Synaptic transmission is the main avenue of neuronal communication and can be affected by a multitude of factors, both intracellularly and extracellularly. The effects of pH changes on synaptic transmission have been studied for many years across many different models. Intracellular acidification at the presynaptic terminal is known to occur with increased neuronal activity and can also occur in pathological conditions. The effects of these pH alterations are therefore an important area of study. Here, intracellular acidification using either propionic acid or the ammonium chloride pre-pulse technique was examined for the effects on both spontaneous and evoked synaptic transmission at the neuromuscular junction in larval Drosophila. The fly NMJ is glutamatergic and is used as a model of graded synaptic transmission. Propionic acid is shown to increase spontaneous quantal event frequency while also attenuating evoked transmission and depolarizing the cell. Ammonium chloride withdrawal has more diverse and complex effects that are shown to be dose- and condition-dependent. These studies are significant in further developing a model of the effects of intracellular acidification on evoked and non-evoked synaptic transmission
