Chromosome distribution of intracisternal A-particle sequences in the Syrian hamster and mouse

Metaphase chromosomes of Syrian hamster and BALB/c mice were hybridized in situ with radiolabeled probes derived from cloned intracisternal A-particle (IAP) genes of the corresponding species. The DNAs of these species are known to contain about 900 and 1,000 copies, respectively, of the retrovirus-like IAP sequence elements per haploid genome. Multiple IAP sequences were found on all chromosomes of both hamster and mouse. In the hamster, more than half of the IAP sequences were located in regions of non-centromeric constitutive heterochromatin, at an average concentration per unit chromosome length 5 times greater than in the euchromatic regions. The other dispersed sequences showed marked local variations in concentration along the chromosome lengths; both discrete foci and large grain clusters were observed as well as regions apparently lacking IAP sequences. Within the resolution of the techniques, IAP sequences appeared to be more evenly distributed over the mouse chromosomes; however, some prominent variations in concentration were seen. The number of potentially active IAP genes in the Syrian hamster, and by extension in the mouse, may be restricted by the preferential location of IAP sequences in genetically inert regions of the genome.     

Involvement of Calcium in the Regulation of Serotonin N-Acetyltransferase in Retina

The possible involvement of calcium in the regulation of retinal serotonin N-acetyltransferase (NAT) activity was investigated using eye cups of Xenopus laevis cultured in defined medium. Omitting CaCl2 from the culture medium completely inhibited the dark-dependent increase of NAT activity at night. Approximately 10(-4)-10(-3) M free Ca2+ was found to be required for the maximal increase of NAT activity in the dark. Other divalent cations--Ba2+, Sr2+, and Mn2+--did not substitute for Ca2+. Antagonists of voltage-sensitive calcium channels, including nifedipine, methoxyverapamil (D600), Co2+, and Mg2+, were found to be effective inhibitors of the dark-dependent increase of retinal NAT activity. Trifluoperazine also decreased retinal NAT activity. These studies indicate that the increase of retinal NAT activity in the dark is mediated by a specific Ca2+-dependent process and that Ca2+ influx through voltage-sensitive calcium channels is involved.     

Characteristics of the β-Adrenoreceptor from Neuronal and Glial Cells in Primary Cultures of Rat Brain

The cellular characteristics of the beta-adrenoreceptor in glial and neuronal cells from the newborn rat brain were determined by (-)-[125I]iodocyanopindolol binding. In membranes from both cell types, the binding was saturable and from competition assays the potency series of (-)-isoproterenol greater than (-)-epinephrine = (-)-norepinephrine greater than (+)-isoproterenol was observed. 5'-Guanylyl-imidodiphosphate reduced the affinity of (-)-isoproterenol for the beta-adrenoreceptor from glial cells but had no effect on agonist affinity in neuronal cells. Chronic treatment of both cell types with (-)-isoproterenol reduced the receptor content and the capacity of the agonist to increase the cellular cyclic AMP content. However, the receptor recovery after chronic agonist treatment was faster in glial cells (72 h) than neuronal cells (120 h) and was blocked by cycloheximide. Treatment of both types with the irreversible beta-blocker bromoacetylalprenololmentane (2 microM) reduced the receptor content by 78% but no receptor recovery was observed for 120 h after the initial receptor loss. The data indicated that the majority of beta-adrenoreceptors in both cell types are the beta-1 subtype, but show some differences in receptor-agonist interactions. Furthermore, these CNS cells may be useful models for regulatory studies on the beta-adrenoreceptor.     

Decreased Incorporation of [3H]Inositol and [3H]Glycerol into Glycerolipids of Sciatic Nerve from the Streptozotocin Diabetic Rat

The incorporation of [3H]myo-inositol into individual phosphoinositides and of [3H]glycerol into glycerolipids was determined in sciatic nerve obtained from normal and streptozotocin diabetic rats and incubated in vitro. The uptake of inositol into lipid was approximately linear with time. More than 80% of the label was present in phosphatidylinositol with the remainder divided about equally between phosphatidylinositol phosphate and phosphatidylinositol-4,5-bisphosphate. Labeling was unchanged 2 weeks after induction of diabetes, but was reduced by 32% after 20 weeks of the disease. Glycerol incorporation occurred primarily into phosphatidylcholine and triacylglycerol and was depressed up to 45% into major phosphoglycerides in nerves from both 2- and 20-week diabetic animals. Triacylglycerol labeling was also substantially decreased, and the reduction was comparable in intact and epineurium free nerve, suggesting that a metabolically active pool of this compound, which is sensitive to hyperglycemia and/or insulin deficiency, is located in or immediately adjacent to the nerve fibers. The considerable decline in incorporation of these lipid precursors in diabetic nerve may be related to impaired inositol transport and to decrease overall energy utilization by the tissue.     

