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Biomedical subjects

R W Snow

Publications and source records attributed to R W Snow.

At least 127 records · Page 7Linked to original sources
PubMed1986

Drinking locations and frequency of drunkenness among Mississippi DUI offenders.

Using data collected from convicted drunken drivers, relationships between self-reported frequency of drunkenness, frequency of drinking in seven types of drinking places, and sociodemographic characteristics are examined. Drunk drivers who are young, White, and who infrequently attend worship services are more likely than others to report a high frequency of drunkenness. Self-reported frequency of drunkenness is found to be more strongly related to drinking locations than to sociodemographic characteristics, however. The best predictors of the frequency of drunkenness are the frequency of drinking in automobiles and the frequency of drinking in bars or lounges. These relationships remain strong after the effects of sociodemographic characteristics have been controlled. The findings suggest that drunk drivers who drink in automobiles may represent an especially dangerous subgroup, and that policy makers need to give careful consideration to countermeasures designed to curtail drinking in automobiles.

Adolescent↗
PubMed1986

Drinking reasons, alcohol consumption levels, and drinking locations among drunken drivers.

In a DUI offender sample, four drinking reason factors are regressed on alcohol consumption variables and frequency of drinking in seven types of locations. Drinking for "pleasure" and "opposite sex/drunkenness" reasons are associated with both quantity consumed per occasion and away-from-home locations such as automobiles, bars, and parties, suggesting high traffic accident risk. "Escapism" reasons are related to quantity consumed per occasion, but are only weakly associated with specific locations; and "sociability" reasons are associated with drinking in friends' homes, but are not related to high consumption levels. Implications for DUI countermeasures are discussed.

Adolescent↗
PubMed1986

ELISA tests for dapsone and pyrimethamine and their application in a malaria chemoprophylaxis programme.

Enzyme-linked immunosorbent asays (ELISAs) are described for determining levels of dapsone and pyrimethamine in urine. Both assays have a sensitivity of about 20 mug/l and are reproducible, but each produces some false positives. The problem of false positive reactions was partially obviated by requiring positive results in both assays. In a pilot study involving 50 children aged 3 months to 4 years who were given a single dose of Maloprim (pyrimethamine + dapsone), 75% were positive for dapsone 7 days after administration of the drug, while 25% were still positive 15 days after its administration. The corresponding proportions for pyrimethamine were 73% and 30%, respectively. Comparison of the results obtained in a larger chemoprophylaxis trial with those from the pilot study indicated that the assays described could be used to investigate whether antimalarials had been taken.

Child, Preschool↗
PubMed1986

Role of electrical interactions in synchronization of epileptiform bursts.

Four general mechanisms can hypothetically contribute to or mediate localized synchronization of neuronal activity: (a) recurrent excitatory chemical synapses, (b) electrotonic coupling via gap junctions, (c) electrical field effects (ephaptic interactions), and (d) changes in the concentration of extracellular ions (e.g., K+). It has generally been believed that synchronization of epileptiform bursts derives primarily, if not exclusively, from recurrent excitatory chemical synapses. Dual intracellular recordings from the CA3 area of the hippocampus have been used to demonstrate the existence of recurrent synaptic excitation, and computer simulations have provided a theoretical framework for the idea that relatively sparse interactions through recurrent excitatory chemical synapses can generate synchronized bursting after inhibitory pathways are blocked with convulsant agents. Additional experimental studies have supported the hypothesis that a model for seizure discharge, the penicillin-induced paroxysmal depolarization shift (PDS), is associated with a large increase in excitatory synaptic conductance. However, recent studies have suggested that electrical interactions are also likely to play an important role in spike synchronization during epileptic discharges. Several research groups have used in vitro preparations to show that afterdischarges and spontaneous bursts of population spikes (which represent synchronized action potentials) can occur after chemical synaptic transmission has been blocked in solutions containing low [Ca2+]. Although this result was first observed in the CA1 area, it has recently been confirmed in other regions of the hippocampus. These experiments indicate that mechanisms other than chemical synaptic transmission are capable of synchronizing action potentials in the hippocampus. In this chapter, two forms of electrical interaction that could mediate synchronization will be considered: (a) electrotonic coupling through gap junctions and (b) electrical field effects through extracellular space. Changes in the concentration of extracellular ions are another mechanism not involving chemical synapses. However, it seems unlikely that ionic changes act on the rapid time scale of electrical interactions, and their contribution is discussed elsewhere in this volume. We review evidence for the existence of electrotonic coupling and electrical field effects in the hippocampus and neocortex, and discuss their possible involvement in the synchronization of epileptiform events.(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗
PubMed1986

