T-cell responsiveness in Mycobacterium lepraemurium infections in a "resistant" (CBA) and a "susceptible" (BALB/c) mouse strain

Antigen-specific and mitogen-nonspecific T-lymphocyte proliferation and lymphokine release (interleukin 2 and macrophage activation factor) were studied in BALB/c and CBA mice infected intravenously with 10(8) Mycobacterium lepraemurium organisms. The responsiveness of spleen cells from infected animals to Con A and specific MLM antigen declined as the infection progressed. Thus, the decreased responsiveness appeared earlier and was more profound in the relatively susceptible BALB/c strain than in the relatively resistant CBA strain. Nylon-wool-purified, T-cell-enriched spleen cells from both strains, however, responded to both M. lepraemurium antigen and Con A until the later stages of infection (17 weeks postinfection). The relevance of nonspecific immunodepression mediated by nylon-wool-adherent spleen cells to the progressive nature of this infection is discussed.     

Isolation of microsatellite loci in the Capricorn silvereye,Zosterops lateralis chlorocephalus (Aves: Zosteropidae)

The Capricorn silvereye (Zosterops lateralis chlorocephalus) is ideally suited to investigating the genetic basis of body size evolution. We have isolated and characterized a set of microsatellite markers for this species. Seven out of 11 loci were polymorphic. The number of alleles detected ranged from two to five and observed heterozygosities between 0.12 and 0.67. One locus, ZL49, was found to be sex‐linked. This moderate level of diversity is consistent with that expected in an isolated, island population.     

Evidence for regulation of actin synthesis in cytochalasin D-treated HEp-2 cells

In HEp-2 cells treated with 0.2 or 2.0 μM cytochalasin D (CD), the relative rate of actin synthesis increased for about 12 h and then reached a plateau; this increase was suppressed by actinomycin D (AD). When CD was washed from cells which had been treated for 20 h, the elevated rate of actin synthesis declined to the control value within ca 4 h, as the actin-containing cytoskeletal components rearranged by CD recovered their normal morphology. Subsequently, actin synthesis was depressed below control values for a prolonged period; during recovery from 2 h treatment with CD, this depression was of much shorter duration. Re-addition of CD to cells after a 3 h recovery period again induced the cytoskeletal alterations characteristic of CD treatment but did not reverse the prior decline in the rate of actin synthesis. In HEp-2 cells treated with cycloheximide during exposure to CD for 20 h, the relative rate of actin synthesis measured after removal of cycloheximide was twofold higher than with CD alone and such cells exhibited a twofold slower decline in the rate of actin synthesis during recovery from CD in the continued presence of cycloheximide. These effects of cycloheximide, which resemble observations on “super-induction”, suggest that actin synthesis in CD-treated and recovering HEp-2 cells may be regulated by a repressor protein. The possibility that the proposed repressor protein is actin and that actin may thus be a feedback inhibitor of its own synthesis is discussed.     

Termination of inspiration by phase-dependent respiratory vagal feedback in awake normal humans.

Imperceptible levels of proportional assist ventilation applied throughout inspiration reduced inspiratory time (TI) in awake humans. More recently, the reduction in TI was associated with flow assist, but flow assist also reaches a maximum value early during inspiration. To test the separate effects of flow assist and timing of assist, we applied a pseudorandom binary sequence of flow-assisted breaths during early, late, or throughout inspiration in eight normal subjects. We hypothesized that imperceptible flow assist would shorten TI most effectively when applied during early inspiration. Tidal volume, integrated respiratory muscle pressure per breath, TI, and TE were recorded. All stimuli (early, late, or flow assist applied throughout inspiration) resulted in a significant increase in inspiratory flow; however, only when the flow assist was applied during early inspiration was there a significant reduction in TI and the integrated respiratory muscle pressure per breath. These results provide further evidence that vagal feedback modulates breathing on a breath-by-breath basis in conscious humans within a physiological range of breath sizes.     

