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At least 757 records · Page 42Linked to original sources
PubMed1991

Excitation of substantia nigra pars compacta neurones by 5-hydroxy-tryptamine in-vitro.

Incoming serotonergic fibres are known to make direct synaptic contact with dopamine-containing neurones in the substantia nigra pars compacta (SNc). However, the effects of 5-HT (5-hydroxytryptamine) on these cells have not been thoroughly investigated. In the present study we show that application of 10-50 microM 5-HT increases the firing frequency of SNc neurones in-vitro, and produces inward rectification in a voltage region negative to -50mV. This effect is sensitive to extracellular Cs+, but not to Ba2+, and has similar properties as the intrinsic inward rectifier current, Ih. Antagonists of the 5-HT1A and 5-HT2 receptors were inefficacious. It is concluded that 5-HT excites SNc neurones via an enhancement of the conductance underlying Ih.

Animals↗
PubMed1960

The effects of corticosteroids and related compounds on the histamine and 5-hydroxy-tryptamine content of rat tissues.

Daily intramuscular injections of cortisone, prednisolone, triamcinolone, dexamethasone, fludrocortisone and 2-methylfludrocortisone markedly reduced the histamine and 5-hydroxytryptamine contents of the skin and small intestine of rats; there was an increase however, in the amine contents of the stomach. The sex hormones were weaker in these effects while deoxycortone and corticotrophin were inactive. When the skin was depleted of half of its 5-hydroxytryptamine by prolonged treatment with polymyxin B, the rate of recovery of this amine was retarded by the glucocorticoids. The glucocorticoid activity of a steroid and its ability to produce changes in the histamine and 5-hydroxytryptamine contents of tissues are related.

Adrenal Cortex Hormones↗
PubMed1979

The synthesis rate and turnover time of 5-hydroxy-tryptamine in brains of rats treated chronically with morphine.

1. Four schedules of subcutaneous pellet implantation were used to induce tolerance to and physical dependence on morphine in Sprague-Dawley rats. 2. The schedules included implantation of four morphine pellets (each containing 75 mg of morphine free base) during a 3 day period (schedule 1); six pellets during 3 days (schedule 2); six pellets during 7 days (schedule 3) and ten pellets during a 10 day period (schedule 4). 3. A high degree of tolerance and dependence on morphine, comparable to that induced in mouse by implantation of a single morphine pellet for 3 days, was produced with schedule 4. 4. Brain 5-hydroxytryptamine (5-HT) turnover rates as measured by rate of accumulation of 5-HT after monoamine oxidase inhibition by pargyline were not different in rats rendered tolerant to and dependent on morphine according to schedules 1 to 4 when compared with corresponding placebo pellet-implanted rats. 5. The turnover rates of 5-HT in brain of morphine-and placebo pellet-implanted rats (schedule 4) from which the pellets had been removed for 24 h were also similar. 6. It is concluded that tolerance to, and physical dependence upon morphine in the rat is not associated with changes in brain 5-HT dynamics.

Animals↗
PubMed1992

Rabbit isolated renal artery contractions by some tryptamine derivatives, including 2-methyl-5-HT, are mediated by a 5-HT1-like receptor.

1. Despite the fact that 5-hydroxytryptamine (5-HT)-induced contractions of the rabbit isolated renal artery are mediated by a receptor belonging to the heterogeneous 5-HT1-like category, we observed that the so-called selective 5-HT3 receptor agonist, 2-methyl-5-HT, caused a concentration-dependent contraction of this vessel. This study was therefore undertaken to analyze the effects of 2-methyl-5-HT in the renal artery segments, either quiescent or precontracted with U46619 (10(-7) M). alpha-Methyl-5-HT and 5-methoxytryptamine, which have high affinities for 5-HT2 and 5-HT4 receptors, respectively, were used for comparison. 2. In the precontracted vessel segments, the maximum contractile responses obtained with 2-methyl-5-HT, alpha-methyl-5-HT, 5-methoxytryptamine and 5-HT were similar to those in the quiescent segments. However the pD2 values were higher in the precontracted segments, making them about 4-100 fold more sensitive. 3. Neither MDL 72222 (10(-6) M) nor tropisetron (3 x 10(-6) M) suppressed renal artery contractions elicited by 5-HT, 2-methyl-5-HT, alpha-methyl-5-HT or 5-methoxytryptamine, thus ruling out the involvement of 5-HT3 as well as 5-HT4 receptors. 4. On the other hand, both methiothepin (10(-8) and 10(-7) M) and ketanserin (10(-7) and 10(-6) M) caused a rightward shift of agonist concentration-effect curves.The two antagonists had similar pA2 values against the different agonists tested on either quiescent or precontracted vessels, but ketanserin (apparent pA2: 6.6 to 7.0) was between 20-100 fold less potent than methiothepin (apparent pA2: 8.4 to 8.8).5. The results of this functional study permit us to conclude that the contractile effects of 2-methyl-5-HT as well as ct-methyl-5-HT and 5-methoxytryptamine on the rabbit isolated renal artery are mediated by a 5-HT1-like receptor. Since, in addition, the reported ligand binding affinity of 2-methyl-5-HT at 5-HT3 receptors is similar to both the ligand binding affinity and the functional pD2 at 5-HTI sites, this compound cannot be regarded as a selective 5-HT3 receptor agonist. Similarly, a-methyl-5-HT and 5-methoxytryptamine have only a limited selectivity for 5-HT2 and 5-HT4 receptors, respectively.

15-Hydroxy-11 alpha,9 alpha-(epoxymethano)prosta-5↗
PubMed1981

The action of antidepressant drugs on 5-hydroxy-tryptamine uptake by platelets--relationship to therapeutic effect.

The uptake of 5-hydroxytryptamine (5-HT) by the blood platelets of depressive patients treated with amitriptyline and zimelidine has been examined. Both drugs significantly reduce the uptake of 5-HT into the platelet and the degree of inhibition is correlated with the plasma drug level of amitriptyline. No significant correlations could be detected between the degree of inhibition of uptake and clinical change. The accepted mode of action of tricyclic antidepressant drugs, i.e. the inhibition of reuptake of released amines, is discussed.

Antidepressive Agents↗
PubMed1988

Experimental evidence that tryptamine alkaloids do not cause Phalaris aquatica sudden death syndrome in sheep.

The acute toxicity for sheep of 3 alkaloids that occur in Phalaris acquatica was examined by intravenous and oral administration. The lowest tested dose rates that produced clinically observed signs were, for 5-methoxy dimethyltryptamine, 0.1 mg/kg body weight intravenously and 40 mg/kg orally; for gramine, 10 mg/kg intravenously and 500 mg/kg orally; and for hordenine, 20 mg/kg intravenously and 800 mg/kg orally. All induced the clinical signs observed in the nervous form of phalaris toxicity, but none induced the cardiac, sudden death, syndrome.

Alkaloids↗