Surface features, sensory structures, and movement of the newly excysted juvenile Fasciola hepatica L.

Three types of presumed sensory endings were distinguished by scanning electron microscopy: a ciliated type, a domed type, and a pit. The ciliated and domed type were also serially sectioned for transmission electron microscopy. Six of the pit type were observed, a group of 3 on each side of the oral sucker. The ciliated type were found only among the tegumental spines, and on the anterior ventrolateral surfaces except for an anterodorsal pair. The domed type resembled the ciliated type in that it had a ciliary basal body and rootlet but it lacked a cilium. It was found only in the tegument above the suckers where it probably serves as a pressure or contact receptor. Movement in vitro occurred by alternate attachment and release of the suckers with a vermiform peristalsis and the rings of spines between the suckers were considered to aid this movement in vivo.     

Larval apical sensory organ in a neritimorph gastropod,an ancient gastropod lineage with feeding larvae

The Neritimorpha is an ancient clade of gastropods that may have acquired larval planktotrophy independently of the evolution of this developmental mode in other gastropods (caenogastropods and heterobranchs). Neritimorphs are therefore centrally important to questions about larval evolution within the Gastropoda, but there is very little information about developmental morphology through metamorphosis for this group. We used immunolabeling (antibodies binding to acetylated α-tubulin and serotonin) and serial ultrathin sections for transmission electron microscopy to characterize the apical sensory organ in planktotrophic larvae of a marine neritimorph. The apical sensory organ of gastropod larvae is a highly conserved multicellular sensory structure that includes an apical ganglion and often an associated ciliary structure. Surprisingly, the apical ganglion of Nerita melanotragus (Smith, 1884) does not have typical ampullary neurons, a type of sensory neuron consisting of a cilia filled inpocketing that has been described in all other major gastropod groups. N. melanotragus has cilia-filled pockets embedded within the apical ganglion, but these so-called “sensory cups” are cassettes of multiple cells: one supporting cell and up to three multiciliated sensory cells. We suggest that an internalized pocket that is filled with cilia and open to the exterior via a narrow pore may be essential architectural features for whatever sensory cues are detected by ampullary neurons and sensory cups; however, morphogenesis of these features at the cellular level has undergone evolutionary change. We also note a correlation between the number of sensory elements consisting of cilia-filled pockets within the larval apical sensory organ of gastropods and morphological complexity of the velum or length of the trochal ciliary bands.     

The Nervous System of the Male Dinophilus gyrociliatus (Annelida: Polychaeta). I. Number, Types and Distribution Pattern of Sensory Cells

The entire nervous system of the smallest annelid hitherto known, the dwarf male of the highly dimorphic species Dinophilus gyrociliatus , has been reconstructed by means of TEM investigations of serial ultrathin sections. Altogether there are 68 neurons, 40 of which have a sensory function. The structure and distribution of them is described. The receptor endings of the 20 sensory cells of each side are located either in two groups — the anterior receptor group and the posterior receptor group — or are singly positioned in the integument. Structural differences of the apical portion of the dendrites enables four types of receptors to be distinguished: three types with emergent cilia and one type with non-emergent cilia. Neurons with emergent cilia can be monociliated collar cells as well as mono- or multiciliated cells without collar. Special vesicle-in-vesicle structures, are located close to the basal portion of the cilia in some of these cells. The non-emergent cilia border closely to a neighbouring epidermal cell and contain a prominent intraciliary vesicle. The function of receptors is discussed with regard to a comparison with receptors in other polychaete species, structural specializations and their distribution pattern on the animal's surface.     

