Spectral mechanisms in the tree squirrel retina

Summary The retina of the gray squirrel (Sciurus carolinensis) contains rods and cones in a ratio of about 23. The spectral mechanisms in this retina were examined in behavioral and electrophysiological experiments. Tests of color vision revealed that this animal has a spectral neutral point at about 500 nm and, thus, dichromatic color vision. Recordings made from single optic nerve fibers and results obtained from an analysis of the flicker photometric electroretinogram (ERG) indicated that vision in the gray squirrel is based on three spectral mechanisms. One of these, presumably rod-based, has peak sensitivity at about 502 nm. The other two mechanisms reflect the presence of two classes of cone having average peak sensitivity of about 444 nm and 543 nm.     

Effect of inhibitors of gamma-glutamyl transpeptidase on the uptake of glutamate and aspartate into cultured astroglial cells from the glycogen body and cerebral hemispheres of the embryonic chick

Astroglial-like cells from the glycogen body and astroglia from the cerebral hemispheres of chick embryos cultured 6 days in vitro exhibit comparable values of L-glutamate and L-aspartate uptake. The uptake is significantly reduced by inhibitors of gamma-glutamyl transpeptidase.     

Effects of Extracellular Potassium on Glycogen Stores of Astrocytes In Vitro

Astrocyte-enriched and meningeal cell cultures of the rat cerebral cortex were prepared, and their glycogen content was measured after 10-90 min under control (2.5 mM) concentrations of potassium after prefeeding with 20 mM glucose. No net change in glycogen level was noted in either culture over this period. Cell cultures were then exposed to increased concentrations of potassium (5, 10, and 15 mM), and their glycogen content was measured after 10-90 min. Both types of cell culture showed complex and variable changes in glycogen content. In general, increased potassium concentrations caused astrocyte glycogen stores to be reduced at physiological increases of potassium levels (from 2.5 to 5 mM and above), although a period of resynthesis was evident at all potassium concentrations. Meningeal cell glycogen levels were highly variable and only affected by high (10 and 15 mM) levels of potassium. These results are discussed with respect to the theory that changes in the external potassium concentration caused by neuronal activity might act as a signal controlling astrocyte glycogen stores.     

Regulation of Brain and Cerebrospinal Fluid Calcium by Brain Barrier Membranes Following Vitamin D-Related Chronic Hypo- and Hypercalcemia in Rats

Male Fischer-344 rats, 21 days old, were fed diets containing 0 (LOD), 2,200 (CONT), or 440,000 (HID) international units of vitamin D3 per kilogram for 12 weeks. [Ca] was measured in plasma, CSF, brain, and choroid plexus. In addition, 45Ca and 36Cl transfer coefficients (KCa and KCl) for uptake from blood into CSF and brain were determined. Although plasma ionized [Ca]s in LOD and HID rats were 50% and 136%, respectively, of values in CONT animals, CSF and brain [Ca]s ranged from only 85% to 110% of respective CONT values. Choroid plexus [Ca] was increased by 37% after HID diet, but was decreased only 10% after LOD. KCa values at CSF, parietal cortex, and pons-medulla were negatively correlated with plasma ionized [Ca], whereas KCl values at CSF and brain were not different between the diet groups. The findings demonstrate that central nervous system [Ca] is maintained during chronic hypo- or hypercalcemia by saturable transport of Ca at brain barrier membranes. This transport does not seem to involve modulation by 1,25-dihydroxyvitamin D3.     

Depletion of Brain Glutathione in Preweanling Mice by L-Buthionine Sulfoximine

Previous studies indicated that DL-buthionine sulfoximine (DL-BSO), an agent that inhibits the biosynthesis of GSH in liver and other peripheral organs, fails to suppress levels of GSH in the CNS. In the current study, preweanling mice responded to repeated injections of L-BSO with marked declines (79.6-86.5%) of GSH content in brain and spinal cord. In adult mice, the same treatment schedule produced only modest declines (17.8-29.2%) of GSH content in brain and a 55.9% decline in spinal cord. Pretreatment of preweanling mice with L-BSO represents a tool for studying the role of GSH in the CNS.     

Four viral genes independently contribute to attenuation of live influenza A/Ann Arbor/6/60 (H2N2) cold-adapted reassortant virus vaccines.

Clinical studies previously demonstrated that live influenza A virus vaccines derived by genetic reassortment from the mating of influenza A/Ann Arbor/6/60 (H2N2) cold-adapted (ca) donor virus with epidemic wild-type influenza A viruses are reproducibly safe, infectious, immunogenic, and efficacious in the prevention of illness caused by challenge with virulent wild-type virus. These influenza A reassortant virus vaccines also express the ca and temperature sensitivity (ts) phenotypes in vitro, but the genes of the ca virus parent which specify the ca, ts, and attenuation (att) phenotypes have not adequately been defined. To identify the genes associated with each of these phenotypes, we isolated six single-gene substitution reassortant viruses, each of which inherited only one RNA segment from the ca parent virus and the remaining seven RNA segments from the A/Korea/1/82 (H3N2) wild-type virus parent. These were evaluated in vitro for their ca and ts phenotypes and in ferrets, hamsters, and seronegative adult volunteers for the att phenotype. We found that the polymerase PA gene of the ca parent specifies the ca phenotype and that the PB2 and PB1 genes independently specify the ts phenotype. The PA, M, PB2, and PB1 genes of the ca donor virus each contribute to the att phenotype. The finding that four genes of the ca donor virus contribute to the att phenotype provides a partial explanation for the observed phenotypic stability of ca reassortant viruses following replication in humans.     

A statistical analysis for the mouse lymphoma cell forward mutation assay

This paper illustrates the usefulness of solvent control trials and presents a statistical analysis for mouse L5178Y lymphoma data. Examination of solvent control trials establishes that the natural logarithm of mutant frequency is approximately normally distributed and that both the mean and variance of mutant frequency vary by trial. There is little evidence of downturns at higher doses in the dose-response curves studied; therefore, a trend test is proposed for the detection of an increasing dose-response curve. A Monte Carlo investigation confirms that the proposed trend test is better able to detect an increasing dose-response than 4 alternate methods of analysis.     

Respiration and soluble sugar metabolism in sugar pine embryos

Embroys excised from dormant seeds of sugar pine ( Pinus lambertiana Dougl.) incubated at 25°C (non-dormancy-breaking) or stratified at 5°C (dormancy-breaking) were analyzed to determine temperature effects on the relative activities of respiration and fermentative metabolism, the levels of soluble sugers and the activities of the hydrolytic enzymes, invertase and sucrose synthase, as related to the release of dormancy and germinatio. At 25°C, despite a sharp drop in embryo oxygen uptake after 48 h, a simultaneous decline in acetaldehyde and ethanol concentrations indicated that there was not a shift to fermentative metabolism. The concentrations of soluble sugars showed no treatment effects. Embryo invertase (EC 3.2.1.26) activity changed only slightly at either temperature, while stratification was accompanied by a 4-fold increase in sucrose synthase (EC 2.4.1.13) activity (cleavage direction). Upon transfer of stratified seeds to 25°C, embryo sucrose synthase activity rapidly increased almost 10-fold, with the increase beginning prior to germination, while mvertase activity increased 20-fold, concomitant with germination.