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B Fritzsch

Publications and source records attributed to B Fritzsch.

At least 73 records · Page 4Linked to original sources
PubMed1996

Development of the labyrinthine efferent system.

The data presented here show that labyrinthine and facial branchiomotor efferent cells in the chicken and the mouse become postmitotic overlappingly, both spatially and temporally. Differential migration of labyrinthine efferents and facial motoneurons leads to the already described distinct distribution of labyrinthine efferents and facial motoneurons in adult brains. Differences exist between the chicken and the mouse with respect to the origin of labyrinthine efferents (rhombomere 4 and 5 for the chicken; rhombomere 4 alone for the mouse) and the way contralateral labyrinthine efferents form (migration across the floor plate in the chicken; extension of an axon across the floor plate in the mouse). The different routes taken by migrating motoneurons may all be mediated by substances released from the floor plate, some of which were recently characterized. Labyrinthine efferent axons and facial motoneuron axons segregate at distinctly different areas in the chicken and mouse: outside the brain in the former and inside the brain in the latter. Examination of the possible basis for pathway selection tends to support the idea that efferents use intact afferent fibers as highways for their navigation to distinct sensory epithelia.

Animals↗
PubMed1996

Organizational-activational concept revisited: sexual differentiation in an atherinomorph teleost.

Because of its numerous sexually dimorphic characters, the Western mosquitofish Gambusia affinis affinis is an excellent vertebrate system for addressing questions concerning sexual differentiation. In this review, the actions and limits of gonadal sex steroids, specifically testosterone, on the development of the sexually dimorphic anal fin and its axial and appendicular support are described. Data from our laboratory show that the critical period in this species for the anterior transposition of the male anal fin and its appendicular support occurs during the late embryonic period and that this differentiation of the male phenotypic genital areaduring the critical period is regulated by androgen.

Animals↗
PubMed1996

Neuroanatomical and histochemical evidence for the presence of common lateral line and inner ear efferents and of efferents to the basilar papilla in a frog, Xenopus laevis.

The claimed absence of efferents to the basilar papilla in frogs was reexamined in Xenopus laevis with the use of acetylcholinesterase (AChE) histochemistry. We also tested the presence of common lateral line and inner ear efferents by employing neuroanatomical tract tracing techniques. Our data show some AChE-positive fibers to the basilar papilla and all other sensory epithelia of the inner ear in larval and postmetamorphic frogs. Labeling of anterior lateral line and inner ear fibers with different fluorescing dextran amines resulted in a few double labeled efferent cells in the brainstem. Examination of the branching patterns of anterior lateral line efferents revealed collaterals to the inner ear, predominantly to the saccule and the lagena. In addition, two animals showed common efferents between the anterior lateral line and the basilar papilla. In derived anurans, such as ranids, which reportedly lack efferents to the basilar papilla, the basilar papillary afferents have a peripheral course that differs from that in salamanders and Xenopus. If such efferents are, indeed, absent, we propose that changed cues for pathway selection may have enabled only the afferents, and not the efferents, to reach the basilar papilla in derived frogs.

Acetylcholinesterase↗
PubMed1996

Degeneration of vestibular neurons in late embryogenesis of both heterozygous and homozygous BDNF null mutant mice.

The generation of mice lacking specific neurotrophins permits evaluation of the trophic requirements of particular neuronal populations throughout development. In the present study, we examined the developing vestibulocochlear system to determine the time course of neurotrophin dependence and to determine whether competition occurred among developing cochlear or vestibular neurons for available amounts of either brain-derived neurotrophic factor (BDNF) or neurotrophin-4/5 (NT-4/5). Both cochlear and vestibular neurons were present in mice lacking NT-4/5. In contrast, vestibular neurons decreased in number beginning at mid-stages of inner ear development, in mice lacking BDNF. Early in development (E12.5-13), the size of the vestibular ganglion was normal in bdnf -/- mice. Decreased innervation to vestibular sensory epithelia was detected at E13.5-15, when progressive loss of all afferent innervation to the semicircular canals and reduced innervation to the utricle and saccule were observed. At E16.5-17, there was a reduction in the number of vestibular neurons in bdnf -/- mice. A further decrease in vestibular neurons was observed at P1 and P15. Compared to bdnf -/- mice, mice heterozygous for the BDNF null mutation (bdnf +/-) showed an intermediate decrease in the number of vestibular neurons from E16.5-P15. These data indicate a late developmental requirement of vestibular neurons for BDNF and suggest competition among these neurons for limited supplies of this factor.

