Behavioral and Neurophysiological Examination of The C. elegans Neuromuscular Junction

Parker H Stafford, Katrina B Mar, Samuel M Moss

Abstract


Caenorhabditis elegans is a model organism with well-defined neurophysiological characteristics.  Movement in C. elegans is mediated through concurrent contraction on one side of the body and relaxation on the other at the neuromuscular junction (NMJ).  Contraction and relaxation are mediated through cholinergic and GABAergic signaling respectively.  The goal of the current study was to further elucidate these mechanisms of mobility via exposure to nicotine, an acetylcholine receptor agonist, and toluene, which produces mobility impairment in mice, humans, and C. elegans.  Results confirm that acute 10-minute toluene exposure decreases overall motor responsiveness measured one hour later (p<0.05). This behavioral result was correlated with an increase in the expression of unc-47 transcripts (p<0.001; vesicular GABA transporter) and a corresponding increase in synaptobrevin/SNB-1::GFP in GABA motor neurons (p<0.05; synaptic vesicle protein). A modest, yet significant decrease in unc-49 transcripts (p<0.01; GABA-A receptor subunits) was also observed; however, UNC-49::GFP expression did not show a significant reduction (p>0.10). Finally, mobility impairment following acute toluene exposure was reversed with 30 μM nicotine application (p>0.10). Interestingly, application of 30 μM nicotine alone produced impaired mobility at a level similar to the toluene alone condition and resulted in a significant increase in post-synaptic punc-49::UNC-49::GFP (p<.05) but no change in presynaptic punc-47::SNB-1::GFP expression.  These results suggest that toluene exposure is acting pre-synaptically to increase GABA signaling and that nicotine exposure causes an up-regulation of GABA-A receptors.  Taken together, these findings support that the mobility impairment following exposure to these two drugs may result from an imbalance between cholinergic and GABAergic signaling.  Current studies aiming to further our understanding of the neurophysiology of C. elegans mobility examine responsiveness, relative mRNA expression and GFP expression following nicotine, toluene, and GABA application.


Keywords


Toluene, C. elegans, Nicotine

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