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Biomedical subjects

T Segawa

Publications and source records attributed to T Segawa.

At least 181 records · Page 10Linked to original sources
PubMed1980

Effect of imipramine on central 5-hydroxytryptamine turnover and metabolism in rats.

The levels of [3H]-5-HT and [3H]-5-HIAA in P2-fraction from rats treated with a single dose of imipramine were lower at 2, 5 and 10 min after intraventricular administration of [3H]-5-HT, compared with control animals, though these levels were statistically insignificant. Thereafter, however, the values became higher than in the controls. After long-term administration of imipramine, the levels of [3H]-5-HT and [3H]-5-HIAA in P2-fraction were, at any time after intraventricular administration of [3H]-5-HT, significantly lower than those in the fraction from controls. The endogenous contents of tryptophan and 5-HIAA were not altered either with a single dose or by long-term administration of imipramine, however, the content of endogenous 5-HT was decreased by long-term administration of imipramine. These results indicate that the rate of disappearance of 5-HT from presynaptic neurons was accelerated by long-term administration of imipramine.

Animals↗
PubMed1979

Decrease in muscarinic cholinergic response of the rat heart following treatment with 6-hydroxydopa.

Pretreatment with 6-hydroxydopa (6-OHDOPA) at birth produced a decrease in the number of [3H]quinuclidinyl benzilate ([3H]QNB) binding sites in adult rat heart homogenates. The treatment caused hyposensitivity to acetylcholine (ACh) but did not alter the maximal negative inotropic action of ACh in isolated atria of the rat. These results suggest that 6-OHDOPA affects the negative inotropic response to ACh by modifying the receptor number or through an effect on a step between receptor activation and biological response.

Acetylcholine↗
PubMed1979

Effects of concanavalin A on 5-hydroxytryptamine uptake by rabbit blood platelets and on their ultrastructure.

1. Effects of concanavalin A (Con A) and other lectins on 5-hydroxytryptamine (5-HT) uptake by rabbit blood platelets and on their ultrastructure were studied. 2. Uptake of [3H]-5-HT by platelets was decreased by application of Con A, E-PHA (lectin from Phaseolus vulgaris) and lentil-PHA (lectin from Lens culinaris), but not by wheat germ agglutinin (WGA). Con A induced specific changes in the ultrastructure of platelets, causing (i) a change in external appearance from a discoid to an irregularly spherical shape, (ii) re-arrangement of the canalicular system and formation of a concentric structure. These effects of Con A on platelets were antagonized by pretreatment with alpha-methyl-D-mannoside (alpha-MM), a specific inhibitor of Con A binding to glycoprotein. 3. The inhibition of 5-HT uptake by Con A was antagonized by colchicine, vinblastine and sodium nitroprusside (SNP), but not by cytochalasin B. 4. Theophylline, papaverine and dibutyryl cyclic adenosine 3',5'-monophosphate (db cyclic AMP) antagonized the effect of Con A on 5-HT uptake, but dibutyryl cyclic guanosine 3',5'-monophosphate had no effect. Theophylline and db cyclic AMP did not influence the effect of Con A on the ultrastructure of platelets. 5. It is suggested that binding of Con A to specific receptor glycoproteins can inhibit the 5-HT uptake system of platelets. Microtubules, contractile protein and the membrane adenylate cyclase system of platelets may also be regulatory factors in this mechanism.

Animals↗
PubMed1979

The effect of alpha-adrenoceptor antagonists and metiamide on clonidine-induced locomotor stimulation in the infant rat.

1 Subcutaneous injections of clonidine (3.9 X 10(-8) mol/kg to 3.9 X 10(-6) mol/kg) produced forward locomotion and wall climbing in 7-day-old rats in a dose-dependent manner. 2 The effect was reduced significantly by a preceding intraperitoneal injection of phentolamine (7.9 X 10(-6) mol/kg), phenoxybenzamine (7.4 X 10(-6) mol/kg), yohimbine (1.3 X 10(-6) mol/kg) or piperoxan (7.4 X 10(-6) mol/kg). 3 The pA2-values of the antagonists to the clonidine-induced locomotor hyperactivity were: 5.1 (phenoxybenzamine), 5.2 (phentolamine), 6.4 (yohimbine) and 6.0 (piperoxan). 4 Metiamide (2.5 X 10(-4) mol/kg, 5.0 X 10(-4) mol/kg and 1.0 X 10(-3) mol/kg), a histamine H2-receptor blocker, did not affect the clonidine-induced locomotor stimulation. 5 It is suggested that the receptors which mediate clonidine-induced locomotor stimulation could be alpha-adrenoceptors but not histamine H2-receptors in the central nervous system of the infant rat.

