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B R Hu

Publications and source records attributed to B R Hu.

At least 37 records · Page 2Linked to original sources
PubMed1998

Assembly of proteins to postsynaptic densities after transient cerebral ischemia.

Transient ischemia leads to changes in synaptic efficacy and results in selective neuronal damage during the postischemic phase, although the mechanisms are not fully understood. The protein composition and ultrastructure of postsynaptic densities (PSDs) were studied by using a rat transient ischemic model. We found that a brief ischemic episode induced a marked accumulation in PSDs of the protein assembly ATPases, N-ethylmaleimide-sensitive fusion protein, and heat-shock cognate protein-70 as well as the BDNF receptor (trkB) and protein kinases, as determined by protein microsequencing. The changes in PSD composition were accompanied by a 2.5-fold increase in the yield of PSD protein relative to controls. Biochemical modification of PSDs correlated well with an increase in PSD thickness observed in vivo by electron microscopy. We conclude that a brief ischemic episode modifies the molecular composition and ultrastructure of synapses by assembly of proteins to the postsynaptic density, which may underlie observed changes in synaptic function and selective neuronal damage.

Adenosine Triphosphatases↗
PubMed1997

[Studies on desensitization of GABAB receptor coupled adenylate cyclase].

After preincubation of crude synaptic membranes (P2 membranes) with phorber ester (PMA) or GABAB receptor agonist baclofen (BAL), the rate of inhibition of BAL on basal adenylate cyclase (AC) activity and forskolin-stimulated AC activity significantly reduced (desensitized). This effect of BAL did not change after preincubation with forskolin suggesting that the desensitization mechanism of GABAB receptor coupled AC is related with activation of protein kinase C (PKC), but not with protein kinase A. It was further found that the equilibrium dissociation constant (Kd) of GABAB receptor was increased during desensitization. Our results suggest that PKC activation may cause some structural or conformational changes of GABAB receptor, resulting in an uncoupling from G protein and desensitization of GABAB receptor-coupled AC.

Adenylyl Cyclases↗
PubMed1996

[Expression of c-fos mRNA induced by pressure overload in the left ventricle].

In the present study the effect of pressure overload on the expression of protooncogene c-fos in the left ventricle was investigated in rats with abdominal aorta constriction. It was found that a remarkable expression of c-fos was induced by pressure overload and the expression was greatly attenuated by angiotensin converting enzyme inhibitor captopril. In the pressure overload group the angiotensinogen mRNA level was found increased. The above results suggest that angiotensin II is involved in the expression of c-fos due to pressure overload.

Angiotensin-Converting Enzyme Inhibitors↗
PubMed1996

[A study on the change of myocardial neuropeptide Y release induced by electric stimulation and myocardial ischemia in guinea pig heart].

Electrical stimulation of the left stellate ganglion in guinea pig heart evoked a calcium-dependent, exocytotic release of neuropeptide Y (NPY). Stimulation after 10 min of global ischemia (S2), compared with control period stimulation (S1), had no significant effect on the NPY release. The release of NPY produced by the same stimulation after 20 min of ischemia was inhibited to certain extent (S2/S1: 0.72, P < 0.05), whereas the inhibition of NPY release disappeared after 5 min of reperfusion (with a S2/S1 of 1.01). Ischemia alone, without electric stimulation, did not apparently induce NPY release, suggesting that electrical stimulation may induce a calcium-dependent, exocytotic release of NPY. It is further suggested that the inhibition of NPY release may be produced by some metabolites and the abolishment of the inhibition after reperfusion may be due to washout of the metabolites.

Animals↗
PubMed1996

[Improvement of learning and memory functions by GABAB receptor antagonists in mice].

In one trial passive avoidance response in mice, the effects of gamma-aminobutyric acid (GABA)B receptor agonist baclofen and antagonist CGP35348 and CGP36742 on acquisition, consolidation and retrieval of memory were observed. The results showed that the antagonists could significantly promote the acquisition impairment induced by baclofen, the consolidation impairment induced by baclofen and NaNO2, and the retrieval impairment induced by baclofen and 30% alcohol. These results suggest that the GABAB receptor antagonists may become a novel type of drug for the treatment of Alzheimer's disease.

