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Biomedical subjects

J D Turner

Publications and source records attributed to J D Turner.

At least 55 records · Page 3Linked to original sources
PubMed1994

5-HT1A receptor agonists improve the performance of normal and scopolamine-impaired rats in an operant delayed matching to position task.

A series of experiments examined the effects of 5-HT1A ligands alone and in combination with the muscarinic antagonist scopolamine on short term working memory in the rat. The behavioural paradigm was a discrete trial, operant delayed matching to position task, with delays of 0, 5, 15 and 30 s. The 5-HT1A ligands tested were the full agonist, 8-OH DPAT (0, 0.1, 0.3 and 1 mg/kg), the partial agonist, ipsapirone (0, 1, 3 and 10 mg/kg), and the purported antagonist, NAN 190 (0, 1, 2, and 4 mg/kg). 1-PP (0, 0.1, 0.3, 1 mg/kg), the major metabolite of ipsapirone, was also tested. The lowest dose of 8-OH DPAT significantly improved matching accuracy at the longest delay, whereas the highest dose impaired matching accuracy and increased the latency to respond. Ipsapirone also significantly improved the accuracy of performance at a dose of 3 mg/kg, but the doses of 1 and 10 mg/kg did not significantly affect performance. NAN-190, at the highest dose tested (4 mg/kg), impaired matching accuracy, whereas the two lower doses did not significantly affect performance. The highest dose also increased the latency to respond. 1-PP had no effect on performance. Scopolamine HBr (0.14 mg/kg) caused a delay dependent impairment in matching accuracy, and had no effect on missed trials or the latency to respond. Low doses of 8-OH DPAT (0.1 and 0.3 mg/kg) significantly attenuated the scopolamine induced accuracy impairment, whereas 1 mg/kg 8-OH DPAT potentiated the impairment. Ipsapirone (3 mg/kg) also significantly improved the performance of scopolamine impaired rats.(ABSTRACT TRUNCATED AT 250 WORDS)

8-Hydroxy-2-(di-n-propylamino)tetralin↗
PubMed1994

Characterization of lactoferrin binding to the MAC-T bovine mammary epithelial cell line using a biotin-avidin technique.

1. A non-radioisotopic method utilizing a biotin-avidin approach was used to characterize lactoferrin binding to the clonal MAC-T bovine mammary epithelial cell line. 2. Binding of lactoferrin to MAC-T cells and isolated membranes was specific and saturable. 3. Unlabeled lactoferrin competed for and displaced biotin-labeled lactoferrin from binding sites on mammary epithelial cells. In contrast, unlabeled transferrin did not compete. 4. Scatchard analysis of lactoferrin binding to MAC-T cell crude membranes was nonlinear, revealing two classes of binding sites with association constants (Ka) of 2.36 x 10(7) and 3.36 x 10(6) M-1. 5. Binding of lactoferrin to MAC-T cells may be associated with the initial events which result in decreased MAC-T cell proliferation.

Animals↗
PubMed1994

IGF-I-induced IGFBP-3 potentiates the mitogenic actions of IGF-I in mammary epithelial MD-IGF-I cells.

Limited information is available concerning the molecular and cellular mechanisms that regulate expression of insulin-like growth factor-I (IGF-I) binding proteins (IGFBPs) in bovine mammary epithelial cells. Here, we report on the autocrine mechanisms of action of IGF-I and hormonal regulation of expression of IGFBPs in bovine mammary epithelial MD-IGF-I cells which express recombinant IGF-I under the control of the glucocorticoid-inducible mouse mammary tumor virus-long terminal repeat (MMTV-LTR). Levels of IGFBP-3 mRNA and secretion of IGFBP-3 by MD-IGF-I cells were stimulated by IGF-I, insulin (INS), and IGF-I analogs but not prolactin (PRL). Conversely, parental MAC-T cells expressed little IGF-I and secreted primarily IGFBP-2 (29-32 kDa) in response to stimulation with INS, dexamethasone (DEX), or IGF-I analogs. Secretion of recombinant IGF-I caused a 26.5-fold increase in secretion of IGFBP-3, as measured by densitometric analysis of ligand blots, which was associated with a 1.7-fold increase in total DNA. Conditioned media (CM) from MD-IGF-I cells induced with DEX stimulated a 2.8-fold increase in [3H]thymidine incorporation into DNA of parental MAC-T cells, compared with uninduced cells. Moreover, inclusion of exogenous IGF-I with CM from MD-IGF-I cells triggered an additional 3.0-fold increase in label incorporation, but only a 1.6-fold increase in the presence of IGFBP-2-containing media conditions by MAC-T cells.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1994

