TY - JOUR
T1 - Pindolol, a putative 5-hydroxytryptamine(1A) antagonist, does not reverse the inhibition of serotonergic neuronal activity induced by fluoxetine in awake cats
T2 - Comparison to WAY-100635
AU - Fornal, Casimir A.
AU - Martin, Francisco J.
AU - Metzler, Christine W.
AU - Jacobs, Barry L.
PY - 1999/10
Y1 - 1999/10
N2 - The ability of pindolol to enhance the clinical antidepressant response to selective serotonin reuptake inhibitors (SSRIs) is generally attributed to a blockade of the feedback inhibition of serotonergic neuronal activity mediated by somatodendritic 5-hydroxytryptamine (5-HT)(1A) autoreceptors. The current study examined the ability of pindolol to restore the single-unit activity of serotonergic dorsal raphe nucleus neurons in awake cats after acute treatment with the SSRI fluoxetine. The effects of pindolol were compared with those of N-[2-[4-(2-methoxyphenyl)-1-piperazinyl]ethyl]-N-(2- pyridinyl)cyclohexanecarboxamide (WAY-100635), a selective 5-HT(1A) receptor antagonist. Systemic administration of fluoxetine (0.5 and 5 mg/kg i.v.) decreased neuronal firing rates to ~50 and 1%, respectively, of baseline levels. The subsequent administration of cumulative doses of (±)-pindolol (0.1-5 mg/kg i.v.) failed to reverse the neuronal inhibition produced by either dose of fluoxetine. In addition to lacking efficacy as an antagonist in these experiments, (±)-pindolol produced an additional decrease in neuronal activity in animals pretreated with the low dose of fluoxetine. The active enantiomer, (-)-pindolol (1 mg/kg i.v.), also was ineffective in restoring neuronal activity after fluoxetine. In contrast, systemic administration of WAY-100635 completely reversed the effect of fluoxetine (5 mg/kg) at low doses (0.025 mg/kg i.v.), and further elevated the firing rate of these neurons above prefluoxetine baseline levels. Overall, these results indicate that pindolol, unlike WAY-100635, lacks appreciable antagonist activity at 5-HT(1A) autoreceptors. Thus, the clinical efficacy of pindolol in augmenting the antidepressant response to SSRIs, such as fluoxetine, may be unrelated to a restoration of serotonergic neuronal activity.
AB - The ability of pindolol to enhance the clinical antidepressant response to selective serotonin reuptake inhibitors (SSRIs) is generally attributed to a blockade of the feedback inhibition of serotonergic neuronal activity mediated by somatodendritic 5-hydroxytryptamine (5-HT)(1A) autoreceptors. The current study examined the ability of pindolol to restore the single-unit activity of serotonergic dorsal raphe nucleus neurons in awake cats after acute treatment with the SSRI fluoxetine. The effects of pindolol were compared with those of N-[2-[4-(2-methoxyphenyl)-1-piperazinyl]ethyl]-N-(2- pyridinyl)cyclohexanecarboxamide (WAY-100635), a selective 5-HT(1A) receptor antagonist. Systemic administration of fluoxetine (0.5 and 5 mg/kg i.v.) decreased neuronal firing rates to ~50 and 1%, respectively, of baseline levels. The subsequent administration of cumulative doses of (±)-pindolol (0.1-5 mg/kg i.v.) failed to reverse the neuronal inhibition produced by either dose of fluoxetine. In addition to lacking efficacy as an antagonist in these experiments, (±)-pindolol produced an additional decrease in neuronal activity in animals pretreated with the low dose of fluoxetine. The active enantiomer, (-)-pindolol (1 mg/kg i.v.), also was ineffective in restoring neuronal activity after fluoxetine. In contrast, systemic administration of WAY-100635 completely reversed the effect of fluoxetine (5 mg/kg) at low doses (0.025 mg/kg i.v.), and further elevated the firing rate of these neurons above prefluoxetine baseline levels. Overall, these results indicate that pindolol, unlike WAY-100635, lacks appreciable antagonist activity at 5-HT(1A) autoreceptors. Thus, the clinical efficacy of pindolol in augmenting the antidepressant response to SSRIs, such as fluoxetine, may be unrelated to a restoration of serotonergic neuronal activity.
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M3 - Article
C2 - 10490908
AN - SCOPUS:0032821055
SN - 0022-3565
VL - 291
SP - 220
EP - 228
JO - Journal of Pharmacology and Experimental Therapeutics
JF - Journal of Pharmacology and Experimental Therapeutics
IS - 1
ER -