Mobilities of the cercal wind-receptor hairs of the cricket, Gryllus bimaculatus

The deflection sensitivities of cercal filiform hairs of the cricket, Gryllus bimaculatus, were determined by direct measurement. The tangential velocity of deflecting hair shafts in response to stimulus air motion was measured in situ by a laser-Doppler velocimeter with surface scattering of the shaft. The velocity of the stimulus air motion in a small wind tunnel was calibrated by the same velocimeter with smoke from a joss-stick. The mobility of the hair was obtained from former measurements with reference to the latter calibration of the single apparatus. A Gaussian white noise signal was employed as a stimulus waveform, and the stimulus-response transfer function was calculated through a cross-correlation method, which provides greater precision and wider frequency for a longer period of measurement. The mobility of hair was expressed in deflection amplitudes and phase shifts in reference to the velocity sinusoid of a stimulus at various frequencies. The measurements established the following conclusions. The wind receptor hairs comprise an array of mechanical band-pass filters whose best frequencies are inversely proportional to the length. The motion dynamics of the wind-receptor hairs have strong damping. Accepted: 24 February 1998     

Frequency-intensity characteristics of cricket cercal interneurons: units with high-pass functions

Interneurons in the cercal sensory system of crickets respond in a cell-specific manner if the cercal hair sensilla are stimulated by air-particle oscillations at frequencies below about 2000 Hz. We investigated the filter properties of several of these interneurons, and tested the effect of stimulus intensity (typically 0.3–50 mm s⁻¹ peak-to-peak air-particle velocity) on the frequency response in the range 5–600 Hz. We focus on three interneurons (the lateral and medial giant interneurons and interneuron 9-3a) of Acheta domesticus which are characterized by a relatively high sensitivity above ca. 50–200 Hz. The responses of the medial giant interneuron usually increase monotonically with frequency and intensity. Interneuron 9-3a and the lateral giant interneuron exhibit saturation or response decrement at high frequencies and intensities. The lateral giant interneuron has an additional peak of sensitivity below about 40 Hz. Small individual variations in the relative locations of the two response areas of this interneuron within the frequency-intensity field are responsible for a large variability obtained if frequency-response curves are determined for particular intensities. Stimulus frequency does not affect the principal directional preferences of the three interneurons. Nevertheless, if tested individually, the lateral giant interneuron and interneuron 9-3a exhibit small changes of directional tuning. Accepted: 12 November 1997     

Effect of body orientation in the gravitational field on directional sensitivity of the cercal system of neurons in crickets

Changes in the spatial orientation of three-dimensional directional sensitivity diagrams of neurons of the terminal abdominal ganglion of the cricket during body tilting were studied. Spike responses were recorded from neurons of the ganglion to acoustic stimuli in different directions, with the cricket's body tilted at different angles to the horizontal plane. During tilting of the cricket's body the orientation of the directional sensitivity diagrams was found to change parallel with the orientation of the body. Neurons of the abdominal ganglion are excited by cercal sensillae, among which there are receptors which respond to changes in the position of the cricket's body in the gravitational field (gravity receptors). The results suggest that cercal gravity receptors have no specific influence on the directional sensitivity of neurons of the first central division of the cercal system.Institute for Problems in Information Transmission, Academy of Sciences of the USSR, Moscow. Translated from Neirofiziologiya, Vol. 12, No. 6, pp. 604–611, November–December, 1980.     

Stimulus-response properties of cricket cereal filiform receptors

The dynamic ranges and stimulus-response properties of a large sample of cereal filiform receptors in Acheta domesticus were investigated electrophysiologically. The relation between receptor response and stimulus velocity was a sigmoid function, the log-linear portion of which spanned 1–1.5 log units of peak air-current velocity. Different receptors responded over different but overlapping velocity ranges, such that the system velocity sensitivity range spanned at least 2.5 log units. Plots of receptor response amplitude vs. stimulus direction were sinusoidal, with a period of 360°. Long-hair receptors responded in phase with air-current velocity, and intermediate-hair receptors responded in phase with air-current acceleration. These results extend those of Shimozawa and Kanou (1984a) and Kämper and Kleindienst (1990), in which the dynamics of receptor responses were shown to depend on hair length. When individual hairs were directly mechanically deflected, their receptors responded in phase with the first derivative of hair deflection. The signal transform between the air-current stimulus and the receptor response is comprised of two processes, one biomechanical/aerodynamic and one membrane biophysical. The results of this study suggest that the parametric sensitivities of receptors are primarily determined by hair biomechanical/aerodynamic properties.Abbreviation IR infrared     

