Biomedical subjects

Y Misu

Publications and source records attributed to Y Misu.

At least 19 recordsLinked to original sources

PubMed1992

Transmitter-like 3,4-dihydroxyphenylalanine is tonically released by nicotine in striata of conscious rats.

Microdialysis and high performance liquid chromatography with an electrochemical detector were applied to compare the characteristics of nicotine-evoked release of endogenous 3,4-dihydroxyphenylalanine (DOPA) from striata of conscious rats and those of the release of dopamine (DA). Dialysates were collected every 20 min 3-8 h after the start of perfusion. Nicotine was perfused for 20 min through a probe. (+/-)-Nicotine (100-300 microM) constantly and repeatedly released DOPA and DA over a similar time course in a dose-dependent manner. The ratio of the DOPA and DA release evoked was approximately 1:3. The (+/-)-nicotine (200 microM)-induced DOPA release was mecamylamine (500 microM)-sensitive, tetrodotoxin (100 nM)-sensitive and Ca2+ (removal plus 12.5 mM Mg2+ addition)-dependent. The (+)-isomer produced no DOPA release. These characteristics of DOPA release were almost the same as those of DA release. Furthermore, mecamylamine alone inhibited the basal release of DOPA but not of DA. Nicotine released stereoselectively endogenous DOPA via nicotinic acetylcholine receptors from striata of freely moving rats in a manner similar to transmitter DA. These acetylcholine receptors function tonically for the release of DOPA. These findings are further support for our proposal that DOPA is an endogenous neuroactive substance.

Animals↗

PubMed1992

Evidence for L-dopa systems responsible for cardiovascular control in the nucleus tractus solitarii of the rat.

Microinjections of L-DOPA (10-100 ng) into the medial area of the nucleus tractus solitarii (NTS) led to dose-dependent decreases in arterial blood pressure and heart rate in rats treated with i.p. 3-hydroxybenzylhydrazine, a central inhibitor of DOPA decarboxylase, or similarly with intraventricular 6-hydroxydopamine. D-DOPA, dopamine or noradrenaline (100 ng) produced no effect. L-DOPA methyl ester (1 microgram), a competitive antagonist for L-DOPA, microinjected into NTS, blocked the depressor and bradycardic responses to L-DOPA. High K+ (40 mM) released endogenous DOPA in a Ca(2+)-dependent manner from slices of the rat dorsomedial medulla including NTS. These results support the hypothesis that there exist systems of L-DOPA itself responsible for cardiovascular regulation in NTS of rats. This regulatory action of L-DOPA seems to be postsynaptic in nature.

Animals↗

PubMed1992

Transmitter-like basal and K(+)-evoked release of 3,4-dihydroxyphenylalanine from the striatum in conscious rats studied by microdialysis.

Using microdialysis and HPLC, characteristics of the release of endogenous 3,4-dihydroxyphenylalanine (DOPA) from striatum in conscious rats were studied in comparison with those of 3,4-dihydroxyphenylethylamine (dopamine; DA). Purified L-aromatic amino acid decarboxylase (AADC) converted a putative peak of DOPA to DA. The retention time of DOPA differed from that of DA and major metabolites of DA and norepinephrine. The DOPA peak of dialysates comigrated with that of authentic DOPA when the pH of the HPLC buffer was modified. The ratio of the basal release of DOPA:DA was 1:2. 3-Hydroxybenzylhydrazine (NSD-1015; 100 mg/kg, i.p.), an AADC inhibitor, markedly increased the basal release of DOPA but produced no effect on DA. The basal release of DOPA was markedly decreased by alpha-methyl-p-tyrosine (200 mg/kg, i.p.), substantially tetrodotoxin (1 microM) sensitive, and Ca2+ (removal plus 12.5 mM Mg2+ addition) dependent. Fifty millimolar K+ released DOPA and this release was also Ca2+ dependent. These characteristics of the basal and evoked release of DOPA were similar to those of DA. The ratio of the evoked release of DOPA:DA was 1:3. These results indicate that DOPA is released under physiological conditions and by K(+)-induced depolarization in a manner similar to that for transmitter DA from striatum in freely moving rats.

