In vivo modulation of nucleus tractus solitarius (NTS) neurones by activation of 5-hydroxyhyptamine(2) receptors in rats

In in vivo experiments, 5-hydroxytryptamine (5-HT) and (+/-)-2,5-dimethoxy- 4-iodoamphetamine HCl (DOI), a 5-HT, receptor agonist, were applied by iono phoresis to rat nucleus tractus solitarius (NTS) neurones identified by the ir vagal and cardiopulmonary afferent inputs to test whether the response o f NTS cells to 5-HT, receptor activation was related to whether they receiv ed mono-or polysynaptic vagal inputs and their presumed function as defined by their afferent input. Cells were classified on the basis of the variabi lity of the latency of the vagal-evoked spikes: this varied by less than 3 ms for Group 1, from 3 to 5 Ins for Group 2, and more than 5 ms for Group 3 . Both 5-HT and DOI inhibited most Group 1 cells (16/18) and inactive (with out ongoing activity) cells (8/13) in Group 2. Cells inhibited by DOI were also inhibited by cardiopulmonary afferent stimulation, evoked by atrial ph enylbiguanide administration. By contrast, application of 5-HT and DOI exci ted the majority of Group 3 cells (14/19) and Group 2 with ongoing activity (7/9). Cells excited by DOI were also activated by cardiopulmonary stimula tion. Both actions of DOI were reversed by application of ketanserin (n=15) . In conclusion, these data demonstrate that activation of 5-HT, receptors in the NTS produces different effects dependent on whether the neurones rec eived mono- or polysynaptic vagal input and their response to cardiopulmona ry afferent stimulation. (C) 2000 Elsevier Science Ltd. All rights reserved .