Effects of (-)-tertatolol, (-)-penbutolol and (+/-)-pindolol in combination with paroxetine on presynaptic 5-HT function: an in vivo microdialysis and electrophysiological study.
The antidepressant efficacy of selective serotonin reuptake inhibitors (SSRIs) might be enhanced by co-administration of 5-HT1A receptor antagonists. Thus, we have recently shown that the selective 5-HT1A receptor antagonist, WAY 100635, blocks the inhibitory effect of an SSRI on 5-HT cell firing, and enhances its ability to elevate extracellular 5-HT in the forebrain. Here we determined whether the beta-adrenoceptor/5-HT1A receptor ligands (+/-)-pindolol, (-)-tertatolol and (-)-penbutolol, interact with paroxetine in a similar manner. Both (-)-tertatolol (2.4 mg kg(-1) i.v.) and (-)-penbutolol (2.4 mg kg(-1) i.v.) enhanced the effect of paroxetine (0.8 mg kg(-1) i.v.) on extracellular 5-HT in the frontal cortex, whilst (+/-)-pindolol (4 mg kg(-1) i.v.) did not. (-)-Tertatolol (2.4 mg kg(-1) i.v.) alone caused a slight increase in 5-HT however, (-)-penbutolol (2.4 mg kg(-1) i.v.) alone had no effect. In electrophysiological studies (-)-tertatolol (2.4 mg kg(-1) i.v.) alone had no effect on 5-HT cell firing but blocked the inhibitory effect of paroxetine. In contrast, (-)-penbutolol (0.1-0.8 mg kg(-1) i.v.) itself inhibited 5-HT cell firing, and this effect was reversed by WAY 100635 (0.1 mg kg(-1) i.v.). We have recently shown that (+/-)-pindolol inhibits 5-HT cell firing via a WAY 100635-sensitive mechanism. Our data suggest that (-)-tertatolol enhances the effect of paroxetine on forebrain 5-HT via blockade of 5-HT1A autoreceptors which mediate paroxetine-induced inhibition of 5-HT cell firing. In comparison, the mechanisms by which (-)-penbutolol enhances the effect of paroxetine on extracellular 5-HT is unclear, since (-)-penbutolol itself appears to have agonist properties at the 5-HT1A autoreceptor. Indeed, the agonist action of (+/-)-pindolol at 5-HT1A autoreceptors probably explains its inability to enhance the effect of paroxetine on 5-HT in the frontal cortex. Overall, our data suggest that both (-)-tertatolol and (-)-penbutolol are superior to (+/-)-pindolol in terms of enhancing the effect of an SSRI on extracellular 5-HT. Both (-)-tertatolol and (-)-penbutolol are worthy of investigation for use as adjuncts to SSRIs in the treatment of major depression.
Gartside
S E
SE
Oxford University Department of Clinical Pharmacology, Radcliffe Infirmary.
Clifford
E M
EM
Cowen
P J
PJ
Sharp
T
T
D000319:Adrenergic beta-Antagonists / Q000494:pharmacology*; D000818:Animals; D000928:Antidepressive Agents / Q000494:pharmacology*; D004357:Drug Synergism; D004594:Electrophysiology; D066298:In Vitro Techniques; D008297:Male; D008564:Membrane Potentials; D017551:Microdialysis; D017374:Paroxetine / Q000494:pharmacology; D018408:Patch-Clamp Techniques; D010394:Penbutolol / Q000494:pharmacology; D010869:Pindolol / Q000494:pharmacology; D011412:Propanolamines / Q000494:pharmacology; D016548:Prosencephalon / Q000187:drug effects / Q000378:metabolism; D011903:Raphe Nuclei / Q000187:drug effects / Q000378:metabolism; D051381:Rats; D017207:Rats, Sprague-Dawley; D017661:Receptors, Presynaptic / Q000187:drug effects / Q000502:physiology*; D011985:Receptors, Serotonin / Q000187:drug effects / Q000502:physiology*; D012701:Serotonin / Q000502:physiology*; D017367:Selective Serotonin Reuptake Inhibitors / Q000494:pharmacology*; D013876:Thiophenes
D000319:Adrenergic beta-Antagonists; D000928:Antidepressive Agents; D017374:Paroxetine; D010394:Penbutolol; D010869:Pindolol; D011412:Propanolamines; D017661:Receptors, Presynaptic; D011985:Receptors, Serotonin; D012701:Serotonin; D017367:Selective Serotonin Reuptake Inhibitors; D013876:Thiophenes; C005632:tertatolol