Central projections of the nervus terminalis in the bichir,Polypterus palmas

Summary Central pathways of the nervus terminalis (n.t.) in the bichir, Polypterus palmas, were studied with the use of tracing techniques. After application of horseradish peroxidase to the unilateral olfactory mucosa labeled n.t. fibers were traced in seven distinct bundles through the subpallium. Projection areas are found in the precommissural ventral nucleus of the area ventralis telencephali ipsilaterally, the anterior commissure and commissural parts of the periventricular preoptic nucleus bilaterally; few n.t.-fibers cross via the anterior commissure to the contralateral side; no fibers were observed to turn rostrally to the contralateral olfactory bulb. Major targets of the n.t. include a restricted ventral part of the periventricular preoptic nucleus at the level of the optic chiasma bilaterally, and the periventricular nuclei located between the thalamic nuclei and the hypothalamus bilaterally. N.t. fibers continue their course through the ipsilateral hypothalamus and are traced as far as the mesencephalic tegmentum ipsilaterally. N.t. terminations are found consistently within the boundaries of periventricular cell nuclei, suggesting axosomatic synaptic contacts. We propose a differentiation of the n.t. ganglion cells into a distal (mucosal) and proximal (bulbar) type regarding the peripheral cell processes. Our findings are compared with those of other reports on the n.t. system.     

Peripheral projections of nervus terminalis LHRH-containing neurons in the tiger salamander,Ambystoma tigrinum

The peripheral projections of the nervus terminalis (NT) have been difficult to examine due to the weak immunoreactivity of the processes to various antibodies. We performed two experimental manipulations in the tiger salamander in an attempt to increase the luteinizing hormone-releasing hormone-immunoreactive (LHRH-ir) labelling in the peripheral processes of the NT: 1) the NT was sectioned centrally, or 2) a 100 mg melatonin pellet was embedded subcutaneously for 3 days prior to sacriffice. Following these manipulations, animals were sacrifficed and tissue was processed with standard immunocytochemical techniques for the analysis of the distribution of LHRH-ir processes. In the nasal cavity, LHRH-ir fibers were observed projecting 1) into the rostral olfactory epithelium, 2) to Bowman's glands in the lamina propria of the rostromedial olfactory mucosa and ventrolateral mucosa between the main nasal cavity and Jacobson's organ, 3) into the naris constrictor muscle, and 4) along the palatine nerves and ganglia. These lesion and hormone manipulations have enabled the detection of peripheral projections of the NT not observed previously with immunocytochemical procedures alone. The wide distribution of LHRH-ir NT processes in the nasal cavity and cranium suggests that this nerve may influence many different cranial structures during appropriate pheromonal or neuroendocrine events.     

Olfactory and vomeronasal projections and the pathway of the nervus terminalis in ten species of salamanders

Summary Primary olfactory and vomeronasal projections as well as the pathway of the nervus terminalis were studied in 10 representative species of salamandrid and plethodontid salamanders by means of injections of horseradish peroxidase and examination of whole-mount preparations. Olfactory projections are very similar in the different urodeles, but vomeronasal projections differ in shape and number of termination fields. Whereas the direct-developing Plethodontini and Bolitoglossini reveal only one or two fields, the salamandrid species and the members of the plethodontid tribes Desmognathinae and Hemidactyliini, all possessing an aquatic larval stage, exhibit several vomeronasal projection fields. In all species examined centrifugal axons of the nervus terminalis leave the olfactory projection area ventrocaudally and terminate in the preoptic region and the hypothalamus.Abbreviations COM. ANT commissura anterior - DGL displaced glomeruli - HY hypophysis - HYTH hypothalamus - LF lateral fibers of the nervus terminalis - ME medulla oblongata - MF medial fibers of the nervus terminalis - Nt nervus terminalis - Npo nucleus praeopticus     

Tracing of single fibers of the nervus terminalis in the goldfish brain

Summary Central projections of the nervus terminalis (n.t.) in the goldfish were investigated using cobalt- and horseradish peroxidase-tracing techniques. Single n.t. fibers were identified after unilateral application of cobalt chloride-lysine to the rostral olfactory bulb. The central course and branching patterns of individual n.t. fibers were studied in serial sections. Eight types of n.t. fibers are differentiated according to pathways and projection patterns. Projection areas of the n.t. include the contralateral olfactory bulb, the ipsilateral periventricular preoptic nucleus, both retinae, the caudal zone of the periventricular hypothalamus bilaterally, and the rostral optic tectum bilaterally. N.t. fibers cross to contralateral targets in the anterior commissure, the optic chiasma, the horizontal commissure, the posterior commissure, and possibly the habenular commissure. We propose criteria that differentiate central n.t. fibers from those of the classical secondary olfactory projections. Branching patterns of eight n.t. fiber types are described. Mesencephalic projections of the n.t. and of secondary olfactory fibers are compared and discussed with regard to prior reports on the olfactory system of teleosts. Further fiber types for which the association with the n.t. could not be established with certainty were traced to the torus longitudinalis, the torus semicircularis, and to the superior reticular nucleus on the ipsilateral side.     