Animals↗

PubMed1992

L-dopa-like regulatory actions of L-threo-3,4-dihydroxyphenylserine on the release of endogenous noradrenaline via presynaptic receptors in rat hypothalamic slices.

Effects of L-threo-3,4-dihydroxyphenylserine (L-threo-DOPS) on the spontaneous release and the stimulus(2 Hz)-evoked release of endogenous noradrenaline were studied in rat hypothalamic slices with functioning L-aromatic amino acid decarboxylase (AADC) and with AADC inhibition. In non-inhibited slices, spontaneous release was not modified by L-threo-DOPS at 1 pM-100 nM, tended to increase at 1-10 microM and increased at 100 microM. Noradrenaline tissue content slightly increased at 100 microM. Stimulated release was concentration-dependently facilitated at 1-1000 pM and tended to decrease gradually from a maximum at 10 nM-10 microM. Under AADC inhibition, spontaneous release concentration-dependently increased at 10-100 microM by 60% of the increase seen in slices without AADC inhibition. Increase in noradrenaline tissue content was abolished. L-threo-DOPS produced a triphasic pattern on stimulated release; concentration-dependent facilitation at 1-1000 pM similar to that seen in slices with functional AADC, no facilitation at 10-1000 nM, and a concentration-dependent increment at 10-100 microM. The facilitation at 1 nM was stereoselective and was antagonized by (-)-propranolol 10 nM, and no facilitation at 100 nM was restored to the maximum by yohimbine 10 nM, DG-5128 10 nM or S-sulpiride 1 nM. Furthermore, L-threo-DOPS (1-1000 pM)-induced facilitation was competitively antagonized by L-dopa methyl ester, a competitive antagonist for L-dopa, with a pA2 value of 13.6, whereas it was noncompetitively antagonized by (-)-propranolol.

Animals↗

PubMed1992

Effects of nanomolar to submillimolar carteolol on noradrenaline release in the absence and presence of uptake1 and uptake2 blockers in guinea pig pulmonary arteries.

Effects of nanomolar to submillimolar carteolol, a non-selective beta-antagonist, on the evoked release at 1 Hz and the spontaneous release in the absence and presence of uptake1 and uptake2 blockers were studied in pulmonary arteries, isolated from guinea pigs, and then preloaded with [3H]noradrenaline. dl-Carteolol at 10(-8), 10(-7) and 10(-6) M applied at the increasing concentrations inhibited the evoked [3H]-release in untreated arteries and in desipramine and corticosterone-treated arteries. The spontaneous [3H]-release slightly but significantly increased or tended to increase in untreated arteries. dl-Carteolol at 10(-5) and 10(-4) M clearly and concentration-dependently increased the spontaneous [3H]-release in untreated and cocaine-treated arteries. This increase was markedly inhibited by further pretreatment with normetanephrine. The evoked [3H]-release was not altered by dl-carteolol at 10(-5) M, but increased at 10(-4) M. This increase was not modified by cocaine and by cocaine and normetanephrine. d-Carteolol at 10(-5) and 10(-4) M produced effects similar to those of dl-carteolol. Nanomolar to micromolar dl-carteolol inhibits the evoked [3H]-release, which supports our previous conclusion that this inhibition is due to blockade of tonically functioning presynaptic beta 2-adrenoceptors. Carteolol at the higher concentrations seems to become a substrate for an uptake2 mechanism and to produce an unknown sympathomimetic activity in guinea pig pulmonary arteries.

Animals↗

PubMed1991

Picomolar concentrations of L-dopa stereoselectively potentiate activities of presynaptic beta-adrenoceptors to facilitate the release of endogenous noradrenaline from rat hypothalamic slices.