Animals↗
PubMed1995

Alterations of Ca2+/calmodulin-dependent protein kinase II and its messenger RNA in the rat hippocampus following normo- and hypothermic ischemia.

The change in the subcellular distribution of Ca2+/calmodulin-dependent protein kinase II was studied in the rat hippocampus following normothermic and hypothermic transient cerebral ischemia of 15 min duration. A decrease in immunostaining of Ca2+/calmodulin-dependent protein kinase II was observed at 1 h of reperfusion which persisted until cell death in the CA1 region. In the CA3 and dentate gyrus areas immunostaining recovered at one to three days of reperfusion. The CA2+/calmodulin-dependent protein kinase II was translocated to synaptic junctions during ischemia and reperfusion which could be due to a persistent change in the intracellular calcium ion homeostasis. The expression of the messenger RNA of the alpha-subunit of Ca2+/calmodulin-dependent protein kinase II decreased in the entire hippocampus during reperfusion, and was most marked in the dentate gyrus at 12 h of reperfusion. This decrease could be a feedback downregulation of the mRNA due to increased Ca2+/calmodulin-dependent protein kinase II activation. Intraischemic hypothermia protected against ischemic neuronal damage and attenuated the ischemia-induced decrease of Ca2+/calmodulin-dependent protein kinase II immunostaining in all hippocampal regions. Hypothermia also reduced the translocation of Ca2+/calmodulin-dependent protein kinase II and restored Ca2+/calmodulin-dependent protein kinase II alpha messenger RNA after ischemia. The data suggest that ischemia leads to an aberrant Ca2+/calmodulin-dependent protein kinase II mediated signal transduction in the CA1 region, which is important for the development of delayed neuronal damage. Hypothermia enhances the restoration of the Ca2+/calmodulin-dependent protein kinase II mediated cell signalling.

Animals↗
PubMed1995

Persistent translocation of Ca2+/calmodulin-dependent protein kinase II to synaptic junctions in the vulnerable hippocampal CA1 region following transient ischemia.

The influence of brain ischemia on the subcellular distribution and activity of Ca2+/calmodulin-dependent protein kinase II (CaM kinase II) was studied in various cortical rat brain regions during and after cerebral ischemia. Total CaM kinase II immunoreactivity (IR) and calmodulin binding in the crude synaptosomal fraction of all regions studied increase but decrease in the microsomal and cytosolic fractions, indicative of a translocation of CaM kinase II to synaptosomes. The translocation of CaM kinase II to synaptic junctions occurs but not to synaptic vesicles. The translocation in neocortex and CA3/DG (dentate gyrus) is transient, whereas in the hippocampal CA1 region, it persists for at least 1 day of reperfusion. The Ca2+/calmodulin-dependent activity of CaM kinase II in the subsynaptosomal fractions of neocortex is persistently decreased by up to 85%, despite the increase in CaM kinase II IR. The decrease in activity is more pronounced than the decline in IR, suggesting that CaM kinase II is covalently modified in the postischemic phase. The persistent translocation of CaM kinase II in the vulnerable ischemic CA1 region indicates that a pathological process is sustained in the area after the reperfusion phase and this may be of significance for ischemic brain injury.

Animals↗
PubMed1995

Persistent translocation and inhibition of Ca2+/calmodulin-dependent protein kinase II in the crude synaptosomal fraction of the vulnerable hippocampus following hypoglycemia.

Alterations in the levels and activity of Ca2+/calmodulin-dependent protein kinase II (CaM-kinase II) were studied in the rat hippocampus during and after insulin-induced hypoglycemic coma. A permanent loss of CaM-kinase II immunohistostaining in the neuronal layer begins at 10 min of isoelectricity in the tip of the dentate gyrus and at 30-min isoelectricity in the CA1 region. The reduction in immunohistostaining in the neurites is less pronounced. Immunoreactivity of CaM-kinase II on western blots increases in the crude synaptosomal fractions and decreases in cytosolic fraction, indicative of a translocation of CaM-kinase II. The translocation persists for at least 1 day of recovery after 30 min of isoelectricity in the vulnerable hippocampus (dorsomedial hippocampus) but not in the resistant hippocampus (dorsolateral hippocampus). Calmodulin binding to western blots shows changes similar to the immunoblots. Ca2+/calmodulin-dependent activity of CaM-kinase II in the crude synaptosomal fraction is elevated immediately before isoelectricity and is then inhibited during and after 30 min of isoelectricity, despite the increase of CaM-kinase II immunoreactivity. This was seen in the vulnerable hippocampus. The data indicate that stimulus of translocation and inhibition of CaM-kinase II persist during the recovery phase, preceding neuronal degeneration in the vulnerable hippocampus. This may be of significance for hypoglycemia-induced neuronal death.

