Properties of an identified dopamine containing neurone from the snail Helisoma trivolvis

Abstract

1. The giant neurone in the left pedal ganglion of Helisoma trivolvis is homologous with the giant dopamine containing neurone of Planorbis corneus. The neurones have a similar morphology, and both react with glyoxylic acid to produce fluorescence indicative of dopamine. The neurone is referred to as the giant dopaminergic neurone (GDN). 2. Conditions for the extension of neurites and the formation of chemical junctions in culture have been determined for the H. trivolvis GDN. 3. Some electrical properties of the GDN were altered when it was maintained in culture. The peak spike amplitude was increased, action potential half width was decreased and the firing pattern changed. 4. In culture, the GDN formed chemical connections only with neurones with which it was known to form chemical connections in-situ. The chemical connections were of the same sign as those observed in-situ. They formed rapidly within 18 hours, but were not stable and were lost within 48 hours to be replaced by electrical connections. 5. Chemical junctions formed in both directions between the GDN and the large serotonergic neurone (LSN). The direction in which junctions formed could be influenced by plating each neurone out at different times. 6. Local application of dopamine to the axon or axon hillock, but not the soma of the isolated GDN, evoked a fast strongly desensitising, depolarising response. 7. Intracellular perfusion of the GTP analogue GDP-?-S abolished the hyperpolarising effect of dopamine but left the fast depolarising effect intact. 8. Dopamine evoked small unitary outward currents, in outside-out patches prepared from the axon and axon hillock of the isolated GDN. 9. The results suggest that the fast depolarising response to dopamine of the GDN and its follower neurones is directly ligand gated. This is the first evidence of an ion channel that is directly gated by dopamine.