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M K Raizada

Publications and source records attributed to M K Raizada.

At least 73 records · Page 4Linked to original sources
PubMed1996

AT1-receptors and cellular actions of angiotensin II in neuronal cultures of stroke prone-spontaneously hypertensive rat brain.

AT1-receptors, its mRNA and cellular actions of angiotensin II (Ang II) have been compared between neuronal cultures of Wistar Kyoto (WKY) and stroke-prone spontaneously hypertensive (SP-SH) rat brains. Bmax for AT1-receptor binding is 2-fold higher and is associated with a parallel increase in the levels of AT1-receptor mRNA in SP-SH rat brain neurons compared with WKY rat brain neurons. Ang II causes stimulation of both c-fos and norepinephrine transporter (NET) mRNAs in both strains of neurons and this stimulation is also 2-3-fold higher in SP-SH rat brain neurons compared with WKY rat brain neurons. In contrast, Ang II stimulation of PAI-1 mRNA in SP-SH neurons is only 50% that of in WKY rat brain neurons suggesting that SP-SH neurons express a decrease in AT1-receptor coupling with PAI-1 response. These observations demonstrate that SP-SH neurons express AT1-receptor-functions similar to those described for SHR neurons.

Angiotensin II↗
PubMed1996

Regulation of the manganese superoxide dismutase and inducible nitric oxide synthase gene in rat neuronal and glial cells.

Bidirectional communication occurs between neuroendocrine and immune systems through the action of various cytokines. Responses to various inflammatory mediators include increases in intracellular reactive oxygen species (ROS), notably, superoxide anion (O2-) and nitric oxide (NO.). Neurotoxicity mediated by NO. may result from the reaction of NO. with O2, leading to formation of peroxynitrite (ONOO-). ROS are highly toxic, potentially contributing to extensive neuronal damage. We, therefore, evaluated the effects of a variety of inflammatory mediators on the regulation of mRNA levels for manganese superoxide dismutase (MnSOD) and inducible nitric oxide synthase (iNOS) in primary cultures of rat neuronal and glial cells. To determine age-dependent variation of mRNA expression, we used glial cells derived from newborn, 3-, 21-, and 95-day-old rat brains. Interleukin-1 beta, interferon-gamma (IFN-gamma), bacterial lipopolysaccharide (LPS), and tumor necrosis factor-alpha showed significant induction of MnSOD in both glial and neuronal cells. However, only LPS and IFN-gamma increased iNOS mRNA. These data demonstrate that these two genes are similarly regulated in two cells of the nervous system, further suggesting that the oxidative state of a cell may dictate a neurotoxic or neuroprotective outcome.

Aging↗
PubMed1996

Angiotensin II regulation of neuromodulation: downstream signaling mechanism from activation of mitogen-activated protein kinase.

Angiotensin II (Ang II) stimulates expression of tyrosine hydroxylase and norepinephrine transporter genes in brain neurons; however, the signal-transduction mechanism is not clearly defined. This study was conducted to determine the involvement of the mitogen-activated protein (MAP) kinase signaling pathway in Ang II stimulation of these genes. MAP kinase was localized in the perinuclear region of the neuronal soma. Ang II caused activation of MAP kinase and its subsequent translocation from the cytoplasmic to nuclear compartment, both effects being mediated by AT1 receptor subtype. Ang II also stimulated SRE- and AP1-binding activities and fos gene expression and its translocation in a MAP kinase-dependent process. These observations are the first demonstration of a downstream signaling pathway involving MAP kinase in Ang II-mediated neuromodulation in noradrenergic neurons.

Angiotensin II↗
PubMed1996

Lack of cross talk between alpha1-adrenergic and angiotensin type 1 receptors in neurons of spontaneously hypertensive rat brain.

