Release of endogenous serotonin from two identified serotonin-containing neurones and the physiological role of serotonin re-uptake.
1. The amounts of endogenous serotonin (5-HT) released into the medium by the cerebro-buccal ganglionic ring of Aplysia californica incubated in artificial sea water (ASW) were measured. The rate of spontaneous 5-HT release varied between 0.4 and 1.2 p-mole per hour, which is less than 1% of the total 5-HT present in this preparation.2. Direct stimulation of the ordinarily silent 5-HT-containing giant cerebral neurones resulted in a 80-100% increase of the 5-HT released, but only when the 5-HT uptake was blocked by chlorimipramine (1-10 muM).3. High K(+) media (50 mM) also caused a significant increase in the amount of 5-HT released from the preparation provided that chlorimipramine (1-10 muM) was present in the incubation fluid.4. Co(2+) ions (10-30 mM) added to the incubating medium blocked the spontaneous leak of endogenous 5-HT as well as the release, in the presence of chlorimipramine, evoked either by stimulation of the 5-HT-giant cerebral neurones or high K(+)-media.5. In the presence of chlorimipramine or desmethylimipramine, the duration and/or the amplitude of the excitatory or the inhibitory synaptic potentials evoked in the buccal neurones by the stimulation of the 5-HT giant cerebral neurones were markedly enhanced.6. These results strongly support the idea that 5-HT is the synaptic transmitter released at the excitatory and inhibitory junctions established by the 5-HT giant cerebral neurones in the ipsilateral buccal ganglia. In addition, they underline the role of amine re-uptake in the physiological inactivation of 5-HT as a transmitter.
D000200:Action Potentials / Q000187:drug effects; D000818:Animals; D001048:Aplysia; D002997:Clomipramine / Q000494:pharmacology; D003891:Desipramine / Q000494:pharmacology; D066298:In Vitro Techniques; D008564:Membrane Potentials / Q000187:drug effects; D009474:Neurons / Q000502:physiology*; D011188:Potassium / Q000494:pharmacology; D012636:Secretory Rate / Q000187:drug effects; D012701:Serotonin / Q000378:metabolism / Q000502:physiology*; D009435:Synaptic Transmission
D012701:Serotonin; D002997:Clomipramine; D011188:Potassium; D003891:Desipramine