Involvement of regional lymph nodes after penetration of Schistosoma mansoni cercariae in naive and infected mice

The very low density lipoprotein receptor (VLDL-r) is a cell-surface molecule specialized for the internalization of multiple diverse ligands, including apolipoprotein E (apoE)-containing lipoprotein particles, via clathrin-coated pits. Its structure is similar to the low-density lipoprotein receptor (LDL-r), although the two have substantially different systemic distributions and regulatory pathways. The present work examines the distribution of VLDL-r in the central nervous system (CNS) and in relation to senile plaques in Alzheimer disease (AD). VLDL-r is present on resting and activated microglia, particularly those associated with senile plaques (SPs). VLDL-r immunoreactivity is also found in cortical neurons. Two exons of VLDL-r mRNA are differentially spliced in the mature receptor mRNA. One set of splice forms gives rise to receptors containing (or lacking) an extracellular O-linked glycosylation domain near the transmembrane portion of the molecule. The other set of splice forms appears to be brain-specific, and is responsible for the presence or absence of one of the cysteine-rich repeat regions in the binding region of the molecule. Ratios of the receptor variants generated from these splice forms do not differ substantially across different cortical areas or in AD. We hypothesize that VLDL-r might contribute to metabolism of apoE and apoE/A beta complexes in the brain. Further characterizations of apoE receptors in Alzheimer brain may help lay the groundwork for understanding the role of apoE in the CNS and in the pathophysiology of AD.     

Synergistic antimycobacterial activity between ethambutol and the beta-lactam drug cefepime

The contributions of (+/-)-alpha-amino-3-hydroxy-5-methylisoxazole-4-propionic acid (AMPA) and gamma-aminobutyric acid (GABA[A]) receptors in the induction of long-term potentiation (LTP) have been studied in the CA1 region of the rat hippocampus. The results suggest that: (1) in physiological conditions, AMPARs are necessary for the induction of N-methyl-D-aspartate receptor (NMDAR)-dependent LTP since LTP cannot be elicited in the presence of the AMPAR antagonist, 6-cyano-7-nitroquinoxaline-2,3-dione (CNQX). Although a NMDAR-dependent LTP occurs in the presence of a GABA(A) antagonist and high concentrations of divalents cations, blockade of AMPARs leads to a voltage-dependent calcium channels (VDCC)-dependent LTP since its induction is blocked by nifedipine and not by APV. (2) The bicarbonate-induced GABA(A) receptor-mediated depolarizing response is not necessary in the induction of NMDAR-dependent or VDCC-dependent LTP since induction of these two types of LTP were not blocked by acetazolamide or in a nominally bicarbonate-free solution.     

Two structural adaptations for regulating transmitter release at lobster neuromuscular synapses

The distal accessory flexor muscle (DAFM) in the lobster (Homarus americanus) walking leg consists of 5 muscle fiber bundles. All five bundles, one proximal, one distal, and 3 medial, are innervated by one excitatory and one inhibitory motor neuron. Both neurons release more transmitter on the distal bundle than on the proximal bundle. The aim of our studies was to investigate the structural basis of this differentiation. Thin sections cut at 50 microns intervals showed a similar number of excitatory synapses on the two bundles. Freeze-fracture views of excitatory synapses showed that synapse size, active zone number per synapse, and intramembrane particle density in the postsynaptic membrane are similar proximally and distally. Active zones at synapses on the distal bundle are larger and contain about 50% more large intramembrane particles, which are thought to include the voltage-gated Ca2+ channels that couple the action potential to transmitter release, than their counterparts on the most proximal bundle. This difference in channel number appears to produce a disproportionate increase in the probability of transmitter release sufficient to account for most of the proximal-distal disparity in the amplitude of the excitatory postsynaptic potential. In contrast, staining the inhibitor for antibodies to the inhibitory neurotransmitter, GABA, showed that it forms more varicosities on the distal bundle than on the proximal bundle. Because most of the synapses are located in the varicosities, differences in synapse number likely regulate the proximal-distal disparity in the amount of inhibitory transmitter released. Therefore, the regional differentiation in the amount of transmitter released in the DAFM appears to be based on two distinct mechanisms. In the inhibitor, transmitter release appears to be regulated differentially by differences in synapse number. In the excitor, transmitter release appears to be regulated differentially from a similar number of synapses by differences in active zone structure.     

Restoration of X-ray and etoposide resistance, Ku-end binding activity and V(D) J recombination to the Chinese hamster sxi-3 mutant by a hamster Ku86 cDNA

Ku is a heterodimeric protein composed of 86 and 70 kDa subunits that binds preferentially to the double-stranded ends of DNA. Recent molecular characterization of ionizing-radiation sensitive (IRs) mutants belonging to the XRCC5 complementation group demonstrated the involvement of Ku in DNA double-strand break (DSB) repair and lymphoid V(D)J recombination. Here, we describe the isolation of a full-length hamster cDNA encoding the large subunit of the Ku heterodimer and demonstrate that the stable expression of this cDNA can functionally restore IR, Ku DNA end-binding activity and V(D)J recombination proficiency in the Chinese hamster IRs sxi-3 mutant. Moreover, we also demonstrate that sxi-3 cells are hypersensitive to etoposide, a DNA topoisomerase II inhibitor, and that resistance to this drug was restored by the Ku86 cDNA. These experiments suggest that a defect in the large subunit of the heterodimeric Ku protein is the sole factor responsible for the known defects of sxi-3 cells and our data of further support the role of Ku in DNA DSB repair and V(D)J recombination.     