Adrenergic alpha-Antagonists↗
PubMed1979

High potassium-induced, calcium-dependent monoamine release from brain slices of the newborn rat.

To determine the functional significance of monoamines taken up into the newborn rat brain, a high K+-induced, Ca2+-dependent release of noradrenaline (NA), dopamine (DA) or serotonin (5-HT) from brain slices of the newborn rat was investigated and compared with that of the adult animal. Depolarization by increasing the potassium concentration in the medium induced the release of L-[3H]NA,[3H]DA or [3H]5-HT from brain slices prelabelled with the radioactive monoamines in the 2-day- or 3-day-old rat as well as in the adult. The release of three [3H]amines was markedly inhibited by perfusing with Ca2+- free medium in the presence of EGTA (2.0 mM) at both newborn and adult stages, although the inhibitory potency of Ca2+- deficiency in the newborn preparation was lower than in the adult. The degree of the release against [3H]amines initially taken up in the newborn was of the same order of magnitude as those in the adult. It is suggested that NA, DA and 5-HT are stored in a functionally releasable pool of the nerve terminals of the central monoamine neurons in the rat and that these compounds act as neurotransmitters at birth and at the adult stage.

Age Factors↗
PubMed1979

Developmental change in striatal concentration of homovanillic acid and 3,4-dihydroxyphenylacetic acid in response to apomorphine and haloperidol treatment.

The striatal concentration of homovanillic acid (HVA) and 3,4-dihydroxyphenylacetic acid (DOPAC) was estimated following an injection of apomorphine into the developing rat subchronically treated (S.C.) with haloperidol. At the withdrawal stage of haloperidol treatment, striatal HVA and DOPAC levels decreased in the rat aged 14, 24 and 34 days. The haloperidol treatment enhanced the apomorphine-induced reduction of the striatal HVA content at the withdrawal stage in the 24-day-old and 34-day-old rat. These results suggest that a functional link in the feedback control mechanism and dopamine receptors do not fully develop at birth but do so in the early stage of postnatal life.

3,4-Dihydroxyphenylacetic Acid↗
PubMed1978

Regional replication of the bacterial chromosome induced by derepression of prophage lambda. IV. Escape synthesis of gal operon in phage 82.

Derepression of prophage lambda in E. coli strain K12 results in constitutive synthesis of the enzymes directed by the nearby bacterial operon, gal (escape synthesis). Phage 82 fails to cause escape synthesis despite that it lysogenizes the strain K12 at the site identical to that of lambda on the host chromosome. The reason for the observed difference between 82 and lambda is studied in the light of the recent finding that escape synthesis in lambda-lysogen is closely associated to phage-promoted replication of bacterial chromosome contiguous to the prophage including gal operon (escape replication). Excision-defective mutants from 82, 82int or 82xis, do initiate escape synthesis, suggest that the prophage 82 is normally excised too quickly after induction to allow sufficient escape replication. In support of this, much more DNA hybridizable to bacterial DNA contained in lambdagal accumulates after induction if 82int than after induction of 82. Studies with various hybrid phages between 82 and lambda have suggested: 1. The occurrence of gal escape synthesis depends on the nature of the region between b2 and N in the lambda map. 2. Regions of the 82 genome on both sides of the attachment site contribute independently to prevent gal escape synthesis. Implications of these results are discussed with regard to the factors involved in the prophage excision.

Chromosomes, Bacterial↗
PubMed1978

Muscarinic hyposensitivity in the developing rat pretreated with 6-hydroxydopa.

Atropine-induced locomotor stimulation was investigated in the developing rat pretreated with 6-hydroxydopa at birth. The locomotor stimulation by atropine was first observed on day 20 and gradually increased with age. The treatment with 6-hydroxydopa potentiated atropine-induced locomotor stimulation on days later than day 20 and inhibited a pilocarpine-induced catalepsy on day 30. This suggests that central cholinergic neurons, probably in the neostriatum, reach functional maturity between 15 and 20 days, and that the pretreatment with 6-hydroxydopa induced muscarinic hyposensitivity in the developing rat.

Animals↗
PubMed1978

Apomorphine-induced locomotor stimulation in developing rats treated with 6-hydroxydopa.

Apomorphine-induced locomotor stimulation was investigated in the developing rat following injection with 6-hydroxydopa at birth. Treatment with 6-hydroxydopa potentiated locomotor responsiveness to apomorphine in the 20-day-old rat. The 6-hydroxydopa-treated animal at 30 days, however, was less sensitive to the drug than was the control. Apomorphine again elicited more locomotor stimulation in 6-hydroxydopa-treated animals than in the controls on day 50. These results suggest that the altered sensitivity of dopamine receptors induced with 6-hydroxydopa, is influenced by the onset of activity of other "inhibitory" neurons on day 30.

Animals↗