Arguing from potential

Buckle's article is one of three discussing the potentiality of the human embryo in this issue of Bioethics devoted to the subject of embryo research. (See also Michael Lockwood's "Warnock v. Powell (and Harradine): when does potentiality count?" and Richard M. Hare's "When does potentiality count? A comment on Lockwood.") In his essay, Buckle analyzes some of the distinct ways of arguing about potential, and the different senses of potential on which these arguments rely. He also examines some of the criticisms of the argument from the potential and replies to them, and shows why the argument's protagonists and critics are often at cross-purposes.     

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.     

Neighborhood predictors of plant performance

Summary We developed models of inter-individual interference to predict the fecundity of individuals in populations of the annual plant species, Arabidopsis thaliana. An individual plant is modeled as having a neighborhood which is a circular area of fixed radius with the plant at its center. Other plants which share the circle with the focal plant are termed neighbors of the focal plant. We developed an index of neighborhood interference which is the independent variable in a non-linear regression model that predicts individual plant fecundity. We present methods of exploratory data analysis that are useful in determining a best neighborhood radius, defined as that radius which minimizes residual sum of squares, and in deciding on the functional form of the interference index. In developing the interference index for Arabidopsis, we focus on aspects of the spatial distribution of neighbors: their number, distance and angular dispersion.We found that a best (or optimal) neighborhood radius can be resolved, which provides the best predictor of plant performance. Fecundity predictors based on adult neighbors were noticeably better than those based on neighbors at the seedling stage. Rosettes of Arabidopsis may change location during development (they fall over) and the new fallen positions do provide some improvement in the predictor. Taking into account distance to neighbors within the neighborhood provided only negligible improvement in the model. Finally, the incorporation of angular dispersion in the crowding index produced a considerably better fit. The fecundity predictor that included number of neighbors and angular dispersion in the crowding index explained about 70% of the variation in individual seed set.     

Temporal Profiles of Proteins Responsive to Transient Ischemia

The responses of long and short half-lived proteins to ischemia were measured in rat brain during 6 days of recovery from 30 min of transient forebrain ischemia produced by four-vessel occlusion. At the end of the ischemic interval, the neocortical activities of four vulnerable enzymes [ornithine (ODC) and S-adenosylmethionine (SAMDC) decarboxylases, and RNA polymerases I and II] were unchanged, but within 30 min of reperfusion, their activities dropped by 25-50%. The loss of substance P in the striatum and substantia nigra was slower, reaching about 50% by 12 h. On the other hand, the activities of 5 long half-lived enzymes did not change in the neocortex at 5 and 15 h of reperfusion and regional protein concentrations were essentially unaffected over 6 days survival. The rate and extent of normalization of the amounts or activities of the vulnerable proteins varied. RNA polymerase II and ODC activities were restored within 4 h, and ODC showed a biphasic increase in activity, with peaks at 10 h and 2-3 days. RNA polymerase I and SAMDC activities were restored by 18 h and 5 days, respectively, whereas substance P concentrations did not completely recover, even at 6-15 days. The greater the regional reduction of blood flow during ischemia, the larger the net change (gain or loss) of SAMDC or ODC activity and the longer the time required to normalize the activities of these enzymes. The average rate of proteolysis, assessed by measuring the rate of clearance of 14C from protein prelabeled with [14C]bicarbonate, was abnormal during the first 2 days of reperfusion. Postischemic changes in both protein synthesis and degradation could affect the amounts of some of the proteins responsive to transient ischemia.     

The ultrastructure and formation of the calcareous ossicles in the body wall of the sea cucumber Leptosynapta clarki (Echinodermata,Holothuroida)

Summary The calcareous ossicles of the burrowing sea cucumber Leptosynapta clarki have been examined by scanning and transmission electron microscopy. The ossicles occur in the dermis of the body wall and comprise three main types: 1) curved rods; 2) miliary granules; and 3) anchorshaped structures that are paired with oval plates. Rods average about 80 m in length, and miliary granules are typically 20–30 m long. Both of these ossicles appear to form a protective skeleton in regions where the water vascular system and accompanying nerves are located. Anchors and plates are scattered throughout the interambulacra of the body at densities ranging from 2–8/mm². Each anchor measures about 145 m long and is attached to the plate underlying it by a flexible ligament that is composed of collagen fibrils. Tetracycline labeling studies indicate that anchors and plates take several months to reach full size. All developing ossicles appear to be surrounded by a syncytial network of sclerocytes that characteristically possess numerous mitochondria and a conspicuous external lamina. Fully formed anchors lie directly beneath the epidermis and do not protrude through the outermost layer of the body wall. During burrowing, the curved flukes of the anchorshaped ossicles may provide added traction as the buccal tentacles dig through the sediment.List of abbreviations a anchor - ar ambulacral region - cm circular muscle layer of body wall - cs cytoplasmic sheath - d dermis - ep epidermis - f fluke - ild inner layer of dermis - k keel - me myoepithelium - mg miliary granule - n nerve - old outer layer of dermis - os ossicle - pl plate - s sclerocyte - sh shank - st stock     

