(full paper is archived in the Miller Library)
Title: The effect of a snail secretion on serotonin-induced activity in the buccal ganglia of Aplysia californica
Student Author(s): Mak, Caroline
Faculty Advisor(s): Gilly, William
%E Thompson, Stuart
Location: Final Papers Biology 176H
Date: June 2001
Abstract: The snail Calliostoma canaliculatum secretes a yellow mucous ('Yellow Stuff' or YS) in response to attack from predatory starfish Pisaster giganteus and Pycnopodia helianthoides. Previous studies have shown that YS inhibits the opening of voltage-gated potassium channels, and the active component responsible for this action is proposed to be a serotonin dimer derivative, 6-bromo-2-mercaptotryptamine. Because serotonin is a crucial neurotransmitter in invertebrates, components of YS may also have an effect on the behaviour of neural networks where serotonin plays a role. Several lines of experiments were carried out to identify any possible relationships between the actions of these two compounds. Behavioural studies on the brittle star Ophiopteris papillosa, showed a similar response to both these compounds immediate arm retraction. Results from these experiments established a biologically relevant concentration of YS for further testing. Control experiments carried out in Shaker potassium channels expressed in Xenopus oocytes demonstrated that at this concentration, YS did not lead to a slowing of K-current activation. Additional experiments were performed using the buccal ganglia of Aplysia californica. B cells in this ganglia contain serotonin receptors and many of the cells and synaptic connections are modulated by serotonin. Single electrode recordings from B cells after application of serotonin demonstrated a marked increase in spontaneous activity (action potentials and post-synaptic potentials). Subsequent application of YS significantly decreased this activity, and further application of serotonin after YS had been washed away, renewed activity. This suggests that in the neural circuits involved in stimulation by serotonin, YS may function as an antagonist, and therefore Yellow Stuff may be acting in invertebrates via neuromodulatory pathways that involve serotonin.