. The Biological bulletin. Biology; Zoology; Biology; Marine Biology. NEUROMODULATION IN APLYSIA 259. r VARICOSITIES BRANCH POINTS M Figure 9. Simplified diagram illustrating the activation of parallel cAMP-dependent pathways by neurites that release serotonin (5-HT) onto the cell bodies of sensory neurons. Transient elevation of cAMP in the soma produces rapid but short-lasting effects on membrane con- ductance (\i>lul lines) via activation of protein kinase (PK). In addition, it produces persistent effects on membrane conductance and neuronal structure (dashedlines). The mechanism underly
. The Biological bulletin. Biology; Zoology; Biology; Marine Biology. NEUROMODULATION IN APLYSIA 259. r VARICOSITIES BRANCH POINTS M Figure 9. Simplified diagram illustrating the activation of parallel cAMP-dependent pathways by neurites that release serotonin (5-HT) onto the cell bodies of sensory neurons. Transient elevation of cAMP in the soma produces rapid but short-lasting effects on membrane con- ductance (\i>lul lines) via activation of protein kinase (PK). In addition, it produces persistent effects on membrane conductance and neuronal structure (dashedlines). The mechanism underlying these long-term ef- fects is not known, but regulation of gene expression and protein synthesis appears to be involved. Because cAMP in sensory neurons is broken down rap- idly (Bernier et a/., 1982; Schwartz ct ai. 1983), long- term changes must depend on a more persistent cellular process. A likely model, then, is one in which the transient cAMP signal activates at least two pathways (Fig. 9). cAMP produces a rapid but short-lasting modulation of membrane currents, decreasing membrane conductance. In addition, a slower but more enduring mechanism is also activated, producing long-term changes in membrane conductance and cell structure. The mechanisms under- lying these long-term alterations are not known, but reg- ulatory pathways that alter protein synthesis or gene expression are presumably involved. Indeed, long-term enhancement of synaptic transmission and membrane excitability are affected by inhibitors of protein and RNA synthesis (Montarolo et ai, 1986; Dale et ai. 1987; Schacher et ai, 1988). In addition, serotonin appears to activate regulatory proteins that bind to DNA (Dash et ai, 1990). As a consequence, messenger RNA is synthe- sized (Zwartjes et ai, 1990), and the incorporation of amino acids into proteins of sensory neurons is altered (Barzilai et ai, 1989; Eskin et ai, 1989). Other mecha- nisms, such as post-translational modification of proteins (Greenber
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Keywords: ., bookauthorlilliefrankrat, booksubjectbiology, booksubjectzoology
