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Biomedical subjects

K L Smith

Publications and source records attributed to K L Smith.

At least 163 records · Page 9Linked to original sources
PubMed1992

Bovine neutrophil responses to parenteral vitamin E.

Twenty-eight Holsteins were tested to determine effects of dietary and parenteral vitamin E supplementation during the dry period on plasma alpha-tocopherol and in vitro neutrophil functions at calving. Cows were assigned to one of four experimental groups receiving either supplemental dietary vitamin E, injections of vitamin E, both dietary and injections of vitamin E, or neither source of supplemental vitamin E during the dry period in a 2 x 2 factorial arrangement. Cows receiving parenteral vitamin E were injected subcutaneously with 3000 IU of vitamin E (dl-alpha-tocopherol) at 10 and 5 d prior to anticipated calving. Cows not receiving parenteral vitamin E were injected with a placebo. Experimental groups receiving dietary vitamin E during the dry period were supplemented with 1040 IU/d compared with none for controls. Cows injected with vitamin E had greater plasma alpha-tocopherol concentration 5 d after the first injection, at calving, and 1 wk after calving than did cows injected with placebo. Plasma alpha-tocopherol concentrations did not differ between dietary vitamin E treatment groups from calving through 4 wk postpartum. No interaction was found between dietary and parenteral supplementation of vitamin E on plasma alpha-tocopherol concentration. Neutrophils from cows injected with vitamin E had greater intracellular kill of bacteria at calving than did neutrophils from placebo-injected cows. Neither phagocytic index nor percentage of neutrophils phagocytizing differed between vitamin E-injected and placebo-injected cows. Dietary vitamin E during the dry period had no effect on neutrophil function at calving. Intracellular kill and plasma alpha-tocopherol were correlated at calving.

Administration, Oral↗
PubMed1992

Efficacy of an Escherichia coli J5 mastitis vaccine in an experimental challenge trial.

An Escherichia coli (O111:B4) J5 bacterin was tested for efficacy in reducing IMI and severity of clinical coliform mastitis in an experimental challenge trial. Ten cows were immunized at drying off, 30 d after drying off, and at calving. Ten control cows were not immunized. Right front quarters of all cows were infused with a heterologous strain of E. coli approximately 30 d after calving. Vaccinated cows had lower bacterial counts in milk and lower rectal temperatures than unvaccinated controls following intramammary challenge. Milk production and DMI were more depressed in controls than in vaccinated cows. Milk SCC did not differ between experimental groups. Mean serum IgG titer to whole cell E. coli J5 was significantly greater in vaccinated than in unvaccinated cows at 30 d after drying off, day of challenge, and 7 d postchallenge. Milk IgG titer to E. coli J5 was higher at challenge in vaccinated than in control cows. Vaccination with the E. coli J5 bacterin did not prevent IMI but did reduce severity of clinical signs following intramammary experimental challenge with a heterologous E. coli strain.

Animals↗
PubMed1992

Susceptibility of Escherichia coli isolated from intramammary infections to phagocytosis by bovine neutrophils.

Thirteen Escherichia coli isolated from naturally occurring IMI were tested for susceptibility to phagocytosis by bovine blood neutrophils. Isolates were opsonized in pooled serum collected from nine healthy lactating cows. Bacteria isolated from IMI first diagnosed within 3 d after calving were more resistant to phagocytosis than were isolates from IMI originating during either the first half of the dry period or later during lactation. Duration of the IMI was negatively correlated with both phagocytic index and percentage of neutrophils phagocytizing within bacterial isolates from IMI originating at calving and during lactation. Phagocytosis was independent of duration of IMI within isolates from IMI originating during the first half of the dry period. Susceptibility to in vitro phagocytosis by neutrophils was not related to O antigen serotype, encapsulation, or growth in dry cow secretion.

Animals↗
PubMed1992

Effect of supplementing periparturient cows with vitamin E on distribution of alpha-tocopherol in blood.

