Organization of neuropeptide tyrosine-like immunoreactive system in the brain of the Antarctic fish, Trematomus bernacchii

Antarctic notothenioids have developed unique freezing-resistance adaptatio ns, including brain diversification, to survive in the subzero waters of th e Southern Ocean surrounding Antarctica. In this study we have investigated the anatomical distribution of neuropeptide tyrosine (NPY)-like immunoreac tive elements in the brain of the Antarctic fish Trematomus bernacchii, by using an antiserum raised against porcine NPY. Perikarya exhibiting NPY-lik e immunoreactivity were observed in distinct regions of the brain. The most rostral group of immunoreactive perikarya was found in the telencephalon, within the entopeduncular nucleus. In the diencephalon, three groups of NPY -like immunoreactive perikarya were found in the hypothalamus. Two groups o f positive cell bodies were found in distinct populations of the preoptic n ucleus, whereas the other group was found in the nucleus of the lateral rec ess. More caudally, NPY immunoreactivity was detected in large neurons loca ted in the subependymal layers of the dorsal tegmentum of the mesencephalon , medially to the torus semicircularis. NPY-like immunoreactive nerve fibre s were more widely distributed throughout the telencephalon to the rhombenc ephalon. High densities of nerve fibres and terminals were observed in seve ral regions of the telencephalon, olfactory bulbs, hypothalamus, tectum of the mesencephalon and in the ventral tegmentum of the rhombencephalon. The distribution of NPY-like immunoreactive structures suggests that, in Tremat omus, this peptide may be involved in the control of several brain function s, including olfactory activity, feeding behaviour, and somatosensory and v isual information. In comparison with other neuropeptides previously descri bed in the brain of Antarctic fish, NPY is more widely distributed. Our dat a also indicate the existence of differences in the brain distribution of N PY between Trematomus and other teleosts. In contrast with previous results reported in other fish, Trematomus contains positive fibres in the olfacto ry bulbs and immunoreactive perikarya in the nucleus of the lateral recess, whereas NPY-immunopositive cell bodies are absent in the thalamus and rhom bencephalon, and no NPY immunoreactivity is present in the pituitary. These differences Could be related to the Antarctic ecological diversity of noto thenioids living at subzero temperatures.