Traumatic brain injury causes a decrease in M2 muscarinic cholinergic receptor binding in the rat brain

Numerous studies indicate that an acute, excessive activation of muscarinic acetylcholine receptors (mAChR) contributes to the pathophysiological sequela of TBI. The present study examined the effect of moderate fluid percussion traumatic brain injury (TBI) on binding to M1 and M2 mAChR subtypes in the hippocampal formation and adjacent cortex using quantitative autoradiography. Injured animals along with concurrent controls were sacrificed by in situ freezing at 3 h or 24 h following TBI. Slide-mounted tissue sections were incubated in either [³H]pirenzipine (23 nM) for M1 or [³H]AFDX384 (9 nM) for M2 mAChR subtype labeling. Binding of [³H]pirenzipine to the M1 mAChR subtype was not significantly altered by TBI when compared to sham-injured animals. [³H]AFDX384 binding to the M2 mAChR subtype was significantly decreased at 24 h in hippocampal CA2-3 region and dorsal blade of the dentate gyrus (P < 0.05) The difference observed between M1 and M2 subtypes suggests that these muscarinic subtypes may differentially contribute to the pathophysiology of TBI.