RATIONALE: Temporal differentiation in the free-operant psychophysical procedure is sensitive to the 5-hydroxytryptamine (5-HT)1A receptor agonist 8-hydroxy-2-(di-n-propylamino)-tetralin (8-OH-DPAT) and the 5-HT2 receptor agonist 2,5-dimethoxy-4-iodo-amphetamine (DOI); both drugs shift the psychophysical curve leftwards, reducing the indifference point, T50. We have examined the effect of the 5-HT releasing agent fenfluramine on temporal differentiation. OBJECTIVE: We examined whether fenfluramine's effect on temporal differentiation can be antagonised by the 5-HT1A receptor antagonist N-[2-(4-[2-methoxy-phenyl]-1-piperazinyl)ethyl]-N-2-pyridinylcyclohexane-carboxamide (WAY-100635) and the 5-HT2A receptor antagonist ketanserin, and compared the effects of fenfluramine, DOI and 8-OH-DPAT in intact rats and rats whose 5-HTergic pathways had been destroyed by 5,7-dihydroxytryptamine. METHODS: Rats were trained under the free-operant psychophysical procedure to press levers A and B in 50-s trials in which reinforcers were provided intermittently for responding on A in the first half, and B in the second half of the trial. Percent responding on B (%B) was recorded in successive 5-s epochs of the trials; logistic psychophysical curves were fitted to the data for derivation of timing indices (T50, time corresponding to %B=50%, and Weber fraction). Experiment 1 examined the effects of acute treatment with fenfluramine, and the interaction between fenfluramine and the 5-HT1A and 5-HT2A receptor antagonists WAY-100635 and ketanserin; experiment 2 compared the effects of fenfluramine, 8-OH-DPAT and DOI in intact rats and rats whose 5-HTergic pathways had been destroyed by intra-raphe injection of 5,7-dihydroxytryptamine. Concentrations of 5-HT and catecholamines in the brain were measured by high-performance liquid chromatography. RESULTS: Experiment 1: fenfluramine (2 mg/kg) reduced T50; this effect was attenuated by ketanserin (1.0 mg/kg) but not by WAY-100635 (100 microg/kg). Experiment 2: 8-OH-DPAT (100 microg/kg) and DOI (250 microg/kg) reduced T50 in both groups; fenfluramine reduced T50 only in the sham-lesioned group. Levels of 5-HT were reduced by 80% in the lesioned group; catecholamine levels were not affected. CONCLUSIONS: The results suggest that fenfluramine affects temporal differentiation via the release of endogenous 5-HT which acts mainly on postsynaptic 5-HT2A receptors.
RATIONALE: Temporal differentiation in the free-operant psychophysical procedure is sensitive to the 5-hydroxytryptamine (5-HT)1A receptor agonist 8-hydroxy-2-(di-n-propylamino)-tetralin (8-OH-DPAT) and the 5-HT2 receptor agonist 2,5-dimethoxy-4-iodo-amphetamine (DOI); both drugs shift the psychophysical curve leftwards, reducing the indifference point, T50. We have examined the effect of the 5-HT releasing agent fenfluramine on temporal differentiation. OBJECTIVE: We examined whether fenfluramine's effect on temporal differentiation can be antagonised by the 5-HT1A receptor antagonist N-[2-(4-[2-methoxy-phenyl]-1-piperazinyl)ethyl]-N-2-pyridinylcyclohexane-carboxamide (WAY-100635) and the 5-HT2A receptor antagonist ketanserin, and compared the effects of fenfluramine, DOI and 8-OH-DPAT in intact rats and rats whose 5-HTergic pathways had been destroyed by 5,7-dihydroxytryptamine. METHODS:Rats were trained under the free-operant psychophysical procedure to press levers A and B in 50-s trials in which reinforcers were provided intermittently for responding on A in the first half, and B in the second half of the trial. Percent responding on B (%B) was recorded in successive 5-s epochs of the trials; logistic psychophysical curves were fitted to the data for derivation of timing indices (T50, time corresponding to %B=50%, and Weber fraction). Experiment 1 examined the effects of acute treatment with fenfluramine, and the interaction between fenfluramine and the 5-HT1A and 5-HT2A receptor antagonists WAY-100635 and ketanserin; experiment 2 compared the effects of fenfluramine, 8-OH-DPAT and DOI in intact rats and rats whose 5-HTergic pathways had been destroyed by intra-raphe injection of 5,7-dihydroxytryptamine. Concentrations of 5-HT and catecholamines in the brain were measured by high-performance liquid chromatography. RESULTS: Experiment 1: fenfluramine (2 mg/kg) reduced T50; this effect was attenuated by ketanserin (1.0 mg/kg) but not by WAY-100635 (100 microg/kg). Experiment 2: 8-OH-DPAT (100 microg/kg) and DOI (250 microg/kg) reduced T50 in both groups; fenfluramine reduced T50 only in the sham-lesioned group. Levels of 5-HT were reduced by 80% in the lesioned group; catecholamine levels were not affected. CONCLUSIONS: The results suggest that fenfluramine affects temporal differentiation via the release of endogenous 5-HT which acts mainly on postsynaptic 5-HT2A receptors.
Authors: S S al-Zahrani; M Y Ho; D N Velazquez Martinez; M Lopez Cabrera; C M Bradshaw; E Szabadi Journal: Psychopharmacology (Berl) Date: 1996-10 Impact factor: 4.530
Authors: T H C Cheung; G Bezzina; C L Hampson; S Body; K C F Fone; C M Bradshaw; E Szabadi Journal: Psychopharmacology (Berl) Date: 2007-08-01 Impact factor: 4.530
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Authors: T H C Cheung; G Bezzina; K Asgari; S Body; K C F Fone; C M Bradshaw; E Szabadi Journal: Psychopharmacology (Berl) Date: 2006-03-15 Impact factor: 4.530
Authors: Adam L Halberstadt; Ivan S Sindhunata; Kees Scheffers; Aaron D Flynn; Richard F Sharp; Mark A Geyer; Jared W Young Journal: Neuropharmacology Date: 2016-03-25 Impact factor: 5.250
Authors: S Body; T H C Cheung; C L Hampson; F S den Boon; G Bezzina; K C F Fone; C M Bradshaw; E Szabadi Journal: Psychopharmacology (Berl) Date: 2008-11-19 Impact factor: 4.530