Detailed ultrastructure of the Hirudo (Annelida: Hirudinea) salivary gland.

Medical leeches have been widely used in medical applications and treatments for millennia. Studies on the salivary glands of blood-sucking leeches have focused on their bioactive secretions and mechanisms of action, with little attention to ultrastructure. In this study, we examined dissected embryonic and adult Hirudo verbana salivary glands by scanning electron microscopy (SEM). Gland cells of embryos were physically separated while adults displayed highly developed cell bunches in which each cell was connected to others by fine channels. Channels from each bunch combined to form a larger canal that opened to the jaw. Secreted material from these glands prevent blood from clotting and allow the adult to feed while sucking blood.

Correct spelling of a recently described species of Helobdella (Annelida: Clitellata: Hirudinea).

In a recently published article (Saglam et al. 2018) the name of a new species of Hirudinea (Annelida, Clitellata) was simultaneously published in three different ways, as Helobdella serendipitious (Saglam et al. 2018: 61, 70, 71, 73), Helobdella serendipitous (ibid.: 63, 65, 66, 67, 68, 69, 70, 71, 72, 73, 74), and as Helobdella serendipidous (ibid.: 75). Acting as first reviser according to Article 24 of the International Code of Zoological Nomenclature (ICZN 1999) here we determine serendipitous as the correct spelling of the species epitheton.

Phylogenetic and morphological resolution of the Helobdella stagnalis species-complex (Annelida: Clitellata: Hirudinea).

The glossiphoniid freshwater leech, Helobdella stagnalis, was described by Linnaeus 1758 based on common European specimens. The presence of a brown, chitinous scute on the dorsal-anterior surface, as observed on leeches elsewhere in the world, has generally led to the classification of all scute-bearing members of the genus as H. stagnalis. Here we describe the morphology and behavior of the type species from Europe, and analyze H. stagnalis-like specimens collected worldwide. We present evidence for at least four distinct scute-bearing Helobdella species that can be morphologically resolved. Maximum Parsimony (MP) and Bayesian Inference (BI) analyses at the mitochondrial cytochrome c oxidase subunit I (COI) locus further supported this notion, with divergence values suggesting a mid-Miocene ancestor of this successful group of cosmopolitan hirudineans. New species, Helobdella echoensis nov. sp., Helobdella eriensis nov. sp., and Helobdella serendipitious nov. sp., are described, based on morphological, anatomical and molecular data. Current distribution patterns of Helobdella spp. suggest a robust, global dispersal mechanism, as well as local pockets of endemism.

Elaborate ultrastructure of the Hirudo (Annelida: Hirudinae) cocoon surface.

Species of medicinal leeches (Hirudo medicinalis, H. verbana, and H. sulukii) secrete hard-shelled cocoons. When initially deposited, a cocoon is surrounded by a foam. Over a short time, the foam is transformed into a three-dimensional structure. We show here that this peripheral structure likely forms by the solidification and dehydration of a moderately viscous, proteinaceous substance that surrounds bubbles of various sizes. The resulting matrix-like structure comprises a network of curved branches juxtaposed at ∼120° and taper in width as a function of distance from the outer cocoon wall. The material is proteinaceous, and traps environmental material in its composition, especially silicon. The geometry of compartments and abundance of silicon on branch surfaces suggest a mechanism for trapping water to prevent desiccation in a terrestrial environment.

Connections of Anterior Thalamic Visual Centers in the Leopard Frog, Rana pipiens.

