Amygdalin is known as vitamain B₁₇, and it was called laetrile. Amygdalin is composed of two molecules of glucose, one molecule of benzaldehyde which induces an analgesic action, and one molecule of hydrocyanic acid which is an anti-neoplastic compound. Amygdalin had been used to treat cancers and relieve pain. In order to evaluate whether the analgesic action of amygdalin is related with descending pain control system, we performed patch clamp study. In the present study, the modulatory effects of amygdalin on glycine- and glutamate-induced ion currents in periaqueductal gray (PAG) neurons were investigated using the nystatin-perforated patch clamp method. Continuous application of lipopolysaccharides (LPS) on PAG neurons resulted in increased glycine-induced ion current, and in decreased glutamate-induced ion current. In contrast, continuous application of amygdalin with LPS resulted in decreased glycine-induced ion current increased by LPS, and increased glutamate- induced ion current decreased by LPS in concentration- and time-dependent fashion. These results demonstrate that amygdalin modulates neuronal activity of PAG by modulation of glycine and glutamate. Based on the present results, it can be suggested that amygdalin participates in the regulation of the descending pain control system in the level of PAG neurons. The present study demonstrated that activation of the descending pain control system is one of the possible analgesic mechanisms of amygdalin.

Keywords: cyclooxygenase-2, periaqueductal gray neurons (PAG), glycine, glutamate, patch clamp, amygdalin