The localisation of the extraneuronal monoamine transporter (EMT) in rat brain

The extraneuronal monoamine transporter plays an important role in the inactivation of monoamine transmitters. A basal extraneuronal tissue expression of this transporter has been reported, but it is also expressed in CNS glia. As little is known about the expression pattern and the function of the extraneuronal monoamine transporter in the brain, we performed a detailed investigation. Firstly, a northern blot analysis of different rat organs revealed that the transporter is strongly expressed in placenta, lung and heart and less prominently in the whole brain, brain stem, intestine, testis, epididymis, stomach, kidney and skeletal muscle. It was not expressed in cerebellum, liver and embryo. Using an in situ hybridization to the rat brain, we detected a marked and highly confined expression of the extraneuronal monoamine transporter in the area postrema, but in no other brain areas. These findings were confirmed by polyclonal antibodies against rat extraneuronal monoamine transporter showing an intensive signal in the area postrema, although a few cells in the cerebellum and the brain stem also showed a signal. Additionally, a partly overlapping expression pattern of the monoamine oxidase-B was detected. Summarizing, we firstly describe a marked and highly confined expression of the extraneuronal monoamine transporter in the rat area postrema by in situ hybridisation which may play a role in physiological functions of this circumventricular organ such as emesis, food intake and the regulation of cardiovascular functions.     

Aquaporin-1 in blood vessels of rat circumventricular organs

Although the water channel protein aquaporin-1 (AQP1) is widely observed outside the rat brain in continuous, but not fenestrated, vascular endothelia, it has not previously been observed in any endothelia within the normal rat brain and only to a limited extent in the human brain. In this immunohistochemical study of rat brain, AQP1 has also been found in microvessel endothelia, probably of the fenestrated type, in all circumventricular organs (except the subcommissural organ and the vascular organ of the lamina terminalis): in the median eminence, pineal, subfornical organ, area postrema and choroid plexus. The majority of microvessels in the median eminence, pineal and choroid plexus, known to be exclusively fenestrated, are shown to be AQP1-immunoreactive. In the subfornical organ and area postrema in which many, but not all, microvessels are fenestrated, not all microvessels are AQP1-immunoreactive. In the AQP1-immunoreactive microvessels, the AQP1 probably facilitates water movement between blood and interstitium as one component of the normal fluxes that occur in these specialised sensory and secretory areas. AQP1-immunoreactive endothelia have also been seen in a small population of blood vessels in the cerebral parenchyma outside the circumventricular organs, similar to other observations in human brain. The proposed development of AQP1 modulators to treat various brain pathologies in which AQP1 plays a deleterious role will necessitate further work to determine the effect of such modulators on the normal function of the circumventricular organs.     

生长抑素的生理作用及其与哺乳动物冬眠启动的关系

生长抑素(somatostatin, SS)是一种具有抑制性作用的脑肠肽,在哺乳动物的中枢神经系统及消化系统中广泛分布,具有抑制多种垂体激素的分泌、维持胃肠道功能等重要作用。冬眠是一种低体温和低代谢状态,以全身多器官功能暂时"休止"为特征,依据生长抑素特殊的"刹车"作用,推测其与冬眠启动过程相关。本文综述了生长抑素的生理作用及其与哺乳动物冬眠启动的关系。     

Neural mechanisms of emesis

Emesis is a reflex, developed to different degrees in different species, that allows an animal to rid itself of ingested toxins or poisons. The reflex can be elicited either by direct neuronal connections from visceral afferent fibers, especially those from the gastrointestinal tract, or from humoral factors. Emesis from humoral factors depends on the integrity of the area postrema; neurons in the area postrema have excitatory receptors for emetic agents. Emesis from gastrointestinal afferents does not depend on the area postrema, but probably the reflex is triggered by projections to some part of the nucleus tractus solitarius. As with a variety of other complex motor functions regulated by the brain stem, it is likely that the sequence of muscle excitation and inhibition is controlled by a central pattern generator located in the nucleus tractus solitarius, and that information from humoral factors via the area postrema and visceral afferents via the vagus nerve converge at this point. This central pattern generator, like those for motor functions such as swallowing, presumably projects to the various motor nuclei, perhaps through interneuronal pathways, to elicit the sequential excitation and inhibition that controls the reflex.     

