DIFFERENTIAL ENRICHMENT OF CELLS FROM EMBRYONIC RAT CEREBRA BY CENTRIFUGAL ELUTRIATION

—Centrifugal elutriation was used to obtain different populations of cells dissociated from 16-day-old rat embryo cerebra. The cell populations recovered were viable and could be maintained for several weeks in vitro. Sterile conditions were maintained throughout a preparation. Rat pups were removed by Caesarean section, the cerebra dissected and the cells dissociated by brief exposure to trypsin (0.125%, 6 min). An equivalent volume of elutriation medium (Dulbecco's medium containing 1% fetal calf serum, sodium bicarbonate, penicillin and streptomycin, EDTA, and deoxyribonuclease) was added to the trypsin-cell suspension, the dissociated cells pelleted, resuspended in elutriation medium and counted. Up to 4 x 10⁸ cells were injected into the previously sterilized elutriator. Seven fractions were usually recovered from a preparation. The first fraction contained primarily red blood cells and cell debris, which could not be maintained in vitro. Upon culture, fraction 2 consisted of predominantly non-neuronal cells, while fractions 3–6 contained neuronal and non-neuronal cells. The morphological characteristics of the neurons differed in these fractions. Fraction 7 contained cells that had reaggregated during the elutriation procedure and exhibited a variety of cell types in vitro.     

Seasonal patterns of CO2 and water vapor exchange of three salt marsh succulents

Summary Diurnal carbon dioxide exchange patterns of three salt marsh succulents, Borrichia frutescens, Batis maritima and Salicornia virginica, were determined on a seasonal basis in the marsh at Sapelo Island, Georgia. Year-round photosynthetic activity was observed in these species though winter rates of CO₂ exchange were reduced. Net primary productivity, estimated using gas exchange techniques, agreed with previously reported harvest data. The role of light and temperature in the control of seasonal photosynthetic changes was investigated. A similar variation in light utilization with season was found in all three species, while seasonal temperature acclimation was species dependent. Less than 20% of fixed CO₂ was lost through dark respiration in any of the species.Water use in the salt marsh succulents was found to be relatively inefficient. High rates of transpiration were observed both summer and winter in the succulents.The succulents were judged to be C₃ plants on the basis of several criteria.Contribution No. 391 from the University of Georgia Marine Institute     

Identifying human cells capable of metabolizing various classes of carcinogens

Human cells that appear capable of metabolizing various classes of carcinogens have been identified using one of two methods: metabolism of tritiated benzo(a)pyrene to aqueous-acetone soluble forms or inhibition of cellular DNA synthesis. Each of the assay systems was optimized and the results on 15 human epithelial cell lines were compared. One or more cell lines were found to activate each of four classes of carcinogens examined: polycyclic hydrocarbons, aromatic amines, heterocyclic hydrocarbons, and nitrosamines. Cells that appeared capable of metabolizing polycyclic hydrocarbons or aromatic amines by these methods were also found to produce metabolites which were cytotoxic to cocultivated human xeroderma pigmentosum fibroblasts after a 48-hr exposure to the carcinogen.     

Lethal white foals in matings of overo spotted horses

Overo is a variable pattern of white coat color spotting which occurs in several breeds of horses in the United States. Occasionally, when overos are crossed inter se white foals are born which die soon after birth. Both intestinal tract abnormalities and isoerythrolysis have been reported in these foals. This report presents data which show that neonatal isoerythrolysis (NI) is not involved in the death of the white foals. Further research is needed to define the nature of the lethal anomaly, as well as the genetics, of overo and lethal white foals.     

Intracellular recording of cerebral cortical actions of prostaglandin F2α (PGF2α)

Our reported data on the cortical inhibitory actions of prostaglandin F_2α (PGF_2α) and the diversity of data in the literature on cerebral PG actions are examined here in the light of intracellular recording which provides the requisite membrane data for the first time. Thus, 1) intracellular recording from the cat cerebral cortex is obtained for the actions of PGF_2α and for norepinephrine (NE) and serotonin (5HT). 2) The parallel changes in firing and polarization and the simultaneous transmembrane conductance changes are qualitatively identical for PGF_2α, NE and 5HT. 3) The reduction in firing accompanied by hyperpolarization indicates that PGF_2α, NE and 5HT all inhibit these cells. 4) The ionic species responsible for this inhibition is such that it increased the transmembrane resistance, and this was true for all three. 5) The changes in membrane parameters, identical in direction for PGF_2α and NE, but stronger for the latter, constitute conditions that can lead to competitive inhibition and therefore conote, presumably, actions at the same or related receptors. Such competition with evoked cortical field potentials is shown in the preceding paper.     