Ultrastructural study of sensory cells of the proboscidial glandular epithelium of Riseriellus occultus (Nemertea,Heteronemertea)

Only one sensory cell type has been observed within the glandular epithelium of the proboscis in the heteronemertine Riseriellus occultus. These bipolar cells are abundant and scattered singly throughout the proboscis length. The apical surface of each dendrite bears a single cilium enclosed by a ring of six to eight prominent microvilli. The cilium has the typical 9×2 + 2 axoneme arrangement and is equipped with a cross-striated vertical rootlet extending from the basal body. No accessory centriole or horizontal rootlet was observed. Large, modified microvilli (stereovilli) surrounding the cilium are joined together by a system of fine filaments derived from the glycocalyx. Each microvillus contains a bundle of actin-like filaments which anchor on the indented inner surface of a dense, apical ring situated beneath the level of the ciliary basal body. The tip of the cilium is expanded and modified to form a bulb-like structure which lies above the level where the surrounding microvilli terminate. In the region where the cilium emerges from the microvillar cone, the membrane of the microvillar apices makes contact with a corresponding portion of the ciliary membrane. At this level microvilli and cilium are apparently firmly linked by junctional systems resembling adherens junctions. The results suggest that these sensory cells may be mechanoreceptors. © 1996 Wiley-Liss, Inc.     

Sensory and secretory cells ofOphryotrocha puerilis (Polychaeta)

Summary As revealed by glyoxylic acid induced fluorescence, the protandric polychaeteOphryotrocha puerilis possesses different types of catecholaminergic primary bipolar sensory cells, the perikarya of which are located beneath the epidermis. About 20 of such receptors are situated in each segment but they are mostly found on antennae, palps, urites and parapodial cirri. The dendrites of these sensory neurones run to the cuticle and dilate to form receptive endings. Three different types of dendritic endings could be distinguished: (1) multiciliary receptors with 4–8 cilia and ciliary rootlets, (2) monociliary receptors with microvilli arranged like a funnel and electron-dense cuffs and (3) monociliary receptors of the collar-type with, constantly, ten microvilli surrounding one single central cilium. The latter type is also characterized by rootlet fragments. Dendrites and dilated receptive endings of all three types contain clear (putative secretory) vesicles, multivesicular bodies and mitochondria. Pharmacological treatment (dopamine, reserpine) does not affect the number of secretory vesicles of the receptor neurones. Extra vesicular storage of catecholamines is discussed. Secretory cells of unknown function containing large numbers of electron-dense vesicles are usually found in close association with sensory cells.Abbreviations CA catecholamines - DA dopamine - RE reserpine     

Innervation of the maxillary vibrissae in mice as revealed by anterograde and retrograde tract tracing

Vibrissae are a unique sensory system of mammals that is characterized by a rich and diverse innervation involved in numerous sensory tasks with the potential for species-specific differences. In the present study, indocarbocyanine dyes (DiI and PTIR271) and confocal microscopy were combined to study the innervation of the mystacial vibrissae and vibrissa-specific sensory neuron distribution in the maxillary portion of the trigeminal ganglion of the mouse. The deeper regions of the vibrissa cavernous sinus (CS) contained a dense plexus of free nerve endings, possibly of autonomic fibers. The superficial part of this sinus displayed a massive array of corpuscular endings. Innervation in the region of the ring sinus consisted of Merkel endings and different morphological variances of lanceolate endings. The region of the inner conical body had a circular plexus of free nerve endings. In addition to confirming previous observations obtained by a variety of other techniques and ultrastructural studies, our studies revealed denser terminal receptor endings in a different distribution pattern than previously demonstrated in studies using the rat. We also revealed the distribution of sensory neurons in the trigeminal ganglion using retrograde tracing with fluorescent tracers from two nearby vibrissae. We determined that the populations of sensory neurons innervating the two vibrissae were largely overlapping. This suggests that the somatotopic maps of vibrissal projections reported at the different levels in the neuraxis are not faithfully reproduced at the level of the ganglion.This work was supported by a grant from the NIDCD (RO1 DC 005590; BF), the Egyptian government (AM), and the NIH (ES00365-01 and RR-02-003; LH).     

Characterization of a thy1.2 GFP transgenic mouse reveals a tissue-specific organization of the spinal dorsal horn

In this study, transgenic mice in which membrane-linked enhanced green fluorescent protein (mGFP) is expressed from the Thy1.2 promoter were used. In these mice, a subpopulation of small to medium sized DRG neurons double stained for IB4 but not for CGRP. Most of the peripheral terminals traversed the dermis and ramify within the epidermis and form superficial terminals. Within the spinal cord, these afferents terminated exclusively within the substantia gelatinosa (SG). A second fibre type in the skin also expressed mGFP, and formed club-shaped endings towards the bases of hairs. Injury to the sciatic nerve resulted in mGFP loss from the SG ipsilateral to the nerve injury, but also in the corresponding region contralaterally. Together, these findings reveal the specificity of connectivity of a defined subpopulation of DRG sensory neurons innervating the epidermis and this will facilitate analysis of their physiological functions.     

