Regulation of nestin expression after cortical ablation in adult rat brain

During embryogenesis, transient expression of nestin in proliferating neuroepithelial stem cells signals the commitment of progenitor cells to differentiate. Although adult mammalian brain contains very little nestin, significant upregulation of nestin has been reported following cerebral injury, leading to speculation that nestin may be involved in brain repair. In this study, we assessed the temporal profile of nestin expression following ablation injury of the sensory barrel cortex and investigated the influence of contralateral whisker stimulation on nestin expression. Since the adult mammalian brain contains proliferating neuronal progenitor cells that can be labeled with bromodeoxyuridine (BrdU), we also determined the association of nestin reexpression with BrdU-labeled cells. Nestin reexpression was detected predominantly in the ipsilateral cortex 3 days post-ablation. There was no significant nestin upregulation in the subcortical region. Nestin reexpression was most marked surrounding the lesion, but also extended throughout the entire lateral cortex. Nestin in the ipsilateral cortex subsided by day 7, although perilesional nestin expression was still apparent 28 days post-injury. Western blot analysis of nestin expression 3 days post-ablation confirmed a significant two-fold increase in nestin expression (p<0.05). Double immunofluorescence labeling demonstrated that the majority of nestin expression occurred in astrocytes. We were unable to detect any colocalization with neuronal makers. However, BrdU-labeled cells, which were readily detected in the subventricular zone prior to injury, were readily detected in the perilesional area 3 days post-ablation, concomitant with nestin in this area. Confocal microscopy detected several BrdU-positive cells expressing nestin. Taken together, the data support a potential role for nestin reexpression in brain repair.

Preconditioning with cortical spreading depression decreases intraischemic cerebral glutamate levels and down-regulates excitatory amino acid transporters EAAT1 and EAAT2 from rat cerebal cortex plasma membranes

We previously reported a 50% reduction in cortical infarct volume following transient focal cerebral ischemia in rats preconditioned 3 days earlier with cortical spreading depression (CSD). The mechanism of the protective effect of prior CSD remains unknown. Recent studies demonstrate reversal of excitatory amino acid transporters (EAATs) to be a principal cause for elevated extracellular glutamate levels during cerebral ischemia. The present study measured the effect of CSD preconditioning on (a) intraischemic glutamate levels and (b) regulation of glutamate transporters within the ischemic cortex of the rat. Three days following either CSD or sham preconditioning, rats were subjected to 200 min of focal cerebral ischemia, and extracellular glutamate concentration was measured by in vivo microdialysis. Cortical glutamate exposure decreased 70% from 1,772.4 +/- 1,469.2 microM-min in sham-treated (n = 8) to 569.0 +/- 707.8 microM-min in CSD-treated (n = 13) rats (p <0.05). The effect of CSD preconditioning on glutamate transporter levels in plasma membranes (PMs) prepared from rat cerebral cortex was assessed by western blot analysis. Down-regulation of the glial glutamate transporter isoforms EAAT2 and EAAT1 from the PM fraction was observed at 1, 3, and 7 days but not at 0 or 21 days after CSD. Semiquantitative lane analysis showed a maximal decrease of 90% for EAAT2 and 50% for EAAT1 at 3 days post-CSD. The neuronal isoform EAAT3 was unaffected by CSD. This period of down-regulation coincides with the time frame reported for induced ischemic tolerance. These data are consistent with reversal of glutamate transporter function contributing to glutamate release during ischemia and suggest that down-regulation of these transporters may contribute to ischemic tolerance induced by CSD.

Human T-cell lymphotropic virus type 1 myositis, peripheral neuropathy, and cerebral white matter lesions in the absence of spastic paraparesis

BACKGROUND

The human T-cell lymphotropic virus type 1 (HTLV-1) is associated with a chronic, progressive myelopathy termed tropical spastic paraparesis or HTLV-1-associate myelopathy. An increasing number of reports suggest that the spectrum of neurologic diseases associated with HTLV-1 is quite diverse.

DESIGN

Case study.

SETTING

A university teaching hospital (Ottawa General Hospital, Ottawa, Ontario).

