A 5-HT(7) receptor-mediated depolarization in the anterodorsal thalamus. I. Pharmacological characterization.
Little is currently known regarding the electrophysiological response elicited by 5-hydroxytryptamine-7 (5-HT(7)) receptor stimulation in the brain. Previous anatomical studies have shown that the anterior thalamus expresses a high density of 5-HT7 receptors. Therefore, we used whole-cell recording techniques in the in vitro brain slices to examine the effects of serotonin on neurons of the anterodorsal nucleus of the thalamus (ADn). Bath application of 5-HT induces a large membrane depolarization and inward current in neurons of the ADn. Since these cells expressed 5-HT7 receptor mRNA, as determined by single-cell reverse transcriptase-polymerase chain reaction, we pharmacologically characterized the 5-HT receptor mediating this response. We found that the 5-HT1 and 5-HT7 agonists 5-carboxamidotryptamine (5-CT) and 5-methoxytryptamine mimicked the response to 5-HT, whereas the 5-HT2 agonist 2,5-dimethoxy-4-iodoamphetamine did not. Consistent with the involvement of a 5-HT7 receptor, 5-CT was approximately 18 times more potent than 5-HT. Furthermore, administration of the 5-HT(1A) and 5-HT7 agonist 8-hydroxydipropylaminotetralin mimicked and antagonized the effect of serotonin, suggesting it acted as a partial agonist. To determine if either the 5-HT1 or 5-HT7 receptor mediated the 5-HT-induced inward current, we used antagonists. We found that the 5-HT7 ligands ritanserin, methylsergide, LSD, and mesulergine could inhibit the 5-HT-induced inward current, whereas the 5-HT1 antagonist cyanopindolol had no effect. The pA(2) value determined for mesulergine closely approximated that expected for a 5-HT7 receptor. Finally, we found that bath application of the selective antagonist SB-269770 blocks the 5-HT-induced inward current. These results identify the receptor mediating the serotonin-induced membrane depolarization in the ADn as the 5-HT7 subtype.
Department of Psychiatry and Behavioral Neurosciences, Wayne State University School of Medicine, Detroit, MI 48201, USA.
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Chapin
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Andrade
D017371:8-Hydroxy-2-(di-n-propylamino)tetralin / Q000494:pharmacology; D000818:Animals; D004305:Dose-Response Relationship, Drug; D066298:In Vitro Techniques; D008238:Lysergic Acid Diethylamide / Q000494:pharmacology; D008297:Male; D008564:Membrane Potentials / Q000187:drug effects; D051381:Rats; D017207:Rats, Sprague-Dawley; D011985:Receptors, Serotonin / Q000502:physiology*; D020133:Reverse Transcriptase Polymerase Chain Reaction; D012701:Serotonin / Q000494:pharmacology; D013788:Thalamus / Q000187:drug effects* / Q000502:physiology
D011985:Receptors, Serotonin; C104425:serotonin 7 receptor; D012701:Serotonin; D017371:8-Hydroxy-2-(di-n-propylamino)tetralin; D008238:Lysergic Acid Diethylamide