Showing papers on "Area postrema published in 1979"

An autoradiographic examination of the central distribution of the trigeminal, facial, glossopharyngeal, and vagal nerves in the monkey.

Abstract: The central distributions of primary afferent axons in cranial nerves V, VII, IX, and X have been re-examined autoradiographically after 3H-proline injections into their peripheral ganglia. Fiber-labeling after subtotal injections of the trigeminal ganglion, besides confirming earlier classical descriptions, suggests that trigeminal fibers of the ophthalmic and mandibular (but not maxillary) branches enter the ventrolateral part of the nucleus of the solitary tract (NST). Injection of VII's geniculate ganglion labels fibers which both ascend and descend upon reaching NST. The ascending fibers distribute in a compact and circumscribed zone immediately dorsal to the spinal V nucleus as far rostral as the caudal pole of the principal trigeminal nucleus. The descending fibers distribute to the lateral NST rostral to the level at which X joins the solitary tract. For a short distance caudal to this level, sparse label is confined to a small part of lateral NST ventral to the solitary tract, which corresponds to the zone receiving direct trigeminal afferents. Fiber-labeling after injections of the ganglia of nerves IX and X suggest the following. Although, upon reaching NST, a few fibers of either IX or X ascend as far rostrally as had those of VII, both have a much larger descending component which distributes to more caudal levels of NST. Most of IX's axons appear to end in the lateral NST; only a few travel as far as the obex. Fibers of X, on the other hand, are abundant in the medial and commissural parts of NST. Moreover, only X appears to have a crossed projection in the commissural nucleus and caudal portion of the contralateral NST. A few fibers of vagal origin also appear to enter the area postrema. Whereas fibers of X appear to constitute the solitary tract, few if any fibers of VII or IX travel within that fascicle. A significant descending components of labeled fibers appears in the spinal V tract when the superior ganglion of either IX or X is injected. These fibers distribute mainly in the pars caudalis of the spinal V nucleus and, to a lesser degree, the cuneate nucleus.

Localization of vagal cardioinhibitory preganglionic neurons within rat brain stem

Abstract: In chloralose-urethane anesthetized spinal rats, electrical stimulation of systematically chosen points over the entire caudal brain stem area was carried out to explore the site(s) responsible for vagally mediated bradycardia. A dorsomedial locus including the nucleus dorsalis and the adjacent structures, the nucleus tractus solitarius, the nucleus commissuralis and the area postrema, and a ventrolateral locus around the nucleus ambiguus were found to elicit bradycardia with low threshold and high responsiveness. In another series of experiments, horseradish peroxidase (HRP) was iontophoretically administered through a glass capillary microelectrode into the identified cardiac branch of the vagus nerve of rats in order to localize more precisely the cells of origin of vagal cardioinhibitory fibers within the brain stem. Distribution of the HRP-labeled cells was not confined to one area, but these cells were found within the nucleus dorsalis, the reticular formation surrounding the nucleus ambiguus and an intermediary zone between the two nuclei. Such a pattern of distribution of vagal cardioinhibitory preganglionic cells is discussed in relation to phylogenetic and ontogenetic development of the vagal motor nuclei.

Physiological and pharmacological characterization of the area postrema pressor pathways in the normal dog.

Abstract: SUMMARY Previous studies have implicated the area postrema (AP) as a site responsible for the centrally mediated neurogenic effects of angiotensin II. To clarify its role further we characterized in mongrel dogs: 1) the onset and offset transients of the pressor response due to electrical stimulation of the AP; 2) the peripheral efferent autonomic pathways; and 3) the immediate and long-term hemodynamic effects of AP ablation. Large pressor responses (+30 ± 4 mm Hg) due to increased peripheral resistance were obtained at low stimulus strength (20-80 MA) via electrodes stereotaxically lowered into the area postrema. Rises in arterial pressure were due to augmented sympathetic activity because they were prevented by sympathetic ganglionic blockade. and were unaffected by either vagotomy or beta-adrenergic blockade. In conscious, trained, instrumented dogs thermocoagulation of the AP caused transient hypertension (40 ± 1%) and tachycardia. Subsequently, mild hypotension due to decreases in cardiac output and peripheral resistance was a feature persisting for 4 additional weeks of measurements. The mild changes in resting hemodynamics were associated with a large fall in the normal lability of heart rate and cardiac output sustained for the entire period of observation. The hypotensive effects of AP ablation were accompanied by significantly reduced vasoconstrictor effects of I.V. injected angiotensin II at all doses tested (0.5-5 fig). Vascular responses to I.V. norepinephrine (5-40 ng) were augmented. Since electrical stimulation causes hypertension and ablation results in sustained hypotension, the data indicate that the AP participates in the regulation of blood pressure by the central nervous system.

