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Biomedical subjects

M J Lewis

Publications and source records attributed to M J Lewis.

At least 325 records · Page 18Linked to original sources
PubMed1972

Hypothalamic norepinephrine: circadian rhythms and the control of feeding behavior.

The time of day is a decisive determinant of the effects of l-norepinephrine on feeding behavior. During the dark, direct application of l-norepinephrine to the hypothalamus of rats suppressed feeding behavior. During the light, treatment with the same dose of l-norepinephrine facilitated feeding behavior. Thus, l-norepinephrine has dual and opposite effects on feeding behavior. A hypothalamic substrate that fluctuates in a circadian rhythm could account for both actions of l-norepinephrine.

Animals↗
PubMed1971

A biochemical subdivision of one phage type of Salmonella typhimurium.

A total of 1537 strains of Salmonella typhimurium belonging to seven prevalent phage types were examined on solid media for their ability to ferment rhamnose, xylose and inositol, for colicine production and for nutritional requirements. Most of the strains in each phage type were almost completely homogeneous, especially in their sugar fermentation reactions. However, strains of phage type 1 a/2 were not homogeneous, but could be assigned to one of four subgroups on the basis of ability to ferment inositol, inhibition of growth by meso-tartrate and auxotrophy for nicotinic acid. The subdivision proved to have epidemiological value. The inhibition of growth by meso-tartrate was observed on a defined medium containing citrate as the energy source. Inhibition did not occur if glucose, casein hydrolysate or aspartic acid were added to the medium.

Aspartic Acid↗
PubMed1971

Some Factors Which Affect Amino Acid Uptake by Saccharomyces carlsbergensis.

When fully grown cells of Saccharomyces carlsbergensis were suspended in a solution of glucose and labeled amino acids, there was a lag phase before rapid uptake of certain amino acids. During this lag, significant amounts of sugar were utilized. The lag phase varied in length, depending upon the amino acid under study, but could be shortened by aeration of the cells and eliminated by their preincubation in glucose solution. Divalent metal ions, especially Ca added during the early stages of the lag phase, increased the length of the lag, an effect that could be reversed by washing with ethylenediaminetetraacetate, but amino acids which normally showed little or no lag before uptake were insensitive to Ca. The rate of uptake of amino acids or of sugar was essentially unaffected by Ca, whereas 2,4-dinitrophenol caused an overall decrease in the rate of uptake of all amino acids tested. The relevance of these observations to commercial brewing practice is shown.

Journal Article↗
PubMed1969

R factors.

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Drug Resistance, Microbial↗
PubMed1967

Glucose-induced Release of Amino Acids from Saccharomyces carlsbergensis by Action on the Cytoplasmic Membrane.

When washed yeast cells grown under appropriate conditions were suspended in glucose solution there was a sudden release of alpha-amino nitrogen into the medium. This released material was of low molecular weight, and its composition was closely similar to that of the intracellular free amino acid pool. During the leakage of amino acids, the yeast did not efficiently absorb labeled amino acids added to the test medium, despite the rapid uptake and metabolism of glucose. Uptake of a labeled amino acid and reabsorption of the released alpha-amino nitrogen occurred almost simultaneously. When these yeast cells were exposed to glucose in the presence of calcium ions, leakage was strongly inhibited. Butanol under the same conditions increased glucose-induced leakage of cell contents. The adenosine triphosphatase activity of intact yeast cells exposed to glucose was greater than that of cells exposed to water. Yeast cells treated with glucose prior to equilibration with sorbose exhibited less ability to retain the sorbose when washed at 0 C than did cells pretreated with water. It was concluded that glucose-induced leakage of amino acids was the result of two factors acting together. These were (i) a change in membrane permeability associated with glucose uptake, and (ii) a temporary shortage of energy for amino acid uptake or retention.

Journal Article↗
PubMedDate not supplied

Ro15-4513 enhances and attenuates motor stimulant effects of ethanol in rats.