Regulation of product synthesis in cell cultures of Catharanthus roseus (L) G. Don

Cell suspension cultures of the Madagascan Periwinkle Catharanthus roseus (L) G. Don were maintained on Gamborg's B5 medium and their growth monitored by measuring cellular fresh and dry weight, cell number and mitotic activity. Samples of cells of different ages and physiological states were subcultured onto an alkaloid production medium and their rates of growth and alkaloid accumulation measured over a period of 30–45 days. In two experiments the rate of biomass accumulation was directly related to the rate of cellular serpentine accumulation. Possible mechanisms underlying this phenomenon are discussed in relation to the properties of cells comprising the inocula.     

The nitrogen cycle in lodgepole pine forests,southeastern Wyoming

Storage and flux of nitrogen were studied in several contrasting lodgepole pine (Pinus contorta spp.latifolia) forests in southeastern Wyoming. The mineral soil contained most of the N in these ecosystems (range of 315–860 g · m^–2), with aboveground detritus (37.5–48.8g · m^–2) and living biomass (19.5–24.0 g · m^–2) storing much smaller amounts. About 60–70% of the total N in vegetation was aboveground, and N concentrations in plant tissues were unusually low (foliage = 0.7% N), as were N input via wet precipitation (0.25 g · m^–2 · yr^–1), and biological fixation of atmospheric N (<0.03 g · m^–2 · yr^–1, except locally in some stands at low elevations where symbiotic fixation by the leguminous herbLupinus argenteus probably exceeded 0.1 g · m^–2 · yr^–1).Because of low concentrations in litterfall and limited opportunity for leaching, N accumulated in decaying leaves for 6–7 yr following leaf fall. This process represented an annual flux of about 0.5g · m^–2 to the 01 horizon. Only 20% of this flux was provided by throughfall, with the remaining 0.4g · m^–2 · yr^–1 apparently added from layers below. Low mineralization and small amounts of N uptake from the 02 are likely because of minimal rooting in the forest floor (as defined herein) and negligible mineral N (< 0.05 mg · L^–1) in 02 leachate. A critical transport process was solubilization of organic N, mostly fulvic acids. Most of the organic N from the forest floor was retained within the major tree rooting zone (0–40 cm), and mineralization of soil organic N provided NH₄ for tree uptake. Nitrate was at trace levels in soil solutions, and a long lag in nitrification was always observed under disturbed conditions. Total root nitrogen uptake was calculated to be 1.25 gN · m^–2 · yr^–1 with estimated root turnover of 0.37-gN · m^–2 · yr^–1, and the soil horizons appeared to be nearly in balance with respect to N. The high demand for mineralized N and the precipitation of fulvic acid in the mineral soil resulted in minimal deep leaching in most stands (< 0.02 g · m^–2 · yr^–1). These forests provide an extreme example of nitrogen behavior in dry, infertile forests.     

Commercial freezing of bovine embryos in straws

Bovine embryos were frozen commercially in clear double length $\text{1}\text{2}$ cc French straws with the wick and powder plug in the center of the straw. One-half of the double length straw serves as a handle and contains a color coded $\text{1}\text{4}$ cc straw around which an adhesive backed label has been applied. After plunging into liquid nitrogen, straws are transferred into goblets on canes while under liquid nitrogen. The straws are stored in the liquid phase of a nitrogen tank and canes containing straws are not transferred from one container to another unless the goblet containing the straws is full of liquid nitrogen.Embryos held for longer than 4 hours after collection prior to freezing showed a steady decline in pregnancy rate related to the length of time held prior to freezing. The percentage of embryos thawed and then evaluated as being transferrable was related to the quality of the embryos prior to freeze (Grade 1–93.6%, Grade 2–87.0%, Grade 3–63.8%). There was no statistical difference in pregnancy rates obtained from prefreeze Grade 1 embryos when comparing advanced blastocysts (45.2%), blastocysts (38.7%), early blastoclyst (43.1%) and advanced morula (41.6%).