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.

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.

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.

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.