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There is considerable interest in the use of drugs that selectively block presynaptic (somatodendritic) serotonin 5-HT(1A) receptors for the adjunctive treatment of major depressive disorder. The 5-HT(1A)/beta-adrenoceptor ligands (+/-)-pindolol, (-)-tertatolol, and (-)-penbutolol are currently under clinical investigation, and knowledge of their affinity at different populations of central 5-HT(1A) receptors is needed. Here we have determined the affinity of these drugs for presynaptic and postsynaptic 5-HT(1A) receptors in postmortem human and rat brain using receptor autoradiography and the selective 5-HT(1A) radioligand [(3)H]WAY-100635. The binding of [(3)H]WAY-100635 was specific and saturable and showed high affinity in the rat dorsal raphe nucleus and hippocampus (K(D) = 1.5-1.7 nM). In competition studies, the three compounds had nanomolar affinity and produced monophasic displacement of [(3)H]WAY-100635 binding in all regions of both species. (-)-Penbutolol and (-)-tertatolol had similar affinity for pre-and postsynaptic 5-HT(1A) receptors in both rat and human brain. However, in the human, but not the rat, the affinity of (+/-)-pindolol in dorsal raphe nucleus (K(i) = 8.9 +/- 1. 1 nM) was slightly but significantly higher than that in hippocampus (K(i) = 14.4 +/- 1.5 nM in CA1). In summary, our data show that (+/-)-pindolol, (-)-tertatolol, and (-)-penbutolol are all high-affinity ligands at native human and rat 5-HT(1A) receptors. (-)-Penbutolol and (-)-tertatolol do not discriminate between the pre- and postsynaptic 5-HT(1A) sites tested in either species, but (+/-)-pindolol showed a slightly higher affinity for the presynaptic site in human brain. Further work is needed to establish whether the latter difference is clinically relevant.

Type

Journal article

Journal

J Neurochem

Publication Date

08/2000

Volume

75

Pages

755 - 762

Keywords

Aged, Animals, Anti-Arrhythmia Agents, Autoradiography, Brain, Dentate Gyrus, Female, Hippocampus, Humans, Male, Penbutolol, Pindolol, Piperazines, Propanolamines, Pyridines, Radioligand Assay, Raphe Nuclei, Rats, Rats, Sprague-Dawley, Receptors, Presynaptic, Receptors, Serotonin, Receptors, Serotonin, 5-HT1, Serotonin Antagonists, Synapses, Thiophenes, Tritium