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PubMed1995

[The brain of the Agnatha].

The brain of the Agnatha, especially of the hagfish, is discussed from the viewpoint of the telencephalon and the olfactory, visual, trigeminal, and vestibulolateral sensory systems. Myxiniformes and Petromyzontiformes, which were an independent group in the Ordovician, are thought to represent some parallels of ancestral vertebrate brains. It is interesting to study the brain of the Agnatha to investigate the process of the evolution of the vertebrate brain. In comparison with the lamprey, the hagfish has subcutaneous eyes under an unpigmented patch of skin, 4 paired tentacles at the rostral tip of the head, one semicircular canal on each side, a regressed ventricular system, a "primordium hippocampi" of unresolved homology in the telencephalon, no pineal body, fusion of the habenula of both sides, a tectum opticum with unclear laminations, no macroscopical cerebellum, and optic decussation within the hypothalamus. The arrangements of the trigeminal subnuclei of the descending tract are different from each other, unlike those of other gnathosomata. In the hagfish, the distribution of fibers carrying input of the vestibulum and lateral line system within the area vestibulo-lateralis differs from that of the lamprey, which resembles the teleosts and cartilaginous fish in this respect. These differences may be caused by an independent origin within the Agnatha. The basic organization of the brain of the Agnatha, such as the prosencephalon, mesencephalon, and rhombencephalon are common to the gnathostomata, although some variations in development are included in the sensory centers and higher centers of information processing. The sensory neurons within the brain are found in the medulla oblongata in the Agnatha, whereas in the gnathostomata the mesencephalic nucleus of the trigeminal nerve has been formed in connection with the development of the mandibula.

Animals↗
PubMed1977

The role of the electrosensory system in postural control of the weakly electric fish Eigenmannia virescens.

The role of the electrosensory inputs in postural control was examined in the weakly electric fish Eigenmannia virescens. These fish exhibit tonic postural tilt in response to a tilted plexiglas substrate in both transverse and longitudinal planes (rolling and head-up pitching responses, respectively), but not to electrically "transparent" agar substrate. The fish's pitching and rolling responses were abolished when the electrosensory inputs from the trunk were bilaterally eliminated even though the fish's visual and mechanosensory lateral-line systems remained intact. Unilateral lesion abolished the rolling response but not the pitching response. These results demonstrate the functional role of the electrosensory system in postural control, in addition to its known role in social communication and in object location, and the underlying neuronal mechanism is discussed.

Animals↗
PubMed1992

Distribution and innervation of lateral line organs in the axolotl.

The lateral line system in axolotls consists of three types of receptors and the cranial nerves that innervate them. Superficial neuromasts, which are mechanoreceptors, are distributed in lines on both the head and trunk. Eight cephalic and three trunk lines can be distinguished on the basis of their innervation and differences in the orientation of the major axes of their neuromasts. A combination of histological techniques reveals that five separate pairs of cranial nerves innervate the neuromasts: anterodorsal lateral line nerves innervate cephalic supraorbital and infraorbital lines; anteroventral lateral line nerves innervate cephalic angular, oral, jugal, and preoperculomandibular lines of the cheek and lower jaw; middle and supratemporal lateral line nerves innervate the cephalic postotic lines; and posterior lateral line nerves innervate the trunk lines. In addition to lines of neuromasts, a second class of mechanoreceptive lateral line organs, pit organs, also occur on the head. Pit organs are smaller than neuromasts but are innervated in a manner identical to that of neuromasts: the sensory hair cells of a single pit organ are innervated by two afferent fibers and a single efferent fiber. Although they occur in localized clusters rather than lines, the four distinct pit organ clusters occurring in axolotls are referred to as the anterior, middle, middle cheek, and gular pit lines as they appear to be homologous to the similarly named pit lines in fishes on the basis of their topography and innervation. In addition to neuromasts and pit organs, ampullary organs comprise a third class of lateral line receptors and are restricted to the head. These electroreceptors occur singly or in small clusters adjacent to the neuromast lines and along the base of the external gills. The ampullary organs adjacent to the supraorbital and infraorbital lines are innervated by the anterodorsal lateral line nerves, whereas all other ampullary organs of the head are innervated by the anteroventral lateral line nerves. Thus postotic ampullary organs and neuromasts of the head are innervated by different lateral line nerves. Examination of the sensory ganglia of the lateral line nerves with respect to the ganglia of the other cranial nerves indicates varying levels of fusion. The ganglia of the anterodorsal lateral line and profundal-trigeminal nerves are totally separate throughout their rostrocaudal extent. The ganglia of the anteroventral lateral line and facial nerves form a fused ganglionic complex with the larger pigmented cells of the anteroventral nerve occupying the dorsal portion of the ganglionic complex.(ABSTRACT TRUNCATED AT 400 WORDS)

