Microscopic aspects of electrosensory system on the partially euryhaline lesser guitarfish

ABSTRACT The electrosensory system on elasmobranchs consists of subcutaneous electroreceptor organs known as ampullae of Lorenzini. The present study investigated the ampullae of Lorenzini morphology of the lesser guitarfish Zapteryx brevirostris, using light microscopy and scanning electron microscopy. The pore number found in the ventral skin surface is much higher than that found in the dorsal portion, characteristic of species that inhabit the euphotic zone. Under light microscopy it was possible to observe that the wall canal consists of a single layer of squamous epithelial cells. The canal features distal expansion, where the ampullae are located with up to six alveoli. The sensory epithelium of ampullae is composed by cubic cells, with oval nucleus, restricted to the interior of the alveoli. With analysis the clusters under scanning electron microscopy, it was possible to observe the structure and the random arrangement of individual ampullae, canals and nerves. The distribution of dorsal and ventral pores and ampullae in Z. brevirostris resembled those of the same family. The number of alveoli per ampullae was similar to that found in euryhaline elasmobranchs species, suggesting that the morphological organization in Z. brevirostris is linked to its possible evolutionary transitory position among batoids.

An IFT-A protein is required to delimit functionally distinct zones in mechanosensory cilia.

BACKGROUND: Conserved intraflagellar transport (IFT) particle proteins and IFT-associated motors are needed to assemble most eukaryotic cilia and flagella. Proteins in an IFT-A subcomplex are generally required for dynein-driven retrograde IFT, from the ciliary tip to the base. We describe novel structural and functional roles for IFT-A proteins in chordotonal organs, insect mechanosensory organs with cilia that are both sensory and motile. RESULTS: The reduced mechanoreceptor potential A (rempA) locus of Drosophila encodes the IFT-A component IFT140. Chordotonal cilia are shortened in rempA mutants and an IFT-B protein accumulates in the mutant cilia, consistent with a defect in retrograde IFT. A functional REMPA-YFP fusion protein concentrates at the site of the ciliary dilation (CD), a highly structured axonemal inclusion of hitherto unknown composition and function. The CD is absent in rempA mutants, and REMPA-YFP is undetectable in the absence of another IFT-A protein, IFT122. In a mutant lacking the IFT dynein motor, the CD is disorganized and REMPA-YFP is mislocalized. A TRPV ion channel, required to generate sensory potentials and regulate ciliary motility, is normally localized in the cilia, proximal to the CD. This channel spreads into the distal part of the cilia in dynein mutants and is undetectable in rempA mutants. CONCLUSIONS: IFT-A proteins are located at and required by the ciliary dilation, which separates chordotonal cilia into functionally distinct zones. A requirement for IFT140 in stable TRPV channel expression also suggests that IFT-A proteins may mediate preciliary transport of some membrane proteins.

Adaptation as a mechanism for gain control in an insect thermoreceptor.

Adaptation controls the gain of the input-function of the cockroach's cold cell during slowly oscillating changes in temperature. When the oscillation period is long, the cold cell improves its gain for the rate of temperature change at the expense of its ability to code instantaneous temperature. When the oscillation period is brief, however, the cold cell reduces this gain and improves its sensitivity for instantaneous temperature. This type of gain control has an important function. When the cockroach ventures from under cover and into moving air, the cold cell is confronted constantly with brief changes in temperature. To be of any use, a limit in the gain for the rate of change seems to be essential. Without such a limit, the cold cell will always indicate temperature change. The decrease in gain for the rate of change involves an increase in gain for instantaneous temperature. Therefore the animal receives precise information about the temperature at which the change occurs and can seek an area of different temperature. If the cockroach ventures back under cover, the rate of change will become slow. In this situation, a high gain improves the ability to signal slow temperature changes. The cockroach receives the early warning of slow fluctuations or even creeping changes in temperature. A comparison of the cold cell's responses with the temperature measured inside of small, cylindrical model objects indicates that coding characteristic rather than passive thermal effects of the structures enclosing the cold cell are responsible for the observed behavior.

Sensilla position on antennae influences afferent terminal location in glomeruli.

The spatial distribution of chemosensory afferent terminals within glomeruli, with respect to their peripheral origin, was investigated using differential staining of afferents in the cockroach. In all glomeruli, the axon terminals of afferents originating from the more distal regions of the flagellum tended to occur in the more distal regions of the glomeruli, relative to the axonal entry side. Afferent terminals tend to be spatially separated, on the basis of their circumferential origin on the flagellum, in pheromone-receptive glomerular complexes and posterodorsally located large glomeruli; however, they were randomly scattered in anteroventrally located small glomeruli. These results revealed that the location of afferent terminals strongly reflects the three-dimensional position of their olfactory receptor neurons in pheromone-receptive glomeruli, but the relationship is weaker in other glomeruli.

