The housefly interfacetal hair: ultrastructure of a presumed mechanoreceptor

Morphology of interommatidial sensilla of Discocephalini (Heteroptera: Pentatomidae: Discocephalinae)

Interommatidial sensilla have been explored for their taxonomic value and other aspects in Diptera and Lepidoptera. In Heteroptera, Eurystethus is the only genus where these structures were examined in delimiting subgenera and species. This study investigates the presence, distribution, and morphology of interommatidial sensilla in Discocephalinae species and discusses the sensilla's value for cladistic and taxonomic appraisals. Twenty species of 18 genera were analyzed: 16 Discocephalini genera, one genus in Ochlerini, and one genus in Edessinae. Species' heads were observed from photographs taken with light microscopy (LM) and scanning electron microscopy (SEM). From these images, we identified eleven types of sensilla, classified into chaetica, trichoidea and coeloconica. In LM, only sensilla chaetica with a length of 40-100 μm were visible, present in six species. Under the SEM at least one type of sensillum was visible in 19 of the 20 species analyzed. No difference between the various kinds of sensilla were apparent between males and females or adults and nymphs of a given species. Both subgenera of Eurysthetus have the same type of sensillum (chaeticum type I), which suggests this is not a delimiting feature. We conclude that sensilla chaetica can be a valuable character to delimit groups of genera within Discocephalini.

Ultra-Morphology and Mechanical Function of the Trichoideum Sensillum in Nabis rugosus (Linnaeus, 1758) (Insecta: Heteroptera: Cimicomorpha)

The present study aims to investigate the morphological features of the antennal sensilla by using SEM and TEM. The construction of a 3D model of trichoideum sensillum using Amira software is presented in this paper. Five sensillum types, namely trichoideum, chaeticum, campaniformium, coeloconicum, and basiconicum, were recorded. This model exhibits the mechanosensillum components, including the embedded hair in a socket attached by the joint membrane and the dendrite connected to the hair base passing through the cuticle layers. TEM images present the dendrite way, micro-tubules inside the dendritic sheath, and terminal structure of the tubular dendrite body and so-called companion cells included in the receptor, e.g., tormogen and trichogen. The parameters noted for the external structure and ultrastructure of the mechano-receptor indicate that they are specific to a particular type of sensillum and would be useful in developing the model for a biosensor. Results show that bio-inspired sensors can be developed based on morphological and ultrastructural studies and to conduct mechanical studies on their components.

Subcellular neuronal quasicrystals: Implications for consciousness

Neuron neurotransmitter receptors are in general pentameric. This enables them to form pentagonal components in biological quasicrystals (similar to mathematical aperiodic tilings). As quasicrystals have been proposed to require quantum effects to exist this might introduce such effects as a component of neurotransmission and thus consciousness. Microtubules may play a role in the clustering of the receptors into quasicrystals, thus modulating their function and may even form quasicrystals themselves. Other quaiscrystals in neurons are potentially formed by water, cholera toxin complexes, and the cytoskeletal components actin and ankyrin.

Subcellular neuronal quasicrystals: Implications for consciousness

Neuron neurotransmitter receptors are in general pentameric. This enables them to form pentagonal components in biological quasicrystals (similar to mathematical aperiodic tilings). As quasicrystals have been proposed to require quantum effects to exist this might introduce such effects as a component of neurotransmission and thus consciousness. Microtubules may play a role in the clustering of the receptors into quasicrystals, thus modulating their function and may even form quasicrystals themselves. Other quaiscrystals in neurons are potentially formed by water, cholera toxin complexes, and the cytoskeletal components actin and ankyrin.

Interommatidial sensilla of the praying mantis: their central neural projections and role in head-cleaning behavior

The compound eye of the praying mantis is covered with approximately 600 bristles and campaniform sensilla. Their afferents project to the brain, and to the suboesophageal and prothoracic ganglia. Cutting the eye branch of the dorsal tegumentary nerve (DTN), the peripheral nerve innervating the corneal sensilla, makes it impossible to initiate head grooming by tactile stimulation of the eye. This stimulus is a strong releaser of grooming behavior in normal animals. Head grooming can be initiated, after cutting the eye branch of the DTN, by stimulation of the frons (the operation leaves the sensory innervation of this part of the cuticle intact). Frame-by-frame analysis of films of head grooming after cutting the nerve reveals a reduction of the speed at which the forelimb is brushed across the surface of the head and eye. The significance of this finding is discussed in terms of a putative feedback loop from the corneal sensilla to the motor neurons controlling the grooming movements.

