Corydalis tuber is the root of Corydalis yahusuo

WANG classified as Papaveraceae. Aqueous extract from Corydalis tuber is known to stimulate blood circulation and relieve pain. It has traditionally been used for the treatment of neuralgia, dysmenorrhea, and gastrointestinal spasm. The analgesic and spasmolytic properties of the Corydalis tuber are essentially ascribed to several alkaloids: DL-tetrahydropalmatine (THP), D-cotydaline, and corydalis H, I, J, K, and L. The alkaloids exhibited analgesic, antiarrhythmic, antithrombic, antiinflammatory, anticataractic, antihypertensive, and antiallergic activities. Among others, THP is a very effective monoamine depletor in the brain and also possesses analgesic, sedative, hypnotic, and antihypertensive actions. The transmission of nociceptive information may be altered by various neuronal circuits within the central nervous system (CNS). One of them is a descending pain control system, which consists of three major components: the periaqueductal gray (PAG) of the midbrain, the rostroventral medulla (RM) including the nucleus raphe magnus, and the spinal dorsal horn. Of these, modulation of pain in the PAG matter is the most extensively studied pain control system. PAG is known as a major target of analgesic action of the opioid in the CNS. Stimulation within the midbrain PAG produces an opioid receptor-mediated analgesia. Opioid peptides and opiates produce analgesia by activating the descending pain modulatory pathways, especially at the level of the PAG. They also regulate the nociceptive transmission in part by inhibiting the release of transmitters. The effects of opiates and opioid peptides also have been reported to activate potassium channels or to inhibit calcium channels. It is proposed that endogenous opioid peptides can activate PAG output neurons by inhibiting inhibitory interneurons. The amino acid glycine is a major inhibitory neurotransmitter in the brain and spinal cord. The inhibitory action of glycine is mediated by a strychnine-sensitive glycine receptor and a glycine-gated chloride ion channel. Inhibitory glycine synapses in the brainstem and spinal cord are closely implicated in the transmission of nociception, in which glycine inhibits neurotransmission and relieves pain. In addition, the glycine-mediated inhibitory effect induces muscle relaxation, whereas inhibition of glycine receptors by strychnine induces convulsion. The analgesic mechanism of Corydalis tuber in the context of the descending pain control system has not yet been clarified. In the present study, the modulation of Corydalis tuber on glycine-activated ion current in the acutely dissociated PAG neurons was investigated using a nystatin-perforated patch-clamp technique under voltage-clamp conditions.