The expression pattern of four odorant-binding proteins in male and female silk moths, Bombyx mori.

Four recombinant odorant-binding proteins of Bombyx mori, pheromone-binding protein (PBP), general odorant-binding protein 1 (GOBP1), general odorant-binding protein 2 (GOBP2) and antennal binding protein X (ABPX), were expressed in E. coli and used to raise polyclonal antisera. Immunoblots of antennal homogenates showed that these antisera were specific. In Western blot analysis and immunocytochemical labelling experiments, the sera against recombinant PBP and GOBP2 of B. mori gave identical results as sera against native PBP and GOBP2 of Antheraea polyphemus, respectively, thus confirming earlier results obtained with the latter. Labelling consecutive cross sections of various sensillum types with all four antisera revealed different labelling patterns in male and female sensilla (s.) trichodea and s. basiconica. Long s. trichodea in males and females represented uniform labelling types, whereas for short s. trichodea, s. intermedia, and s. basiconica a great variety of labelling patterns was observed, some being more common than others. Long s. trichodea, which in males are uniformly tuned to the pheromone components bombykol and bombykal, all strongly expressed PBP; labelling with antisera against the other three odorant-binding proteins hardly was above background, only in some hairs GOBP1 was expressed somewhat more strongly. Long s. trichodea of females, which respond specifically to linalool and benzoic acid, showed a different labelling pattern. Here, we observed strong labelling with antibodies against GOBP2 and medium labelling with anti-GOBP1, sometimes with anti-ABPX. S. basiconica in both sexes most commonly co-expressed GOBP1 and GOBP2, but other patterns were occasionally found, with some of them showing PBP expression, also in females. The great variety of labelling types in short s. trichodea, s. intermedia, and s. basiconica suggests a similar variety of functional subtypes as observed in plant odour-sensitive sensilla of other moth species.

Is the number of antennal plate organs (sensilla placodea) greater in hygienic than in non-hygienic Africanized honey bees?

Hygienic behavior is a desirable trait in honey bees (Apis mellifera L.), as hygienic bees quickly remove diseased brood, interrupting the infectious cycle. Hygienic lines of honey bees appear to be more sensitive to the odors of dead and diseased honey bee brood, and Africanized honey bees are generally more hygienic than are European honey bees. We compared the number of sensilla placodea, antennal sensory structures involved in the perception of odor, in 10 bees from each of six hygienic and four non-hygienic colonies of Africanized honey bees. The sensilla placodea of three of the terminal segments (flagellomeres) of the right antenna of each bee were counted with a scanning electron microscope. There were no significant differences in the mean numbers of sensilla placodea between the hygienic and non-hygienic bees, though the variance was higher in the hygienic group. Flagellomere 4 had significantly more sensilla placodea than flagellomeres 6 and 8. However, there was no significant difference between the other two flagellomeres. As hygienic bees are capable of identifying dead, injured, or infested brood inside a capped brood cell, sensilla placodea probably have an important role in enabling worker bees to sense sick brood. However, we did not find greater numbers of this sensory structure in the antennae of hygienic, compared to non-hygienic Africanized honey bees

Recent advances in insect olfaction, specifically regarding the morphology and sensory physiology of antennal sensilla of the female sphinx moth Manduca sexta.

The antennal flagellum of female Manduca sexta bears eight sensillum types: two trichoid, two basiconic, one auriculate, two coeloconic, and one styliform complex sensilla. The first type of trichoid sensillum averages 34 microm in length and is innervated by two sensory cells. The second type averages 26 microm in length and is innervated by either one or three sensory cells. The first type of basiconic sensillum averages 22 microm in length, while the second type averages 15 microm in length. Both types are innervated by three bipolar sensory cells. The auriculate sensillum averages 4 microm in length and is innervated by two bipolar sensory cells. The coeloconic type-A and type-B both average 2 microm in length. The former type is innervated by five bipolar sensory cells, while the latter type, by three bipolar sensory cells. The styliform complex sensillum occurs singly on each annulus and averages 38-40 microm in length. It is formed by several contiguous sensilla. Each unit is innervated by three bipolar sensory cells. A total of 2,216 sensilla were found on a single annulus (annulus 21) of the flagellum. Electrophysiological responses from type-A trichoid sensilla to a large panel of volatile odorants revealed three different subsets of olfactory receptor cells (ORCs). Two subsets responded strongly to only a narrow range of odorants, while the third responded strongly to a broad range of odorants. Anterograde labeling of ORCs from type-A trichoid sensilla revealed that their axons projected mainly to two large female glomeruli of the antennal lobe.