Animals↗
PubMed1996

A simple and reliable technique to combine oligonucleotide probe in situ hybridization with neuronal tract tracing in vertebrate embryos.

We describe a simple and reliable combination of in situ hybridization with neuronal tracing. The technique uses recent advances in the field of neuronal tract tracing including fast diffusing, low molecular weight dextran amines and fade resistant fluorescent dyes, and combines them with in situ hybridization using a sensitive oligonucleotide probe. Using this technique we have investigated the mRNA encoding the trkB receptor for brain-derived neurotrophic factor in identified facial and vestibular afferent and efferent neurons. We found very low levels of trkB mRNA in facial efferent neurons, whereas in the vestibular afferent neurons, clear labeling for the trkB mRNA could be seen. This technique can be applied to the developing embryo to study topology of a variety of cellular markers with reference to neuronal population or fibers identified by their origin or target.

Animals↗
PubMed1996

How does the urodele ear develop?

An overview is provided of the structural and molecular events causing the transformation of undifferentiated epidermal cells together with the underlying mesenchyme to become the complex, three-dimensional ear. While tremendous progress has been achieved in a few model systems, enough is not yet known about the comparative embryology of ear development to provide causal explanations of the adult structural differences among species. It is hoped that the changes in selector and/or structural genes, as well as changes in the spatiotemporal induction of structural gene activation, and possible changes in the interaction between the various embryonic sources which contribute to the ear, will soon be understood. The most promising new avenue for research appears to be studies which combine classical transplantation tissue experiments with modern gene expression analyses and modern in vitro assays of the role of putative morphogens or trophic factors. It is emphasized that it is not understood what is missing in the developmental program of those salamanders which have lost a basilar papilla. Direct comparison of gene expression patterns and xenoplastic transplantations in salamanders of comparable stages which either do or do not develop this organ should help to clarify the molecular events that have led to this major evolutionary novel feature of the vertebrate ear.

Ambystoma mexicanum↗
PubMed1995

Tangential migration of luteinizing hormone-releasing hormone (LHRH) neurons in the medial telencephalon in association with transient axons extending from the olfactory nerve.

During embryonic development, luteinizing hormone-releasing hormone (LHRH) neurons migrate to the brain from the medial olfactory epithelium through the olfactory nerve. LHRH neurons enter the brain and migrate tangentially along the medial edge of the telencephalon in close association with a neural cell adhesion molecule (N-CAM) enriched fiber bundle. In the current work we wished to determine whether this N-CAM enriched fiber bundle is an extension of the olfactory nerve. Ablation experiments, immunocytochemistry and diI implants all suggest that LHRH neurons migrate in association with a very small subset of transient N-CAM enriched neuronal processes which extend out of the olfactory nerve proper to the septal-preoptic area.

Animals↗
PubMed1995

Development of midbrain and anterior hindbrain ocular motoneurons in normal and Wnt-1 knockout mice.

