Abstract
The complexity surrounding presynaptic recordings in mammals is a significant barrier to the study of presynaptic mechanisms during neurotransmission in the mammalian central nervous system (CNS). Here we describe an adult fly neuromuscular junction (NMJ), the ciberial muscle 9 (CM9) NMJ, which allows for the recording of both evoked (EPSPs) and spontaneous postsynaptic excitatory potentials (mEPSPs) at a mature glutamatergic synapse. Combined with CM9-specific genetic technologies, the CM9 NMJ provides a powerful experimental system to better understand the regulation of neurotransmitter release at a mature synapse.
Keywords: Drosophila, Aging, Neuromuscular junction, Neurotransmission
Background
A significant hurdle in defining changes in presynaptic function during aging has been due to the lack of a simple model system for performing the electrophysiological recordings necessary to thoroughly characterize the release of neurotransmitter from the presynaptic nerve terminal. Existing rodent models suffer from the significant cost issues associated with aging studies and the technical difficulty of using electrophysiological recordings on single defined nerve terminals with consistent release parameters. To overcome these obstacles, we have pioneered a model synaptic system in the adult Drosophila for analyzing the effects of age on presynaptic function during neurotransmission, the CM9 NMJ located on the fly proboscis (Rawson et al., 2012; Mahoney et al., 2014; Mahoney et al., 2016) (Figure 4A). Briefly, the presynaptic arbor of the CM9 motor neuron (MN) converges upon the 15 muscle fibres of the CM9 muscle to form 35 individual distinct innervations (Rawson et al., 2012). The CM9 MN has been shown to be necessary for the contraction of the CM9 muscle and is the only source of glutamatergic input for the CM9 muscle (Kimura et al., 1986; Gordon and Scott, 2009). Given the highly-conserved nature of the mechanisms underlying synaptic vesicle (SV) release between flies and mammals, and the resemblance to the central synapses found in the mammalian CNS, this makes the CM9 NMJ a powerful model for investigating presynaptic function.
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