma have shifted from rat to mouse models.…”

Anhedonia following mild traumatic brain injury in rats: A behavioral economic analysis of positive and negative reinforcement

“…All rats were assessed for acoustic startle reflex (ASR) because we previously found suppression of ASR to be a consistent outcome of mTBI following lateral fluid percussion injury. [32][33][34] Assessment of ASR was performed as previously described. 32 ASR was assessed in individual, sound-attenuated chambers, each equipped with an exhaust fan, one speaker to maintain background noise (68dB) and another speaker for delivery of the acoustic stimuli (86, 96, and 102dB; 100 ms).…”

“…[32][33][34] Assessment of ASR was performed as previously described. 32 ASR was assessed in individual, sound-attenuated chambers, each equipped with an exhaust fan, one speaker to maintain background noise (68dB) and another speaker for delivery of the acoustic stimuli (86, 96, and 102dB; 100 ms). A single session consisted of 24 trials (8 repetitions of 3 intensities), in which the acoustic stimulus was presented immediately after a 250ms baseline period.…”

“…Rats were prepared for lateral fluid percussion injury, as previously described. 32,35 Briefly, rats were anesthetized with a mixture of ketamine and xylazine (60 mg/7 mg per kg body weight, 1 ml/kg, i.p.). A craniectomy was created in the left or right parietal bone plate (4 mm diameter, centered at -3.0mm posterior to and ±3.5mm lateral to Bregma).…”