Ambystoma mexicanum↗
PubMed1997

Evolution of nerve development in frogs. II. Modified development of the peripheral nervous system in the direct-developing frog Eleutherodactylus coqui (Leptodactylidae).

We use whole-mount immunohistochemistry to describe the pattern of development of cranial nerves and muscles in the direct-developing leptodactylid frog Eleutherodactylus coqui. Comparison with nerve development in the biphasically developing frogs Physalaemus pustulosus (Leptodactylidae) and Discoglossus pictus (Discoglossidae; described in a companion paper) allows us to infer the ancestral leptodactylid ontogenetic pattern and the extent to which it has been modified during the evolution of direct development in Eleutherodactylus. While early embryonic development of cranial nerves and muscles is remarkably conserved in E. coqui, most transitory embryonic and larval characters (e.g., occipital and spinal myotomes together with their innervation, the distorted course of trigeminal and facial nerves, ventral branchial arch muscles, a subset of branchial-nerve rami and the lateral-line system) never develop. However, a few larva-typical characters are recapitulated, including Rohon-Beard cells and an anastomosis between the vagal and hypoglossal nerve. In addition to the abbreviation of ontogeny by loss of larva-specific traits, dramatic dissociations and heterochronic shifts of characters can be observed in E. coqui. The onset of development of limb and trunk innervation has been pre-displaced to early embryonic stage. Moreover, the reorientation of cranial muscles and nerves corresponding to late metamorphic events in biphasically developing anurans occurs relatively much earlier and is less pronounced in E. coqui resulting in an extreme condensation of ontogeny.

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

Nearfield detection of dipole sources by the goldfish (Carassius auratus) and the mottled sculpin (Cottus bairdi).

Surprisingly few behavioral data exist on dipole source detection by fish, despite the fact that dipole sources more closely approximate biologically relevant signals than do more nearly monopole sources such as loudspeakers, the stimulus used in nearly all fish auditory studies. In this study, dipole source detection is investigated for two fish species that differ in both their auditory and lateral line systems, the two systems capable of detecting dipole sources. Conditioned suppression of respiration in the goldfish and an unconditioned orienting response in the mottled sculpin were used to measure detection of a 6 mm diameter, sinusoidally vibrating sphere as a function of vibration frequency and source distance. Sound pressure thresholds for the goldfish were nearly independent of distance (15-60 mm) at 800 Hz, but increased with distance at 50 Hz, as they did for the mottled sculpin. The slopes of 50 Hz source level-distance functions, however, differed between the two species. Slopes for the goldfish were independent of distance, remaining at around 8 dB per distance doubling, which is near the 6 dB per distance doubling measured for sound pressure attenuation away from the source, but less than the 18 dB per distance doubling for incompressible flow, measured with an anemometer. Those for the mottled sculpin increased with increasing distance, approaching 18 dB per distance doubling. The nonlinear increase in source level necessary to reach threshold detection was quite similar to the nonlinear decrease in incompressible flow levels measured with the anemometer. Nonlinear increases with distance for 50 Hz sources near the trunk of the mottled sculpin were also similar to those near the head of the fish, where changes in source frequency had little effect on source level-distance functions. These results indicate that sound pressure detection by the ear is important for dipole detection by the goldfish, but that incompressible flow detection by the lateral line is more important for the mottled sculpin. They also indicate that fish such as the goldfish, with a pressure-sensitive swimbladder, are capable of detecting dipole sources at greater distances than are fish without such structures.

Acoustic Stimulation↗
PubMed2004

Development of the zebrafish lateral line.

