Search PubMed⌕ Search

Biomedical subjects

C A Fuller

Publications and source records attributed to C A Fuller.

At least 37 records · Page 2Linked to original sources
PubMed1998

Biochemical evidence for a conserved interaction between bacterial transferrin binding protein A and transferrin binding protein B.

As an adaptation to the iron-restricted environment of the host, some bacterial pathogens possess iron acquisition pathways mediated by surface receptors that specifically bind transferrin from the host. The receptor is composed of two receptor proteins, TbpA and TbpB, which are both capable of binding to transferrin. Previous studies have demonstrated that affinity isolation of TbpB from Neisseria meningitidis or Haemophilus influenzae with immobilized human transferrin required the homologous TbpA, implicating a TbpA-TbpB interaction. In this study, we demonstrated that TbpA from either species can facilitate isolation of either TbpB, indicating that the TbpA-TbpB interaction is conserved within these species. Extension of these studies to veterinary pathogens in which a TbpA-Tf complex is used to affinity isolate heterologous TbpBs, demonstrated an interaction between the receptor proteins from N. meningitidis and Actinobacillus pleuropneumoniae. Further delineation of the TbpA-TbpB-transferrin interaction with recombinant chimeric N. meningitidis/A. pleuropneumoniae TbpBs has identified a region encoded by the first 1/4 of the tbpB gene which is involved in Tf binding.

Actinobacillus pleuropneumoniae↗
PubMed1998

Effects of hyperdynamic fields on input-output relationships and long-term potentiation in the rat hippocampus.

The effects of a 2G force environment on synaptic plasticity were examined in the rat hippocampus. Field potentials from neurons in the CA1 pyramidal cell layer were evoked by stimulation of the afferent Schaffer collateral/commissural fibers in an in vitro slice preparation. Input-output (I-O) relationships of the circuit were determined before and after tetanizing stimuli given to induce long term potentiation (LTP), a form of neural plasticity. I-O curves from animals exposed to 2G via centrifugation for either 2 or 14 days were not different from those obtained in control (1G) animals. Similarly, induction of LTP was equivalent in all groups, showing increases in maximum amplitude, slope and midpoint response of the fitted Boltzmann functions compared to un-tetanized controls. Comparison of slices from dorsal and ventral hippocampus showed the location of the slice had no effect of LTP expression. We conclude that, in contrast to other reports of functional changes in the central nervous system under altered force environments, cellular mechanisms of synaptic plasticity, which may underlie learning and memory, are preserved in the hippocampus.

Action Potentials↗
PubMed1998

Chronic 2G exposure affects c-Fos reactivity to a light pulse within the rat suprachiasmatic nucleus.

This study examined the effect of the hyperdynamic environment on the function of the retinohypothalamic tract. Rats were exposed to either 2 days or 21 days of 2G via centrifugation. During the last hour of 2G exposure, one series of rats was exposed to a 1 hour phase-shifting light pulse while the second series of rats did not receive a light pulse. In addition a groups of 1G controls was exposed to the same 1 hour lighting paradigm. All animals were processed for c-Fos within the SCN. The 1G controls showed the normal response to light in which significantly greater numbers of c-Fos positive neurons were found in the SCN of the light pulsed rats relative to that of the nonlight pulsed rats. However, rats exposed to 2 days of 2G did not show the same response to light. Light pulsed rats and nonlight pulsed rats exhibited few c-Fos positive neurons within the SCN. A recovery in the effect of light to induce c-Fos reactivity within SCN neurons occurred in the rats exposed to 21 days of 2G. These results suggest that exposure to 2G can temporarily suppress the responsiveness of the SCN to the phase-shifting effects of light mediated by the retinohypothalamic tract.

Adaptation, Physiological↗
PubMed1997

Effects of hypergravic fields on serotonergic neuromodulation in the rat hippocampus.

The effects of 7 day exposure to 2G fields on serotonergic modulation at two synapses on a hippocampal pathway were examined by recording dentate gyrus and CA1 pyramidal cell layer electrical activity. Serotonin decreased the amplitude of the population spike (synchronous action potentials in hundreds of neurons) in both the dentate gyrus and CA1 regions of rats exposed to 2G fields for 7 days. The inhibition, averaging 26 +/- 4% (mean +/- SEM) in the dentate gyrus and 80 +/- 5% in the CA1 region, was not significantly different from inhibitory responses observed in 1G controls. The 5-HT1A agonist 8-OH-DPAT mimicked this inhibition in the dentate and CA1 regions of 1G rats. 8-OH-DPAT responses were not affected by exposure to 2G fields. We conclude that the hippocampus contains surplus 5-HT receptors so that decreases in receptor density reported in receptor binding studies do not result in a decrease in modulatory capability. A model to account for the physiological pathway that relates gravitational field strength to 5-HT receptor density without changing the effectiveness of 5-HT neuromodulation is discussed.

