Browsing by Subject "Area postrema"

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    The circumventricular organs
    (Universidad de Murcia. Departamento de Biología Celular e Histología, 2017) Kaur, Charanjit; Ling, Eng Ang
    The circumventricular organs (CVOs) are midline structures located around the third and fourth ventricles that are characterized by a lack of blood-brain barrier. The pineal gland, median eminence, neurohypophysis and the subcommisural organ are classified as secretory, whereas the subfornical organ, area postrema and the organum vasculosum of the lamina terminalis as the sensory CVOs. Glial cells consisting of astrocytes and microglia/macrophages are present in all these organs. The pineal gland, neurohypophysis and the median eminence lack the presence of neurons that are present in the rest of the CVOs. Most of the CVOs are lined by ependymal cells except for the pineal and the neurohypophysis. Modified ependymal cells known as tanycytes are present in the ependymal lining. These organs are important sites for communication with the cerebrospinal fluid as well as between the brain and peripheral organs via blood-borne products as they lack the blood-brain barrier.
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    Ultrastructure of the area postrema of the monkey, Macaca fascic ularis
    (Murcia : F. Hernández, 1987) Ling, E. A.; Wong, W.C.
    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 I5pm 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 externa1 basal lamina of the perivascular space. Synapses in the neuropil predominantly of the axodendritic variety were observed. h o n terminals containing round agranular vesicles were seen to make synaptic contacts with the neurona1 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.