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1. Extracellular 5-hydroxytryptamine (5-HT) was determined in dorsal raphe nucleus (DRN), median raphe nucleus (MRN) and nucleus accumbens by use of microdialysis in unanaesthetized rats. 2. Infusion of the gamma-aminobutyric acid (GABA)A receptor agonist muscimol into DRN and MRN resulted in decreased 5-HT in DRN and MRN, respectively. Muscimol infusion(More)
In vivo microdialysis was used to determine if morphine produces increases in extracellular serotonin in specific brain sites. With citalopram included in the dialysis solution to block reuptake, serotonin was measured in 11 brain sites of unanesthetized rats. After systemic morphine (10 mg/kg, s.c.), increases in extracellular serotonin were observed in(More)
Regulation of serotonin release by gamma-aminobutyric acid (GABA) and glutamate was examined by microdialysis in unanaesthetized rats. The GABA(A) receptor agonist muscimol, or the glutamate receptor agonists kainate, alpha-amino-3-hydroxy-5-methyl-4-isoxazolaproprionate or N-methyl-D-aspartate were infused into the dorsal raphe nucleus (DRN) while(More)
The effect of morphine on serotonin (5-HT) was examined by microdialysis in unanesthetized and anesthetized rats. In unanesthetized rats, morphine (10 mg/kg, s.c.) produced increases in extracellular 5-HT in nucleus accumbens (n. accumbens) and dorsal raphe nucleus (DRN), but not in the dorsal hippocampus. Similarly, extracellular 5-HT in the n. accumbens,(More)
1. Fentanyl is a micro -opioid analgesic that might disinhibit 5-HT neurons and thus increase 5-HT efflux. However, fentanyl also binds to 5-HT(1A) receptors, and if it activates 5-HT(1A) somatodendritic autoreceptors, the resultant inhibition might offset opioid-mediated increases in 5-HT efflux. To test this hypothesis, we used microdialysis to study(More)
Opioid receptor subtypes may have site-specific effects and play different roles in modulating serotonergic neurotransmission in the mammalian central nervous system. To test this hypothesis, we used in vivo microdialysis to measure changes in extracellular serotonin (5-hydroxytryptamine; 5-HT) in response to local infusion of mu-, delta-, and kappa-opioid(More)
Systemic administration of selective serotonin reuptake inhibitors (SSRIs) elicits larger increases in serotonin (5-HT) in raphe than in forebrain sites. Because serotonergic neuronal activity is suppressed, the mechanism underlying SSRI-induced increases in extracellular 5-HT is unclear. This study determined whether local infusion of SSRIs also elicited(More)
Regulation of serotonin (5-HT) release may be altered during the development of opioid tolerance and dependency. To test this hypothesis, changes in extracellular 5-HT during prolonged administration of morphine were determined by microdialysis in the dorsal raphe nucleus (DRN) of freely behaving rats. Morphine or placebo pellets were implanted s.c. As(More)
The effect of morphine on serotonin (5-HT) and 5-hydroxyindoleacetic acid (5-HIAA) in the CNS of unanesthetized rats was investigated by microdialysis. Morphine was administered either subcutaneously, by local perfusion into the diencephalon, or by intraraphe microinjection. Systemic administration of morphine resulted in a significant increase in both(More)
To characterize the effects of morphine on serotonin (5-HT) in the central nervous system, we used microdialysis in freely behaving rats. Subcutaneous injection of morphine sulfate produced a dose-dependent increase in extracellular 5-HT in the dorsal raphe nucleus (DRN) and a forebrain site, the nucleus accumbens (NAcc). To determine the site of action for(More)