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Traumatic brain injury causes a decrease in M2 muscarinic cholinergic receptor binding in the rat brain
M M DeAngelis1, R L Hayes, B G Lyeth
1Department of Surgery, Medical College of Virginia/Virginia Commonwealth University, Richmond 23298-0693.
Abstract:
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]pirenzepine (23 nM) for M1 or [3H]AFDX384 (9 nM) for M2 mAChR subtype labeling. Binding of [3H]pirenzepine 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 differences observed between M1 and M2 subtypes suggests that these muscarinic subtypes may differentially contribute to the pathophysiology of TBI.
Insights
Traumatic brain injury (TBI) significantly decreased M2 muscarinic acetylcholine receptors (mAChR) in the hippocampus 24 hours post-injury. M1 mAChR binding remained unaffected, suggesting differential roles in TBI pathophysiology.
Area of Science:
- Neuroscience
- Pharmacology
- Pathophysiology
Background:
- Muscarinic acetylcholine receptors (mAChR) play a crucial role in brain function.
- Excessive mAChR activation is implicated in the negative outcomes following traumatic brain injury (TBI).
- Understanding the specific roles of mAChR subtypes in TBI is essential for developing targeted therapies.
Purpose of the Study:
- To investigate the impact of moderate fluid percussion TBI on M1 and M2 mAChR binding.
- To determine if TBI differentially affects M1 and M2 mAChR subtypes in the hippocampus and cortex.
Main Methods:
- Quantitative autoradiography was used to assess mAChR subtype binding.
- Specific radioligands ([3H]pirenzepine for M1, [3H]AFDX384 for M2) were employed.
- Tissue samples were collected at 3 and 24 hours post-TBI.
Main Results:
- TBI did not significantly alter M1 mAChR binding in the hippocampus and cortex.
- A significant decrease in M2 mAChR binding was observed at 24 hours post-TBI in specific hippocampal regions (CA2-3, dentate gyrus).
Conclusions:
- M2 mAChR subtypes are vulnerable to TBI, showing reduced binding in key hippocampal areas.
- M1 and M2 mAChR subtypes appear to be differentially affected by TBI, suggesting distinct pathophysiological contributions.