Can Therapeutic Hypothermia Diminish the Impact of Traumatic Brain Injury in Drosophila melanogaster ?

Background/main objectives: No effective strategy exists to treat the well-recognized, devastating impact of traumatic brain injury (TBI) and chronic traumatic encephalopathy (CTE), which is the brain degeneration likely caused by repeated head trauma. The goals of this project were (1) to study the effects of single and recurrent TBI (rTBI) on Drosophila melanogaster's (a) life span, (b) response to sedatives, and (c) behavioral responses to light and gravity and (2) to determine whether therapeutic hypothermia can mitigate the deleterious effects of TBI.

Methods: Five experimental groups were created: (1) control, (2) single TBI or concussion; (3) concussion + hypothermia, (4) rTBI, and (5) rTBI + hypothermia. A "high-impact trauma" (HIT) device was built, which used a spring-based mechanism to propel flies against the wall of a vial, causing mechanical damage to the brain. Hypothermia groups were cooled to 15°C for 3 minutes. Group differences were analyzed with chi-square tests for the categorical variables and with ANOVA tests for the continuous variables.

Results: Survival curve analysis showed that rTBI can decrease Drosophila lifespan and hypothermia diminished this impact. Average sedation time for control vs concussion vs concussion + hypothermia was 78 vs 52 vs 61 seconds ( P  < .0001). Similarly, rTBI vs rTBI/hypothermia groups took 43 vs 59 seconds ( P  < .0001). Concussed flies preferred dark environments compared with control flies (risk ratio 3.3, P  < .01) while flies who were concussed and cooled had a risk ratio of 2.7 ( P  < .01). Flies with rTBI were almost 4 times likely to prefer the dark environment but only 3 times as likely if they were cooled, compared with controls. Geotaxis was significantly affected by rTBI only and yet less so if rTBI flies were cooled.

Conclusions: Hypothermia successfully mitigated many deleterious effects of single TBI and rTBI in Drosophila and may represent a promising breakthrough in the treatment of human TBI.