SKIN CHEMORECEPTOR ACTIVATION AND MOTOR BEHAVIOR
Chemoreception is not restricted to olfaction; solitary chemosensory cells (SCCs) are present in the skin of fish and other aquatic vertebrates, including brook and silver lampreys. With GLFC funding, we have investigated SCCs in the sea lamprey. In adults, these are numerous on cutaneous papillae around the nostril, around the oral disc, around the gill pores, and on the dorsal fins. Depending on their location, SCCs are innervated by different nerves, but their central projection pattern is similar, as each links to motor control centers. We have confirmed chemosensory function of gill SCCs by recording responses to chemical stimuli. We now propose to characterize the response profiles of these different populations of papillar SCCs as well as the movement responses induced by their chemical stimulation using an in vitro approach. We will identify the molecules eliciting the most potent movement responses. Our general hypothesis is that different semiochemicals exert differential effects on the nasal, oral, branchial, and fin SCCs populations, and different motor behaviors (movements) will ensue. The goal of the proposed research is to provide new biological tools for sea lamprey population management by establishing which molecules are the most effective at activating the different SCC populations and inducing motor behavior.
OBJECTIVES: We will pursue three objectives: 1) to determine and compare the chemical response profiles of the SCCs on oral, nasal, branchial, and fin papillae by testing isolates of naturally occurring stimuli; 2) to characterize in vitro "behavioral" responses induced by stimulating the four SCC populations; 3) to isolate the molecules responsible for eliciting SCC responses and the ensuing motor responses using an activity guided fractionation strategy.
METHODS: We will address these three objectives using electrophysiological and biochemical techniques. 1) The chemical response profiles of the 4 SCCs populations will be determined by testing solutions of naturally occurring stimuli using an in vitro skin preparation. Extracellular electrodes will be placed over the papillae to record multiunit activity during chemical stimulation. Chemical stimulation will be delivered either by a glass micropipette connected to a pressure ejection system or by a solenoid regulated system. Stimuli will include water conditioned by prey, water from spawning habitat, as well as pheromones but the emphasis will be put on putative repellents such as predator odors, alarm substances, territorial pheromones, and necromones. The strength of the response of the SCCs will be used as an indicator of stimulus potency. 2) The behavioral responses to stimuli found to activate the SCCs will be characterized in an in vitro preparation including the SCCs system and the CNS, using motor nerve roots recordings as a monitor of fictive behavior (the in vitro corollary of behavior). 3) We will rely on an activity guided fractionation strategy to identify the active compounds of the stimulatory naturally occurring stimuli. Solutions of naturally occurring stimuli will be subjected to solid phase extraction, fractionated with liquid chromatography, and examined for potency by electrophysiological recording as described in objective 1. The chemical structures of active components will be elucidated by either nuclear magnetic resonance or crystallographic X-ray diffraction, and further confirmed by spectra of synthesized compounds.
RELEVANCE TO PROGRAM: This proposal is submitted to the chemosensory communication systems area. The use of pheromones and chemical repellents are among the most promising strategies for managing sea lamprey populations. While these methods rely on olfactory stimuli, lampreys also possess a diffuse chemosensory system. Selective aversive or attractive SCC agonists may act synergistically with molecules stimulating the olfactory system to maximize lamprey attraction or deterrence while minimally irritating non-target species.
DELIVERABLES/PRODUCTS: The proposed experiments will provide significant gains in understanding how the diffuse chemosensory system affects movement in the sea lamprey, and in identifying particular putative repellents that stimulate this system, such as alarm cues. The most significant deliverables will be the identification of compounds that act on the SCC system to produce strong motor responses, as well as knowledge of the underlying neural mechanisms. These findings will be published in peer-reviewed journals. This project will support the training of students and post-doctoral fellows.