Ultrastructural and histochemical changes in the murine zona pellucida during the final stages of oocyte maturation prior to ovulation

The ultrastructural morphology of the mouse zona pellucida was studied in preovulatory follicles from the ovaries of immature mice treated with exogenous gonadotrophins. The ovaries were fixed in the presence of cetylpyridinium chloride, which precipitates carbohydrates, so that their loss during fixation and processing is substantially reduced. The semi-thin araldite sections obtained from osmicated material were viewed by conventional light microscopy, while the ultra-thin sections were examined by transmission electron microscopy. A parallel series of semi-thin sections of non-osmicated ovaries was deresined and subsequently stained with periodic acid Schiff (PAS). The morphological appearance of the zona pellucida in preovulatory oocytes changed during the final stages of oocyte maturation. A close correlation was observed between the ultrastructural appearance of the zona pellucida and that observed following PAS staining during the period studied. Real differences were observed in the location, density, and distribution of glycoconjugates within the zona pellucida during the final stages of oocyte maturation prior to and immediately following germinal vesicle breakdown. Similar changes in the zona were observed in adult females autopsied during proestrus and oestrus. The changes in the density and distribution of glycoconjugates are likely to have important consequences for fertilization by affecting sperm-zona binding and sperm-egg interactions.     

Relative inefficiency of soluble recombinant CD4 for inhibition of infection by monocyte-tropic HIV in monocytes and T cells

Macrophages are major viral reservoirs in the brain, lungs, and lymph nodes of HIV-infected patients. But not all HIV isolates infect macrophages. The molecular basis for this restrictive target cell tropism and the mechanisms by which HIV infects macrophages are not well understood: virus uptake by CD4-dependent and -independent pathways have both been proposed. Soluble rCD4 (sCD4) binds with high affinity to gp 120, the envelope glycoprotein of HIV, and at relatively low concentrations (less than 1 microgram/ml) completely inhibits infection of many HIV strains in T cells or T cell lines. HTLV-IIIB infection of the H9 T cell line was completely inhibited by prior treatment of virus with 10 micrograms/ml sCD4: no p24 Ag or HIV-induced T cell syncytia were detected in cultures of H9 cells exposed to 1 x 10(4) TCID50 HTLV-IIIB in the presence of sCD4. Under identical conditions and at a 100-fold lower viral inoculum, 10 micrograms/ml sCD4 had little or no effect on infection of monocytes by any of six different HIV isolates by three different criteria: p24 Ag release, virus-induced cytopathic effects, and the frequency of infected cells that express HIV-specific mRNA. At 10- to 100-fold higher concentrations of sCD4, however, infection was completely inhibited. Monoclonal anti-CD4 also prevented infection of these same viral isolates in monocytes. The relative inefficiency of sCD4 for inhibition of HIV infection in monocytes was a property of the virion, not the target cell: HIV isolates that infect both monocytes and T cells required similarly high levels of sCD4 (100 to 200 micrograms/ml) for inhibition of infection. These data suggest that the gp120 of progeny HIV derived from macrophages interacts with sCD4 differently than that of virions derived from T cells. For both variants of HIV, however, the predominant mechanism of virus entry for infection is CD4-dependent.     

In-vivo studies of mammary development in the goat using magnetic resonance imaging (MRI)

Mammary development and regression were measured in goats in vivo using magnetic resonance imaging (MRI). Measurements were made during the first and second cycles of pregnancy, lactation and involution. In primiparous goats, and exponential pattern of growth was evident during gestation and for the first 2 weeks of lactation. Parenchyma volume correlated significantly with milk yield across goats during early lactation, and across stage of lactation within goats. Milking was discontinued in Week 26 of the first lactation. Involution was characterized by an initial accumulation of fluid (over 2 days) followed by reabsorption; parenchyma volume did not decrease significantly until the 3rd week of involution, which was also the time at which these goats were mated to start their second gestation. Their udders still contained significant quantities of fluid (40-60% of the gross volume), but parenchyma volume was also greater (by 4.7-fold) than in goats beginning their first gestation. By Week 15 of gestation there was no longer a parity difference in parenchyma; the udders of first-gestation goats had grown significantly, but those of second-gestation goats had not. Conversely, between gestation Week 15 and lactation Week 2 mammary growth was significantly more rapid in the second cycle, such that the udder was larger at the start of the second lactation.     

Tetanus Toxin-Induced Effects on Extracellular Amino Acid Levels in Rat Hippocampus: An In Vivo Microdialysis Study

Abstract: Tetanus toxin is a potent neurotoxin that is widely considered to produce its effect through impairment of inhibitory neurotransmission. We report the effect of a single unilateral intrahippocampal injection of tetanus toxin on extracellular levels of neuroactive amino acids in freely moving rats, at times ranging between 1 and 7 days posttreatment. Tetanus toxin treatment did not alter extracellular levels of aspartate, glutamate, and taurine at any time during the study. However, although extracellular GABA levels were unaffected by toxin injection 1, 2, and 3 days after treatment, they were reduced (45 ± 8% of contralateral vehicle-injected level) at day 7. Challenge with a high K⁺ concentration, 7 days after treatment, produced elevations in extracellular levels of taurine and GABA in both vehicle- and toxin-injected hippocampi, with evoked levels of GABA being lower in the toxin-treated side (39 ± 16% of contralateral vehicle-injected level). Aspartate and glutamate levels were not increased by high-K⁺ infusion. These findings are discussed in relation to the possible role that an imbalance in excitatory/inhibitory tone may play in the production of tetanus toxin-induced neurodegeneration.