Geotechnical and mineralogical characterisations of marine-dredged sediments before and after stabilisation to optimise their use as a road material.

Dredging activities to extend, deepen and maintain access to harbours generate significant volumes of waste dredged material. Some ways are investigated to add value to these sediments. One solution described here is their use in road construction following treatment with hydraulic binders. This paper presents the characterisation of four sediments, in their raw state and after 90 days of curing following stabilisation treatment with lime and cement, using a combination of novel and established analytical techniques to investigate subsequent changes in mineralogy. These sediments are classified as fine, moderately to highly organic and highly plastic and their behaviour is linked to the presence of smectite clays. The main minerals found in the sediments using X-ray diffraction (XRD) and automated mineralogy are quartz, calcite, feldspars, aluminium silicates, pyrite and halite. Stabilisation was found to improve the mechanical performances of all the sediments. The formation of cementitious hydrates was not specifically detected using automated mineralogy or XRD. However, a decrease in the percentage volume of aluminium silicates and aluminium-iron silicates and an increase of the percentage volume of feldspars and carbonates was observed.

Characterization of harbor sediments from the English Channel: assessment of heavy metal enrichment, biological effect and mobility.

For a full assessment of the environmental risk posed by dredged sediments not only the anthropogenic enrichment of contaminants, but also their mobility and biological impact should be considered. This study reports on the enrichment factor (EF), mobility, and Adverse Effect Index (AEI) of metals and metalloids in nine dredged sediments. Significant enrichment of As, Cd, Pb and Zn with respect to background values is detected, and calculated AEI values for these elements suggest that it is possible that a corresponding biological effect may be observed. Correlation coefficients also reveal a link between mobility in HCl and enrichment for Cd, Cr, Ni, Pb and Zn, however As and Cu do not display such a link, possibly suggesting that the source of contamination for these elements is less recent. Mobility and enrichment are two parameters which are often studied separately; however this paper shows that in some cases strong correlations occur.

The neurofilament infrastructure of a developing presynaptic calyx.

Calyx-type synapses appear to be specifically designed to support fast, reliable, high-frequency excitatory transmission. In the chick ciliary ganglion, calyx terminals from preganglionic neurons in the midbrain form early in development on ciliary neurons. We find that labeling the calyx membranes with a lipophilic dye delivered by diffusion down the preganglionic nerve reveals a large membrane structure engulfing the postsynaptic cell by the end of embryogenesis. In contrast, labeling the calyces with a water-soluble dye by diffusion through the preganglionic nerve suggests large discontinuities in the calyx. A similar pattern of discontinuities is seen when presynaptic neurofilaments are labeled with antibodies selective for highly phosphorylated neurofilaments. The neurofilament infrastructure of the calyx first appears as a single thick bundle, which subsequently bifurcates during development and eventually generates a fine meshwork of filaments subdivided by several large neurofilament bundles encircling the postsynaptic cell body. The large bundles probably produce protruding ridges in the otherwise thin calyx cup, accounting for the disparity in staining patterns observed with membrane and cytosolic dyes. The postsynaptic membrane also undergoes restructuring during development with the appearance of large folded mats of somatic spines heavily invested with nicotinic receptors. The large presynaptic neurofilament bundles do not overlap the postsynaptic receptor clusters but do codistribute with large tracks of presynaptic microtubules. The neurofilament bundles may act as girders to provide structural support while at the same time defining conduits for microtubule-dependent transport of materials and rapid propagation of electrical signals throughout the extended calyx.

Direct recording of nicotinic responses in presynaptic nerve terminals.

Nicotinic acetylcholine receptors are widely expressed in the nervous system, but their functions remain poorly understood. One attractive hypothesis is that the receptors act presynaptically to modulate synaptic transmission. We provide a direct demonstration of presynaptic nicotinic receptors in situ by using whole-cell patch-clamp techniques to record currents in large presynaptic calyces that midbrain neurons form on ciliary neurons. Bath application of nicotine induced inward currents in the calyces capable of generating action potentials that overrode the limited space clamp achievable. The inward currents reversed near 0 mV and showed inward rectification common for neuronal nicotinic receptors. Tetrodotoxin (TTX) blocked the action potentials but not the inward currents. alpha-Bungarotoxin blocked both, consistent with the presynaptic receptors containing alpha7 subunits. Recording from the postsynaptic ciliary neurons during nicotine exposure revealed EPSCs that TTX blocked, presumably by blocking presynaptic action potentials. The postsynaptic cells also displayed bimodal inward currents caused by their own nicotinic receptors; the bimodal currents were not blocked by TTX but were blocked partially by alpha-bungarotoxin and completely by D-tubocurarine. Dye-filling with Lucifer yellow from the recording pipette confirmed the identity of patched structures and showed no dye transfer between calyx and ciliary neuron. When calyces or ciliary neurons were labeled en mass with neurobiotin and biocytin through nerve roots, dye transfer was rarely observed. Thus, electrical synapses were infrequent and unlikely to influence calyx responses. Immunochemical analysis of preganglionic nerve extracts identified receptors that bind alpha-bungarotoxin and contain alpha7 subunits. The results unambiguously document the existence of functional presynaptic nicotinic receptors.