The amphibian retina projects to two discrete regions of neuropil in the anterior thalamus: the neuropil of Bellonci and the corpus geniculatum. These retinorecipient areas are encompassed within a larger zone of surrounding neuropil we call the NCZ (for neuropil of Bellonci/corpus geniculatum zone). The NCZ is characterized electrophysiologically by a distinctive tonic oscillatory response to blue light; it appears to be a visual module involved in processing the stationary visual environment. Using horseradish peroxidase (HRP), we mapped the connections of the NCZ. Retrogradely labeled cell bodies are found in: (1) the contralateral anterior thalamus; (2) both retinas; and (3) the posterior medial dorsal thalamus (PMDT). Anterogradely labeled fibers are found in: (1) the contralateral anterior thalamus; (2) the ipsilateral PMDT; (3) the ipsilateral neuropil lateral to the posterior tuberculum in the ventrolateral posterior thalamus; and (4) the ipsilateral anterior medulla. There are no direct connections between the NCZ and the telencephalon, the tectum, or the suprachiasmatic nucleus. Applying HRP to the PMDT, we found that its inputs are limited to the contralateral and ipsilateral NCZ and the contralateral PMDT. Thus, PMDT appears to be a satellite of the NCZ. Blue light elicits tonic oscillatory electrical responses in the PMDT quite similar to the responses to blue light in the NCZ. We discuss how the leopard frog NCZ and the mammalian ventral lateral geniculate nucleus share anatomical and physiological properties.

Representation of the visual field in the anterior thalamus of the leopard frog, Rana pipiens.

We used physiological and anatomical methods to elucidate how the visual field is represented in the part of the dorsal anterior thalamus of the leopard frog that receives direct retinal projections. We recorded extracellularly while presenting visual stimuli, and characterized a physiologically defined region that encompasses the retinal projections as well as an extended zone beyond them. We probed the area systematically to determine if the zone is organized in a visuotopic map: we found that it is not. We found that units in this region respond only to stimuli in the contralateral half of the visual field, which is similar to what is seen in the dorsal lateral geniculate nucleus in mammals. When we backfilled retinal ganglion cells from application of HRP to the anterior thalamus, we found labeled cells only in those parts of the retina corresponding to the contralateral hemifield, confirming our physiological observations.

Mechanics of cocoon secretion in a segmented worm (Annelida: Hirudinidae).

Clitellate annelids (e.g., segmented earthworms, leeches) secrete proteinaceous cocoons into which eggs are deposited. The process of cocoon production is characterized by the coordinated release of micro-granules from secretory cells positioned asymmetrically within the clitellum. Collectively, these assemble into a tubular cocoon sheath that is sealed at either end by globular opercula. By transmission electron microscopy (TEM), we show here that granules destined to the cocoon operculum in the leech, Erpodbdella obscura, display a series of concentric rings surrounding a structureless core with dimensions approximating a single nanoglobule found in the operculum. Upon their channeling to the surface through narrow tubules, granules are secreted into the cocoon lumen where they appear to fragment upon contact with the operculum matrix. The distribution of partial concentric ring structures throughout the operculum suggests that granular fusion causes dynamic fragmentation of outer surface material, which thereafter integrates into operculum nanoglobules and cavities. Other granules within the same secretory cell display a punctate pattern and likely fuse with the cocoon sheath prior to crystallization.

The Arabidopsis CURVY1 (CVY1) gene encoding a novel receptor-like protein kinase regulates cell morphogenesis, flowering time and seed production.

BACKGROUND: A molecular-level understanding of the loss of CURVY1 (CVY1) gene expression (which encodes a member of the receptor-like protein kinase family) was investigated to gain insights into the mechanisms controlling cell morphogenesis and development in Arabidopsis thaliana. RESULTS: Using a reverse genetic and cell biology approaches, we demonstrate that CVY1 is a new DISTORTED gene with similar phenotypic characterization to previously characterized ARP2/3 distorted mutants. Compared to the wild type, cvy1 mutant displayed a strong distorted trichome and altered pavement cell phenotypes. In addition, cvy1 null-mutant flowers earlier, grows faster and produces more siliques than WT and the arp2/3 mutants. The CVY1 gene is ubiquitously expressed in all tissues and seems to negatively regulate growth and yield in higher plants. CONCLUSIONS: Our results suggest that CURVY1 gene participates in several biochemical pathways in Arabidopsis thaliana including (i) cell morphogenesis regulation through actin cytoskeleton functional networks, (ii) the transition of vegetative to the reproductive stage and (iii) the production of seeds.

