Morphine Sulfate and Naloxone Hydrochloride Decrease EPSP Amplitude at the Crayfish Neuromuscular Junction

Abstract

We tested for the presence of opioid receptors at the crayfish neuromuscular junction by measuring the effects of morphine and naloxone on EPSP amplitudes. If opioid receptors were present, we expected morphine to decrease EPSP amplitudes and naloxone to reverse morphines effect. Our results show that morphine decreased EPSP amplitude, but naloxone failed to reverse morphine's effect. Naloxone appliedexclusively, unexpectedly decreased EPSP amplitudes. Our results did not support the existence of known opioid receptors. However, our results suggest that morphine does have an effect at this junction. Thiseffect could be due to nonspecific binding, unintended chemical interference, or the existence of an undiscovered opioid receptor. Our results could lead to future experiments leading to the discovery of anunknown opioid receptor or experiments regarding how morphine elicits a decrease in EPSPs in the absence of opioid receptors.