Cholinergic modulation of the Ca2+ response to bradykinin in neuroblastoma cells.

Fura 2 imaging was used to measure intracellular Ca2+ signals in N1E-115 mouse neuroblastoma cells during combined activation of bradykinin (BK) and cholinergic receptors. BK and carbachol (CCh) both activate phospholipase C (PLC) and cause Ca2+ release from inositol 1,4,5-trisphosphate (IP3)-sensitive Ca2+ stores. The Ca2+ signal in response to CCh is prolonged by the activation of Ca2+ influx, but BK does not appear to activate the influx pathway. When BK and CCh are applied together (BK+CCh), the Ca2+ response is composed of both Ca2+ release and Ca2+ influx. Ca2+ influx is also activated by BK+CCh in a subset of cells that does not respond with a intracellular Ca2+ concentration increase when CCh is presented by itself. This suggests that CCh stimulates a Ca(2+)-silent cholinergic receptor that is not coupled to Ca2+ release but acts synergistically with BK receptors to activate Ca2+ influx. Pertussis toxin reduces influx without affecting release, indicating that the G protein that modulates the influx pathway is different from the G protein responsible for activating PLC. Cholinergic stimulation also causes progressive heterologous desensitization of BK-evoked Ca2+ release. Desensitization has the unique property of continuing to develop after the cholinergic agonist is removed and the cholinergic Ca2+ response has fully recovered. Heterologous desensitization is not the result of Ca2+ store depletion or a long-lasting inhibition of PLC or IP3-dependent Ca2+ release. Instead, it appears to involve an early step in the BK-signaling cascade, possibly at the level of the B2 receptor or associated G proteins.

Synaptic currents generated by neuronal acetylcholine receptors sensitive to alpha-bungarotoxin.

Nicotinic acetylcholine receptors are widely distributed throughout the nervous system, but their functions remain largely unknown. One of the most abundant is a class of receptors that contains the alpha 7 gene product, has a high relative permeability to calcium, and binds alpha-bungarotoxin. Here, we report that receptors sensitive to alpha-bungarotoxin, though concentrated in perisynaptic clusters on neurons, can generate a large amount of the synaptic current. Residual currents through other nicotinic receptors are sufficient to elicit action potentials, but with slower rise times. This demonstrates a postsynaptic response for alpha-bungarotoxin-sensitive receptors on neurons and suggests that the functional domain of the postsynaptic membrane is broader than previously recognized.

Intracellular calcium signals in response to bradykinin in individual neuroblastoma cells.

The Ca indicator fura 2 was used to study the modulation of cytoplasmic Ca by bradykinin (Bk) in single N1E-115 murine neuroblastoma cells. Increases in cytoplasmic Ca in response to Bk were mediated by the B2 receptor subtype. Responses to high concentrations of Bk (1-100 nM) were homogeneous and characterized by a rapidly rising transient that decayed to baseline in the continued presence of agonist, with a half-time of 15 s. Responses to low concentrations of Bk (100-500 pM) were more heterogeneous, with longer latencies and often with oscillations. Pretreatment with thapsigargin for 20 min prevented the Ca response, showing that the Ca change results from intracellular Ca release. Removal of external Ca had little effect on the response to Bk, indicating that the agonist does not activate Ca influx. The extent of Ca release and refilling after Bk was tested with ionomycin. A saturating dose of Bk (20 nM) mobilizes > 90% of stored Ca within 30 s, and this is replaced slowly. Replacement of external Na by N-methyl-D-glucamine to block Na/Ca exchange affected the Ca response, causing decreases in latency and in the period of Ca oscillations and increases in overall duration and peak amplitude of the response.

Expanding rural primary care training by employing information technologies: the need for participation by medical reference librarians.

The use of rural sites to train badly needed primary care providers requires access to sophisticated medical information not traditionally available outside of academic health centers. Medical reference librarians can play a key role in the development of primary care training sites in rural settings. Electronic information technologies, with proactive support from medical reference librarians, can provide current and detailed information without concern for distance from the health science center library. This paper discusses recent developments in technology, describes current challenges to the application of this technology in rural settings, and provides policy recommendations for medical reference librarians to enhance rural primary care training.