Single photon emission computed tomographic blood flow and magnetic resonance volume imaging of basal ganglia in Huntington''s disease

During oogenesis in Drosophila, germ cells appear in sequential clusters of 16 interconnected cells. The events surrounding the differentiation of these cells are not fully understood. Here we present genetic and morphological analysis of mutations in the gene stand still (stil). Through complementation analyses we have refined the location of this gene to cyological region 49B-C. Our analyses of ovaries from ethylmethane sulfonate (EMS)-induced mutant alleles of this gene suggest that mutations in the stil gene produce a wide range of phenotypic abnormalities, from the absence of germ cells in the most severe alleles, to egg chambers with cytoskeletal defects in the less severe alleles. Our results suggest a role for this gene in specifying or maintaining a cytoskeletal component, with consequences during oogenesis and possibly during germ line sex determination.     

The generation effect and the modeling of associations in memory

The search of associative memory (SAM) model of Gillund and Shiffrin (1984) was applied to data of two experiments that examined the generation effect (Slamecka & Graf, 1978). Subjects studied a list of related word pairs, in which they either read both words in the pair or generated the right- hand response term using the left-hand stimulus term plus the response word fragment as generation cues. Experiment 1 manipulated encoding condition within subjects and used an incidental learning procedure. Experiment 2 manipulated encoding condition between subjects and used an intentional learning procedure. Memory was tested with recognition, cued recall, and free recall. A higher order association model gave a better and more parsimonious fit to the results than did an item-level association model. The relationship between various versions of SAM and current accounts of the generation effect are discussed, particulary the two-factor theory of Hirshman and Bjork (1988).     

Protein kinase C-mediated inhibition of transmembrane signalling through CCK(A) and CCK(B) receptors

1. The rat CCK(A) and CCK(B) receptors were stably expressed in Chinese hamster ovary (CHO-09) cells in order to compare modes of signal transduction and effects of protein kinase C (PKC) thereupon. 2. Spectrofluorophotometry of Fura-2-loaded cells revealed that both receptors retained their pharmacological characteristics following expression in CHO cells. Sulphated cholecystokinin-(26-33)-peptide amide (CCK-8-S) increased the cytosolic Ca2+ concentration ([Ca2+]i) in CCK(A) cells, measured as an increase in Fura-2 fluorescence emission ratio, 1000 fold more potently than its non-sulphated form (CCK-8-NS) (EC50 values of 0.19 nM and 0.18 microM, respectively). By contrast, CCK-8-S and CCK-8-NS were equally potent in CCK(B) cells (EC50 values of 0.86 nM and 1.18 nM, respectively). The CCK(A) receptor agonist JMV-180 increased [Ca2+]i only in CCK(A) cells. Likewise, pentagastrin increased [Ca2+]i only in CCK(B) cells. Finally, CCK-8-S-induced Ca2+ signalling through the CCK(A) receptor was most potently inhibited by the CCK(A) receptor antagonist L364,718, whereas the CCK(B) receptor antagonist L365,260 was more potent in CCK(B) cells. 3. Receptor-mediated activation of adenylyl cyclase was measured in the presence of the inhibitor of cyclic nucleotide phosphodiesterase activity, 3-isobutyl-1-methylxanthine. CCK-8-S and, to a lesser extent, CCK-8-NS, but not JMV-180 or pentagastrin, stimulated the accumulation of cyclicAMP in CCK(A) cells. By contrast, none of these agonists increased cyclicAMP in CCK(B) cells. 4. Short-term (3 min) pretreatment with the PKC activator 12-O-tetradecanoylphorbol 13-acetate (TPA) evoked a rightward shift of the dose-response curve for the Ca2+ mobilizing effect of CCK-8-S in both cell lines. In addition, short-term TPA pretreatment markedly reduced CCK-8-S-induced cyclicAMP accumulation in CCK(A) cells. In both cases, the inhibitory effect of TPA was abolished by the PKC inhibitors, GF-109203X and staurosporine, whereas no inhibition was observed with the inactive phorbol ester, 4-alpha-phorbol 12-myristate 13-acetate. 5. During prolonged TPA treatment, the cells gradually recovered from phorbol ester inhibition and in the case of CCK-8-S-induced Ca2+ mobilization complete recovery was achieved after 24 h of TPA treatment. Western blot analysis revealed that this recovery was paralleled by down-regulation of PKC-alpha, suggesting the involvement of this PKC isotype in the inhibitory action of TPA. 6. This study demonstrates that following expression in CHO cells (i) both CCK(A) and CCK(B) receptors are coupled to Ca2+ mobilization, (ii) only CCK(A) receptors are coupled to cyclicAMP formation and (iii) with both receptors signalling is inhibited by PKC.