Synaptic contacts on glial cells in the abdominal ganglion of Aplysia californica.

Two types of glial cells have been identified in the neuropil and in the subcapsular space of the abdominal ganglion of Aplysia californica. In the neuropil, a first type of glial cell has a light staining cytoplasm and gives rise to processes which may contain bundles of filaments, a flocculent material or bundles of microtubules and membranous sacs. Synaptic contacts have been seen very rarely on their somata and more frequently on their "filamentous" and "flocculent" processes. A second type of glial cell has a darkly staining cytoplasm and gives rise to dense processes. Synaptic contacts are frequently seen on these processes. In the subcapsular zone, there are also two types of glial cells, one with a clear and the other with a dense cytoplasm. The processes of the clear glial cells contain glycogen-like particles and sometimes bundles of filaments. These processes surround the bundles of neuronal profiles which form the perisomatic plexus. Such enveloping processes receive synaptic contacts from the neuronal profiles in the bundles. The dense glial cells of the subcapsular zone also receive synaptic contacts, but this is a rare occurrence.