Central serotonergic modulation of heart rate in Aplysia californica.

Abstract

Studies have shown that sensitization is mediated in Aplysia californica by serotonin. This process, which causes both short-term and long-term enhancement of defensive behaviors such as gill withdrawal or tail withdrawal, can be mimicked by the application of serotonin to the nervous system. However, the cardiovascular response to sensitization has received little attention. In a previous study Litowitz demonstrated that in vitro heart rate increased immediately following sensitizing stimulation and remained elevated for at least 90 minutes (1994). This study explores the hypothesis that serotonin acts as a neuromodulator which promotes sensitization of heart rate, and when applied to the nervous system, duplicates the cardiovascular response produced by sensitizing noxious stimuli. In this experiment, the cardiovascular response to serotonin was monitored in an in vitro preparation. Heart rate was recorded following three sequential applications of serotonin to the head ganglia (5x10-5M or 5x10-6M). Significant short-term increases in heart rate lasting 10 minutes were observed after each application of 5x10-5M serotonin. These results indicate that serotonin, acting at the central nervous system, can promote short-term enhancement of cardiovascular function.