Tadashi Noto

Biorhythm of arginine-vasopressin in the paraventricular, supraoptic and suprachiasmatic nuclei of rats

The diurnal variations in content of arginine-vasopressin in the supraoptic nucleus, the paraventricular nucleus and the suprachiasmatic nucleus of rats were determined using radioimmunoassay. In the supraoptic nucleus and the paraventricular nucleus the arginine-vasopressin level was relatively constant during the light phase (the inactive phase). When it became dark, the level of arginine-vasopressin lowered during the early and middle dark phase and then increased to the highest level during the late dark phase. In the suprachiasmatic nucleus the level was stable during the light phase, while in the early and the late dark phase it was significantly higher than that in the middle dark phase.

Spontaneous Release of γ‐Aminobutyric Acid Formed from Putrescine and Its Enhanced Ca2+‐Dependent Release by High K+ Stimulation in the Brains of Freely Moving Rats

The spontaneous release of [3H]γ‐aminobutyric acid ([3H]GABA) in various areas of rat brain in jected with [3H]putrescine was examined using a push pull perfusion technique. The release in a 25‐min perfusate was highest in the caudate‐putamen. The effect of high K+ stimulation on the release of [3H]GABA formed from [3H]putrescine was examined in the caudate‐putamen. The release was enhanced by high K+ solution in a Ca2+‐dependent manner.

A study on the release mechanism of vasopressin and oxytocin

The changes in plasma levels of arginine-vasopressin (AVP) and oxytocin (OXT) of rabbits by intraventricular administration of various drugs and their effects on the release of both hormones from the isolated posterior pituitary of rats were examined. An intraventricular injection of hypertonic saline, carbachol, angiotensin II, prostaglandin E2 or histamine to a rabbit increased the concentrations of plasma AVP and OXT, whereas serotonin decreased their plasma levels. Noradrenaline increased the concentration of OXT, but not that of AVP. Dopamine did not significantly affect the plasma level of either hormone. The release of AVP and OXT from the posterior pituitary fragments of rats was stimulated by changing the osmolality of the perfusion medium in vitro. Perfusion with medium containing dopamine suppressed the release of both hormones. However, the other bioactive amines and the drugs mentioned above did not affect the release of AVP and OXT.

Effects of L-Threo- and erythro-3,4-dihydroxyphenylserine on learning performance and concentrations of brain noradrenaline and its metabolites in rats

Effects of L-threo and L-erythro-3,4-dihydroxyphenylserine [DOPS, precursor amino acids for noradrenaline (NA)] on the learning performance in a maze paradigm designed to model on the water maze paradigm using a multicomputerized behavioral analysis system were studied. A marked facilitation of learning performance was observed in rats after an intraventricular injection of 5 micrograms L-threo-DOPS (the s-NA precursor), and this effect was inhibited by a simultaneous administration of 1 or 2 micrograms propranolol (a beta-adrenergic antagonist). As concentrations of brain NA, 3-methoxy-4-hydroxyphenylglycol, and normethanephrine were increased by the injection of 5 micrograms L-threo-DOPS, the effect seemed to be derived from activation of beta-adrenoceptors in the CNS by the formed s-NA. On the other hand, an intraventricular injection of 5 micrograms L-erythro-DOPS (the r-NA precursor) attenuated the learning performance, and this effect was probably caused by the formed r-NA from L-erythro-DOPS.

Determination of putrescine in brain tissue using gas chromatography-mass spectrometry

We used gas chromatography-mass spectrometry to assay putrescine in minute regions of single rat brains. Acid extraction, partial purification on Amberlite CG 120, and derivatization with pentafluoropropionic anhydride preceded the gas chromatography-mass spectrometry. A moving-needle solventless system and a direct inlet system were also used to increase sensitivity. Putrescine was measured accurately at the picomole level; the mean concentration of this polyamine in five regions of rat brain found by this method was 2.7-3.8 times higher than reported by other researchers.

Distribution of Putrescine in Rat Brain Measured by Gas Chromatography‐Mass Spectrometry

Abstract: We measured putrescine levels in minute sites of single rat brains using a sensitive, specific assay involving gas chromatography‐mass spectrometry. The putrescine level was measured in 20 sites of single rat brains: three sites in the cerebral cortex, six sites in the hypothalamus, three sites in the basal ganglia, three sites in the thalamus, three sites in the limbic system, and two sites in the cerebellum. The level of putrescine was very high in the hypothalamus, high in the basal ganglia and limbic system, and low in the thalamus, cerebellum, and two of the three sites in the cerebral cortex. The highest levels were in the anterior hypothalamic area and the lateral hypothalamic area, and the lowest levels were in the vermis and the lobe of the cerebellum.