Organization of the ribosomal ribonucleic acid genes in various wild-type strains and wild-collected strains of Neurospora

Summary The organization of the ribosomal DNA (rDNA) repcat unit in the standard wild-type strain of Neurospora crassa, 74-OR23-1A, and in 30 other wild-type strains and wild-collected strains of N. crassa, N. tetrasperma, N. sitophila, N. intermedia, and N. discreta isolated from nature, was investigated by restriction enzyme digestion of genomic DNA, and probing of the Southern-blotted DNA fragments with specific cloned pieces of the rDNA unit from 74-OR23-1A. The size of the rDNA unit in 74-OR23-1A was shown to be 9.20 kilobase pairs (kb) from blotting data, and the average for all strains was 9.11+0.21 kb; standard error=0.038; coefficient of variation (C.V.)=2.34%. These data indicate that the rDNA repeat unit size has been highly conserved among the Neurospora strains investigated. However, while all strains have a conserved HindIII site near the 5 end of the 25 S rDNA coding sequence, a polymorphism in the number and/or position of HindIII sites in the nontranscribed spacer region was found between strains. The 74-OR23-1A strain has two HindIII sites in the spacer, while others have from 0 to at least 3. This restriction site polymorphism is strain-specific and not species-specific. It was confirmed for some strains by restriction analysis of clones containing most of the rDNA repeat unit. The current restriction map of the 74-OR23-1A rDNA repeat unit is presented.     

Dopamine- and octopamine-sensitive adenylate cyclase in the brain of adultCulex pipiens mosquitoes

The effects of dopamine and octopamine on adenylate cyclase activity were studied on the head homogenate of adult Culex pipiens mosquitoes in vitro. Both dopamine and octopamine were shown to increase the cyclic AMP content in the homogenate. The antagonist haloperidol blocked the production of cyclic AMP induced from dopamine but had no effect on the production of cyclic AMP induced by octopamine at the concentrations tested. The opiate agonist etorphine was ineffective at reducing cyclic AMP levels induced by either dopamine or octopamine at the concentrations tested.     

Dinitrogen fixation by obligate and facultative anaerobic bacteria in association with cellulolytic fungi

The anaerobic bacteriumClostridium butyricum is the major contributor to nitrogen gains by a cellulolytic/nitrogen-fixing population isolated from straw. Growth of the anaerobe is supported by the products of fungal cellulases. The facultative anaerobeEnterobacter cloacae does not make a significant direct contribution to nitrogen fixation but in association withC. butyricum allows the anaerobe to grow under aerobic conditions. The major function ofE. cloacae is though to be provision of oxygen-depleted microsites.     

Postnatal Changes in Cathepsin D in Rat Neural Tissue

Cathepsin D, an aspartyl endopeptidase, was analyzed in cortex from forebrain and cerebellum, spinal cord, and optic and sciatic nerves, and in the liver of rats from 1 to 120 days of age. Cathepsin D was quantitated in tissue extracts by measurement of enzyme specific activity on a substrate of [methyl-¹⁴C]-methylated hemoglobin and by radioimmunoassay. Immunocytochemistry was used to ascertain the identity of the mixed cell types that contributed to the cathepsin D detected. As quantitated by radioimmunoassay, immunoreactive cathepsin D varied between 0.2 and 1 ng/μg of total protein. Maximum activity occurred at approximately the 15th postnatal day; the least amount of immunoreactive cathepsin D was found at 30 or 60 days of age. A subsequent increase of varying magnitude occurred at postnatal day 120. There was good correspondence between immunoreactive enzyme and enzyme specific activity, which ranged from 1 to 4 ng/μg of total protein, and the activities determined by the two methods provided similar, but not identical, developmental profiles. Cathepsin D was demonstrated by immunocytochemistry to be present in most neurons, in all choroid plexus epithelium, and in certain oligodendrocytes from the first postnatal day. Cathepsin D was present in oligodendrocytes in cord lateral funiculi and optic nerve by the first postnatal day, and by the sixth postnatal day many oligodendrocytes were abundantly stained. In contrast, oligodendrocytes in the corpus callosum and in the cerebellar white matter did not contain demonstrable cathepsin D until postnatal days 10 and 15, respectively. These results indicate a role for cathepsin D during the postnatal development of rat CNS and suggest that this proteinase may be involved in the steps of myelination.