ABSTRACT
By means of newly developed electron microscopical techniques (electron spectroscopic imaging, ESI; electron energy loss spectroscopy, EELS; immunogold labelling) a specific accumulation of endogenous calcium within the synaptic cleft and a distinct localization of a high-affinity Ca(2+)-ATPase at the inner sides of the pre- and postsynaptic membrane of nerve cells from fish brain have been demonstrated. Additionally, a differentiation-dependent expression of polysialoganglioside epitopes on the outer surface of nerve terminals in clustered arrangements was demonstrated using their ultracytochemical detection by means of the monoclonal antibody Q211. These results which are in agreement with parallel biochemical investigations on modulatory effects of exogenous gangliosides on a high-affinity Ca(2+)-ATPase in the CNS of vertebrates support our hypothesis that Ca(2+)-ganglioside complexes act as modulators for the processes of synaptic transmission and long-term neuronal adaptations.