Neutrophil function in vitro: diapedesis and phagocytosis.

The function of neutrophils within the mammary gland was modeled in vitro to include diapedesis and phagocytosis. The bovine mammary cell line, MAC-T3, provided a mammary epithelial monolayer for use as a biologically meaningful barrier to neutrophil diapedesis. Features included characteristic transepithelial resistance, tight junctional complexes, and polarity. Continuous readings of transepithelial resistance indicated a stable resistance over several hours. Staphylococcus aureus, at concentrations of 1 x 10(7) and 2 x 10(9) cfu/ml, did not appear to have any deleterious effects on monolayer integrity over short-term (1 to 2 h) exposure. Neither resting nor challenged neutrophils caused short-term damage to the monolayer. Transepithelial resistance of the monolayers remained unchanged even as neutrophils were actively migrating through the monolayer. Further work using the MAC-T3 cell line and electrical resistance to assess cell monolayer integrity could provide much insight into the mechanisms underlying degeneration of mammary epithelial cells. The ability of neutrophils to phagocytose foreign particles is important for protection of the mammary gland. Neutrophils from proven bulls varied in their rate and capacity of phagocytosis. Correlations between neutrophil function and production traits were negative and small. In vitro analysis of neutrophil function provides another tool for the study of natural mastitis resistance.

Animals↗
PubMed1994

Production of various forms of plasminogen activator and plasminogen activator inhibitor by cultured mammary epithelial cells.

We examined amounts and types of plasminogen activator and plasminogen activator inhibitor produced by cultured bovine mammary epithelial cells. The MAC-T and two other mammary epithelial cell lines, MACT-UV1 and MACT-UV2 derived from the parental MAC-T cells by subcloning, were used as model systems. Cells were cultured in a medium free of serum and protein. Data showed that MACT-UV2 cells produced 6.2 and 17.2% more plasminogen activator than MACT-UV1 and parental MAC-T cells, respectively. Addition of amiloride, a specific urokinase-plasminogen activator inhibitor, dramatically decreased the activity in the culture medium of parental and subclonal lines, indicating that urokinase-plasminogen activator was present. Zymography revealed the presence of urokinase-plasminogen activator with an approximate molecular mass of 50,000 kDa in the culture medium of parental MAC-T cells. The culture medium of the subclonal lines contained urokinase-plasminogen activator and tissue-plasminogen activator with approximate molecular masses of 50,000 and 75,000 kDa, respectively. Complexes of both types of plasminogen activators with plasminogen activator-inhibitor-1 were detected in the culture medium of subclonal lines.

Animals↗
PubMed1994

Proliferation of a bovine mammary epithelial cell line in the presence of bacterial virulence factors.

Effects of bacterial virulence factors on bovine mammary cell structure and function are not well defined. In this study, we evaluated the influence of specific bacterial virulence factors on proliferation of a bovine mammary epithelial cell line. The MAC-T cells were cultured in the presence of medium only, Staphylococcus aureus alpha-toxin, Staph. aureus beta-toxin, Escherichia coli endotoxin, Streptococcus uberis capsule, or hyaluronidase. Cells were cultured in the presence of virulence factors for 48 h at 37 degrees C. The MAC-T cell proliferation was inhibited by all concentrations of endotoxin and alpha-toxin and by most concentrations of hyaluronic acid capsule and hyaluronidase > 7.8 micrograms/ml. Staphylococcus aureus beta-toxin had no effect on MAC-T cell proliferation. Virulence factors produced by mastitis pathogens may influence mammary epithelial cell proliferation in vivo, which could be important during the periparturient period, when mammary tissue undergoes rapid differentiation and growth.