Nucleus rostrolateralis: an expansion of the epithalamus in some actinopterygii.

The diencephalic nucleus rostrolateralis (RL) in the African butterfly fish (Pantodon buchholzi) is a brain nucleus identified in fewer than a dozen of the ∼25,000 species of actinopterygian fishes. Located in the rostrolateral diencephalon, this nucleus in Pantodon receives direct and indirect visual input from the superior visual field. Its lack of precedent or consistent phylogenetic expression creates a difficulty in interpreting the functional role of this nucleus within the visual system. By tracing experiments, RL was found to be afferent to nucleus interpeduncularis (IP) and the target of cells from the subpallium of the telencephalon. RL is a component of a descending telencephalic pathway involved in at least one behavior at the intersection of limbic and somatic activities--feeding. The parallelism between the ventral telencephalon--RL--IP and the limbic/striatal--habenula--IP pathway (the dorsal diencephalic conduction system, DDCS) suggests that RL is a component within the DDCS. Moreover, the hodological connections of RL suggest that RL is likely a hypertrophy of the lateral habenula.

Operculum ultrastructure in leech cocoons.

Clitellate annelids (i.e., oligochaetes including leeches) secrete cocoons as part of their normal reproductive cycle. Typically, the cocoon sheath is passed over the head of the leech and sealed at both ends by opercula (i.e., glue-like material secreted by the clitellum). Both the fibrous cocoon wall (CW) and opercula are chemically-related biomaterials that share unusual physiochemical properties, including thermal and chemical resiliency. To explore the underlying morphology of the operculum, we examined cocoons from four leech species (i.e., Myzobdella lugubris, Theromyzon tessulatum, Erpobdella obscura, and Erpobdella punctata) by transmission (TEM) and scanning electron microscopy (SEM). Transmission electron micrographs of all opercula revealed a common, ultrastructural pattern comprising an electron-dense mosaic of ordered polygons that surrounded interspersed cavities. The long axes of cavities were often oriented directionally, suggesting that operculum material is pliable prior to solidification and distorted as a consequence of cocoon deposition. Concomitantly, the operculum permeates jagged edges of the cocoon sheath sealing the cocoon, which provides a mechanically strong CW/operculum boundary. SEM of leech opercula revealed globular nanoparticles comparable to that observed in bioadhesives from disparate animal phyla (e.g., mussel, barnacle, sea star), suggesting a convergent mechanism of bioadhesion among animals.

Bilateral efferents from nucleus isthmi to the optic tectum in goldfish (Carassius auratus) are spatially restricted.

The projection from nucleus isthmi (NI) to the optic tectum (OT) was investigated in the goldfish, Carassius auratus, by retrograde transport of biocytin applied at various sites in a tectal lobe. In previous studies, this projection is described as predominantly from the ipsilateral NI and maps topographically along the approximate rostrocaudal axis of both brain areas. However, the rostromedial tectal lobe, the tectal region representing the binocular visual field, receives afferents from both the ipsilateral and the contralateral NI. The contralateral isthmic neurons are found at the most caudal position in NI and are not topographic with the tectum. The bilateral projection from NI to the tectum may play a role in functions requiring the coordination of both eyes.

Light intensity mediated polarotaxis in Pontella karachiensis (Pontellidae, Copepoda).