Impact of new information technologies on training and continuing education for rural health professionals.

Recently developed and emerging information and communications technologies offer the potential to move the clinical training of physicians and other health professionals away from the resource intensive urban academic health center, with its emphasis on tertiary care, and into rural settings that may be better able to place emphasis on the production of badly needed primary care providers. These same technologies also offer myriad opportunities to enhance the continuing education of health professionals in rural settings. This article explores the effect of new technologies for rural tele-education by briefly reviewing the effect of technology on health professionals' education, describing ongoing applications of tele-education, and discussing the likely effect of new technological developments on the future of tele-education. Tele-education has tremendous potential for improving the health care of rural Americans, and policy-makers must direct resources to its priority development in rural communities.

The muscarinic receptor agonist oxotremorine methiodide evokes a nicotinic response in mammalian sympathetic neurons.

Oxotremorine methiodide, a congener of oxotremorine, is used as a muscarinic receptor agonist. Responses to oxotremorine methiodide and nicotinic receptor agonists were examined in cultured guinea-pig celiac ganglion neurons using whole-cell voltage clamp techniques. At holding potentials between -30 and -60 mV, a brief application of oxotremorine methiodide produced fast and slow inward current transients, depending upon the concentration applied. Slowly developing inward current transients, characteristic of muscarinic responses, were produced by lower concentrations (EC50: 0.3 microM) and were blocked by atropine. Rapid inward current transients, characteristic of nicotinic responses, were produced by higher concentrations of oxotremorine methiodide (EC50: 168 microM) and were blocked by d-tubocurarine. Thus oxotremorine methiodide, at concentrations of 10 microM and greater, produced an initial nicotinic fast inward current transient followed by a slow muscarinic inward transient. The fast inward transients were similar to responses evoked by the nicotinic receptor agonists acetylcholine, nicotine and 1,1-dimethyl-4-phenyl-piperazinium iodide and were not antagonized by atropine. We conclude that oxotremorine methiodide acts as a nicotinic and muscarinic receptor agonist in celiac sympathetic ganglion neurons.

The aminoglycoside G418 suppresses muscarinic receptor-activated calcium release in stably transfected murine N1E-115 neuroblastoma cells.

The aminoglycoside G418 inhibited the release of calcium (Ca2+) from internal stores coupled to muscarinic receptors in murine N1E-115 neuroblastoma cells carrying the aminoglycoside resistance gene neomycin phosphotransferase (NPT). No significant effect was observed on responses coupled to histamine or bradykinin receptors. Cells were transfected using the eukaryotic expression vector pH beta APr-1-neo and selected using G418. Two groups were differentiated either in the continued presence of G418 or in the absence of G418. Carbachol (1 mM), histamine (200 microM) and bradykinin (100 nM) were administered to cells for thirty seconds and changes in [Ca2+]i were measured with fluorescence video microscopy of single cells loaded with the Ca2+ indicator fura-2. The effects of G418 on carbachol evoked Ca2+ release included a 73% reduction in the number of cells responding, a two fold increase in the time to reach half-maximal response, a 35% reduction of the peak [Ca2+]i in response to agonist and an elevation of resting [Ca2+]i from 99 +/- 14 nM (mean +/- S.E.M.) to 155 +/- 27 nM. Acute application (20 min) of G418 to transfected cells differentiated without G418 also reduced the percentage of cells responding to carbachol. This effect was less pronounced in non-transfected parent cells. Thus, the mechanism might involve a metabolite of G418 produced in cells expressing NPT. These results indicate that G418 attenuates Ca2+ release coupled to muscarinic receptors.

Developing a medical informatics education program to support a statewide health information network.

The Florida Health Information Network (FHIN) was established in October 1989 to provide biomedical information services to the University of Florida Health Science Center (HSC) and to health professionals throughout the state--especially the northern thirty-nine counties of the state. FHIN services are available to all affiliates of the HSC and by annual subscription to nonaffiliates. At present, FHIN services include database access, circulation services, document delivery, and information services. Training network users has been an objective since the inception. Training has targeted both the HSC Library staff and HSC users and now is expanding to include remote users. Because many users have had insufficient experience with computers, the library has to teach the mechanics of access and network use and to instruct users regarding applications and database searching. This paper describes the development and implementation of the medical informatics education program. Topics include library staff training; educational offerings for HSC faculty, staff, and students; development and implementation of the remote training program; and organizational and budgetary implications for the construction of such a program.

