Properties of an identified dopamine-containing neurone in culture from the snail Helisoma.

The giant neurone in the left pedal ganglion of the snail Helisoma trivolvis is homologous with the giant dopaminergic neurone of Planorbis corneus, because the neurones have a very similar location and morphology, and react similarly with glyoxylic acid to produce an intense blue fluorescence, indicating the presence of dopamine. Each of these neurones is therefore referred to as a giant dopaminergic neurone, or GDN. Conditions for the extension of neurites and formation of chemical junctions in culture have been determined for the H. trivolvis GDN, and compared with other neurones from this species. The pattern of neurites that extended from the neurone was indistinguishable from that of another identified aminergic neurone, the large serotonergic neurone (LSN), but differed markedly from many other central neurones. However, the type of substrate also greatly affected the pattern of the neurites observed. Some of the electrical properties of the GDN in culture differed from those recorded in situ: peak spike amplitude was increased, spike half-width reduced and the firing pattern of the neurone was altered. However, the resting membrane potential was very similar. The GDN formed chemical and electrical junctions in culture. The chemical junctions formed were of the same type as those found in situ. They formed rapidly, within 18 h after plating, but were not stable and were lost within 48 h, to be replaced by a non-rectifying electrical junction. A chemical junction may form in either direction between the GDN and the LSN, but only rarely did such junctions allow transmission in both directions, as observed in situ. Experiments in which neurones were plated out at different times suggested that the direction of formation of the chemical junction was not dependent on the degree or state of neurite extension.