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Notes: Summary We have studied the suppression of firing in single LGN cells of cat and monkey in response to visual stimulation of the nondominant eye. In the cat LGN most of the cells of each of the main laminae show this nondominat suppression. X cells having their dominant input from the ipsilateral eye were suppressed to a significantly greater degree than any other cell type in the cat LGN. In the monkey LGN nondominant suppression was absent in all 19 X-like cells studied, whereas 6 of 21 Y-like cells showed nondominant suppression. Thus nondominant suppression is present in the magnocellular laminae of the monkey LGN, where the Y-like cells are found, but appears to be absent from the parvocellular laminae, where the X-like cells are found.

Notes: Abstract Binocular non-dominant suppression (NDS) in the dorsal lateral geniculate nucleus (LGNd) of the cat was studied by recording from single neurons in the LGNd of anaesthetized, paralysed cats while stimulating the non-dominant eye with a moving light bar. The maintained discharge rate of LGNd neurons was varied by stimulating the dominant eye in various ways: by varying the size or contrast of a flashed spot, by varying the inner diameter of a flashed annulus of large outer diameter, by varying the velocity of a moving light bar, and by covering the eye. Non-dominant suppression was quantified either as the decrease in the maintained discharge rate (the “dip”), expressed as spikes per second, or as the ratio of the dip to the maintained discharge rate (the “dip ratio”). At low maintained discharge rates the dip, although low in value, frequently approached the maintained rate, i.e. the dip ratio approached unity. As the maintained discharge rate increased the dip value also increased, but more slowly than the maintained discharge rate, i.e. the dip ratio decreased. At maintained discharge rates above about 30 spikes/s, in many neurons the dip appeared to be approaching a constant value. This strong dependence of NDS on the maintained discharge rate of the LGNd neuron suggests that the inhibitory input to the cell arises from a region of the brain that receives an input both from the non-dominant eye and from the LGNd cell. Reasons are given for thinking that this region is the perigeniculate nucleus. Because of the strong dependence of dip and dip ratio on the maintained discharge rate, it was necessary to adopt stringent criteria when comparing NDS in two different sets of neurons or of the same set of neurons in different conditions. We recognized a significant difference in NDS between two classes of neurons or between two states only if: (1) there was no significant difference between the maintained discharge rates, and (2) there was a significant difference for both dip and dip ratio between the two classes or states. Using these criteria we found: (1) no difference between non-lagged X (XNL) and non-lagged Y (YNL) cells, (2) no difference between on-centre and off-centre cells for either XNL or YNL cells, (3) no difference between XNL cells and lagged X (XL) cells. However, there was a significant difference between cells in lamina A and those in lamina A1 for both XNL and YNL cells, dip and dip ratio values being about twice as great in lamina A. In cats in which one optic nerve had been pressure-blocked so as to prevent conduction in the largest axons (Y fibres), loss of conduction in Y fibres crossing the chiasm and projecting to the contralateral LGNd did not affect NDS. Loss of conduction in Y fibres projecting to the ipsilateral LGNd caused a complete loss of NDS in the non-lagged Y cells of lamina A and a substantial decrease in the NDS of the nonlagged X cells of lamina A. The latter cells must, therefore, be partly suppressed by non-Y fibres, presumably X fibres. It also follows that all the NDS of cells in lamina A1 is mediated by non-Y fibres, probably X fibres. Thus, NDS in the cat is partly class-specific and partly not. The discharge of retinal ganglion cells also protects the LGNd cells against NDS. The contribution of Y fibres to this anti-suppressive action was also examined. Contralaterally projecting Y fibres make no contribution. Ipsilaterally projecting Y fibres exert an anti-suppressive action on non-lagged X cells in lamina A1. It follows also that the anti-suppressive action on cells in lamina A mediated by contralaterally projecting fibres is due to non-Y fibres, presumably X fibres. Thus, both the suppressive and the anti-suppressive actions of Y fibres are mediated only by the uncrossed pathway.

Notes: EPR-Investigations on the Photolysis of Halogenated Organic Compounds. II. CHBr3 and CBr4 in Glassy and Polycrystalline MatricesPhotolysis of CHBr3, CDBr3 and CBr4 in glassy and polycrystalline matrices (alcohols, diethylether, benzene derivatives and KBr) at T ≥ 77 K yields stationary e.p.r.-spectra in the range of effective g-factor from 2.2 to 1.9. By comparison of the spectra of CHBr3 and CDBr3, exposed to γ-rays and u.v. light respectively, and the spectra of these compounds in matrices it was shown that the photolysis in matrices produces the species \documentclass{article}\pagestyle{empty}\begin{document}$ {\rm CBr}_4\,^{_{\bar.}} $\end{document}, ·CBr3 and α-Br-radicals from the halogenated compounds and HĊO, ·CH3, CH3ĊHOH, RĊHOH, and ·C2H5 from the matrix. Photolysis of halogenated compounds in CH3OH and CD3OD yields only HĊO and ·CH3 together with a very small amount of bromine-containing radicals. In all other investigated matrices the concentration of bromine containing species is controlled by physical and chemical properties of the matrix. Time development of the \documentclass{article}\pagestyle{empty}\begin{document}$ {\rm CBr}_4\,^{_{\bar.}} $\end{document}-radical and of those generated from the matrix is different and gives insight into the complex photoreaction in solid matrices.

Notes: Aryltropylium salts exhibit an unusually effective self quenching of fluorescence in dependence on their concentration in dichlòromethane. The quenching process is investigated by static and time resolved fluorescence measurements. The observed biexponential fluorescence decay is interpreted by the emissions of ion pairs and free cations. The rate constant of fluorescence quenching by formation ion pair is two orders of magnitude greater than the diffusion constant.

Notes: About the Deactivation Behaviour of Photoexcited Aryltropyliumions. II. Fluorescence Quenching of AryltropyliumionsThe properties of aryltropyliumions in the excited singlet state were studied. These ions are very strong acceptors. So the fluorescence is quenched by aromatic donors. The rates of fluorescence quenching depend on the ionization potential of the donor. This fact is discussed in terms of mechanisms derived by WELLER et al. The results were related to the light stability of aryltropyliumions.

Notes: EPR-Investigations on the Photolysis of Halogenated Organic Compounds I. Pure Halogenated Compounds (CBr4, CHBr3, CCl4 and CHCl3)EPR-spectra of CBr4, CHBr3 and CDBr3, exposed to u.v.-light and γ-rays respectively, are presented. They are discussed and compared with the results of the photolysis of CH2Br2, CH3Br and CCl4, CHCl2, CH2Cl2 and CH3Cl. Under stationary conditions at 77K it was possible to identify paramagnetic species like \documentclass{article}\pagestyle{empty}\begin{document}$ {\rm CBr}_4\,^{_{\bar.}} $\end{document}, ·CBr3, ·CH3, ·C2H5, ·CCl3 and trapped electrons.

Notes: Electrochemistry of Organic Cations. Arylsubstituted Tropylium SaltsThe electrochemical behaviour of some mono- and diarylsubstituted tropylium perchlorates in acetonitrile was investigated and is discussed in connection with their u. v.-vis absorption spectra.