Norepinephrine causes downregulation of angiotensin II (Ang II) receptors in Wistar-Kyoto rat (WKY) brain neuronal cultures. The aim of this study was to compare the cross talk between Ang II and alpha1-adrenergic receptors in these neuronal cultures. Norepinephrine causes a 66 percent decrease in Bmax of Ang II type 1 (AT1) receptors in neuronal cultures of WKY brain. This decrease is mediated by the interaction of norepinephrine with the alpha1a-adrenergic receptor subtype. Norepinephrine also causes a decrease in mRNA levels for AT1 receptors. A maximal decrease of 83 percent in AT1, receptor mRNA is observed in 8 hours with 100 micromol/L norepinephrine, is blocked by 5-methyluradipil, and involves inhibition of AT1 receptor transcription. Furthermore, decreases in the AT1 receptor and its mRNA are associated with a significant attenuation of AT1 receptor-mediated stimulation of norepinephrine transporter mRNA in WKY brain neurons. In contrast, norepinephrine does not decrease AT1 receptors or mRNA and has no effect on Ang II stimulation of norepinephrine transporter mRNA in neuronal cultures of spontaneously hypertensive rat brain. Thus, these data show that norepinephrine-mediated downregulation of AT1 receptors is associated with a parallel decrease in AT1 mRNA and Ang II stimulation of norepinephrine transporter mRNA and involves the alpha1a-adrenergic receptor in neurons of WKY brain. This cross talk between the two receptors is lacking in neurons of spontaneously hypertensive rat brain.

Animals↗
PubMed1996

Regulation of norepinephrine transport system by angiotensin II in neuronal cultures of normotensive and spontaneously hypertensive rat brains.

Brain angiotensin II (Ang II) plays a key role in blood pressure control in part by interacting with catecholamines (CA) and by stimulation of sympathetic pathways. The significance of Ang-CA interaction is further heightened by the presence of a hyperactive brain Ang II system in spontaneously hypertensive (SH) rat, a genetic model for essential hypertension. Neuronal cells in primary culture from the hypothalamus-brainstem that mimic in vivo situations in so far as many cellular actions of Ang II are concerned, have been used in the present study to elucidate Ang II regulation of CA by determining its cellular action on the norepinephrine transporter (NET) system. Ang II causes both acute and chronic stimulation of [3H]-norepinephrine (NE) uptake in neuronal cultures of Wistar Kyoto (WKY) rat brain. Acute stimulation begins as early as 5 min, reaches maximal levels in about 30 min in the presence of 100 nM Ang II, and is blocked by losartan, a specific antagonist for AT1 receptor subtype. In addition, this acute stimulation appears to be a posttranscriptional event and does not involve protein kinase C (PKC) or NET gene transcription. Chronic stimulation of [3H]-NE uptake by Ang II persists throughout the duration of Ang II incubation (24 h), is dose dependent, and is also mediated by AT1 receptor subtype. However, chronic stimulation of [3H]-NE uptake involves PKC, cfos, and NET gene transcription. Ang II also stimulates [3H]-NE uptake in neuronal cultures of SH rat brain, both acutely and chronically, by mechanisms similar to those observed in neuronal cultures of WKY rat brain. The stimulation of NET by Ang II is 2-fold higher than that seen in WKY and is consistent with increased AT1 receptor gene transcription and increased functional AT1 receptors in SH rat brain neurons compared with WKY rat brain neurons. The Ang II stimulation of the NET system is also higher in adult SH compared with WKY rats in vivo. These observations show that 1) Ang II stimulates the NET system both acutely and chronically, the former involving activation of preexisting transporters and the latter involving NET gene transcription and translation; and 2) Ang II stimulation of the NET system is elevated in SH rat brain neurons.

Angiotensin II↗
PubMed1996

Angiotensin II regulation of plasminogen activator inhibitor-1 gene expression in neurons of normotensive and spontaneously hypertensive rat brains.