The origin of the vomiting response: a neuroanatomical hypothesis

The connections of area postrema include a set of nuclei with a common topographical location immediately deep to the ependyma or pia mater. These nuclei are all within two principal synapses of the area postrema and can be reached by more than one route from it. There is direct evidence that, like the area postrema, a number of these nuclei participate in vomiting. It is suggested that the paraventricular system may act as a distributed pattern generator for the several processes known to be integrated in the emetic response. It is also suggested that the other functions of the paraventricular nuclei, mainly homeostatic in mammals, have all evolved from a prototypical behaviour pattern of escape from, and subsequent avoidance of, noxious stimuli. Thus, through this system of nuclei, blood pressure, respiration, gastrointestinal motility and secretion, fluid and electrolyte balance, and the ingestion of food may all be influenced by noxious situations.     

History and status of the area postrema

The history of morphological and functional studies on the area postrema (AP) is traced for significant landmarks from 1896, when its name was conferred by Retzius, to 1960 when the foundation of inquiry had become firmly set. A comparative anatomical survey of the medulla oblongata identifies the AP in mammals and birds but not in amphibians and lower phyla even though other members of the so-called circumventricular organ system are represented in the more ancient creatures. Existence of the AP in reptiles is insufficiently documented. The transition from water- to land-dwelling animal life affords propitious neural remodeling for the emergence of the AP in evolving species. No vital role is known to be served by the AP. Nonetheless, its physical interposition between the blood and cerebrospinal fluid and its shared functions with the nucleus tractus solitarii indicate a capability for widespread somatovisceral influence in response to particular perturbations. It is suggested that the diverse systemic expressions of postremal activation are encompassed in the general syndrome of nausea and vomiting.     

Immumochemical and immunocytochemial characterization of a novel monoclonal antibody recognizing a 140 kDa protein in cerebral pericytes of the rat

Summary A monoclonal antibody that recognizes a 140 kDa peripheral plasma membrane protein in pericytes of nervous tissues of the rat is described. Microvessels of brain cortex and perineurium of peripheral nerves are shown to react positively to this antibody. The antigen is absent in brain regions that lack a blood-brain barrier, i.e., choroid plexuses and area postrema. Antigen expression starts as early as day 18 of embryonic development. By means of immuno-electron microscopy the 140 kDa antigen was detected as clusters along the entire circumference of cerebral pericytes. The same antigenic determinant is also expressed in apical domains of plasma membranes of a variety of transporting epithelia, such as hepatocytes, enterocytes of the small intestine, and epithelial cells of proximal tubules of the kidney. We postulate the 140 kDa protein as being a constituent of the pericytes involved in regulative functions of the blood-brain barrier.     

Receptor sites for atrial natriuretic factors in brain and associated structures: an overview

1. Recent data have clearly shown the existence of specific receptor binding sites for atrial natriuretic factors (ANF) or polypeptides in mammalian brain tissues. 2. Ligand selectivity pattern and coupling to cGMP production suggest that brain ANF sites are similar to high-affinity/low-capacity sites found in various peripheral tissues (kidney, adrenal gland, blood vessels). These brain ANF sites possibly are of the B-ANP subtype. 3. High densities of ANF binding sites are found especially in areas of the central nervous system associated with the control of various cardiovascular parameters (such as the subfornical organ and area postrema). However, high densities of sites are also present in other regions such as the hippocampus, cerebellum, and thalamus in the brain of certain mammalian species, suggesting that brain ANF could act as a neuromodulator of noncardiovascular functions. 4. The density of brain ANF binding sites is modified in certain animal models of cardiovascular disorders and during postnatal ontogeny, demonstrating the plasticity of these sites in the central nervous system (CNS). 5. Specific ANF binding sites are also found in various other CNS-associated tissues such as the eye, pituitary gland, and adrenal medulla. In these tissues ANF appears to act as a modulator of fluid production and hormone release. 6. Thus, ANF-like peptides and ANF receptor sites are present in brain and various peripheral tissues, demonstrating the existence of a family of brain/heart peptides.     