8-Hydroxy-2-(di-n-propylamino)tetralin↗
PubMed1997

Eimeria (Protozoa: Eimeriidae) from North American sciurids, Glaucomys sabrinus and Tamias townsendii: with a description of a new species.

From 1990 to 1991, 11 northern flying squirrels, Glaucomys sabrinus, and 30 Townsend's chipmunks, Tamias townsendii, were live-trapped, marked, and released in MacDonald Forest, Benton Co., Oregon and their feces at each capture examined for the presence of coccidian parasites. Two eimerians were found in G. sabrinus: Eimeria dorneyi and a second species we describe here as new. One species, Eimeria vilasi, was identified from T. townsendii. Sporulated oocysts of the new eimerian are strongly ellipsoidal, pointed at 1 end, and are 47.2 x 25.0 (41-52 x 22-31) microns with ovoidal sporocysts, 19.0 x 10.5 (17-21 x 9-11) microns. A micropyle and oocyst residuum are absent, but, occasionally, a polar granule is present in the oocyst. In the sporocysts, Stieda and substieda bodies are present, as is a membrane-bound residuum. Sporulated oocysts of E. dorneyi are uniformly ellipsoidal, 23.0 x 14.7 (17-26 x 13-16) microns with elongate ellipsoidal sporocysts, 11.6 x 5.7 (9-13 x 5-7) microns. A micropyle and oocyst residuum are absent, but 1 polar granule is present. A Stieda body is present, but sub- and parastieda bodies are absent. The sporocyst residuum is composed of granules in a compact mass. Here we provide phototype (hapantotype) specimens archived in a nationally accredited museum and a line drawing (cartoon) to supplement the one provided by Soon and Dorney because their drawing did not show the sporocyst residuum given in the written description.

Animals↗
PubMed1996

Primate circadian rhythms during spaceflight: results from Cosmos 2044 and 2229.

The circadian timing system (CTS) coordinates an animal's physiology and behavior both internally and with the 24-h day. Previous studies have suggested that the CTS is sensitive to changes in gravity. To examine this question, the expression of the CTS in four juvenile male rhesus macaques (Macaca mulatta) were studied in space. These animals were flown on the Cosmos 2044 and 2229 missions. Activity, heart rate, and axillary and brain (Cosmos 2229) temperatures were recorded. In both flights, the subjects exhibited delays in the phasing of their temperature rhythms and a decrease in mean heart rate compared with ground control studies. These data are in support of other studies that demonstrate that the CTS is sensitive to changes in the gravitational environment. Furthermore, the data also support the concept of a multioscillator organization of the primate CTS due to the differential responses of the rhythms measured.

Animals↗
PubMed1996

Energy expenditure in rhesus monkeys (Macaca mulatta) during spaceflight using doubly labeled water (2H2(18)O).

The mean daily energy expenditure rates of three rhesus monkeys (Macaca mulatta) were determined during spaceflight on the joint US-Russian Cosmos 2044 and 2229 missions by the doubly labeled water (2H2(18)O) method. In-flight values were compared with ground data obtained from seven measurements taken from six chair-adapted control monkeys. The mean energy expenditure for the ground control determinations was 94.5 +/- 6.4 kcal.kg-1.day-1 (n = 6). The mean in-flight energy expenditure, 55.1 +/- 8.0 kcal.kg-1.day-1 (n = 3), was significantly less than the mean ground control value (P < 0.05). These data suggest that energy expenditure in restrained rhesus monkeys is significantly reduced during spaceflight.

Animals↗
PubMed1996

Population dynamics of two species of Eimeria (Apicomplexa: Eimeriidae) in deer mice (Peromyscus maniculatus): biotic and abiotic factors.

I investigated whether biotic factors (competitive exclusion between parasites and host immunity), abiotic factors (high temperature, low temperature, and rainfall), or a combination of the 2 affected the population dynamics of Eimeria arizonensis and Eimeria delicata in naturally infected deer mice (Peromyscus maniculatus). There was no evidence of competitive exclusion between E. arizonensis and E. delicata, nor were E. arizonensis population dynamics affected by host immunity (young deer mice were not infected significantly more frequently than adults). However, high temperatures were negatively associated with the prevalence of observed infections (r = -0.725, P < 0.001), suggesting sporulation of oocysts might be affected. In contrast, juvenile deer mice were infected with E. delicata more frequently than adults (z = 2.05, P < 0.02), suggesting that host immunity plays a role in the population dynamics of E. delicata. Temperature and rainfall during oocyst sporulation were not significantly associated with the prevalence of observed E. delicata infections. Finally, there was no evidence that a combination of biotic and abiotic factors was important in the population dynamics of either eimerian. Thus, the population dynamics of E. arizonensis seem to be controlled by abiotic factors, whereas those of E. delicata seem to be affected by biotic factors.

