Monoaminergic Orchestration of Motor Programs in a Complex C. elegans Behavior
Figure 7
Model: Tyramine orchestrates the C. elegans escape response through the activation of ionotropic and metabotropic receptors.
(A) Silhouettes of the four phases of the C. elegans anterior touch escape response. Images were adapted from a movie of an animal executing an escape response. See text for details. (B) Schematic representation of the neural circuit that controls the C. elegans escape response. Synaptic connections (triangles) and gap junctions (bars) are as described by White et al. (1986) [20]. Green plus signs represent excitatory connections, and red minus signs indicate inhibitory connections. Sensory neurons are shown as triangles, command neurons required for locomotion are hexagons, and motor neurons are depicted as circles. The compass indicates anterior (A), posterior (P), ventral (V), and dorsal (D) directions. C. elegans sinusoidal locomotion is propagated by alternatively contracting and relaxing opposing ventral and dorsal body wall muscles of the animal using cholinergic (DB and VB for forward and DA and VA for backward locomotion) and GABAergic (VD and DD) motor neurons. Anterior touch induces the activation of the tyramine release from the RIM motor neurons (blue cells). Solid lines represent synaptic activation of LGC-55 in neurons and muscles (purple cells) that result in the inhibition of forward locomotion and suppression of head movement in the initial phase of the escape response. Dashed lines represent extrasynaptic activation of SER-2 in the GABAergic VD motor neurons (green cells). The activation of SER-2 causes a decrease in GABA release on the ventral side animal. This allows the hypercontraction of muscles on the ventral side of the animal, thus facilitating the execution of a ventral omega turn.