Holstein cows were fed 0 or 1000 IU/d of supplemental vitamin E during the dry period and injected with placebo or 3000 IU of vitamin E at 10 and 5 d prior to anticipated calving. Blood was collected at various times, starting at 60 d prepartum (dry off) and concluding 30 d postpartum, and separated into plasma, red blood cells, and neutrophils. Oral supplementation increased concentrations of alpha-tocopherol in plasma and red blood cells on 10 d, but not on 5 d prepartum. Injection of vitamin E increased alpha-tocopherol in plasma, red blood cells, and neutrophils at d 5 prior to and on the day of parturition. Concentrations of alpha-tocopherol and cholesterol in plasma were correlated, and both were at their nadir at parturition. Concentrations of alpha-tocopherol in plasma and red blood cells were correlated, but the correlation increased when plasma alpha-tocopherol was expressed per unit of cholesterol. alpha-Tocopherol in plasma and neutrophils had a low correlation. Injection of alpha-tocopherol increased its concentration in plasma, red blood cells, and neutrophils during the periparturient period. Concentration of alpha-tocopherol in plasma of periparturient cows may be limited by its low lipid content, and transport mechanisms for alpha-tocopherol may differ between red blood cells and neutrophils.

Animals↗
PubMed1992

The ontogeny of hippocampal local circuits and focal epileptogenesis.

Our understanding of the pathophysiological mechanisms underlying the childhood epilepsies is rudimentary at this time. However, results of recent studies in animal models have lead to a number of important hypotheses concerning age-dependent alterations in seizure susceptibility. In area CA3 of hippocampus it appears that during a critical period when this brain area is particularly prone to electrographic seizures, an overabundance of recurrent excitatory synapses may exist. At the same time the synapses themselves appear to be functionally different than their mature counterpart. Age-dependent differences in the properties of postsynaptic NMDA receptors seem to contribute to enhanced seizure susceptibility. In recent years significant progress has been made in unravelling the fundamental processes that underlie the formation of connections between developing neurons. Over-production of early-formed axon collaterals appears to be common-place in the CNS. Moreover, the selection of appropriate patterns of connectivity appear to be dependent in large part on the patterning of neurophysiologic activity. In this regard the NMDA receptor seems to play a pivotal role in synapse consolidation. Based on these observations and the central role recurrent excitation appears to play in hippocampal seizures, it seems entirely plausible that excessive abnormal neuronal discharging that occurs during seizures early in life could result in the consolidation of abnormal numbers of recurrent excitatory synapses. This miswiring of hippocampal networks might be responsible for the marked seizure susceptibility into adulthood and might even contribute to complex partial epilepsy in individuals with a history of childhood seizures.

Adult↗
PubMed1991

Anticachectic and antitumor effect of eicosapentaenoic acid and its effect on protein turnover.

The effect of the polyunsaturated fatty acids eicosapentaenoic acid (EPA) and gamma-linolenic acid (GLA) on host body weight loss and tumor growth has been investigated in mice bearing a cachexia-inducing colon adenocarcinoma, the MAC16. EPA effectively inhibited both host weight loss and tumor growth rate in a dose-related manner with optimal effects being observed at a dose level of 1.25 to 2.5 g/kg. At these concentrations host body weight was effectively maintained, and there was a delay in the progression of growth of the tumor, such that overall survival was approximately doubled in EPA-treated animals, using the criteria dictated by the United Kingdom Coordinating Committee for the welfare of animals with neoplasms. Even when tumor growth resumed, weight loss did not occur. Animals bearing the MAC16 tumor showed a decreased protein synthesis and an increased degradation in skeletal muscle. Treatment with EPA significantly reduced protein degradation without an effect on protein synthesis. The effect of GLA on both host body weight loss and tumor growth was much less pronounced than that of EPA, with an effect only being seen at a dose of 5 g/kg, at which some toxicity was observed. In vitro studies showed that while EPA was effective in inhibiting tumor-induced lipolysis, GLA was ineffective in this respect. However, prostaglandin E1, which is formed from GLA in vivo, showed partial reversal of tumor-induced lipolysis and probably accounted for the anticachectic effect of GLA. These results suggest that EPA as the pure fatty acid should be considered for clinical investigation as both an anticachectic and antitumor agent, since prior work has shown that the other major component of fish oil docosahexaenoic acid is without pharmacological activity in this system.

Animals↗
PubMed1991

Costs associated with selected preventive practices and with episodes of clinical mastitis in nine herds with low somatic cell counts.