Interactions between (-)-isoproterenol and DOPA on the release of endogenous noradrenaline (NA) evoked by electrical field stimulation (2 Hz, alternative polarity) were studied in rat superfused hypothalamic slices in the presence of 3-hydroxybenzylhydrazine, an inhibitor of L-aromatic amino acid decarboxylase, and cocaine. Isoproterenol (0.3-3 nM) facilitated the NA release in a concentration-dependent manner, while 10 pM L-DOPA alone produced no effect. This facilitation at 0.3-3 nM was potentiated by 20-70% by simultaneously applied 10 pM L-DOPA but that at 3 nM was not modified by 10 pM D-DOPA. This potentiation of the isoproterenol (3 nM)-induced facilitation of the NA release was concentration-dependent at 1-10 pM of L-DOPA. L-DOPA methyl ester (1 nM) antagonized the L-DOPA (10 pM)-induced potentiation of the facilitation of the NA release by 3 nM isoproterenol to a level of the facilitation by isoproterenol alone, whereas 10 nM (-) propranolol antagonized both the facilitation by isoproterenol alone and its potentiation by L-DOPA to a control level. Picomolar concentrations of L-DOPA stereoselectively act on a recognition site for itself, and then potentiate activities of presynaptic beta-adrenoceptors to facilitate the NA release from rat hypothalamic slices.

Animals↗

PubMed1991

Ipsilateral but not contralateral blockade of excitatory amino acid receptors in the caudal ventrolateral medulla inhibits aortic baroreceptor reflex in rats.

The caudal ventrolateral medulla (CVLM) contains vasodepressor neurons which, when activated, decrease vasomotor tone. To investigate whether excitatory amino acid receptors in the CVLM of the rat are involved in mediation of the aortic baroreceptor reflex, we microinjected amino acid antagonists unilaterally into the CVLM and examined their effects on the depressor response to electrical stimulation of the aortic nerve which contains mainly baroreceptor afferent fibers in rats. Male Wistar rats were anaesthetized with urethane, paralyzed and artificially ventilated. To block reflex vagal effects, methylatropine (1 mg/kg) was given intravenously. Kynurenate (227 ng), an excitatory amino acid antagonist, injected ipsilaterally but not contralaterally into the CVLM markedly inhibited the depressor response to aortic nerve stimulation, while both injections produced a similar small increase in basal blood pressure. Muscimol (1 ng), a GABA receptor agonist, injected ipsilaterally into the CVLM partly inhibited the baroreflex response, while it produced a moderate increase in basal blood pressure. 2-Amino-5-phosphonovalerate (APV) (10 ng), a N-methyl-D-aspartate (NMDA) receptor antagonist, and MK-801 (30 ng), a NMDA receptor channel blocker, partly inhibited the baroreflex response. MK-801 (30 ng) injected into the CVLM reduced the depressor response to the NMDA receptor agonist NMDA (0.3 ng) but not to the quisqualate receptor agonist quisqualate (0.1 ng) and the kainate receptor agonist kainate (0.1 ng), while kynurenate (227 ng) inhibited the depressor response to all three excitatory amino acid receptor agonists. These findings provide further evidence for the presence of excitatory amino acid receptors involved in mediating the aortic baroreceptor reflex in the rat CVLM.(ABSTRACT TRUNCATED AT 250 WORDS)

2-Amino-5-phosphonovalerate↗

PubMed1991

Nanomolar L-dopa facilitates release of dopamine via presynaptic beta-adrenoceptors: comparative studies on the actions in striatal slices from control and 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP)-treated C57 black mice, an animal model for Parkinson's disease.

Effects of L-DOPA (0.1-10,000 nM) on spontaneous release (Sp), evoked release (S) and tissue content (C) of dopamine (DA) were studied comparatively in superfused striatal slices from control and 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP)-treated C57 black mice to obtain evidence for L-DOPA-induced facilitation of S via presynaptic beta-adrenoceptors. In control slices, isoproterenol-induced concentration-dependent increases in S were propranolol-sensitive. L-DOPA at 0.1-3 nM tended to increase the S of DA with a concomitant tendency of increases in Sp. L-DOPA at 10-1 x 10(4) nM concentration-dependently increased Sp. L-DOPA at 1-10 microM tended to increase S and 10 microM increased C. In slices from MPTP-treated mice, the absolute amounts of Sp, S and C decreased by half compared to those in control slices. L-DOPA at 3 nM facilitated S without increasing Sp. This facilitation was antagonized by propranolol at 3 nM. L-DOPA at 30 nM decreased S from the peak facilitation, which contrasted with no effect in the control slices. However, 10-100 nM L-DOPA increased Sp more markedly than that in the control slices. L-DOPA at 100 nM increased S and C, which contrasted with no effect in the control slices. In conclusion, nanomolar L-DOPA facilitates the S of DA via presynaptic beta-adrenoceptors at concentrations lower than those required to induce conversion to DA even in striatal slices from the MPTP-treated mice model for Parkinson's disease.(ABSTRACT TRUNCATED AT 250 WORDS)

1-Methyl-4-phenyl-1,2,3,6-tetrahydropyridine↗

PubMed1991

L-dihydroxyphenylalanine methyl ester is a potent competitive antagonist of the L-dihydroxyphenylalanine-induced facilitation of the evoked release of endogenous norepinephrine from rat hypothalamic slices.

