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At least 19 recordsLinked to original sources

PubMed1976

[The localization of the acetylcholinesterase in the area postrema and area subpostrema of the rat. Light and electron microscopical investigations (author's transl)].

In perfusion fixed material was studied the localization of acetylcholinesterase in the region of rat Area postrema on frozen slides and chopped tissue light and electron microscopically. In the light microscope there was a week reaction in the parenchyma cells of the Area postrema and the capillary endothelium and some nerve fibres of the Area subpostrema. Electron microscopically was demonstrated the AChE in the perinuclear cisterna, in the cisternae of the rough endoplasmatic reticulum and the neurotubuli of the axons and dendrites in the Area postrema. It was also evidenced the AChE-reaction in the pinocytic vesicles of the capillary endothelium, the axons, dendrites and some other structural elements of the neuropil in the Area subpostrema. The results were discussed from the standpoint of the functional morphology.

Acetylcholinesterase↗

PubMed1988

Area postrema and alcohol: effects of area postrema lesions on ethanol self-administration, pharmacokinetics, and ethanol-induced conditioned taste aversion.

An investigation was carried out to test the hypothesis that the area postrema (AP) may detect ethanol as a blood-borne toxin and thereby mediate aversive postingestinal effects of the drug. These aversive effects in turn may impose an upper limit on the amount of drug that can be consumed. In Experiment 1 rats had continuous access to water and a 4% ethanol solution. Animals with AP lesions drank more ethanol than sham-operated controls. No differences in drug disposition or metabolism were found when these rats were injected with ethanol and blood ethanol levels were measured. If the AP lesions resulted in increased ethanol drinking because of a reduction in the aversive effects of the drug, then the lesions might also be expected to attenuate a conditioned taste aversion induced by ethanol. In Experiment 2, groups of lesioned and sham-operated rats drank a novel tasting fluid and then were given i.p. injections of ethanol (0.9, 1.2, or 1.6 g/kg) or vehicle. Similar degrees of aversion to the taste of the fluid developed in both the lesioned and the sham-control groups. Since the AP lesion did not result in the attenuation of the ethanol-induced conditioned taste aversion, it was suggested that the AP may not mediate the aversive consequences of ethanol and that the increased ethanol self-administration observed in Experiment 1 may be due to other effects of the lesion.

Alcohol Drinking↗

PubMed1975

[The ventricular surface of the area postrema and the adjacent area subpostrema in the rabbit brain].

The ependymal surface of the area postrema (rabitt) was examined by scanning and transmission electron microscopy. The flattened ependymal cells show few microvilli. Towards the central canal, the ependymal cells change gradually to a columnar shape; the number of microvilli increases concomitantly. The area postrema ependymal cell surface mostly bears a single cilia. In contrast, a region immediately adjacent to the area postrema, which has been named area subpostrema (Gwyn and Wolstencroft 1968), shows cilia arranged in bunches. These cilia are regularly covered with colloid -- like droplets. A period-acid-bisulfit-aldehydthionine method (Specht 1970) permits to identify these droplets with glyproteids.it has been suggested that the droplets might derive from the area subpostrema ependymal cells. Above the ependymal surface of the area postrema, a great number of fine unmyelinated neuronal processes and thicker processes are observed. Some of them show bulb-like endings. These terminals contain small vesicles, dense cored vesicles (400...800 A), and mitochondria which are mostly characterized by a single central prismatic tubule. The plasmalemma of some bulbs is in a synaptic contact with the apical plasmalemma of the ependyma, while other bulbs see to end freely in the ventricle. Some neuronal processes penetrate between ependymal cells of the area postrema into the ventricular lumen.

Animals↗

PubMed1999

Prolactin receptor localization to the area postrema.

The area postrema, which lacks a blood-brain barrier, was examined for the presence of prolactin receptors, which would render it a potential site for vascular prolactin to directly interact with neuronal elements. Using an in vitro autoradiographic technique, frozen sections of New Zealand white rabbit medulla were incubated with radiolabelled ovine prolactin alone (total binding) or radiolabelled ovine prolactin in the presence of excess unlabelled ovine prolactin (non-specific binding). The specificity of the binding was also assessed using excess unlabelled human prolactin or ovine LH. While excess unlabelled ovine and human prolactin caused a statistically significant reduction in radio labeled prolactin binding, unlabelled LH was without effect. Results reveal the presence of specific prolactin binding sites within the area postrema, a previously unknown prolactin target area of the CNS.