RESULTS

Serum creatine kinase levels were elevated (1091 U/L). Antibodies for HTLV-1 were detected by Western blot analysis and confirmed by polymerase chain reaction. Human immunodeficiency virus antibodies were not detected. Findings of nerve conduction studies revealed an axonal neuropathy, while results of needle electromyography were consistent with mixed neuropathic and myopathic changes. Findings of a muscle biopsy supported the presence of polymyositis. Magnetic resonance imaging scans of the brain showed chronic, extensive cerebral white matter involvement of more than 7 years' duration. Treatment with oral steroids resulted in an approximate 40% decrease in serum creatine kinase levels within 1 month and a marked improvement in strength.

CONCLUSIONS

A broad spectrum of neurologic disorders is associated with HTLV-1, which may or may not include spastic paraparesis. Patients with myopathies and/or neuropathies of unknown origin who are from areas endemic for HTLV-1 should be screened for this retrovirus, even in the absence of spastic paraparesis.

Musical auditory hallucinosis from Listeria rhombencephalitis

BACKGROUND

Complex auditory hallucinations have rarely been reported in cases of brainstem stroke or tumor.

METHOD

Case study.

RESULTS

A patient with acute Listeria rhombencephalitis complained of formed musical auditory hallucinations on the side of recent sensorineural deafness. MRI revealed an abscess in the middle cerebellar peduncule with extensive surrounding edema.

CONCLUSIONS

Disruption of brainstem auditory pathways may cause complex auditory hallucinations. Potential pathogenetic mechanisms are discussed and a diagnostic approach is proposed.

Stimulation of glucose transport in skeletal muscle by hypoxia

Hypoxia caused a progressive cytochalasin B-inhibitable increase in the rate of 3-O-methylglucose transport in rat epitrochlearis muscles to a level approximately six-fold above basal. Muscle ATP concentration was well maintained during hypoxia, and increased glucose transport activity was still present after 15 min of reoxygenation despite repletion of phosphocreatine. However, the increase in glucose transport activity completely reversed during a 180-min-long recovery in oxygenated medium. In perfused rat hindlimb muscles, hypoxia caused an increase in glucose transporters in the plasma membrane, suggesting that glucose transporter translocation plays a role in the stimulation of glucose transport by hypoxia. The maximal effects of hypoxia and insulin on glucose transport activity were additive, whereas the effects of exercise and hypoxia were not, providing evidence suggesting that hypoxia and exercise stimulate glucose transport by the same mechanism. Caffeine, at a concentration too low to cause muscle contraction or an increase in glucose transport by itself, markedly potentiated the effect of a submaximal hypoxic stimulus on sugar transport. Dantrolene significantly inhibited the hypoxia-induced increase in 3-O-methylglucose transport. These effects of caffeine and dantrolene suggest that Ca2+ plays a role in the stimulation of glucose transport by hypoxia.

Characterization of glucose transporter-enriched membranes from rat skeletal muscle: assessment of endothelial cell contamination and presence of sarcoplasmic reticulum and transverse tubules

The subcellular origin of membranes from rat skeletal muscle that contain insulin-responsive glucose transporters was investigated. Rat skeletal muscle membranes were prepared by isopycnic centrifugation in sucrose gradients. In vivo insulin treatment increased the content of GLUT-4 glucose transporters in the 25% sucrose fraction (enriched in the plasma membrane marker 5'-nucleotidase) and decreased it in the 35% sucrose fraction (devoid of plasma membrane markers). The possibility of endothelial cell membrane contamination in these fractions was investigated using a mouse monoclonal antibody, MRC OX-43, raised against a cell surface protein specific to rat vascular endothelium. MRC OX-43 did not react with any of the muscle membrane fractions, but did recognize a protein of around 100 kDa in extracts of human endothelial cells and rat aorta. An antibody to the dihydropyridine receptor of skeletal muscle, IIC12, was used to determine the presence of transverse tubules in these fractions. IIC12 reacted positively with a 180-kDa protein in purified rat transverse tubules. In contrast, this antibody did not cross-react with the 25% or 35% sucrose fractions. The 25% sucrose fraction was devoid of calsequestrin and ryanodine receptor, cisternal sarcoplasmic reticulum markers. However, small amounts of these proteins were detected in the 35% sucrose fraction. The results suggest that the 25% sucrose fraction represents plasma membranes, while the 35% sucrose fraction is an insulin-sensitive intracellular fraction that contains, but is not enriched in, sarcoplasmic reticulum cisternae. The results further show that insulin-induced recruitment of GLUT-4 transporters in skeletal muscles can be demonstrated independently of GLUT-4 recruitment in endothelial cells.

