The glial cells of the cerebral ganglia of Helix pomatia L. (Gastropoda, Pulmonata). II. Uptake of ferritin and 3H-glutamate.

Abstract

1. With Helix pomatia intracerebral injections of ferritin were carried out (maximal incubation time: 45 min). First, the marker spreads with time via the enxtracellular space throughout the cerebral ganglia and, secondly, is transported out of the ganglia. Electron microscopical studies showed that all glial cell types take up great amounts of ferritin by endocytosis. The plasmatic glial cells at the periphery incorporate more of the marker than the filamentous glial cells in the centre. No uptake of ferritin by neurons or axons was observed. In vitro studies proved that ferritin can penetrate from the connective tissue capsule into the ganglia only after disruption of the neural lamella and damaging of the peripheral glial processes. 2. 3H-glutamate, a putative transmitter of the CNS of Helix pomatia, was injected into the hemocoel of active snails (incubation times: 15 min, 1h, 6h, 3d). Light microscopical evaluation of radioautographs showed that great quantities of the tracer penetrate into the ganglia. The bulk of it is taken up by glial cells, whereas the neurons exhibit only small amounts of the tracer. The studies with ferritin as well as those with 3H-glutamate indicate that the glial cells of the cerebral ganglia of Helix pomatia act as a "hemolymph-neuron barrier". A dominant role of the plasmatic glial cells according to these processes is discussed.