Relative contributions of organ shape and receptor arrangement to the design of cricket’s cercal system

Understanding the relative contributions of the shape of a sensory organ and the arrangement of receptors to the overall performance of the organ has long been a challenge for sensory biologists. We tackled this issue using the wind-sensing system of crickets, the cerci, two conical abdominal appendages covered with arrays of filiform hairs. Scanning electron microscopy coupled with 3D reconstruction methods were used for mapping of all cercal filiform hairs. The hairs are arranged according to their diameter in a way that avoids collisions with neighbours during hair deflection: long hairs are regularly spaced, whereas short hairs are both randomly and densely distributed. Particle image velocimetry showed that the variation in diameter of the cercus along its length modifies the pattern of fluid velocities. Hairs are subject to higher air flow amplitudes at the base than at the apex of the cercus. The relative importance of interactions between receptors and the air flow around the organ may explain the performance of the cricket's cercal system: it is characterised by a high density of statistically non-interacting short hairs located at the base of the cercus where sensitivity to air currents is the highest.     

Directional selectivities of near-field filiform hair mechanoreceptors on the crayfish tailfan (Crustacea: Decapoda)

Directional selectivities of mechanoreceptors that innervate filiform hairs on the crayfish tailfan were investigated with unidirectional, sinusoidal, water-motion stimuli. These recordings provide the first representative sample from filiform hair sensilla on the entire tailfan. The filiform hair receptors exhibit unimodal directional selectivity patterns that were well fitted by a cardioid function with a half-width of 122°. The preferred directions correspond to the major axis of hair motion, and are perpendicular to the orientation of lateral branches on the main hair shaft. Pooled plots of preferred directions demonstrate quadrimodal patterns on the telson and endopods which are associated with hair location, and a bimodal pattern on the exopods. For each appendage, the combination of the overall pattern of preferred directions with “coarse coding” of direction by individual receptors provides sensitivity to a full 0–360° range of water motion and the potential to discriminate the direction of water motion throughout this range. The results demonstrate several similarities to the wind-sensitive cercal receptor system in orthopteroid insects, and suggest that crustacean filiform hair receptors provide a sufficient sensory basis for behavioral orientation to water currents and shorelines. Accepted: 5 January 1998     

Honeybee phonoreceptors]

Bee phonoreceptors are revealed by electrophysiological method. These are hair sensillae located between facet eyes and occipital commissure. The region of the highest sensitivity of receptors in within the range of the maximum energy of various sound signals used in the communication of bees. The receptors exactly distinguish the signals according to their duration and intensity.     

Modeling the active process of the cochlea: phase relations, amplification, and spontaneous oscillation.

The high sensitivity and sharp frequency selectivity of acoustical signal transduction in the cochlea suggest that an active process pumps energy into the basilar membrane's oscillations. This function is generally attributed to outer hair cells, but its exact mechanism remains uncertain. Several classical models of amplification represent the load upon the basilar membrane as a single mass. Such models encounter a fundamental difficulty, however: the phase difference between basilar-membrane movement and the force generated by outer hair cells inhibits, rather than amplifies, the modeled basilar-membrane oscillations. For this reason, modelers must introduce artificially either negative impedance or an appropriate phase shift, neither of which is justified by physical analysis of the system. We consider here a physical model based upon the recent demonstration that the basilar membrane and reticular lamina can move independently, albeit with elastic coupling through outer hair cells. The mechanical model comprises two resonant masses, representing the basilar membrane and the reticular lamina, coupled through an intermediate spring, the outer hair cells. The spring's set point changes in response to displacement of the reticular lamina, which causes deflection of the hair bundles, variation of outer hair cell length and, hence, force production. Depending upon the frequency of the acoustical input, the basilar membrane and reticular lamina can oscillate either in phase or in counterphase. In the latter instance, the force produced by hair cells leads basilar-membrane oscillation, energy is pumped into basilar-membrane movement, and an external input can be strongly amplified. The model is also capable of producing spontaneous oscillation. In agreement with experimental observations, the model describes mechanical relaxation of the basilar membrane after electrical stimulation causes outer hair cells to change their length.     

