Lithium can transform ear placodes of Xenopus into multiple otic vesicles connected by tubes.
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Animals↗
Biomedical subjects
B Fritzsch
Publications and source records attributed to B Fritzsch.
Dextran amines in neuronal tracing.
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Amines↗
Neurogenesis and learning.
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Animal Communication↗
Dendritic distribution of two populations of ganglion cells and the retinopetal fibers in the retina of the silver lamprey (Ichthyomyzon unicuspis).
The distribution of ganglion cells in the retina of the silver lamprey, Ichthyomyzon unicuspis, was revealed by retrograde labeling from the optic nerve with horseradish peroxidase (HRP) and fluorescent-labeled dextrans in live animals and with the fluorescent dye DiI in aldehyde-fixed tissue. The majority of ganglion cells (74%) termed the "outer ganglion cells," are multipolar and are located at the vitread boundary of the inner nuclear layer. The remaining ganglion cells (26%), termed the "inner ganglion cells" are bipolar and are distributed in a sublamina within the inner plexiform layer. The dense, dendritic meshwork of the outer ganglion cells is largely restricted to the sclerad half of the inner plexiform layer with some cells possessing dendrites which pass through the inner nuclear layer to terminate within the outer plexiform layer. The dendrites of the inner ganglion cells form a thin, dendritic network apposing the inner limiting membrane. Axons from both populations of ganglion cells originate from dendrites or the soma and form fascicles lying adjacent to the outer ganglion cell somata. Retinopetal fibers, originating from bilaterally distributed neurons of the tegmental midbrain, were thin and varicose and ran parallel to the ganglion cell axons to terminate either with a varicose enlargement or a few short sidebranches in the sclerad third of the inner plexiform layer. The unusual organization of the lamprey retina and outgroup comparison with hagfish suggests that agnathans share a presumably primitive type of retinal ganglion cell organization compared to that of gnathostomes.
Animals↗
Ipsilateral retinofugal projections in a percomorph bony fish: their experimental induction, specificity and maintenance.
Adult bony fish possess only a small ipsilateral retinofugal projection, if any. Experimental manipulation, such as unilateral enucleation, can lead to an enhancement of this projection. We examined the patterns of, as well as the conditions for the development and maintenance of an enhanced ipsilateral retinofugal projection (EIRP) after nerve crush, after enucleation, and after various combinations of both types of surgery in juvenile and adult Haplochromis burtoni (Cichlidae). Retinal projections were labeled either unilaterally with horseradish perixodase, or with the lipophilic fluorescent dye DiI in aldehyde-fixed animals, or bilaterally with differently colored fluorescent dextran amines. Unilateral nerve crush always leads to the regeneration of retinofugal fibers to the contralateral tectum but spares some contralateral diencephalic nuclei. In addition, unilateral or bilateral nerve crush in many cases, and unilateral enucleation in some cases, leads to the development of an EIRP to the ipsilateral diencephalon and tectum. This EIRP persists (4 months and longer postoperatively) in only 10% of the unilaterally enucleated animals, in none of the animals subjected to unilateral nerve crush and in 79% of the animals subjected to bilateral nerve crush. All unilaterally enucleated animals in which the remaining, contralateral optic nerve was crushed develop and maintain an EIRP. These data suggest that nerve crush alone is sufficient to cause regenerating fibers to project, at least transiently, to the ipsilateral side of the brain. When the normal contralateral projection is either absent or in the process of regeneration, an EIRP can be maintained. In the latter case, alternate bands or patches of ipsi- and contralateral fibers in the tectum may result. Ipsilateral fibers follow unusual pathways by recrossing at the rostral diencephalon. Likewise, regenerating contralateral retinal fibers grow differently in this area; here, where the optic-nerve projection is reorganized into the optic tract, many regenerating fibers are deflected to the ipsilateral side of the brain. Despite atypical routes taken by some fibers, the EIRP nevertheless ends only in specific retinorecipient areas. An EIRP develops independently of the age of the animal, independently of the time lapse between enucleation and nerve lesion, and independently of persisting debris. However, in animals receiving an optic nerve lesion a long time after unilateral enucleation, the size of the EIRP and its tectal extent are reduced compared to that in animals enucleated around the same time as receiving the crush of the contralateral optic nerve.