Age Factors↗
PubMed1995

Circadian rhythms of temperature and activity in obese and lean Zucker rats.

The circadian timing system is important in the regulation of feeding and metabolism, both of which are aberrant in the obese Zucker rat. This study tested the hypothesis that these abnormalities involve a deficit in circadian regulation by examining the circadian rhythms of body temperature and activity in lean and obese Zucker rats exposed to normal light-dark cycles, constant light, and constant dark. Significant deficits in both daily mean and circadian amplitude of temperature and activity were found in obese Zucker female rats relative to lean controls in all lighting conditions. However, the circadian period of obese Zucker rats did not exhibit differences relative to lean controls in either of the constant lighting conditions. These results indicate that although the circadian regulation of temperature and activity in obese Zucker female rats is in fact depressed, obese rats do exhibit normal entrainment and pacemaker functions in the circadian timing system. The results suggest a deficit in the process that generates the amplitude of the circadian rhythm.

Activity Cycles↗
PubMed1995

Acute exposure to 2G phase shifts the rat circadian timing system.

The circadian timing system (CTS) provides internal and external temporal coordination of an animal's physiology and behavior. In mammals, the generation and coordination of these circadian rhythms is controlled by a neural pacemaker, the suprachiasmatic nucleus (SCN), located within the hypothalamus. The pacemaker is synchronized to the 24 hour day by time cues (zeitgebers) such as the light/dark cycle. When an animal is exposed to an environment without time cues, the circadian rhythms maintain internal temporal coordination but exhibit a "free-running" condition in which the period length is determined by the internal pacemaker. Maintenance of internal and external temporal coordination are critical for normal physiological and psychological function in human and non-human primates. Exposure to altered gravitational environments has been shown to affect the amplitude, mean, and timing of circadian rhythms in species ranging from unicellular organisms to man. However, it has not been determined whether altered gravitational fields have a direct effect on the neural pacemaker, or affect peripheral physiological systems that express these circadian parameters. In previous studies, the ability of a stimulus to phase shift circadian rhythms was used to determine whether a stimulus has a direct effect on the neural pacemaker. The present experiment was performed in order to determine whether acute exposure to a hyperdynamic field could phase shift circadian rhythms.

Animals↗
PubMed1995

Oocyst output, periodicity, and immunity of two deer mouse (Peromyscus maniculatus) eimerians (Eimeria arizonensis and Eimeria delicata).

We compared the life histories of 2 eimerians (Eimeria arizonensis and Eimeria delicata), which co-occur in the deer mouse (Peromyscus maniculatus). Laboratory-reared deer mice were given 10(3), 10(4) (E. delicata), or 10(3), 10(4), or 10(5) (E. arizonensis) oocysts by stomach intubation. Eimeria arizonensis infections lasted longer (11-13 days) than E. delicata infections (9-10 days). Eimeria arizonensis infections also produced more oocysts for each oocyst ingested at both levels compared. Both parasites exhibited periodicity in oocyst output at all levels compared. However, peaks in E. arizonensis output occurred at approximately 20-24-hr intervals, whereas peaks in E. delicata output occurred at 12-16-hr intervals. Finally, deer mice developed immunity to both eimerians after only 1 inoculation at all levels tested. Based on these parameters, we expect E. arizonensis to have a greater reproductive potential than E. delicata in free-living deer mice.

Analysis of Variance↗
PubMed1994

Influence of gravity on the circadian timing system.

The circadian timing system (CTS) is responsible for daily temporal coordination of physiological and behavioral functions both internally and with the external environment. Experiments in altered gravitational environments have revealed changes in circadian rhythms of species ranging from fungi to primates. The altered gravitational environments examined included both the microgravity environment of spaceflight and hyperdynamic environments produced by centrifugation. Acute exposure to altered gravitational environments changed homeostatic parameters such as body temperature. These changes were time of day dependent. Exposure to gravitational alterations of relatively short duration produced changes in both the homeostatic level and the amplitude of circadian rhythms. Chronic exposure to a non-earth level of gravity resulted in changes in the period of the expressed rhythms as well as in the phase relationships between the rhythms and between the rhythms and the external environment. In addition, alterations in gravity appeared to act as a time cue for the CTS. Altered gravity also affected the sensitivity of the pacemaker to other aspects of the environment (i.e., light) and to shifts of time cues. Taken together, these studies lead to the conclusion that the CTS is indeed sensitive to gravity and its alterations. This finding has implications for both basic biology and space medicine.

Adaptation, Physiological↗