Neuronal cells in primary culture from the hypothalamus-brain stem areas of normotensive [Wistar-Kyoto (WKY)] and spontaneously hypertensive (SH) rat brains have been used in the present study to investigate an interaction between the brain renin-angiotensin II system and the plasminogen activator system. This is an attempt to further our understanding of the role of brain Ang II in the control of neuronal development and differentiation through its regulation of the extracellular matrix. Ang II caused a 10-fold stimulation of plasminogen activator inhibitor-1 (PAI-1) messenger RNA (mRNA) in WKY rat brain neuronal cultures. The stimulation was mediated by the AT1 receptor subtype and was accompanied by an increase in PAI-1 gene transcription and the synthesis of cellular PAI-1 protein. The stimulation involved activation of protein kinase C, and alterations in the intracellular Ca2+ pool caused a significant inhibition of Ang II stimulation of PAI mRNA. Ang II stimulation of PAI-1 mRNA succeeded its action on c-fos mRNA and was attenuated by c-fos antisense oligonucleotide. Although PAI-1 gene expression was also stimulated by Ang II in neuronal cultures of SH rat brain, two differences between WKY and SH rat brain neurons were observed: 1) the level of Ang II stimulation in SH rat neurons was 50% of that in WKY rat neurons; and 2) Ang II stimulation of c-fos was 2.4-fold higher in SH neurons than in WKY neurons, but c-fos antisense oligonucleotide did not attenuate the stimulatory action of Ang II on PAI-1 mRNA in SH neurons. These observations suggest that the changes in the Ang II-mediated signaling pathways and/or the regulatory region(s) of the PAI-1 gene may contribute to the differential actions of Ang II in WKY and SH rat brain neurons.

Angiotensin II↗
PubMed1996

Angiotensin II regulation of tyrosine hydroxylase gene expression in the neuronal cultures of normotensive and spontaneously hypertensive rats.

In the present study we investigated the regulation of tyrosine hydroxylase (TH) by angiotensin II (Ang II) in an attempt to provide cellular and molecular evidence that this hormone has increased neuromodulatory actions in the spontaneously hypertensive (SH) rat brain. Neuronal cells in primary culture from the hypothalamus-brain stem of both normotensive [Wistar-Kyoto (WKY)] and SH rats have been used. These cultures mimic in vivo situations. Ang II caused a time-dependent increase in TH activity in WKY rat brain neurons. A maximal increase of 2.5-fold was observed with 100 nM Ang II in an actinomycin- and cycloheximide-dependent process. In addition, Ang II caused a parallel increase in TH messenger RNA (mRNA) levels, with a maximal stimulation of 5-fold in 4 h by 100 nM Ang II in WKY rat brain neurons. The stimulation of TH mRNA was mediated by the AT1 receptor subtype, resulted from an increase in its transcription, and involved activation of phospholipase C and protein kinase C. Antisense oligonucleotide for c-fos attenuated Ang II stimulation of TH mRNA in a time- and dose-dependent fashion, indicating an involvement of c-fos as a putative third messenger in Ang II stimulation of TH. Ang II also caused stimulation of TH activity and its mRNA levels in neuronal cultures of SH rat brain by a mechanism similar to that observed for neuronal cultures of WKY rat brain, involving AT1 receptors, protein kinase C, and c-fos. However, the stimulation of TH activity and that of TH mRNA were approximately 30% and 80% higher, respectively, in the SH rat brain neurons than those in the WKY rat brain neurons. In vivo experiments have been carried out to validate the elevated response of TH gene expression to Ang II in SH rat brain neuronal cultures. Ang II stimulated both TH activity and TH mRNA levels in the hypothalami and brain stems of adult WKY and SH rats. The level of stimulation in the brain of the SH rat was significantly higher than that in the WKY rat. These observations are consistent with an increase in AT1, receptor gene expression and suggest that increased TH gene expression could be the cellular/molecular basis for the greater neuromodulatory action of Ang II in the SH rat brain.

Angiotensin II↗
PubMed1996

AT1 receptor density changes during development of hypertension in hyperinsulinemic rats.

In a previous study we showed that the renin-angiotensin system (RAS) plays a role in the etiology of fructose-induced hypertension. To our knowledge, no previous study has evaluated changes in angiotensin II (Ang II) type I receptor (AT1) density in fructose-fed rats that are insulin resistant and hypertensive. The purpose of this study was to determine the changes in plasma Ang II and AT1 density associated with the elevation of blood pressure in fructose-treated rats. Male Sprague-Dawley rats were divided into two groups and were fed either normal rat chow or a 60% fructose-enriched diet for four weeks. Plasma Ang II and serum insulin levels of the fructose-treated rats were significantly elevated (p < 0.01) by the end of the second week of fructose treatment. Plasma Ang II levels of the fructose-fed rats returned to basal levels by the end of the fourth week of dietary treatment, whereas the serum insulin levels consistently remained elevated. Blood pressure was significantly elevated in the fructose-fed rats within two weeks of fructose treatment. Elevation of blood pressure was associated with left ventricular hypertrophy. Furthermore, there was a significant increase in AT1 receptor density in the ventricles and a significant decrease in AT1 receptor density in the aortas of fructose-fed rats at the end of fourth week. There were no significant changes in receptor density in the hypothalami or adrenal glands of fructose-treated rats. These results suggest that chronic fructose treatment activates the renin-angiotensin system, which is manifested by an increase in plasma Ang II, elevation of blood pressure, cardiac hypertrophy, and changes in AT1 receptor density.

