5-Hydroxytryptamine(1A) and 5-hydroxytryptamine(1B) receptors stimulate [S-35]guanosine-5'-O-(3-thio)triphosphate binding to rodent brain sections as visualized by in vitro autoradiography

[S-35]Guanosine-5'-O-(3-thio)triphosphate ([S-35]GTP gamma S) binding to G proteins was measured by in vitro autoradiography in guinea pig and rat brain sections after activation by 5-hydroxytryptamine (5-HT) receptor agonists. 5-Carboxamidotryptamine stimulated binding strongly in hippocampus and lateral septum and weakly in substantia nigra. This effect was blocked in the substantia nigra by the 5-HT1B/1D receptor antagonist GR-127,935 and in the former two regions by the 5-HT1A antagonist NAN-190. 5-HT1B/1D receptor agonists stimulated binding in substantia nigra and in areas containing 5-HT1A receptors. In guinea pig substantia nigra, 5-(nonyloxy)-tryptamine maximally stimulated [S-35]GTP gamma S binding by 54%, with an EC50 value of 62 nM; at 100 mu M, this agonist increased binding by similar to 200% in hippocampus (with a 2-fold weaker EC50 value). The distribution of [H-3]8-OH-DPAT binding sites was identical to that of the [S-35]GTP gamma S labeling stimulated by the 5-HT1A agonist (R)-8-hydroxy-2-dipropylaminotetralin [(R)-8-OH-DPAT)]. (R)-8-OH-DPAT, (S)-8-OH-DPAT, and buspirone stimulated [S-35]GTP gamma S binding in hippocampus by 340%, 140%, and 78%, with EC50 values of 71, 51, and 132 nM. Enhanced [S-35]GTP gamma S binding was not detected in the presence of 5-HT1F, 5-HT2, 5-HT4, and 5-HT7 receptor agonists, Because activation of mu-opioid, muscarinic M-2, histamine H-3, and cannabinoid receptors was also visualized successfully, these data suggest that only receptors coupled to pertussis toxin-sensitive G proteins can be seen by [S-35]GTP gamma S binding autoradiography. This study also shows that different 5-HT receptors coupled to these proteins can show a wide range of [S-35]GTP gamma S binding stimulation. Although the functional significance of these variations is unclear, this technique offers advantages over receptor autoradiography because it does not require high affinity radioligands and provides a measure of agonist efficacies in various brain regions.