Atrial natriuretic factor (ANF) binding sites in brain and related structures

Visualization of [¹²⁵I]ANF binding sites in rat brain by an autoradiographic technique demonstrated that these sites are highly localized in areas such as the olfactory bulb, subfornical organ, area postrema and nucleus tractus solitarius. This distribution suggests that certain cardiovascular effects of ANF could be centrally mediated and that the existence of brain ANF-related peptides should be considered. Finally, moderate densities of [¹²⁵I]ANF binding sites are found in the rat and guinea pig eye while low densities are seen in pituitary and pineal gland.     

Comparative genomics using fugu: a tool for the identification of conserved vertebrate cis-regulatory elements

With the imminent completion of the whole genome sequence of humans, increasing attention is being focused on the annotation of cis-regulatory elements in the human genome. Comparative genomics approaches based on evolutionary conservation have proved useful in the detection of conserved cis-regulatory elements. The pufferfish, Fugu rubripes, is an attractive vertebrate model for comparative genomics, by virtue of its compact genome and maximal phylogenetic distance from mammals. Fugu has lost a large proportion of nonessential DNA, and retained single orthologs for many duplicate genes that arose in the fish lineage. Non-coding sequences conserved between fugu and mammals have been shown to be functional cis-regulatory elements. Thus, fugu is a model fish genome of choice for discovering evolutionarily conserved regulatory elements in the human genome. Such evolutionarily conserved elements are likely to be shared by all vertebrates, and related to regulatory interactions fundamental to all vertebrates. The functions of these conserved vertebrate elements can be rapidly assayed in mammalian cell lines or in transgenic systems such as zebrafish/medaka and Xenopus, followed by validation of crucial elements in transgenic rodents.     

Effects of glutamate-induced excitotoxicity on calretinin-expressing neuron populations in the area postrema of the rat

We mapped the distribution of calretinin-immunoreactive neuron populations in a circumventricular organ of the rat, the area postrema, and investigated their sensitivity to excitotoxic stimuli mediated by subcutaneously administered monosodium glutamate. We were specifically interested to ascertain whether the presence of calretinin can, per se, confer an in vivo intrinsic resistance for area postrema neurons to glutamate excitotoxicity. We found that dense populations of calretinin-positive neurons displayed a subregional compartmentation in coronal sections of the area postrema along its rostrocaudal axis. We demonstrated that calretinin-positive neurons differ in their sensitivities to monosodium glutamate depending on their position within the area postrema. Neurons in the caudal area postrema were the most sensitive ones, while those in the rostral area postrema were spared of degeneration. We conclude that calretinin-positive neurons in the area postrema are not uniformly protected against glutamate excitotoxicity. It is possible that differences in the local concentrations of monosodium glutamate due to regional heterogeneities in density and permeability of the capillary bed rather than neuronal expression of calretinin account for the observed effects.     