Muscarinic inhibition of two potassium currents in guinea-pig prevertebral neurons: differentiation by extracellular cesium.

Muscarinic responses were studied in dissociated guinea-pig celiac ganglion neurons using the whole-cell voltage-clamp technique. Muscarine (0.025-1 mM; EC50 = 95 microM) administered to cells for 1.5 s evoked inward shifts in holding current in 53 of 74 cells. The amplitude of the inward current transients decreased with hyperpolarization and the null potential averaged -71 +/- 3.4 mV (n = 11). The currents that underlie the responses to muscarine were examined with hyperpolarizing voltage stepping protocols to -100 mV from a holding potential of -30 mV. Eighty-one per cent of cells displayed voltage-dependent current relaxations characteristic of the M-potassium current. Twenty per cent of responding cells displayed no M-current but only a voltage-independent current consistent with a leak current. In the latter type of cells, the muscarine-evoked inward currents reversed near EK and became outward at more hyperpolarized potentials. Analysis of steady state I-V relationships before and after bath application of muscarine showed that the two muscarine-sensitive potassium currents were distributed differently among three types of cells: (i) with M-current (18%); (ii) with leak current (18%); and (iii) with M-current and with leak current (64%). Cesium and barium were used to differentiate the M-current and the muscarine-sensitive leak current. Barium (2 mM) reduced the M-current and the leak potassium current, whereas cesium (2 mM) reduced the M-current but did not affect leak current. Thus, barium reduced the amplitude of muscarinic responses by 79% but cesium reduced them by only 14%. We conclude that muscarinic responses in guinea-pig celiac neurons are produced by suppression of two K+ currents: the M-current and a muscarine-sensitive leak current. These two currents are differentially susceptible to the potassium channel blockers barium and cesium.

CCKA receptors mediate slow depolarizations in cultured mammalian sympathetic neurons.

The effect of cholecystokinin octapeptide (CCK-8) was examined in guinea-pig celiac ganglion (CG) neurons in primary culture using standard intracellular recording techniques. Sulfated CCK-8 (CCK-8S; 1 microM) evoked slow depolarizing responses in 94% of CG neurons tested. In contrast, membrane potential was not affected by nonsulfated CCK-8 (CCK-8NS; 1 microM), CCK tetrapeptide (CCK-4; 1 microM), or gastrin (1 microM). The selective CCKA receptor antagonist L 364,718 potently inhibited CCK-8S-induced slow depolarizations (IC50 2.9 pM). In contrast, the selective CCKB receptor antagonist L 365,260 was a weak inhibitor of CCK-8S-induced slow depolarizations (IC50 1.3 microM). The depolarizing responses to CCK-8S were associated with an average increase in cell input resistance of 61%. Single electrode voltage clamp experiments indicated that CCK-8S-induced depolarizations were associated with a slow inward shift in holding current. Thus, the present findings indicate that guinea-pig cultured CG neurons are endowed with excitatory CCKA receptors the activation of which elicits a decrease in membrane conductance, thereby resulting in slow depolarizations.

Electrophysiological properties and cholinergic responses in guinea-pig celiac ganglion neurons in primary culture.

Prevertebral neurons enzymatically dissociated from celiac ganglia of adult guinea-pigs were maintained in long-term primary culture. Cells were plated at a density of 95 +/- 15 cm-2, and intracellular electrical activity was measured between 2 and 7 weeks after dissociation. Neurite outgrowth began within 24 h of enzymatic dissociation. Cell survival dropped below 50% after more than two weeks in culture. The resting potential (-53 mV +/- 0.8), time constant (12 ms +/- 1.3), input resistance (47 M omega +/- 8.6), rheobase (0.33 nA +/- 0.02), degree of accommodation, spike amplitude (70 mV +/- 3.0), after hyperpolarization amplitude (-9.5 mV +/- 0.55), and after hyperpolarization duration (88 ms +/- 7.6) in these cells were not different from those recorded from neurons in intact celiac ganglia. A larger proportion (greater than 90%) of cells exhibited fast accommodation (phasic) in response to depolarizing current pulses. Unevoked (spontaneous) depolarizations and action potentials were observed. The cells responded to pressure ejected acetylcholine. Two types of responses consisted of an early rapid depolarization which was attenuated by hexamethonium and a later slow depolarization which was attenuated by atropine. We conclude that prevertebral neurons from guinea-pigs can be maintained in long-term primary culture, that they retain electrophysiological properties similar to intact ganglia and exhibit complex responsivity to acetylcholine.