Serotonin-mediated endocytosis of apCAM: an early step of learning-related synaptic growth in Aplysia.
The long-term facilitation of synaptic efficacy that is induced by serotonin in dissociated cell cultures of sensory and motor neurons of Aplysia is accompanied by the growth of new synaptic connections. This growth is associated with a down-regulation in the sensory neuron of Aplysia cell adhesion molecules (apCAMs). To examine the mechanisms of this down-regulation, thin-section electron microscopy was combined with immunolabeling by gold-conjugated monoclonal antibodies specific to apCAM. Within 1 hour, serotonin led to a 50% decrease in the density of gold-labeled complexes at the surface membrane of the sensory neuron. This down-regulation was achieved by a heterologous, protein synthesis-dependent activation of the endosomal pathway, which leads to internalization and apparent degradation of apCAM. The internalization is particularly prominent at sites where the processes of the sensory neurons contact one another and may act there to destabilize process-to-process contacts that normally inhibit growth. In turn, the endocytic activation may lead to a redistribution of membrane components to sites where new synapses form.
Bailey
C H
CH
Center for Neurobiology and Behavior, College of Physicians and Surgeons of Columbia University, New York, NY.
Chen
M
M
Keller
F
F
Kandel
E R
ER
D000818:Animals; D000841:Anisomycin / Q000494:pharmacology; D000911:Antibodies, Monoclonal; D001048:Aplysia / Q000502:physiology*; D015815:Cell Adhesion Molecules / Q000378:metabolism*; D002462:Cell Membrane / Q000378:metabolism / Q000648:ultrastructure; D002478:Cells, Cultured; D003034:Coated Pits, Cell-Membrane / Q000378:metabolism / Q000648:ultrastructure; D004705:Endocytosis / Q000187:drug effects*; D007150:Immunohistochemistry; D008854:Microscopy, Electron; D009046:Motor Neurons / Q000502:physiology / Q000648:ultrastructure; D009475:Neurons, Afferent / Q000502:physiology / Q000648:ultrastructure; D012701:Serotonin / Q000494:pharmacology*; D013569:Synapses / Q000502:physiology* / Q000648:ultrastructure; D014909:Wheat Germ Agglutinins / Q000378:metabolism
D000911:Antibodies, Monoclonal; D015815:Cell Adhesion Molecules; D014909:Wheat Germ Agglutinins; D012701:Serotonin; D000841:Anisomycin