The pit organs of elasmobranchs: a review.

Elasmobranchs have hundreds of tiny sensory organs, called pit organs, scattered over the skin surface. The pit organs were noted in many early studies of the lateral line, but their exact nature has long remained a mystery. Although pit organs were known to be innervated by the lateral line nerves, and light micrographs suggested that they were free neuromasts, speculation that they may be external taste buds or chemoreceptors has persisted until recently. Electron micrographs have now revealed that the pit organs are indeed free neuromasts. Their functional and behavioural role(s), however, are yet to be investigated.

Cell turnover in neuromasts of zebrafish larvae.

The numbers and positions of cells undergoing cell death and proliferation in the neuromasts of 10 day old zebrafish larvae were assessed to investigate the ability of supporting cells to differentiate into hair cells. Evaluations of cell death and proliferation showed that a subpopulation of cells located in the centre of the neuromast undergo cell death, and a different subpopulation located at the periphery proliferate. This suggests that cell death of hair cells and proliferation of mantle supporting cells occurs as part of normal development, creating constant turnover of hair cells. We show that the caspase inhibitor zVADfmk reduces cell death while the aminoglycoside neomycin specifically induces an increased amount of cell death in the central population of cells. Both of these treatments affect the rate of proliferation of the peripheral subpopulation of cells in the neuromast suggesting that a feedback mechanism occurs regulating cell death and proliferation. We propose that the dying population of cells are hair cells and the proliferating cells are 'mantle' supporting cells, which is in agreement with previous observations suggesting that supporting cells can give rise to hair cells following hair cell death.

Morphological and cytological ontogenesis of the ampullae of lorenzini and lateral line canals in the Oman shark, Iago omanensis Norman 1939 (Triakidae), from the Gulf of Aqaba, Red Sea.

The Oman shark, Iago omanensis, is a small, placental viviparous species encountered in great numbers in the deeper waters of the Gulf of Aqaba, Red Sea. It reproduces year-round, providing an opportunity to study ontogenesis of organ systems at various stages of development. This study examines the morphological and cytological development of the mechanoreceptive lateral line (LL) system and the electrosensory Ampullae of Lorenzini. Female I. omanensis were collected bimonthly from the Gulf of Aqaba at depths of 300-800 m and sacrificed with an overdose of MS222. Their uteri were dissected and the embryos separated and fixed for light and electron microscopy. A total of 260 embryos of varying dimensions were studied. The first primordia of neuroectodermal LL neuromasts are seen in embryos of 18 mm TL. These then sink into the dermis, ripen, and develop tubuli that join to form the LL canal systems, especially developed on the head. In contrast, the primordia of Ampullae of Lorenzini start out as groups of embryonic cells situated subdermally. In embryos of 24-26 mm TL initially they develop into tubuli. With growth, the ampullar alveoli gradually widen at their ends to form the sensory epithelium. The ampullar tubuli elongate, bringing the alveoli to sites over the rostrum and head, where the ampullar capsules are formed. The presynaptic electrosensory cells are attached to afferent neural extensions forming sensory rami which extend, as in adult sharks, to the dorsal nucleus in the medulla. In preterm juveniles of 150-160 mm TL, the LL system and the Ampullae of Lorenzini are fully developed cytologically. The results of this study support the hypothesis that the LL system and electrosensory Ampullae of Lorenzini develop as separate modalities and that their structural similarity is due to the origin from the embryonic neuroectoderm. The dichotomy of their evolution occurred in very early ancestry as an ecomorphological adaptation to different sensory functions.

Organization of the antennal motor system in the sphinx moth Manduca sexta.

The antennae of the sphinx moth Manduca sexta are multimodal sense organs, each comprising three segments: scape, pedicel, and flagellum. Each antenna is moved by two systems of muscles, one controlling the movement of the scape and consisting of five muscles situated in the head capsule (extrinsic muscles), and the other system located within the scape (intrinsic muscles) and consisting of four muscles that move the pedicel. At least seven motoneurons innervate the extrinsic muscles, and at least five motoneurons innervate the intrinsic muscles. The dendritic fields of the antennal motoneurons overlap one another extensively and are located in the neuropil of the antennal mechanosensory and motor center. The density of motoneuronal arborizations is greatest in the lateral part of this neuropil region and decreases more medially. None of the motoneurons exhibits a contralateral projection. The cell bodies of motoneurons innervating the extrinsic muscles are distributed throughout an arching band of neuronal somata dorsal and dorsolateral to the neuropil of the antennal mechanosensory and motor center, whereas the cell bodies of motoneurons innervating the intrinsic muscles reside mainly among the neuronal somata situated dorsolateral to that neuropil.