Functional anatomy of the peripheral olfactory system of the African lungfish Protopterus annectens owen: development of the primary olfactory pathway during postembryonic growth

Seven specimens of the African lungfish ranging in size from 4 to 350 gm were used for the study of changes in the olfactory nerve and bulb during postembryonic growth as expressed by the increasing number of lamellae of the olfactory organ. Serial semithin sections were used, and the data were studied mathematically. The number of axons of the olfactory nerve, the surface area of the bulb, and the number of mitral cells increase exponentially; the mitral cell density decreases exponentially; and the calculated average convergence (counted axons/counted mitral cells) of axons onto the cells of the bulbar relay increases exponentially. Convergence figures obtained are smaller than those cited by other authors; two factors might explain this: first the mode of calculation, and second the fact that every year this fish undergoes a 6-month starvation stage marked by degeneration of the primary olfactory structure. A preliminary view of the primary olfactory pathway using serial-section reconstructions is proposed: An orderly projection of the mucosa onto the bulb takes place after a 90 degrees rotation of the system of two perpendicular axes which apply to both the olfactory organ and the olfactory bulb. This study suggests an original attempt at relating the postembryonic change in convergence and projection to the primary processing of the olfactory message.     

A neurofibrillar body in the perikaryon of nervus terminalis ganglion cells in teleosts

Summary In three species of Teleosts (Tinea tinea L., Leuciscus cephalus cabeda Risso, Epinephelus guaza L.) a round strongly argentophilic body of considerable size occurs in the cytoplasm of the nervus terminalis ganglion cells. In Tinea, surgical interruption of functional connections of the ganglion cells does not produce any apparent change either in the number or in the size of these cytoplasmic bodies.Electron microscopical observations show that the neurofibrillar body is made up of densely packed and irregularly arranged bundles. In cross section, each of these bundles appears to be composed of neurofilaments (100 Å in thickness) and neurotubules (diameter: 300 Å). Each tubule is surrounded by 9–10 filaments equi-distant from one another, and at a distance of 30–40 Å from the central tubule.The authors are indebted to Prof. G. Palladini for helpful histochemical advice, to Prof. B. Bertolini for electron micrographs and to Mr. D. Scorsini for skilful technical assistance.     

Neuropilin-2 regulates the development of selective cranial and sensory nerves and hippocampal mossy fiber projections

Neuropilin-1 and neuropilin-2 bind differentially to different class 3 semaphorins and are thought to provide the ligand-binding moieties in receptor complexes mediating repulsive responses to these semaphorins. Here, we have studied the function of neuropilin-2 through analysis of a neuropilin-2 mutant mouse, which is viable and fertile. Repulsive responses of sympathetic and hippocampal neurons to Sema3F but not to Sema3A are abolished in the mutant. Marked defects are observed in the development of several cranial nerves, in the initial central projections of spinal sensory axons, and in the anterior commissure, habenulo-interpeduncular tract, and the projections of hippocampal mossyfiber axons in the infrapyramidal bundle. Our results show that neuropilin-2 is an essential component of the Sema3F receptor and identify key roles for neuropilin-2 in axon guidance in the PNS and CNS.     

