Search PubMed⌕ Search

Biomedical subjects

D M Simpson

Publications and source records attributed to D M Simpson.

At least 145 records · Page 8Linked to original sources
PubMed1983

Latency changes in the human somatosensory evoked potential at extreme depths.

Somatosensory evoked potentials to lower limb stimulation were recorded from the three participants in a recent chamber dive to a world depth record of 686 m (2250 ft). Because of the 10% nitrogen breathing mixture, both inert gas narcosis and high pressure nervous syndrome were factors in the dive. Latencies of evoked potential peaks were measured relative to the peak of the first cortical component, P1, in order to separate central from peripheral effects. Several peak latencies changed systematically during compression. The several components of the somatosensory evoked potential appeared differentially sensitive to either inert gas narcosis or the high pressure nervous syndrome with increasing depth. The latencies of all peaks following the initial cortical P1 were shorter at depth than in surface control recording. This is consistent with a state of hyperexcitability in the brain that is felt to characterize the high pressure nervous syndrome. Changes in peak latency were consistent across subjects and in some cases achieved statistical significance despite the small number of subjects available for testing. Although these findings are preliminary, they suggest that evoked potential latencies may have value as a means of following the effects of extreme pressure on the central nervous system.

Atmosphere Exposure Chambers↗
PubMed1979

Properties of a gonococcal inhibitor produced by Escherichia coli.

Strains of Escherichia coli can inhibit the in vitro growth of Neisseria gonorrhoeae. One E. coli strain released a potent agar-diffusible gonococcal growth inhibitor which was extracted and assayed in an agar well assay system. The culture conditions necessary to produce the inhibitor were determined. The inhibitor was bacteriostatic, in most cases, for N. gonorrhoeae. Based on ultrafiltration and column chromatography, the inhibitor appeared to have a molecular weight in the range of 1200 to 2000. Evidence that the molecule contained charged sites was obtained by membrane binding and column chromatography. The inhibitor was stable to extremes of heat, cold and pH. It was not volatile or susceptible to proteolytic enzymes, lysozyme, lipase, DNAase, RNAase or certain chelating agents. Its activity was completely blocked by ferric ammonium citrate. This inhibitor is dissimilar to previously reported gonococcal inhibitors of bacterial origin.

Escherichia coli↗
PubMed1977

Effects of lipids on the activity of ferrochelatase.

Removal of lipids from submitochondrial particles or detergent-solubilized mitochondrial preparations of rat liver resulted in a 90% loss of ferrochelatase (protochemeferro-lyase, EC 4.99.1.1) activity. The addition of either a fatty acid or phospholipid restored enzyme activity; the extent of reactivation being correlated with the degree of unsaturation of the fatty acid or acyl chain and independent of the polar head group of the phospholipid, Arrhenius plots of the ferrochelatase activities of submitochondrial particles and detergent-solubilized mitochondrial preparations showed transition temperatures of 37 and 28.5 degrees C, respectively. Ferrochelatase of submitochondrial particles or detergent-solubilized preparations had an absolute requirement for Ca2+. The ferrous salt of oxalic acid, a Ca2+ chelator, was a very poor substrate for these preparations. In contrast, ferrochelatase activities of fatty acid- or lipid-supplemented acetone extracts of these preparations were not dependent on the presence of Ca2+ and ferrous oxalate served as substrate for these extracts.20

Animals↗
PubMed1977

Behavioral withdrawal following several psychoactive drugs.

The chronic administration of several psychoactive drugs has been suggested to produce behavioral withdrawal syndromes in the absence of physical withdrawal. The present study employed four representative psychoactive drugs, amphetamine, chlorpromazine, iproniazid, and desipramine, in a common behavioral paradigm using electrical stimulation of the brain to test for behavioral withdrawal. Behavior differing from both predrug and drug produced behavior occurred following the termination of amphetamine, iproniazid and chlorpromazine administration. The first two drugs produced an increase in self stimulation during administration, followed by a very significant decrease after the drugs were discontinued. Chlorpromazine administration on the other hand, produced a decrease in self stimulation rates, followed by a rebound increase after termination of treatment. No systematic effects were observed with desipramine. The relationship between the behavioral effects of these drugs during and following treatment and possible homeostatic mechanism influencing response tendencies is discussed.