Structural diversity of the ordinary and specialized lateral line organs.

Lateral line organ, a superficial sensory system in amphibia and fish which provides the animal with information about its surrounding environment, is divided classically into two main different types, ordinary and specialized, whose functions are mechanoreceptive and electroreceptive, respectively. Although it has great diversity, the basic sensory unit, which is usually called "neuromast," is composed of sensory cells embedded in accessory cells. The functions of the latter are to support the sensory cells and to secrete the material that covers the organs, forming a cupular structure or filling a canal which enables the organ to communicate with the exterior. Sensory cells of mechanoreceptive neuromasts have a tuft of processes included in the cupular material; these are a kinocilium and a group of stereocilia with a typical staircase arrangement. The displacement of the stereocilia towards or away from the kinocilium produces different stimuli. The electroreceptive organs are more diverse. They include ampullary and tuberous organs. The latter can be subdivided into different types: knollenorgans, mormyromasts, gymnarchomasts, etc. All of these present a great diversity among species, but their morphology is less reported than that of the mechanoreceptive organs. This paper summarizes the structural features of the main different types of lateral line organs, as well as their taxonomic distribution and different patterns of distribution along the surface of the animal.

Multiple factors shape development of olfactory glomeruli: insights from an insect model system.

The antennal system of the moth Manduca sexta is a useful model for studies of the development of olfactory glomeruli, the complex synaptic structures that typically underlie the initial processing of olfactory input in vertebrates and invertebrates. In this review, we summarize cellular events in the construction of glomeruli in Manduca and highlight experiments that reveal factors that influence glomerulus development. By methodically manipulating each of various cell types, both neuronal and glial, that contribute to glomerular architecture, we have found that: olfactory receptor axons lay a template for developing glomeruli, stabilization of the template by glial cells is necessary to permit subsequent steps in development of the glomeruli, and the hormone that regulates adult development causes production of adequate numbers of glial cells. Neither electrical activity nor the presence of a serotonin-containing neuron that persists throughout development is required for a glomerular pattern to develop; these factors might, however, influence the synaptic organization of individual glomeruli.

Graviceptor development in jellyfish ephyrae in space and on Earth.

Graviceptor (rhopalium) development in Aurelia aurita ephyrae which developed on Earth and in space during the nine-day NASA SLS-1 mission was compared. The space-developed ephyrae made graviceptors which were morphologically similar to those of their ground-based controls. Rhopalia of both groups developed statocysts with statoliths, ocelli, ciliated mechanoreceptor cells, and immature touch-plates with one type of hair cell. The number of rhopalia formed per arm of ephyrae of both groups revealed no significant differences. The number of statoliths formed per rhopalium was statistically higher in ephyrae which were induced to form in space with iodine than in L(Launch)+8h controls. Statolith numbers were not significantly different between Earth-formed control ephyrae and those formed from polyps induced on Earth and then sent into space 24h and 48h later. Statolith loss from rhopalia was significantly enhanced in the space-maintained ephyrae in ASW as compared to their controls. Ephyrae formed through thyroxine treatment and those maintained in thyroxine in space had statolith numbers comparable to thyroxine-treated controls. Pulsing abnormalities seen in some space-developed ephyrae suggest that some space-formed ephyrae may have developed abnormal rhopalia because normal rhopalia development and function is necessary for normal pulsing.

Fine structure of a developing insect olfactory organ: morphogenesis of the silkmoth antenna.

The olfactory organ of the silkmoth Antheraea polyphemus is the feathered antenna which carries about 70,000 olfactory sensilla in the male. It develops within 3 weeks from a leaf-shaped epidermal sac by means of segmental primary and secondary indentations which proceed from the periphery towards the centerline. During the first day post-apolysis, the antennal epidermis differentiates into segmentally arranged, alternating sensillogenic and non-sensillogenic regions. Within the first 2 days post-apolysis, the anlagen of olfactory sensilla arise from electron-dense mother cells in the sensillogenic epidermis. The axons of the developing sensilla begin to form the primary innervation pattern during the second day. The sensilla develop approximately within the first 10 days to their final shape, while the indentations are completed during the same period of time. The indentations are most probably driven by long basal extensions of epidermal cells, the epidermal feet. Primary indentations follow the course of segmentally arranged tracheal bundles and form the segments of the antenna. The secondary indentations follow the course of the primary segmental nerves which are reconstructed by this process. During the remaining time of development, the cuticle of the antenna and the sensory hairs is secreted by the epidermal and the hair-forming cells.

