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  • 1
    ISSN: 1432-2072
    Keywords: 5-HT1 antagonist ; 5-HT1A receptor function ; 5-HT1B receptor function ; TVX Q 7821 ; 5-HT2 receptor function ; 5-HT-mediated behaviour ; Isapirone
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract The effects of 2-(4-(4-(2-pyrimidinyl)-1-piperazinyl)-butyl)-1,2-benzoisothiazol-3(2H)one-1,1-dioxide hydrochloride (isapirone, TVX Q 7821), a putative 5-HT1 receptor antagonist, has been studied on various models of 5-HT receptor sub-type function. In mice TVX Q 7821 produced a dose-dependent inhibition of the hypothermia induced by 8-hydroxy-2-(di-n-propylamino)tetralin (8-OH-DPAT) with an ED50 of 5.3 mg/kg suggesting that TVX Q 7821 was an antagonist of the presynaptic (possibly somato-dendritic) 5-HT1A receptor. TVX Q 7821 did not alter the locomotor response to the suggested 5-HT1B agonist RU 24969. The rate of mouse brain 5-HT synthesis was accelerated by TVX Q 7821 (10 mg/kg). 5-HT2 receptor-mediated head twitch behaviour induced by precursor loading with 5-HTP was unaffected by TVX Q 7821 (10 mg/kg) pretreatment 75 min earlier, but the head-twitch induced by the agonist 5-methoxy-N,N-dimethyltryptamine was enhanced by prior treatment with TVX Q 7821. In rats the hypothermia induced by 8-OH-DPAT was partially antagonised by TVX Q 7821 while the behavioural “serotonin syndrome” induced by 8-OH-DPAT (a possible post-synaptic 5-HT1B-mediated effect) was unaffected by TVX Q 7821 as was the locomotion induced by RU 24969. The data suggest that TVX Q 7821 is a good presynaptic 5-HT1A antagonist in mice, as indicated by the 8-OH-DPAT-induced hypothermia and 5-HT synthesis rate studies. It did not antagonise 5-HT1B-mediated behaviour in mice or rats and appeared to have an antagonist action at pre- but not post-synaptic 5-HT1A receptors in rats.
    Type of Medium: Electronic Resource
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  • 2
    ISSN: 1432-2072
    Keywords: Lithium ; 5-Hydroxytryptamine ; 5-HT1 receptor ; 5-HT2 receptor ; a 2-Adrenoceptor ; 8-OH-DPAT ; Clonidine ; Mouse
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract Lithium administration (LiCl, 10 mmol/kg, SC on day 1, followed by 3 mmol/kg twice daily subsequently) for 14 days to mice produced attenuation of the hypothermic response to injection of 8-hydroxy-2-(di-n-propyla-mino)tetralin (8-OH-DPAT, 0.5 mg/kg SC). Head twitch responses to the 5-HT-receptor agonist 5-methoxy-N,N-dimethyltryptamine (2.5 mg/kg IP) and to precursor loading with carbidopa (25 mg/kg, IP) and 5-hydroxytryptophan (100 mg/kg IP) were similarly attenuated. By contrast with this reduction of 5-hydroxytryptamine (5-HT) function mediated by the 5-HT1A and 5-HT2 receptor sub-types, repeated lithium administration had no effect on the motor response to a putative 5-HT1B receptor agonist 5-methoxy-3(1,2,3,6-tetrahydropyridin-4-yl)1H indole (RU 24969, 3 mg/kg IP). Alpha2 adrenoceptor function, assessed by the sedation response to clonidine (0.25 mg/kg, IP), was also attenuated by repeated lithium administration. It is proposed that these actions may explain the emergence of lithium as an adjunct to the treatment of refractory depressive illness.
