Spontaneous Electrical Activity and Spikes in the Tail of Marine Cercariae

Spontaneous electrical activity is recorded in two species of marine cercariae, Cryptocotyle lingua and Himasthla elongata, with different types of swimming—by glass microelectrode recordings. Slow local field potentials (sLFPs) of low amplitude and fast high amplitude action potentials (APs) are found. The shape of the sLFPs is different in the species and correlates with the type of swimming. Fast high amplitude APs are recorded for the first time in cercariae. The limited number of APs included in the swimming pattern of larva suggests a key role for the spiking neurons in initiating the motility pattern in the cercaria and needs further research. 1. Introduction Free-living trematode larvae, cercariae, are nonfeeding minute organisms whose only role is to find and infect the next host, a step which is crucial for the survival of the parasite species. In the case of important diseases, such as schistosomiasis and cercarial dermatitis, cercariae represent the infective stage penetrating actively the human skin. Much basic information about the nervous system of trematodes is needed before the development of antiparasitic drugs is possible. The finding of the neuromechanisms of initiation and regulation of motility patterns in the larva is among the essential questions to be answered. Cercariae often demonstrate fast sensory-motor reactions to different stimuli; for reference see Haas [1]. Small size, short life span of the larva organisms, and the absence of visually identified neurons bring technical difficulties in the study of the cercarial nervous system. The basic physiology of larval motility has not been studied in detail. No up-to-date information on the rapid signal transmission by means of action potentials in the nervous system of cercariae is available. Spontaneous electrical activity has been investigated only in cercariae of Proterometra macrostoma (Faust, 1918) Horsfall, 1933, by suction electrode recording; for reference see Rowley et al. [2]. Swimming cercariae show distinctive behavioural patterns related to their strategy of host finding and infection and can be divided into two groups: cercariae with a continuous swimming pattern and cercariae with an intermittent type of swimming pattern, where active phases alternate with passive phases when the cercariae soar in the water [1]. The difference in the swimming patterns correlates with the details of morphology in the tail—the larval locomotory organ, which is shown for two species chosen for the present research [3]. Here, we compare the electrical activity in cercariae of