Abstract: Localization and expression of GnRH receptor (GnRHR) mRNA in the nervous system,Hatscheks pit and gonads of amphioxus,Branchiostoma belcheri,were investigated immunohistochemically using digoxigenin-labled oligonycleotide probe.The results showed that the nerve cells in midbrain and nerve tuber,the epithelia cells of Hatscheks pit and germocyte in testis and ovary of different development stages had GnRHR mRNA hybridization signal.It was worthwhile noting that some strong GnRHR mRNA hybridization signal were found for the first time in the funnel-like structure,a part of midbrain extension.The signal substance distributed in the cytoplasm,but the nucleus showed negative reaction.These results in dicated that the nervous system,Hatscheks pit and gonads of amphioxus were all capable of synthesizing GnRH receptors,which acted as target cells of GnRH in the nervous system,Hatscheks pit and gonads.Thus,the present study provided an authentic proof that GnRH might stimulate the secretory activity of Hatscheks pit epithelia cells and regulate gonadal development and maturation and reproduction activity on molecular level.It was suggested that the infundibulum-like structure might have two physiological functions:1) to act as a "transformation station" mediating the informative transfer and regulation between brain and Hatscheks pit;2)to be a regulation center to stimulate or inhibit the secretory act ivity of Hatscheks pit.