Mechanics of trichobothria in orb-weaving spiders (Agelenidae,Araneae)

Summary When a fly is humming at a distance of about one centimetre from an orb-weaving spider (Agelenidae) the trichobothria on the spider's extremities are deflected by air streams and air vibrations. Frequency analysis of the hum of the two prey animals,Drosophila andMusca, shows that the effective sound velocities of the harmonics with frequencies inferior to some five hundred Hz exceeds that of higher frequencies by a factor of at least 5. Biologically relevant resonances would, therefore, have to be looked for in the range of a few hundred Hz. Frequency response diagrams show that single hairs have no resonance between a few Hz and approximately 2 kHz. The maximal relative amplitude of hairs of different lengths shifts from the longer to the shorter hairs with increasing frequency. As this is only a minor effect, however, it appears that there is no frequency discrimination by the mechanical apparatus. Constant air streams with a velocity of 40 mm/s cause hair deflection of about 10 degrees (the hair's bend is neglibible). Similarly, near-field particle velocity of sound fields up to a few hundred Hz is well transmitted. The mechanical directional sensitivity does not depend on the azimuthal angle of deflection. Thus, information about direction and velocity of stationary and near-field air movements is transmitted without deformation by the mechanical apparatus. This is well matched with the fact that the hair is multiply innervated.Supported by grants of the Deutsche Forschungsmeinschaft in the field of the Schwerpunktprogramm Rezeptorphysiologie     

An electrophysiological study of sound sensitive neurons in the ‘Primitive ear’ of Acheta domesticus

Crickets have two types of mechanisms for the reception of environmental sounds: (1) the tympanal organs in the two forelegs and (2) the freely articulated setal receptors on the abdominal ceri. The cercal setal receptors have hitherto received much less experimental attention as decoders of biologically significant sounds than have the tympano-receptors. In the present study the cercal auditory system of Acheta domesticus was examined electrophysiologically to determine its auditory frequency sensitivity, the tuning characteristics of individual units, and the synchronization between nerve impulses and stimulus frequency. Both pre- and postsynaptic units were examined in the fifth abdominal ganglion; several of the observed response patterns were compared with those of homologous cercal sensory neurons in Periplaneta americana. The results show that (1) A. domesticus possesses an elaborate array of cercal receptors which are highly sensitive to sounds, (2) the cercal setal receptors are more sensitive and numerous in the cricket than in the cockroach, and (3) the cercal auditory system can decode stimulus information by narrow tuning in individual cells and by synchronous discharge patterns; firing frequencies range up to 300 Hz in presynaptic sensory units and 60 Hz in the postsynaptic giants. The response patterns were related to the structure of the receptor and the behavioural adaptations of the insect.     

The cercal receptor system of the praying mantid,Archimantis brunneriana Sauss.