Effect of DL-erythro-dihydroxyphenylserine on the locomotor activity of the mouse

Effect of dihydroxyphenylserine (DOPS) on the locomotor activity of mice pretreated with beta-phenylisopropylhydrazine was studied using an Animex activity meter. An intraperitoneal injection of DL-erythro-DOPS (200 mg/kg) suppressed significantly the locomotor stimulation by the MAO inhibitor, while DL-threo-DOPS (200 mg/kg) had no effect. Only slight suppression was observed after the administration of 100 mg/kg of DL-erythro-DOPS. Effect of DOPS on the concentrations of brain catecholamines and serotonin of mice pretreated with the MAO inhibitor was also analysed. The administration of DL-erythro-DOPS significantly increased the concentration of noradrenaline, while DL-threo-DOPS did not affect the contents of brain amines in the experimental condition. The suppressive effect of DL-erythro-DOPS on the locomotor stimulation by the MAO inhibitor was confirmed by a simultaneous administration of the amino acid and d-phenylisopropylmethylamine to mice. Based on these findings, the neural mechanisms of the locomotor activity and a clinical application of DL-erythro-DOPS to the manic syndrome were discussed.

Effects of prostaglandin E2 and D2 on the release of vasopressin and oxytocin

The effects of prostaglandin (PG) E2 and D2 on the plasma levels of arginine-vasopressin (AVP) and oxytocin (OXT) in rabbits, and on the release of the both hormones from the isolated posterior pituitary of rats were examined. An intraventricular administration of PGE2 to a rabbit raised the plasma levels of the both hormones. An intraventricular injection of PGD2 also increased the plasma level of OXT but not that of AVP. The release of AVP and OXT from fragments of the posterior pituitary of a rat was not influenced by perfusion with Eagle MEM medium containing 10(-6) or 10(-5) M PGE2 and D2.

Formation of γ‐Amino‐β‐Hydroxybutyric Acid from 2‐Hydroxyputrescine in Rat Brain

Abstract: γ‐Amino‐β‐[3H]hydroxybutyric acid ([3H]‐GABOB) was formed in rat brain from 2‐[3H]‐hydroxyputrescine that had been chemically synthesized from 2‐oxoputrescine and [3H]sodium borohydride. After the injection of 2‐[3H]hydroxyputrescine into the lateral ventricle of a rat brain, the rat was killed and then the brain was removed. [3H]GABOB in the brain was identified by a combination of ion‐exchange chromatography, high‐voltage paper electrophoresis, and recrystallization of the radioactive compound with authentic GABOB.

Formation of GABOB from 2-hydroxyputrescine and its anticonvulsant effect

To investigate the formation of gamma-amino-beta-hydroxybutyric acid from 2-hydroxyputrescine in mammalian organs, the radioactive diamine was synthesized and was injected into rats intraperitoneally or intraventricularly. After intraperitoneal injection, the radioactive amino acid was detected in various organs, but formation of the stereoisomer of the amino acid (gamma-amino-alpha-hydroxybutyric acid) was not demonstrated. Intraventricular injection of the radioactive diamine also resulted in the formation of gamma-amino-beta-hydroxybutyric acid in the rat brain. In vivo experiments using monoamine oxidase or diamine oxidase inhibitors suggested the participation of both enzymes in the formation of the amino acid from the diamine in rat organs other than the brain, where diamine oxidase appeared to play the major role. To investigate the anticonvulsant effect of 2-hydroxyputrescine, the threshold of pentylenetetrazol-induced generalized convulsions was measured in rats after the intraventricular injection of 2-hydroxyputrescine. Both R(-)- and S(+)-2-hydroxyputrescine had an anticonvulsant effect, with a greater elevation of the threshold being observed after injection of the R(-) form. Time course experiments suggested that this anticonvulsant effect depended on the formation of gamma-amino-beta-hydroxybutyric acid from 2-hydroxyputrescine in the rat brain. The anticonvulsant action of gamma-amino-beta-hydroxybutyric acid was also examined, and the stimulation of Cl- influx plus the inhibition of GABA uptake into brain membrane vesicles were indicated to be involved.