Analysis of Variance↗
PubMed1993

Transport of casein submicelles and formation of secretion granules in the Golgi apparatus of epithelial cells of the lactating mammary gland of the rat.

Lactating mammary glands fixed by perfusion with 5% glutaraldehyde subsequently were postfixed with potassium ferrocyanide reduced osmium or were treated with tannic acid. Stained thin sections were examined with the electron microscope and stereopairs were prepared. The distribution of casein submicelles was analyzed in the various components of the Golgi apparatus. The Golgi stacks were composed of five or six elements, all of which contained casein submicelles 20 nm in diameter. The cis-tubular network or cis-element, as well as the underlying three or four midsaccules, showed these casein submicelles either attached to their membrane or free in the lumen. The trans-most element of the stacks formed distended prosecretory granules in which both isolated or clustered casein submicelles were suspended in an electron-lucent fluid. These micellar aggregates increased in size and became progressively more compact to form spherical dense bodies or casein micelles, in which the individual 20 nm particles could easily be resolved. Casein micelles were seen in secretory granules in addition to a wispy material of low density. The numerous small spherical vesicles (80 nm or larger) seen on the cis, lateral, or trans aspects of the stacks did not appear to contain free casein submicelles. This raises questions regarding the role of these vesicles in the transport of casein macromolecules through the Golgi stacks. It was noticeable that in this Golgi apparatus a trans-Golgi network was limited to a few small residual tubules free from casein submicelles. It thus appears that the greater part of the trans-most Golgi element gives rise to the large prosecretory granules. After leaving the Golgi region and prior to exocytosis, the secretory granules often fuse to form larger granules before exocytosis.

Animals↗
PubMed1993

Structure of the Golgi apparatus in stimulated and nonstimulated acinar cells of mammary glands of the rat.

The structural features of the Golgi apparatus of acinar cells of mammary glands were examined with the electron microscope in 3 groups of rats: (1) in lactating female animals at 8 days postpartum, which served as controls; (2) in female rats sacrificed at various intervals from 2 to 30 hours following separation from their 8-day old pups; and (3) in females separated from their 8-day-old pups for a period of 12 hours and returned to their litters for durations of 1, 2, 4, and 8 hours. In animals of group 2, the Golgi stacks remained identical to that of controls between 2 and 8 hours. At 12 hours and later, the Golgi stacks decreased progressively in size, but the number of elements composing the stacks remained similar to that of lactating females and all contained casein submicelles. At 24 and 30 hours, typical secretory granules containing casein micelles disappeared from the trans aspect of the stacks. The earliest and most striking changes observed in the Golgi apparatus of the rats of group 2 took place at 12 hours. At this time, the prosecretory and secretory granules decreased considerably in volume and lost most of their electron-lucent content. This indicated that the delivery of small molecules, i.e., lactose and H2O, to these structures was soon altered following arrest of the sucking stimulus. In animals of group 3, the size of prosecretory and secretory granules and the amount of their electron-lucent content reverted to normal at 4 hours. Thus the influx of lactose and H2O into these structures appears to be rapidly restored after returning the pups to their mothers. The decrease in size of the Golgi stacks noted at 12, 18, and 24 hours following arrest of lactation (group 2), was accompanied by an increase in number of small vesicles that formed clusters next to the Golgi stacks and in "wells." Thus in these regressing Golgi stacks, many of the associated small vesicles appear to arise by vesiculation of the saccules.

Animals↗
PubMed1993

Striated anchoring fibrils-anchoring plaque complexes and their relation to hemidesmosomes of myoepithelial and secretory cells in mammary glands of lactating rats.