Die arterielle und venöse Versorgung der Area postrema der Ratte

Zusammenfassung Eine Methode zur Darstellung von Hirngefäßen nach vorhergehender Perfusionsfixierung wird beschrieben.Die Blutversorgung der Area postrema erfolgt aus einem arteriellen Halbring, der um das caudale Ende der Rautengrube zieht. Der Halbring wird hauptsächlich aus Zweigen der Aa. cerebelli inff. antt. und der Aa. spinales postt. gespeist. Er stellt ein erstes arterielles Verteilersystem dar. Das zweite System umfaßt die Area postrema unmittelbar (Schenkelarterien und Transversalarterien). An seiner Bildung nehmen die Rami dorsales arteriae vertebralis teil. Als ein drittes Verteilersystem auf Arteriolen- und Kapillarebene kann man das intrapiale Netzwerk ansehen.Die venösen Gefäße entsprechen weitgehend den arteriellen. Im Unterschied zu den Arterien kommunizieren die Venen beider Seiten nicht miteinander, ihre Ursprungsgebiete überschneiden sich kaum. Lediglich dem arteriellen Halbring entspricht der Semicirculus der Gabelvenen.Verbindungen der Area postrema mit ihren Nachbargebieten bestehen auf der Ebene größerer Gefäße nicht. Kapilläre Beziehungen, besonders zum Plexus chorioideus, kommen vor.Die Kapillaren bilden in der Area postrema ein dichtes Gefäßnetz, z.T. sind Venolen sinusartig erweitert. Kleine Gefäße werden oft von weiten perivasculären Räumen umgeben. Gegen den extra- und intraventriculären Rand der Area postrema nehmen die Kapillarschlingen an Zahl zu.Die funktionelle Bedeutung der Area postrema aus der Sicht ihrer Gefäßversorgung und ihres Kapillaraufbaus wird diskutiert.

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The arterial and venous supply of the area postrema in the rat

Summary A method to demonstrate cerebral vessels with an injected gelatine ink mixture is described.The area postrema is supplied with blood from an arterial semicircle surrounding the caudal end of the fossa rhomboidea. The semicircle in its turn is maintained mainly by branches from the arteriae cerebellares inff. antt. and the arteriae spinales postt. and represents a first arterial system of blood distribution. A second system encloses the area postrema directly, in the formation of which the rami dorsales arteriae vertebralis have their share. The arterioles and capillaries of the intrapial network can be regarded as a third system of distribution.The venous system corresponds largely to the arterial one. In contrast to the arteries, however, the veins of both sides do not communicate and their sources of origin do not overlap significantly. Only the venous semicircle is in accordance with the arterial one.Except for capillary communications in particular with the choroid plexus, there are no vascular connections between the area postrema and its adjoining regions of the brain. The capillaries of the area postrema form a dense network. The venoles are partly enlarged to sinuses. The small vessels are often surrounded by wide perivascular spaces. In the extra and intraventricular surface of the area postrema the capillary loops increase in number.The functional significance of the area postrema is discussed under the aspect of its supply with vessels and the arrangement of its capillaries.

     

Mast cells in the human brain

Mast cells, as adjudged by the metachromatic staining of their cytoplasmic granules, were found in 79% of the 97 humans brains studied. They were most numerous and most consistently present in the infundibulum, pineal organ, area postrema and choroid plexuses. They were also numerous in the leptomeninges surrounmding the pineal organ and infundibulum. Occasional mast cells were also seen within the supraoptic crest, the subfornical organ, the ventricles and the leptomeninges at sites other than over the infundibulum and pineal organ. They were not detectable elsewhere in the brain or spinal cord. In the infundibulum, pineal organ, area postrema and telencephalic choroid plexuses mast cells were most numerous in young individuals (i.e., 0-19 years of age); thereafter, their numbers progressively decreased with aging. Elsewhere mast cell numbers remained about the same with aging. Except in the area postrema where mast cells were more numerous and more consistently present in males, sex-related differences in mast cell number or distribution were not detected. No differences in either the abundance, the distribution or the percentage of individuals possessing mast cells at any of these sites were apparent between 'normative' brains, lesioned brains ('stroke', lobotomy, etc.) or those from individuals with either congenital or acquired encephalopathies.     

Evolution of proteins of macroglobulin family

The first representatives of proteins of the macroglobulin family appeared 500–700 million years ago. At present representatives of this family have been revealed in crustaceans, molluscs, fish, amphibians, reptiles, ticks, insects, birds, and mammals, the macroglobulin family in blood of some species being represented simultaneously by several proteins that have different molecular weight and partly duplicate functions of each other. In different species, they are present as monomers, dimers, or tetramers. The distinguishing feature of each protein subunit is the presence of a “trap” with cyclic thioether on the bottom and of a sufficiently large hydrophobic area. All representatives are able to form complexes with different regulatory substances through covalent or hydrophobic bonds, which allows them to perform a wide range of regulatory functions. The ancient origin, evolutionary conservatism, widespread presence, and a diversity of regulatory functions permit proteins of the macroglobulin family to be considered as the main regulatory biomolecules of organism fluid media.     