The lateral line system is simple (comprising six cell types), its sense organs form according to a defined and reproducible pattern, and its neurons are easily visualized. In the zebrafish, these advantages can be combined with a wealth of genetic tools, making this system ideally suited to a combined molecular, cellular and genetic analysis. Recent progress has taken advantage of these various qualities to elucidate the mechanism that drives the migration from head to tail of the sense organ precursor cells, and to approach the questions surrounding axonal guidance and target recognition.

Animals↗
PubMed1998

Afferent and efferent connections of nucleus praeeminentialis in the channel catfish: a reevaluation.

Nucleus praeeminentialis (nPr) is an isthmic nucleus that has been described in the brains of electrosensory teleost fishes and a single non-electrosensory species. The nucleus receives axon collaterals of ascending medullary sensory lemniscal neurons. Axons of nPr neurons project in turn back down onto those same populations of medullary projection neurons via a descending parallel fiber system (the molecular layer or cerebellar crest). Thus nPr forms a link in a sensory feedback loop that modulates the activity of neurons that relay information from medulla to midbrain. The purpose of this study is to investigate the nature of the afferent and efferent connections of the nPr with the specific aim of investigating other sources of input into this modulatory circuit. Transport of neuronal tracers (horseradish peroxidase, DiI and dextran amines) revealed that nPr has extensive interconnections with nuclei in the basal metencephalon, cerebellum, octavolateralis column and basal medulla. A previously described source of afference, the torus semicircularis in the mesencephalon, was not indicated by our studies. Our studies suggest that in addition to regulating the sensitivity and resolution of electrosensory and mechanosensory lateral line systems, the nPr may play a role in the resolution of signal ambiguities posed by auditory or vestibular stimulation of the saccular endorgan of the inner ear.

Afferent Pathways↗
PubMed1977

Observations on the lateral-line sense organs of the Salamander Neurergus crocatus crocatus Cope (Amphibia: Urodela).

The lateral-line system of the subadult and adult Neurergus crocatus crocatus Cope is retained throughout the life. It is constructed of pear-shaped sense organs or neuromasts which in the subadults are confined entirely to the epidermis with their apices opening distally to the exterior at the general level of the epidermal surface whereas in the adults they are embedded proximally more than halfway in the dermis with their distal apices opening into shallow grooves slightly below the regular epidermal surface. Dimensional differences are also observed between these organs in both stages. The neuromasts are constructed of 4 distinct cell types: sense cells, basal cells, sustentacular cells and mantle cells. These cells differ morphologically, structurally, topographically and functionally. The sense cells are clup-shaped, sensory, central in position and couched among the extremely elongated supporting basal and sustentacular cells, all of which are covered laterally by the extremely slender protective mantle cells. In both the mature and larvae, differences are observed among these cells in their size, number, location and arrangement. The sense organs are richly-supplied and well-nourished with vascular and nervous supplies.

Animals↗
PubMed1996

Plasticity of retinal ribbon synapses.

Ribbon synapses differ from conventional chemical synapses in that they contain, within the cloud of synaptic vesicles (SV's), a specialized synaptic body, most often termed synaptic ribbon (SR). This body assumes various forms. Reconstructions reveal that what appear as rod- or ribbon-like profiles in sections are in fact rectangular or horseshoe-shaped plates. Moreover, spherical, T-shaped, table-shaped, and highly pleomorphic bodies may be present. In mammals, ribbon synapses are present in afferent synapses of photoreceptors, bipolar nerve cells, and hair cells of both the organ of Corti and the vestibular organ. Synaptic ribbons (SR's) are also found in the intrinsic cells of the third eye, the pineal gland, and in the lateral line system. The precise function of SR's is enigmatic. The prevailing concept is that SR's function as conveyor belts to channel SV's to the presynaptic membrane for neurotransmitter release by means of exocytosis. The present article reviews the evidence that speaks for a plasticity of these organelles in the retina and the third eye, as reflected in changes in number, size, shape, location, and grouping pattern. SR plasticity is especially pronounced in the mammalian and submammalian pineal gland and in cones and bipolar cells of teleost fishes. Here, SR number and size wax and wane according to the environmental lighting conditions. In the pineal SR numbers increase at night and decrease during the day. In teleost cones, SR's are in their prime during daytime and decrease or disappear at night, when transmitter release is enhanced. In addition to numerical changes, SR's may also exhibit changes in size, shape, grouping pattern, and location. In the mammalian retina of adults, in contrast to the developing retina, the reported signs of SR plasticity are subtle and not always consistent. They may reflect changes in function or may represent signs of degradation. To distinguish between the-two, more detailed studies under selected experimental conditions are required. Probably the strongest evidence for SR plasticity in the mammalian retina is that in hibernating squirrels SR's leave the synaptic site and accumulate in areas as far as 5 microns from the synapse. Changes in shape include the occurrence of club-shaped SR's and round SR's or synaptic spheres (SS's). SS's may represent a special type of synaptic body, yet belonging to the family of SR's, or may be related to the catabolism of SR's. SR number is regulated by Ca2+ in teleost cones, whereas in the mammalian pineal gland cGMP is involved. An interesting biochemical feature of ribbon synapses is that they lack synapsins. The presently reviewed results suggest to us that SR's do not primarily function as conveyor belts, but are devices to immobilize SV's in inactive ribbon synapses.

