Lungfish Neoceratodus Research Articles

Taurine, amino acid transmitters, and related molecules in the retina of the Australian lungfish Neoceratodus forsteri: a light-microscopic immunocytochemical and electron-microscopic study.

The morphology of the retina of the Australian lungfish Neoceratodus forsteri was investigated by means of light- and electron microscopy, whilst immunocytochemical studies were performed to determine the cellular distributions of the major amino acid neurotransmitters and other amino acids. The distributions of glycine and GABA were similar to those previously described for teleost, amphibian and mammalian retinae. Labelling was abundant in amacrine cells, whilst GABA was also present in one layer of horizontal cells and some bipolar cells. Taurine was present in both rods and cones, but, unlike the mammalian or avian retina, was absent from other cellular structures, including glial elements. Unexpectedly, the photoreceptor terminals lacked an apparent content of the excitatory amino acid transmitter glutamate. The glutamate that was present in the rods and cones occupied a crescentic arc corresponding to the location of glycogen-rich paraboloids. Asparagine was also present in rods, albeit in the modified mitochondria that formed the elipsoids of the rod inner segments. Arginine, the precursor for formation of nitric oxide, was present in glial cells, and in the paraboloids of both rods and cones.

Taurine, amino acid transmitters, and related molecules in the retina of the Australian lungfish Neoceratodus forsteri: a light-microscopic immunocytochemical and electron-microscopic study

Taurine, amino acid transmitters, and related molecules in the retina of the Australian lungfish Neoceratodus forsteri: a light-microscopic immunocytochemical and electron-microscopic study

Neuropeptides in the Australian lungfish Neoceratodus forsteri: effects in vivo and presence in autonomic nerves.

The Australian lungfish Neoceratodus forsteri is one of the few extant species of a phylogenetically ancient group. Immunohistochemistry showed the presence of galanin-, vasoactive intestinal polypeptide (VIP)-, neurotensin-, substance P-, and calcitonin gene-related peptide (CGRP)-like immunoreactivities in nerve fibers in the heart, lung, and gut, with a coexistence of VIP-, galanin-, and somatostatin-like immunoreactivity in the lung and galanin- and somatostatin-like immunoreactivity in the gut. About 20% of the substance P-immunoreactive fibers in gut and lung contained CGRP-like material. Major vessels showed a sparse innervation. In free-swimming unanesthetized fish, neurotensin (1 nmol/kg), galanin (1 nmol/kg), and bombesin (10 nmol/kg) reduced the heart rate. In two specimens tested, the effect of neurotensin was partially antagonized by atropine. Galanin and bombesin reduced and cholecystokinin 8 (CCK-8-S) increased blood flow to the lung. Neurotensin decreased, CCK-8-S increased, and substance P had no effect on dorsal aortic pressure, and all three decreased flow to the gut. It can be concluded from the present study that the general vertebrate pattern of cardiovascular and visceral nervous control by several neuropeptides is present also in Neoceratodus.

Lungfish Neurohypophysial Hormones: Chemical identification of Mesotocin in the Neurointermediate Pituitary of the Australian Lungfish Neoceratodus forsteri

The neurohypophysial hormones contained in the neurointermediate lobe of the pituitary of the Australian lungfish Neoceratodus forsteri have been investigated. Mesotocin was identified by coelution with the synthetic peptide in high-pressure liquid chromatography, by Edman amino acid sequencing, by mass spectrometry, by C-terminal sequencing through carboxypeptidase Y, and cleavage with prolyl endopeptidase. Vasotocin, if present, would be in very small amounts and hydrins were not detected. Oxytocin appears absent. Although Neoceratodus and Protopterus have different habitats, the former being permanently aquatic, the latter burrowing during estivation, the proportions of neurohypophysial hormones stored in neurohypophysis were roughly similar in the two species and not apparently affected by environmental conditions.