Comparison of the hemodynamic changes produced by electrical stimulation of the area postrema and nucleus tractus solitarii in the dog.

Abstract: SUMMARY Previous studies have implicated the area postrema (AP) as a site responsible for the centrally mediated neurogenic effects of angiotensin II. To clarify further its possible role in the central control of blood pressure, stainless steel electrodes were lowered stereotaxically into the AP of morphine-chloralose-anesthetized dogs after surgical exposure of the walls of the 4th ventricle just anterior to the obex. In all experiments, large pressor responses were obtained at a relatively low stimulus strength (range: 20-80 jiA, 20-60 Hz); the increases in pressure (average: 30 ± 4 mm Hg) were rapid in onset and sustained for the 10- to 20-second duration of the stimulus. Hemodynamically, the pressor response during AP stimulation was due to increases in both cardiac output (+211 ± 37 ml/ min) and peripheral resistance (+0.81 ± 0.33 U). An increase in heart rate contributed to the onset but not the plateau of the pressor response. Reconstruction of electrode tracts in all experiments corroborated that these pressor responses originated in the AP. The specificity of these cardiovascular responses was confirmed further by repeating the same kind of stimuli with electrodes placed in the nucleus tractus solitarii (NTS). In contrast to the effects obtained during AP stimulation, bradycardia (-41 ± 6 beats/min) and hypotension (-29 ± 5 mm Hg) were characteristic features. The fall in blood pressure during NTS stimulation was secondary to the pronounced bradycardia and decreased cardiac output. The data suggest that the AP is part of a previously unrecognized pathway which is distinct from the primary baroreflex pathway with relays in the adjacent NTS. Circ Res 45:136-143, 1979 THE MULTIPLICITY of actions of angiotensin II has led several investigators to explore the possibility that this hormone could have an effect within the central nervous system. This idea, first suggested by Bickerton and Buckley in 1961, lay dormant until recent years when Scroop and Lowe (1968) and Ferrario et al. (1970) showed that the infusion of angiotensin into the circulation of the dog's brain raised arterial blood pressure by a mechanism not involving direct vascular smooth muscle constriction. Since previous experiments (Ferrario et al., 1972; Gildenberg et al., 1973; Joy and Lowe, 1970) showed that the pressor effects of angiotensin in the medulla required the integrity of the area

Fine structure of the ependyma and intercellular junctions in the area postrema of the rat

Abstract: Ependymal cells and their junctional complexes in the area postrema of the rat were studied in detail by tracer experiments using horseradish peroxidase (HRP) and colloidal lanthanum and by freeze-etch techniques, in addition to routine electron microscopy. The ependyma of the area postrema is characterized as flattened cells possessing very few cilia, a moderate amount of microvilli, a well-developed Golgi apparatus and rough endoplasmic reticulum. Numerous vesicles or tubular formations with internal dense content were found to accumulate in the basal processes of ependymal cells; the basal process makes contact with the perivascular basal lamina. It is suggested that the dense material in the tubulovesicular formations is synthesized within the ependymal cell and discharged into the perivascular space. The apical junctions between adjacent ependymal cells display very close apposition, with a gap of 2–3 nm, but no fusion of adjacent plasma membranes; they thus represent a transitional form between the zonulae adhaerentes present in the ordinary mural ependyma and the zonulae occludentes in the choroidal epithelium. A direct intercommunication between the ventricular cerebrospinal fluid (CSF) and the blood vascular system indicates that a region exists lacking a blood-ventricular CSF barrier.

Afferent and efferent connections of the area postrema demonstrated by the horseradish peroxidase method

Abstract: The previous autoradiographic study of the efferent connections of the arca postrema have been completed by using horseradish peroxidase (H.R.P.) as a marking agent. These two labelling techniques have made it possible to determine two categories of structures connected with A.P.: those with afferent connections (Nucleus ambiguus), or efferent connections (mesencephalic nucleus of V, Locus coeruleus, griseum centrale and inferior and superior colliculi) and those having both types of connections (Nucleus tractus solitarii (N.F.S.), Dorsal vagal nucleus, nucleus intercalatus, hypoglossal nucleus). The afferent and efferent pathways of the A.P. identified with H.R.P. coincide with the catecholaminergic pathways demonstrated in the rat by Lindvall and Bjorklund (1974).

