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This study was concerned with the ultrastructural changes that occur in axons and glial cells during peripheral nerve regeneration in the cockroach <i>Periplaneta americana</i>. Metathoracic nerve 5 was cut and regeneration of the proximal stump was studied using electron microscopy. Nerve 5 was surrounded by an acellular layer, the neural lamella. Underneath this structure was a layer of glial cells which formed the perineurium. Lanthanum penetration stopped between the perineurial cell processes, revealing them to be the site of the blood-brain barrier (BBB). Underlying the perineurium were the axons, surrounded by the subperineurial glial cells. Extracellular matrix was present between subperineurial glial processes. After cutting nerve 5, the initial changes in the proximal stump were a result of the degeneration of sensory axons. Haemocytes accumulated outside the nerve and morphologically similar granule-containing (g-c) cells appeared inside the nerve. After the first week signs of regeneration were distinguishable. These included axonal sprouting, glial proliferation and extracellular matrix production. Many small axonal sprouts were formed by regrowing axons. These became grouped into bundles, surrounded by glial processes, as the nerve outgrowth elongated. Glial proliferation by cell division began after the first week, and reached a maximum rate between two and three weeks. It is possible that mitosis of glial cells may be triggered by contact with the sprouting axons. Freeze-fracture studies of the tip of the growing nerve showed that formation of gap and septate unctions took place between the glial cells. This junctional assembly was asynchronous. Reinnervation of the coxal muscles occurred 8 weeks after the nerve was cut. At this stage the nerve was composed of several axonal bundles, each containing large and small axons. The nerve did not completely resemble the control even after 16 to 20 weeks of regeneration. Lanthanum incubation showed that the tracer was again excluded by the perineurial cells, indicating that the BBB of the regrown nerve reappeared at 8 weeks. Glial repair was studied following selective glial disruption using localised application of ethidium bromide. This treatment killed the perineurial and subperineurial glial cells. The repair of the glial system involved the transitory appearance of g-c cells in the nerve. 11 days after ethidium bromide treatment, new glial cells were present and lanthanum was excluded by the perineurial cell layer. Preinjection of microspheres into the haemolymph, which were taken up by phagocytic haemocytes, reduced the numbers of g-c cells that appeared in the nerve after ethidium bromide treatment. This lengthened the time required for glial repair. Cell division of neuroglial cells was observed. Cells derived from haemocytes and glial cell division were probably involved in the replacement of the damaged glial cells after ethidium bromide treatment. This study shows that glial cells play an important role in peripheral nerve regeneration in insects, forming the environment through which the regenerating axons grow.

Recently, hydrogen peroxide (H₂O₂), and its free-radical product the hydroxyl radical (OH·), have been identified as major sources of DNA damage in living organisms. We examined DNA repair of hydrogen peroxide damage, using a standard bacteriophage T4 test system in which several different types of repair could be determined. Post-replication recombinational repair and denV-dependent excision repair had little or no effect on H₂O₂ damage. Also, an enzyme important in repair of H₂O₂-induced DNA damage in the E. coli host cells, exonuclease III, was not utilized in repair of lethal H₂O₂ damage to the phage. However, multiplicity reactivation, a form of recombinational repair between multiply infecting phage genomes, was found to repair H₂O₂ damages efficiently. The RAD52 gene of Saccharomyces cerevisiae and genes 46 and 47 of bacteriophage T4 are essential for most recombination and recombinational repair in their respective organisms. The RAD52 gene was introduced into expression vectors which were used to transform E. coli. RAD52 expression was induced, and its ability to complement either gene 46 or gene 47 phage mutants was determined with respect to phage growth, recombination, and recombinational repair. RAD52 gene expression allowed growth of gene 46 and gene 47 mutants under otherwise restrictive conditions, as measured by plaque formation and burst size. The RAD52 gene also restored the ability of gene 46 and gene 47 mutants to undergo recombination of rII markers. Furthermore, the RAD52 gene restored recombinational repair after UV irradiation of gene 46 and gene 47 mutants. The published DNA sequence of RAD52 was compared with the published sequences of genes 46 and 47. Although overall homologies were only marginally significant, RAD52 and gene 46 had substantial sequence similarity over a limited region. These results indicate that the recombinational repair pathway found in phage T4 may be ubiquitous for DNA damage caused by endogenous exidative reactions. Furthermore, they indicated that an essential element of the recombination mechanism in both procaryotic viruses and eucaryotes arose from a common ancestor. Procaryotes and eucaryotes are thought to have diverged at least one billion years ago. Thus, recombination apparently arose early in evolution.

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No description available.