Concinnocotyla (Monogenea: Polystomatidae), a new genus for the polystome from the Australian lungfish Neoceratodus forsteri

Pseudopolystoma australensis is redescribed from new material from the Australian lungfish Neoceratodus forsteri (Dipnoi) from a natural population in Queensland, Australia. It is transferred to a new genus, Concinnocotyla, as Concinnocotyla australensis n. comb. in a new subfamily, the Concinnocotylinae. The genus Concinnocotyla differs from all other polystome genera in each of the following characters: haptoral suckers bilaterally symmetrical rather than radially symmetrical, with elaborate skeleton of sclerites rather than no sclerites; hamuli, a single pair between marginal hooklets I and II rather than between II and III; a pocket posteriorly on each caecum that opens dorsally; sperm-filled sac between pockets; testes numerous, discrete, cylindrical; seminal vesicle large, discrete, muscular; penis elongate, muscular, unarmed, extensile; penis-bulb large, muscular, with intrinsic glands; host, a dipnoan. A detailed description of the adult parasite is presented and its unique features are discussed. The absence of a true oral sucker is noted. Confirmation of a polystome from a natural population of Australian lungfish has interesting evolutionary implications.

Dorsomedial telencephalon of lungfishes: A pallial or subpallial structure? criteria based on histology, connectivity, and histochemistry

The dorsomedial telencephalon of lepidosirenid lungfishes has been interpreted in two divergent ways: earlier investigators regarded it as a subpallial (septal) structure; more recently, it has been reinterpreted as the medial pallium (hippocampus). To resolve this question, we identified parameters that are conclusive in their association with either the medial pallium or the septum in anamniotes. The present study examines the position of ependymal thickenings and the distribution of acetylcholinesterase (AchE) in the cerebral hemispheres of the African lungfish Protopterus, the Australian lungfish Neoceratodus, and the amphibian species Xenopus and Ambystoma. In addition, projections from the hypothalamus (paraventricular organ) to the telencephalon are investigated in Protopterus. Ependymal specializations are located dorsally and ventrally in the lateral ventricles of amphibians, but laterally and medially in lungfishes. In Protopterus, the paraventricular organ projects to the medial telencephalic hemisphere, but not to the dorsal roof. High levels of AchE are present in restricted neuropil regions of the medial hemisphere and in the ventral and ventrolateral telencephalon, but they are lacking in the dorsal roof. Intensely AchE-stained neuronal cell bodies are located in the ventral telencephalon (rostrally) and the dorsomedial telencephalon (at mid-level). In Neoceratodus, AchE staining is pronounced in the septal area, but absent in the pallium. The terminal nerve proper lacks AchE stain in Protopterus; nerve fibres of the preoptic nerve are AchE-positive in both lungfish species. In Xenopus, AchE staining of fibers and terminals is restricted to the subpallium (medial septum, tuberculum olfactorium, striatum, nucleus accumbens, and medial amygdala); cell bodies are AchE positive in parts of the subpallium and rostral pallium. Comparison of cytological, histochemical, and "connectional" parameters substantiates the interpretation that the dorsomedial telencephalon of lungfishes represents a subpallial, but not a "medial pallial" structure. The dorsomedial part of the lepidosirenid telencephalon corresponds to the septum in the most plesiomorphic living lungfish, Neoceratodus forsteri, but it differs considerably from the dorsomedial telencephalon (medial pallium) in amphibians.

The otoliths of a chimaera, the New Zealand elephant fishCallorhynchus milii

Abstract The elephant fish Callorhynchus milii (Holocephalidae) has a pair of well‐developed otoliths corresponding (in relative position) to the astericus and sagitta in teleosts. Although the elephant fish apparently lacks a lapillus, there are a well‐developed set of cristae at the base of the semicircular canals. The cristae presumably serve the same balance function as the lapillus. The semicircular canal system also contains a well‐developed ductus endolymphaticus, filled with irregular calcium carbonate otoconia. A different type of oto‐conia are found fused together to form the two otoliths. This latter type of otoconia, a crenellated spherulite, is similar to those found aggregated in the otolith of the lungfish Neoceratodus forsteri, and found as loose otoconia in association with the sagitta in some species of teleosts.