Exercise induces recruitment of the "insulin-responsive glucose transporter". Evidence for distinct intracellular insulin- and exercise-recruitable transporter pools in skeletal muscle

Acute exercise, like insulin, increases D-glucose uptake into rat hind limb muscles. Here we examine the distribution of the muscle glucose transporters GLUT-4 and GLUT-1 in plasma membrane and intracellular membrane fractions of skeletal muscle prepared from control, exercised, and acutely insulin-treated rats. Immunoblotting with an anti-GLUT-4 polyclonal antibody showed that acute insulin treatment (by hind limb perfusion or in vivo injection) increased GLUT-4 transporters in a plasma membrane fraction and decreased them in an intracellular membrane fraction. Exercise also increased the GLUT-4 transporters in the plasma membrane, but in contrast to insulin, did not significantly decrease them in the intracellular fraction. Immunoblotting with anti-GLUT-1 antibody revealed that this transporter is largely localized in the plasma membrane. Neither insulin nor exercise significantly increased GLUT-1 transporters in the plasma membrane. The data show that GLUT-4 is an insulin-responsive glucose transporter in skeletal muscle and, furthermore, that GLUT-4 also responds to acute exercise. The results are consistent with recruitment of GLUT-4 glucose transporters to the plasma membrane from intracellular stores. Moreover, exercise-sensitive GLUT-4 transporters do not originate from the insulin-sensitive intracellular membrane fraction, suggesting the existence of distinct intracellular insulin- and exercise-recruitable GLUT-4 transporter pools.

Phenylarsine oxide and the mechanism of insulin-stimulated sugar transport

The actions of phenylarsine oxide (PAO) on hormone receptors and transport processes are reviewed with particular reference to the mechanism of insulin-stimulated sugar transport. It is suggested that as well as reaction with vicinal -SH groups, vicinal -SH/-OH and -SH/-CO2H groups should also be considered as potential reaction sites for PAO. The relatively high levels of these vicinal combinations of groups in many hormone receptors makes them particularly susceptible to reaction with PAO. In the case of insulin-stimulated sugar transport PAO does not inhibit insulin binding to its receptor at low concentrations but may react directly with the glucose transporters in some cells. A hypothesis is proposed suggesting that PAO may react specifically with one transporter isoform (GLUT-4) which is found almost exclusively in rat adipocytes, skeletal muscle and heart tissue (i.e. insulin responsive tissue) whereas in insulin unresponsive cells such as erythrocytes the GLUT-1 isoform is the predominant transporter which is not inhibited by PAO.

Exercise modulates the insulin-induced translocation of glucose transporters in rat skeletal muscle

Insulin and acute exercise (45 min of treadmill run) increased glucose uptake into perfused rat hindlimbs 5-fold and 3.2-fold, respectively. Following exercise, insulin treatment resulted in a further increase in glucose uptake. The subcellular distribution of the muscle glucose transporters GLUT-1 and GLUT-4 was determined in plasma membranes and intracellular membranes. Neither exercise nor exercise----insulin treatment altered the distribution of GLUT-1 transporters in these membrane fractions. In contrast, exercise, insulin and exercise----insulin treatment caused comparable increases in GLUT-4 transporters in the plasma membrane. The results suggest that exercise might limit insulin-induced GLUT-4 recruitment and that following exercise, insulin may alter the intrinsic activity of plasma membrane glucose transporters.

The role of insulin receptor sulphydryl groups in insulin binding and cellular response in rat adipocytes

Phenylarsine oxide (PAO), an agent which reacts with vicinal sulphydryl groups and dithiothreitol (DTT), a disulphide reducing agent, inhibited insulin binding to intact adipocytes with half maximal inhibition occurring at 28 microM and 340 microM, respectively. Pretreatment of adipocytes with DTT (2mM) prevented insulin stimulation of glucose uptake by approximately 50%. The marked inhibition of insulin binding to adipocytes by PAO and DTT is consistent with the involvement of the receptor cysteine-rich region of hormone binding. Furthermore, DTT inhibition of insulin binding suggests that the integrity of disulphide bridges is critical for insulin binding. The inhibitory effect of DTT and PAO on insulin binding were not additive, instead addition of DTT to PAO-treated adipocytes effected 15% reversal of binding inhibition. The marked inhibition of insulin binding by addition of low concentrations of DTT (0.2-2.0mM) to intact adipocytes is in contrast to the previously reported biphasic response for the effect of DTT on insulin binding to isolated plasma membranes from rat adipocytes (Schweitzer et al. Proc. Natl. Acad. Sci. U.S.A. 77, 4692-4696, 1980). Scatchard plots for 125I-iodoinsulin binding to adipocytes in the basal state were linear. In contrast, Scatchard analysis of insulin binding to plasma membranes prepared from both basal and insulin-stimulated adipocytes yielded severely curvilinear plots. The data suggests that (i) fundamental differences exist between the receptor state in intact cells and isolated plasma membranes and (ii) that a disulphide-rich region within the insulin receptor, other than the previously reported class I and class II disulphide bridges, is critical for insulin binding and cellular response.

