A comparison of the responses of cortical neurones to iontophoretically applied tryptamine and 5-hydroxytryptamine in the rat.
Tryptamine, applied iontophoretically to cortical neurones, had predominantly depressant effects. In contrast 5-hydroxytryptamine (5HT) exhibited excitatory effects on many neurons. On over 40% of neurones responsive to both 5HT and tryptamine the amines had opposite effects. A comparison of the magnitude of the depressant responses revealed that tryptamine was a much more effective depressant agent than 5HT. The iontophoretic transport numbers for 5HT and tryptamine were similar, indicating that the apparently greater potency of tryptamine was genuine. Electrolytic lesions of the medial forebrain bundle did not alter the relative effects of the amines, suggesting that there was a post-synaptic origin for the difference. Finally, the indoleamine antagonist metergoline was found to block selectively the tryptamine responses with little effect on 5HT responses, at low concentrations. The results suggest that tryptamine may possess post-synaptic effects unrelated to direct agonist actions at 5HT receptors.
D000818:Animals; D001831:Body Temperature / Q000187:drug effects; D002540:Cerebral Cortex / Q000187:drug effects*; D003864:Depression, Chemical; D007478:Iontophoresis; D008297:Male; D008711:Metergoline / Q000494:pharmacology; D009474:Neurons / Q000187:drug effects*; D051381:Rats; D011919:Rats, Inbred Strains; D012701:Serotonin / Q000494:pharmacology*; D014363:Tryptamines / Q000378:metabolism / Q000494:pharmacology*
D014363:Tryptamines; D008711:Metergoline; D012701:Serotonin