Ecto-ATPase/phosphatase activity in the olfactory sensilla of the spiny lobster, Panulirus argus: localization and characterization.

Electrophysiological studies have shown that the olfactory organ (antennule) of the spiny lobster, Panulirus argus, has chemoreceptors that are selectively excited by adenine nucleotides in seawater. Biochemical studies have revealed that these same nucleotides can be rapidly dephosphorylated by ectoenzymes associated with the olfactory sensilla (aesthetascs). In this study the distribution of ecto-ATPase/phosphatase activity within aesthetascs was determined cytochemically and the nature of the adenine-nucleotide dephosphorylating activity was dissected biochemically. Cytochemically, the distribution of ATP-dephosphorylating activity was similar to that shown previously for AMP and beta-glycerol phosphate; i.e., cerium phosphate reaction product was specifically localized to the transitional zone where the sensory dendrites develop cilia and branch to form the outer dendritic segments. Unlike the dephosphorylation of AMP and beta-glycerol phosphate, Mg2+ or Ca2+ was required for ecto-ATPase/phosphatase activity. Biochemical measures of both AMP- and ATP-dephosphorylating activity within aesthetascs corroborated the cytochemical evidence that these activities are localized to the transitional zone. A major portion of the AMP dephosphorylation (about 67%) derives from nonspecific alkaline phosphatase activity that is insensitive to levamisole and L-bromotetramisole. In contrast, nonspecific phosphatase activity accounted for a much smaller part of the ATP dephosphorylation (about 15%). Ectoenzymatic activity in the transitional zone may be an important means of removing excitatory/inhibitory nucleotides from this region.

The cell coat of the sensory and supporting cells of the rainbow trout saccular macula as demonstrated by reaction with ruthenium red and tannic acid.

The surface of most cells is covered by glycoconjugates. The composition and thickness of the surface coat varies among different cell types. The purpose of the present study was to demonstrate the presence of and to characterize the cell coat surrounding the cells in the saccular macula of the rainbow trout. Tissues were fixed in Karnovsky's fixative containing either ruthenium red (0.5, 1, or 2%) or tannic acid (1, 2, or 4%). The apical surface of the sensory and supporting cells reacted with both agents. Varying the concentration of the compounds within a certain range did not significantly affect the degree of tissue staining. Whereas ruthenium red staining was distributed evenly along the luminal surface of the epithelium and along the length of the stereocilia, tannic acid formed electron-dense clumps on the luminal surface of sensory and non-sensory cells and in the basal region of the macular epithelium. The stereocilia of the sensory cells also exhibited tannic acid-positive, electrondense precipitate, particularly near the distal ends of these processes, while uniform staining of the plasma membrane was seen along their lengths. The results of this study suggest that the trout saccular macula is provided with extracellular microenvironments which may be necessary for functional integrity.

An electronmicroscopic study of the lateral line organ of the guppy, Poecilia reticulatus var.

We examined the ultrastructure of the lateral line of the guppy, Poecilia reticulatus var. by using both scanning electron microscopy and transmission electron microscopy. The neuromast was seen to be composed of receptor cells, supporting cells and mantle cells. The receptor cell has one kinocilium and approximately 29 stereocilia. Two kinds of nerve endings were found in the basal portion of the receptor cells. These two types of nerve endings were similar to the efferent and afferent nerves reported previously. The cytoplasm of the supporting cells contains numerous mitochondria, filaments and melanin-like granules. The lateral wall of the neuromast is covered by a few layers of crescent-shaped mantle cells.

[Surface structure of the olfactory organ of marine teleosts]. / Struktura poverkhnosti organa obonianiia morskikh kostistykh ryb.

By means of the electron scanning microscope, structure of the olfactory rosella has been investigated in 5 species of marine Teleostei. Among the species investigated variability in number and arrangement is observed in the olfactory rosella folds. Arrangement order of the receptor and indifferent epithelia of the fold is presented by four types. Interspecies differences in organization of the sensory epithelium is revealed in ratio of various types of receptor and secretory cells. In Teleostei flagellar olfactory cells are the most numerous. In the Limanda yokohamae sensory epithelium certain flagella are described, that essentially differ by their size from usual receptor flagella and, evidently, are their complexes. The secretory cells are found in indifferent and sometimes in sensory epithelium as dark ostia; they are most numerous in mediosmatics. Some of the ostia are like wide craters and are, evidently, ostia of ducts of multicellular olfactory glands.