Summary The cerci of the praying mantid, Archimantis brunneriana Sauss., are paired segmented sensory organs located at the tip of the abdomen. Basally the cercal segments are slightly flattened dorso-ventrally and are fused to such a degree that it is difficult to distinguish them. Distally the segments become progressively more flattened laterally and their boundaries become more obvious.Two types of sensilla are present on the cerci, trichoid sensilla and filiform sensilla. Trichoid hairs are longest on the medial side of the cerci and toward the cercal base. On the proximal cercal segments they are grouped toward the middle of each segment while they are more uniformly distributed on the distal segments. Filiform sensilla are found at the distal end of each segment except the last and are most abundant on the middle segments of the cercus. Both the number of cercal segments and the number of sensilla are variable. Trichoid hairs are highly variable in appearance from short and stout to long and thin. They arise from a raised base, have a fluted shaft, and some have a pore at the tip. They are innervated by from one to five dendrites, one of which is always considerably larger than the others. Some of the dendrites continue out into the shaft of the hair.Filiform hairs have fluted shafts and are mounted in a flexible membrane within a cuticular ring in a depression. They are innervated by a single large sensory neuron, the dendrite of which passes across a flattened area on the inner wall of the lumen of the hair. The dendritic sheath forms the lining of the ecdysial canal and is therefore firmly attached to the hair. The dendrite is attached to the sheath by desmosomes distally and is penetrated by projections of the sheath more proximally. A fibrous cap surrounds the dendrite and may hold it in place relative to the hair.The cercal receptor system of Archimantis is compared to those of cockroaches and crickets.     

A calanoid copepod Gladioferens imparipes,holding to surfaces

Gladioferens imparipes, a calanoid copepod from estuaries in Western Australia, displays behaviour and associated morphology which is unusual among calanoids. Adult and copepodid stages make temporary attachment to underwater surfaces using fine hair sensillae on the surface of the prosome. A clear pattern can be seen in the number and arrangement of hair sensillae in early copepodid stages. Line drawings, photomicrographs and an S.E.M. are used to illustrate the structures. Laboratory studies with live copepods in a flow chamber show that adult animals may hold position against water currents. It is hypothesized that this behaviour influences the distribution pattern in an estuary where low velocity tidally induced water movement occurs, and may be of value in enabling the copepod to exist beyond the distribution of a major predator.     

Electrophysiology of trichobothria in orb-weaving spiders (Agelenidae,Araneae)

Summary Trichobothria of the house spidersTegenaria atrica (C.L. Koch) andTegenaria derhami (Scopoli) were stimulated by linear deflection of the hair from its resting position to one side. The pulse response of the receptor cell was analyzed. At angular deflection velocities of 10^–21 deg/ms the receptor begins to discharge at an angle of 3 degrees. While the mean pulse rate remains constant during deflections of 10^–210^–1deg/ms the pulse train may be interrupted by repeated breaks. Discharge continues when the hair is bent proximally beyond the bothrium edge. When the hair is bent distally and touches the bothrium edge, however, discharge ceases. Responsible for this phenomenon seems to be an asymmetry of hair suspension. — Repeated deflection leads to logarithmically ascending latency curves and logarithmically falling curves of the pulse numbers. The function coefficients depend on velocities and repetition rates of the deflections. The adaptational effect is heightened by preceding stationary deflection in the direction of the dynamical stimulus. The mean pulse rate as a function of hair deflection velocity increases logarithmically. The mean pulse rate as a function of hair movement direction obeys a cosine law, provided that a given velocity and a definite deflection angle are used.Supported by grants of the Deutsche Forschungsgemeinschaft given to Prof. Dr. P. Görner in the field of the Schwerpunktprogramm RezeptorphysiologieThe present paper is part of a doctoral thesis. My thanks are due to Prof. Dr. P. G6rner for the theme, many valuable discussions and his constant readiness to help.     

Behavioral analyses of wind-evoked escape of the cricket, Gryllodes sigillatus

The wind-evoked escape behavior of the cricket Gryllodes sigillatus was investigated using an air puff stimulus. A high velocity air puff elicited the escape behavior in many crickets. The crickets tended to escape away from the stimulus source, but the direction was not accurately oriented 180 degrees from the stimulus. After bilateral cercal ablation, only a few crickets showed wind-evoked escape behavior, and their response rates did not increase even 19 days after ablation. Therefore, information on air motion detected by cercal filiform hairs is essential for triggering wind-evoked behavior. After unilateral cercal ablation, the 81.3% response rate of intact crickets decreased to 16.5%, that is, it decreased to almost 20% that of intact crickets. One week after unilateral cercal ablation, the response rate recovered to more than 60% that of intact crickets. However, the accuracy rate of the escape direction of G. sigillatus showed no change even immediately after the unilateral cercal ablation. Therefore, both cerci are not necessarily required to determine the escape direction. The behavioral characteristics of wind-evoked escape of G. sigillatus are compared with those of another species of cricket, Gryllus bimaculatus. The two species of cricket employ different strategies for wind-evoked escape.     