Animals↗
PubMed1995

[Angiotensin II induces c-fos and c-myc proto-oncogene expression in the left ventricle].

In the present study, the effects of angiotension II on the expression of protooncogene c-fos and c-myc in the left ventricle were investigated on Langedorff heart preparations. It was observed that angiotensin induced both c-fos and c-myc expression in a dose-dependent manner and the c-fos expression showed an earlier appearance than c-myc. All these induced expressions were blocked by a Angiotensin II receptor antagonist saralasin. The Angiotensin II induced expression of c-fos was also blocked by TTX, but the c-myc gene expression was unaffected.

Angiotensin II↗
PubMed1994

Tyrosine phosphorylation and activation of mitogen-activated protein kinase in the rat brain following transient cerebral ischemia.

Activation of trophic factor receptors stimulates tyrosine phosphorylation on proteins and supports neuronal survival. We report that in the recovery phase following reversible cerebral ischemia, tyrosine phosphorylation increases in the membrane fraction of the resistant hippocampal CA3/dentate gyrus (DG) region, whereas in the sensitive CA1 region or striatum, tyrosine phosphorylation is less marked or decreases. In the cytosolic fractions, a 42-kDa protein, identified as mitogen-activated protein (MAP) kinase, is markedly phosphorylated and activated immediately following ischemia, in particular in CA3/DG, but not in striatum. In the CA1 region, phosphorylation of MAP kinase is less intense and decreases later during reperfusion, which could explain the delay of neuronal degeneration in this structure. The data suggest that in ischemia-resistant neurons the growth factor receptor-coupled signaling cascade is stimulated and, through its effects on DNA transcription and mRNA translation, supports neuronal survival.

Animals↗
PubMed1994

Changes in the tyrosine phosphorylation of mitogen-activated protein kinase in the rat hippocampus during and following severe hypoglycemia.

The changes in the levels of tyrosine-phosphorylated proteins in the cytosolic fraction of the rat hippocampus subjected to severe hypoglycemia were analyzed. A marked increase in tyrosine phosphorylation of a 43-kDa protein was observed at 30 min of isoelectric EEG and 30 min and 1 h of recovery. Immunostaining of the same blot with antibody against mitogen-activated protein (MAP) kinase demonstrated a double band of approximately 42 and 43 kDa. The increased tyrosine phosphorylation of MAP kinase during hypoglycemic coma and the early recovery period suggests that MAP kinase may be involved in neuronal degeneration and repair.

Animals↗
PubMed1993

Postischaemic changes in protein synthesis in the rat brain: effects of hypothermia.

Protein synthesis, measured as [14C]-leucine incorporation into proteins, was studied in the normothermic rat brain following 15 min of transient cerebral ischaemia and 1 h, 24 h and 48 h of recirculation, and in the hypothermic (33 degrees C) brain following 1 h and 48 h of recirculation. Ischaemia was induced by bilateral common carotid occlusion combined with hypotension. Following normothermic ischaemia, incorporation of [14C]-leucine was depressed by 40-80% at 1 h of recirculation in all brain regions studied. At 48 h postischaemia, incorporation returned to normal or above normal levels in the inner layers of neocortex, the CA3 region, the striatum and the dentate gyrus, while in the outer layers of neocortex and in the hippocampal CA1 region the incorporation was persistently decreased by 26% and 40% respectively. At 24 and 48 h postischaemia, protein synthesis in the CA1 region and the striatum could be attributed to proliferating microglia. Intra-ischaemic hypothermia ameliorated the persistent depression of protein synthesis in the CA1 region at 48 h postischaemia, and a two-fold increase compared to the normothermic group was observed both in the CA1 region and the striatum. In the cortex, eucaryotic initiation factor 2 activity transiently decreased at 30 min postischaemia. In animals subjected to intra-ischaemic hypothermia, the eucaryotic initiation factor 2 activity was reduced by 50% of control at 30 min of recirculation compared with 77% in normothermic animals. We conclude that the postischaemic depression of protein synthesis is in part caused by a decrease in eucaryotic initiation factor 2 activity.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1993