Polarization sensitivity provides animals with information not available in the intensity or spectral domains. We examined the polarotaxis reactions in the epiplanktonic copepod Pontella karachiensis. Polarotaxis reactions were intensity dependent. At intensities corresponding to ambient daylight, P. karachiensis showed an attraction to a polarized light field; while at low intensities, corresponding to nighttime illumination, it showed negative polarotaxis. P. karachiensis's eye contained two classes of photoreceptors, each class with microvilli at orthogonal orientation to the other. P. karachiensis' eye structure can provide information regarding the polarization percentage but is not sufficient to calculate the exact e-vector orientation. The threshold for polarotoxisis response was 20-30%. Animals responded similarly to horizontal and vertical polarization; and also showed negative phototaxis, affected by light polarization. Results suggest that P. karachiensis responds to polarized light analogously to changes in brightness. The dynamic pattern of polarotaxis responses suggests that polarization sensitivity may enable P. karachiensis to detect other planktonic animals.

Spatial distribution of a fusiform cell in the optic tectum of Pantodon buchholzi, the African butterfly fish (Teleostei, Osteoglossomorpha).

Pantodon buchholzi, the African butterfly fish, inhabits an ecological niche just below the water surface. At that position, each eye necessarily views into the air through the surface of the water and into the water. Since Pantodon is an obligatory surface feeder, the ventral retina viewing the aerial environment provides all visual information for prey acquisition. The visual pathway of this fish reflects the divided visual field with structural differences in the retina and brain corresponding to the different views. In this study, we describe a specific type of neuron in the tectum that, due to its intrinsic structure, likely integrates visual and mechanoreceptor inputs. Because of its spatial distribution, this type of neuron is a candidate as a basic element in a network involved with prey acquisition.

Extracellular noise-induced stochastic synchronization in heterogeneous quorum sensing network.

Quorum sensing is a bacterial mechanism used to synchronize the coordinated response of a microbial population. Because quorum sensing in Gram-negative bacteria depends on release and detection of a diffusible signaling molecule (autoinducer) among a multicellular group, it is considered a simple form of cell-cell communication for the purposes of mathematical analysis. Stochastic equation systems have provided a common approach to model biochemical or biophysical processes. Recently, the effect of noise to synchronize a specific homogeneous quorum sensing network was successfully modeled using a stochastic equation system with fixed parameters. The question remains of how to model quorum sensing networks in a general setting. To address this question, we first set a stochastic equation system as a general model for a heterogeneous quorum sensing network. Then, using two relevant biophysical characteristics of Gram-negative bacteria (the permeability of the cell membrane to the autoinducer and the symmetry of autoinducer diffusion) we construct the solution of the stochastic equation system at an abstract level. The solution indicates that stable synchronization of a quorum sensing network is robustly induced by an environment with a heterogenous distribution of extracellular and intracellular noise. The synchronization is independent of the initial state of the system and is solely the result of the connectivity of the cell network established through the effects of extracellular noise.

The mechanism for stochastic resonance enhancement of mammalian auditory information processing.

BACKGROUND: In a mammalian auditory system, when intrinsic noise is added to a subthreshold signal, not only can the resulting noisy signal be detected, but also the information carried by the signal can be completely recovered. Such a phenomenon is called stochastic resonance (SR). Current analysis of SR commonly employs the energies of the subthreshold signal and intrinsic noise. However, it is difficult to explain SR when the energy addition of the signal and noise is not enough to lift the subthreshold signal over the threshold. Therefore, information modulation has been hypothesized to play a role in some forms of SR in sensory systems. Information modulation, however, seems an unlikely mechanism for mammalian audition, since it requires significant a priori knowledge of the characteristics of the signal. RESULTS: We propose that the analysis of SR cannot rely solely on the energies of a subthreshold signal and intrinsic noise or on information modulation. We note that a mammalian auditory system expends energy in the processing of a noisy signal. A part of the expended energy may therefore deposit into the recovered signal, lifting it over threshold. We propose a model that in a rigorous mathematical manner expresses this new theoretical viewpoint on SR in the mammalian auditory system and provide a physiological rationale for the model. CONCLUSION: Our result indicates that the mammalian auditory system may be more active than previously described in the literature. As previously recognized, when intrinsic noise is used to generate a noisy signal, the energy carried by the noise is added to the original subthreshold signal. Furthermore, our model predicts that the system itself should deposit additional energy into the recovered signal. The additional energy is used in the processing of the noisy signal to recover the original subthreshold signal.

