[Toxicological study of amikacin following intravenous drip infusion. 1. Acute toxicity in rats, rabbits and dogs, and subacute toxicity in rabbits]

Acute toxicity of amikacin sulfate (AMK) was studied in rats, rabbits and dogs following 1 hour drip intravenous infusion (1 hour d.i.v.), and compared with those after intravenous injection (i.v.). Subacute toxicity was studied in rabbits following 1 hour d.i.v. of AMK at doses of 400, 200, 100 and 25 mg/kg for 36 days. Acute toxicity: Acute toxicity of AMK by 1 hour d.i.v. was extremely diminished as compared with that by i.v. judging from LD50, the toxicity was approximately 1/6 in rats and approximately 1/2 in rabbits and dogs. No difference was observed between males and females. Subacute toxicity: 1. No death was found in all rabbits. 2. At the doses of 25 mg/kg and 100 mg/kg, there were no significant changes or signs recognized as toxicological effects of AMK. 3. At the dose of 200 mg/kg, very slight renal damages were observed histopathologically in all the 5 rabbits. 4. At the dose of 400 mg/kg, slight or moderate renal damages were observed in all the rabbits. Those were mainly dilatation of renal proximal tubules, hydropic swelling and degeneration of renal proximal tubular epithelium. No significant impairment effect of AMK was found in heart, lung, liver and other organs. 5. From these results, it is considered that the maximum no effect dose from a view point of safety is about 100 mg/kg in this study.

Ascospore development in the fission yeasts Schizosaccharomyces pombe and S. japonicus

The fine structure of ascospore formation in the fission yeasts Schizosaccharomyces pombe and Schizosaccharomyces japonicus var. japonicus was studied by serial thin-sectioning and electron microscopy. The morphogenetic events were almost the same in both species. Ascospore development was initiated by the formation of the forespore membrane on the cytoplasmic side of the differentiated nucleus-associated organelle (NAO) in the interval between meiosis I and II in S. pombe, or during the post-meiotic nuclear division in S. japonicus, and the process proceeded almost synchronously through the two or four nuclei in the ascus. The forespore membrane developed by fusion of the cytoplasmic vesicles and this was clearly demonstrated in S. japonicus where the behaviour of vesicles involved in the forespore membrane development could be traced as they were marked by the presence of electron-dense granules. The staining technique, by phosphotungustic acid—chromic acid (PTA-CA) after treatment with periodic acid, was used to attempt to elucidate the origin and the nature of the forespore membrane. The method specific to plasmalemma-type membranes stained both ascus and ascospore plasmalemmas; the forespore membrane was not stained at first but developed the same affinity for stain as the plasma membrane in the course of ascospore development. The results suggest that the forespore membrane did not come directly from the ascus plasma membrane, but from another membrane system such as the endoplasmic reticulum. Spore wall material was deposited in the space between the inner and outer leaflets of the forespore membrane.

Multiple postsynaptic dopamine receptors and behavioral manifestation

Previously we demonstrated the existence of non- and positive-cooperative dopamine receptors in rat striatum in [3H] apomorphine binding experiments. Non-cooperative sites were sensitive to the inhibition of sulpiride while cooperative sites were not. In the present study results dealing with the involvement of those two types of postsynaptic dopamine receptors in different behavior manifestations is shown employing lisuride hydrogen maleate (LHM). LHM elicited contralateral turnings in 6-hydroxydopamine lesioned rats unilaterally in the striatum whereas it caused ipsilateral turnings in kainic acid lesioned rats as was observed following the administration of apomorphine. Furthermore, the effect of LHM on rotating behavior was abolished by the pretreatment with sulpiride. On the other hand, LHM inhibited apomorphine induced stereotyped behavior whereas the sulpiride failed to block it. These results suggested the dual action of LHM on multiple postsynaptic dopamine receptors. The results also indicated that non-cooperative postsynaptic dopamine receptors are involved in rotating behavior while cooperative receptors participate in the elicitation of stereotypy.

A further study on constrictor responses of dog coronary arterial strips to acetylcholine under potassium-contracture

Experiments were designed to clarify what mechanisms are involved in the contraction of dog coronary artery induced by acetylcholine. Helical strips cut from the left circumflex coronary artery were suspended in a bath filled with oxygenated Krebs-Ringer solution at 37 degrees C, and tension developments were recorded isometrically. During potassium-contracture acetylcholine produced further contractions of the strips, which were significantly depressed by atropine together with phentolamine or atropine together with d-tubocurarine. In the strips prepared from dogs in which 6-hydroxydopamine was administered 2 hrs before isolation of hearts, acetylcholine-induced contraction was suppressed by atropine alone. Norepinephrine produced contractions in these strips, which were blocked by phentolamine. Results indicate that acetylcholine may directly constrict the artery through a muscarinic action and simultaneously produce norepinephrine release from sympathetic nerve endings by acting on presynaptic nicotinic receptors resulting in the contraction of the artery.

Effects of dopaminergic agonists and antagonists on [3H]apomorphine binding to striatal membranes: sulpiride lack of interactions with positive cooperative [3H]apomorphine binding

Effects of dopaminergic agonists and antagonists on [3H]apomorphine binding to striatal membranes of rat brain was examined. Haloperidol and spiroperidol exhibited biphasic inhibition of [3H]apomorphine binding; one of which had the Hill coefficient of 0.9, whereas the other had that of 0.4. The former accounted for 65% of [3H]apomorphine binding while the latter consisted of 35% of the binding. Furthermore, the latter disappeared after kainic acid lesions. On the other hand, sulpiride and metoclopramide reduced [3H]apomorphine binding to 31% with the Hill coefficient of 0.9. The inhibition of [3H]apomorphine binding with the Hill coefficient of 0.4 which was shown by haloperidol and spiroperidol was not observed for sulpiride and metoclopramide. Previously, we demonstrated non- and positive-cooperative [3H]apomorphine binding to stiatal membranes. In the present study, it has been also shown that sulpiride inhibits non-cooperative [3H]apomorphine binding leaving that with allosteric properties unaffected. No inhibition of dopamine-sensitive adenylate cyclase was observed by 10(-4) M sulpiride while 90% inhibition was obtained with 10(-5) M haloperidol. From those results, it is suggested that non-cooperative [3H]spomorphine binding is not coupled with dopamine-sensitive adenylate cyclase.