SUPPRESSION AND RESTORATION OF THE MICROPHONIC OUTPUT FROM THE LATERAL LINE ORGAN AFTER LOCAL APPLICATION OF STREPTOMYCIN.
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Animals↗
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Neuropeptides and monoamines in the torus semicircularis of the carp (Cyprinus carpio).
The distribution of vasoactive intestinal polypeptide, gastrin-releasing peptide, gamma-melanocyte-stimulating hormone, alpha-neo-endorphin, angiotensin II, cholecystokinin-8, serotonin, and tyrosine hydroxylase has been studied in the nuclei lateralis and centralis of the Cyprinus carpio torus semicircularis using an indirect immunoperoxidase technique. In both nuclei, we found vasoactive intestinal polypeptide, gastrin-releasing peptide, gamma-melanocyte-stimulating hormone, alpha-neo-endorphin, serotonin, and tyrosine hydroxylase immunoreactive fibers, whereas the torus semicircularis was not immunoreactive for cholecystokinin-8 and angiotensin II. Moreover, no immunoreactive cell bodies containing peptides or monoamines were observed. The presence of these peptides and monoamines in both the nuclei lateralis and centralis suggests that such substances might be involved in the control of the visual, auditive, and/or lateral line information systems.
Animals↗
FUNCTIONAL ANATOMY OF THE VESTIBULAR AND LATERAL LINE ORGANS.
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Animals↗
Lateral line hair cell maturation is a determinant of aminoglycoside susceptibility in zebrafish (Danio rerio).
Developmental differences in hair cell susceptibility to aminoglycoside-induced cell death has been observed in multiple species. Increased sensitivity to aminoglycosides has been temporally correlated with the onset of mechanotransduction-dependent activity. We have used in vivo fluorescent vital dye markers to further investigate the determinants of aminoglycoside induced hair cell death in the lateral line of zebrafish (Danio rerio). Labeling hair cells of the lateral line in vivo with the dyes FM 1-43, To-Pro-3, and Yo-Pro-1 served as reliable indicators of hair cell viability. Results indicate that hair cell maturation is a determinant of developmental differences in susceptibility. The age dependent differences in susceptibility to aminoglycosides are independent of the onset of mechanotransduction-dependent activity as measured by FM 1-43 uptake and independent of hair cell ability to take up fluorescently conjugated aminoglycosides.
Animals↗
Localization of anosmin-1a and anosmin-1b in the inner ear and neuromasts of zebrafish.
Anosmin-1, encoded by the KAL-1 gene, is the protein defective in the X-linked form of Kallmann syndrome. This human developmental disorder is characterized by defects in cell migration and axon target selection. Anosmin-1 is an extracellular matrix protein that plays a role, in vitro, in processes such as cell adhesion, neurite outgrowth, axon guidance, and axon branching. The zebrafish possesses two orthologues of the KAL-1 gene: kal1a and kal1b, which encode anosmin-1a and anosmin-1b, respectively. Previous in situ hybridization studies have shown that kal1a and kal1b mRNAs are expressed in undetermined cells of the inner ear but not in neuromast cells. Using specific antibodies against anosmin-1a and anosmin-1b, we report here that both proteins are expressed in sensory hair cells of the inner ear cristae ampullaris and the lateral line neuromasts. Accumulation of these proteins was observed mainly at the level of the hair bundle and also at the cell membrane. In neuromast hair cells, immunogold scanning electronmicroscopy demonstrated that anosmin-1a and anosmin-1b were present at the surface of the stereociliary bundle. In addition, anosmin-1a, but not anosmin-1b, was detected on the track of the ampullary nerve. This is the first report of anosmin-1 expression in sensory hair cells of the inner ear and lateral line, and along the ampullary nerve track.
Animals↗
Dynamic expression of the osmosensory channel trpv4 in multiple developing organs in zebrafish.
Transient receptor potential channels function in a wide spectrum of tissues and transduce sensory stimuli. The vanilloid (capsaicin) channel TRPV4 is sensitive to osmotic changes and plays a central role in osmoregulatory responses in a variety of organisms. We cloned a zebrafish trpv4 cDNA and assayed its expression during embryogenesis. trpv4 is expressed as maternal mRNA in 4-cell embryos and later zygotic expression is first observed in the forming notochord at the one somite stage. Notochord expression persists to 24 hpf when broad expression in the brain is observed. At 32 hpf trpv4 expression is observed in the endocardium, restricted primarily to the ventricular endothelium. Low level expression of trpv4 is also seen from 32-48 hpf in the pronephric kidney with strongest expression in the most distal nephron segment and in the cloaca. Expression is also observed in lateral line organs starting at 32 hpf, primarily in the hair cells. At 72 hpf, expression of trpv4 in heart, kidney, brain, and lateral line organs persists while expression in the notochord is down-regulated.
Amino Acid Sequence↗
A synchronization-desynchronization code for natural communication signals.