Animals↗

PubMed1985

Muscarinic cholinergic receptors in area postrema and brainstem areas regulating emesis.

Central cholinergic pathways modulate both the perception of excessive motion stimuli and the expression of motion sickness symptoms, such as nausea and vomiting. Specific brainstem areas which mediate motion-induced emesis include the area postrema (AP), vagal nuclear complex (VNC), reticular formation (RF) at the site of the vomiting center, and the vestibular complex (VC). In this report, histological studies indicated the cellular organization of brainstem structures mediating emesis was similar in bovine and squirrel monkey brain. The objective of this study was to characterize biochemical and pharmacological properties of muscarinic cholinergic receptors assayed by 3H-QNB binding in these regions of bovine brainstem. Scatchard analyses of specific 3H-QNB binding showed an uneven distribution of muscarinic receptors, with high densities of sites in VNC and AP, intermediate levels in RF and lowest receptor concentrations in VC. Dissociation constants for 3H-QNB, measured in saturation and kinetic experiments, were similar in all brainstem regions. The pharmacological potency of cholinergic agonists and antagonists was the same as reported for muscarinic receptors labeled in other brain areas or peripheral organs. Several drugs which potently inhibited 3H-QNB binding in bovine brainstem also exhibited antiemetic activity in a squirrel monkey model of motion-induced emesis. The antimotion sickness effects of these drugs may be due, in part, to their antagonism of muscarinic receptors in brainstem areas regulating emesis.

Animals↗

PubMed1999

Impaired osmoregulatory responses in rats with area postrema lesions.

Area postrema lesions (APX) in adult male rats produced a robust spontaneous intake of 0.5 M NaCl, as reported previously. The largest NaCl intakes (up to 108 ml/day) were observed when there was little incidental damage in the medial subnucleus of the nucleus of the solitary tract adjacent to the caudal and middle portions of the area postrema. Rats with discrete APX also drank substantial amounts of 0.5 M NaCl when access to saline was restricted to 7 h/day (up to 30 ml in 1 h, 48 ml in 7 h). Such large NaCl intakes stimulated considerable water ingestion and renal sodium excretion, but together these responses usually were insufficient for osmoregulation during the 7-h test period. After systemic administration of hypertonic NaCl solution, rats with APX excreted less Na(+) in urine and secreted less vasopressin and oxytocin than control rats did. The prominent salt appetite, insufficient thirst and natriuresis in response to an ingested NaCl load, and blunted natriuresis and neurohypophysial hormone secretion in response to an injected NaCl load, all indicate that osmoregulatory responses are impaired in rats after APX.

Animals↗

PubMed1994

Lithium chloride-induced anorexia, but not conditioned taste aversions, in rats with area postrema lesions.

Area postrema (AP) lesions were produced by vacuum aspiration in adult male Sprague-Dawley rats. Consistent with previous findings, when water-deprived rats were allowed to drink novel flavored fluids immediately before treatment with LiCl (3 mEq/kg, i.p.), sham-operated and non-operated control rats demonstrated a pronounced aversion to the fluids whereas rats with AP lesions did not decrease fluid consumption significantly. However, in a 30-min test period after overnight food deprivation, rats with AP lesions reduced food intake significantly and to an equivalent degree as control animals when pretreated with LiCl (3 mEq/kg, i.p. or i.v.). These and other results are consistent with the traditional view that AP mediates the sensation of nausea produced by LiCl treatment (hence the loss of conditioned taste aversions after AP lesions), but suggest that neither nausea nor AP is necessary for the marked disinclination to eat that is induced in rats by acute administration of LiCl.

Analysis of Variance↗

PubMed1984

The structure of the mammalian area postrema.

