Kiyomi Yamatsu

Extracellular accumulation of glutamate in the hippocampus induced by ischemia is not calcium dependent — In vitro and in vivo evidence

Calcium dependency of ischemia-induced increase in extracellular glutamate in the hippocampus was studied in vitro and in vivo. Perfusion of a low pO2 medium without glucose (in vitro ischemia) induced an increase in extracellular glutamate in rat hippocampal slices. This increase did not depend on Ca2+, which is in contrast with the observation that about 40% of membrane depolarization (50 mM KCl)-evoked release was Ca2+-dependent. In vivo cerebral ischemia of 5 min duration in gerbils also caused Ca2+-independent increase in extracellular glutamate in the hippocampus. The data suggest that the increase in extracellular glutamate induced by ischemia is not due to the enhanced release of neurotransmitter glutamate.

E2020 - THE PHARMACOLOGY OF A PIPERIDINE CHOLINESTERASE INHIBITOR

Alzheimer’s disease is associated with a relative decrease in the activity of the cholinergic system in the cerebral cortex and other areas of the brain (Bowen, 1981). This discovery has led to the development of agents designed to increase cholinergic function in the CNS. One such group of agents, the cholinesterase (ChE) inhibitors, increase the concentration of acetylcholine (ACh) by inhibiting one or more of the enzymes which hydrolyze it, i.e, acetylcholinesterase (AChE) and butyrylcholinesterase (BuChE).

Analgesic effects of dynorphin-A and morphine in mice

To investigate whether or not dynorphin-A is analgesic, the effect of this peptide was tested in comparison with that of morphine in mice. Dynorphin-A produced a potent analgesic effect in the acetic acid writhing and tail pinch tests, but a weak effect in the tail flick test when given by intracerebroventricular injection. In contrast, morphine caused a potent analgesia in all the tests. Dynorphin-A was more effective when given by intrathecal injection than by intracerebroventricular injection, whereas morphine was equipotent by both injection routes. The results suggest that dynorphin-A is analgesic and that its analgesia may be differentiated from that of morphine.

Dimethyl sulfoxide (DMSO) is mutagenic for bacterial mutagenicity tester strains

We used the Ames method with the modification of pre-incubation to evaluate the potential mutagenicity of DMSO. We performed the assays using nine different Ames Salmonella strains and Escherichia coli strains WP2 and WP2uvrA. DMSO was found to be mutagenic for Salmonella typhimurium TA1537 and TA2637 (the latter strain being isogenic to TA1537 but carrying plasmid pKM101) and for E. coli WP2uvrA. The mutagenic activity of DMSO observed at a concentration of 33% was about 10 times higher than the background level (65 revertants induced) for TA1537 after 20 min of incubation, where some lethal toxicity was observed. The mutagenicity of DMSO was observed in the presence and absence of rat liver S9 mix.

Mutagenicity of benzoquinones for Ames Salmonella tester strains

The mutagenicity of 12 simple benzoquinone (BQ) derivatives was studied using five different Ames Salmonella mutagenicity tester strains in the presence and absence of S9 mix. Seven of the BQs used displayed mutagenicity with and/or without S9 mix, and most of them produced a marginal increase in revertants. p-Benzoquinone (p-BQ) showed the most potent mutagenic activity (17 induced revertants/nmol/plate for strain TA104 without S9 mix) among the BQs tested. TA104, which is sensitive to oxidative mutagens, was the most sensitive to the mutagenicity of the BQs of the five strains used, while the second most sensitive strain was TA2637, which detects bulky DNA adducts. Significant reductions in the mutagenicity of p-BQ, and 2,3-diCl-5,6-diCN-BQ without S9 mix were observed in the presence of catalase. These findings suggest that the mutagenicity of BQs for S. typhimurium is attributable to oxidative injury after BQ reduction and to DNA adducts that form with BQs that have electrophilic substituents.

Ganglioside-induced inhibition of in vivo immune response in mice

In vitro immunomodulatory properties of gangliosides have been well characterized such as the ganglioside-induced modulation of CD4 on T lymphocytes and inhibition of lectin-induced proliferative response of lymphocytes. These findings have led to an interesting suggestion that gangliosides play a role as in vivo immune modulators, although this possibility is not clearly defined yet. We then first confirmed in vitro effects of gangliosides on murine immunocytes and examined in vivo effects of gangliosides on immune response in mice. Murine spleen cells that were treated with a ganglioside mixture (GS) purified from bovine brain exhibited a marked decrease in CD4 expression, while CD8 expression was slightly suppressed. Transplantation of GS-untreated control immunocytes that were isolated from syngeneic mice into the immune suppressed mice by X-ray irradiation restored in vivo immune responses, while GS-treated cells could not. Immune response was assayed by the evaluation of footpad swelling which was induced by immunization with sheep erythrocytes as antigens. Moreover, intramuscular administration of gangliosides into mice suppressed both immediate (Arthus)-type and delayed-type allergic reactions. These results suggest that gangliosides would be potential in vivo immune modulators.

The Role of Glutamate Decarboxylase and GABA Transaminase in Post Mortem GABA Increases in Discrete Regions of Rat Brain

ABSTRACT Preliminary experiments were performed to establish the optimal microwave irradiation time required to protect the brain from post mortem metabolism of GABA. Following this study, the high-energy phosphates, which deplete rapidly during brain ischemia and/or anoxia, were measured along with GABA to further acertain the utilization of the proper irradiation time. The metabolic enzymes in the GABA system are known to be more rapidly destroyed by microwave treatment than those in the high-energy phosphate system. The regional distribution of GABA in discrete regions of the rat brain was then determined and compared for animals sacrificed by decapitation or microwave irradiation (5kW, 1 sec). As generally accepted, the GABA content found in most regions after decapitation was higher than that after microwave irradiation. However, the degree of post mortem GABA increase varied from region to region. For example, the GABA content in the substantia nigra, superior colliculus, inferior colliculus and hypothalamus increased by 86, 112, 119 and 37 percent, respectively, when compared to the control levels obtained with microwave irradiation. In other regions, such as the striatum and the thalamus, the post mortem GABA increase was not significant. The regional distribution of GAD activity paralleled that of the GABA concentration, whereas the regional distribution of GABA-T activity was not necessarily consistent with the GABA concentration and the GAD activity. The correlation between the regional post mortem GABA increase and the GAD and GABA-T activities in the present study, however, indicate that both enzymes may be involved in determining the degree of post mortem GABA increase in individual brain regions.