Biomedical subjects
Publications and source records attributed to K Negishi.
N4-Aminocytosine reacted with acetone and acetaldehyde to form hydrazones that were readily revertible to the parent compound. With pyruvate, in contrast, it formed a stable hydrazone. By use of bromopyruvate, N4-aminocytosine was linked to glutathione.
Experiments were performed on isolated retinas of teh carp (Cyprinus carpio) to investigate the effects of locally applied amino acids on the transretinal potential and the membrane potential of horizontal cells. A minute quantity of each solution of an amino acid was applied locally at different layers by means of pressure-microinjection. The responses were induced by alternating central and annular stimuli of white light. Amino acids applied locally at the distal layer (receptor surface or outer plexiform layer) in the centrally stimulated area, caused, at concentrations of 25--50mM, rapid changes in the light-induced potential, whereas those microinjected into the inner plexiform layer did not. When applied locally at the distal layer, amino acids abolished the proximal PIII response and reduced the amplitude of S-potentials, particularly in response to a central stimulus. However, the resting potential of horizontal cells was depolarized only slightly by acidic amino acids. The results suggest that the passive membrane properties of horizontal cells are not altered significantly by the amino acids applied. Differential susceptibilities of the PII component to acidic and neutral amino acids were found; the former did not change or, in some cases, enlarged, whereas the latter abolished it. Possibly, neutral amino acids interfere with a neural mechanism generating the PII component.
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The effects of some amino acids (Glu, Gly and GABA), applied in 3 different manners (electrophoretically, in the superfusate and by pressure-microinjection), were investigated on spontaneous and light-induced spike discharges in the isolated carp retina. When applied electrophoretically or by pressure-microinjection in the inner plexiform layer (IPL), the agents acted directly on spike-generating units. Electrophoretic application of Glu at IPL consistently increased while Gly and GABA always decreased spike discharges regardless of the light-induced response patterns, when the tangential distance between the recording and injection electrodes was 25--100 micron. Increasing the distance up to 400 micron diminished the effects, but did not invert them. When added to the superfusate, the amino acids produced a dual action (two different sequential effects); Glu (5 mM) initially decreased and increased spike discharges, while Gly and GABA (5 mM) produced opposite effects. Gly and GABA tended to suppress selectively off-discharges (of ON--OFF units and certain OFF-center units), leaving on-discharges (of ON--OFF units and certain ON-center units) unaffected. The amino acids produced different effects on some units, when applied by pressure-microinjection into OPL or IPL. When injected in OPL Glu suppressed, while in IPL it activated spike discharges, whereas Gly and GABA caused opposite changes to those observed with Glu. Therefore, the action of the agents when pressure-microinjected in OPL is equivalent to the initial action of the agents applied in the superfusate. The dual actions of the agents are assumed to be mediated by bipolar cells, resulting in disfacilitation (Glu) or in disinhibition (Gly or GABA) of spike-generating units.
The effects on spike discharges of acetylcholine chloride (ACh), applied electrophoretically at the inner plexiform layer, were examined in air-exposed and superfused preparations of the isolated carp retina. Most of spike-generating units examined (147 of 204 units; 72%) were sensitive to electrophoretically applied ACh. Among the ACh-sensitive ones, 125 units (85%), including all ON-center, most ON-OFF and two-thirds of OFF-center units, were activated, whereas 22 units (15%), including mainly OFF-center units, were suppressed by the agent. In retinas superfused with a medium containing 20 mM M2+ and 0.5 mM Ca2+, units ceased in their spontaneous and light-induced discharges, but they were activated by electrophoretically applied ACh. The ACh-induced activation was reduced in magnitude or abolished during an exposure of the retina to a medium containing hexamethonium chloride (25 micrometer), whereas the ACh-induced suppression was reduced by atropine sulfate (25 micrometer) more effectively than by hexamethonium. Therefore, the results suggest that nicotinic receptors are involved in the ACh-activation, whereas both, but predominantly muscarinic, receptors may participate in the ACh-suppression of spike discharges in the carp retina.
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The effects of catecholamines (CA) and certain related compounds on the horizontal cell membrane potential were examined in the retina of the teleost (Eugerres plumieri). Each CA compound (dopamine, noradrenaline, and adrenaline) had a similar effect on each class of horizontal cell (photopic L- and C-type, scotopic L-type). The threshold effect, seen with 25-50 microM CA, was an enlargement of both center and surround responses in general. At higher concentrations (100-200 microM), CA augmented the center response and attenuated the surround considerably; these reciprocal changes usually were associated with moderate depolarization. Recovery took place in 15-20 min. The results indicate that up to a certain concentration CA do not affect directly the transmission from photoreceptors to horizontal cells. The lateral propagation of S-potential, however, appears selectively affected by CA. alpha-Methylnoradrenaline, 5-hydroxydopamine, and serotonin caused the same effect on horizontal cells as CA. Reserpine, clonidine, and L-dopa mimic the CA effect only after prior application of CA. Phentolamine blocked while propranolol, haloperidol, and pimozide did not influence the DA effect. We conclude that alpha-adrenergic receptors probably are involved in the CA-induced changes observed in horizontal cells.
Wistar rats from one supplier have been shown to exhibit the atypical body temperature responses to morphine. In contrast to commonly used rats, in which morphine induced dose-dependent changes in body temperature, the initial administration of morphine (5, 10, 20, and 40 mg/kg, s.c.) to rats of this particular strain produced a consistent and prominent hyperthermia. This hyperthermia is mediated via an action on the typical morphine receptors since it was completely prevented by a specific narcotic antagonist, naloxone. Effects of neurohumoral modulators on the hyperthermia have been investigated in these rats. Pretreatment of animals with p-chlorophenylalanine, alpha-methyltyrosine, phenoxybenzamine or propranolol did not alter the hyperthermia. In contrast, the s.c. administration of 1 mg/kg of either tertiary or quaternary anticholinergic drug such as scopolamine, atrophine, methscopolamine and methylatropine significantly inhibited the hyperthermia. These results suggest that morphine causes hyperthermia in some strains of rats by a cholinergic mechanism and the involvement of an adrenergic or serotonergic mechanism in this case appears unlikely.
Cytosine residues in 32P-labeled E. coli tRNA Leu 1 were modified by treatment of the tRNA with the semicarbazide-bisulfite reagents [Hayatsu, H. (1976) Biochemistry 15, 2677-2682]. Analysis of the modification sites showed that only four cytidine residues, i.e. C35, C53, C85 and C86, reacted. They were identical with the cytidines of this tRNA accessible to methoxyamine [Chang, S. E. and Ish-Horowicz, D. (1974) J. Mol. Biol. 84, 375-388] and the accessibility was consistent with the conformational features recognized for tRNA in general. The rapidity and the simple nature of this modification demonstrate that the semicarbazide-bisulfite reaction is a useful tool in studying conformations of polynucleotides.
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A girl aged 14 years, who showed local skin lesions and generalized reactions such as fever, hepatosplenomegaly, hypergammaglobulinaemia and pancytopenia following mosquito bites, has been evaluated with various immunological methods. The intracutaneous tests, P-K tests and RAST confirmed the presence of specific IgE antibody against mosquito antigens, but no precipitating antibody was detected by either the double immunodiffusion or immunofluorescent antibody techniques. As far as the type IV reaction is concerned, the skin test failed to show a positive delayed skin reaction, but the lymphocyte incorporation of 3H-TdR exhibited a maximal response with smaller doses than the controls.
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