Nerve growth factor attenuates cholinergic deficits following traumatic brain injury in rats

Traumatic brain injury (TBI) results in chronic derangements in central cholinergic neurotransmission that may contribute to posttraumatic memory deficits. Intraventricular cannula (IVC) nerve growth factor (NGF) infusion can reduce axotomy-induced spatial memory deficits and morphologic changes observed in medial septal cholinergic neurons immunostained for choline acetyltransferase (ChAT). We examined the efficacy of NGF to (1) ameliorate reduced posttraumatic spatial memory performance, (2) release of hippocampal acetylcholine (ACh), and (3) ChAT immunoreactivity in the rat medial septum. Rats (n = 36) were trained prior to TBI on the functional tasks and retested on Days 1-5 (motor) and on Day 7 (memory retention). Immediately following injury, an IVC and osmotic pump were implanted, and NGF or vehicle was infused for 7 days. While there were no differences in motor performance, the NGF-treated group had significantly better spatial memory retention (P < 0.05) than the vehicle-treated group. The IVC cannula was then removed on Day 7, and a microdialysis probe was placed into the dorsal hippocampus. After a 22-h equilibration period, samples were collected prior to and after administration of scopolamine (1 mg/kg), which evoked ACh release by blocking autoreceptors. The posttraumatic reduction in scopolamine-evoked ACh release was completely reversed with NGF. Injury produced a bilateral reduction in the number and cross-sectional area of ChAT immunopositive medial septal neurons that was reversed by NGF treatment. These data suggest that cognitive but not motor deficits following TBI are, in part, mediated by chronic deficits in cholinergic systems that can be modulated by neurotrophic factors such as NGF.