Modulation of neuronal activity by glial cells in the retina

Glial-neuronal communication was studied by monitoring the effect of intercellular glial Ca2+ waves on the electrical activity of neighboring neurons in the eyecup preparation of the rat. Calcium waves in astrocytes and Müller cells were initiated with a mechanical stimulus applied to the retinal surface. Changes in the light-evoked spike activity of neurons within the ganglion cell layer occurred when, and only when, these Ca2+ waves reached the neurons. Inhibition of activity was observed in 25 of 53 neurons (mean decrease in spike frequency, 28 +/- 2%). Excitation occurred in another five neurons (mean increase, 27 +/- 5%). Larger amplitude Ca2+ waves were associated with greater modulation of neuronal activity. Thapsigargin, which reduced the amplitude of the glial Ca2+ increases, also reduced the magnitude of neuronal modulation. Bicuculline and strychnine, inhibitory neurotransmitter antagonists, as well as 6-Nitro-7-sulphamoylbenzo[f]quinoxaline-2,3-dione (NBQX) and D(-)-2-amino-7-phosphonoheptanoic acid (D-AP7), glutamate antagonists, reduced the inhibition of neuronal activity associated with glial Ca2+ waves, suggesting that inhibition is mediated by inhibitory interneurons stimulated by glutamate release from glial cells. The results suggest that glial cells are capable of modulating the electrical activity of neurons within the retina and thus, may directly participate in information processing in the CNS.     

A transposable partitioning locus used to stabilize plasmid-borne hydrogen oxidation and trifolitoxin production genes in a Sinorhizobium strain

Improved nitrogen-fixing inoculum strains for leguminous crops must be able to effectively compete with indigenous strains for nodulation, enhance legume productivity compared to the productivity obtained with indigenous strains, and maintain stable expression of any added genes in the absence of selection pressure. We constructed a transposable element containing the tfx region for expression of increased nodulation competitiveness and the par locus for plasmid stability. The transposon was inserted into tetA of pHU52, a broad-host-range plasmid conferring the H2 uptake phenotype. The resulting plasmid, pHUTFXPAR, conferred the plasmid stability, trifolitoxin production, and H2 uptake phenotypes in the broad-host-range organism Sinorhizobium sp. strain ANU280. The broad applications of a transposon conferring plasmid stability are discussed.     

Sialomucin complex, a heterodimeric glycoprotein complex. Expression as a soluble, secretable form in lactating mammary gland and colon

Ascites 13762 rat mammary adenocarcinoma cells express abundantly on their cell surfaces a heterodimeric glycoprotein complex composed of a sialomucin ascites sialoglycoprotein (ASGP)-1 and a transmembrane subunit ASGP-2. The latter, which contains two epidermal growth factor-like domains, binds the receptor tyrosine kinase p185(neu), suggesting that the complex is bifunctional as well as heterodimeric. Immunoblot analyses using monoclonal antibodies prepared against the complex demonstrate high levels of expression in rat lactating mammary gland and colon. Immunolocalization studies with anti-ASGP-2 indicate that ASGP-2 is present in these two tissues in the apical regions of secretory epithelial cells. Both mammary gland and colon contain a soluble, secretable form of ASGP-2, which is not found in the ascites cells; milk and mammary gland also have the membrane form. Immunoblot analyses using a COOH-terminal-specific polyclonal antibody indicate that the soluble form of ASGP-2 is missing its COOH-terminal domains. Both the soluble and membrane forms of ASGP-2 are similar to the membrane-associated form from the 13762 adenocarcinoma with respect to Mr, antigenicity, and association with ASGP-1. The presence of ASGP-1 in milk suggests that it is a candidate for the uncharacterized high Mr milk mucin, MUCX. ASGP-2 expression is up-regulated in mammary gland during pregnancy, because it is undetectable in virgin and early pregnant rats but abundant in the gland from late pregnant and lactating animals. However, compared with the lactating mammary gland, the 13762 ascites cells overexpress ASGP-2 by more than 100-fold, which may contribute to their malignancy. These combined results indicate that sialomucin complex is a unique secreted product in the mammary gland and colon, whose behavior is different from that in the mammary ascites tumors, and which may play important roles in mammary and intestinal physiology.     