The actions of the imidazobenzodiazepine, Ro15-4513 (2.5 mg/kg IP), ethanol (0.50 g/kg, 0.75 g/kg, 1.25 g/kg), and Ro15-4513 in combination with ethanol were assessed using low activity male Charles River (CD) rats. Horizontal (ambulatory) and nonhorizontal (rearing, grooming, etc.) activity were measured in the open field with a Digiscan activity system. When Ro15-4513 was given alone, animals responded in a manner similar to that of the control animals. Ethanol alone, however, resulted in a significant enhancement of activity, with the effect being most pronounced at 0.50 g/kg for horizontal activity and 1.25 g/kg for nonhorizontal activity. A potentiation of the ethanol-induced stimulant effect was observed following pretreatment with Ro15-4513 on the horizontal activity measure for the 1.25 g/kg ethanol group. An attenuation of activity was observed for this group on the nonhorizontal activity measure. Ro15-4513, however, did not affect the stimulation produced by the other doses of ethanol on the nonhorizontal measure. The results suggest that possibility of distinct neurochemical mechanisms in the mediation of horizontal and nonhorizontal activity and that, perhaps, GABA-benzodiazepine mechanisms may play different roles in mediating their ETOH-induced stimulant effect.

Animals↗
PubMedDate not supplied

Ro15-4513 antagonizes depression of open-field horizontal activity by ethanol in rats.

The imidazobenzodiazepine, Ro15-4513, has been shown to antagonize some of the behavioral effects of ethanol (ETOH). In rats having relatively little experience in the open field, the actions of ETOH (0.75 g/kg IP), Ro15-4513 (1.25 mg/kg and 2.5 mg/kg, IP), and Ro15-4513 in combination with ETOH were measured on horizontal activity. Rats receiving ETOH showed a significant depression in horizontal activity. Doses of Ro15-4513 given alone produced no significant differences in activity from baseline levels. Rats pretreated with Ro15-4513 prior to receiving ETOH, however, showed a significant attenuation of the ETOH induced depression of activity. These results indicate that Ro15-4513 is effective in attenuating the depressive effects of ETOH in the open field in rats having little experience in the apparatus.

Animals↗
PubMedDate not supplied

Neurobehavioral studies of ethanol reward and activation.

Although generally considered to be a depressant drug, ethanol has both stimulant and depressant effects on behavior. This biphasic action of ethanol may be related to its reinforcing effects and to the neurobehavioral events that occur with changes in blood alcohol concentration (BAC). Ethanol was found to reduce the threshold and increase response rates for brain stimulation reward (BSR) at lateral hypothalamic, but not ventral noradrenergic bundle brain sites. These effects were also found to only occur when testing occurred on the ascending limb of the BAC. Studies of the effects of ethanol on open-field activity showed that the stimulant effects of low doses of ethanol were also seen only during the ascending limb of the BAC; depression was usually found during the descending limb. Neurochemical data from other investigators suggest that the facilitation of BSR and stimulation of activity may be mediated by mesolimbic dopamine systems.

Animals↗
PubMedDate not supplied

Ethanol-induced stimulation and depression on measures of locomotor activity: effects of basal activity levels in rats.

Male Sprague-Dawley rats selected for low (LA) and high activity (HA) were used to investigate the biphasic actions of ethanol (EtOH) (20% v/v) on spontaneous measures of activity. Following IP injections of low to moderate doses of EtOH (0.10 g/kg and 0.50 g/kg), horizontal and vertical activities were assessed at 0-10- and 30-40-min intervals. Rats preselected for LA exhibited an increase in performance on both measures. The stimulatory effect, however, was observed only during the 0-10-min session with the lowest dose of EtOH (0.10 g/kg). The 0.50-g/kg dose had no effect on either measure at the 0-10-min interval; however, both doses suppressed activity at the 30-40-min interval. In contrast, activity was suppressed in HA animals independent of the EtOH dose level or time interval. These results demonstrate that basal response profiles are important predictors of behavioral activation following low stimulant doses of EtOH. Moreover, the results demonstrate the importance of selecting animals for basal activity levels to reliably interpret the mechanisms controlling the stimulant and depressant effects of EtOH.

Animals↗