Morphine protects for head trauma induced cognitive deficits in mice

Victims of minor traumatic brain injury (mTBI) can show long lasting cognitive, emotional and concentration difficulties, amnesia, depression, apathy and anxiety. The symptoms are generally known as a post-concussive syndrome without clear morphological brain defects. Endogenous opiates are released after impact to the brain, suggesting they may play a role in TBI pathophysiology. Furthermore, the administration of opiates to the brain of injured animals has been shown to affect the injury, induce cellular changes and also have protective qualities for neurological impairments. Here, we examined the protective properties of the opiate morphine on cognitive performances following minimal brain injury in mice. For this purpose, we have used our non-invasive closed-head weight drop model in mice, which closely mimics real life mTBI and examined mice performance in the Morris water maze. Our procedure did not cause visible structural or neurological damage to the mice. A single morphine injection administrated immediately after the induction of minimal TBI protected the injured mice from cognitive impairment, checked 30, 60 and 90 days post injury. However, mice injected with morphine that were examined 7 days after the injury did not show better performance than the saline injected mice. Our results indicate that morphine has long but not short-term effects on the cognitive ability of brain-injured mice. Although the exact nature of opioid neuroprotection is still unknown, its elucidation may lead to the much-needed treatment for traumatic brain injury.