Direct Postsynaptic Responses to Stimulation of Serotonin-containing Neurones

Abstract

THERE is one giant serotonin-containing neurone in each metacerebral ganglion of the slug Limax maximus and of the snail Helix pomatia. These cells can be identified histochemically and their content of serotonin can be measured by bioassay of individually dissected neurones. The amine is localized in small electron dense granules in the cytoplasm of these cells and also, in certain conditions, in particles with the appearance of lysosomes (ref. 1 and unpublished data of G. A. C. and N. N. Osborne). Dye injection experiments with ‘Procion Yellow’, using the method of Stretton and Kravitz², show that each giant neurone in Helix pomatia gives off three main axonal branches. One branch passes across the cerebral commissure to the other group of cerebral ganglia, another can be traced to the ipsilateral cerebral-buccal connective, and the third passes into the ipsilateral exterior lip nerve.