Using high performance liquid chromatography with electrochemical detection, we attempted to find among L-dopa-related analogs a competitive antagonist against L-dopa-induced facilitation of impulse (2 Hz)-evoked endogenous norepinephrine (NE) release from rat hypothalamic slices. At the first screening in the presence of cocaine and 3-hydroxybenzylhydrazine (NSD-1015), a L-aromatic amino acid decarboxylase inhibitor, L-dopa (1-100 nM) concentration-dependently facilitated NE release. L-dopa (1 microM) reduced NE release. D-dopa, L-phenylalanine, 3-O-methyl-dopa, 3,4-dihydroxyphenylacetic acid or L-dopa-phosphate at 1 to 1000 nM, and carbidopa (1-10 nM), did not mimic L-dopa. L-dopa methyl ester (0.3-10 nM) concentration-dependently decreased NE release, suggesting that it is antagonistic, whereas L-threo-3,4-dihydroxyphenylserine (0.001-1 nM) concentration-dependently mimicked L-dopa. At the second screening in the additional presence of S-sulpiride, L-dopa (1-1000 nM) concentration-dependently facilitated NE release. Maximum effect was seen at 0.3 to 1 microM. Pretreatment with carbidopa (0.1-10 nM) or L-dopa phosphate (0.01-0.1 nM) was somewhat antagonistic. L-Dopa methyl ester (3-30 nM) in a concentration-dependent manner shifted the concentration-facilitation curve for L-dopa to the right: Schild plots gave a straight line with a slope of 1.00 and pA2 was 8.9, whereas l-propranolol (1-100 nM) concentration-dependently reduced maximal effect of L-dopa without rightward shift of the curve. L-Dopa methyl ester and some large neutral amino acids inhibited uptake of [3H]-L-dopa into slices in the presence of NSD-1015.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗

PubMed1990

Evidence that endogenous catecholamines are involved in alpha 2-adrenoceptor-mediated modulation of the aortic baroreceptor reflex in the nucleus tractus solitarii of the rat.

Microinjections of alpha-methylnoradrenaline and tyramine into the rat nucleus tractus solitarii (NTS) potentiated the depressor and bradycardiac responses to aortic nerve stimulation whereas yohimbine injected similarly inhibited them. NTS pretreatment with yohimbine inhibited the baroreflex potentiation effects of alpha-methylnoradrenaline and tyramine whereas intraventricular pretreatment with 6-hydroxydopamine inhibited only that of tyramine. These results provide evidence that endogenous catecholamines in the rat NTS are involved in alpha 2 adrenoceptor-mediated modulation of the aortic baroreceptor reflex.

Animals↗

PubMed1990

Nicotine releases stereoselectively and Ca2(+)-dependently endogenous 3,4-dihydroxyphenylalanine from rat striatal slices.

In superfused slices of rat striatum, nicotine-evoked release of endogenous 3,4-dihydroxyphenylalanine (DOPA) was studied in comparison with that of dopamine (DA). (+/-)-Nicotine (0.1-10 microM) constantly and repetitively released DOPA and DA over a similar time course in a concentration-dependent manner. The ratio of DOPA and DA evoked was approximately 1:2-3. The turnover rate of DOPA was about 300 times higher compared to DA. (+/-)-Nicotine (10 microM)-induced DOPA release was mecamylamine (20 microM)-sensitive, Ca2(+)-dependent and tetrodotoxin (0.3 microM)-insensitive. The (+)-isomer induced no DOPA release. These characteristics of DOPA release were almost the same as those of DA. Nicotine evokes endogenous DOPA via nicotinic cholinergic receptors in a manner similar to the transmitter DA. These findings further support a probable role of DOPA as a neuroactive substance in the rat central nervous system.

