Acute nicotine exposure and modulation of a spinal motor circuit in embryonic zebrafish

The zebrafish model system is ideal for studying nervous system development. Ultimately, one would like to link the developmental biology to various aspects of behavior. We are studying the consequences of nicotine exposure on nervous system development in zebrafish and have previously shown that chronic nicotine exposure produces paralysis. We also have made observations that the embryos moved in the initial minutes of the exposure as the bend rates of the musculature increased. This nicotine induced behavior manifests as an increase in the rate of spinal musculature bends, which spontaneously begin at approximately 17 h post fertilization. The behavioral observations prompted the systematic characterization of nicotine-induced modulation of zebrafish embryonic motor output; bends of the trunk musculature. We first characterized embryonic motor output in zebrafish embryos with and without their chorions. We then characterized the motor output in embryos raised at 28 degrees C and 25 degrees C. The act of dechorionation along with temperature influenced the embryonic bend rate. We show that nicotine exposure increases embryonic motor output. Nicotine exposure caused the musculature bends to alternate in a left-right-left fashion. Nicotine was able to produce this phenotype in embryos lacking supraspinal input. We then characterize the kinetics of nicotine influx and efflux and demonstrate that nicotine as low as 1 microM can disrupt embryonic physiology. Taken together, these results indicate the presence of nicotinic acetylcholine receptors (nAChRs) associated with embryonic spinal motor circuits early in embryogenesis.