    Type of Medium: Electronic Resource
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  • 3
    ISSN: 1432-2072
    Keywords: Lithium ; 5-Hydroxytryptamine ; 5-HT1 receptor ; 8-OH-DPAT ; P-Chlorophenylanine ; 5-HT-mediated behaviour ; Rat
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract Administration of lithium chloride (10 mmol/kg on day 1 and 3 mmol/kg twice daily on subsequent days, SC) for 3–14 days enhances the components of the serotonin syndrome produced by 8-hydroxy-2-(di-propylamino)tetralin (8-OH-DPAT) in the rat. The hypothermic response produced simultaneously was unaltered. Following lithium administration for 3 days the motor response to 5-methoxy,N,N-dimethyltryptamine was also facilitated. These data suggest that lithium administration enhances post-synaptic 5-HT receptor-mediated behavioural responses. (−)-Propranolol (20 mg/kg, IP) but not (+)-propranolol (20 mg/kg IP) fully antagonised the facilitated response to 8-OH-DPAT seen following lithium administration; ritanserin (200 μg/kg, IP) was without effect. These findings favour a mechanism for the action of lithium involving the 5-HT1A receptor. Depletion of 5-hydroxytryptamine (5-HT) with parachlorophenylalanine (PCPA, 300 mg/kg, IP on day 1 and 2 of lithium administration) did not prevent the facilitation by lithium of the response to 8-OH-DPAT. These data strengthen the suggestion that lithium has its effect on 5-HT1A-mediated motor function by a post-synaptic action. By contrast, motor responses to the putative 5-HT1B receptor agonist 5-methoxy-3-(1,2,3,6-tetrahydro-pyridin-4-yl)-1H-indole (RU 24969) were unaltered by repeated lithium administration.
    Type of Medium: Electronic Resource
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  • 4
    ISSN: 1432-2072
    Keywords: 8-OH-DPAT ; 5-Hydroxytryptamine (5-HT) ; 5-HT1 receptor ; Parachlorophenylalanine (PCPA) ; Clenbuterol ; Quipazine
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract The hypothermic and motor behavioural responses to 8-hydroxy-2-(di-n-propylamino)tetralin (8-OH-DPAT) have been investigated in the rat. The dose-effect relationship showed that hypothermia appeared at a lower dose than a definite motor syndrome. The hypothermic response to 8-OH-DPAT was attenuated following depletion of 5-hydroxytryptamine (5-HT) by repeated intraperitoneal (IP) administration of parachlorophenylalanine (200 mg/kg) or by injection of 5,7-dihydroxytryptamine (5,7-DHT, 100 μg) into the region of the third ventricle; the motor behavioural response produced simultaneously was not. Indeed, after 5,7-DHT, it was increased. Quipazine (1 mg/kg, IP) antagonised the hypothermic response and facilitated the motor behaviour. Clenbuterol (2.5 mg/kg, IP) increased both hypothermic and motor responses. (±)-propranolol was without effect on the simple hypermotility produced by 8-OH-DPAT, although it is known to antagonise the hypothermic and stereotyped motor responses. It is concluded that 8-OH-DPAT probably produces its hypothermic effects by actions at 5-HT receptors located presynaptically on 5-HT neurones, while the stereotyped components of the serotonin syndrome appear to be mediated by post-synaptic receptors.
    Type of Medium: Electronic Resource
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  • 5
    ISSN: 1432-2072
    Keywords: 5-Hydroxytryptamine (5-HT) ; 5-HT1A receptor ; Electroconvulsive shock ; Antidepressants ; 8-OH-DPAT ; Zimeldine ; Desipramine ; Tranylcypromine ; Flurazepam
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract The hypothermia and motor behavioural syndrome produced in rats by injection of the 5-HT1A ligand 8-hydroxy-2-(di-n-propylamino)tetralin (8-OH-DPAT) has been studied following administration of electroconvulsive shock under halothane anaesthesia (ECS) and during the administration of antidepressant drugs. Repeated ECS attenuated the hypothermic response to 8-OH-DPAT (0.1 mg/kg SC) immediately after the last of five shocks given spread out over 10 days with a maximal effect 21 days after the final shock. A single ECS was without effect. The serotonin syndrome produced by 8-OH-DPAT (0.75 mg/kg SC) was also attenuated, although simple motility was increased. Zimeldine (20 mg/kg) and desipramine (20 mg/kg), when given once daily for 14 days also attenuated the hypothermia and the serotonin syndrome provoked by 8-OH-DPAT. The hypothermic response was somewhat reduced 24 h after a single injection of zimeldine but not 45 min after zimeldine (5 mg/kg IP). At a high dose (20 mg/kg) tranylcypromine clearly attenuated both responses 24 h after a single injection. Tranylcypromine (6 mg/kg IP) showed a smaller effect after a single injection but attenuated the behavioural syndrome on repeated administration. Repeated injection of flurazepam (10 mg/kg IP) was without effect on either the behavioural or hypothermic response to 8-OH-DPAT. These findings are consistent with the view that responses mediated via the 5-HT1A receptor may be involved in the mechanism of action of antidepressant treatments.
    Type of Medium: Electronic Resource
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