Computer-aided veterinary learning at the University of Cambridge

An approach of computer-assisted learning in veterinary education at the University of Cambridge, involving the development of four types of learning module, is outlined. A tutorial on regional perineural anaesthesia in the horse, based on the familiar tape-slide format but with significant improvements, is described. A question and answer self-assessment package and a computer-based 'digital lecture' are also discussed, together with a case simulation involving the investigation of a polydipsic dog. All the tutorials were developed using standard software packages and image digitising processes. The philosophy behind the development of these computer-assisted learning packages is discussed.     

Cytokine-mediated neuronal apoptosis

Cytokines have been reported to induce neuronal injury via the free radical nitric oxide (NO); however, the precise mechanism underlying cytokine-mediated neurotoxicity is unclear. We investigated the hypothesis that cytokine-mediated neurotoxicity in primary cultures of human fetal neurons occurs via an apoptotic mechanism triggered by NO. Treatment of mixed neuronal/glial cell cultures with interferon (IFN)-gamma plus interleukin (IL)-1 beta for 13 days induced a high output of NO accompanied by marked neuronal loss. The NO synthase inhibitor N-monomethyl-L-arginine (NMMA) significantly attenuated cytokine-induced neuronal loss, confirming the involvement of NO. Cytokine-mediated neuronal injury was accompanied by morphologic changes and a DNA fragmentation pattern consistent with apoptosis. Treatment of neuronal cell cultures with NMMA protected against cytokine-mediated apoptotic death. These findings, using primary human neuronal cell cultures, support the hypothesis that cytokine-mediated neurotoxicity involving NO proceeds via an apoptotic mechanism. These findings could lead to the development of new therapies for neurodegenerative diseases involving glia, cytokines, and NO.     

Leishmania donovani attachment stimulates PKC-mediated oxidative events in bone marrow-derived macrophages

We investigated activation signaling events in bone marrow-derived macrophages after infection with Leishmania donovani, an intracellular parasite of macrophages. Leishmania donovani infection caused a general suppression of activation parameters like O2- and NO production. However, conditions which allow parasite attachment and prevent entry resulted in triggering of O2- and NO production and stimulation of O2 consumption. Optimal NO and O2- production occurred when bone marrow-derived macrophages and Leishmania ratio was 1:100. The activation signal for O2- production was initiated 15 min after parasite attachment, whereas augmentation of NO production started 6 h after attachment Activation of O2- and NO generation by L. donovani attachment was inhibited by staurosporine as well as by prolonged treatment of phorbol myristate acetate suggesting a protein kinase C-dependent mechanism. Translocation studies showed that protein kinase C activity in cell membrane fraction rapidly and transiently increased following parasite attachment. No such protein kinase C translocation event occurred in L. donovani infected bone marrow-derived macrophages. Phorbol myristate acetate was found to stimulate membrane translocation of protein kinase C in parasite attached cells whereas it was impaired in infected cells. However, both attachment and infection induced a similar shift of phorbol receptors from cytosolic to membrane fraction indicating that in infected cells the translocation of protein kinase C protein was not impaired but the activity of the membrane associated enzyme was somehow inhibited. These results suggest that although internalization of intracellular parasites like L. donovani caused inhibition of nitrite and superoxide release, mere attachment on macrophage surface resulted in an activation of protein kinase C-mediated downstream oxidative events.     

G proteins in adipocytes and preadipocytes: characterization, subcellular distribution, and potential roles for Gi2 and/or Gi3 in the control of cell proliferation

Guanosine triphosphate (GTP)-binding protein subunits were studied by immunoblot analysis in particulate fractions from mature adipocytes, confluent preadipocytes, and in vitro-differentiated preadipocytes. Mature adipocytes express Gi alpha 1, Gi alpha 2, Gi alpha 3, Go alpha, Gq/11 alpha, G13 alpha and the long and short isoforms of Gs alpha, but no Gz alpha or G12 alpha. Confluent and differentiated preadipocytes differ in having a higher content of Gi alpha 3 and G13 alpha and expressing G12 alpha. In contrast, they lack Gi alpha 1, Go alpha, and the short from of Gs alpha. The G-protein alpha subunits Gi alpha 2, Gs alpha (long isoform), and Gq/11 alpha, and G-protein beta subunits were unchanged throughout the differentiation process. By immunoblot and indirect immunofluorescence studies on confluent preadipocytes, we showed that Gi alpha 2 is present in the endoplasmic reticulum and marginally in plasma membranes and nuclei. In contrast, antibodies to Gi alpha 3 stained the Golgi apparatus. The role of G proteins on preadipocyte proliferation was studied using Bordetella pertussis toxin. Exposure of growing cells to this toxin in the presence of fetal calf serum (FCS) decreased [3H]thymidine incorporation by 40% and induced a 40% increase in doubling time. This resulted in a 30% decrease in cell number per well after 48 h. These effects of B. pertussis toxin did not appear to be related to an increase in cyclic adenosine monophosphate (cAMP) concentration, because forskolin had the opposite effect on cell proliferation. Finally, B. pertussis toxin prevented serum-induced Raf1 association to the plasma membrane, possibly by disrupting FCS-induced G beta gamma effects on the Ras/Raf1 pathway. Since Go alpha and Gi alpha 1 subunits were absent in preadipocytes, we conclude that Gi2 and/or Gi3 proteins transduce some mitogenic signals of FCS through release of G beta gamma subunits. The subcellular distribution of Gi alpha 2 and Gi alpha 3 suggests that part of their functions result from interactions with components other than the plasma membrane.     

Stimulation of gluconeogenesis with 1,3-butanediol in the perfused rat liver

An intensified synthesis of glucose is observed in gluconeogenesis from endogenous precursor only for the first 30 min of perfusion. Pyruvate introduction into the medium raises phosphoenolpyruvate carboxykinase and fructose-1,6-diphosphatase activities in the liver and determines maintenance of the glucose formation high rate for 90 min of perfusion. 1,3-butanediol is found to have a stimulating effect on gluconeogenesis from pyruvate. Introduction of 1,3 bytanediol into perfusate decreases the redox state of free NAD-pairs, increases the content of phosphoenolpyruvate, malate. ATP and the phosphoenolpyruvate carboxykinase and fructose-1.6-diphosphatase activity in the perfused liver.     

Renal clearance of digoxin in premature neonates

The renal clearances of digoxin and creatinine were determined in seven premature neonates (mean gestational age = 29.9 wk, range = 26 to 36 wk) at a postnatal age of 1 to 9 days (mean = 4.1 days). The corrected renal digoxin clearance (mean, 10.4 ml/min/1.73 m2; range, 2.5 to 36.7) was highly dependent on gestational age and body weight, r being 0.95 and 0.96, respectively (exponential curve). The linear slope of corrected renal digoxin clearance vs. creatinine clearance plot approached unity (r = 0.99), indicating that digoxin and creatinine were handled similarly by the kidney in these premature neonates (i.e. glomerular filtration with some degree of tubular secretion). Our finding of slower renal digoxin clearance helps to explain the higher serum levels and longer half-life of this drug in premature neonates.