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THE ANATOMY AND PHYSIOLOGY OF AN EXTRA-NASAL CHEMOSENSORY SYSTEM IN THE SEA LAMPREY
Barbara Zielinski1,2 and Réjean Dubuc3,4
1Department of Biological Sciences, University of Windsor, Windsor, Ontario.
2Great Lakes Institute for Environmental Research, University of Windsor, Windsor Ontario
3Groupe de Recherche en Activité Physique Adaptée, Department of Exercise Science,
Université du Québec à Montréal, Montréal, Québec
4Groupe de Recherche sur le Système Nerveux Central, Department of Neurosciences,
Université de Montréal, Montréal, Québec.
Behaviors such as migration, reproduction, and feeding are driven by chemical cues in the sea lamprey. Under previous GLFC funding, we characterized the neural substrate underlying olfactory-motor behavior in lampreys and these studies have been the basis for research on combinations of olfactory molecules that could attract or repulse lampreys to eventually control their behavior in the environment. However, chemoreception is not restricted to olfaction; solitary chemosensory cells (SCCs) are present in the skin of aquatic vertebrates, including brook and silver lampreys. During the granting period, we investigated the presence of SCCs in the sea lamprey. We showed that sea lampreys possess cutaneous papillae that contain numerous microvilli-bearing cells. These papillae are located at four sites - around the nostril, around the oral disc, on the posterior rim of the branchial openings, and on the dorsal fins. Through the application of immunochemical techniques, we showed that these microvillar cells have the biochemical properties contingent with SCCs. An assessment of the SCC density on the branchial papillae at different life stages established that SCCS are more numerous in adult lampreys, thus suggesting a role in adult-specific behaviors such as: upstream migration, nest site selection and/or spawning. Physiological experiments confirmed the chemosensory function of these cells and established their response profile. Then, we showed that depending on their location, papillar SCCs are innervated by different cranial or spinal nerves; branchial papillae are innervated by the glossopharyngeal and vagus nerve, oral and nasal papillae are innervated by the trigeminal nerve, and fin papillae are innervated by spinal dorsal roots. The central projection pattern of neurons innervating oral and branchial papillae, however, is similar, and suggests a strong link to the motor system. This motor link is supported by physiological experiments showing that glossopharyngeal and vagus sensory inputs are relayed to the reticulospinal (RS) cells, the command neurons for swimming. Indeed the results show that chemical activation of the branchial SCCs could induce sustained activity in RS cells. Altogether, these findings provide a whole new way of looking at how lampreys respond to semiochemicals in their environment, thus generating important new knowledge for population management.