Different vascular permeability between the sensory and secretory circumventricular organs of adult mouse brain

The blood-brain barrier (BBB) prevents free access of circulating molecules to the brain and maintains a specialized brain environment to protect the brain from blood-derived bioactive and toxic molecules; however, the circumventricular organs (CVOs) have fenestrated vasculature. The fenestrated vasculature in the sensory CVOs, including the organum vasculosum of lamina terminalis (OVLT), subfornical organ (SFO) and area postrema (AP), allows neurons and astrocytes to sense a variety of plasma molecules and convey their information into other brain regions and the vasculature in the secretory CVOs, including median eminence (ME) and neurohypophysis (NH), permits neuronal terminals to secrete many peptides into the blood stream. The present study showed that vascular permeability of low-molecular-mass tracers such as fluorescein isothiocyanate (FITC) and Evans Blue was higher in the secretory CVOs and kidney as compared with that in the sensory CVOs. On the other hand, vascular permeability of high-molecular-mass tracers such as FITC-labeled bovine serum albumin and Dextran 70,000 was lower in the CVOs as compared with that in the kidney. Prominent vascular permeability of low- and high-molecular-mass tracers was also observed in the arcuate nucleus. These data demonstrate that vascular permeability for low-molecular-mass molecules is higher in the secretory CVOs as compared with that in the sensory CVOs, possibly for large secretion of peptides to the blood stream. Moreover, vascular permeability for high-molecular-mass tracers in the CVOs is smaller than that of the kidney, indicating that the CVOs are not totally without a BBB.     

Neuropeptide Y receptors in rat brain: autoradiographic localization

Neuropeptide Y (NPY) receptor binding sites have been characterized in rat brain using both membrane preparations and receptor autoradiography. Radiolabelled NPY binds with high affinity and specificity to an apparent single class of sites in rat brain membrane preparations. The ligand selectivity pattern reveals strong similarities between central and peripheral NPY receptors. NPY receptors are discretely distributed in rat brain with high densities found in the olfactory bulb, superficial layers of the cortex, ventral hippocampus, lateral septum, various thalamic nuclei and area postrema. The presence of high densities of NPY and NPY receptors in such areas suggests that NPY could serve important functions as a major neurotransmitter/neuromodulator in the central nervous system.     

Fine structure of synaptic contacts in the first order giant fibre system of the squid

Summary Scanning electron microscopy and the penetration of horseradish peroxidase, especially from the ventricular surface, has been utilized to determine the distinctive properties of the posterior portion of the area postrema. This part of the organ is characterized by a non-ciliated surface composed of flattened cells, which appear less permeable to cisternally injected peroxidase than the ciliated ependymal cells covering the anterior part of the area postrema. However, more diffuse and rapid penetration of peroxidase into the posterior region is achieved by way of the perivascular spaces which appear in direct communication with the CSF. No such filling is noted in the anterior area postrema. The posterior portion also contains cells which appear to be rapidly penetrated by horseradish peroxidase and which may be important as a sensing mechanism. The chief distinction of the anterior part of the area postrema appears to be the presence of vascular connections with the choroid plexus.This work has been supported in part by Grant NB08549-02 from the National Institute of Neurological Diseases and Stroke and Health Science Advancement Award F-304-FR06115.     