The effect of homozygotic Wnt-1-/- mutations on the development of ocular motoneurons was examined with the lipophilic dye DiI and compared to control and phenotypic wild-type mouse embryos. A piece of DiI-soaked filter paper was inserted into the orbit, the midbrain, or rhombomere 5 of the hindbrain in six paraformaldehyde-fixed litters (10.5, 12.5, and 14.5 days postcoitum) containing Wnt-1, Wnt+/-, and Wnt-1+/+ individuals and three control litters. We labeled all ocular motoneurons retrogradely and all relevant nerves anterogradely in all control and phenotypic wild-type animals. In all phenotypically identified Wnt-1-/- mutants we could always label the abducens nerve and motoneurons and the optic fibers to the thalamus, but we were unable to label oculomotor or trochlear nerves or motoneurons. In addition to Wnt-1 knockout mutants, we also labeled mice from the WZT9B transgenic line carrying a lacZ reporter gene driven by the Wnt-1 gene enhancer. In these embryos we tested for co-localization of Wnt-1 expression in biotinylated dextran amine-labeled ocular motoneurons using a newly developed technique. In younger embryos we obtained evidence for co-localization of the beta-galactosidase reaction product derived from lacZ gene activity in some retrogradely filled oculomotor motoneurons and adjacent to other oculomotor and the trochlear motoneurons. Acetylcholine esterase, a marker of early differentiating cholinergic neurons, showed a similar topology with respect to the lacZ reaction product. Thus, at least some future oculomotor motoneurons express Wnt-1, whereas others and the trochlear motoneurons caudal to the ventral midbrain expression of Wnt-1 may be exposed to the short range diffusion of the Wnt-1 gene product. Thus, the Wnt-1-/- mutation precludes formation or survival of midbrain and anterior hindbrain neurons, including oculomotor and trochlear motoneurons.

Animals↗
PubMed1995

Electroreceptors and mechanosensory lateral line organs arise from single placodes in axolotls.

The lateral line system in salamanders consists of mechanoreceptive neuromasts and pit organs, distributed in lines on the head and trunk, and electroreceptive ampullary organs located adjacent to the cephalic lines of mechanoreceptors. Although numerous studies have documented that neuromast and pit organs and the cranial nerves that innervate these receptors arise from a dorsolateral series of placodes, there is no agreement concerning the number of these placodes, the specific groups of receptors that arise from them, or the embryonic origin of ampullary organs. A developmental model was recently proposed (Northcutt et al., 1994) in which all these placodes, except for the most posterior one, elongate to form sensory ridges whose central zones initially form neuromast and pit organ primordia and whose lateral zones subsequently form ampullary primordia. To test this model, individual placodes were unilaterally extirpated, or placodes from pigmented wild-type axolotl embryos were homotopically or heterotopically transplanted into albino hosts. Extirpation resulted in the loss of all three receptor classes, and both homotopic and heterotopic transplants produced pigmented receptors of all three classes in albino hosts. The receptors in the heterotopic transplants still formed lines which occasionally retained their normal orientation despite differentiating in an ectopic environment. These experiments demonstrated that, as previously postulated, specific lines of neuromasts and pit organs do arise from each placode, and ampullary organs also arise from many of the same placodes. The distribution of receptors that develop following incomplete extirpation or heterotopic transplantation also indicates that each placode is patterned regarding receptor classes and orientation prior to sensory ridge formation.

Ambystoma↗
PubMed1994

Development of the anal fin appendicular support in the western mosquitofish, Gambusia affinis affinis (Baird and Girard, 1854): a reinvestigation and reinterpretation.