Nine dairy herds (mean size, 149 cows) with bulk-tank milk somatic cell counts of less than 300,000 cells/ml and greater than 80% of cows with Dairy Herd Improvement Association linear somatic cell counts less than or equal to 4 were selected for study. Each herd was monitored for 12 consecutive months. Duplicate quarter-milk specimens were collected from each cow for bacteriologic culturing at beginning of lactation, cessation of lactation, and at the time of each clinical episode of mastitis. Streptococcus agalactiae was never isolated and Staphylococcus aureus was isolated from less than 1% of all quarters. There were 554 episodes of clinical mastitis. During the year of study, the incidence rate of clinical mastitis varied from 15.6 to 63.7% of cows among the 9 herds. Mean costs per cow per year in herd for mastitis prevention were: $10 for paper towels, $3 for nonlactating cow treatment, and $10 for teat disinfectants. Mean cost associated with clinical mastitis was $107/episode. Approximately 84% ($90) of the costs attributed to a clinical episode were associated with decreased milk production and nonsalable milk. Costs of medication and professional veterinary fees per clinical episode varied significantly among the 9 herds. Three of the herds did not have a veterinarian treat a clinical episode of mastitis during the year of study even though 2 of these herds had the first and third highest incidence rates of clinical mastitis. When calculated on a per cow in herd basis, mean costs of $40/cow/year were attributed to clinical mastitis.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1991

Calcium modulation of the N-methyl-D-aspartate (NMDA) response and electrographic seizures in immature hippocampus.

Recordings from the CA3 region of hippocampal slices indicate a developmental change in the divalent cation sensitivity of the response elicited by N-methyl-D-aspartate (NMDA) application. In parallel experiments a developmental difference is demonstrated in the capacity of extracellular calcium to modulate electrographic seizure generation. Calcium modulation of the NMDA-elicited response may contribute to the pronounced capacity of immature hippocampus to generate electrographic seizures. Under these conditions activity dependent changes in extracellular calcium could have a greater influence on ion flow produced by activation of the NMDA receptor. The possibility that changes in the receptor isoform may occur during development would have widespread implications for normal cognitive functions and dysfunctions during brain maturation.

Age Factors↗
PubMed1991

Confocal microscopy and three-dimensional reconstruction of electrophysiologically identified neurons in thick brain slices.

Three-dimensional morphology and electrophysiology were correlated from individual neurons in a thick brain slice preparation. The hippocampal formation from immature and adult rats was cut transverse to the longitudinal axis into 500 microns-thick slices which were maintained under physiologic conditions. Individual neurons were impaled and physiologically characterized using microelectrodes. Recordings were made from the soma and in some cases from a dendrite. The impaled neurons were filled through the microelectrode with the fluorescent dye lucifer yellow and imaged by confocal scanning laser microscopy using an analog preprocessor. As many as 180 optical sections were recorded as a function of depth through the slices. Images are presented as a series of optical sections, stereo pairs, or three-dimensional reconstructions. Both stereo contouring and volume rendering methods were employed, and the reconstructions were viewed from any arbitrary perspective. Dendritic and axonal fields were separated from each other and displayed separately or as different pseudocolors. The three-dimensional reconstructions provided perspectives that were difficult or impossible to appreciate by viewing the optical sections or conventionally formed stereo pairs.

Animals↗
PubMed1991

Ultrastructural investigation of neurons identified and localized using the confocal scanning laser microscope.

Studies of labeled neurons at the light-microscopic level often pinpoint a substructure of particular interest, i.e., a synapse or a spine. An ultrastructural investigation would explain a lot about how these structures arose, how they function, and how they are regulated. Finding a small region in a large block can require constant checking during sectioning, until past the structure. In our pursuit of the synaptic structure of varicosities on the axons of neurons identified physiologically and morphologically at the light level, we have combined confocal scanning laser microscopy (CSLM) with conventional and high-voltage electron microscopy (EM). CSLM images were collected in the reflection mode to view neurons filled with horseradish peroxidase and stained with nickel-intensified diaminobenzidine, which is compatible with EM. The CSLM optical sections provided a record of what one should expect to see at regular intervals throughout the depth of the tissue block. We have shown that the CSLM greatly simplified the task of localizing small structures in brain tissue prepared for EM.

Animals↗
PubMed1991

Antibodies to iron-regulated outer membrane proteins of coliform bacteria isolated from bovine intramammary infections.

Expression of iron-regulated outer membrane proteins (OMP) by Escherichia coli and Klebsiella pneumoniae initially isolated from bovine intramammary infections (IMI) was investigated. Additionally, the presence of antibodies in bovine serum and mammary secretion directed against the iron-regulated OMP was examined. Outer membrane proteins were separated by sodium-dodecyl polyacrylamide electrophoresis. Detection of immunoglobulin G directed against OMP was by immunoblotting. All Gram-negative bacteria expressed iron-regulated OMP when grown in skim milk or trypticase soy broth plus iron chelator, alpha-alpha'-dipyridyl. Immunoglobulin G directed against the iron-regulated OMP, as well as the major OMP and several other proteins, was detected in serum and milk of lactating cows with or without Gram-negative bacterial IMI. Antibody against the iron-regulated OMP was detected also in colostrum, secretion from the involuted gland, and in newborn calf serum 4 days after ingesting colostrum.

