The nematode, Caenorhabditis elegans, has become an expedient model for studying neurotransmission. C. elegans is unique among animal models, as the anatomy and connectivity of its nervous system has been determined from electron micrographs and refined by pharmacological assays. In this video, we describe how two complementary neural stimulants, an
acetylcholinesterase inhibitor, called
aldicarb, and a
gamma-aminobutyric acid (
GABA) receptor antagonist, called
pentylenetetrazole (PTZ), may be employed to specifically characterize signaling at C. elegans neuromuscular junctions (NMJs) and facilitate our understanding of antagonistic neural circuits. Of 302 C. elegans neurons, nineteen GABAergic D-type motor neurons innervate body wall muscles (BWMs), while four GABAergic neurons, called RMEs, innervate head muscles. Conversely, thirty-nine motor neurons express the excitatory
neurotransmitter,
acetylcholine (ACh), and antagonize
GABA transmission at BWMs to coordinate locomotion. The antagonistic nature of GABAergic and
cholinergic motor neurons at body wall NMJs was initially determined by
laser ablation and later buttressed by
aldicarb exposure. Acute
aldicarb exposure results in a time-course or dose-responsive
paralysis in wild-type worms. Yet, loss of excitatory ACh transmission confers resistance to
aldicarb, as less ACh accumulates at worm NMJs, leading to less stimulation of BWMs. Resistance to
aldicarb may be observed with ACh-specific or general synaptic function mutants. Consistent with antagonistic
GABA and ACh transmission, loss of
GABA transmission, or a failure to negatively regulate ACh release, confers
hypersensitivity to
aldicarb. Although
aldicarb exposure has led to the isolation of numerous worm homologs of neurotransmission genes,
aldicarb exposure alone cannot efficiently determine prevailing roles for genes and pathways in specific C. elegans motor neurons. For this purpose, we have introduced a complementary experimental approach, which uses PTZ. Neurotransmission mutants display clear phenotypes, distinct from
aldicarb-induced
paralysis, in response to PTZ. Wild-type worms, as well as mutants with specific inabilities to release or receive ACh, do not show apparent sensitivity to PTZ. However,
GABA mutants, as well as general synaptic function mutants, display anterior convulsions in a time-course or dose-responsive manner. Mutants that cannot negatively regulate general
neurotransmitter release and, thus, secrete excessive amounts of ACh onto BWMs, become paralyzed on PTZ. The PTZ-induced phenotypes of discrete mutant classes indicate that a complementary approach with
aldicarb and PTZ exposure paradigms in C. elegans may accelerate our understanding of neurotransmission. Moreover, videos demonstrating how we perform pharmacological assays should establish consistent methods for C. elegans research.