Striated anchoring fibrils (SAF) are associated with the basement membrane underlying myoepithelial and acinar cells of mammary glands. Their proximal extremities are inserted in electron-dense areas of the lamina densa, the anchoring plaques seen facing the hemidesmosomes of both myoepithelial and acinar cells. In the case of myoepithelial cells, the hemidesmosomes show a thick cytoplasmic plaque applied to the basal plasma membrane in which cytoplasmic filaments are inserted. Facing this plaque but on the extracellular aspect and at a short distance of 5-10 nm, there is a thin layer of electron-dense nodular material called the subcell membrane plate, which is connected to the plasma membrane by short filamentous bridges. Between this subcell membrane plate and the anchoring plaque, there is an abundance of fine anchoring filaments crossing the lamina lucida. Such anchoring filaments are less abundant in the lamina lucida outside the hemidesmosomal areas. In the case of acinar cells, the cytoplasmic plaques of the hemidesmosomes are thin and the associated cytoplasmic filaments less conspicuous. No distinct subcell membrane plate is seen on the extracellular aspect of the plasma membrane facing the cytoplasmic plaque of the hemidesmosomes. However, in this area numerous anchoring filaments cross the lamina lucida between the plasma membrane and the SAF-anchoring plaque complex. The abundance, in these cells, of hemidesmosomes and their association with SAF-anchoring plaque complexes seen in the basement membrane must constitute a strong attachment for both myoepithelial and acinar cells and bind them to the underlying collagen fibrils, thus preventing their detachment from the connective tissue during the contractions of myoepithelial cells during milk ejection.

Actin Cytoskeleton↗
PubMed1993

Effects of NBM lesions with two neurotoxins on spatial memory and autoshaping.

Four groups of Wistar rats received either vehicle, quisqualate, or one of two different ibotenic acid infusions into the basal forebrain. Following recovery from surgery, all rats were tested in three distinct behavioral paradigms: the Bättig radial arm maze, the Barnes circular platform, and autoshaping in an operant chamber. The results showed that the size and site of the ibotenic acid lesion had a profound effect on acquisition performance in some, but not all, procedures. Performance in the Bättig maze and acquisition of a food-rewarded lever press were in particular disrupted by ibotenic acid lesions. The severity of the reduction in cortical choline acetyltransferase (ChAT) did not correlate with performance in the tests. Quisqualate produced the largest reduction in ChAT levels but had no significant effect on performance in any of the three procedures used. Anatomic analysis revealed severe nonspecific damage to the striatum following ibotenic acid that was more pronounced in the group receiving a highly concentrated solution of ibotenic acid as compared to rats infused with a greater volume but less concentrated solution of the neurotoxin. Striatal damage was much less severe following quisqualic acid infusions. However, both types of neurotoxins produced equivalent nonspecific degeneration of the reticular thalamic nucleus. These data confirm reports that nonspecific damage appears to define the severity of ibotenic acid lesions on subsequent behavioral performance.

Animals↗
PubMed1993

Lactogenic hormones and extracellular matrix regulate expression of IGF-1 linked to MMTV-LTR in mammary epithelial cells.

The cell line MD-IGF-1, containing an ovine IGF-1 cDNA driven by the mouse mammary tumor virus-long terminal repeat (MMTV-LTR) promoter, was used to study expression of IGF-1 linked to the MMTV-LTR in bovine mammary epithelial cells in response to various hormonal and substratum stimuli. Acute sensitivity of the MMTV-LTR promoter to glucocorticoids and sex steroids was ascertained by transient transfection of parental MAC-T cells with an MMTV-CAT construct. Specifically, CAT activity was induced by glucocorticoids, but not by 17 beta-estradiol or progesterone. Induction of MD-IGF-1 cells with dexamethasone (DEX) alone triggered a 29.5-fold increase in secretion of recombinant IGF-1 (348.9 vs 11.8 pg/micrograms DNA), and stimulated a 1.7-fold increase in total DNA within 72 h. Growth of MD-IGF-1 cells was enhanced by exogenous IGF-1, insulin, and TGF-alpha. In contrast, TGF-beta inhibited cell proliferation, while epidermal growth factor, estrogen, progesterone, and testosterone had no effect. Extracellular matrix from the Engelbreth-Holm-Swarm (EHS) tumor, in the presence of DEX, prolactin (PRL), and insulin stimulated a 29.4-fold increase in secretion of IGF-1 (591.9 pg/microgram DNA), compared with cells in absence of hormones (20.1 pg/micrograms DNA). EHS and DEX plus PRL triggered a 63.2-fold increase in IGF-1 secretion (689.1 pg/micrograms DNA), compared with MD-IGF-1 cells cultured on plastic (10.9 pg/micrograms DNA), in the absence of hormones. These data indicate that the MMTV-LTR is regulated by both lactogenic hormones and extracellular matrix in MD-IGF-1 cells and that the MMTV-LTR may be a useful regulatory element for targeting expression of foreign proteins in bovine mammary epithelial cells.

