Y. Wang et al., EFFECTS OF 5-HT AND 5-HT1A RECEPTOR AGONISTS AND ANTAGONISTS ON DORSAL VAGAL PREGANGLIONIC NEURONS IN ANESTHETIZED RATS - AN IONOPHORETIC STUDY, British Journal of Pharmacology, 116(4), 1995, pp. 2291-2297
1 Effects of ionophoretic administration of 5-hydroxytryptamine (5-HT)
and selective 5-HT1A receptor agonists and antagonists on identified
dorsal vagal preganglionic and dorsal raphe neurones were studied in p
entobarbitone sodium or chloral hydrate-anaesthetized rats, respective
ly. 2 Extracellular recordings were made from 176 preganglionic neuron
es in the dorsal vagal nucleus (DVN). Application of 5-HT at low curre
nts (less than or equal to 10 nA) increased the activity of these neur
ones. However, at increased currents (10-60 nA), it had a predominantl
y depressant effect. Application of selective 5-HT1A receptor antagoni
sts, (+/-)-pindolol or WAY-100635, attenuated the excitatory responses
evoked by 5-HT. 3 Ionophoresis of the 5-HT1A receptor agonist, 8-hydr
oxy-2-(di-n-propylamino)tetralin (8-OH-DPAT) (5-30 nA) increased the f
iring rate of 19 and decreased that of 67 of the 104 vagal neurones te
sted. Other 5-HT1A receptor agonists, flesinoxan and N,N-di-n-propyl-5
-carboxamidotryptamine (DP-5-CT) also had predominantly depressant eff
ects. 4 (+/-)-Pindolol attenuated excitations but not inhibitions evok
ed by 8-OH-DPAT. Surprisingly, WAY-100635 and 8-OH-DPAT produced the s
ame effect on these neurones and when applied together, WAY-100635 fai
led to attenuate the 8-OH-DPAT responses. 5 Dorsal raphe neurones were
identified by their low, regular firing rate and their subsequent his
tological localization. 8-OH-DPAT reversibly reduced the activity in a
ll 7 neurones tested and this was antagonized by WAY-100635 in all 3 n
eurones tested. 6 In conclusion, 5-HT applied to vagal preganglionic n
eurones evokes excitatory and inhibitory responses. The excitatory, bu
t not the inhibitory responses may be mediated, at least in part, by a
ctivation of 5-HT1A receptors.