Development of the sexually dimorphic anal fin appendicular support of an internal fertilizing bony fish Gambusia affinis affinis was investigated by staining whole-mounted embryos, immature, and adult female and male G. a. affinis with alizarin red S and alcian blue. The tissue was examined histologically to assess development of the amphicelous centrum and to verify specificity of the stains. Our data confirm earlier claims about the development of the male and female characteristics in this species, and we provide for the first time direct embryonic evidence suggesting that development of the sexually dimorphic anal fin appendicular support is biphasic: (1) anteriorization of the most anterior caudal segments, and (2) growth and elongation of hemal arches of vertebrae 14-16. The first process involves a sequential homeotic transformation of hemal arches of vertebrae 11-13 through resorption of mineralized connective tissue, thus forming parapophyses that bear pleural ribs. This process begins in undifferentiated embryos and proceeds similarly in postnatal males and females. During the same period, the second process, likely induced by male gonadal hormones, causes the addition of mineralized connective tissue at the hemal arches of vertebrae 14-16. This second process, which occurs only in males, elongates the hemal arches of vertebrae 14-16 anteriorly. This elongation apparently translocates the anal fin appendicular support (including parts of the hemal spine of the hemal arch of vertebra 13) to the level of vertebra 11. It appears that the developmental programs of both female and male G. a. affinis create an area of 6 vertebrae which are markedly different from any vertebrae anterior to 11 and posterior to 16. We propose to term the area including these vertebrae and the associated anal fin, the genital area. We also propose that the first process, homeotic transformation of caudal into precaudal segments, is regulated by differential expression of control genes, such as homeobox genes, whereas the second process is regulated by gene expression under the control of male gonadal hormones. Conflicting data in the literature can be resolved with this model. Appropriate tests of the model are proposed.

Animals↗
PubMed1993

Origin and migration of trochlear, oculomotor and abducent motor neurons in Petromyzon marinus L.

The development of the ocular motor system was studied in 3- to 6-year old larval lampreys with two different retrograde tracers. Motor neurons of the oculomotor and trochlear nuclei are situated closely to one another in younger larvae. Cases in which only trochlear neurons were labelled revealed trochlear motor neurons scattered from the midbrain tegmentum through the anterior medullary velum. We believe this distribution reflects the place of final mitosis (midbrain tegmentum) and subsequent migration (anterior medullary velum) of lamprey trochlear motor neurons. Evidence is also presented for contralateral migration of oculomotor motor neurons and for ventrolateral migration of abducent motor neurons. The distances covered by migrating ocular motor neurons range from 100 to 150 microns in small larvae; these are distances that could be covered easily during the several years duration of larval development in lampreys.

Abducens Nerve↗
PubMed1993

Ipsilateral retinopetal projection of the nucleus olfactoretinalis (NOR) during development and regeneration: a DiI study in a cichlid fish.

The development and regeneration of the ipsilateral retinopetal projection of the nucleus olfactoretinalis (NOR) in the cichlid fish Haplochromis burtoni was studied with 1,1'-dioctadecyl-3,3,3',3'-tetramethyl indocarbocyanine perchlorate (DiI) in fixed tissue. Throughout development most NOR cells projected to the contralateral retina. Only an insignificant, transient elevation of a projection to the ipsilateral retina was found in a few animals; however, after severing the contralateral processes of NOR cells by either enucleation or nerve crush, many animals had significantly more NOR cells with a regenerated process to the ipsilateral retina. Nevertheless, within a few weeks of surgery, the number of animals with ipsilaterally projecting cells were reduced to control values. The transiently enhanced ipsilateral projections to the retina imply changes in the guiding mechanism after these operations and the existence of control mechanisms against unusual connections to the retina in this bony fish.

Animals↗
PubMed1993

Regenerating retinal fibers display error-free homing along undamaged normal fibers.

After crushing one optic nerve in a bony fish, retinal fibers regenerate to both tecta. Anterograde labelling indicates that the ipsilaterally regenerating fibers have a rather straight growth, apparently along the undamaged fibers of the contralateral retina. In contrast, the contralaterally regenerating fibers deviate widely from a straight course. Retrograde labelling shows a mirror-symmetric distribution of regenerated ipsilateral and resident contralateral ganglion cells in a comparable annulus. In contrast, ganglion cells in the regenerated contralateral retina show no topological order after comparable small Dil applications to the ventrolateral tectum. These data suggest that regenerating fibers can orient on the undisturbed, contralateral fibers.

Animals↗
PubMed1993

Fiber pathways and positional changes in efferent perikarya of 2.5- to 7-day chick embryos as revealed with DiI and dextran amines.

