Evidence for time-place learning in the Morris water maze without food restriction but with increased response cost

Time-place learning is the ability to distinguish between resources that vary in location at different times of day. Only one previous report has demonstrated successful time-place learning without using food as reward. In this experiment, satiated rats failed to form time-place discriminations in a Morris water maze while food deprived rats did, leading to the conclusion that food system activation is necessary for time-place learning. However, in addition to food system activation, response cost was also increased, which previously has been demonstrated to be effective in allowing the formation of time-place discriminations. The purpose of these two experiments is to test whether food system activation or heightened response cost allowed for time-place learning in the Morris water maze. In the first experiment, we replicate the failure to find time-place discriminations in the Morris water maze without food restriction and without increased response cost. In the second experiment, we found that increased response cost without food restriction was effective in allowing the formation of a time-place discrimination. The implications of this result are discussed in light of the timing mechanism used for time-place discriminations, the nature of the response cost, and the event-time-place tripartite association.     

Transferable antibiotic resistance elements in Haemophilus influenzae share a common evolutionary origin with a diverse family of syntenic genomic islands

Transferable antibiotic resistance in Haemophilus influenzae was first detected in the early 1970s. After this, resistance spread rapidly worldwide and was shown to be transferred by a large 40- to 60-kb conjugative element. Bioinformatics analysis of the complete sequence of a typical H. influenzae conjugative resistance element, ICEHin1056, revealed the shared evolutionary origin of this element. ICEHin1056 has homology to 20 contiguous sequences in the National Center for Biotechnology Information database. Systematic comparison of these homologous sequences resulted in identification of a conserved syntenic genomic island consisting of up to 33 core genes in 16 beta- and gamma-Proteobacteria. These diverse genomic islands shared a common evolutionary origin, insert into tRNA genes, and have diverged widely, with G+C contents ranging from 40 to 70% and amino acid homologies as low as 20 to 25% for shared core genes. These core genes are likely to account for the conjugative transfer of the genomic islands and may even encode autonomous replication. Accessory gene clusters were nestled among the core genes and encode the following diverse major attributes: antibiotic, metal, and antiseptic resistance; degradation of chemicals; type IV secretion systems; two-component signaling systems; Vi antigen capsule synthesis; toxin production; and a wide range of metabolic functions. These related genomic islands include the following well-characterized structures: SPI-7, found in Salmonella enterica serovar Typhi; PAP1 or pKLC102, found in Pseudomonas aeruginosa; and the clc element, found in Pseudomonas sp. strain B13. This is the first report of a diverse family of related syntenic genomic islands with a deep evolutionary origin, and our findings challenge the view that genomic islands consist only of independently evolving modules.     

Identification of a bifunctional lipopolysaccharide sialyltransferase in Haemophilus influenzae: incorporation of disialic acid

The lipopolysaccharide (LPS) of non-typeable Haemophilus influenzae (NTHi) can be substituted at various positions by N-acetylneuraminic acid (Neu5Ac). LPS sialylation plays an important role in pathogenesis. The only LPS sialyltransferase characterized biochemically to date in H. influenzae is Lic3A, an alpha-2,3-sialyltransferase responsible for the addition of Neu5Ac to a lactose acceptor (Hood, D. W., Cox, A. D., Gilbert, M., Makepeace, K., Walsh, S., Deadman, M. E., Cody, A., Martin, A., M?nsson, M., Schweda, E. K., Brisson, J. R., Richards, J. C., Moxon, E. R., and Wakarchuk, W. W. (2001) Mol. Microbiol. 39, 341-350). Here we describe a second sialyltransferase, Lic3B, that is a close homologue of Lic3A and present in 60% of NTHi isolates tested. A recombinant form of Lic3B was expressed in Escherichia coli and purified by affinity chromatography. We used synthetic fluorescent acceptors with a terminal lactose or sialyllactose to show that Lic3B has both alpha-2,3- and alpha-2,8-sialyltransferase activities. Structural analysis of LPS from lic3B mutant strains of NTHi confirmed that only monosialylated species were detectable, whereas disialylated species were detected upon inactivation of lic3A. Furthermore, introduction of lic3B into a lic3B-deficient strain background resulted in a significant increase in sialylation in the recipient strain. Mass spectrometric analysis of LPS indicated that glycoforms containing two Neu5Ac residues were evident that were not present in the LPS of the parent strain. These findings characterize the activity of a second sialyltransferase in H. influenzae, responsible for the addition of di-sialic acid to the LPS. Modification of the LPS by di-sialylation conferred increased resistance of the organism to the killing effects of normal human serum, as compared with mono-sialylated or non-sialylated species, indicating that this modification has biological significance.     

