Exogenous NAAG Decreases the Excitatory Post-Synaptic Response at the Crayfish Neuromuscular Junction

Abstract

Glutamate is widely held to be one of the most abundant neurotransmitters in the nervous systems of many organisms. Another neuromodulator, N-Acetylaspartylglutamate (NAAG), has been shown to exhibit both agonistic and antagonistic properties at various glutamatergic receptors. Much current research seeks to determine its role at synapses. We sought to determine the role of NAAG at the neuromuscular junction of crayfish, and to compare its effects with those of glutamate. Using intracellular recording techniques, we measured the Excitatory Post-Synaptic Potentials (EPSP) of stimulated crayfish muscle cells in regular saline, in the presence of exogenous NAAG, and in the presence of exogenous glutamate. Our results support our hypothesis that the addition of NAAG results in a decreased amplitude of EPSPs in comparison to those of the baseline measurements. Our results also indicate that the addition of exogenous glutamate increases the amplitude of the EPSP, demonstrating the independence of NAAG as a neuromodulator. An analysis of the paired-pulse ratio indicates that NAAG may act post-synaptically at the crayfish neuromuscular junction.