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Vol. 297, Issue 1, 395-402, April 2001
Departments of Psychiatry and Behavioral Neurosciences and
Pharmacology, and the Cellular and Clinical Neurobiology Training
Program, Wayne State University School of Medicine, Detroit, Michigan
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-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-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.
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