Ultrastructural observations on the sensory papillae of juvenile and adult Gorgoderina vitelliloba (Trematoda: Gorgoderidae)

Hoole D. and Mitchell J.B. 1981. Ultrastructural observations on the sensory papillae of juvenile and adult Gorgoderina vitelliloba (Trematoda : Gorgoderidae). International Journal for Parasitology11: 411–417. Ultrastructural observations have been made on the juvenile and adult stages of Gorgoderina vitelliloba from Rana temporaria. Four types of sensory papillae occur; button, rosette, ciliated and domed. Button papillae, which contain a ciliary-rootlet but lack a cilium, occur on the oral sucker, dorsal preacetabular surface and the lateral margins of the fluke. Scanning electron microscopical observations reveal that the tegumental protuberances of the papilla are transformed from a spiked or conical appearance in juvenile flukes to a rounded form in adult flukes. Rosette papillae, which also contain a rootlet, occur on the lip of the ventral sucker of both juvenile and adult flukes. Ciliated papillae only occur on the oral sucker of juvenile flukes. Domed papillae, which contain a large area of electron-dense material, occur on the internal surface of the ventral sucker of both juvenile and adult flukes. The functions of papillae and their possible role in the migration of the parasite are discussed.     

A kinematic study of crawling behavior in the leech,Hirudo medicinalis

The medicinal leech crawls along a solid substrate by repeated alternating extensions and shortenings of the body. Extension occurs with the posterior sucker attached and the head sucker free. The head sucker then attaches, followed by shortening and release of the tail sucker. The tail sucker is then pulled toward the head, where it reattaches to the substrate. The head sucker then releases, and another crawling cycle begins (Figs. 1, 5). There are two crawling variants: inchworm crawling, in which the head and tail suckers are closely apposed at the end of a cycle and the body forms a loop above the substrate, and vermiform crawling, in which the suckers are placed farther apart and the body remains fairly close to the substrate (Fig. 1). The cycle period and the distance traveled during a cycle are greater in inchworm than in vermiform crawling; however, the velocity of travel is the same for both (Fig. 2). For both variants, the interval between head sucker attachment and tail sucker release is similar at all cycle periods and has a value consistent with direct interneuronal conduction of a signal from head sucker sensory neurons to tail sucker motor neurons. The interval between tail sucker attachment and head sucker release, however, is longer and varies with the cycle period, suggesting a more complex interneuronal circuit in the pathway from tail sucker sensory neurons to head sucker motor neurons (Fig. 4). The onsets of the components of the crawling cycle (extension, post-extension pause, shortening, and post-shortening pause) show an anteroposterior lag (Figs. 5, 7). For both variants, the travel time between segments varies directly with the period (Fig. 8). For both crawl types, the durations of the cycle components vary directly with the period, with several exceptions (Figs. 9, 10). A model is presented that summarizes the coordination of the various motor events in a cycle of leech crawling (Figs. 11 and 12).     

The function of the suckers of larval net-winged midges (Diptera: Blephariceridae)

1. Larval net-winged midges (Diptera: Blephariceridae) possess six ventral suckers that enable them to inhabit swift streams. Each sucker consists of a suction disc and a cavity with a piston. Large muscles are inserted within the piston, as well as at the base of the suction disc. This structure infers that both attachment and release of the sucker is achieved by vertical movements of the piston.
2. Live observations of blepharicerid larvae revealed that the sucker is indeed attached by an upward movement of the piston, but that the cavity is flooded when the sucker is released. The piston is lowered only at the end of a sucker 'step', expelling water from the cavity.
3. During foraging, the maxilla and the piston of the first sucker are moved synchronously, indicating that the first sucker functions as a holdfast thus facilitating grazing.
4. The adhesive forces, as well as the relative size of blepharicerid suckers, differ amongst species. They are highest in Hapalothrix lugubris and lowest in Liponeura cordata , which correlates with the hydraulic stress to which the larvae of these species are exposed in their preferred habitat. The balance between the efficiency of their retention structure and the hydraulic conditions of their preferred habitat defines a key dimension of their ecological niche.     