Animals↗

PubMed1990

Evaluation of a 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP)-treated C57 black mouse model for parkinsonism.

We evaluated neurochemically, behaviorally, and neuropathologically the availability of 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP)-treated C57 black (BL) mice as a model for Parkinson's disease. The dopamine and 3,4-dihydroxyphenyl acetic acid content in the striatum, measured by high-performance liquid chromatography with an electrochemical detector, decreased by 70% at 10 and 20 days after the withdrawal of MPTP (30 mg/kg, i.p. twice daily for 5 days). During these days, the mice showed a decrease in locomotor activity and exhibited akinesia in both pole and traction tests. Light microscopically, 44% of the MPTP-treated mice showed neuronal degeneration in the substantia nigra 1 month after the withdrawal (damaged group), and 56% showed no change (undamaged group). Morphometric analysis revealed that the number of neurons in the substantia nigra decreased by 33% on the average in both groups. Electron microscopically, an electron-dense degeneration of most neurons was seen in the substantia nigra of the damaged group, and even in the undamaged group, loss of rough endoplasmic reticulum and mitochondrial deformity were seen in 50-70% of the neurons. Electron-dense bodies were seen in the striatum of both groups. These results show the validity of the MPTP-treated C57 BL mice as a suitable model for parkinsonism, including Parkinson's disease.

Animals↗

PubMed1990

Electrical stimulation-evoked release of endogenous aspartate from rat medulla oblongata slices. Effects of inhibitors of aspartate aminotransferase and GABA transaminase.

The effects of aminooxyacetic acid (AOAA), an aspartate aminotransferase (AAT) inhibitor, L-canaline, an ornithine aminotransferase inhibitor, and gamma-acetylenic GABA and gabaculine, both gamma-aminobutyric acid transaminase (GABA-T) inhibitors, on the release of aspartate from slices of rat medulla oblongata and hippocampus were studied. The slices were superfused and electrically stimulated. There was a Ca2(+)-dependent stimulus-evoked release of endogenous aspartate. AOAA (10(-4) and 10(-3) M) decreased the evoked release of aspartate in the medulla oblongata but not in the hippocampus. In addition, AOAA produced a decrease in the spontaneous efflux and tissue content of aspartate in the medulla oblongata. L-Canaline (5 x 10(-5) M), gamma-acetylenic GABA (10(-4) M) and gabaculine (10(-5) M) did not affect the evoked release of aspartate in the medulla oblongata, while these agents produced a decrease in spontaneous efflux and tissue content of aspartate. These findings suggest that AAT participates in the synthesis of transmitter aspartate in the medulla oblongata of the rat. It appears that there are the pools of transmitter aspartate and non-transmitter aspartate in the rat medulla oblongata.

4-Aminobutyrate Transaminase↗

PubMed1990

L-dopa methyl ester antagonizes competitively L-dopa-induced facilitation of noradrenaline release from rat hypothalamic slices.

In rat hypothalamic slices, antagonism by L-DOPA methyl ester and (-)-propranolol against L-DOPA-induced facilitation of endogenous noradrenaline (NA) release was characterized under the inhibition of dopadecarboxylase. L-DOPA at 10 nM to 1 microM facilitated the evoked NA release in a concentration-dependent manner. L-DOPA methyl ester (3, 10 and 30 nM) progressively shifted the concentration-release curve for L-DOPA to the right: Schild plots gave a straight line with a slope of 1.00 and pA2 was 8.9. This antagonistic action was not mimicked by L-phenylalanine, a substrate for L-DOPA transport system. In contrast, 10 and 100 nM propranolol concentration-dependently reduced the maximal effect of L-DOPA without rightward shift of the concentration-release curve. L-DOPA methyl ester is a potent competitive antagonist for the action of L-DOPA, and the recognition site of L-DOPA differs from presynaptic beta-adrenoceptors.

Animals↗

PubMed1990

Carteolol is a useful tool to prove the tonically functioning nature of presynaptic beta-adrenoceptors on peripheral noradrenergic neurons but not on central catecholaminergic neurons.