Animals↗
PubMed1993

Effect of mammary-derived growth inhibitor on proliferation of MAC-T bovine mammary epithelial cells.

An established bovine mammary epithelial cell line (MAC-T) was used as a model to examine the effect of mammary-derived growth inhibitor on mammary epithelial cell proliferation. Prior to each proliferation assay, cells were synchronized in G1/G0 by culturing for 24 h without serum. Flow cytometry revealed that 90% of cells were in G1/G0, 4% in G2/M, and 6% in the S-phase after serum deprivation. Approximately 2 x 10(3) cells per well were seeded onto 24-well plates. Cells were incubated for 5 to 6 d with various amounts of mammary-derived growth inhibitor (0 to 100 ng/ml). Mammary-derived growth inhibitor and medium were changed daily. Mammary-derived growth inhibitor decreased mammary epithelial cell proliferation at .1 ng/ml. Synchronization of cells in G1/G0 was necessary for inhibition of cell proliferation. Cells not arrested by serum deprivation were not responsive to mammary derived-growth inhibitor. Inhibition of cell proliferation was transient and observed up to 96 h in culture. Mammary-derived growth inhibitor appears to act in vitro by inhibiting the resumption of stationary cell proliferation following starvation.

Animals↗
PubMed1992

Mapping of GABAA receptor alpha 5 and alpha 6 subunit-like immunoreactivity in rat brain.

The distribution of the alpha 5 and alpha 6 subunits of the GABAA receptor has been mapped in rat brain using affinity-purified antibodies generated against peptide sequences unique to the respective polypeptides. alpha 5 Subunit-like immunoreactivity was of low density but was distributed across several cell groups including cortical interneurones, hippocampal CA3 pyramidal neurones, the anterior thalamic reticular nucleus and cerebellar Purkinje neurones. alpha 6 Subunit-like immunoreactivity was observed in high density in cerebellar granule cells. These patterns are compatible with in situ hybridisation studies and provide a further anatomical substrate for GABAA receptor heterogeneity in the CNS.

Amino Acid Sequence↗
PubMed1992

Binding of [3H]SCH23390 to a non-dopaminergic site in bovine kidney.

Binding of the D1 dopamine receptor antagonist [3H]SCH23390 to bovine renal cortical membranes has been studied. Specific binding of [3H]SCH23390 was saturable and reversible and stereoisomers of SCH23390 competed stereoselectively. In contrast, competition with the isomers of butaclamol was not stereoselective and dopamine failed to compete for the [3H]SCH23390 binding site. The site is therefore not a D1 dopamine receptor. Competition studies with a very wide range of compounds failed to define the nature of the [3H]SCH23390 binding sites in renal cortex whereas in parallel studies the characteristics of [3H]SCH23390 binding in caudate nucleus were entirely consistent with those of D1 dopamine receptors. The nature of [3H]SCH23390 binding in preparations of tubular and glomerular membranes was found to be virtually identical to those of crude renal cortical membranes indicating lack of compartmentation of these sites. Autoradiographic studies of [3H]SCH23390 binding in bovine kidney showed significantly higher levels of binding sites in renal cortex compared with renal medulla and this was confirmed by direct ligand binding studies.

Animals↗