Animals↗
PubMed1972

The neutrophilic leukocyte in wound repair a study with antineutrophil serum.

The role of the neutrophilic leukocyte in wound healing was investigated by observing the progress of repair in the absence of these cells. Circulating neutrophils were eliminated in guinea pigs by the administration of antineutrophil serum (ANS) 24 hr before wounding and by daily injections throughout a 10 day period of healing. Control animals received normal rabbit serum at the same dose levels and times. The wounds consisted of six linear incisions in the dorsal skin of the animals.The contents of 24-hr neutropenic and control wounds were compared by quantitating the major cellular and extracellular wound components using a histometric technique. At 24 hr, there were no differences between control and neutropenic wounds in the per cent of total wound volume occupied by mononuclear leukocytes and fibrin. The neutropenic wounds had no neutrophils, had a significantly decreased volume of fluid space, and an increased volume of red cells, as compared with controls. The differences in numbers of erythrocytes and amount of fluid space in these two sets of wounds may be related to substances within neutrophils that promote lysis of erythrocytes or affect vascular permeability. In spite of the lack of neutrophils in the ANS-treated animals during the 10 days of healing, no differences were observed between the control and neutropenic wounds relative to the rate of wound debridement or the extent of repair. The wounds from the two groups of animals were identical in cellularity and degree of connective tissue formation. These observations support the notion that neither wound debridement nor the formation of granulation tissue are dependent upon the presence of neutrophils. A neutrophil response in early wounds is not an essential antecedent to the infiltration of monocytes, as suggested by previous investigations.

Animals↗
PubMed1971

Effects of heterologous antineutrophil serum in guinea pigs. Hematologic and ultrastructural observations.

Two pools of rabbit anti-guinea pig neutrophil serum (ANS) were prepared using an intravenous (ANS I) or subcutaneous (ANS II) route of immunization with proteose peptone-stimulated peritoneal exudate neutrophils (PMNs) from albino guinea pigs. In vitro, both pools of ANS contained high titers of agglutinating antibodies to neutrophils and lower titers against lymphocytes and red cells. Agglutinins against all three cell types could be selectively removed by absorption. The in vivo hematologic effects of both the absorbed and unabsorbed antisera were examined after intraperitoneal administration, and the effects of ANS on neutrophils in blood, bone marrow, and peritoneal cavity were examined by light and electron microscopy of spleen, liver, lung, lymph node, buffy coat, bone marrow and pellets of peritoneal cells removed at various time intervals within 24 hours. Injection of either antisera caused a rapid decrease in circulating neutrophils and lymphocytes, which reached their lowest levels within 12 hours. Neutrophils that disappeared from the circulation were sequestered primarily in liver and spleen where they were phagocytized, as morphologically intact cells, by macrophages and then rapidly digested. Immature bone marrow neutrophils as young as early myelocytes were ingested by macrophages in the marrow at 6 hours or later after ANS. Neutrophils that were phagocytized were apparently opsonized by ANS since there was no ultrastructural evidence of neutrophil lysis in blood or bone marrow after ANS treatment. However, both lysed and ingested neutrophils were observed in the peritoneal cavity. Absorption of ANS with neutrophils removed the ability of the serum to produce neutropenia. However, absorption of ANS with lymphocytes did not alter the lymphopenia produced by the antiserum. The fate of lymphocytes leaving the peripheral circulation was not apparent. Lymphocytes did not accumulate in liver or spleen sinusoids and were not ingested by macrophages in these organs, as were the neutrophils. There was no evidence of paracortical depletion or extensive phagocytosis of lymphocytes in lymph nodes after ANS, as other investigators have reported after administration of antilymphocyte serum.

Agglutination↗
PubMedDate not supplied

Information overload disrupts digit recall performance in schizophrenics.

The effect of auditory information overload on schizophrenics was examined by using a modified forward digit recall task. When memory capacity was exceeded, schizophrenics, but not controls, showed severe disruptions in performance on individual trials. Theories to account for the disruptions are discussed. A combination of factors, rather than simply limited information handling capacity, appears best able to account for the phenomenon. It is emphasized that further understanding of active cognitive process requires examination of trial by trial individual subject data.

Adult↗