Depolarizing responses recorded from nodose ganglion cells of the rabbit evoked by 5-hydroxytryptamine and other substances.

Membrane potential changes induced by 5-hydroxytryptamine (5-HT), gamma-aminobutyric acid (GABA) and 1,1-dimethyl-4-phenyl piperazinium (DMPP) were recorded from nodose ganglia (NG) by the sucrose-gap method. An amount of 0.002-0.5 mumol of the depolarizing agent was injected into the superfusion stream to the ganglion. Responses to 5-HT were also evoked from superior cervical (SCG) and dorsal root ganglia (DRG). 5-Hydroxytryptamine elicited depolarizations of graded amplitude. Maximal responses were 4.5 +/- 0.4 mV in nodose ganglia compared to 2.2 +/- 0.2 mV in superior cervical and 0.6 +/- 0.1 mV in dorsal root ganglia (means +/- SEM). In nodose ganglia, GABA induced smaller maximal depolarizations than did 5-HT, similar to those evoked by DMPP; dopamine was a weak depolarizing agent while substance P was apparently inactive. The dose-response curve for 5-HT in nodose ganglia was parallel to that for 5-HT in superior cervical ganglia and significantly to the left (ED50 values 0.029 and 0.098 mumol). Curves for 5-HT and GABA in nodose ganglia were superimposable. The high sensitivity of nodose ganglia cells to 5-HT is briefly discussed. Analogues of 5-HT lacking a hydroxyl group at position 5 on the nucleus were relatively inactive as depolarizing agents. Picrotoxin (10(-6)-10(-5) M) reduced or suppressed responses in nodose ganglia to GABA, whereas responses to 5-HT and DMPP were not much affected or, in the case of 5-HT, sometimes somewhat reduced. Quipazine (10(-6) M) was a selective antagonist of 5-HT responses in nodose ganglia; those to GABA and DMPP were not significantly altered. Neither trazodone nor LSD displayed antagonist properties at 5-HT receptors in nodose ganglia.