XING, Bin; SHEARER, Joesph; COOPER, Robin L.: The influence of culture media on synaptic transmission at larval Drosophila neuromuscular junction

The larval Drosophila neuromuscular junction (NMJ) has proven to be a excellent testing ground for understanding key aspects in the fundamentals of synaptic transmission in relation to the function of ion channels, subtypes of glutamate receptors, and the function of synaptic proteins in the presynaptic nerve terminal. In addition, recent advances in our knowledge of bi-directional communication between the nerve-muscle of Drosophila are helping to uncover developmental and maintenance cues that may well be applicable to all chemical synapses. Unfortunately many of the physiological solutions used prior to the development of a medium (i.e., HL3) that allows stable physiological measures for a few hours (Stewart et al., 1994; J. Comp. Physiol. A. 175:179-191) have proven to produce artifactual neuromuscular synaptic responses. Likewise, we have demonstrated that culture mediums (Schneider’s and M3) commonly used to culture CNS neurons of Drosophila completely block glutamatergic synaptic transmission at the NMJ. The depressed postsynaptic excitatory potentials (EPSPs) partially recovers from exposure to the standard culture mediums upon switching to the HL3 medium in acute conditions. In addition, preliminary attempts in long-term culturing (5days) of the filleted 3rd instar NMJ has shown great promise with a modified HL3 medium (addition of FCS, gentamycin and glucose). It is likely that previous culture mediums of neurons may lead to artifactual growth of neurites since synaptic transmission may be compromised as well as the function of autoreceptors on the neurons.