Gambian cultural preferences in the use of insecticide-impregnated bed nets.

In field trials of permethrin-treated bed nets in a large Mandinka village, 95% of people were already sleeping under locally-made nets. They lasted about 6 years and cost about US$9.00 ($1.50 per year). Two permethrin dips per year added a further $0.60 per year (1985 prices). Non-immune children slept in beds shared with adults, and people wanted nets for many reasons, not just malaria protection. Fifty-eight per cent of people preferred opaque sheeting to open netting; sheeting gave more privacy, lasted longer, gave better protection from very small insects, dust, rats, etc. White was the colour preferred by 90% of interviewees. Comparing Mandinka with Wolof and Fula, there were ethnic differences in net owning and the proportion of children sleeping in beds with a mattress.

Adult↗
PubMed1985

Effects of phenytoin on field bursts of rat hippocampal slices in low-calcium solutions.

Recurring bursts of population spikes, a simple model of epileptiform activity, can be produced by exposing slices of rat hippocampus to saline containing 0.2 mM [Ca2+] and 4.0 mM [Mg2+], at which concentration chemical synaptic activity is blocked. Phenytoin at 7.3-73 microM shortened the duration of these bursts. At 73 microM the bursts were slowed and often eliminated. This model appears to be more sensitive to the action of phenytoin than the penicillin model of epileptiform bursting.

Animals↗
PubMed1985

Computer simulations indicate that electrical field effects contribute to the shape of the epileptiform field potential.

In the presence of convulsant drugs such as picrotoxin, neurons in the hippocampal-slice preparation generate synchronized depolarizing bursts. This synchrony occurs on a time scale of tens of milliseconds and is produced by excitatory synaptic interactions between neurons. The synaptic interactions themselves occur on a time scale of tens of milliseconds. The "epileptiform" local-field potential during such synchronized bursts is comb-shaped ("ringing"), whereas the field potential expected if action potentials in neighboring neurons were uncorrelated is noisy and not comb-shaped. This suggests that individual action potentials are locally synchronized on a time scale of 1 ms. We have previously shown, using computer simulations, that electrical interactions--mediated by currents flowing in the extracellular medium--can plausibly explain action-potential synchronization in experiments where chemical synapses are blocked. The present simulations demonstrate that electrical interactions can also account for action-potential synchronization--and thus the "ringing" shape of the field potential--during epileptiform bursts, where excitatory synapses are functional. The field potential is thus a modulating influence on, as well as a reflection of, underlying neuronal transmembrane events.

Action Potentials↗
PubMed1984

Electrical fields directly contribute to action potential synchronization during convulsant-induced epileptiform bursts.

Synchronous field-potential bursts were induced in hippocampal slices with picrotoxin. Differential recording between intracellular and adjacent extracellular electrodes during paroxysmal depolarization shifts revealed rapid transmembrane depolarizations (TMDs), which were spike prepotentials generated by electrical field effects. These experiments demonstrate that endogenous electrical fields contribute to spike synchronization in the presence of convulsant drugs when excitatory chemical synapses are functional.

Action Potentials↗
PubMed1984

Synchronous epileptiform bursts without chemical transmission in CA2, CA3 and dentate areas of the hippocampus.