Effects of carteolol on norepinephrine (NE) release were studied at 2 Hz mainly in rat hypothalamic slices. Isoproterenol at 1 and 10 nM concentration-dependently facilitated NE release. Isoproterenol (10 nM)-induced facilitation was antagonized by 1 and 10 nM dl-carteolol, but not antagonized by 1 nM d-carteolol. dl-Carteolol alone at 1 nM to 10 microM did not inhibit NE release. In brainstem slices, 10 nM isoproterenol also facilitated NE release, and this facilitation tended to be antagonized by 1 nM dl-carteolol. Nanomolar concentrations of carteolol stereoselectively antagonized isoproterenol-induced facilitation of NE release via presynaptic beta-adrenoceptors in rat hypothalamic slices.

Adrenergic beta-Antagonists↗

PubMed1990

L-dopa facilitates the release of endogenous norepinephrine and dopamine via presynaptic beta 1- and beta 2-adrenoceptors under essentially complete inhibition of L-aromatic amino acid decarboxylase in rat hypothalamic slices.

In rat hypothalamic slices, L-aromatic amino acid decarboxylase (AADC) was assayed, and the actions of L-DOPA on impulse (2 Hz)-evoked norepinephrine (NE) and dopamine (DA) release were studied under inhibition of AADC. Slices were incubated with L-DOPA, and DA and NE produced by conversion of the precursor were analyzed by high performance liquid chromatography with electrochemical detection (HPLC-ECD). In the slices, the Km and Vmax of AADC were 131 microM and 122 pmol/min/mg protein, respectively. NSD-1015, an AADC inhibitor, caused a noncompetitive type of inhibition, and the K1 value was 0.086 microM. In the presence of 20 microM NSD-1015, which was expected to cause 99.6% inhibition of AADC, L-DOPA (0.01-100 nM) concentration-dependently facilitated the release of NE from the superfused slices, and the L-DOPA (10 nM)-induced facilitation was antagonized by 100 nM ICI 89,406 and 100 nM ICI 118,551, a selective beta 1- and beta 2-adrenoceptor antagonist, respectively. This action of L-DOPA was not modified by 30 microM tropolone, an inhibitor of catechol-O-methyl-transferase. L-DOPA at 0.01-1 nM similarly facilitated the release of DA. A quantitative analysis revealed that the L-DOPA-induced increase in NE and DA release was much higher by a factor of 3 to 4 orders than was the amount of DA and NE converted from L-DOPA. These results add further support to the hypothesis that L-DOPA itself acts as a neuroactive substance in the rat central nervous system.

3,4-Dihydroxyphenylacetic Acid↗

PubMed1990

Hypotension decreases GABA levels in brainstem regions of the rat.

Concentrations of gamma-aminobutyric acid (GABA) and other amino acids were measured in microdissected areas of the rostral ventro-lateral medulla (RVL), nucleus tractus solitarii (NTS) and caudal ventrolateral medulla (CVL) of the rat, and effects on the amino acid levels, of hypotension induced by hexamethonium and nifedipine were examined. Hexamethonium and nifedipine decreased concentrations of GABA in all the regions studied, while concentrations of glycine, beta-alanine and taurine were not affected by these agents. Both agents caused a prolonged fall in blood pressure. These results strongly suggest that a decrease in blood pressure produces a decrease in GABA levels in the brainstem regions of the rat.

Alanine↗

PubMed1990

Genetically altered brain amino acid metabolism in spontaneously hypertensive rats: a study by using young spontaneously hypertensive rats and renal hypertensive rats.

Previously we demonstrated altered amino acid levels in brainstem regions of adult spontaneously hypertensive rats (SHR). For comparison, in this study, we determined amino acid concentrations in discrete brainstem regions in young prehypertensive SHR and renal hypertensive rats. In prehypertensive SHR, the content of glutamate was increased in the rostral ventrolateral medulla and the caudal ventrolateral medulla, and the content of beta-alanine was decreased in the nucleus tractus solitarii. In renal hypertensive rats, there was no change in glutamate and beta-alanine contents in all the regions. The profiles of contents of glutamate and beta-alanine in the brainstem regions in young SHR but not in renal hypertensive rats are the same as those found previously in adult SHR. Thus, the results of the present study suggest that the altered amino acid metabolism in the brainstem of SHR may be genetically inherent.

Amino Acids↗