The area postrema in mammals other than rodents and lagomorphs is a bilateral mound of gelatinous-appearing tissue that protrudes into the caudal fourth ventricle on either side of the obex. In rodents and lagomorphs it is a single midline structure at the apex of the calamus scriptorius. The vasculature is derived mainly from the posterior inferior cerebellar arteries and consists mainly of sinusoidal capillaries. It appears to constitute a portal system, at least in the rat. Many of the capillaries are fenestrated, and many large perivascular spaces with both vascular and parenchymal basal laminae are present. The cell population is composed of flattened ependymal cells exhibiting microvilli, and of small neurons, normal astrocytes, glialoid cells, and a very few oligodendroglia. Mast cells are occasionally present. The glialoid cells appear to be the predominant cell type and exhibit great numbers of vascular podia. Axodendritic synapses are numerous and axosomatic synapses are occasionally seen in the parenchyma. Synaptic vesicles are mainly of the clear-cored type but large dense-cored vesicles are commonly observed in some axon terminals.

Animals↗

PubMed1977

The area postrema and control of arterial blood pressure; absence of hypertension after excision of the area postrema in rats.

Acute surgical excision of the area postrema (AP) in the rat failed to affect arterial blood pressure or heart rate. The was no effect on cardiovascular reflex responses during diving or on the heart rate responses to acute decreases or increases of blood pressure caused by bradykinin or angiotensin, respectively. Electrolytic lesions of the AP in acute experiments caused variable damage to the nucleus tractus solitarii (NTS). In these rats large variations in blood pressure occurred. Excision of the AP in a chronic experiment failed to change blood pressure, heart rate, water intake or plasma renin activity. In contrast, bilateral electrolytic lesions of the NTS at the level of the AP caused a severe acute hypertension and completely blocked cardiovascular reflex responses. Hypertension also existed in rats with NTS lesions studied for a longer period of time. There experiments failed to confirm the hypothesis that the AP exerts a tonic inhibitory control of basal blood pressure. Hypertension previously reported after ablation of the AP may be explained by damage to the NTS.

Acute Disease↗

PubMed1984

Effects of dose and of partial body ionizing radiation on taste aversion learning in rats with lesions of the area postrema.

The effect of area postrema lesions on the acquisition of a conditioned taste aversion following partial body exposure to ionizing radiation was investigated in rats exposed to head-only irradiation at 100, 200 and 300 rad or to body-only irradiation at 100 and 200 rad. Following head-only irradiation area postrema lesions produced a significant attenuation of the radiation-induced taste aversion at all dose levels, although the rats still showed a significant reduction in sucrose preference. Following body-only exposure, area postrema lesions completely disrupted the acquisition of the conditioned taste aversion. The results are interpreted as indicating that: (a) the acquisition of a conditioned taste aversion following body-only exposure is mediated by the area postrema; and (b) taste aversion learning following radiation exposure to the head-only is mediated by both the area postrema and a mechanism which is independent of the area postrema.

Animals↗

PubMed1989

Microcirculation of the area postrema. Permeability and vascular responses.

The area postrema is a circumventricular organ that plays an important role in neurohumoral regulation of the circulation. We have developed a method to examine permeability and vascular responses of the microcirculation of the area postrema in vivo. A craniotomy was performed over the dorsal brain stem in anesthetized rats, and blood vessels to the area postrema were visualized with fluorescein microscopy. Extravasation of sodium fluorescein (MW, 386), but not 150 kDa (MW) fluorescein isothiocyanate-dextran, occurred in the area postrema under control conditions. There was no extravasation of fluorescein or dextran in the brain stem under control conditions. Acute hypertension produced marked disruption of the barrier to 150 kDa dextran in the area postrema, compared with minimal disruption in the brain stem. We tested the hypothesis that the area postrema has greater permeability to small molecules than the brain stem and that this permeability might be accompanied by distinctive vascular responses. Topical suffusion of adenosine and ADP produced similar dose-related dilation of arterioles to area postrema and dorsal brain stem. Topical and intravenous vasopressin produced similar dose-related constriction of vessels to area postrema and brain stem. Electron microscopy in rats demonstrated that a barrier to horseradish peroxidase, which is absent in capillaries in the area postrema, is present in arterioles that supply the area postrema.(ABSTRACT TRUNCATED AT 250 WORDS)

Acute Disease↗

PubMed1986

Conditioned taste aversions and changes in motor activity in lithium-treated rats. Mediating role of the area postrema.

