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Choline acetyltransferase in organotypic cultures of rat septum and hippocampus
Insights
Septal cholinergic neurons develop choline acetyltransferase (CAT) and acetylcholinesterase (AChE) activity in vitro. Hippocampal tissue presence accelerates CAT development, highlighting the importance of target-derived factors.
Area of Science:
- Neuroscience
- Developmental Biology
- Cell Biology
Background:
- Choline acetyltransferase (CAT) activity in the hippocampus originates from medial septum neurons.
- Hippocampal CAT development occurs within the first three weeks post-birth in rats.
Purpose of the Study:
- To investigate the development of CAT and acetylcholinesterase (AChE) in rat septal and hippocampal cultures.
- To determine if cholinergic septal neurons develop enzyme activity independently of hippocampal targets.
Main Methods:
- Organotypic cultures of fetal rat septum and postnatal rat hippocampus were utilized.
- Choline acetyltransferase (CAT) activity was measured.
- Acetylcholinesterase (AChE) histochemistry was performed.
Main Results:
- Septal explants demonstrated a significant increase in CAT activity (up to 10-fold) in vitro over 3-4 weeks.
- AChE-positive cells and fibers were observed in septal explants, indicating cholinergic differentiation.
- The presence of hippocampal tissue accelerated CAT development in septal cultures.
- No CAT activity was detected in hippocampal cultures, confirming the absence of intrinsic cholinergic neurons.
Conclusions:
- Septal cholinergic neurons can develop CAT and AChE activity in vitro without direct contact with target cells.
- Hippocampal tissue promotes the development of septal cholinergic neurons, suggesting trophic support.
- This study confirms the extrahippocampal origin of hippocampal cholinergic innervation.
Abstract:
Choline acetyltransferase (CAT) activity in the hippocampus originates almost exclusively in axons from neurons located in the medial septum. In the rat, the development of CAT in the hippocampus takes place during the first 3 weeks after birth. The development of CAT was studied in organotypic cultures of fetal rat septum and early postnatal rat hippocampus. In some septal explants, enzyme activity increased up to 10-fold during the first 3-4 weeks in vitro. Acetylcholinesterase (AChE) histochemistry showed the presence of AChE-positive cells and fibers in many explants. Thus it appears that septal cholinergic neurons develop CAT and AChE activity even without making contact with their target cells. However, the development of CAT was accelerated by the presence of hippocampal tissue. No CAT activity was found in the hippocampal cultures, confirming that there are few, if any, intrinsic cholinergic cell bodies in the hippocampus.