Initiation of protein synthesis and heat-shock protein-72 expression in the rat brain following severe insulin-induced hypoglycemia.

Following stress such as heat shock or transient cerebral ischemia, global brain protein synthesis initiation is depressed through modulation of eucaryotic initiation factor (eIF) activities, and modification of ribosomal subunits. Concomitantly, expression of a certain class of mRNA, heat-shock protein (HSP) mRNA, is induced. Here we report that the activity of eucaryotic initiation factor-2 (eIF-2), a protein that participates in the regulation of a rate-limiting initiation step of protein synthesis, transiently decreases following insulin-induced severe hypoglycemia in the rat brain neocortex. Expression of HSP 72, a 72-kDa HSP, in surviving neurons was seen at 1-7 days of recovery following 30 min of hypoglycemic coma, but not at 1 h and 6 h of recovery. In the neocortex, HSP 72 was first seen in layer IV, and later also in surviving neurons in layer II. In the CA1 region and in the crest of dentate gyrus, HSP 72 expression was evident in cells adjacent to irreversibly damaged neurons. In the CA3 region and the hilus of dentate gyrus, HSP 72 was expressed in a few scattered neurons. In septal nucleus, HSP 72 was expressed in a lateral to medial fashion over a period of 1-3 days of recovery. We conclude that severe insulin-induced hypoglycemia induces a stress response in neurons in the recovery phase, including inhibition of protein synthesis initiation, depression of eIF-2 activity, and a delayed and prolonged expression of HSP 72 in surviving neurons. The HSP 72 expression may be a protective response to injurious stress.

Animals↗
PubMed1993

Heat-shock inhibits protein synthesis and eIF-2 activity in cultured cortical neurons.

Stress, such as heat-shock, hypoxia and hypoglycemia, inhibits the initiation of protein synthesis. The effects of heat-shock on protein synthesis, eucaryotic initiation factor 2 (eIF-2) activity, protein kinase C (PKC), and casein kinase II (CKII) activities were studied in primary cortical neuronal cultures. In neurons exposed to heat-shock at 44 degrees C for 20 min, protein synthesis is inhibited by more than 80%, and is accompanied by a 60% decrease in eIF-2 activity. Steady state PKC and CK II activities were not affected by heat-shock. Vanadate (200 microM), a protein phosphotyrosine phosphatase inhibitor, partially prevented the depression of eIF-2 activity during heat-shock, and increased CKII activity by 90%. In contrast, staurosporine (62nM), a protein kinase C inhibitor, did not affect eIF-2 activity. We conclude that heat-shock causes a change in the phosphorylation/dephosphorylation of regulatory proteins leading to a depressed eIF-2 activity and protein synthesis in neurons.

Alkaloids↗
PubMed1993

Changes in tyrosine phosphorylation in neocortex following transient cerebral ischaemia.

Growth factor receptors activate protein tyrosine kinases, which are important for cell growth and survival. The protein tyrosine kinase (PTK) activity and the levels of phosphotyrosine (Ptyr) containing proteins were studied in the rat neocortex exposed to 15 min of transient cerebral ischaemia. The levels of the Ptyr containing proteins increase during recovery in the synaptosomal fraction, while the changes in the light membrane fraction are less marked. Protein tyrosine phosphorylation in the cytosol decreases. The differential changes in the levels of phosphotyrosine proteins in the particulate and cytosolic fractions suggest that the signal cascade from membrane bound receptors through tyrosine phosphorylation in the cytosol may be interrupted following ischaemia. This may be of importance for the development of neuronal damage.

Animals↗