The role of the area postrema in mediating taste aversions conditioned with the administration of lithium was examined in experiment 1. Rats with lesions of the area postrema or with sham lesions were given pairings of a novel taste with either intraperitoneally or intragastrically administered lithium chloride (LiCl; 10 mg/kg of a 0.15 M solution of lithium chloride) or a similar concentration of NaCl (control groups). Sham-lesioned rats exhibited strong taste aversions when lithium was used for the conditioning procedure and given intraperitoneally or intragastrically (P less than 0.01). Rats with lesions of the area postrema failed to develop taste aversions after the administration of lithium by either route. In experiment 2, rats with lesions of the area postrema and rats with sham lesions were given 30 min access to a 0.12 M solution of NaCl and 2 days later to a 0.12 M solution of lithium. The sham-lesioned animals drank less lithium than NaCl (P less than 0.02) and exhibited depressions in levels of activity following the ingestion of lithium. Rats with lesions of the area postrema drank more lithium than the sham-lesioned rats (P less than 0.01) and did not show behavioral depression after the ingestion of lithium. These data suggest that in the absence of the chemically-sensitive area postrema intragastrically administered lithium does not produce conditioned taste aversions or depression of activity in rats.

Animals↗

PubMed1976

[Light and electron-cytochemical analysis of acetylcholin-positive esterase-structures in the area postrema and subpostrema in rats].

Localization of acetylcholinesterase (AChE) in the area postrema and area subpostrema of the rat was investigated by light- and electronmicroscopic histochemical methods. AChE-positive small cells probably identical with parenchyma cells are spread evenly in the area postrema. Since axosomatic synapses and axons could not be identified, the neuronal character of these cells could not be unequivocally proved. AChE-positive suggests, however that the parenchyma cells of the area postrema of the rat are more closely related to neurons than to glial cells. Capillaries possessing fenestrated endothelium of the area postrema and various types of glial cells do not exert any AChE-positivity. The area postrema is surrounded by a meshwork of AChE-positive capillaries, constituting the area subpostrema. Since we found no signs of AChE synthesis in the endothelial cells of these capillaries, the possibility of dendritic secretion as the source of AChE activity of the basement membrane and pinocytotic vesicles, cannot be excluded. On the basis of the results it seems possible that the AChE activity is related to the specific structure of the basement membrane; participation of enzyme activity in the presumed function of the area postrema and area subpostrema is suggested.

Acetylcholinesterase↗

PubMed2003

Adrenomedullin influences dissociated rat area postrema neurons.

The area postrema (AP) is one of a specialized group of central nervous system (CNS) structures devoid of a significant blood-brain barrier (BBB), collectively known as the circumventricular organs (CVO). While peptides are normally excluded from access to most regions of the CNS, the AP contains neurons with a high density of receptors for many circulating peptides, very likely including those for adrenomedullin (AM). In this study, whole-cell patch-clamp recordings were obtained from 114 dissociated rat AP neurons. The mean resting membrane potential (RMP) of these neurons (n=79) was -54.3+/-0.8 mV, the mean input resistance (IR) was 3.1+/-0.2 GOmega and the spike amplitude of neurons included in this study was always greater than 90 mV. Current-clamp studies showed that bath application of AM depolarized 39.2% (31 of 79) and hyperpolarized 45.6% (36 of 79) of neurons tested. Both effects were found to be concentration dependent from 10(-12) to 10(-7) M. These data support the idea that specific populations of CNS neurons within the AP are directly influenced by AM and support the concept that AM may act at AP to influence central autonomic control. We also examined the roles of specific ion channels in regulating the AM-induced excitability of AP neurons through voltage-clamp studies. These experiments suggest potential actions of AM in modulating voltage gated calcium channels, effects which have the additional consequence of inhibiting calcium activated potassium conductances (I(K(Ca))). These data demonstrate direct effects of AM on dissociated AP neurons and identify ion channels, the modulation of which, may underlie these effects.

Adrenomedullin↗

PubMed1983

Organization of the projections of a circumventricular organ: the area postrema in the rat.