The remarkable lungfish otolith

Abstract Otoliths and macula from the Australian lungfish Neoceratodus forsteri were examined by light and scanning electron microscopy. The otoliths, corresponding to the sagitta and lapillus in teleosts, were found to consist of crystalline oto‐conia consisting of calcite, aragonite, and a previously undescribed form of calcium carbonate bound in what appears to be a protein matrix. The inner‐vation and hair‐cell anatomy of the lungfish macula exactly parallels those of teleosts. Thus in function the otolith appears similar to teleosts, whereas its crystal complement has parallels in mammals, reptiles, and chondrichthyans.

The role of hormones in regulation of carbohydrate metabolism in the Australian lungfish Neoceratodus forsteri

Adrenaline, arginine vasopressin, arginine vasotocin, and glucagon, all at 10 −6 M, stimulate glycogen breakdown and glucose release from hepatic tissue of Neoceratodus forsteri cultured in vitro. Adrenaline acts via a β-adrenergic receptor in this species. Gluconeogenesis from 2 m M lactate occurred at a rate of 680 ± 39 nmol/g liver/h. This rate of gluconeogenesis was unaffected by the addition of 10 −6 M adrenaline.

Structure of Intestine, Pancreas, and Spleen of the Australian Lungfish, Neoceratodus forsteri (Krefft)

The structure of the intestine and its adnexa in the Australian lungfish Neoceratodus forsteri (Krefft), is described from four adult specimens and compared with that of other lungfish. In all lungfish genera the intestine is thick and straight and contains a complicated spiral valve; a pyloric fold separates the foregut from the midgut. In Neoceratodus the coiling of the intestinal lumen begins in the prepyloric or gastric region, unlike in other vertebrates with a spiral valve, where it begins behind the pylorus. The spiral valve of Neoceratodus begins as a deep groove on the right side of the foregut, just behind the glottis. Such a prepyloric groove is present but poorly developed also in the lungfishes Protopterus and Lepidosiren and contains a prepyloric spleen in all genera. A separate postpyloric spleen is situated in the free margin of the spiral valve, i.e. in the axis of the intestine. The spleen has a heavily pigmented cortex containing large amounts of iron. The pancreas, buried in the spiral valve in front of the pylorus in Neoceratodus, contains numerous islets of Langerhans, similar to those of tetrapods. This is unexpected because the islets ofProtopterus, described by Gabe in 1969, are more like the large, encapsulated “Brockmann bodies” of teleosts.

Respiratory properties of blood and pattern of gas exchange in the lungfish Neoceratodus forsteri (Krefft)

Blood respiratory properties and gas exchange patterns have been studied in the lungfish Neoceratodus. O 2 - Hb dissociation curve reveals a high affinity for o 2 (P 50 of 11 mm Hg at P co 2 3.5 mm Hg). No Root effect but a pronounced Bohr effect was discernible. Temperature exerted only a minor influence on the affinity for O 2. The Co 2 dissociation curves conform to the shape observed in other classes of vertebrates and show a steep initial portion. The buffering capacity of the blood was low being 13.3 mMol/l/pH. An increased buffering power upon reduction of Hb was apparent. During rest in well oxygenated water, gill breathing prevailed entirely. Pulmonary arterial blood assumed to represent mixed arterial blood characteristically showed a Pco 2 averaging 3.5 mm Hg. Pao 2 was 40 mm Hg corresponding to an o 2 saturation of 95 %. The pulmonary venous blood showed gas partial pressures in equilibrium with those in pulmonary arterial blood and air, documenting the minor importance of the lung as a gas exchanger during these conditions. When the fish was artificially exposed to air P a o 2 diminished to 10–15 mm Hg with a concurrent increase in P a co 2 to 20 mm Hg in 30 min. While the lung performed well as an 02 absorber during air exposure it was totally inefficient in eliminating CO 2. The data indicate that Neoceratodus is unfit to live out of water for any length of time.