Treatment of vertigo with betaserk in patients with vascular and traumatic cerebral injuries

Managed care's focus on patient-centered care has made the need for point-of-care (POC) clinical systems more critical than ever. This article examines some of the more common POC options available, explains what nurses need to know to choose among them, and suggests ways to ensure that nursing's needs are addressed in the selection process.     

Ascorbate modulates glutamate-induced excitations of striatal neurons

To assess the role of ascorbate (AA), an antioxidant vitamin, in modulating striatal activity, single-unit recording was combined with iontophoresis in awake, unrestrained rats. Brief applications of AA (20 s, 5-80 nA) elicited few changes in either basal activity or activity evoked by continuous application of glutamate (GLU), but relatively high AA ejection currents (>40 nA) often inhibited fast-firing units. Comparable results were obtained with the antioxidant isomer, iso-AA, suggesting the AA-induced inhibition represents a high-dose, antioxidant effect. When applied for prolonged periods (2-4 min) at doses that failed to alter basal activity, AA either enhanced or attenuated the excitatory response to test pulses of GLU. The AA-induced enhancement occurred more frequently (16 vs. 6 applications) and was characterized by a more rapid (shorter onset and peak latencies) and more pronounced (greater peak magnitude) excitation to GLU without an evident change in offset latency. In most cases, further increases in AA ejection current attenuated the GLU response. Iso-AA, in contrast, had only inhibitory effects, which occurred at moderate- to high-dose applications. Collectively, these results suggest that AA, apart from its antioxidant effects, modulates phasic changes in striatal excitability induced by GLU. Because extracellular levels of striatal AA fluctuate in relation to behavioral activation, this neuromodulatory action of AA may contribute to behaviorally relevant changes in sensorimotor responsivity.     

Viral contamination of food products: a poorly understood public health problem

Throughout the world there have been several epidemics of food-borne diseases (FBD) about which there is lack of sufficient information for public health institutions to take appropriate measures. This study was conducted for the purpose of contributing to the dissemination of information on these diseases and their etiologic agents, epidemiology, and control. The study was based on data from 61 sources, including review articles, reports of outbreaks, and databases. Results reveal considerable underregistration and lack of data on FBD throughout the various countries, with viruses being the second most important cause of FBD in the United States of America. Two agents, Norwalk virus and hepatitis A virus, were the fifth and sixth most frequent causes, respectively, although the former was the single most frequent cause of FBD in 1982 and the second most frequent cause of water-borne diseases during the period from 1986 to 1988. Despite the scarcity of information on the problem, rotavirus, poliovirus, hepatitis E virus, astrovirus, and small gastroenteric viruses are also important causes of FBD. We also discuss the importance of viral zoonoses, especially hemorrhagic fevers transmitted by contact with rodent feces and tick-borne viral encephalitides (Lassa fever). There is discussion of the controversial mad cow disease and its potential transmission through food products, as well as of dietary aspects of the management of AIDS and other viral infections. Finally, measures for the prevention and control of FBD are described.     

Liver function following pregnancy complicated by the HELLP syndrome

Serum levels of aminotransferases, lactate dehydrogenase, gammaglutamyl transferase, alkaline phosphatase, albumin and conjugated bilirubin, measured in 54 women at a median of 31 months (range 3-101) after pregnancies complicated by the HELLP syndrome, were not elevated. Total bilirubin levels, however, were elevated in 20% of these women; this represents a significant difference from the prevalence in 151 women with a previous normal pregnancy (chi2 = 12.23, P < 0.001), or in the normal female population (chi2 = 22.34, P < 0.00001). This raises the possibility that a dysfunction of the bilirubin-conjugating mechanism represents a risk factor for the development of the HELLP syndrome.