Effects of selective serotonin and serotonin/noradrenaline reuptake inhibitors on extracellular serotonin in rat diencephalon and frontal cortex.
Some clinical reports suggest that tricyclic antidepressants which block both noradrenaline and serotonin (5-HT) reuptake (SNRIs) are more effective than selective 5-HT reuptake inhibitors (SSRIs) in treating severe depression. Moreover, one neurochemical study reported larger increases in extracellular 5-HT in rat frontal cortex in response to the tricyclic antidepressant imipramine compared to the SSRI fluoxetine. However, imipramine, which blocks both 5-HT and noradrenaline reuptake, also binds with relatively high affinity to receptors for noradrenaline, histamine and acetylcholine. Thus, to test the hypothesis that compounds that inhibit both 5-HT and noradrenaline reuptake produce larger increases in 5-HT efflux, we compared the effects of acute systemic administration of several SNRIs and SSRIs. Extracellular 5-HT was measured using microdialysis probes implanted in the diencephalon and frontal cortex of unanesthetized rats. We tested the SSRIs paroxetine (0.3-10 mg/kg), citalopram (10-20 mg/kg) and fluoxetine (10 mg/kg), the nonselective tricyclic antidepressant imipramine (20 mg/kg) and the more selective SNRIs duloxetine (3-30 mg/kg) and venlafaxine (30-50 mg/kg). During the lights-off period, paroxetine and duloxetine increased 5-HT in the diencephalon approximately 300 and approximately 200%, respectively. During the lights-on period, paroxetine and duloxetine each increased 5-HT approximately 400% in the diencephalon. In the frontal cortex, both paroxetine and duloxetine increased 5-HT approximately 200%. Citalopram and venlafaxine each increased 5-HT in the diencephalon approximately 300%. Fluoxetine and imipramine increased 5-HT in the diencephalon by approximately 125 and approximately 80%, respectively. Thus, these results do not support the hypothesis that compared to SSRIs, compounds which inhibit both 5-HT and noradrenaline reuptake have a larger acute effect on extracellular 5-HT.
Felton
Tracy M
TM
Department of Cell Biology and Neuroscience, Nelson Biological Laboratories, Rutgers University, 604 Allison Road, Piscataway, NJ 08854, USA. matthews@axon.rutgers.edu
Kang
Tommy B
TB
Hjorth
Stephan
S
Auerbach
Sidney B
SB
D018759:Adrenergic Uptake Inhibitors / Q000494:pharmacology*; D000818:Animals; D004027:Diencephalon / Q000187:drug effects* / Q000378:metabolism; D005110:Extracellular Space / Q000378:metabolism; D005625:Frontal Lobe / Q000187:drug effects* / Q000378:metabolism; D007279:Injections, Subcutaneous; D008297:Male; D017551:Microdialysis; D009638:Norepinephrine / Q000378:metabolism*; D051381:Rats; D017207:Rats, Sprague-Dawley; D012701:Serotonin / Q000378:metabolism*; D017367:Selective Serotonin Reuptake Inhibitors / Q000494:pharmacology*; D013997:Time Factors
D018759:Adrenergic Uptake Inhibitors; D009638:Norepinephrine; D012701:Serotonin; D017367:Selective Serotonin Reuptake Inhibitors