Autonomic and neuroendocrine actions of adrenomedullin in the brain: mechanisms for homeostasis

In addition to its role as a potent vasodilator, adrenomedullin (ADM) affects an animal's physiological status through its effects in the brain. We have shown that circulating ADM activates neurons, including nitric oxide (NO)-producing neurons, in autonomic centers of the brain such as the hypothalamic paraventricular nucleus (PVN). Systemic ADM gains access to the brain through the area postrema (AP), a brainstem circumventricular organ, and the PVN is a major target of these ADM-sensitive AP neurons. Neurons expressing the preproADM (ppADM) gene are distributed throughout the brain, with high levels in autonomic centers. Lipopolysaccharide (LPS, immune stress), restraint (psychological stress), and 24 h dehydration all down-regulate ppADM gene expression in different subsets of autonomic centers. Receptor-activity-modifying protein (RAMP) 2 and RAMP3, ADM receptor subunits, are expressed in autonomic centers including the PVN and supraoptic nucleus. Intracerebroventricular injections of ADM increase arterial pressure, heart rate, tyrosine hydroxylase mRNA levels in the locus coeruleus, plasma levels of ACTH, and NO production in the hypothalamus. ADM excites putative GABAergic and cholinergic neurons in dissociated cells from a basal forebrain integrative center, the diagonal band of Broca. These results demonstrate that the signalling components necessary for ADM to influence physiological systems are present in the brain and that ADM is an important transmitter of brain autonomic pathways which are involved in regulating homeostatic balance.     

Sorting food from stones: the vagal taste system in Goldfish, Carassius auratus

The sense of taste, although a relatively undistinguished sensory modality in most mammals, is a highly developed sense in many fishes, e.g., catfish, gadids, and carps including goldfish. In these species, the amount of neural tissue devoted to this modality may approach 20% of the entire brain mass, reflecting an enormous number of taste buds scattered across the external surface of the animal as well as within the oral cavity. The primary sensory nuclei for taste form a longitudinal column of nuclei along the dorsomedial surface of the medulla. Within this column of gustatory nuclei, the sensory system is represented as a fine-grain somatotopic map, with external body parts being represented rostrally within the column, and oropharyngeal surfaces being represented caudally. Goldfish have a specialization of the oral cavity, the palatal organ, which enables them to sort food particles from particulate substrate material such as gravel. The palatal organ taste information reaches the large, vagal lobe with a complex laminar and columnar organization. This lobe also supports a radially-organized reflex system which activates the musculature of the palatal organ to effect the sorting operation. The stereotyped, laminated structure of this system in goldfish has facilitated studies of the circuitry and neurotransmitter systems underlying the goldfish’s ability to sort food from stones.     

Complex relationships between the pineal organ and the medial habenular nucleus-pretectal region of the mouse as revealed by S-antigen immunocytochemistry

Summary S-antigen-immunoreactive pinealocytes located in the deep portion of the pineal organ of inbred and wild pigmented mice give rise to long, beaded processes penetrating into the habenular and pretectal regions. In addition, the medial habenular nuclei and the pretectal area contain S-antigen-immunoreactive perikarya, which resemble pinealocytes in size, shape and immunoreactivity and are considered as pinealocyte-like epithalamic cells. Immunoblotting techniques reveal that a single protein band of approximately 48 kDa molecular weight accounts for this immunoreactivity. As shown with the use of the electron microscope, the majority of the S-antigen-immunoreactive processes is closely apposed to immunonegative neuronal profiles and perikarya of the habenular and pretectal regions. S-antigen-immunoreactive processes and perikarya of both pinealocytes of the deep pineal organ and pinealocyte-like epithalamic cells may form the postsynaptic element in conventional synapses involving axons provided with clear synaptic vesicles. Thus, certain mammalian pinealocytes may receive and transmit signals via point-to-point connections resembling neuro-neuronal contacts. These results challenge the concept that the mammalian pineal organ exerts its influence exclusively via the release of melatonin into the general circulation. Furthermore, they provide evidence (i) that neuronal circuits not involving the sympathetic system participate in the regulation of pineal functions in mammals, and (ii) that intimate histogenetic and functional relationships exist between the pineal organ and the habenular-pretectal nuclei in mammals.