Spatial scale and the determinants of plant species richness

Traditional ecological theory has stressed the importance of competitive interactions in regulating species richness. Recent research has transcended this viewpoint by considering the role of stochastic processes, mosaic phenomena and nonequilibrium conditions in the regulation of richness. This growing body of work indicates that the determinants of plant species richness may vary predictably over different spatial scales.     

Constitutive and IL 1-regulated murine complement gene expression is strain and tissue specific

To study the molecular mechanisms accounting for strain- and tissue-specific variations in the production of complement proteins, complementary DNA probes were used to assess qualitative and quantitative differences in specific mRNA content of complement proteins C2, factor B, and C3 in extracts of tissues (liver, lung, spleen, kidney, and peritoneal macrophages) isolated from various mouse strains. Northern blot analysis of total hepatic RNA revealed differences in C2, factor B, and C3 mRNA levels in strains that share B10 background but differ in the H-2 region (e.g., H-2k, H-2u, H-2d, H-2f). In each instance, hepatic mRNA specific for the individual gene product corresponded in amount to the serum levels. By contrast, specific mRNA content of C2 and factor B in macrophages differed significantly from those observed in liver for each strain. Modulation of C2, factor B, and C3 expression was studied after in vivo administration of recombinant IL 1 or endotoxin to H-2k (B10.AKM) or H-2u (B10.PL) strain mice. As assessed by Northern blot analysis, neither endotoxin nor IL 1 affected liver C2-specific mRNA but increased specific C2 mRNA levels in kidney and lung. For both strains, IL 1 increased specific factor B mRNA in all tissues examined except for the H-2u strain liver factor B mRNA content, which was not affected by IL 1, whereas that of H-2k mice was increased. The lack of factor B modulation by IL 1 in the H-2u lines was specific to that gene and not a reflection of a generalized IL 1 unresponsiveness. Differences in tissue and strain specific constitutive and IL 1-regulated expression of the C3 gene were also observed in the H-2u and H-2k strains.     

Phencyclidine (PCP) injected in the nucleus accumbens increases extracellular dopamine and serotonin as measured by microdialysis

Phencyclidine (PCP; 20 micrograms in 0.5 microliter) was tested by local brain injection for neurochemical effects in the nucleus accumbens and striatum of rats. Changes in dopamine turnover could not be detected in postmortem tissue assays. In contrast, extracellular levels of dopamine significantly increased as measured by microdialysis in freely moving animals. PCP also increased extracellular levels of serotonin and decreased 3,4-dihydroxyphenylacetic acid (DOPAC), but did not change homovanillic acid (HVA) or 5-hydroxyindoleacetic acid (5HIAA). Microdialysis suggests that PCP acts in some dopamine terminal regions to increase extracellular dopamine and serotonin.     

Segregation analysis with uncertain ascertainment: application to Fanconi anemia.

A Bayesian solution for making inferences about segregation parameters with no information about the ascertainment is presented. Inferences about the segregation probability and the probability of being sporadic are made through the posterior marginal distribution of these parameters after integrating out the ascertainment probability, the nuisance parameter. The method was tested with real and simulated data and performed well. Original Fanconi anemia data, for which no information about the ascertainment was available, were then analyzed, with results that confirmed a monogenic autosomal recessive mode of inheritance.     

Clastogen-induced chromosomal breakage as a marker for first trimester prenatal diagnosis of Fanconi anemia

Summary Using cultured trophoblast cells obtained by chorionic villus biopsy, we diagnosed Fanconi anemia (FA) in two pregnancies and excluded it in eight pregnancies at risk for the syndrome. Baseline chromosomal breakage and breakage induced by diepoxybutane (DEB) were analyzed. Increased breakage was used as a marker for the syndrome. Our results were unambiguous and provide a reliable method for prenatal detection of FA in the first trimester of pregnancy.     

Chemically Mediated Transmission at a Giant Fiber Synapse in the Central Nervous System of a Vertebrate

The hatchetfish, Gasteropelecus, possesses large pectoral fin adductor muscles whose simultaneous contraction enables the fish to dart upwards at the approach of a predator. These muscles can be excited by either Mauthner fiber. In the medulla, each Mauthner fiber forms axo-axonic synapses on four "giant fibers," two on each side of the midline. Each pair of giant fibers innervates ipsilateral motoneurons controlling the pectoral fin adductor muscles. Mauthner fibers and giant fibers can be penetrated simultaneously by microelectrodes close to the synapses between them. Electrophysiological evidence indicates that transmission from Mauthner to giant fiber is chemically mediated. Under some conditions miniature postsynaptic potentials (PSP's) are observed, suggesting quantal release of transmitter. However, relatively high frequency stimulation reduces PSP amplitude below that of the miniature potentials, but causes no complete failures of PSP's. Thus quantum size is reduced or postsynaptic membrane is desensitized. Ramp currents in Mauthner fibers that rise too slowly to initiate spikes can evoke responses in giant fibers that appear to be asynchronous PSP's. Probably both spikes and ramp currents act on the same secretory mechanism. A single Mauthner fiber spike is followed by prolonged depression of transmission; also PSP amplitude is little affected by current pulses that markedly alter presynaptic spike height. These findings suggest that even a small spike releases most of an immediately available store of transmitter. If so, the probability of release by a single spike is high for any quantum of transmitter within this store.     

DIURNAL VARIATION IN THE LABELING INDEX OF MOUSE EPIDERMIS: A DOUBLE ISOTOPE AUTORADIOGRAPHIC DEMONSTRATION OF CHANGING FLOW RATES

A diurnal rhythmicity in the labeling index was observed in the epidermis of hairless mice, injected with either ¹⁴C- or ³H-thymidine, at different times during a 24 hr period. A modified autoradiographic technique, using ¹⁴C- and ³H-thymidine and two overlying emulsion layers, makes it possible to clearly differentiate synthesizing cells which are singly labeled with either carbon-14 or tritium, and cells labeled with both isotopes. At various times during a 24 hr period, hairless mice were injected with thymidine-2-¹⁴C and colcemid, followed at 2 or 3 hr by a second injection of ³H-thymidine. The labeling indices were calculated for the ¹⁴C- and ³H-thymidine injection times. These labeling indices were consistent with the control, single isotope, labeling indices and exhibited the same diurnal rhythm. Cells singly labeled with ³H- or ¹⁴C-thymidine have either started or completed DNA synthesis during the interval between the two injections. Flow rates into and out of DNA synthesis, throughout the 24 hr period, can be calculated from these singly labeled cells. The flow rates varied rhythmically throughout the day and paralleled changes in the labeling indices. The influx and efflux flow rates, at all times measured, were not equal. The influx flow rate was reflected in the efflux rate at a time later equal to the duration of S. By means of these flow rates, the per cent of cells in DNA synthesis was calculated for each hour during a 24 hr period. The resulting labeling index curve matches the observed 24 hr diurnal rhythm in labeling indices. By extension of these flow rates through mitosis, the resulting mitotic index curve is comparable to the reported 24 hr diurnal rhythm in mitotic indices.