Animals↗
PubMed1999

Zebrafish stat3 is expressed in restricted tissues during embryogenesis and stat1 rescues cytokine signaling in a STAT1-deficient human cell line.

Transcription factors of the STAT family are required for cellular responses to multiple signaling molecules. After ligand binding-induced activation of cognate receptors, STAT proteins are phosphorylated, hetero- or homodimerize, and translocate to the nucleus. Subsequent STAT binding to specific DNA elements in the promoters of signal-responsive genes alters the transcriptional activity of these loci. STAT function has been implicated in the transduction of signals for growth, reproduction, viral defense, and immune regulation. We have isolated and characterized two STAT homologs from the zebrafish Danio rerio. The stat3 gene is expressed in a tissue-restricted manner during embryogenesis, and larval development with highest levels of transcript are detected in the anterior hypoblast, eyes, cranial sensory ganglia, gut, pharyngeal arches, cranial motor nuclei, and lateral line system. In contrast, the stat1 gene is not expressed during early development. The stat3 gene maps to a chromosomal position syntenic with the mouse and human STAT3 homologs, whereas the stat1 gene does not. Despite a higher rate of evolutionary change in stat1 relative to stat3, the stat1 protein rescues interferon-signaling functions in a STAT1-deficient human cell line, indicating that cytokine-signaling mechanisms are likely to be conserved between fish and tetrapods. Dev Dyn 1999;215:352-370.

Amino Acid Sequence↗
PubMed2001

Early efferent innervation of the zebrafish lateral line.

We examined the efferent innervation of the lateral line in zebrafish larvae. Three efferent nuclei were previously reported for the posterior line, two in the hindbrain and one in the ventral hypothalamus. Here we show that the same three nuclei innervate the anterior line as well. The rhombencephalic neurons innervate either the anterior or the posterior line. The diencephalic neurons seem to innervate both lines as well as the ear. The diencephalic efferents are labeled by anti-tyrosine hydroxylase antibodies and probably use dopamine as a transmitter. They are among the very first catecholaminergic neurons to differentiate in the brain and extend branches into the lateral line system almost as soon as the latter forms. We discuss possible functions of the rhombencephalic and diencephalic efferents.

Animals↗
PubMed1984

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↗
PubMed2003

Postembryonic development of the cranial lateral line canals and neuromasts in zebrafish.

The development of the cranial lateral line canals and neuromast organs are described in postembryonic zebrafish (0-80 days postfertilization). Cranial canal development commences several weeks after hatch, is initiated in the vicinity of individual neuromasts, and occurs in four discrete stages that are described histologically. Neuromasts remain in open canal grooves for several weeks during which they dramatically change shape and increase in size by adding hair cells at a rate one-tenth that in the zebrafish inner ear. Scanning electron microscopy demonstrates that neuromasts elongate perpendicular to the canal axis and the axis of hair cell polarization and that they lack a prominent nonsensory cell population surrounding the hair cells-features that make zebrafish neuromasts unusual among fishes. These results demand a reassessment of neuromast and lateral line canal diversity among fishes and highlight the utility of the lateral line system of postembryonic zebrafish for experimental and genetic studies of the development and growth of hair cell epithelia.

