Quantitative studies of postnatal changes in synapses in rat superficial motor cerebral cortex

Summary Quantitation of synapses at different postnatal ages has been undertaken in the cerebral cortex of the rat. In this study axial ratios of presynaptic bags, proportion of cortex occupied by presynaptic bags and numbers of synapses per unit volume of cortex have been estimated. Observations on synaptic vesicle packing densities have also been made.Synaptic bags become increasingly spherical up to 7 days of age and become more elongated thereafter. The proportion of cortex occupied by presynaptic bags increases rapidly up to 7 days of age and then at a decelerated rate up to maturity. The number of synapses per unit volume increases slowly over the first four days after which there is a rapid increase to 14 days, followed by a decelerated rate.The average presynaptic bag shows marked changes in volume with increasing age which indicate the probability of two stages of synaptic development. This two stage development is further reflected in the estimates on vesicle packing densities. The implications of the results are discussed in relationship to changes in functional activity of the cortex during postnatal development.The authors wish to express their thanks to Mr. R. Birchenough and Mr. J. Manston for much technical assistance.     

Metabolism of iodomethane in the rat

1. The LD(50) of iodomethane orally administered to rats is 76mg./kg. body wt. but repeated daily doses of 30-50mg./kg. body wt. are without effect. 2. Oral doses of iodomethane to rats are rapidly converted into S-methylglutathione in the liver, and S-methylglutathione is excreted in the bile. 3. The conjugation process has been reproduced in vitro and shown to be enzymically catalysed. 4. S-Methylglutathione is degraded to S-methylcysteine by kidney homogenates. 5. Only a small proportion of a dose of iodomethane or of S-methylcysteine is excreted as compounds related to methylmercapturic acid. 6. Paper chromatography of extracts of livers from normal and dosed rats supports the view that GSH is the predominant non-protein thiol present.     

Plaque Development and Induction of Interferon Synthesis by RMC Poliovirus.

Johnson, Terry C. (University of Minnesota, Minneapolis), and Leroy C. McLaren. Plaque development and induction of interferon synthesis by RMC poliovirus. J. Bacteriol. 90:565-570. 1965.-Plaque development by RMC poliovirus on human amnion cell monolayers was investigated with regard to autointerference and to the effect of acid-agar overlay on plaquing efficiency. The virus was inhibited by acid-agar overlay, thereby exhibiting the d(-) marker typical of attenuated poliovirus strains. In addition, a lack of RMC poliovirus plaque development on HeLa cell monolayers was shown to be the result of an agar inhibitor which could be removed by NaCl extraction. By use of a simplified plaque reduction assay, it was shown that interferon production was responsible for the autointerference phenomenon. Interferon synthesis did not correlate with the ages in vitro of human amnion cell cultures. Fibroblasts originating from the chorionic membrane produced negligible amounts of the inhibitor. Interferon synthesis by human amnion cells infected with RMC poliovirus was inhibited by actinomycin D. The addition of guanidine hydrochloride to infected cultures immediately after RMC poliovirus adsorption markedly inhibited interferon synthesis, although after 2 hr (postadsorption) guanidine had no effect on interferon production.