The differentiation of facial motoneurons and inner ear (octaval) efferents was examined in chicken embryos by applying DiI or dextran amines to the cut VII/VIII nerve (peripheral label) or to the basal/floor plate of rhombomeres 4/5 (central label). Central labeling found axons of these efferent neurons to leave the brain as early as 2.5 days of incubation. Peripheral labeling identified cell bodies ipsilaterally in rhombomeres 4 and 5 at 2.5 days. Central labeling at 3.5 days showed these fibers to have fully segregated into separate pathways to the facial nerve and the inner ear and that the octaval efferent axons had reached the otocyst wall. By 3.5 days many peripherally labeled octaval efferent somata were found in the floor plate and by 5 days they were found bilaterally. At 6 days, selective peripheral labeling of either the VIIth or VIIIth nerve showed that the contralateral population consisted of octaval efferents and central label applied to the floor plate of rhombomeres 4/5 identified fibers that entered the octaval nerve via the facial root and entered the vestibular sensory epithelia. Together these data suggest an initial mingling of two different motoneuron populations (facial and octaval) in rhombomeres 4/5 and a subsequent segregation by differential migration. Our data also find a much earlier arrival of octaval efferent axons at the otic vesicle than previously described and suggest a contralateral migration of many octaval efferents beginning shortly after their axons reach the facial nerve root.

Animals↗
PubMed1993

Fast axonal diffusion of 3000 molecular weight dextran amines.

The distances of anterograde and retrograde axonal movement per hour were examined for dextran amines of 3000, 10,000 and 40,000 molecular weights (MW) conjugated to different fluorochromes (Cascade blue, fluorescein, tetramethylrhodamine, Texas red) or to biotin. Lateral line nerves of Xenopus laevis tadpoles were used as an easily accessible test system. Only 10,000 and 3000 MW dextran amines underwent significant anterograde and retrograde movement. Dextrans of 3000 MW progressed about twice as far (2 mm/h at 22 degrees C) than 10,000 MW dextrans. Dextrans conjugated to different fluorochromes or to biotin did not show differences in their distance covered. Tracers traveled over the same distance in amphibians pre-treated with either 1 microM colchicine for 2-6 h or 10 micrograms/ml nocodazole for 5 h prior to the application to depolymerize microtubules needed for active transport. This suggests that diffusion is the major mechanism of movement for dextran amines over short distances. In the developing Xenopus retina, 3000 MW dextrans traveled from the optic disc as far away as the ora serrata within 1 h. In mouse embryos, chicken embryos and larval lampreys dextran amines progress within 1 h from cut peripheral nerves through efferent and afferent tracts. These data show that 3000 MW dextrans can be used in much the same way as 10,000 MW dextrans, but label neuronal profiles in a shorter time in a wide variety of species.

Ambystoma↗
PubMed1993

DiI reveals a prenatal arrival of efferents at the differentiating otocyst of mice.

We have reinvestigated the time of arrival of efferent fibers at the developing otocyst of mice employing diffusion of the lipophilic dye DiI in fixed tissue. In contrast to almost all previous reports, our data indicate a prenatal arrival of efferent fibers. A few efferent fibers were found to enter the eighth nerve root at embryonic day (ED) 10 1/2. Retrogradely labelled efferent cell bodies were at this stage coextensive with those of the facial motor nucleus, but started to segregate by ED 12. In contrast to retrogradely labelled facial motor neurons, labelled efferent neurons were bilaterally distributed in the hindbrain with a few projecting to both otocysts as early as ED 12. Anterograde labelling from the brain showed efferent fibers in the vestibular ganglion by ED 11. Invasion of the future vestibular sensory epithelia started by ED 12. Growth cones of efferent fibers had also reached the future cochlear sensory epithelium but invasion was only achieved by a few filopodia at this stage. The early arrival of efferents at the future sensory epithelia demonstrated here may allow an as yet unexplored interaction of efferent fibers with the proliferating and/or differentiating hair cells.

Animals↗