Animals↗
PubMed2006

Control of cell migration in the zebrafish lateral line: implication of the gene "tumour-associated calcium signal transducer," tacstd.

The sensory organs of the zebrafish lateral-line system (neuromasts) originate from migrating primordia that move along precise pathways. The posterior primordium, which deposits the neuromasts on the body and tail of the embryo, migrates along the horizontal myoseptum from the otic region to the tip of the tail. This migration is controlled by the chemokine SDF1, which is expressed along the prospective pathway, and by its receptor CXCR4, which is expressed by the migrating cells. In this report, we describe another zebrafish gene that is heterogeneously expressed in the migrating cells, tacstd. This gene codes for a membrane protein that is homologous to the TACSTD1/2 mammalian proteins. Inactivation of the zebrafish tacstd gene results in a decrease in proneuromast deposition, suggesting that tacstd is required for the deposition process.

Amino Acid Sequence↗
PubMed1990

The evolution of metamorphosis in amphibians.

A survey is provided of the external transformations that coincide with metamorphosis or a water-to-land transition, and of transformations during water-to-land transition in the retinal projection, the brain stem, the lateral-line system, and the inner ear of amphibians. Among the three orders of amphibians, the frogs are characterized by more pronounced transformations during the water-to-land transition than are the other two orders. Some of the progressive and regressive changes in the sensory and nervous system are presented and a scenario is suggested for the evolution of these transformations among amphibians. Suggestions that metamorphosis in frogs can recapitulate the water-to-land transition of ancestral amniotic vertebrates are refuted.

Amnion↗
PubMed1995

Postmetamorphic changes in auditory sensitivity of the bullfrog midbrain.

During metamorphosis, the lateral line system of ranid frogs (Rana catesbeiana) degenerates and an auditory system sensitive to airborne sounds develops. We examined the onset of function and developmental changes in the central auditory system by recording multi-unit activity from the principal nucleus of the torus semicircularis (TSp) of bullfrogs at different postmetamorphic stages in response to tympanically-presented auditory stimuli. No responses were recorded to stimuli of up to 95 dB SPL from late-metamorphic tadpoles, but auditory responses were recorded within 24 hours of completion of metamorphosis. Audiograms from froglets (SVL < 5.5 cm) were relatively flat in shape with high thresholds, and showed a decrease in most sensitive frequency (MSF) from about 2500 Hz to about 1500 Hz throughout the first 7-10 days after completion of metamorphosis. Audiograms from frogs larger than 5.5 cm showed continuous downward shifts in MSF and thresholds, and increases in sharpness around MSF until reaching adult-like values. Spontaneous activity in the TSp increased throughout postmetamorphic development. The torus increased in volume by approximately 50% throughout development and displayed changes in cell density and nuclear organization. These observations suggest that the onset of sensitivity to tympanically presented airborne sounds is limited by peripheral, rather than central, auditory maturation.

Aging↗
PubMed1993

Pit organs in axolotls: a second class of lateral line neuromasts.

The lateral line system of axolotls (Ambystoma mexicanum) consists of mechanoreceptive neuromasts and electroreceptive ampullary organs. All neuromasts in salamanders are located superficially and are organized into lines that are homologous to canal neuromasts in fishes. Ampullary organs are confined to the head and generally are located adjacent to the lines of superficial neuromasts. Axolotls, however, also possess a third class of receptors; these form restricted patches on the head and are possibly homologous to the superficial pit organs in fishes. In order to test this hypothesis the morphology of the suspected pit organs was examined with scanning electron microscopy, and a number of their physiological properties were determined. Pit organs are approximately half the size of neuromasts and have fewer hair cells, although these hair cells do possess kinocilia and stereocilia like those of neuromasts. Pit organs also possess cupulae and exhibit a pattern of innervation identical to that of neuromasts. Pit organs and neuromasts also exhibit similar rates of spontaneous activity, are excited by weak water currents but not weak electric stimuli, and are not inhibited by magnesium ions. Pit organs appear to have slightly lower rates of spontaneous discharge than neuromasts, however, and have slightly lower displacement thresholds to low frequency wave stimuli. These data support the contention that the pit organs of axolotls constitute a second class of neuromasts homologous to the pit organs of fishes.

Ambystoma mexicanum↗