Slices of rat hippocampus maintained in a medium containing Mn2+ and lowered Ca2+ concentration, which demonstrably blocked chemical synapses, generated spontaneous bursts of population spikes in all cell body layers after 30-60 min of incubation. Therefore, electrical interactions alone can synchronize neuronal activity in the hippocampus, and they are probably important during epileptiform events.

Animals↗
PubMed1983

Electrophysiological and optical changes in slices of rat hippocampus during spreading depression.

Spreading depression (SD) was studied with intracellular and extracellular recordings and with photometry in slices of rat hippocampus. Repetitive electrical stimulation could initiate SD in either normal medium or in low-Ca2+ medium containing Mn2+, especially during transient hypoxia. The extracellular voltage near CA1 pyramidal somata and dendrites became negative by approximately 18 mV during SD. This negativity peaked more slowly in low-Ca2+ medium containing Mn2+. The wave of negativity propagated across the slice in both media at approximately 6 mm/min. Input resistance of pyramidal neurons became undetectable during SD, and differential voltage recording between neurons and adjacent extracellular space demonstrated that transmembrane potential approached zero. Slices became more opaque during SD. Photometry revealed approximately 10% increase in reflectance and a similar decrease in transmittance of white light, which occurred with a time course similar to the extracellularly recorded voltage shift. These data support the hypothesis that SD represents a large increase in membrane permeability associated with substantial movements of water. The persistance of SD in a bathing solution that blocked electrically evoked postsynaptic potentials suggests that the contribution of synaptic transmitter release to the propagation of SD should be reappraised.

Animals↗
PubMed1982

Characterization of the synaptic actions of an interneuron in the central nervous system of Tritonia.

The motor program that drives the swimming behavior of the marine mollusk Tritonia diomedea is generated by three interneuronal populations in the cerebral ganglia. One of these populations, the pair of C2 neurons, is shown to also exert powerful synaptic actions upon most cells in the contralateral pedal ganglion. Intracellular staining with Co2+ showed that the C2 neurons projected to the contralateral pedal ganglion as a single unbranched axon, and nearly all contralateral pedal neurons received monosynaptic input from C2. Orthodromic stimulation of most peripheral nerves caused monosynaptic excitation of C2 by afferent sensory cells and, in some cases, monosynaptic inhibition from an unidentified source. C2 neurons produced four types of postsynaptic potential (PSP) on pedal neurons: (1) a fast, Cl- -mediated inhibition (FIPSP); (2) a fast, Na+ -mediated excitation (FEPSP); (3) a slow, K+ -mediated inhibition (SIPSP); and (4) a slow, conductance-decrease excitation (SEPSP). All four could be recorded simultaneously in some pedal neurons. The C2 neurons appear to be high-order, multiaction neurons involved in both the generation of a complex motor program and the coordination of ancillary neuronal activity.

Action Potentials↗
PubMed1982

Evidence for peptide-mediated neurotransmission in a molluskan brain.

The previous report (Snow, 1982) characterized the monosynaptic actions of an identified cerebral interneuron (C2) in the marine mollusk Tritonia. The C2 neurons produce four types of postsynaptic potentials in an identified pedal neuron (Pd5). A high-molecular-weight (approximately 1400 daltons by Sephadex G-15 gel filtration) compound, which could mimic the four postsynaptic responses in Pd5, was isolated from C2 somata. The C2 somata had the ultrastructural characteristics of peptide-secreting cells, including profuse rough endoplasmic reticulum and large (170 nm average diameter) dense secretory vesicles. These data are consistent with the hypothesis that the synaptic transmitter of C2 neurons is a peptide(s).

Animals↗
PubMed1982

Coupling in rat hippocampal slices: dye transfer between CA1 pyramidal cells.

