Chronic nicotine treatment attenuates alpha 7 nicotinic receptor deficits following traumatic brain injury

Traumatic brain injury (TBI) often causes a persistent and debilitating impairment of cognitive function. Although the neurochemical basis for TBI-induced cognitive dysfunction is not well characterized, some studies suggest prominent involvement of the CNS cholinergic system. Previous studies from our laboratories have shown that alpha 7* nicotinic cholinergic receptors (nAChrs) are especially vulnerable to the pathophysiological effects of TBI. Hippocampal and cortical alpha-[(125)I]-bungarotoxin (BTX) expression of alpha 7* nAChrs is significantly decreased in many brain regions following TBI and this reduction persists for at least 3 weeks following injury. In the present study we evaluated whether chronic nicotine infusion could attenuate TBI-induced deficits in alpha 7* nAChr expression. Male Sprague-Dawley rats were sham-operated, or subjected to mild or moderate unilateral cortical contusion injury. Immediately following brain injury, osmotic mini-pumps that delivered chronic saline or nicotine (0.125 or 0.25 mg/kg/h) were implanted. The animals were euthanatized and the brains prepared for nAChr quantitative autoradiography, 7 days following surgery. Brain injury caused significant decreases in BTX binding in several regions of the hippocampus. TBI-induced deficits in alpha 7* nAChr density were reversed in four of the six hippocampal brain regions evaluated following chronic nicotine administration. If TBI-induced deficits in alpha 7* nAChr expression play a role in post-injury cognitive impairment, pharmacological treatments which restore nAChr binding to control levels may be therapeutically useful.