Environmental stress and bacterial infection in channel catfish, Ictalurus punctatus Rafinesque

Channel catfish, Ictalurus punctatus , were injected intraperitoneally with a sublethal dose of Aerornonas hydrophila and then stressed for 144 h by being maintained either in a dissolved oxygen concentration of 1·5 mg/1, 1·2 mg/1 total ammonia, and/or 6·5 mg/1 free CO₂ with a continuous inflow of water. A significant difference in percentage of mortality was noted between treatments ( P < 0·05). The trunk kidneys of surviving stressed fish had significantly higher total bacterial counts than non-stressed controls. A. hydrophila was isolated from 67% of the stressed fish and 9% of the control fish. Edwardsiella tarda , apparently endemic in the population, was isolated from 43% of the stressed fish and 7% of the control fish. Histopathological lesions were in the gills, liver, spleen, trunk kidney, and head kidney of stressed fish, but not control fish.     

Factors influencing the fecundity of Moniliformis moniliformis (Acanthocephala): constant diet and varied dose

Aspects of the reproductive performance of Moniliformis moniliformis were investigated in rats allowed to feed ad libitum on a purified diet containing 1% (w/w) fructose as an energy source for the worms. The rats were infected with either 10, 20, 40 or 80 cystacanths each with the intention of investigating density-dependent effects on worm fecundity. The establishment of the worms in the gut was independent of dose, but survival, growth and reproductive performance generally were shown to be related to the infective dose given to the rats. The effects could not be related to the absolute numbers of worms present in the small intestine at post-mortem examination. In general, some unidentified regulatory process appeared to operate to create severe density-dependence in survival so that surviving parasites were not present in numbers expected to generate competition. Attainment of sexual maturity, growth and the production of mature eggs by worms from rats given doses of 80 cystacanths each were delayed compared with worms from rats given the other doses, but eventually the performance of the high-dose worms caught up. Worms attached more anteriorly in the small intestine grew bigger and produced more mature eggs. Possible mechanisms responsible for the observed effects are discussed.     

Dissociation of lepidopterous tissues with proteolytic enzymes: Comparison of collagenase,trypsin, and pronase

The fat body and certain other tissues of lepidopterous larvae and diapausing pupae can be completely dissociated by incubation in crude or purified collagenase. Damage to the cells is minimal. Dissociation with trypsin is incomplete, and pronase causes extensive damage. All three enzymes act principally by digesting the extracellular connective sheath that envelops the individual lobes of fat body, since the cells at this stage are not intrinsically cohesive. The experimental findings support the notion that collagen is an important structural component of insect connective membranes.     

PATTERNS OF ALLOZYME DIVERSITY IN THE WEST INDIES CYCAD ZAMIA PUMILA (ZAMIACEAE)

The West Indies cycad, Zamia pumila, is restricted to the Greater Antilles, northern Bahama Islands, Florida, and the southeastern coast of Georgia. An electrophoretic study based on nine enzymes compared 21 accessions from throughout the range of the species. Lower levels of intrapopulation variation than those reported for ferns, other gymnosperms, and angiosperms were discovered for the two more extensively sampled populations. However, this variation was similar to that found in other island taxa and in the endemic Australian cycad, Macrozamia communis. In contrast, allozyme divergence among accessions of Z. pumila appeared relatively high, mostly as a result of rare alleles restricted in geographic distribution. The age and biogeography of Z. pumila may gave contributed to population differentiation. Also, mean number of alleles per locus was low for the species (1.75). Finally, the time-since-divergence value (10.8 million years ago) between Z. pumila and its closest extant relative, Z. splendens, was much smaller than the age of Z. pumila suggested by the fossil record and historical geology of the Caribbean (30–60 million years ago). Together, these data indicate that biochemical evolution within this species, and perhaps in all cycads, is slow when compared to that of noncycad seed plants.     