Animals↗
Development of tectal neurons in the perciform teleost Haplochromis burtoni. A Golgi study.
The differentiation of the tectum mesencephali of Haplochromis burtoni (Teleostei, Cichlidae) was studied using a modified Golgi rapid impregnation. The analysis concentrated on the gradient of differentiation of four neuronal types, type I, IIIu, VI and XII, in 15-day-old larvae. The following developmental steps taken by these neuronal types are identified: (1) morphogenesis and growth are largely independent developmental events. Tectal neurons first develop their typical dendritic morphology. The tectal lamination, as indicated by the spatial relationships of the dendrites of tectal neurons, is acquired already in 15-day-old larvae. Subsequently the neurons grow to their adult size. Intersegments of dendrites elongate considerably. Dendritic and axonal reorganization and/or intersegmental growth may take place. (2) The teleost cell types I and VI show variable positions of their perikaryon in 15-day-old larvae, but not in adults. It is suggested that they translocate their perikaryon inside their stem dendrite, while their dendrites are already well developed.
Animals↗
Efferents to the labyrinth of the river lamprey (Lampetra fluviatilis) as revealed with retrograde tracing techniques.
The cells of origin of centrifugal fibres to the labyrinth were examined in a jawless vertebrate, the lamprey, with several retrograde tracers (horseradish peroxidase (HRP), fluorescein isothiocyanate (FITC) and rhodamine coupled dextran-amines (FDA and RDA), and cobalt-lysine) that had been applied to the eighth nerve. With all 3 techniques, up to 20 cells were consistently labelled ipsilaterally, adjacent to the Mauthner cell; none were labelled on the contralateral side. The axons of the efferent cells emanate either from lateral dendrites or the perikaryon and course laterally towards the ipsilateral eighth nerve root. The dendrites ramify widely in the basal plate and may thus receive diverse inputs. The same tracers were applied to the lateral-line nerve and afferent fibres were labelled but no efferent cells, thus confirming previous reports. These data suggest that lampreys have an efferent innervation to the labyrinth but not to the lateral line.
Animals↗
The trochlear motoneurons of lampreys (Lampetra fluviatilis): location, morphology and numbers as revealed with horseradish peroxidase.
The cells of origin of the trochlear nerve of Lampetra fluviatilis have been labelled with horseradish peroxidase (HRP) in order to compare the location and morphology of trochlear motoneurons with those of other vertebrates and to gain insight into the phylogenetic changes of the trochlear system. About 126 bipolar and tripolar trochlear motoneuron perikarya are found in a dorsal tegmental position close to the trochlear root. Only approximately 16% of the labelled cells are on the ipsilateral side of the brain, i.e. they lie predominantly contralateral as in gnathostome vertebrates. Dorsally directed dendrites reach the area of lateral-line and retinofugal fibres, and may establish functional contacts. In addition, each motoneuron has a ventral dendrite that extends towards the fasciculus longitudinalis medialis and to the ventral tegmentum. The dendrites branch close to the oculomotor root. Lampreys show a low muscle fibre to motoneuron ratio (4.5:1), i.e., they resemble amniotic vertebrates more than other anamniotic vertebrates. These data demonstrate both closer resemblance and larger differences of cyclostome and gnathostome trochlear motoneurons than previously suggested.
Animals↗
The lateral-line and inner-ear afferents in larval and adult urodeles.
