Pharmacological identification of cholinergic receptor subtypes: modulation of locomotion and neural circuit excitability in Drosophila larvae

• Published in: Neuroscience 2019-07, Vol.411, p.47-64
• Main Authors: Malloy, Cole A., Somasundaram, Eashwar, Omar, Aya, Bhutto, Umair, Medley, Meagan, Dzubuk, Nicole, Cooper, Robin L.
• Format: Article
• Language: English
• Subjects: acetylcholine; Animals; behavior; Behavior, Animal - drug effects; Cholinergic Agonists - pharmacology; Cholinergic Antagonists - pharmacology; Drosophila; Drosophila melanogaster; electrophysiology; Larva; Locomotion - drug effects; Motor Activity - drug effects; Neural Pathways - drug effects; Neurons - drug effects; pharmacology
• ISSN: 0306-4522; 1873-7544
• DOI: 10.1016/j.neuroscience.2019.05.016

Acetylcholine (ACh) is an abundant neurotransmitter and neuromodulator in many species. In Drosophila melanogaster ACh is the neurotransmitter used in peripheral sensory neurons and is a primary excitatory neurotransmitter and neuromodulator within the central nervous system (CNS). The receptors that facilitate cholinergic transmission are divided into two broad subtypes: the ionotropic nicotinic acetylcholine receptors (nAChRs) and the metabotropic muscarinic acetylcholine receptors (mAChRs). This receptor classification is shared in both mammals and insects; however, both the pharmacological and functional characterization of these receptors within the Drosophila nervous system has lagged behind its mammalian model counterparts. In order to identify the impact of ACh receptor subtypes in regulating the performance of neural circuits within the larval CNS, we used a behavioral and electrophysiological approach to assess cholinergic modulation of locomotion and sensory-CNS-motor circuit excitability. We exposed intact and semi-intact 3rd instar larvae to ACh receptor agonists and antagonists to observe their roles in behavior and regulation of neural circuit excitability and to investigate AChR pharmacological properties in vivo. We combined this with targeted AChR RNAi-mediated knockdown to identify specific receptor subtypes facilitating ACh modulation of circuit efficacy. We identify a contribution by both mAChRs and nAChRs in regulation of locomotor behavior and reveal they play a role in modulation of the excitability of a sensory-CNS-motor circuit. We further reveal a conspicuous role for mAChR-A and mAChR-C in motor neurons in modulation of their input-output efficacy. •We show that both acetylcholine receptor subtypes modulate locomotor behavior.•We show that both receptor subtypes modulate the excitability of a sensory-CNS-motor circuit innervating larval muscle 6.•We show that A and C-type muscarinic receptors are prominent in modulating motor neuron input-output efficacy.•We confirm that nicotinic receptors modulate the excitability of sensory-CNS-motor input to larval muscle 6.•We reveal important Drosophila acetylcholine receptor pharmacological properties in vivo.