Discriminative responses of squid (Loligo pealeii) photoreceptors to polarized light.

Cephalopods behaviorally respond to polarized light. Electrophysiology experiments with the squid, Loligo pealeii, demonstrated that spike responses from individual photoreceptors are a cosine2 function of the e-vector orientation of a polarized stimulus. The discrimination limit to this polarization sensitivity depended upon the difference between the orientation of a polarized stimulus with a preferred e-vector. The limit ranged from 2 degrees to 9.2 degrees with a direct stimulus in the dark or 4.8 degrees -22.1 degrees with non-directed background illumination and the cells were least discriminative at the preferred orientations. This limit can be explained partly by the variability in anatomical alignment of microvilli in the photoreceptors around a dominant axis. A few light-sensitive retinal fibers showed no polarization sensitivity. The coding of polarization information suggests that light intensity is transformed into an average spike rate. This average results from silent periods interspersed between bursts of spikes, each burst possessing a consistent interspike interval. The variations in the length and frequency of silent periods depend upon the difference between the polarization e-vector and a preferred e-vector orientation. The minimal discriminated orientation of a squid photoreceptor agrees well with the minimum behavioral discrimination of polarized light by another cephalopod, the octopus.

A pallial visual area in the telencephalon of the bony fish Polypterus.

The dorsal (P2) and lateral (P3) pallial zones of bichirs receive a substantial projection from nucleus medianus of the posterior tuberculum. Although nucleus medianus does not receive a direct retinal input, its close proximity to ascending tectal efferents suggests that it might receive a tectal input and form a segment of a retinotectal-tubercular pathway to the pallium. In order to test this possibility, evoked responses to light flashes were electrophysiologically recorded and tectal efferents were experimentally determined in bichirs. These experiments suggest that a single visual field exists across the dorsal and lateral pallial zones and that this field is mediated by nucleus medianus, which does receive a direct tectal projection. This visual pathway appears to be uniquely derived and not homologous to any other known pathway in tetrapods. Furthermore, these results support the contention that the P2 and P3 pallial zones in bichirs are subdivisions of a single pallial zone.

Clustered phylogenetic distribution of nucleus rostrolateralis among ray-finned fishes.

Nucleus rostrolateralis, which was named for its location in the rostrolateral part of the diencephalon of neopterygian fishes, has been identified in a variety of species based on position, cytoarchitecture, hodology, and/or histochemistry. The phylogenetic distribution of the nucleus is highly sporadic, however. Due to this distribution, nucleus rostrolateralis cannot be regarded as phylogenetically homologous, but it might be an example of syngeny, or generative homology, which applies to characters that have the same genetic and/or developmental basis inherited from a common ancestor, whether or not the character itself has a phylogenetic distribution congruent with a monophyletic taxon--i.e., in general terms, an example of either phylogenetic homology or parallelism. To test whether the nucleus occurs in closely related taxonomic clusters, as might be expected for a character with a shared generative basis, a number of species of cyprinids and atherinomorphs (both teleost taxa) were examined for its presence. Many of the species examined appear to lack the nucleus, but a clustered occurrence of it was found within both taxa. Within cyprinids, nucleus rostrolateralis occurs in all three members examined of the Subfamily Rasborinae. Within atherinomorphs, it occurs in both members examined of the Tribe Poeciliini (of the Subfamily Poeciliinae, Family Poeciliidae) and in the one member examined of the Family Anablepidae. The clustered occurrence of nucleus rostrolateralis supports the hypothesis that it is an example of syngeny. Its postulated shared generative basis appears to derive from the common ancestor of the entire neopterygian radiation despite the rare occurrence of the character itself.