Angiotensin II↗
PubMed1995

Delivery of angiotensin II type 1 receptor antisense inhibits angiotensin action in neurons from hypertensive rat brain.

Increased brain angiotensin II (AII) type 1 receptor (AT1R) expression has been implicated in the hyperactive brain angiotensin system and the development and maintenance of hypertension in the genetically spontaneously hypertensive (SH) rat. Neuronal cells in primary culture from the cardioregulatory-relevant brain areas (hypothalamus/brainstem) mimic increased brain AT1R gene expression and AT1R function of the adult SH rat. They have been utilized in the present study to determine whether cellular actions of AII could be regulated by the transfer of AT1R antisense (AT1R-AS) with the use of a retroviral-mediated gene delivery system developed for the central nervous system cultures. AII stimulates norepinephrine (NE) uptake in neuronal cultures of both normotensive (Wistar Kyoto) and SH rat brains. This neuromodulatory action is mediated by the AT1R subtype, is significantly higher in SH neurons, and is associated with a parallel stimulation of mRNAs for c-fos and NE transporter. Infection of neuronal cultures with a retrovirus vector that contains AT1R-AS (LNSV-AT1R-AS) results in an inhibition of AT1R-mediated stimulation of both c-fos and NE transporter mRNA, as well as NE uptake in both strains of rats; however, the inhibition is more pronounced in SH neurons compared with Wistar Kyoto rat brain neurons. The higher sensitivity of the SH rat brain neurons is further supported by our observation that a certain dose of LNSV-AT1R-AS that fails to induce inhibition of cellular actions of AII in WKY neurons causes a significant inhibition of AII actions in SH neurons. These observations show that retrovirally mediated delivery of AT1R-AS could be used to selectively control the actions of AII in primary neuronal cultures from SH rat brain.

Angiotensin II↗
PubMed1995

Retrovirus-mediated transfer of an angiotensin type I receptor (AT1-R) antisense sequence decreases AT1-Rs and angiotensin II action in astroglial and neuronal cells in primary cultures from the brain.

The AT1-R has been implicated in many cellular and physiological actions of angiotensin II (AII) in the brain. A retrovirus vector (LNSV) containing an AT1B-R antisense sequence (AT1B-AS) (termed LNSV-AT1B-AS) was constructed and used to determine the feasibility of using viral-mediated gene transfer to control AT1-Rs and AII actions in astroglial and neuronal cells in primary cultures from rat brain. Briefly, a 1.26-kb antisense sequence corresponding to nt -132 to +1128 of AT1-R cDNA was cloned into the LNSV vector, the vector was transfected into PA317 cells, and transfected cells were selected in G418. Incubation of brain cells with culture medium containing LNSV-AT1B-AS viral particles showed that AT1B-AS was integrated into the genome and transcribed in brain cells. This was associated with a significant decrease in AT1-Rs and in the AII-stimulated increase of c-fos mRNA, a measure of AT1-R function. These observations show that the AT1B-AS gene can be transferred into astroglial cells in culture by LNSV and that such a transfer inhibits AT1-Rs and the AII stimulation of cellular activities. In addition, the usefulness of this approach to study AII-dependent pathophysiology in primary neuronal cultures from brain, in particular, is established.

Angiotensin I↗
PubMed1995

Angiotensin II increases glucose uptake and glucose transporter-1 mRNA levels in astroglia.