Cardiovascular actions of lungfish bradykinin in the unanaesthetised African lungfish, Protopterus annectens

Bradykinin (BK) isolated from plasma of the African lungfish, Protopterus annectens, contains four amino acid substitutions compared with BK from mammals (Arg(1)-->Tyr, Pro(2)-->Gly, Pro(7)-->Ala, Phe(8)-->Pro). Bolus intra-arterial injections of synthetic lungfish BK (1-1000 pmol/kg body wt.) into unanaesthetised, juvenile lungfish (n=5) produced a dose-dependent increase in arterial blood pressure and pulse pressure. The maximum pressor response occurred 2-3 min after injection and persisted for up to 15 min. The threshold dose producing a significant (P<0.01) rise in pressure was 50 pmol/kg and the maximum increase, following injection of 300 pmol/kg, was 9.3 +/- 2.3 mmHg. Injection of the higher doses of lungfish BK produced a significant (P<0.05) increase in heart rate (2.8 +/- 0.8 beats/min at 100 pmol/kg). In contrast, bolus intra-arterial injections of mammalian BK, in doses up to 1000 pmol/kg, produced no significant cardiovascular effects in the lungfish. The data support the existence of a functioning kallikrein-kinin system in the lungfish and demonstrate that the ligand-binding properties of the receptor(s) mediating the cardiovascular actions of lungfish BK are appreciably different from mammalian B1 and B2 receptors.     

A mitochondrial DNA phylogeny of African clawed frogs: phylogeography and implications for polyploid evolution

The African clawed frogs (Silurana and Xenopus), model organisms for scientific inquiry, are unusual in that allopolyploidization has occurred on multiple occasions, giving rise to tetraploid, octoploid, and dodecaploid species. To better understand their evolution, here we estimate a mitochondrial DNA phylogeny from all described and some undescribed species. We examine the timing and location of diversification, and test hypotheses concerning the frequency of polyploid speciation and taxonomy. Using a relaxed molecular clock, we estimate that extant clawed frog lineages originated well after the breakup of Gondwana, about 63.7 million years ago, with a 95% confidence interval from 50.4 to 81.3 million years ago. Silurana and two major lineages of Xenopus have overlapping distributions in sub-Saharan Africa, and dispersal-vicariance analysis suggests that clawed frogs originated in central and/or eastern equatorial Africa. Most or all extant species originated before the Pleistocene; recent rainforest refugia probably acted as "lifeboats" that preserved existing species, rather than "species pumps" where many new successful lineages originated. We estimate that polyploidization occurred at least six times in clawed frogs.     

Epithelial crypts: A complex and enigmatic olfactory organ in African and South American lungfish (Lepidosireniformes,Dipnoi)

African lungfish (Protopterus ) seem unique among osteognathostomes in possessing a potential vomeronasal organ homolog in form of accessory epithelial crypts within their nasal cavity. Many details regarding structural and functional properties of these crypts are still unexplored. In this study, we reinvestigate the issue and also present the first data on epithelial crypts in the South American lungfish Lepidosiren paradoxa . The nasal cavities of L. paradoxa and Protopterus annectens were studied using histology, scanning electron microscopy, and alcian blue and PAS staining. In both species, the epithelial crypts consist of a pseudostratified sensory epithelium and a monolayer of elongated glandular cells, in accordance with previously published data on Protopterus . In addition, we found a new second and anatomically distinct type of mucous cell within the duct leading into the crypt. These glandular duct cells are PAS positive, whereas the elongated glandular cells are stainable with alcian blue, suggesting distinct functions of their respective secretions. Furthermore, the two lungfish species show differently structured crypt sensory epithelia and external crypt morphology, with conspicuous bilaterally symmetrical stripes of ciliated cells in L. paradoxa . Taken together, our data suggest that stimulus transport into the crypts involves both ciliary movement and odorant binding mucus.     

The relative congruence of cranial and genetic estimates of hominoid taxon relationships: implications for the reconstruction of hominin phylogeny

Previous analyses of extant catarrhine craniodental morphology have often failed to recover their molecular relationships, casting doubt on the accuracy of hominin phylogenies based on anatomical data. However, on the basis of genetic, morphometric and environmental affinity patterns, a growing body of literature has demonstrated that particular aspects of cranial morphology are remarkably reliable proxies for neutral modern human population history. Hence, it is important to test whether these intra-specific patterns can be extrapolated to a broader primate taxon level such that inference rules for understanding the morphological evolution of the extinct hominins may be devised. Here, we use a matrix of molecular distances between 15 hominoid taxa to test the genetic congruence of 14 craniomandibular regions, defined and morphometrically delineated on the basis of previous modern human analyses. This methodology allowed us to test directly whether the cranial regions found to be reliable indicators of population history were also more reliable proxies for hominoid genetic relationships. Cranial regions were defined on the basis of three criteria: developmental-functional units, individual bones, and regions differentially affected by masticatory stress. The results found that all regions tested were significantly and strongly correlated with the molecular matrix. However, the modern human predictions regarding the relative congruence of particular regions did not hold true, as the face was statistically the most reliable indicator of hominoid genetic distances, as opposed to the vault or basicranium. Moreover, when modern humans were removed from the analysis, all cranial regions improved in their genetic congruence, suggesting that it is the inclusion of morphologically-derived humans that has the largest effect on incongruence between morphological and molecular estimates of hominoid relationships. Therefore, it may be necessary to focus on smaller intra-generic taxonomic levels to more fully understand the effects of neutral and selective evolutionary processes in generating morphological diversity patterns.     