Synchronous spiking of neural populations is hypothesized to play important computational roles in forming neural assemblies and solving the binding problem. Although the opposite phenomenon of desynchronization is well known from EEG studies, it is largely neglected on the neuronal level. We here provide an example of in vivo recordings from weakly electric fish demonstrating that, depending on the social context, different types of natural communication signals elicit transient desynchronization as well as synchronization of the electroreceptor population without changing the mean firing rate. We conclude that, in general, both positive and negative changes in the degree of synchrony can be the relevant signals for neural information processing.
Action Potentials↗
Anemone repair proteins as a potential therapeutic agent for vertebrate hair cells: facilitated recovery of the lateral line of blind cave fish.
Blind cave fish use the lateral line sensory system to detect nearby objects. The fish responds to sudden perturbations in the water column by initiating startle responses in which they swim more rapidly. Normal startle responses disappear after trauma caused by a single 15 s immersion in calcium free water, but return within 5 days if the traumatized fish are treated with 'repair proteins' isolated from sea anemones. Polyclonal antibodies raised to fraction beta, a specific chromatographic fraction of repair proteins, bind to hair cells within superficial neuromasts. Likewise, biotinylated fraction beta binds to hair cells in neuromasts. Neuromast hair cells exposed to calcium free water followed by repair proteins have more compact hair bundles than do hair cells exposed only to calcium free water. We propose that anemone repair proteins replace linkages between stereocilia destroyed by exposure to calcium free water.
Animals↗
Sensitivity, polarity, and conductance change in the response of vertebrate hair cells to controlled mechanical stimuli.
Hair cells, the primary receptors of the auditory, vestibular, and lateral-line sensory systems, produce electrical signals in response to mechanical stimulation of their apical hair bundles. We employed an in vitro preparation and intracellular recording to investigate the transduction mechanism of hair cells in the sacculus from the inner ear of the bullfrog (Rana catesbeiana). When stimulated directly by mechanical deflection of their hair bundles, these cells gave graded responses up to 15 mV in amplitude; the peak sensitivity was about 20 mV/micron deflection. The depolarizing component of the receptor potential corresponding to stimuli directed towards the kinocilium. Depolarizing responses were associated with a membrane resistance decrease, and hyperpolarizing responses with a resistance increase. Action potentials, possibly calcium spikes, were occasionally evoked in hair cells by mechanical or electrical stimulation.
Animals↗
A study of the orientation of the sensory hairs of the receptor cells in the lateral line organ of fish, with special reference to the function of the receptors.
The morphology of the hair bundles on top of the receptor cells in the lateral line organ of the teleost fish Lota vulgaris is described. Each receptor cell shows a distinct morphological polarization. Two groups of receptor cells can be distingiushed, one consisting of cells polarized towards the head, the other consisting of cells polarized towards the tail. In the crista ampullaris all cells are polarized in the same direction. An hypothesis is proposed for the function of the receptor cells in the lateral line organ and the labyrinth based on a correlation of morphological and functional polarization.
Animals↗
SOME OBSERVATIONS ON THE FINE STRUCTURE OF THE LATERAL LINE ORGAN OF THE JAPANESE SEA EEL LYNCOZYMBA NYSTROMI.
The fine structure of the lateral line organ of the Japanese sea eel Lyncozymba nystromi has been studied with the electron microscope. The sensory epithelium of the lateral line organ consists of a cluster of two major types of cells, the sensory hair cells and the supporting cells. The sensory cell is a slender element with a flat upper surface provided with sensory hairs, Two different types of synapses are distinguished on the basal surface of the receptor cell. The first type is an ending without vesicles and the second type is an ending with many vesicles. These are presumed to correspond to the afferent and the efferent innervations of the lateral line organ. The fine structure of the supporting cells and the morphological relationship between the supporting cells and the receptor cells were observed. The possible functions of the supporting cells are as follows: (a) mechanical and metabolic support for the receptor cell; (b) isolation of the individual receptor cell; (c) mucous secretion and probably cupula formation; (d) glial function for the intraepithelial nerve fibers. Both myelinated and unmyelinated fibers were found in the lateral line nerve. The mode of penetration of these fibers into the epithelium was observed.
Animals↗
THE ULTRASTRUCTURE OF THE KINOCILIUM OF THE SENSORY CELLS IN THE INNER EAR AND LATERAL LINE ORGANS.
The bundle of sensory hairs protruding from the top of each receptor cell in the vestibular and lateral line organs in the teleost fish (burbot) Lota vulgaris is composed of a number of stereocilia and one kinocilium located in the periphery of the bundle. The ultrastructure of the kinocilium and its basal body is described. It is found that the kinocilium is morphologically polarized by the asymmetric arrangement of its component fibers and of the basal body by the presence of a basal foot. Peripheral fibers 5 and 6 of the kinocilium and the basal foot of the basal body are oriented away from the stereocilia; that is, in a direction coinciding with the direction of excitatory stimulation. The findings are discussed in terms of directional sensitivity.
Animals↗
Sensory brain areas in mesopelagic fishes.