Animals↗
PubMed1991

The relationship between oral spelling and phonological breakdown in a conduction aphasic.

Unsolicited oral spelling has been observed in conduction aphasics during word-production difficulty (Kohn, 1985), but has never been examined systematically. In the present study, the possible role of oral spelling in the word-production process of a conduction aphasic (JM) is explored. Oral spelling occurred much more frequently during picture naming than during either oral reading or repetition, and it seemed to be operating as a strategy to lessen the phonemic output deficit often observed in this syndrome.

Aphasia, Broca↗
PubMed1991

Age-dependent alterations in the operations of hippocampal neural networks.

Results from numerous studies suggest that the functioning of rat hippocampal neural networks during the second postnatal week of life differs distinctly from that in the mature brain. During this critical period, network behavior might be considered hyperexcitable. Spontaneous network-driven bursts of synaptic potentials, which have not been reported in mature hippocampus, are commonly observed. While these events could be attributable to a late onset of GABAergic synaptic transmission, results suggest that this is not the case. In the immature hippocampus orthodromic stimulation leads to prolonged depolarizations and often repetitive synchronized discharging of the entire CA3 population. These events are in many ways reproduced by application of drugs that suppress GABAergic synaptic transmission. The synchronized discharging of the CA3 population is blocked by excitatory amino acid antagonists. This finding, coupled with our growing understanding of the role that recurrent excitation plays in CA3 network functioning, has led to the hypothesis that the differences in network behavior early in life may be largely attributable to an overabundance of local-circuit recurrent excitatory synapses. With maturation, axon collaterals and attendant synapses would regress to achieve an adult complement. Results from dual intracellular recordings as well as anatomical studies of individual CA3 pyramidal cells support this hypothesis. Unique properties of the NMDA receptor at these recurrent excitatory synapses early in life may also promote network excitability. The participation of extracellular Ca2+ in the voltage dependency of the NMDA receptor-linked iontophore could also contribute to synapse consolidation during maturation and thus in the establishment of network connectivity.

Aging↗
PubMed1991

Intramammary challenge with Escherichia coli following immunization with a curli-producing Escherichia coli.

Holstein and Jersey cattle were immunized with a curli-producing strain of Escherichia coli (pCRL65/A012) or a noncurli-producing strain (pUC18/HB101) to determine differences in resistance to establishment of experimental intramammary infection. Cows (n = 6 per group) were immunized at 14 d prior to drying off, 7 d of involution, and at calving with 3 x 10(10) E. coli in Freund's Incomplete Adjuvant. At 30 d of lactation, one mammary quarter of each cow was infused with a wild strain of E. coli (727). Escherichia coli 727 was isolated from a naturally occurring intramammary infection and produced curli. All challenged quarters became infected, and all cows developed acute clinical mastitis. Geometric mean duration of intramammary infections was 6 d for both immunization groups. All infections were spontaneously eliminated within 10 d. No differences occurred between immunization groups in blood selenium and glutathione peroxidase activity, plasma selenium, number of E. coli 727 isolated from secretion after challenge, rectal temperature and SCC response, clinical status of mammary quarters, or DMI. Reduction in milk production after challenge was greater for cows immunized with E. coli pCRL65/A012. Immunization of dairy cattle with a curli-producing strain of E. coli did not protect against experimental intramammary challenge during lactation.

Animals↗
PubMed1991

Serratia species isolated from bovine intramammary infections.

Intramammary infections from which Serratia spp. were isolated were studied over a 32-mo period in a research dairy herd consisting of approximately 120 lactating cows. A total of 29 Serratia spp. intramammary infections were detected and accounted for 9% of all Gram-negative bacterial intramammary infections. Serratia marcescens was the most common Serratia spp. isolated. Origin of intramammary infections was 48.3% during the first half of the dry period, 31% during the last half of the dry period, and 20.7% during lactation. A total of 64% of intramammary infections that were first detected during the first half of the dry period persisted to calving. Geometric mean number of lactation days infected for all infections was 55. Intramammary infections that originated during the first half of the dry period were present in lactation for a significantly greater number of days compared with intramammary infections new during the last half of the dry period or lactation. A total of 48% of infections were clinical. Serratia spp. intramammary infections tended to be of long duration compared with other Gram-negative bacterial intramammary infections and were highly associated with the dry period.

Animals↗