A 5-HT7 Receptor-Mediated Depolarization in the Anterodorsal Thalamus. I. Pharmacological Characterization

• Published in: The Journal of pharmacology and experimental therapeutics 2001-04, Vol.297 (1), p.395-402
• Main Authors: Chapin, Esther M., Andrade, Rodrigo
• Format: Article
• Language: English
• ISSN: 0022-3565; 1521-0103
• DOI: 10.1016/S0022-3565(24)29551-3

Little is currently known regarding the electrophysiological response elicited by 5-hydroxytryptamine-7 (5-HT7) receptor stimulation in the brain. Previous anatomical studies have shown that the anterior thalamus expresses a high density of 5-HT7receptors. 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-HT7receptor 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-HT1A 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 pA2 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.