The inner-ear and lateral-line afferents were studied in members of almost all urodele families and in two primitive representatives of anurans and gymnophionans by means of transganglionically transported horseradish peroxidase. The lateral-line projection patterns are, when present, identical in all urodeles and gymnophionans. This is in agreement with the presence of ampullary organs in all urodeles and gymnophionans which possess a lateral-line neuromast system. In contrast, even the most primitive anurans lack both ampullary organs and the dorsal projection of afferents from these organs. In urodeles the inner-ear afferents are found to enter the rhombencephalon via the octaval nerve and bifurcate in the neuropil lateral to the nucleus magnocellularis into a short ascending and a longer descending subpial fascicle. Fibers of the ascending fascicle reach the tip of the lateral recess and terminate in the eminentia granularis. Collaterals are confined to the ipsilateral lobulus lateralis and end presumably as mossy fibers. The descending fascicle ends at the obex level with only a few fibers reaching the second spinal segment. Besides extensive fiber supply to the cells of the ipsilateral ventral-zone column, collaterals are found to reach the reticular formation, nucleus cerebelli, nucleus fasciculus solitarius, intermediate nucleus and several motor nuclei. Differences in the octaval projection among urodele families are limited to variation in its size relative to that of the lateral-line projection. Only species that develop without free-living larvae differ markedly with respect to the absence of lateral-line projections and, presumably, the lateral-line nuclei of the alar plate that exists in larvae. Almost all urodeles that possess a lateral-line system as larvae retain a complete lateral-line system, including neuromasts and ampullary organs, after metamorphosis. Only Salamandra and Chioglossa lose most of their lateral-line afferents and presumably all lateral-line organs around metamorphosis. The octavolateralis projections in urodeles are found to be strikingly similar to those in lampreys, sharks, sturgeons, and, especially, gymnophionans. This points to a great conservatism of this pattern, at least among anamniotic vertebrates. However, even primitive anurans such as Ascaphus differ markedly from these patterns in that they show no ampullary organs or dorsal lateral-line projection but a dorsal projection of the inner ear. Outgroup comparison with other anamniotic vertebrates indicates that the pattern in anurans is derived from the more generalized lateral-line and inner-ear projection pattern as represented in many urodeles and gymno
Amphibians↗
The amphibian octavo-lateralis system and its regressive and progressive evolution.
The phylogenetic and ontogenetic changes in the octavolateralis system of sarcopterygian fish and tetrapods, presumed to be important for the formation of an amphibian auditory system, are reviewed. The lateral line system shows rudimentation of lines and loss of ampullary electroreceptors in many amphibians; in some amphibians it never develops. The metamorphic changes of the lateral-line system show different patterns in the different amphibian lineages with metamorphic retention in most urodeles and metamorphic loss in most anurans. The multitude of both ontogenetic and phylogenetic changes of the lateral line system among amphibians do exclude any prediction as to how this system might have changed in ancestral amniotes. The most important auditory epithelium of the tetrapod inner ear, the basilar papilla, seems to be primitively present in all tetrapods and Latimeria. In two amphibian lineages there is a trend towards rudimentation and loss of the basilar papilla. Only in the third order, the anurans, a tympanic ear develops and the inner ear shows a progressive evolution of the auditory epithelia. Together with the known differences in the periotic labyrinth of amphibians and amniotes, this scenario suggests a parallel evolution of the amniotic and anuran auditory periphery. All mechanoreceptive hair cells of the lateral line system and the inner ear appear to receive a common and bilateral efferent innervation. Among amphibians this pattern is represented only in some urodeles, whereas anurans show a derived pattern with loss of a bilateral component and presumably also of a common neuromast/inner ear component. Changes in the rhombencephalic nuclei which receive octavo-lateralis afferent fibers show a trend towards development of auditory nuclei only in the anuran lineage. The phylogenetic appearance of an auditory nucleus in this lineage coincides with the complete absence of formation of ampullary electroreceptors. In contrast, the earlier claim of a correlation between a metamorphic loss of the lateral line system and the formation of an auditory nucleus is not supported by more recent data: an auditory nucleus develops in anurans already prior to metamorphosis and is present in all anurans even when they retain the neuromast system. In anurans with a metamorphic loss of the neuromasts, the second order neurons degenerate as well. This independence of the auditory and the second order lateral line nuclei is further substantiated by their separate projection to other brain areas, like the torus semicircularis of the midbrain, and their functional properties.(ABSTRACT TRUNCATED AT 400 WORDS)
Amphibians↗
Electron microscopical evidence for common inner ear and lateral line efferents in urodeles.
The efferents of the lateral line system and the inner ear were examined in urodeles using retrograde labelling with horseradish peroxidase (HRP). The Golgi-like filling thus achieved allowed tracing of the axons of efferent cells from one inner ear to the other and from the lateral line nerves into both inner ears. Electron microscopic examination of the inner ear revealed HRP label only in vesicle filled terminals on hair cells traditionally considered as efferent synapses. These data confirm earlier claims of common bilateral inner ear and lateral line efferents. In addition, the efferent nature of retrogradely labelled rhombencephalic cells is proven by their continuity with ultrastructurally identified efferent synapses in the inner ear.