The second polar lobe of theSabellaria cementarium embryo plays an inhibitory role in apical tuft formation

Summary The embryo ofSabellaria cementarium (Polychaeta) forms a polar lobe at each of the first two cleavage divisions which becomes absorbed into one of the blastomeres at the end of the division. Lobe removal experiments show that the polar lobe preceding first cleavage is necessary for the development of the apical tuft and the posttrochal region of the trochophore larva. The polar lobe preceding second cleavage is smaller than the first polar lobe and is necessary only for post-trochal region development. In blastomere isolation experiments, isolates containing the C but not the D blastomere form apical tufts. Isolates containing the D but not the C blastomere do not form apical tufts. When the polar lobe preceding second cleavage is removed and the C and D blastomeres are separated and raised in isolation, each can form an apical tuft. When the second cleavage is equalized with sodium dodecyl sulfate (SDS) such that both the C and the D blastomeres receive second polar lobe material, no apical tuft is formed. These results suggest that apical tuft determinants are distributed to both the C and D blastomeres at second cleavage but that the second polar lobe contains an inhibitor for apical tuft formation which is shunted to the D blastomere after the completion of second cleavage.     

The identification of dimethylphenylarsine as a microbial metabolite using a simple method of chemofocusing

Candida humicola acts on benzenearsonic acid to produce dimethylphenylarsine, which was identified by mass spectroscopy following the chemofocusing of the volatile metabolite onto a mercuric chloride impregnated filter. The same technique established that trimethylarsine is the volatile metabolic product obtained from C. humicola treated with 4-NH₂-2-OHC₆H₃AsO(OH)₂ and (CH₃)₃AsO. Arsanilic acid, 4-NH₂C₆H₄AsO(OH)₂, is not metabolized to a volatile arsine.     

Heterochromatin accumulation,disposition and diversity in Gibasis karwinskyana (Commelinaceae)

C-banding differences within Gibasis karwinskyana (Roem & Schult.) Rohw. were reassessed using dual fluorochrome staining. Pronounced differences in C-band pattern between two subspecies with identical basic karyotypes were due to different chromosomal locations of AT-rich and GC-rich heterochromatin. The AT-rich component had an equilocal distribution in the karyotype and has evidently been accumulated at telomeres, as shown by its prevalence in supernumerary segments and B chromosomes. The GC-rich component also varied in amount, but was limited to nucleolus organizing regions (NORs) and centromeres. Centromeres and telomeres are suggested to constitute separate, although perhaps interdependent, centres of heterochromatin amplification. The possible role of nuclear architecture in determining the accumulation, distribution and spread of these sequences is discussed.Abbreviations H Hoechst 33258 - CMA chromomycin A3 - NOR nucleolus organizing region - SS supernumerary segment - Q quinacrine dihydrochloride - H⁺ H etc. indicate enhanced (+) and quenched (-) fluorescence with the stated fluorochrome by H.C. Macgregor     

Resolution of Biphasic Binding of the Opioid Antagonist Naltrexone in Brain Membranes

In synaptosomal membranes from rat brain cortex, in the presence of 150 mM NaCl, the opioid antagonist [3H]naltrexone bound to two populations of receptor sites with affinities of 0.27 and 4.3 nM, respectively. Guanosine-5'-(3-thiotriphosphate) had little modulating effect and did not alter the biphasic nature of ligand binding. On the other hand, receptor-selective opioids differentially inhibited the two binding components of [3H]naltrexone. As shown by nonlinear least-squares analysis, the mu opioids Tyr-D-Ala-Gly-(Me)Phe-Gly-ol or sufentanil abolished high-affinity [3H]naltrexone binding, whereas the delta-selective ligands [D-Pen2,D-Pen5]enkephalin, ICI 174,864, and oxymorphindole inhibited and eventually eliminated the low-affinity component in a concentration-dependent manner. These results indicate that, in contrast to the guanine nucleotide-sensitive biphasic binding of opioid-alkaloid agonists, the heterogeneity of naltrexone binding in brain membranes reflects ligand interaction with different opioid-receptor types.