The Role of Serotonin in Tritonia diomedea

The within-swim pattern of cycle periods in Tritonia swimmingchanged when the behavior was repeatedly elicited suggestingthat an excitatory process reaches a ceiling or wanes over repeatedtrials. Exposure to subthreshold stimuli enhanced swimming inresponse to a subsequent super-threshold stimulus, perhaps usinga similar excitatory process. In reduced preparations, subthresholdstimuli increased action potential activity in identified serotonergicneurons. Finally, stimulating serotonergic neurons enhanceda fictive swimming pattern, much like subthreshold stimuli enhancedthe swimming behavior. Both within-swim and across-swim changesin the swimming behavior may be caused by increased activityin identified serotonergic neurons. Comparative study suggeststhat ancestral serotonergic systems facilitated network oscillationsfor the production of rhythmic behaviors such as feeding andlocomotion. This concept of serotonin as oscillatizer is usedto explain the role of serotonergic neurons in Tritonia. Implicationsfor human mental health are discussed.