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Updated: Aug 13, 2026

Quantifying Synapses: an Immunocytochemistry-based Assay to Quantify Synapse Number
Published on: November 16, 2010
Acetylcholine content and distribution in rat cortical synaptosomes after in vivo exposure to quinolinic acid
R H Metcalf1, D L Riddell, R J Boegman
1Department of Pharmacology and Toxicology, Queen's University, Kingston, Ont. Canada.
Abstract:
In this study, changes in the concentration and subcellular distribution of rat cortical synaptosomal acetylcholine (ACh) was investigated after a single injection of quinolinic acid (QUIN) into the nucleus basalis magnocellularis (nbM). In the P2 fraction of normal animals the ACh concentration was 235 +/- 18 pmol/mg protein. Of this, 64 +/- 10% was recovered in the particulate (P3) fraction and 24 +/- 1% in the soluble (S3) fraction. Cortical synaptosomes (P2) prepared 0.5 h after injecting either 600 or 1000 nmol of QUIN contained significantly higher concentrations of ACh (372 +/- 127 and 496 +/- 77 pmol/mg protein, respectively) when compared to the amount of ACh in control animals. The ACh concentration in the P2 fraction was still elevated 3 h after injecting 600 nmol QUIN, however, synaptosomal ACh decreased significantly 3 h after rats were treated with 1000 nmol QUIN. Determination of subcellular ACh 0.5 h after injecting QUIN revealed that neither dose of QUIN produced a change in the distribution of ACh between P3 and S3. However, 3 h after injecting QUIN, a shift in the subcellular distribution of ACh to the cytoplasmic fraction (S3) was observed with 1000 nmol QUIN. These results show that QUIN-induced depolarization of nbM neurons which project to the cortex produce both dose-dependent and time-dependent changes in synaptosomal ACh concentration and subcellular distribution.
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