Mitochondrial function and bioenergetic trade‐offs during lactation in the house mouse (Mus musculus)

Energy allocation theory predicts that a lactating female should alter the energetic demands of its organ systems in a manner that maximizes nutrient allocation to reproduction while reducing nutrient use for tasks that are not vital to immediate survival. We posit that organ‐specific plasticity in the function of mitochondria plays a key role in mediating these energetic trade‐offs. The goal of this project was to evaluate mitochondrial changes that occur in response to lactation in two of the most energetically demanding organs in the body of a rodent, the liver and skeletal muscle. This work was conducted in wild‐derived house mice (Mus musculus) kept in seminatural enclosures that allow the mice to maintain a natural social structure and move within a home range size typical of wild mice. Tissues were collected from females at peak lactation and from age‐matched nonreproductive females. Mitochondrial respiration, oxidative damage, antioxidant, PGC‐1α, and uncoupling protein levels were compared between lactating and nonreproductive females. Our findings suggest that both liver and skeletal muscle downregulate specific antioxidant proteins during lactation. The liver, but not skeletal muscle, of lactating females displayed higher oxidative damage than nonreproductive females. The liver mass of lactating females increased, but the liver displayed no change in mitochondrial respiratory control ratio. Skeletal muscle mass and mitochondrial respiratory control ratio were not different between groups. However, the respiratory function of skeletal muscle did vary among lactating females as a function of stage of concurrent pregnancy, litter size, and mass of the mammary glands. The observed changes are predicted to increase the efficiency of skeletal muscle mitochondria, reducing the substrate demands of skeletal muscle during lactation. Differences between our results and prior studies highlight the role that an animals’ social and physical environment could play in how it adapts to the energetic demands of reproduction.     

Morphometric Analysis of Normal, Mutant, and Transgenic CNS: Correlation of Myelin Basic Protein Expression to Myelinogenesis

The neurological mutant mice shiverer (shi) and myelin deficient (shimld) lack a functional gene for the myelin basic proteins (MBP), have virtually no myelin in their CNS, shiver, seize, and die early. Mutant mice homozygous for an MBP transgene have MBP mRNA and MBP in net amounts approximately 25% of normal, have compact myelin, do not shiver or seize, and live normal life spans. We bred mice with various combinations of the normal, transgenic, shi, and shimld genes to produce mice that expressed MBP mRNA at levels of 0, 5, 12.5, 17.5, 50, 62.5, and 100% of normal. The CNS of these mice were analyzed for MBP content, tissue localization of MBP, degree of myelination, axon size, and myelin thickness. MBP protein content correlated with predicted MBP gene expression. Immunocytochemical staining localized MBP to white matter in normal and transgenic shi mice with an intensity of staining comparable to the degree of MBP gene expression. An increase in the percentage of myelinated axons and the thickness of myelin correlated with increased gene expression up to 50% of normal. The percentage of myelinated axons and myelin thickness remained constant at expression levels greater than 50%. The presence of axons loosely wrapped with oligodendrocytic membrane in mice expressing lower amounts of MBP mRNA and protein suggested that the oligodendroglia produced sufficient MBP to elicit axon wrapping but not enough to form compact myelin. Mean axon circumference of myelinated axons was greater than axon circumference of unmyelinated axons at each level of gene expression, further evidence that oligodendroglial cells preferentially myelinate axons of larger caliber.(ABSTRACT TRUNCATED AT 250 WORDS)     

Histoplasmosis and Thrombocytopenic Purpura: Transmission by Renal Homotransplantation

Two patients with disseminated histoplasmosis are reported. One patient presented with severe thrombocytopenic purpura and splenomegaly. Histoplasmin skin test, blood and bone marrow cultures and smears, sputum cultures, and chest radiographs were negative for Histoplasma capsulatum. She died on the sixth hospital day from a massive intracerebral hemorrhage. Cardiorespiratory function was maintained until one kidney was removed for homotransplantation. The second patient, with chronic glomerulonephritis and uremia, received the renal homograft from the first patient. Initial signs of homograft rejection developed five days postoperatively. Diffuse thrombocytopenic purpura occurred shortly thereafter. Spores of Histoplasma capsulatum were observed in blood smears, in leukocyte concentrates, and in five-day leukocyte cultures from the blood obtained prior to death. Disseminated histoplasmosis was found in both patients at autopsy. The severe platelet deficit in both cases suggests that systemic histoplasmosis should be considered as a cause of thrombocytopenic purpura.To our knowledge, this is the first reported instance of direct transmission of Histoplasma capsulatum, and must be considered a hazard in homotransplantation.In vitro leukocyte cultures as a method for early diagnosis of certain disseminated fungous infections needs further investigation.     

Endurance training alters alanine and glutamine release from muscle during contractions

The release of alanine and glutamine from perfused muscle of trained and control animals was investigated. Release rates did not differ between trained and control muscle at rest. During contractions in trained muscle, alanine release was higher than at rest, while glutamine release was transiently increased. Phenylalanine release did not differ between trained and control muscle, implying that protein degradation was not increased in trained muscle. The muscle cellular adaptations to training include a selective modification of amino acid output, which could potentially influence gluconeogenic flux and alter muscle ammonia levels during contractions.     

Conversion of glucose, acetate and lactate to CO2 and fatty acids in liver and adipose tissue of prairie voles (Microtus ochrogaster)

Production of CO2 and fatty acids from acetate, glucose and lactate was determined in slices of liver and adipose tissue from prairie voles fed either a high-starch or a high-cellulose diet. Acetate and lactate were oxidized to CO2 and converted to fatty acids at greater rates than was glucose in both liver and adipose tissue. Fatty acid synthesis occurred at greater rates in adipose tissue than in liver. Fatty acid synthesis per adipocyte increased with increased adipocyte diameter. Fiber content of diets had only minimal effect on metabolic activities of liver and adipose tissue.