Anion exchange in the giant erythrocytes of African lungfish

Carbon dioxide transport in African lungfish Protopterus aethiopicus blood conformed to the typical vertebrate scheme, implying a crucial and rate-limiting role of erythrocyte Cl^–/HCO₃^– exchange. The rate coefficient for unidirectional Cl^– efflux via the anion exchanger ( k , s⁻¹) increased with temperature in African lungfish, but values were well below those reported in other species. The erythrocytes of African lungfish were, however, very large (mean cellular volume = 6940 µm³), and the ratio of cell water volume to membrane surface area was high ( V _w A _m⁻¹ = 1·89). Hence, the apparent Cl^– permeability ( P _Cl =  kV _w A _m⁻¹, µm s⁻¹) was close to that in other vertebrates. The plot of ln P _Cl against the inverse absolute temperature was left-shifted in the tropical African lungfish compared to the temperate rainbow trout Oncorhynchus mykiss , which supports the idea that P _Cl is similar among animals when compared at their preferred temperatures. Also, Q ₁₀ for anion exchange calculated from P _Cl values in African lungfish was 2·0, supporting the idea that the temperature sensitivity of erythrocyte anion exchange matches the temperature sensitivity of CO₂ production and transport in ectothermic vertebrates.     

The spleen of the African lungfish Protopterus annectens: freshwater and aestivation

We describe the structure of the spleen of the African lungfish Protopterus annectens in freshwater conditions, and after 6?months of aestivation. The spleen is formed by cortical tissue that surrounds the splenic parenchyma. The cortex is a reticulum that contains two types of granulocytes, developing and mature plasma cells, and melanomacrophage centres (MMCs). The parenchyma is divided into lobules that show a subcapsular sinus and areas of red pulp and white pulp. Red pulp contains vascular sinuses and atypical cords formed by delicate trabeculae. White pulp also contains vascular sinuses and cords. Structural data indicate that red pulp is involved in erythropoiesis, destruction of effete erythrocytes, and plasma cell differentiation. White pulp appears to be involved in the production of immune responses. Macrophages and sinus endothelial cells constitute the reticulo-endothelial system of the spleen. After aestivation, the number of MMCs increases, and spleen tissue is infiltrated by lymphocytes, granulocytes, and monocytes. Also, white pulp is reduced, and sinus endothelial cells undergo vacuolar degeneration. Lungfish spleen shares structural characteristics with secondary lymphoid organs of both ectothermic and endothermic vertebrates, but appears to have evolved in unique ways.     

New information on the cranial anatomy of Acrocanthosaurus atokensis and its implications for the phylogeny of Allosauroidea (Dinosauria: Theropoda)

Background

Allosauroidea has a contentious taxonomic and systematic history. Within this group of theropod dinosaurs, considerable debate has surrounded the phylogenetic position of the large-bodied allosauroid Acrocanthosaurus atokensis from the Lower Cretaceous Antlers Formation of North America. Several prior analyses recover Acrocanthosaurus atokensis as sister taxon to the smaller-bodied Allosaurus fragilis known from North America and Europe, and others nest Acrocanthosaurus atokensis within Carcharodontosauridae, a large-bodied group of allosauroids that attained a cosmopolitan distribution during the Early Cretaceous.

Methodology/Principal Findings

Re-evaluation of a well-preserved skull of Acrocanthosaurus atokensis (NCSM 14345) provides new information regarding the palatal complex and inner surfaces of the skull and mandible. Previously inaccessible internal views and articular surfaces of nearly every element of the skull are described. Twenty-four new morphological characters are identified as variable in Allosauroidea, combined with 153 previously published characters, and evaluated for eighteen terminal taxa. Systematic analysis of this dataset recovers a single most parsimonious topology placing Acrocanthosaurus atokensis as a member of Allosauroidea, in agreement with several recent analyses that nest the taxon well within Carcharodontosauridae.

