Investigating the Modulation of Drosophila melanogaster Body-wall Muscle Contraction by the Neuropeptide DPKQDFMRFamide

Abstract

The chemical synapse is the site of communication between a neuron and its target cell, where an electrical impulse depolarizes the presynaptic cell causing chemical release. The chemicals released at the synapse are signaling molecules referred to as transmitters and co-transmitters that exert effects on the target cell and can sometimes modulate the effects of each other. A class of signaling molecules, known as neuropeptides, can act as transmitters or can be released as hormones that can modulate chemical synapses and ultimately affect many physiological functions. The neuropeptide, DPKQDFMRFamide, is an important neuromodulator of neuromuscular junctions in the fruit fly, Drosophila melanogaster. DPKQDFMRFamide has previously been shown to enhance excitatory junctional potentials (EJPs) elicited by specific neurons, to enhance nerve-evoked contractions, and to induce contractions directly in Drosophila 3rd instar larval body-wall muscles. This thesis investigated how the DPKQDFMRFamide peptide modulates muscle contractions elicited by the excitatory transmitter of the neuromuscular junction, L-glutamate, in D.melanogaster 3rd instar larvae. Effects were assessed by co-applying peptide with L-glutamate after removing the central nervous system. The results indicate that DPKQDFMRFamide enhances glutamate-evoked contractions in a dose-dependent manner, and there was synergy between the effects of L-glutamate and DPKQDFMRFamide on muscle contraction. DPKQDFMRFamide increased membrane depolarization in muscle when co-applied with glutamate, and it enhanced contractions induced by caffeine in the absence of extracellular calcium. Thus, the peptide appears to act at the cell membrane to increase depolarization and at, or downstream of the sarcoplasmic reticulum (SR) to enhance caffeine-induced contractions. However, the effects of DPKQDFMRFamide do not appear to involve the 2nd messenger nitric oxide or the calcium/calmodulin activated protein kinase, CaMKII.