Insulin processing and signal transduction in rat adipocytes

A glycine-HCl buffer (glycine, 50 mM/NaCl, 0.15 M/HCl, pH 3.5) was used to strip insulin bound to adipocyte cell surfaces. Adipocytes retained their integrity in the glycine buffer and their binding capacity for [125I]iodoinsulin could be completely recovered on transfer of the cells to physiological media. At 37 degrees C, [125I]iodoinsulin binds rapidly to plasma membrane receptors; maximal binding occurs within 10 min. At this temperature, the initial binding is followed by rapid internalization, degradation of the hormone and subsequent loss of label. Insulin treatment, at 37 degrees C, induced internalization of 37% of the plasma membrane insulin receptors. Phenylarsine oxide (PAO), a confirmed inhibitor of protein internalization, allowed insulin binding but completely inhibited degradation of the hormone. Monensin, a carboxylic ionophore which impairs uncoupling hormone-receptor complexes, effectively restricted insulin degradation over short time periods (less than 30 min). Addition of monensin to insulin-stimulated cells did not impair D-glucose uptake. It has previously been reported that PAO inhibits hexose transport through the direct interaction with the glucose transporters and low concentrations of PAO (1 microM) transiently inhibit insulin-stimulated glucose uptake. This recovery phenomenon was again observed when PAO was added to insulin-stimulated, monensin-treated adipocytes. The data suggests that lysosomal degradation of insulin is not requisite for signal transduction.

Exercise-induced increase in glucose transporters in plasma membranes of rat skeletal muscle

A previously developed technique for the isolation of plasma and intracellular membrane fractions from rat skeletal muscle was used to investigate transporter migration after insulin treatment or a bout of exercise (45 min of treadmill). Glucose-inhibitable cytochalasin-B binding was used to estimate the number of glucose transporters. Insulin and exercise caused increases in glucose uptake into the hindlimb muscles of 5- and 3-fold, respectively. Each stimulus also caused a 2-fold increase in the number of glucose transporters in plasma membranes prepared from hindlimb muscles. The insulin-induced increase in plasma membrane transporters was accompanied by a concomitant decrease in transporters from the intracellular pool. In contrast to insulin, there was no concomitant decrease in the number of cytochalasin-B-binding sites in the intracellular membrane fraction from exercised muscles. The ability of both insulin and exercise to increase the number of transporters in the plasma membrane is in accordance with recruitment of transporters as one cause of increased transport activity. However, the inability of exercise to decrease the number of transporters in the insulin-sensitive intracellular pool suggests the existence of either a second recruitable transporter pool or masked glucose transporters in the plasma membrane that are unmasked by the muscle contractile activity.

Inhibition by forskolin of insulin-stimulated glucose transport in L6 muscle cells

