We have recently identified a new small peptide from human brain

It is a tetrapeptide with the structure of Asn-Ala-Gly-Ala

which has been termed "Naga Peptide". It shows potent analgesic effect in rabbit when injected into brain ventricle

central grey or venous. This analgesic effect can be antagonized by naloxone

It is assumed to be mediated by morphine receptors. The content of Naga peptide in human and rabbit CSF were increased markedly after electro-acupuncture

and the pain threshold was also incre- ased markedly at the same time. The increament of Naga was parallel to the rise of pain threshold. The amount of Naga peptide in CSF was increased markedly after in- jection of Naga intravenously

and the pain threshold of the rabbit was also increased markedly at the same time. The increment of Naga in CSF was parallel to the rise of pain threshold. These results show that Naga peptide may be one of the endogenous opioid peptide and related to the acupuncture.