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  • Title: Role of Aplysia cell adhesion molecules during 5-HT-induced long-term functional and structural changes.
    Author: Han JH, Lim CS, Lee YS, Kandel ER, Kaang BK.
    Journal: Learn Mem; 2004; 11(4):421-35. PubMed ID: 15254221.
    Abstract:
    We previously reported that five repeated pulses of 5-HT lead to down-regulation of the TM-apCAM isoform at the surface of Aplysia sensory neurons (SNs). We here examined whether apCAM down-regulation is required for 5-HT-induced long-term facilitation. We also analyzed the role of the cytoplasmic and extracellular domains by overexpressing various apCAM mutants by DNA microinjection. When TM-apCAM was up-regulated in SNs by DNA microinjection, five pulses of 5-HT failed to produce either synaptic facilitation or an enhancement of synaptic growth, suggesting that down-regulation of apCAM is required for 5-HT-induced EPSP enhancement and new varicosity formation. However, disrupting the extracellular domain function of overexpressed apCAM with a specific antibody restored 5-HT-induced excitatory postsynaptic potential increase but not synaptic growth. The overexpression of the MAP Kinase mutant of TM-apCAM, which is not internalized by 5-HT, inhibited new varicosity formation, but did not inhibit excitatory postsynaptic potential increase. Deletion mutants containing only the cytoplasmic portion of apCAM blocked 5-HT-induced synaptic growth but not excitatory postsynaptic potential increase. Thus, our data suggest that TM-apCAM may act as a suppressor of both synaptic-strength enhancement in pre-existing synapses and of new synaptic varicosity formation in the nonsynaptic region, via different mechanisms.
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