The terminal abdominal ganglion of the wood cricket Nemobius sylvestris

The abdominal cerci of the wood cricket, Nemobius sylvestris, are covered by a variety of hair‐like sensilla that differ in length, thickness, and articulation. Fillings from the cercal nerves with cobalt chloride and fluorescent dyes revealed the projection of sensory axons into the terminal abdominal ganglion of the ventral nerve chain. Two projection areas on each side of the terminal abdominal ganglion midline could be identified: a posterior cercal glomerulus and an anterior bristle neuropil. Axons from some cercal sensilla ascend through the connectives to reach the metathoracic ganglionic mass. As their axons pass through each segmental abdominal ganglion, they project medial arborization. Cross‐sections of the terminal abdominal ganglion and retrograde fills with cobalt chloride and fluorescent dyes from connectives revealed several small cells and seven pairs of giant ascending interneurons organized symmetrically. Giant somata are located contralateral to their axons (diameters between 20 and 45 μm). The cercal projections overlap extensively with the dendritic fields of the giant interneurons. In the terminal abdominal ganglion, we identified nine longitudinal tracts, two major tracts, and seven smaller ones. The functional implications of the neuranatomical organization of the system are discussed on a comparative basis. J. Morphol., 2008. © 2008 Wiley‐Liss, Inc.     

The structure and development of a somatotopic map in crickets: The cercal afferent projection

A group of club-shaped sensilla called clavate hairs, located on the cercus of crickets (Acheta domesticus), are part of a specialized sensory system which monitors the orientation of a cricket with respect to the earth's gravitational field. The clavate hairs occur in rows which run proximodistally on the medial aspect of the cercus and each hair can be identified by specifying which row a hair is in and what position it is in within the row. The array of hairs is constant from individual to individual, and thus each hair can be identified in each specimen. The soma of a single bipolar sensory neuron is located in the integument below each hair; its dendrite projects into the hair and its axon projects to a well-defined area of the abdominal ganglion called the cercal glomerulus. All of the neurons within a row project to a particular area of the cercal glomerulus and different rows project to different areas within the glomerulus. Within a row neurons project to slightly different parts of the target area for that row. Thus a highly ordered projection pattern is produced which is tentatively called somatotopic. The development of the first clavate neuron to appear was examined from the first instar to the adult instar. The terminal arborization of this first hair was in no way unusual and its growth paralleled ganglion growth, maintaining a relatively constant position with respect to ganglion coordinates. A second clavate neuron behaved similarly, its arborization was fully formed when the receptor first appeared in the third instar and merely enlarged as the ganglion grew.     

Development of cricket sensory hairs: changes of dynamic mechanical properties

Summary Mechanical oscillation properties of cricket (Acheta domesticus) filiform hair sensilla were measured at different larval stages, as an indication of larval sensory capacities and for comparison with data in the literature on central nervous changes during development. The hairs were stimulated by airborne vibration over a frequency range of 10 to 220 Hz. Best frequency, angular displacement at best frequency, slope of angular-displacement tuning curve and phase of hair deflection relative to air particle velocity were tested for correlation with hair length, which is proportional to the age of a sensillum. The ranges found for the various oscillation parameters in early larval stages were similar to or larger than those in adults. Oscillation properties changed with both the developmental stage of the hair sensilla and that of the whole animal. Four individually identifiable hair sensilla were analysed separately; the sensory neurons of two of them are known to change synaptic properties during maturation. Angular displacement at a given stimulus intensity was maximal for all hairs after differentiation, and decreased during further development. The hairs did not show clear common changes for any of the other oscillation parameters. Yet particular changes were found for individual hairs.     