The projections of the rat area postrema were analysed using anterograde and retrograde axonal transport techniques. Discrete injections of wheat germ agglutinin conjugated to horseradish peroxidase (WGA-HRP) into the area postrema produced anterograde labeling in specific medullary and pontine nuclei. In the medulla, anterograde labeling was present in the internal solitary zone and dorsal division of the medial solitary nucleus, both of which also contained a small number of retrogradely labeled perikarya. Prominent projections to the dorsal motor nucleus of the vagus were seen only if the WGA-HRP injections in the area postrema invaded dorsal solitary nuclei. In the pons, anterograde labeling was present in the parabrachial nuclei, the dorsolateral tegmental nucleus, and the pericentral division of the dorsal tegmental nucleus. By far the major pontine projection was to the dorsolateral region of the middle one-third of the rostrocaudal extent of the parabrachial nuclei. Retrograde fluorescent tracing studies indicated that most area postrema neurons take part in this parabrachial projection. The area postrema projection to the parabrachial nuclei was bilaterally distributed, whereas that from the dorsal solitary nuclei was primarily ipsilateral. The external solitary zone, immediately subadjacent to the area postrema, neither received area postrema projections nor participated in the projections to the parabrachial nuclei. Fluorescent retrograde double labeling studies confirmed the bilateral nature of the area postrema projection to the parabrachial nuclei. In addition, because no doubly labeled neurons were observed it appears that individual area postrema neurons project to either side but not both sides of the dorsal pons. Thus, numerous neuronal pathways exist for the transfer of blood-borne information (that cannot cross the blood-brain barrier) from the area postrema to other brain regions.

Animals↗

PubMed1990

Nicotine-induced conditioned taste aversions are enhanced in rats with lesions of the area postrema.

Lesions, which destroy the area postrema and damage the adjacent nucleus of the solitary tract, attenuate or abolish conditioned taste aversions (CTA) induced by a variety of pharmacological agents. In the present experiment 2 groups of male rats received lesions of the area postrema and 2 groups were given sham lesions. One lesioned group and one sham-lesioned group were twice conditioned with 30-min access to a novel 0.15% saccharin solution followed by injection of nicotine (1 mg/kg, IP). The other 2 groups were similarly conditioned with saccharin followed by saline injections. In subsequent two-bottle choice tests (saccharin vs. water), the saline-injected rats exhibited strong preferences for saccharin, the sham-lesioned rats injected with nicotine showed a weak but significant (p less than 0.05) aversion to saccharin, and the area postrema-lesioned rats injected with nicotine displayed a significantly (p less than 0.05) stronger CTA than the drug-injected sham-lesioned animals. In Phase 2 all rats were given novel chocolate metrecal (30 min) followed by injection of scopolamine HCl (1 mg/kg, IP). The area postrema-lesioned rats showed significant (p less than 0.01) preference for the chocolate taste relative to the aversions shown by the sham-lesioned animals. Thus, area postrema lesions attenuated a scopolamine-induced CTA, but enhanced a nicotine-induced aversion. These results suggest that nicotine and scopolamine act at different neural sites in producing CTAs.

Animals↗

PubMed1984

Amines and other transmitter-like compounds in the bovine area postrema.

The bovine area postrema (AP) was examined for the presence of monoamines and other neuroactive substances which might act as neurotransmitters in the nucleus. High performance liquid chromatography indicated the occurrence of noradrenaline, adrenaline, dopamine and serotonin within the AP. Thin layer chromatography of dansylated derivatives of the AP revealed the presence of gamma amino butyric acid (GABA), glycine, glutamate and aspartate. Finally, direct immunofluorescence histochemistry localised substance P-like and serotonin-like immunoreactivity within neuronal fibres and varicosities in the AP and in the subjacent nucleus tractus solitarius. Dopamine-beta-hydroxylase-like immunoreactivity was found in neuronal perikarya throughout the AP, nucleus tractus solitarius and dorsal motor nucleus of the vagus. These studies provide evidence that dopamine, serotonin, noradrenaline and GABA may all act as neurotransmitters in the bovine AP.

Animals↗

PubMed1981

Detection of dopamine receptors in the area postrema.

[3H]Spiroperidol labeled dog area postrema membranes with high affinity (KD, 0.1 nM) and stereospecificity. The displacement of the radioligand by different dopamine agonists and antagonists indicated that the labeled sites were dopaminergic in nature. Guanine nucleotides decreased agonist affinity for the labeled sites without affecting the affinity for antagonists. Adenylate cyclase in the area postrema was stimulated by guanine nucleotides and sodium fluoride but not by dopamine. The results suggest that the dopamine receptor in the area postrema can be classified as D2-type receptors.

Adenylyl Cyclases↗