Inspiratory neuron activity in the ventrolateral medulla of the dog

The purpose of this study was to describe the distribution and activity pattern of respiratory neurons located in the ventrolateral medulla (VLM) of the dog. Spike activity of 129 respiratory neurons was recorded in 23 ketamine-anesthetized spontaneously breathing dogs. Pontamine blue dye was used to mark the location of each neuron. Most VLM neurons displaying respiratory related spike patterns were located in a column related closely to ambigual and retroambigual nuclei. Both inspiratory and expiratory neurons were present with inspiratory units being grouped more rostrally. The predominant inspiratory neuron firing pattern was "late" inspiratory, although eight "early" types were located. All expiratory firing patterns were the late expiratory variety. Each neuron burst pattern was characterized by determining burst duration (BD), spikes per burst (S/B), peak frequency (PF), time to peak frequency (TPF), rate of rise to peak frequency (PF/TPF), and mean frequency. CO2-induced minute ventilation increases were associated with decreases in BD and TPF and increases in PF, S/B, and PF/TPF. In 11 experiments the relative influences of vagotomy and tracheal occlusion on late inspiratory units were compared. Tracheal occlusion increased late inspiratory BD and S/B but did not alter PF/TPF. Vagotomy increased BD and S/B beyond those obtained by tracheal occlusion and, in some neurons, decreased the PF/TPF. We conclude that the location of respiratory units in the VLM of the dog is similar to that in other species, the discharge pattern of VLM respiratory units is similar to those in cat VLM, and vagotomy and tracheal occlusion affect discharge patterns differently.     

Chromosome 8 breakpoint far 3'' of the c-myc oncogene in a Burkitt''s lymphoma 2;8 variant translocation is equivalent to the murine pvt-1 locus.

The 2;8 variant translocation of human Burkitt's lymphomas is closely related cytogenetically to the t(6;15) of murine plasmacytomas; both involve a reciprocal exchange between the Ig kappa locus and a band region indistinguishable from that bearing the c-myc oncogene. To define their molecular relationship, we have compared cloned chromosome 8 DNA from the t(2;8) breakpoint in the human Burkitt's lymphoma JBL2 with cloned DNA from the murine pvt-1 locus, the major chromosome 15 breakpoint region in murine t(6;15). DNA sequencing and Southern blot analysis shows that these two regions are homologous. Thus the t(2;8) in JBL2 is the molecular equivalent of many murine t(6;15). The murine pvt-1 locus lies an unknown distance 3' of c-myc; analysis of DNA from several tumours with c-myc amplification reveals that pvt-1 is co-amplified in at least one case, placing pvt-1 approximately 100-500 kb 3' of c-myc. The significance of these results with respect to the role of pvt-1 in tumorigenesis is discussed.     

Cell envelope phospholipid changes in a moderate halophile during phenotypic adaptation to altered salinity and osmotic stress

Abstract The increased content of negatively-charged phospholipids in membranes of Vibrio costicola grown at high salinities is mediated by increased phospholipid synthesis of phosphatidylglycerol relative to phosphatidylethanolamine. This phenomenon provides a system for investigating the factors involved in triggering and controlling haloadaptation in this moderately halophilic bacterium. We review recent experiments, which show that when subjected to sudden increases in external salinity, V. costicola senses both the absolute NaCl concentration and the magnitude of the salt shift. We show that the latter is sensed at least in part via osmotic pressure effects, since shift-up into sucrose-containing media triggers comparable changes in growth and in phospholipid composition and synthesis.     

Trichinella spiralis: selective intestinal immune deviation in the rat

In rats, infections with 100-2000 Trichinella spiralis muscle larvae lead to a prompt immunity that is expressed in parasite expulsion within 14 days. Rats infected with more than 2000 larvae display impaired immunity with rejection delayed by 50% (7 days) or more. Suppression is selective for expulsive immunity as the antifecundity response of rats is directly proportional to dose and is expressed sooner in heavily infected subjects. Suppression of intestinal expulsive immunity was suggested by the fact that, with low doses (2000 larvae or less), worm rejection was inhibited by cortisone, whereas cortisone inhibited antifecundity but had no discernable effect on worm rejection in high-dose infections. Evidence for local immune deviation as opposed to systemic immunosuppression was obtained in experiments using parabiotic rats. When one partner was infected with 6000 worms and the other with 200, the rat infected with 200 parasites showed earlier rejection than was seen in single controls infected with 200 worms. The prolonged survival of high-dose adults was not accompanied by a change in the site of worm residence in the gut. Immunological parameters such as serum antibody levels, the number of activated cells or specific anti-T. spiralis lymphocytes in thoracic duct lymph were all increased in a dose-dependent manner. These experiments therefore demonstrate a novel autoprotective mechanism by which adult T. spiralis selectively reduce the expression of expulsive immunity in the gut.     