Parvatrema chaii n. sp. (Digenea: Gymnophallidae) from mice experimentally infected with metacercariae collected from surf-clam, Mactra veneriformis

Parvatrema chaii n. sp. (Digenea: Gymnophallidae) is described using the worms recovered from experimentally infected mice in Korea. The metacercariae were collected from surf-clams, Mactra veneriformis, from a tidal flat in Sochon-gun, Chungchongnam-do. The metacercariae were elliptical (0.262 x 0.132 mm), and the genital pore had an anterior arch of 16-17 sensory papillae in scanning electron microscopic view. Adult worms were ovoid to foliate (0.275-0.303 by 0.140-0.150 mm), and their characteristic features included the presence of lateral lips, short esophagus, genital pore located some distance anterior to the ventral sucker, club-shaped seminal vesicle, a compact to slightly lobed vitellarium, elliptical eggs (0.018-0.020 by 0.010-0.013 mm), and absence of the ventral pit. This gymnophallid is classified as a member of the genus Parvatrema because of the location of the wide genital pore some distance from the ventral sucker, and the absence of the ventral pit. It differs from previously reported Parvatrema species, including the type species, P. borinquenae. In particular, the morphologies of the vitellarium and the genital pore with an anterior arch of 16-17 sensory papillae are unique features. Therefore, we propose it as a new species, Parvatrema chaii n. sp. (Digenea: Gymnophallidae).     

Comparative morphology of cercal structures in true crickets and their allies (Orthoptera, Ensifera): a phylogenetic perspective

 Cercal structures are surveyed in a large number of crickets sensu lato (Orthoptera, Ensifera, Gryllidea) to analyse their diversity and check for their potential phylogenetic interest. Several other Ensifera are also examined for outgroup comparisons. The main results indicate that Gryllidea can be characterised by several features of their cerci, namely the irregular alignment and the varied size of club-shaped setae. Peculiar features of cercal structures may also be autapomorphic of Gryllidea subclades, such as the presence of wedges on the surface of club-shaped setae (Grylloidea, Gryllotalpidae), the presence of scale-like setae (Mogoplistidae) or that of apical pores on trichoid setae (Myrmecophilidae, Myrmecophilinae), for example. At the scale of Ensifera, three characters are of phylogenetic interest: the presence of club-shaped setae in Gryllidea and Stenopelmatidae, the presence of inner rims inside the sockets of filiform and, when present, club-shaped setae in Gryllidea and, if confirmed, in Rhaphidophoridae, and the occurrence of microtrichiae on the cerci surface in Gryllidea and Rhaphidophoridae. Accepted: 4 October 1998     

Anatomy of the sensory nervous system in Craspedella pedum (Plathelminthes, Temnocephalida): DiO staining after fixation and in vivo

 The microanatomy of the nervous system of Craspedella pedum is described based on staining of the sensory nerves with DiO (3,3′-dioctadecyloxacarbocyanine perchlorate) in whole worms after fixation. The high resolution and reproducibility of this method revealed that the microanatomy of the nervous system is uniform within this species to rather minute details. Although the lateral and ventral cords have a similar diameter, the ventral nerve cords are very poor in sensory fibres. Such a high level of functional differentiation of nerve cords has not been known in representatives of the Plathelminthes. In vivo staining reveals numerous DiO-accumulating sensory neurons in the anterior portion of the body and a few pairs in its posterior half. The morphology of some neurons is described. Several neurons were identified and our data suggest that most, if not all, sensory neurons are identificable cells. Accepted: 16 December 1997     

Ciliated sensory receptors of the unactivated metacestode of Hymenolepis microstoma

The fine structure of the ciliated sensory endings of the unactivated metacestode of Hymenolepis microstoma is described. The type I sensilla, localized in areas of the scolex and sucker tegument, are characterized by a long cilium (1.20 × 0.20 μ) embedded in a bulb containing two electron-dense collars and three to five mitochondria. The type II sensilla, located in tegumentary pits of the rostellum, are characterized by a short cilium (0.62 × 0.28 μ) possessing ciliary rootlets, embedded in a bulb containing a single electron-dense collar and one to three mitochondria. Both sensory cilia are characterized by a 9 + 6 + 1 microtubular substructure. The sensory bulbs contain large numbers of membrane bound electron-lucent vesicles; neurotubules are absent at this stage of development.     