In this study, we have investigated the effects of angiotensin II (ANG II) on glucose uptake into astroglia cultured from adult rat hypothalamus and brain stem. ANG II (30 min to 4 h; 10(-9) to 10(-6) M) stimulated time- and concentration-dependent increases in the uptake of 2-deoxy-D-[3H]glucose into cultured astroglia. This effect of ANG II (10(-7) M) is via AT1 receptors and protein kinase C (PKC), since it was inhibited by losartan (10(-6) M) and staurosporine (10(-6) M), respectively. Furthermore, this ANG II action was inhibited by both cycloheximide (1 microgram/ml) and actinomycin D (10(-6) M), indicating that synthesis of new glucose transporters is involved. This was confirmed by the finding that ANG II (30 min to 4 h; 10(-9) to 10(-5) M) stimulated time- and concentration-dependent increases in the steady-state levels of glucose transporter-1 (GLUT-1) mRNA in these cultures. In addition, the increase in steady-state levels of GLUT-1 mRNA elicited by ANG II was mediated by AT1 receptors and PKC. These data suggest that ANG II stimulates glucose uptake into cultured astroglia via a pathway that involves AT1 receptors, PKC, and increased steady-state levels of GLUT-1 mRNA.

Angiotensin II↗
PubMed1994

Peptide receptors in astroglia: focus on angiotensin II and atrial natriuretic peptide.

Astroglial cells derived from the mammalian central nervous system contain a wide variety of peptide receptors, including specific sites for angiotensin II (AII) and atrial natriuretic peptide (ANP). The AII receptors present in these cells are primarily of the AT1 subtype. The ANP receptors present in these cells consist of a mix of ANP-A and ANP-B sites ("biological receptors") and also ANP-C sites ("clearance receptors"). Available evidence indicates that activation of AII receptors results in a stimulation of astroglial proliferation, whereas ANP has an antiproliferative effect in these cells. Intracellular pathways which may mediate these effects of AII and ANP on cell proliferation are discussed, including the presentation of novel data on the activation of protein kinase C and of glucose uptake by AII. We also consider the possibility that the opposing actions of AII and ANP on astroglial proliferation may represent another facet of the mutual antagonism between these two peptides, which has been observed throughout mammalian systems.

Angiotensin II↗
PubMed1994

Receptor-mediated effects of angiotensin II on neurons.

Aside from its well-known and numerous actions at peripheral tissues, the octapeptide angiotensin II (ANG II) elicits specific receptor-mediated effects within the central nervous system. In this review we focus on the receptor-mediated actions of ANG II on neurons. The distribution of ANG II receptors in the brain and physiological, electrophysiological, and cellular effects mediated by these receptors are discussed. This is extended to a review of the characteristics of ANG II receptor subtypes on cultured neurons and the cellular and genomic actions mediated by these receptors. Finally, we develop this information into speculative models for the cellular effects mediated by each ANG II receptor subtype in neurons.

Angiotensin II↗
PubMed1994

Growth factor-induced neurite growth in primary neuronal cultures of dogs with neuronal ceroid lipofuscinosis.

Neuronal ceroid lipofuscinosis (NCL) is a type of lysosomal storage disease resulting in the progressive deterioration of neuronal function. Little is known about the genetics, pathophysiology and biochemical basis of this disease. This is, in part, due to the complexity of the central nervous system and the lack of an in vitro model. In this report, we describe the conditions to establish neuronal cells in primary culture from the brains of newborn English setters with NCL, a canine model for this disease. Over 80% of the neuronal cells from normal dog brain establish well-developed interconnecting networks of long neurites. On the contrary, approximately 50% of the neurons cultured from NCL dog brains do not assemble neurites. Of those NCL neurons with processes, the neurites are routinely shorter and fewer in number than those seen in normal cultures. In addition, the characteristic inclusion bodies, pathological markers for this disease in vivo, are prevalent in the soma of cultured neuronal cells isolated from NCL dog brain. A time-dependent maturation of the inclusion bodies suggests a progression of the disease state in culture. The reduced ability of the NCL neurons to establish neurites prompted us to examine the effects of growth factors on neurite assembly. Our data show that insulin-like growth factor I, epidermal growth factor and platelet-derived growth factor are capable of stimulating neurite outgrowth of NCL neurons. We report the establishment and morphological characterization of neuronal cultures from normal and NCL dog brains. The abnormal morphology of cultured NCL neurons can, in part, be alleviated by supplementing the medium with growth factors. The results suggest that this cellular model of NCL will be useful to study the molecular and physiological mechanisms of NCL disease, as well as to test potential therapeutic agents and candidate genes.