Observations on the self-cure reaction and other forms of immunological responsiveness against Haemonchus contortus in sheep

Self-cure reactions and immunological responses preventing establishment of Haemonchus contortus in sheep may operate as separate entities. In one experiment, self-cure occurred when challenge infection with 5000 larvae was superimposed on an infection with 5000 larvae given to worm-free sheep 6 weeks previously. Resident worms were rejected and establishment of infection by incoming larvae was impeded. The latter effect was not observed in sheep treated similarly but with resident parasites removed by treatment with oxfendazole before challenge. In another experiment, younger worm-free sheep primed by three infections with 2000 larvae at intervals of 2 weeks or a single infection with 6000 larvae were challenged with 10,000 larvae 6 weeks after the first priming infection. Self-cure was not incited but establishment of infection was impeded in sheep primed with three divided doses of larvae whether or not priming infections had been removed by oxfendazole. Infection regimes used for priming did not influence numbers of arrested fourth-stage larvae derived from challenge infection. However, more arrested larvae were present when challenge was superimposed on extant infections, indicating that resident worms or a factor activated by their presence induced developmental arrest. In a third experiment, large burdens with H. contortus were established in sheep immunosuppressed with the corticosteroid, dexamethasone, at the time of infection. Self-cure was not triggered by a challenge infection given 32 days later either in these sheep, or in sheep with a smaller worm burden derived from infection given without immunosuppression. Faecal egg counts, however, indicated that development of the challenge infection was prevented in both groups of sheep.

Investigation of self-cure is restricted by lack of a predictable system for reproducing the phenomenon. Self-cure was induced by a single infection with 5000 larvae in mature sheep but not with 6000 larvae in immature sheep. Three infections with 3000 larvae given at intervals of 2 weeks to mature sheep did not prime for self-cure. Procedures aimed at heightening immediate hypersensitivity, i.e. treatment with pertussis vaccine or concurrent infections with Ostertagia circumcincta, did not promote self-cure reactivity in the latter situation.     

Philomena oncorhynchi: Effect of hormones on maturation in anadromous sockeye, Oncorhynchus nerka

Adult sockeye salmon, Oncorhynchus nerka (Walbaum), treated with salmon pituitary extract in July survived for up to 47 days and developed nuptial colours in both male and female fish during this period, whereas no such characteristics appeared in untreated control fish. Furthermore, results showed that 20 of 50 adult female Philomena oncorhynchi recovered from the 15 treated fish contained fully developed tailed larvae in the uterus as compared with only one of 44 female P. oncorhynchi from 31 untreated control fish. None of 51 worms from 13 stilboestrol treated adult sockeye showed development in utero beyond an elongated embryo, nor did the host fish develop nuptial colours. P. oncorhynchi and its immature sockeye host (approx. 1 year prior to spawning) remained unaffected by any of three separate hormone treatment experiments using injection of salmon pituitary extract, injection of 17-β-estradiol, and stilboestrol mixed in the food.     

Vitellin and vitellogenin concentrations during oögenesis in the first gonotrophic cycle of the house fly,Musca domestica

The house fly, Musca domestica, contains at least two native vitellin and two vitellogenin proteins. Both vitellins appear to have an identical vitellogenin partner. The major native vitellin has a mol. wt of 281 K Daltons, and the major native vitellogenin has a mol. wt of 283 K Daltons. These proteins are composed of three subunits with mol. wt of 48, 45 and 40 K Daltons. The relationship of the subunits to the native proteins is not known.Haemolymph vitellogenin levels are cyclical during oögenesis with no detectable amounts in previtellogenic flies and low levels in postvitellogenic flies. The highest level of vitellogenin, 10.5 μg/μl, occurred in flies with stage-7 ovaries. The vitellogenin levels during oögenesis fit a parabolic curve and the fat body vitellogenin content during oögenesis showed this same pattern.Uptake of vitellogenin into the ovary during each stage of oögenesis also fit a parabolic curve and produced a high linear correlation with haemolymph vitellogenin levels. The greatest uptake was 37 μg/stage and occurred during stage 6.     

Crystallisation and preliminary X-ray data of ribulose-1,5-bisphosphate carboxylase from spinach

Crystals of a tertiary complex of spinach ribulose-1,5-bisphosphate carboxylase/oxygenase with the activators Mg²⁺ and CO₂ have been grown. These crystals diffract strongly to 1.6 Å resolution. The spacegroup is C222₁ with unit cell dimensions a = 158.6 Å, b = 158.6 Å, c = 203.4 Å. Additional local symmetry is apparent in the pattern of absences and the intensity distribution of the X-ray precession photographs. The photographs have been interpreted in terms of a molecule (consisting of eight large and eight small subunits, L₈S₈) with 222 symmetry and a molecular centre shifted 2 Å in the x direction from the origin of the unit cell. The asymmetric unit contains half the L₈S₈ molecule. The intensity distribution suggests that the molecular symmetry does not deviate far from 422. These crystals are compared with other crystalline forms of the enzyme and the implications of these results are discussed.