Efferent projections of the area postrema demonstrated by autoradiography.

Abstract: The efferents connections of the area postrema (AP) have been studied autoradiographically following iontophoretic injections of 3H-glycine or 3H-leucine into the area postrema. Precise control of the diffusion of the labelled amino acids injected iontophorectically into the AP was made using the technique of sectioning with a cryostat. AP projects to a great number of structures. Projections to nucleus tractus solitarius (NFS), dorsal vagal nucleus, nucleus intercalatus, nucleus praepositus hypoglossi, nucleus hypoglossal, the mesencephalic nucleus of V nerve, locus coeruleus and superior and inferior colliculi are shown bilaterally. The density of the efferents was greatest to the NFS and the LC. Corelations are suggested with functional mechanisms of cardiovascular regulation.

Regeneration and myelination in autonomic ganglia transplanted to intact brain surfaces

Abstract: Fragments of superior cervical ganglia (SCG) from donor rats between newborn and three months of age were transplanted either into the fourth ventricle, onto the dorsal surface of the medulla or in contact with the area postrema of recipient rats aged 6–14 days (allografts) and 3–4 weeks (autografts). Except for the meninges, the entire brain surface and parenchyma was undisturbed. The regenerative capacity of the transplanted ganglia and its interaction with the brain surfaces was followed for post-operative periods between 1h and six months.

Distribution of LHRH in the rat and mouse brain with special reference to the tanycytes

Abstract: The distribution of luteinizing hormone-releasing hormone (LHRH) was studied in the rat and mouse brain by means of light and electron microscopic immunohistochemistry using the peroxidase-antiperoxidase method. An immunoreactive product to LHRH antiserum was found near the blood vessels of the vascular organ of the lamina terminalis. In the arcuate nucleus-median eminence region, an immunoreactive material occurred bilaterally in the hypothalamic tissue around the tuberoinfundibular sulci. Electron microscopy revealed that immunoreactive fibers observed light microscopically contain numerous granules 100–130 nm in diameter. No immunoreactive product was located in the tanycytes of the median eminence, the perikarya of hypothalamic neurons, and the parenchyma of several circumventricular organs (subfornical organ, subcommissural organ, pineal organ, area postrema).

Fine structure of the ependymal cells in the area postrema of the domestic fowl.

Abstract: The ultrastructure of the ependymal cells in the area postrema of the domestic fowl was studied by scanning and transmission electron microscopy. The ependymal surface of the area postrema is covered with many furrows and ridges. These ridges consist of ependymal cells aggregated in a fan-like shape. The ependymal cell lacks clustered cilia, microvilli are few, and a long basal process extends through the parenchymal layer of the area postrema. Within the cytoplasm as well as in the basal process, a spherical body with a diameter ranging from 1.5 to 2 gmm is occasionally observed.

Uptake of exogenous protein by supraependymal cells of the feline area postrema

Abstract: Supraependymal cells occurring on the surface of the feline area postrema were examined for phagocytic ability. It was shown that they could ingest exogenous horseradish peroxidase that was experimentally introduced into the brain ventricular system. The cells thus bear functional as well as ultrastructural attributes of macrophages, similar to those found in the third ventricle and subarachnoid space.

Effect of arrhythmogenic doses of deslanoside on the uptake of monoamines in cardiac and brain tissue, and in platelets*

Abstract: The effect of in vivo administration of toxic doses of deslanoside to anesthetized cats on the active transport of serotonin (r 3H]-5-HT), norepinephrine (r 3H]-NE) and or dopamine ([3H]-DA) was determined. In cardiac and brain tissue, and platelets obtained at the onset of deslanoside-induced ventricular fibrillation, it was found that deslanoside inhibited the uptake of [3H]-NE into the left ventricle and the uptake of (3H]-S-HT into the area postrema and into platelets.

The area postrema and the long-term regulation of blood pressure

Abstract: The area postrema (AP) is a medullary structure sensitive to low doses of circulating angiotensin II (AII). Both administration of AII and electrical stimulation of the AP cause similar cardiovascular pressor responses. The removal of the AP in dogs results in slight hypotension, decreased hemodynamic variability and blunted vasoconstrictor responses to injected AII but not norepinephrine (NE). These data indicate that the AP may be part of a sympatho-facilitory pathway involved in the regulation of blood pressure.