Neuropeptide tyrosine in the brain of the African lungfish, Protopterus annectens: Immunohistochemical localization and biochemical characterization

Abstract

Lungfishes, which share similarities with both fishes and amphibians, represent an interesting group in which to investigate the evolutionary transition from fishes to tetrapods. In the present study, we have investigated the localization and biochemical characteristics of neuropeptide Y (NPY)-immunoreactive material in the central nervous system of the African lungfish, Protopterus annectens. NPY-immunoreactive cell bodies were found in various regions of the brain, most notably in the telencephalon (septal area, ventral striatum, and nucleus accumbens), in the diencephalon (preoptic nucleus, periventricular region of the hypothalamus, and ventral thalamus), and in the tegmentum of the mesencephalon. A strong immunoreaction was also detected in cell bodies of the nervus terminalis. Immunoreactive nerve fibers were particularly abundant in the ventral striatum, the nucleus accumbens, the diagonal band of Broca, the hypothalamus, and the mesencephalic tegmentum. Positive fibers were also seen in the median eminence and in the neural lobe of the pituitary. The NPY-immunoreactive material localized in the brain and pituitary was characterized by combining high-performance liquid chromatography (HPLC) analysis and radioimmunological quantitation. The displacement curves obtained with synthetic porcine and frog NPY and serial dilutions of brain and pituitary extracts were parallel. Reversed-phase HPLC analysis of telencephalon, diencephalon, and pituitary extracts resolved a major NPY-immunoreactive peak that coeluted with frog NPY. The similarity between the distribution of NPY-containing neurons and the biochemical characteristics of the immunoreactive peptide in the brain of lungfish and frog strongly favors a close phylogenetic relationship between dipnoans and amphibians.

Immunohistochemical Distribution of Neuropeptide Y-Related Substance in the Brain and Hypophysis of the Arctic Lamprey, <i>Lethenteron japonica</i>

“…In the rat hypothalamus, intragranular costorage of NPY and arginine vasopressin in the paraventricular magnocellular neurons was reported, strongly suggesting that the paraventricular nucleus is an origin of the NPY-ir fibers found in the hypophysis [Kagotani et al, 1990]. In the teleosts [Subhedar et al, 1996] and lungfish [Vallarino et al, 1995], the preoptic nucleus includes NPY-ir cells, whereas no NPY-ir cells were demonstrated in the preoptic nuclei of African clawed toad [Tunihof et al, 1994], dogfish [Chiba and Honma, 1992], sturgeon [Chiba and Honma, 1994], and bichir [Chiba, 1997]. Origin(s) of the NPY-ir fibers in the lamprey neurohypophysis should be experimentally analyzed in the future.…”

“…Immunohistochemical data for NPY-ir innervation in the hypophyses of the following fish groups have been reported: Elasmobranchii [Vallarino et al, 1988;Chiba and Honma, 1992], Chondrostei [Chiba and Honma, 1994], Polypteriformes [Chiba, 1997], Dipnoi [Vallarino et al, 1995], and Teleostei [Pontet et al, 1989;Batten et al, 1990;Danger et al, 1991;Vecino and Ekström, 1992;Magliulo-Cepriano and Schreibman, 1993;Chiba et al, 1996;Subhedar et al, 1996]. However, in Agnatha, the NPY-ir innervation in the hypophysis is indistinct or negligible in the brown hagfish [Chiba et al, 1993].…”

“…A number of immunohistochemical studies have provided basic data on the organization of NPY-like-immunoreactive (NPY-ir) structures in the brains of primitive vertebrates including the major fish groups: cyclostomes [Van Dongen et al, 1985;Chiba et al, 1993], elasmobranchs [Vallarino et al, 1988;Chiba and Honma, 1992], primitive bony fishes [Chiba and Honma, 1994;Vallarino et al, 1995;Chiba, 1997], and teleosts [Pontet et al, 1989;Batten et al, 1990;Danger et al, 1991;Vecino and Ekström, 1992;Magliulo-Cepriano and Schreibman, 1993;Chiba et al, 1996;Subhedar et al, 1996].…”

Distribution of GAD-immunoreactive neurons in the diencephalon of the African lungfishProtopterus annectens: Colocalization of GAD and NPY in the preoptic area

“…Lungfish thus represent a group of particular interest in which to investigate the evolutionary transition between fish and tetrapods (Romer, 1966;Miles, 1977;Rosen et al, 1981). We have previously described the distribution of NPY-containing neurons in the brain of the African lungfish Protopterus annectens, and we have shown the occurrence of numerous cell bodies and fibers in the hypothalamus (Vallarino et al, 1995b). In contrast, to our knowledge, the mapping of GABA-containing neurons has not yet been determined in the CNS of Dipnoans.…”

“…We have previously shown that the preoptic nucleus of P. annectens possesses several populations of neurons containing different neuropeptides, including ␣-MSH (Vallarino et al, 1992), gonadotropin-releasing hormone (King et al, 1995), FMRFamide (Vallarino et al, 1995a), NPY (Vallarino et al, 1995b), atrial natriuretic factor (Vallarino et al, 1996), somatostatin (Vallarino et al, 1997), and enkephalins . In the course of the present study, we have noticed that the distribution of GAD-positive perikarya in the periventricular preoptic nucleus overlaps that described for NPY-immunoreactive neurons.…”