Intracellular location of unoccupied 1,25-dihydroxyvitamin D receptors: a nuclear-cytoplasmic equilibrium

In order to investigate the subcellular distribution of unoccupied 1,25-dihydroxyvitamin D3 receptors, highly purified cytoplasts and nucleoplasts were prepared from two kidney cell lines (PK1 and MDBK). This was accomplished utilizing the technique of enucleation by cytochalasin B and density gradient centrifugation. Unoccupied 1,25-dihydroxyvitamin D3 receptors were found in both the nuclear and cytosolic compartments, with approximately 70% of the receptors localized in the cytoplasm. When cells were pretreated with 1,25-[3H]dihydroxyvitamin D, prior to enucleation, it was found that 90% of the receptor-hormone complex was associated with nucleoplasts, thus demonstrating that cytochalasin B treatment does not alter the high-affinity association of the receptor-hormone complex with the nucleus. The ratio of unoccupied receptor/protein was found to be the same in whole cells, cytoplasts, and nucleoplasts for both cell types. The ratio of unoccupied receptor/DNA was highest in cytoplasts and lowest in nucleoplasts. Taken together, these data indicate that the unoccupied 1,25-dihydroxyvitamin D receptor is generally associated with cell proteins and not specifically associated with cell DNA. We therefore propose, at least for these cells, that the unoccupied 1,25-dihydroxyvitamin D receptor exists in equilibrium between the nuclear and cytosolic compartments of the whole cell, and receptor-hormone binding shifts this equilibrium to favor nuclear localization.     

Imino-proton resonances of yeast tRNAPhe studied by two-dimensional nuclear Overhauser enhancement spectroscopy

Application of two-dimensional nuclear Overhauser enhancement (NOE) spectroscopy to yeast tRNAPhe in H2O solution demonstrates that all imino-proton resonances, related to the secondary structure, and nearly all imino proton resonances, originating from the tertiary structure, can be assigned efficiently by this method. The results corroborate the assignments of the imino-proton resonances of this tRNA as established previously by one-dimensional NOE experiments (only the assignment of base pairs G1 X C72 and C2 X G71 should be reversed). The advantages of two-dimensional NOE spectroscopy over one-dimensional NOE spectroscopy for the assignments of imino-proton resonances and the structure elucidation of tRNA are illustrated and discussed. Furthermore, the use of non-exchangeable proton resonances as probes of the molecular structure is explored.     

Pulsatile secretion of gonadotrophins, ovarian steroids and ovarian oxytocin during prostaglandin-induced regression of the corpus luteum in the cow

A luteolytic dose (500 micrograms) of cloprostenol was given on Day 12 of the oestrous cycle to 5 heifers. Blood samples were collected simultaneously from the caudal vena cava and jugular vein at 5-20-min intervals from -6 to 0 (control period), 0 to 12 and 24 to 36 h after PG injection. Pulses of LH were secreted concomitantly with pulses of FSH during all sampling periods. However, during the control period separate FSH pulses were detected resulting in a shorter (P less than 0.01) interpulse interval for FSH than LH (93 versus 248 min). LH and FSH pulse frequencies increased (P less than 0.01) beginning 1-3 h after PG to interpulse intervals of 59 and 63 min, respectively, and continued to be maintained 24-36 h after PG. Concomitantly there was a 2-3-fold increase (P less than 0.01) in basal concentrations and pulse amplitude for LH (but not FSH). FSH basal concentrations and pulse amplitudes decreased (P less than 0.05) in 3 heifers 24-36 h after PG. Pulsatile secretion of oestradiol was observed at frequencies similar to LH during the periods 4-12 h (3 heifers) and 24-36 h (2 heifers) after PG, respectively, resulting in higher (P less than 0.05) mean oestradiol concentrations. Progesterone concentrations in the vena cava increased (P less than 0.01) 5-10 min after PG but decreased (P less than 0.01) 67% by 20 min after PG. This decrease was followed by a rise (P less than 0.05) beginning 2-3 h after PG and lasting for an average of 3.3 h.(ABSTRACT TRUNCATED AT 400 WORDS)