Ultrastructure and mechanical properties of an insect mechanoreceptor: stimulus-transmitting structures and sensory apparatus of the cercal filiform hairs of Gryllus

1. The following features of the cercal filiform hairs of the cricket Gryllus were investigated: (a) the ultrastructure and geometrical peculiarities of the various auxiliary structures in the region of the hair base, as well as those of (b) the stimulus-receiving outer segment of the dendrite (including the tubular body), and (c) the mechanical properties (directionality and linearity and frequency dependence of mobility) of the hair. 2. When stimulated by vibrations of the medium, the filiform hairs show regular or irregular oscillations depending on stimulus intensity. At higher stimulus intensities (xi > congruent to 100 microns at 100 Hz) the hairs flutter irregularly in various directions, at somewhat lower intensities preferentially in the plane of best mobility in even lesser intensities in the plane of stimulus vector. In the plane ob best mobility the maximal angle of deflection from the resting position is 5.3 +/- 1.4 degrees. 3. The dependence of hair mobility on stimulus frequency was tested in the range 20-1000 Hz. Best mobility was found in the range 100-200 Hz. 4. The directional characteristic of hair mobility has the form of a figure eight. Hairs can be grouped into three classes on the basis of direction (with respect to the long axis of the cercus) of best mobility: parallel (L-hairs), transverse (T-hairs), and diagonal (D-hairs). 5. The plane of best mobility corresponds with the plane symmetry of the hair base. The hair can be deflected furthest from the resting position in the direction of a cuticular peg at the hair base, which projects toward the lumen of the hair and marks the flat side of the tubular body within the terminal dendrite segment. Deflection of the hair shaft in the opposite direction is limited by a fibrous cushion, which exerts a counter-pressure. When the hair is deflected, the cuticular peg causes deformation of the tubular body. 6. The direction of best mobility of the hair is the direction in which the sensory cell is depolarized; the direction of depolarization can thus be determined entirely by morphological criteria.

Fine structure of the compound eyes and interfacetal mechanoreceptors of Cicindela tranquebarica Herbst (Coleoptera: Cicindelidae)

The structure of the compound eyes of adult Cicindela tranquebarica Herbst was examined by use of light, scanning, and transmission electron microscopy. Each ommatidium of these photopic eyes is eucone and has a "subcorneal layer" situated between the corneal lens and crystalline cone. A distal rhabdomere consisting only of microvilli from retinula cell seven, a more proximal, rectangular, fused rhabdom formed from six retinula cells, and a basal, eighth retinula cell with a spherical rhabdomere comprise the light sensitive portions of the ommatidium. The "subcorneal layer" consists of lamellae of endocuticular microfibrils and, in surface view, shows 11 concave polygons. Proximal extensions of the crystalline thread form inter-retinular fibres containing microtubules between retinula cells 1/2, 3/4, 5/6, and 7/1. The primary pigment cells are devoid of pigment granules, but are rich in rough endoplasmic reticulum. Proximal to each retinula cell nucleus are two basal bodies, one perpendicular to the other. The more proximal basal body extends two fibrillar feet proximally which fuse to form a horizontally-banded ciliary rootlet extending the length of the retinula peripheral to the rhabdom. Each ommatidium is surrounded by 16 secondary pigment cells. Interfacetal mechanoreceptors between some adjacent lenses each have a single bipolar neuron, with a dendritic sheath, tubular body, cilium, outer and inner sheath cells, and an axon surrounded by a neurilemma sheath cell.

Interommatidial hair receptor axons extending into the ventral nerve cord in the cricket Gryllus campestris

In the cricket, Gryllus campestris, a branch of the nervus tegumentarius runs to the distal part of the optic lobe. This branch contains the axons of interommatidial hair receptors. The axon terminations extend forward into the trito- and deutocerebrum, and into the subesophageal- and prothoracic ganglia as shown with the cobalt sulfide staining technique. The possible relevance of these connections is discussed.