The cardioactive diterpene forskolin is a known activator of adenylate cyclase, but recently a specific interaction of this compound with the glucose transporter has been identified that results in the inhibition of glucose transport in several human and rat cell types. We have compared the sensitivity of basal and insulin-stimulated hexose transport to inhibition by forskolin in skeletal muscle cells of the L6 line. Forskolin completely inhibited both basal and insulin-stimulated hexose transport when present during the transport assay. The inhibition of basal transport was completely reversible upon removal of the diterpene. In contrast, insulin-stimulated hexose transport did not recover, and basal transport levels were attained instead. This effect of inhibiting (or reversing) the insulin-stimulated fraction of transport is a novel effect of the diterpene. Forskolin treatment also inhibited the stimulated fraction of transport when the stimulus was by 4 beta-phorbol 12,13-dibutyrate, reversing back to basal levels. Half-maximal inhibition of the above-basal insulin-stimulated transport was achieved with 35-50 microM-forskolin, and maximal inhibition with 100 microM. Forskolin did not inhibit 125I-insulin binding under conditions where it caused significant inhibition of insulin-stimulated hexose transport. Forskolin significantly elevated the cyclic AMP levels in the cells; however its inhibitory effect on the above basal, insulin-stimulated fraction of hexose transport was not mediated by cyclic AMP since: (i) 8-bromo cyclic AMP and cholera toxin did not mimic this effect of the diterpene, (ii) significant decreases in cyclic AMP levels caused by 2',3'-dideoxyadenosine in the presence of forskolin did not prevent inhibition of insulin-stimulated hexose transport, (iii) isobutylmethylxanthine did not potentiate forskolin effects on glucose transport but did potentiate the elevation in cyclic AMP, and (iv) 1,9-dideoxyforskolin, which does not activate adenylate cyclase, inhibited hexose transport analogously to forskolin. We conclude that forskolin can selectively inhibit the insulin- and phorbol ester-stimulated fraction of hexose transport under conditions where basal transport is unimpaired. The results are compatible with the suggestions that glucose transporters operating in the stimulated state (insulin or phorbol ester-stimulated) differ in their sensitivity to forskolin from transporters operating in the basal state, or, alternatively, that a forskolin-sensitive signal maintains the stimulated transport rate.

Direct interaction of phenylarsine oxide with hexose transporters in isolated rat adipocytes

It has previously been shown that phenylarsine oxide (PhAsO), an inhibitor of protein internalization, also inhibits stereospecific uptake of D-glucose and 2-deoxyglucose in both basal and insulin-stimulated rat adipocytes. This inhibition of hexose uptake was found to be dose-dependent. PhAsO rapidly inhibited sugar transport into insulin-stimulated adipocytes, but at low concentrations inhibition was transient. Low doses of PhAsO (1 microM) transiently inhibit stereospecific hexose uptake and near total (approx. 90%) recovery of transport activity occurs within 20 min. Interestingly, once recovered, the adipocytes can again undergo rapid inhibition and recovery of transport activity upon further treatment with PhAsO (1 microM). In addition, PhAsO is shown to inhibit cytochalasin B binding to plasma membranes from insulin-stimulated adipocytes in a concentration-dependent manner which parallels the dose-response inhibition of hexose transport by PhAsO. The data presented suggest a direct interaction between the D-glucose transporter and PhAsO, resulting in inhibition of transport. The results are consistent with the current recruitment hypothesis of insulin activation of sugar transport and indicate that a considerable reserve of intracellular glucose carriers exists within fat cells.

Insulin-induced decrease in 5'-nucleotidase activity in skeletal muscle membranes

Insulin releases inositol phosphoglycans from myocytes in culture [(1986) Science 233, 967-972], which display insulinomimetic activity. Because 5'-nucleotidase is anchored to the membrane through inositol-containing phospholipid glycans, we investigated whether insulin could release the enzyme from the membrane. Membranes prepared from hindquarter muscles of rats perfused with insulin showed a 23% decrease in 5'-nucleotidase activity. Isolated membranes from muscle exposed to insulin in vitro also showed a small but reproducible decrease (9%) in 5'-nucleotidase activity relative to unexposed controls. Phospholipase C from Staphylococcus aureus released 60% of the membrane-bound 5'-nucleotidase. We propose that insulin may activate an endogenous phospholipase C that cleaves phospholipid-glycan-anchored proteins.

The action of phenylarsine oxide on the stereospecific uptake of D-glucose in basal and insulin-stimulated rat adipocytes

Phenylarsine oxide (PAO) has been used to inhibit the stereospecific uptake of D-glucose in basal and insulin-stimulated rat adipocytes. The inhibition is dose dependent and is partially reversed by dithiothreitol. The results are consistent with a direct interaction between the glucose transporter and PAO. By manipulating the sequence of exposure of cells to PAO and insulin it is possible to differentiate between the effects of PAO on transport into cells with receptor-rich and transporter-rich plasma membranes. PAO rapidly inhibits transport in insulin-stimulated adipocytes but at low concentrations inhibition is transient and recovery of stereospecific uptake takes place after approx. 20 min. The results can be interpreted in terms of the recruitment mechanism of insulin stimulation of transport and demonstrate that a relatively large intracellular pool of transporters exists after insulin stimulation. It also follows that sulphydryl groups probably play a critical role in the mechanism of glucose uptake.