Treadmill exercise improves memory by up-regulating dopamine and down-regulating D2 dopamine receptor in traumatic brain injury rats

Abstract

Traumatic brain injury (TBI) causes a variety of neuropathological mani-festations including cognitive, emotional, physiological and psychologi-cal deficits. Physical exercise is known to ameliorate neurological im-pairments induced by various brain injuries. We investigated the effects of treadmill exercise on memory impairments due to TBI in relation to dopamine and D2 dopamine receptor. TBI was induced with an electro-magnetic-controlled cortical impact device. The rats in the exercise groups were scheduled to run on a treadmill for 30 min once a day for 28 days after TBI induction. Then, step-down avoidance task, radial 8-arm maze test, immunohistochemistry for tyrosine hydroxylase (TH), and western blot for D2 dopamine receptor were performed. TBI im-paired short-term and spatial learning memories. TBI decreased TH ex-pressions in the prefrontal cortex (PFC), striatum, hippocampus dentate gyrus, and substantia nigra (SN). By contrast, the expressions of D2 do-pamine receptor in the PFC, striatum, hippocampus, and SN were in-creased by TBI. Treadmill exercise alleviated the impairments of short-term and spatial learning memories observed in TBI rats. TH expression was decreased and D2 dopamine receptor expression was increased in TBI rats. Treadmill exercise enhanced TH expression and suppressed D2 dopamine receptor expression in TBI rats. TBI deteriorated short-term and spatial learning memories, in contrast, treadmill exercise alle-viated the TBI-induced memory impairments by up-regulating dopa-mine level and down-regulating D2 dopamine receptor expression.