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Muscarinic cholinergic receptor binding in rat brain following traumatic brain injury
B G Lyeth1, J Y Jiang, T M Delahunty
1Department of Surgery, Medical College of Virginia/Virginia Commonwealth University, Richmond 23298-0693.
Abstract:
Recent evidence suggests that excessive activation of muscarinic cholinergic receptors (mAChRs) contributes significantly to the pathophysiological consequences of traumatic brain injury (TBI). To examine possible alterations in mAChRs after TBI, the affinity (Kd) and maximum number of binding sites (Bmax) of mAChRs in hippocampus, neocortex, brain stem and cerebellum were determined by [3H]QNB binding. Three groups of rats were examined: 1 h post-TBI (n = 21), 24 h post-TBI (n = 21) and sham-injured rats (n = 21). Kd values were significantly higher in hippocampus and brain stem at 1 but not 24 h post-TBI compared with sham-injured controls (P < 0.05). Kd values did not significantly differ in neocortex and cerebellum at 1 or 24 h post-TBI compared with sham-injured controls. Bmax values did not significantly differ in any brain areas at 1 or 24 h post-TBI compared with sham-injured controls. These results show that TBI significantly decreases the affinity of mAChRs in hippocampus and brain stem at an early stage post-TBI, which may contribute to desensitization of mAChRs after TBI. The findings of no change in Bmax values are consistent with a transient elevation in ACh concentrations after TBI.
Insights
Traumatic brain injury (TBI) alters muscarinic cholinergic receptors (mAChRs) in specific brain regions. Early after TBI, mAChR affinity decreases in the hippocampus and brain stem, potentially causing receptor desensitization.
Area of Science:
- Neuroscience
- Neuropharmacology
- Traumatic Brain Injury Research
Background:
- Muscarinic cholinergic receptors (mAChRs) play a role in brain function.
- Excessive mAChR activation is implicated in the negative outcomes of traumatic brain injury (TBI).
Purpose of the Study:
- To investigate potential changes in the affinity (Kd) and density (Bmax) of mAChRs in different brain regions following TBI.
- To understand the early molecular alterations of mAChRs after TBI.
Main Methods:
- Utilized [3H]QNB binding assays to quantify mAChR binding characteristics.
- Examined hippocampus, neocortex, brain stem, and cerebellum in rats at 1 hour and 24 hours post-TBI, comparing them to sham-injured controls.
Main Results:
- A significant decrease in mAChR affinity (increased Kd) was observed in the hippocampus and brain stem at 1 hour post-TBI.
- No significant changes in affinity were detected at 24 hours post-TBI or in the neocortex and cerebellum at either time point.
- Maximum binding site density (Bmax) for mAChRs remained unchanged across all examined brain regions and time points.
Conclusions:
- TBI leads to a significant, early reduction in mAChR affinity in the hippocampus and brain stem.
- This affinity decrease may contribute to mAChR desensitization following TBI.
- The absence of changes in Bmax suggests that the observed effects are related to receptor function rather than density, potentially linked to transient acetylcholine level changes.