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Ultrastructure of the area postrema of the monkey, Macaca fascicularis
Abstract:
The area postrema of the monkey, Macaca fascicularis, were a pair of oval organs at the caudal end of the floor of fourth ventricle. Their ependymal lining was covered by well-developed microvilli with occasional overlying supraependymal cells. Two types of lining cells were present: pyramidad- and flattened cells. The pyramidal cell showed a long extending basal process resting on the underlying blood vessels. In transmission electron microscopy, the organ showed numerous fenestrated sinusoids characterized by a distinct perivascular space containing mast cells, macrophages and collagen fibrils. The parenchyma of the organ was composed of neurons and glial elements. Only one type of neuron ranging from 9.5 to 15 microns could be distinguished. The neurons contained an indented nucleus surrounded by organelle rich cytoplasm. The soma of the neuron was enclosed by glial element resembling astrocyte. The glial processes terminated on the blood vessel where they were "tunnelled" by a variable number of nerve fibres some of which gained a direct access to the external basal lamina of the perivascular space. Synapses in the neuropil predominantly of the axodendritic variety were observed. Axon terminals containing round agranular vesicles were seen to make synaptic contacts with the neuronal soma. No structural changes were observed in the area postrema following bilateral cervical vagotomy. However, degenerating axon terminals were observed in the subpostremal zone 7, 14 and 21 days after vagotomy suggesting a direct afferent projection into this region.
Insights
The area postrema in Macaca fascicularis monkeys contains unique cells and fenestrated blood vessels. Vagotomy did not alter the area postrema but revealed degenerating axons in nearby regions.
Area of Science:
- Neuroscience
- Cell Biology
- Anatomy
Background:
- The area postrema is a circumventricular organ crucial for physiological regulation.
- Its precise cellular structure and neural connections remain areas of active research.
Purpose of the Study:
- To elucidate the ultrastructural morphology of the area postrema in Macaca fascicularis.
- To investigate the impact of vagotomy on the area postrema and adjacent neural structures.
Main Methods:
- Transmission electron microscopy was employed to examine tissue samples.
- Bilateral cervical vagotomy was performed, followed by post-operative analysis at various time points.
Main Results:
- The area postrema exhibits a specialized ependymal lining with microvilli and two cell types: pyramidal and flattened.
- Fenestrated sinusoids with associated perivascular cells were observed.
- Neurons and glial elements, including astrocytes, constitute the parenchyma.
- Vagotomy did not induce structural changes within the area postrema itself.
- Degenerating axon terminals were noted in the subpostremal zone post-vagotomy.
Conclusions:
- The area postrema possesses a distinct cellular architecture and vascular supply.
- Vagotomy suggests potential direct afferent projections to the subpostremal zone, not the area postrema.
- Further research is needed to fully understand the functional implications of these findings.