Specificity and non-specificity of synaptic connections within mammalian visual cortex

It is clear from reviewing the findings of our own studies and those of others that the cerebral cortex has combined two very different strategies of organisation. Firstly it has a strictly defined genetically determined substrate of specific neurons classes, specific rules for which kinds of cells interconnect, a laminar architecture where efferent and afferent relays and interlaminar links are predetermined. But, as well, a second strategy allows great developmental lability in the precise spatial patterns of intralaminar circuits of the excitatory neurons and in the actual weights of excitatory and inhibitory synapses that are contributed to each neuron. This second strategy presumably allows the cortex to be tailor-made to the early experience of each individual and, as well, allow for lability of responses to different conditions of stimulation and adjustment of the system to compensate to some degree for injuries affecting afferents and circuitry in the adult system.     

Reversible hyperphosphorylation and reorganization of vimentin intermediate filaments by okadaic acid in 9L rat brain tumor cells.

Okadaic acid (OA), a protein phosphatase inhibitor, was found to induce hyperphosphorylation and reorganization of vimentin intermediate filaments in 9L rat brain tumor cells. The process was dose dependent. Vimentin phosphorylation was initially enhanced by 400 nM OA in 30 min and reached maximal level (about 26-fold) when cells were treated with 400 nM OA for 90 min. Upon removal of OA, dephosphorylation of the hyperphosphorylated vimentin was observed and the levels of phosphorylation returned to that of the controls after the cells recovered under normal growing conditions for 11 h. The phosphorylation and dephosphorylation of vimentin induced by OA concomitantly resulted in reversible reorganization of vimentin filaments and alteration of cell morphology. Cells rounded up as they were entering mitosis in the presence of OA and returned to normal appearance after 11 h of recovery. Immuno-staining with anti-vimentin antibody revealed that vimentin filaments were disassembled and clustered around the nucleus when the cells were treated with OA but subsequently returned to the filamentous states when OA was removed. Two-dimensional electrophoresis analysis further revealed that hyperphosphorylation of vimentin generated at least seven isoforms having different isoelectric points. Furthermore, the enhanced vimentin phosphorylation was accompanied by changes in the detergent-solubility of the protein. In untreated cells, the detergent-soluble and -insoluble vimentins were of equal amounts but the solubility could be increased when vimentins were hyperphosphorylated in the presence of OA. Taken together, the results indicated that OA could be involved in reversible hyperphosphorylation and reorganization of vimentin intermediate filaments, which may play an important role in the structure-function regulation of cytoskeleton in the cell.     

Kinetic analysis of protonation of a specific site on a buffered surface of a macromolecular body

The kinetics of protonation of a specific site on a macromolecular structure (micelle) in buffered solution was studied with the purpose of evaluating the effect of buffer on the observed dynamics. The experimental system consisted of the following elements: Brij 58 micelles serving as homogeneous uncharged macromolecular bodies, bromocresol green, a well-adsorbed proton detector, and 2-naphthol-3,6-disulfonate as a proton emitter in the bulk. Imidazole was the mobile buffer while neutral red, which has a high affinity for the micellar surface, served as the immobile buffer. An intensive laser pulse ejects a proton from the proton emitter, and the subsequent proton-transfer reactions are measured by fast spectrophotometric methods. The dynamics of proton pulse in buffered solution are characterized by a very rapid trapping of the discharged protons by the abundant buffer molecules. This event has a major effect on the kinetic regime of the reaction. During the first 200 ns the proton flux is rate limited by free-proton diffusion. After this period, when the free-proton concentration decayed to the equilibrium level, the relaxation of the system is carried out by the diffusion of buffer. Thus in the buffered biochemical system, at neutral pH, most of proton flux between active sites and bulk is carried out by buffer molecules--not by diffusion of free protons. Surface groups on a high molecular weight body exchange protons among them at a very fast rate. This reaction has a major role on proton transfer from a specific site to the bulk.(ABSTRACT TRUNCATED AT 250 WORDS)     

Seed Germination and Seedling Growth in Sopubia delphinifolia - a Hemi-root Parasite: Germination Requirements

Requirements for seed germination (emergence of radicle) andseedling formation (emergence of both radicle and cotyledons)of a hemi-root parasite Sopubia delphinifolia were studied inthe absence of any host stimulus, in Petri dish and asepticcultures. Both water washing in trickling tap water as wellas cold treatment were effective in inducing/stimulating germinationand seedling formation in the light. Although ethrel, an ethylenereleasing compound, stimulated radicle emergence it inhibitedthe emergence of the cotyledons. Light was found to be essentialfor germination; none of the growth substances could replacethe light requirement. Light responses seem to be mediated throughthe phytochrome system. The results indicate that the emergenceof the radicle, its further growth into the root and the emergenceof cotyledons are controlled by different factors. Sopubia delphinifolia, hemi-root parasite, seed germination requirements, pretreatment, seedling formation     

In vitro assessment of the toxicity of metal compounds

A review of in vitro mutagenesis assessment of metal compounds in mammalian and nonmammalian test systems has been compiled. Prokaryotic assays are ineffective or inconsistent in their detection of most metals as mutagens, with the notable exception of hexavalent chromium. Mammalian assay systems appear to be similarly inappropriate for the screening of metal compounds based upon the limited number of studies that have employed those compounds having known carcinogenic activity. Although of limited value as screening tests for the detection of potentially carcinogenic metal compounds, the well-characterized in vitro mutagenesis systems may prove to be of significant value as a means to elucidate mechanisms of metal genotoxicity.     

ATP synthase from bovine mitochondria: sequences of imported precursors of oligomycin sensitivity conferral protein, factor 6, and adenosinetriphosphatase inhibitor protein

Oligomycin sensitivity conferral protein (OSCP), factor 6 (F6), and ATPase inhibitor protein are all components of the ATP synthase complex of bovine mitochondria. They are encoded in nuclear DNA. Complementary DNA clones encoding the precursors of these proteins have been isolated from a bovine library by using mixtures of synthetic oligonucleotides as hybridization probes, and their DNA sequences have been determined. The deduced protein sequences show that the OSCP, F6, and inhibitor proteins have N-terminal presequences of 23, 32, and 25 amino acids, respectively. These presequences are not present in the mature proteins. It is assumed that they serve to direct the proteins into the mitochondrial matrix. The cDNA clones have also been employed as hybridization probes to investigate the genetic complexity of the three proteins in cows and humans. These experiments indicate that the bovine and human inhibitor and bovine F6 proteins are encoded by single genes but suggest the possibility of the presence in both species of more than one gene (or pseudogenes) for the OSCP.