Animals↗
Ipsilateral retinofugal and retinopetal projections in normal and monocular cichlid fish.
A previously unknown ipsilateral retinotectal projection in juvenile and adult cichlid fishes is revealed by anterograde labelling with horseradish peroxidase (HRP). Enucleation results in an enlarged ipsilateral projection from the intact eye; after 4 months this projection may cover the tectum almost completely. These data are interpreted as an increase in the normally occurring ipsilateral projection of newly differentiated ganglion cells due to the absence of interocular competition. Conversely, after enucleation cells of the homolateral thalamoretinal nucleus seem, on the basis of retrograde HRP staining to develop a new connection with the remaining eye.
Animals↗
The development of the amphibian trochlear nucleus. An HRP study.
The quantitative and qualitative development of the trochlear nucleus of salamanders and frogs was studied using horseradish peroxidase (HRP) as a retrograde marker. A higher number of labelled motoneurons significantly declined in later larval stages, presumably by cell death, as in birds and mammals. In agreement with this assumption, HRP-filled apoptotic cells were found in larvae. Many more labelled trochlear motoneurons were found in adult than in larval amphibians, and [3H]thymidine labelling showed postlarval cell production in the area of the trochlear nucleus. Data are discussed in the context of cell death and ongoing cell proliferation.
Ambystoma↗
Metamorphic changes within the lateral-line system of Anura.
The metamorphic loss of lateral-line organs, lateral-line nerves and second order lateral-line neurons was examined in two Anuran species. At the onset of metamorphic climax, terminals within the lateral-line neuropil showed accumulation of glycogen-like granules. Neither the lateral-line nerve nor the organs or the nerve terminals inside the organs displayed any sign of degeneration at this stage. A few second order neurons exhibited accumulations of chromatin into conspicuous masses. These cells were partially or completely engulfed by phagocytes. At mid-metamorphosis all lateral-line organs were lost. The proximal parts of the lateral-line nerve fibers entering the rhombencephalic alar plate showed signs of degeneration. Within the lateral-line neuropil, pre- and some postsynaptic elements exhibited the flocculent type of degeneration or, to a lesser extent, the dark type of degeneration. Second order lateral-line neurons underwent an electron-dense or electron-lucent type of degeneration and were taken up by phagocytes. At the end of metamorphic climax the distal parts of the lateral-line nerves showed numerous dark degenerating fibers inside an intact myelin sheath. Within the lateral-line neuropil, numerous dark degenerating presynaptic elements were found next to some elements showing flocculent degeneration. Fewer degenerating second order neurons were found in the alar plate. They showed predominantly the dark type of degeneration. In contrast to earlier reports, our data suggest that the degenerative metamorphic changes observed in the present study are initiated in all parts of the lateral-line system simultaneously, and lead to the complete loss of all lateral-line organs and nerves and presumably all second order lateral-line neurons as well.
Animals↗
The trochlear nerve of amphibians and its relation to proprioceptive fibers: a qualitative and quantitative HRP study.
The cells of origin of the trochlear nerve of urodeles, anurans and gymnophionans were labelled with HRP in order to compare the location and morphology of trochlear motoneurons and to find evidence for sensory fibers in the trochlear nerve of amphibians. Trochlear motoneuron perikarya were found in a ventral tegmental position predominantly on the contralateral side, but an ipsilateral cell was present in some specimens of urodeles and anurans. About 19 motoneurons were labelled in Ambystoma, about 60 motoneurons in Xenopus, and a maximum of 7 cells in Ichthyophis. Decussation of trochlear nerve fibers showed only in Xenopus a highly variable pattern. In urodeles, selective filling of the trochlear nerve labelled in addition to trochlear motoneurons a caudo-medical tectal group of about 20 neurons of the nucleus of the mesencephalic root of the trigeminal nerve. Gymnophionans showed also labelled cells of the mesencephalic trigeminal root in the caudal midbrain close to the trochlear nerve root. In some frogs, a few cells of the mesencephalic trigeminal root were labelled in the caudal tectum and occasionally in the velum medullare anterius. Comparison of the numbers of trochlear nerve fibers with HRP-labelled motoneurons revealed in Xenopus a proportion of 1.2:1, but of 2.7:1 in Ambystoma. However, counting both labelled motoneurons and cells of the mesencephalic trigeminal root resulted in a trochlear nerve fiber to labelled neuron proportion of 1.3:1 in Ambystoma much like in Xenopus. The numbers of superior oblique muscle fibers and of trochlear nerve fibers, but not of HRP-labelled motoneurons, increased significantly with size in Xenopus laevis. We suggest that increased peripheral branching of individual fibers within the trochlear nerve with size rather than differentiation of additional motoneurons takes place in growing postmetamorphic Xenopus. In contrast to other vertebrates studied so far, the trochlear nerve is a mixed nerve in Ambystoma and perhaps in Ichthyophis. Whether this reflects a primitive or a derived condition is at present unclear.