Conclusions/Significance

A revised diagnosis of Acrocanthosaurus atokensis finds that the species is distinguished by four primary characters, including: presence of a knob on the lateral surangular shelf; enlarged posterior surangular foramen; supraoccipital protruding as a double-boss posterior to the nuchal crest; and pneumatic recess within the medial surface of the quadrate. Furthermore, the recovered phylogeny more closely agrees with the stratigraphic record than hypotheses that place Acrocanthosaurus atokensis as more closely related to Allosaurus fragilis. Fitch optimization of body size is also more consistent with the placement of Acrocanthosaurus atokensis within a clade of larger carcharodontosaurid taxa than with smaller-bodied taxa near the base of Allosauroidea. This placement of Acrocanthosaurus atokensis supports previous hypotheses of a global carcharodontosaurid radiation during the Early Cretaceous.     

Localization of choline acetyltransferase and vasoactive intestinal polypeptide-like immunoreactivity in the nervus terminalis of the fetal and neonatal rat

Ganglia of the nervus terminalis have been shown to contain luteinizing hormone-releasing hormone (LHRH) immunoreactive cells in several mammalian species. These cells are always accompanied by clusters of cells non-immunoreactive to antiserum to LHRH. Using immunocytochemical procedures, we found choline acetyltransferase (ChAT) and vasoactive intestinal polypeptide (VIP) present in cell bodies and in nerve processes throughout the peripheral, intracranial and central projections of the nervus terminalis. In addition, a dense plexus of substance P (SP) immunoreactive fibers was seen in the nasal mucosa surrounding the nasal glandular acini and blood vessels. A number of SP reactive fibers were traced with the olfactory nerves through the cribriform plate of the ethmoid bone and appeared to enter the brain in the area of the central roots of the nervus terminalis.     

Ventricle and outflow tract of the African lungfish Protopterus dolloi

We report a morphologic study of the heart ventricle and outflow tract of the African lungfish Protopterus dolloi. The ventricle is saccular and appears attached to the anterior pericardial wall by a thick tendon. An incomplete septum divides the ventricle into two chambers. Both the free ventricular wall and the incomplete ventricular septum are entirely trabeculated. Only a thin rim of myocardium separates the trabecular system from the subepicardial space. The outflow tract consists of proximal, middle, and distal portions, separated by two flexures, proximal and distal. The proximal outflow tract portion is endowed with a layer of compact, well-vascularized myocardium. This portion is homologous to the conus arteriosus observed in the heart of most vertebrates. The middle and distal outflow tract portions are arterial-like, thus being homologous to the bulbus arteriosus. However, the separation between the muscular and arterial portions of the outflow tract is not complete in the lungfish. A thin layer of myocardium covers the arterial tissue, and a thin layer of elastic tissue underlies the conus myocardium. Two unequal ridges composed of loose connective tissue, the spiral and bulbar folds, run the length of the outflow tract. They form an incomplete division of the outflow tract, but fuse at the distal end. The two folds are covered by endocardium and contain collagen, elastin, and fibroblast-like cells. They appear to be homologous to the dextro-dorsal and sinistro-ventral ridges observed during the development of the avian and mammalian heart. Two to three rows of vestigial arterial-like valves appear in the dorsal and ventral aspects of the conus. These valves are unlikely to have a functional role. The possible functional significance of the "gubernaculum cordis," the thick tendon extending between the anterior ventricular surface and the pericardium, is discussed.     

A light- and electron-microscopic study of mesencephalic neurons projecting to the ganglion of the nervus terminalis in the goldfish

Summary After application of various neuronal tracers (horseradish peroxidase, cobalt-chloride lysine, true blue) to the ganglion of the nervus terminalis a small number of neurons was retrogradely labeled in the mesencephalon. As revealed by combined horseradish peroxidase and catecholamine-fluorescence techniques these neurons are located in the isthmic area immediately rostral to, but not within the locus coeruleus. Cobalt-labeled axons of the mesencephalic neurons were traced individually in serial sections. Neurons projecting contralaterally cross in the horizontal commissure. Tracing of single fibers provided no evidence for axon collaterals within this pathway. Retrograde labeling reveals two different types of isthmic neurons afferent to the ganglion of the nervus terminalis: One smaller-sized type is located bilaterally and consists of four to six neurons; another type possessing many dendritic processes was consistently found as only one single cell located contralateral to the side of injection. The existence of two types of neurons was confirmed by their cytological differences: The small-sized type receives only sparse perisomatic input, while the large-sized type shows heavy somatic and dendritic, probably monoaminergic innervation.