HISTORICAL BIOGEOGRAPHY IN NORTH AMERICAN ARID REGIONS: AN APPROACH USING MITOCHONDRIAL-DNA PHYLOGENY IN GRASSHOPPER MICE (GENUS ONYCHOMYS)

Restriction-endonuclease-site variation of mitochondrial DNA (mtDNA) was used to investigate patterns of geographic and phylogenetic divergence within the rodent genus Onychomys. Onychomys has occupied arid habitats in the western North American deserts, shrub-steppes, and grasslands since the late Tertiary. A phylogenetic analysis of the total mtDNA restriction-site variation throughout the range of Onychomys suggests that the distribution of this genus has been affected by the same Quaternary pluvial-interpluvial climatic fluctuations that have resulted in the periodic fragmentation of arid habitats in western North America. Onychomys mtDNA haplotypes define at least five discrete geographical subsets, suggesting that there are five areas of endemism for biota restricted to arid and semiarid habitats in North America. The mtDNA-haplotype phylogeny can be used to infer an hypothesis of historical relationships among the five areas of endemism as follows: ([{(Wyoming Basin + Interior Plains + Colorado Plateaus) + (Columbia Basin + Great Basin)} + Gulf Coastal Plain] + Chihuahuan) + Western Deserts. The results of this study point to the potential use of mtDNA-haplotype phylogenies to reconstruct historical biogeographic events in Quaternary time. The utility of mtDNA variation depends in part on the ecology and distribution of the species being examined. Therefore, our hypothesized area cladogram can be tested by investigating regional relationships in other western North American taxa with distributions similar to Onychomys.     

The architecture of shrubs after defoliation and the subsequent feeding behavior of browsers

We examined regrowth architecture of 4 species of savanna shrubs following 4 levels of defoliation. Defoliation had little effect on the regrowth architecture of honey mesquite ( Prosopis glandulosa ), which is rarely browsed by mammalian herbivores. The 3 acacia species ( Acacia berlandieri , A. greggii , A. schaffneri ) responded to defoliation by increasing leaf and spine density on the regrowth branches, but spine length and branching architecture remained unchanged. Only A. greggii , which is a preferred food plant of many browsers, exhibited an increase in the number and length of current annual growth branches in response to defoliation. The changes in plant architecture due to defoliation had little effect on the subsequent feeding behavior of captive white-tailed deer ( Odocoileus virginianus ). Food intake rate of the deer was most strongly related to internode distance, a parameter not significantly altered by defoliation. This suggests that the architectural responses of these shrubs to defoliation may not provide increased defense against browsing by co-evolved mammals.     

A simple system for plant cell microinjection and culture

Microinjection of plant protoplasts and cells has been recently reported, however a system that combines simplicity of design, harmless immobilization, high resolution visibility and ability to monitor individual target cells is lacking. This report describes a system which combines these features. It consists of a microinjection-microculture dish containing immobilized protoplasts and a simple chamber that maintains sterility and humidity during injection. Highly purified protoplast preparations are plated at low population density as a thin monolayer of widely separated cells embedded in agarose layered over a thicker (0.2 mm at center to 1 mm at edge) layer of agarose-solidified medium. This physical arrangement allows for rapid location, mapping and injection of the immobilized protoplasts and also their subsequent location for growth monitoring. The double layers of agarose provide adequate nutrition for culturing injected cells to the microcalli stage. In addition to protoplast injection, this system was also used to inject 3- to 4-day old nonspherical cells derived from protoplasts. Colony formation rates from injected protoplasts and cells with regenerated walls were equivalent to those of uninjected controls. Furthermore, tobacco protoplasts stored at 4°C in liquid medium for up to two weeks remained fully competent for plating and injection. These cold-stored protoplasts, when injected, formed colonies at rates similar to those from fresh preparations. The ability to store protoplasts without loss of viability considerably increases the ease and convenience of cell injection experiments.Mention of a trademark or proprietary product does not constitute a guarantee or warranty of the product by the USDA, and does not imply its approval to the exclusion of the other products that may also be suitable.