Immunohistochemical distribution of neuropeptide Y-related substance in the brain and hypophysis of the arctic lamprey, Lethenteron japonica.

The distribution of neuropeptide Y (NPY)-like immunoreactivity in the brain and hypophysis of the arctic lamprey, Lethenteron japonica, was studied by the use of polyclonal anti-synthetic porcine NPY antibody. Immunoreactivity was found throughout the brain, with varied densities among different areas. NPY-positive cell bodies were located in the dorsal pallium of the telencephalon; in the preoptic area, the thalamus, and the hypothalamus of the diencephalon; in the tegmentum of the mesencephalon; and in the octavolateralis nucleus, the middle reticular nucleus, and the vagal motor nucleus of the rhombencephalon. The majority of the NPY-positive cells in the thalamus and in the hypothalamus appeared as cerebrospinal fluid-contacting neurons. NPY-positive fibers were widely distributed in the brain and locally dense in the ventromedial part of the lateral pallium, in the posterior part of the interpeduncular nucleus, and in the raphe region. Conversely, they were less dense or well scattered in the olfactory bulb, the lateral pallium except for its ventromedial part, and the optic tectum. NPY-positive innervation in the neurohypophysis was evident, suggesting that involvement of NPY-related substance in the hypothalamo-hypophysial system had occurred in an early stage of vertebrate evolution.