Spike amplitude of single-unit responses in antennal sensillae is controlled by the Drosophila circadian clock

Circadian changes in membrane potential and spontaneous firing frequency have been observed in microbial systems, invertebrates, and mammals. Oscillators in olfactory sensory neurons (OSNs) from Drosophila are both necessary and sufficient to sustain rhythms in electroanntenogram (EAG) responses, suggesting that odorant receptors (ORs) and/or OR-dependent processes are under clock control. We measured single-unit responses in different antennal sensillae from wild-type, clock mutant, odorant-receptor mutant, and G protein-coupled receptor kinase 2 (Gprk2) mutant flies to examine the cellular and molecular mechanisms that drive rhythms in olfaction. Spontaneous spike amplitude, but not spontaneous or odor-induced firing frequency, is under clock control in ab1 and ab3 basiconic sensillae and T2 trichoid sensillae. Mutants lacking odorant receptors in dendrites display constant low spike amplitudes, and the reduction or increase of levels of GPRK2 in OSNs results in constant low or constant high spontaneous spike amplitudes, respectively. We conclude that spike amplitude is controlled by circadian clocks in basiconic and trichoid sensillae and requires GPRK2 expression and the presence of functional ORs in dendrites. These results argue that rhythms in GPRK2 levels control OR localization and OR-dependent ion channel activity and/or composition to mediate rhythms in spontaneous spike amplitude.     

Temperature dependency of cupular mechanics and hair cell frequency selectivity in the fish canal lateral line organ

The mechanical frequency selectivity of the cupula located in the supraorbital lateral line canal and the frequency selectivity of the hair cells driven by the cupula were measured simultaneously in vivo. Laser interferometry was used to measure cupular mechanics and extracellular receptor potentials were recorded to determine hair cell frequency selectivity. Results were obtained from two teleost fish species, the ruffe (Acerina cernua L.), a European temperate zone freshwater fish, and the tropical African knife fish (Xenomiystus nigri). In both species cupular displacement grows with increasing frequency of canal fluid displacement, reaching a maximum at 115 Hz in the ruffe and at 460 Hz in the African knife fish. Cupular best frequencies were independent of temperature. Cut-off frequencies of hair cell frequency selectivity were found to depend on temperature with a Q10 of 1.75, ranging from 116 Hz (4 degrees C) to 290 Hz (20 degrees C), as established in the ruffe. At normal habitat temperatures of the two fish species (ruffe, 4 degrees C; African knife fish, 28 degrees C), this results in hair cell cut-off frequencies that match the two different cupular best frequencies remarkably well. This match suggests adjusted signal transfer in these two peripheral stages of canal lateral line transduction.     

Mechanosensory afferents innervating the swimmerets of the lobster

Feathered hair sensilla fringe both rami of the lobster (Homarus americanus) swimmeret. The sensory response to hair displacement was characterized by recording afferent impulses extracellularly from the swimmeret sensory nerve while deflecting sensilla with a rigidly-coupled probe or controlled water movements. Two populations of hairs were observed: "distal" hairs localized to the distal 1/3 of each ramus and "proximal" hairs near its base. Distal hairs are not innervated by a mechanosensory neuron but instead act as levers producing strain within adjacent cuticle capable of activating a nearby hypodermal mechanoreceptor. Hair deflections of 25 degrees or more are required to evoke an afferent response and this response is dependent on hair deflection direction. The frequency and duration of the afferent discharge evoked are determined by the velocity of hair displacement. Each proximal hair is innervated by a single mechanosensory neuron responding phasically to hair deflections as small as 0.2 degrees in amplitude. Deflection at frequencies up to 5 Hz elicits a single action potential for each hair movement; at higher frequencies many deflections fail to evoke an afferent response. These sensilla, which are mechanically coupled, may be activated by the turbulent flow of water produced by the swimmerets during their characteristic beating movements.