Die Feinstruktur der Ästheten vonChiton olivaceus (Mollusca,Polyplacophora)

The aesthete organs in the shell of the polyplacophoranChiton olivaceus (Spengler) were studied by scanning and transmission electron microscopy. Compared to previously described species they reveal marked differences. In the upper third of the aesthete, photoreceptor cells have been found. The granula of the club-shaped cells, which fill most of the aesthete, are formed in the proximal part of young aesthetes. The secretory cells located in this part increase in size and become gradually club-shaped. The central cells, hitherto the only known sensory cells in this organ, are very variable in their appearence. The apical as well as the subsidiary caps have pores which penetrate the whole cap in the former, whereas the subsidiary caps are proximally and distally covered by a continous envelope. In contrast, an exchange of substances with the surrounding environment cannot be excluded in the apical cap: there are some indications of secretory processes occurring through the shell surface.     

Sensory Afferent Neurotransmission in Caudal Nucleus Tractus Solitarius--Common Denominators

The nucleus of the solitary tract (NTS) receives a wide rangeof sensory inputs including gustatory, gastrointestinal andcardiorespiratory which are loosely segregated viscerotopicallyto subnuclei. Our laboratory has focused on a dorsomedial areaof caudal NTS (mNTS) which is critical for cardiovascular reflexes.Using a brainslice, we study primarily mNTS neurons mono-synapticallyactivated by solitary tract stimulation. mNTS neurons show varyingdegrees of delayed excitation, spike frequency adaptation andafter hyperpolarizations. Sensory afferent transmission is mediatedby glutamate acting at post-synaptic non-NMDA receptors. Glutamaterelease depends on at least four different presynaptic calciumchannels with N-type predominating. This profile of presynapticcalcium channels in NTS is also present at the peripheral soma,but absent from the baroreceptor sensory endings. Many peptidesare associated with these sensory neurons and several modulateglutamatergic transmission in mNTS. Angiotensin II facilitatesexcitatory responses to sensory afferent activation by a presynapticmechanism. Caudal NTS appears to have a framework of synapticand cellular mechanisms in common with other NTS areas and peptidesmay play a critical role modulating this framework. Chem. Senses21: 387–395, 1996.     

Organization of the Nervous System and Sensory Organs in the Larva of the Marine Bryozoan Bowerbankia gracilis (Ctenostomata: Vesiculariidae): Functional Significance of the Apical Disc and Pyriform Organ

The organization of the nervous system and the histology and ultrastructure of the apical disc and the pyriform organ have been investigated by serial sections with light and electron microscopy for the larva of the vesiculariid ctenostome bryozoan Bowerbankia gracilis Leidy 1855. The nervous system consists of four major internal components: (1) a median-anterior nerve nodule; (2) an equatorial, subcoronal nerve ring; (3) paired aboral nerve cords; (4) paired antero-lateral nerve tracts. The nervous system is associated with the ciliated larval surface at the apical disc, the pyriform organ, the corona and the intercoronal cells. The paired aboral nerve cords extend from the apical disc to the nerve nodule, which gives rise to the paired antero-lateral nerve tracts to the pyriform organ and to paired lateral tracts that form the equatorial nerve ring. Ultrastructural evidence is provided for the designation of primary sensory cells in the neural plate of the apical disc and in the juxtapapillary regions of the pyriform organ. Efferent synapses are described between the equatorial nerve ring and the overlying coronal cells, which constitute the primary locomotory organ of the larva. The repertoire of potential functions of the apical disc and pyriform organ are discussed. It is concluded that the apical disc and pyriform organ constitute larval sensory organs involved in orientation and substrate selection, respectively. Their association with the major effector organs of the larva (the corona and the musculature) via the nervous system supports this interpretation.     

