Myelination by cryopreserved xenografts and allografts in the myelin-deficient rat.

This study examined the ability of freshly prepared and cryopreserved canine oligodendrocytes to myelinate axons following transplantation into the myelin deficient (md) rat. The effects of immunosuppression, and the age of the donor tissue, were also examined. Canine glial cells, dissociated from the spinal cords at E50, P2, P20, P28, and P50, were transplanted into the spinal cords of myelin-deficient rats as single cell suspensions. Both cryopreserved (E50 and P28) and freshly dissociated tissue (P2, P20, and P50) were able to form myelin within 13 days of transplantation. Cells from younger donors (< P20) myelinated more md axons than those from older donors. In those rats which received xenografts and which were treated with cyclosporin A there was markedly less cellular infiltration than in untreated animals. For comparison with these xenografts, fresh and cryopreserved adult rat glia were also transplanted. Eight days after transplantation, myelination by allografts of cryopreserved rat glia was qualitatively similar to that produced by freshly prepared cells. These results show that oligodendrocytes transplanted as xenografts are capable of myelinating rat axons, and that cryopreserved glia retain their capacity to myelinate in vivo.

Escherichia coli genes involved in cell survival during dormancy: role of oxidative stress.

When Escherichia coli cells reach stationary phase of growth, specific gene products are synthesized that protect cells while dormant. "Aged" cells may remain viable in cultures for years. For example, agar cultures stored for 38 years still had more than 10(5) viable cells/ml. However, when specific mutants were cultured, the population of these mutants dropped sharply after 4-10 days. This defect is termed "Stationary-Phase-Death". Each mutant strain was hypersensitive to near-ultraviolet radiation and other oxidative agents. Bovine catalase rescued many of the mutants from death in dormancy, suggesting that specific gene products protect "aged" cells against oxidative damage.

Inhibition in the nervous system: models of its roles in choice and context determination.

Neural inhibition has often been regarded as playing an important role in stabilizing and tuning the responses of networks of excitatory neurons. Some partial quantitative bases for this qualitative notion are discussed in the context of current neural network models. Such neural network principles as associative learning, competition, opponent processing, and interlevel resonant feedback are explained and related to behavioral and neurochemical data. Tentative analogies of parts of these model networks with specific neurotransmitter systems are explored; these analogies are likely to become more precise as the networks are further refined.

Catalase HPI influences membrane permeability in Escherichia coli following near-UV stress.

The katG gene in Escherichia coli encodes catalase HPI, which is involved in membrane transport and protects the cell during oxidative stress. Hydrogen peroxide (H2O2) induces synthesis of HPI. We examined the role of HPI in membrane permeability (proline uptake) following exposure to near-ultraviolet radiation (NUV). We found that NUV resulted in the same type of induction as H2O2. KatG::Tn10 cells experienced a large drop in uptake after NUV exposure, and levels remained low following incubation. A strain carrying a katG+ plasmid, however, showed considerably less decrease in uptake after NUV, and uptake quickly resumed upon incubation. Further, in an srd mutant which lacks 4-thiouracil, NUV resulted in only a small drop in proline uptake, which was immediately resumed.

High-frequency percussive ventilation compared with conventional mechanical ventilation.

In seven patients with severe respiratory distress, conventional mechanical ventilation and PEEP were used initially for respiratory support, which was changed to high-frequency percussive ventilation (HFPV) at the same level of airway pressure and FIO2. During both modes of ventilation, patients could breathe spontaneously via a low-threshold demand valve. With HFPV, PaO2 improved significantly (p less than .01) compared with PaO2 during conventional methods. Cardiac output was unaffected by the change to HFPV.