Intracellular injections of Lucifer Yellow-CH (LY) into CA1 pyramidal cells were made in rat hippocampal slices to study dye transfer between neurons as evidence that these cells are electrotonically coupled. Extensive control procedures were performed which substantially reduced inadvertent staining. Over half of the neurons were dye-coupled after injections in stratus pyramidale. Dye coupling occurred even when spike amplitudes were greater than or equal to 70 mV throughout the impalement and was still present after chemical synapses were blocked with a low Ca2+ solution containing Mn2+. Somata of dye-coupled cells were usually located within 35 micrometers (post-fixation) of the injected cell and showed no preferred orientation. Fast prepotentials and dye coupling occurred independently. Neurons in superior cervical ganglia, which were sliced and injected using similar procedures, showed no dye coupling. Intradendritic injections of LY in stratum radiatum also yielded dye coupling between CA 1 pyramidal cells, although the dye coupling was less frequent. Within stratum radiatum, neither extracellular ejections nor intracellular injections of interneurons were associated with multiple staining. Thus, injection of LY into the soma or dendrite of a single CA1 pyramidal cell often resulted in multiple staining, and in many ensembles the somata were well spaced. Control experiments suggested that such dye transfer is not by an extracellular route. This implied that some CA1 cells are electrotonically coupled. Further electrophysiological and morphological studies are required to resolve the discrepancies among various techniques used to evaluate the amount of coupling in the hippocampus.

Animals↗
PubMedDate not supplied

The effects of malaria chemoprophylaxis given by traditional birth attendants on the course and outcome of pregnancy.

A trial of malaria chemoprophylaxis given by traditional birth attendants was undertaken in a rural area of The Gambia where access to antenatal clinics is difficult. Women received one or more doses of Maloprim or placebo from a traditional birth attendant during 1049 of 1208 pregnancies (87%) recorded in 16 villages over a 3-year period. Primigravidae who received Maloprim had a lower parasite rate and a significantly higher mean packed cell volume than primigravidae who received placebo, and their babies were significantly heavier (6% low birth weight vs 22%). In multigravidae chemoprophylaxis reduced malaria parasitaemia but it had no beneficial effect on haemoglobin level and much less effect on birth weight than was observed in primigravidae. However, the mean birth weight of babies born to grandemultigravidae who received chemoprophylaxis was significantly higher than that of babies born to grandemultigravidae who did not.

Antimalarials↗
PubMedDate not supplied

Lack of an association between acute gastroenteritis, acute respiratory infections and malaria in young Gambian children.

The incidence of acute gastrointestinal and acute respiratory infections was measured in 2 groups of approximately 750 Gambian children aged 3-59 months during a 3-year period. One group of children was partially protected against malaria by fortnightly chemoprophylaxis with Maloprim whilst children in the other group were infected much more frequently. Mortality from acute gastroenteritis and from acute respiratory infections was similar in the 2 groups. The proportions of children in each group who complained of gastrointestinal or severe respiratory symptoms on morbidity surveillance were also similar. Thus, no evidence was found to suggest that malaria plays either a direct or indirect role in causing acute gastrointestinal or respiratory infections in young children in The Gambia.

Acute Disease↗
PubMedDate not supplied

A comparative study of Lapudrine (chlorproguanil) and Maloprim (pyrimethamine and dapsone) as chemoprophylactics against malaria in Gambian children.

A comparison has been made of Lapudrine (chlorproguanil) and Maloprim (pyrimethamine +dapsone) as malaria chemoprophylactics when given every two weeks for 3 years to Gambian children under the age of 5 years. Both drugs produced falls in spleen and malaria parasite rates and an increase in packed cell volume. Maloprim, but not chlorproguanil, significantly reduced the incidence of episodes of fever accompanied by malaria parasitaemia. Children who received Maloprim, but not those who received chlorproguanil, grew better than children in the placebo group. This finding suggests that brief clinical episodes of malaria are more important in impairing growth than more prolonged periods of asymptomatic parasitaemia. No serious side-effect attributable to either drug was observed. After chemoprophylaxis had been given for 3 malaria transmission seasons the level of resistance of Plasmodium falciparum to pyrimethamine and to chlorproguanil was about 10%.

Animals↗