[Distribution of neuropeptide Y-like and beta-endorphin-like immunoreactivity in the nervous system and Hatschek's pit of amphioxus, Branchiostoma belcheri].

Using immunohischemical method, we have localized for the first time in the amphioxus, Branchiostoma belcheri, neuropeptide Y (NPY)-like and beta-endorphin (beta-Ep)-like immunoreactivity in nervous system and Hatschek's pit. NPY-immunoreactive (-ir) perikarya appeared in the front and middle areas of the telencephalon and midbrain, as well as in the hindbrain. Dense plexuses of NPY-ir fibers coursed with NPY-ir neurons and formed fine networks. NPY-ir perikarya and fibers were observed in the dorsal and middle areas of spinal cord. Beta-Ep-like immunoreactive perikarya and fibers were located in the front and middle areas of the midbrain, as well as in the spinal cord, but not in the telencephalon and hindbrain. The regions showing beta-Ep immunoreactivity were less than that of NPY. NPY-like and beta-Ep-like immunoreactivity were also found in the Hatschek's pit of amphioxus. These results suggest that NPY and beta-Ep, as an neurotransmitter as in fish, may be involved in the regulation of Hatschek's pit gonadotrophic cells secretory activity in amphioxus, and provide a new morphological evidence for the close relationship between brain and Hatschek's pit in amphioxus.