Ambystoma↗
Visual projections in larval Ichthyophis kohtaoensis (Amphibia: gymnophiona).
The visual projection patterns of retinal efferents were studied in larval Ichthyophis kohtaoensis by means of anterogradely transported HRP. Our results show in all larvae a projection contralateral to a thalamic terminal field, a pretectal terminal field, and a basal optic neuropil, but only a sparse innervation of the contralateral tectum. In addition, all larvae possess an uncrossed projection to a thalamic and a pretectal terminal field. The fibers are bilaterally almost confined to the medial optic tract with only a few fibers running in the marginal and basal optic tract. The ipsilateral and contralateral tracts and terminal fields seem to enlarge during larval life. Comparison with other amphibian orders reveals that larval Ichthyophis are unique in that they develop the medial optic tract and the related thalamic and pretectal terminal fields very early in larval life. In addition they possess only a very sparse tectal projection, though it is the largest projection in larval urodeles and anurans. This suggests a selective phylogenetic loss of those ganglion cells or collaterals which project mainly to the tectum in other amphibian orders and a change in the ontogenetic program leading to an earlier development of the medial optic tract in Ichthyophis as compared to urodeles and anurans.
Amphibians↗
Projection patterns of lateral-line afferents in anurans: a comparative HRP study.
Primary projections of the anterior and posterior lateral-line nerves were traced by means of transganglionic transport of horseradish peroxidase in species belonging to five of the six anuran superfamilies. Both anterior and posterior lateral-line nerve afferents each enter the brain via a single root which divides into two or more bundles. These bundles carry fibers from neuromasts only. No separate dorsal fascicle and no ampullary organs as in urodeles and gymnophions have been found. All bundles join in the neuropil of the nucleus intermedius to form ascending and descending fascicles. Two distinct fascicles are found in species showing little collateralization. No fasciculation is found in species with an elaborate telodendritic arborization. Afferents of the anterior lateral-line nerve run ventromedially and those of the posterior lateral-line nerve dorsolaterally within the ipsilateral nucleus intermedius neuropil. Rostrally they terminate in the vicinity of the eminentia granularis and caudally in the vicinity of the calamus scriptorius. The metamorphic changes in the alar plate do not support the hypothesis of Larsell ('34) as to a change in function of second-order lateral-line neurons into second-order auditory neurons. The rostral part of the nucleus intermedius shows numerous degenerating neurons at metamorphic climax whereas the caudal part becomes part of the nucleus caudalis of adult anurans. Besides the members of the Pipoidea, there is at least the genus Bombina which retains parts of the lateral-line system. The term "dorsal island," its relevance for any part of the anuran brain, and the possible relation between absence of electroreception and the development of the nucleus dorsolateralis are discussed.
Afferent Pathways↗
The origin of centrifugal inner ear fibers of gymnophions (amphibia). A horseradish peroxidase study.
The cells of origin of the centrifugal innervation to the inner ear were investigated in the amphibian order gymnophiona. After applying HRP to the VIIIth nerve inside the otic capsul a Golgi-like labeling was obtained only in a small number of cells in the ipsilateral rhombencephalic basal plate and in the VIIIth nerve afferents. The axons of these cells course after entrance to the raphe and then turn back to the efferent cells in the reticular formation. With respect to the exclusively ipsilateral distribution, the efferent cells of gymnophions resemble those of anurans. With respect to the axon course they resemble those of urodeles, and may thus be regarded as intermediate between the two orders of amphibians. The phylogenetic significance of these findings is discussed.
Amphibians↗