Four areas of the brain that receive primary projections from chemical senses ([1] olfactory bulb, [2] facial and vagal lobes), the eye ([3] optic tectum), and somato- and mechanosensory systems such as the lateral line, vestibular and auditory systems ([4] trigeminal and octavolateral regions) have been studied and relative size differences used to deduce the sensory specializations of 67 species of mesopelagic fishes. One type of analysis used the average relative volumes of brain areas and identified 'specialists' with only one brain area above-average (36%), species 'dominated' by two sensory brain regions (49%), and generalists (15%), with three areas above-average. In addition, a cluster analysis was performed that separated 49 species which were mostly visually oriented from 18 non-visual species, among which 16 were characterized by an association of above-average trigeminal/octavolateral and gustatory areas, and a single species with a dominant olfactory bulb. The results support the idea that these species occupy a rich sensory environment for which the absence of sunlight is compensated by chemical and mechanosensory stimuli as well as by bioluminescent signals. This has lead to the development of specializations for the perception of single stimulus-modes, most notably for the visual system, as well as for combinations of various receptors and central processing areas, with a preference for associating either the chemical senses, including the olfactory and facial/vagal systems, or the trigeminal/octavolateral systems.
Animals↗
Modeling electrosensory and mechanosensory images during the predatory behavior of weakly electric fish.
Black ghost knifefish (Apteronotus albifrons) are nocturnal, weakly electric fish that feed on insect larvae and small crustaceans in the freshwater rivers of South America. In the absence of visual cues, prey detection and localization in this species is likely to rely on weak electrosensory and mechanosensory cues generated by the prey. In this paper, a modeling approach is used to estimate contributions to prey capture behavior from three octavolateralis modalities: the high- (tuberous) and low- (ampullary) frequency components of the electric sense and the high-frequency (canal neuromast) component of the lateral line mechanosensory system. For each of these modalities, the physical stimulus generated by the prey is approximated using a simple dipole model. Model parameters are constrained using previously published data as well as new empirical data on the electrical impedance characteristics of Daphnia magna. Models of electrosensory and mechanosensory stimuli are combined with actual prey strike trajectories from infrared video recordings to reconstruct spatial images of the prey along the sensory surface of the fish during the behavior. Modeling results suggest that all three modalities might contribute and that the relative contributions may change as a function of environmental conditions (e.g., water conductivity) and as a function of time over the course of the prey capture event.
Animals↗
Neural mechanism of the lateral-line organ of fish; fundamental neural mechanism of sensory organs in general.
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Animals↗
ELECTRON MICROSCOPIC AND ELECTROPHYSIOLOGICAL STUDIES ON THE LATERAL LINE CANAL ORGAN.
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Animals↗
Frequency response properties of lateral line superficial neuromasts in a vocal fish, with evidence for acoustic sensitivity.
The mechanosensory lateral line of fish is a hair cell based sensory system that detects water motion using canal and superficial neuromasts. The trunk lateral line of the plainfin midshipman fish, Porichthys notatus, only has superficial neuromasts. The posterior lateral line nerve (PLLn) therefore innervates trunk superficial neuromasts exclusively and provides the opportunity to investigate the physiological responses of these receptors without the confounding influence of canal organs. We recorded single-unit activity from PLLn primary afferents in response to a vibrating sphere stimulus calibrated to produce an equal velocity across frequencies. Threshold tuning, isovelocity, and input/output curves were constructed using spike rate and vector strength, a measure of phase locking of spike times to the stimulus waveform. All units responded maximally to frequencies of 20-50 Hz. Units were classified as low-pass, band-pass, broadly tuned, or complex based on the shapes of tuning and isovelocity curves between 20 and 100 Hz. A 100 Hz stimulus caused an increase in spike rate in almost 50%, and significant synchronization in >80%, of all units. Midshipman vocalizations contain significant energy at and below 100 Hz, so these results demonstrate that the midshipman peripheral lateral line system can encode these acoustic signals. These results provide the first direct demonstration that units innervating superficial neuromasts in a teleost fish have heterogeneous frequency response properties, including an upper range of sensitivity that overlaps spectral peaks of behaviorally relevant acoustic stimuli.
Acoustic Stimulation↗
Onset of neural function in the lateral line.
The development of the nervous system includes the formation of specific neuronal connections. Some insight into the mechanisms by which these connections are made may be obtained by determining the order in which the elements of a developing system begin to function and examining any changes that may occur in the system shortly after it begins functioning. I have investigated the lateral line of the South African clawed frog, Xenopus laevis and I have classified the afferent system into three elements. First, the transduction mechanism, which includes all components that couple the water vibrations to the release of transmitter from the hair cell. Second, the afferent synapse, at which there is transmitter release and subsequent postsynaptic conductance changes. And third, the afferent axon. I report here experiments suggesting that these elements become functional in the following order: first, the axon can conduct action potentials; second, transmission is established; third, the transduction mechanism can modulate transmitter release. This same sequence has been reported in a system related to the lateral line, the auditory pathway of mammals.
Afferent Pathways↗