Species of Proteocephalus Weinland, 1858 (Cestoda: Proteocephalidae), parasites of coregonid and salmonid fishes from North America: taxonomic reappraisal

A taxonomic study of species of Proteocephalus Weinland, 1858 (Cestoda: Proteocephalidae), from coregonid and salmonid fishes in North America, based largely on their type specimens, was carried out. None of the taxa studied possesses obvious autapomorphies that would justify its validity. On the contrary, all species share the following diagnostic features typical of Proteocephalus longicollis (Zeder, 1800) (syn. Proteocephalus exiguus La Rue, 1911), a polymorphic and widely distributed parasite in the Holarctic: (1) a spherical or club-shaped scolex, with sublaterally situated suckers and a vestigial but distinct and relatively large apical sucker; (2) the vagina possessing a well-developed vaginal sphincter and crossing mostly ventrally the proximal part of the cirrus sac; and (3) a long, thick-walled cirrus sac, overlapping vitelline follicles medially by more than its proximal half. Accordingly, Proteocephalus pusillus Ward, 1910; P. laruei Faust, 1920; "P. obtundus" La Rue, 1920 (nomen nudum); P. arcticus Cooper, 1921; P. wickliffi Hunter and Bangham, 1933; P. parallacticus MacLulich, 1943; P. californicus Haderlie, 1950; P. salmonidicola Alexander, 1951; and P. primaverus Neiland, 1952 are considered junior synonyms of P. longicollis.     

Cutaneous overexpression of NT-3 increases sensory and sympathetic neuron number and enhances touch dome and hair follicle innervation

Target-derived influences of nerve growth factor on neuronal survival and differentiation are well documented, though effects of other neurotrophins are less clear. To examine the influence of NT-3 neurotrophin overexpression in a target tissue of sensory and sympathetic neurons, transgenic mice were isolated that overexpress NT- 3 in the epidermis. Overexpression of NT-3 led to a 42% increase in the number of dorsal root ganglia sensory neurons, a 70% increase in the number of trigeminal sensory neurons, and a 32% increase in sympathetic neurons. Elevated NT-3 also caused enlargement of touch dome mechanoreceptor units, sensory end organs innervated by slowly adapting type 1 (SA1) neurons. The enlarged touch dome units of the transgenics had an increased number of associated Merkel cells, cells at which SA1s terminate. An additional alteration of skin innervation in NT-3 transgenics was an increased density of myelinated circular endings associated with the piloneural complex. The enhancement of innervation to the skin was accompanied by a doubling in the number of sensory neurons expressing trkC. In addition, measures of nerve fibers in cross- sectional profiles of cutaneous saphenous nerves of transgenics showed a 60% increase in myelinated fibers. These results indicate that in vivo overexpression of NT-3 by the epidermis enhances the number of sensory and sympathetic neurons and the development of selected sensory endings of the skin.     

Ultrastructural localization of α-galactose-containing glycoconjugates in the rat vomeronasal organ

Binding sites of Griffonia simplicifolia I-B₄ isolectin (GS-I-B₄), which recognizes terminal α-galactose residues of glycoconjugates, were examined in the juxtaluminal region of the rat vomeronasal sensory epithelium and its associated glands of the vomeronasal organ, using a lectin cytochemical technique. Lowicryl K4M-embedded ultra-thin sections, which were treated successively with biotinylated GS-I-B₄ and streptavidin-conjugated 10 nm colloidal gold particles, were observed under a transmission electron microscope. Colloidal gold particles, which reflect the presence of terminal α-galactose-containing glycoconjugates, were present in vomeronasal receptor neurons in the sensory epithelium and secretory granules of acinar cells of associated glands of the epithelium. Quantitative analysis demonstrated that the density of colloidal gold particles associated with sensory cell microvilli that projected from dendritic endings of vomeronasal neurons was considerably higher than that of microvilli that projected from neighboring sustentacular cells. The same was true for the apical cytoplasms of these cells just below the microvilli. These results suggest that of the sensory microvilli and dendritic endings contained a much larger amount of the α-galactose-containing glycoconjugates, compared with those in sustentacular microvilli. Further, biochemical analyses demonstrated several vomeronasal organ-specific glycoproteins with terminal α-galactose.