Animals↗
PubMed1994

Regulation of angiotensin II type 1 receptor mRNA in neuronal cultures of normotensive and spontaneously hypertensive rat brains by phorbol esters and forskolin.

Neuronal cells in primary culture from the brains of normotensive, Wistar-Kyoto (WKY) rats and spontaneously hypertensive (SH) rats express angiotensin II type 1 (AT1) receptors. Treatment of WKY rat brain cultures with a phorbol ester, phorbol 12-myristate 13-acetate (PMA), causes a time- and dose-dependent increase in the levels of an approximately 2.3-kb AT1 receptor mRNA transcript. A maximal stimulation of 4.5-fold in the AT1 receptor mRNA transcript level is observed with 200 nM PMA in 4 h and is blocked by 1 microM staurosporine. Forskolin also increases the AT1 receptor mRNA levels in WKY rat brain neurons in a time- and dose-dependent manner, and a 4.5-fold stimulation is achieved with 50 microM forskolin in 4 h. The stimulatory effects of both PMA and forskolin are completely abolished by coincubation of neuronal cultures with 1 microM actinomycin D. In addition, nuclear run-on assay indicated an increase in the transcription of AT1 receptor mRNA in WKY rat brain neurons treated with either PMA or forskolin. Both PMA and forskolin also stimulate levels of AT1 receptor mRNA in neuronal cultures from brain of the SH rat. The degree of stimulation in these cultures is comparable to that in WKY rat brain neurons. These observations show that although the basal AT1 receptor gene expression is significantly higher in SH rat brain neurons compared with WKY rat brain neurons, the protein kinase C- and protein kinase A-responsive stimulation is not altered. These data suggest a possible involvement of protein kinase C and protein kinase A response elements in AT1 receptor gene expression.

Animals↗
PubMed1993

Insulin-like growth factor I receptors and IGF-I actions in neuronal cultures from the brain.

Neurons in primary culture have been used to study IGF-I receptors and IGF-I-induced cellular actions in the brain. Intact neurons in culture specifically bind [125I]IGF with high affinity. The potency for the competition of [125I]IGF-I binding was IGF-I > IGF-II > insulin. A curvilinear Scatchard plot represented high-affinity (0.15 nM) and low-affinity (3 nM) binding sites with a Bmax of 142 fmol and 618 fmol/mg protein, respectively. These binding sites are predominantly localized on neurites with relatively few sites on the cell soma. IGF-I induced synthesis of protein(s) in the M(r) range of 48,000-50,000 with pI values of 6.1-6.4. These observations show that IGF-I receptor mediates induction of specific proteins and suggest that these proteins may be involved in the neurotrophic activity of IGF-I in the brain.

Animals↗
PubMed1993

Immunohistochemical mapping of angiotensin AT1 receptors in the brain.

A new approach to study angiotensin receptor distribution in the brain has been taken by developing antibodies to partial sequence of the angiotensin II (AII) type-1 receptor subtype (AT1) and demonstrating the presence of receptors with immunohistochemical staining. The antibody to a portion of the 3rd cytoplasmic loop of the AT1 receptor revealed distinctive punctate immunoreactive staining on cell bodies. The cell bodies were distributed in the forebrain in paraventricular and supraoptic nuclei, the organum vasculosum lamina terminalis, median preoptic area and subfornical organ. In the brainstem, the entire locus coeruleus was stained, together with the adjacent mesencephalic and motor nuclei of the trigeminal nerve. The auditory system including the cochlear nucleus and superior olivary nuclei were stained. In the medulla, all the structures involved in blood pressure control were stained including the nucleus of the solitary tract, the 12th nerve nuclei, the rostroventral lateral area and the nucleus ambiguous. Sites where AT2 receptors are located were not stained or staining was limited to specific area such as the medial accessory nucleus of the inferior olive. Immunocytochemical staining of AT1 receptors provides a new and more precise approach to the cellular localization of AII receptors.

Amino Acid Sequence↗