Tateo Shimozawa

Cricket Wind Receptors: Thermal Noise for the Highest Sensitivity Known

The minimum amount of mechanical energy necessary to elicit a neuronal spike in the wind receptor cell of a cricket is determined to be in the order of kBT (4 x 10-21 Joules at 300°K). Insect mechanoreceptors are therefore bordering the range of thermal noise due to Brownian motion when working near to threshold. Evolution, however, has achieved a paradoxical solution for sensory signal transmission in the presence of thermal noise.

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

Abstract 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.

The structure of a hair mechanoreceptor in the antennule of crayfish (Crustacea)

SummaryIn this study we examine the fine structure of mechanosensory hairs in the antennule of crayfish. The sensory hair is a stiff shaft with feather-like filaments. The hairs base is a large expansion of membrane which allows the hair shaft to deflect. The sensory transducing elements are located far from the hair, but are coupled mechanically with the hair shaft by a fine extracellular chorda. The sensory element is a type of scolopidium which consists of a scolopale cell and three sensory cells with a 9 + 0 type ciliary process.This type of scolopidium is characteristic of the chordotonal organ that has no cuticular structure on the surface of the exoskeleton. In this crustacean hair receptor, the deflection of the cuticular hair is transmitted through the chorda to the scolopidium which is a tension-sensitive transducer. The present study reveals that the mechanosensory hair of decapod crustaceans is a chordotonal organ accompanied by a cuticular hair structure. We also discuss comparative aspects of cuticular and subcuticular chordotonal organs in arthropods.

THE SHAPE OF WIND-RECEPTOR HAIRS OF CRICKET AND COCKROACH

Abstract We examined the exact shapes of the thread-like wind-receptor hairs in the cricket and cockroach. The diameters of hairs at various distances from the hair tip as measured by scanning electron microscopy revealed unexpected hair shapes. We had expected, a priori, that the shape of the hair would be a slender linearly tapered cone, but the measurements revealed hairs in the form of extremely elongated paraboloids. The diameter of the wind-receptor hairs varies with the square root of the distance from the hair tip, i.e., the diameter rapidly increases with the distance from the tip and is asymptotic to the base diameter.Both the cricket, Gryllus bimaculatus, and the cockroach, Periplaneta americana, showed the same hair shape. In both insects, the formation of the wind-receptor hair during metamorphosis seems to be controlled by a common cytological program. The shape of the hair constrains the mobility of the wind-receptor hair, because both the drag force caused by moving air and the moment of inertia of motion dynamics are functions of shaft diameter. The shape of the hair is a biological trait which affects the sensory information transmitted to the central nervous system.

Ecdysial growth of the filiform hairs and sensitivity of the cercal sensory system of the cricket,Gryllus bimaculatus

Summary1.The ecdysial growth of cercal filiform hairs was investigated in the cricketGryllus bimaculatus. The length of hairs varied from 40 to 500 μm in the 1st, from 40 to 650 μm in the 3rd and from 30 to 800 μm in the 5th instar nymphs (Fig. 1). Hemimetabolous development causes both hair growth and the appearance of new hairs at each ecdysis (Figs. 2, 3). The newly acquired hairs were shorter than 200 μm in every case (Fig. 4).2.Velocity thresholds of cercal sensory interneurons (CSIs) to sinusoidal air-currents were measured in 3rd instar nymphs (Fig. 5 A, B, C). CSIs 8-1 (medial giant interneuron: MGI) and 9-1 (lateral giant interneuron: LGI) showed threshold curves of acceleration sensitivity similar to those in adults. The thresholds for CSIs 8-1 and 9-1 were on the average higher in nymphs than in adults. The threshold curves for the two velocity-sensitive CSIs 10-2 and 10-3 were similar for nymphs and adults.3.Velocity thresholds of cercal filiform sensilla were measured in 3rd instar nymphs (Fig. 6). In spite of the small size of nymphal hairs, the most sensitive ones showed the same sensitivity as did the long 1000 μm hairs of the adult.4.The filiform hairs in 3rd instar nymphs were supported by a weaker spring than in adults (Fig. 7). Relative stiffness was about 50% of that in the long hairs in adults, but not much different than that in the short hairs.5.Based on a theoretical estimation of hair motion, the threshold angle of a filiform sensillum in the 3rd instar nymph was calculated (Fig. 9). Threshold angles of the long sensilla seemed to be unchanged throughout hemimetabolous development.

Differing afferent connections of spiking and nonspiking wind-sensitive local interneurons in the terminal abdominal ganglion of the cricket Gryllus bimaculatus

Fifteen local spiking interneurons (LSIs) and twentyone local non-spiking interneurons (LNIs) were identified in the terminal abdominal ganglion (TAG) of the cricket Gryllus bimaculatus on the basis of intracellular recording and staining (Figs. 1, 5, 6). Although the majority of LNIs showed sharp directionalities (Fig. 7) the LSIs did not (Fig. 3). The directionality of LNIs varied with the recording sites within a single cell (Fig. 8). Electrical stimulations of the cereal sensory nerve suggested that the LNIs are connected monosynaptically with the sensory afferents of both the cerci, and that LSIs may possess a variety of bilateral combinations of polysynaptic connections with the sensory afferents. We found that the spiking and the non-spiking local interneurons in the cereal sensory system differ not only in their membrane properties, but also in their afferent connections, and concluded that their differing connectivity to the sensory afferents will associate them with different roles in signal processing.

Diversity of Motor Responses Initiated by a Wind Stimulus in the Freely Moving Cricket, Gryllus bimaculatus

Abstract The behavioral responses to a wind stimulus were studied in the freely moving cricket, Gryllus bimaculatus. The observed responses included walking, running, jumping, turning, withdrawing, abdominal lifting, hind-leg lifting, kicking, cercal cleaning, antennal swinging, and “no action” and were classified into five behaviors as functional categories: escape, evasion, offense, surveillance and “no action”. The elicitation of each type of behavior by an identical stimulus was variable and unpredictable. However, the stochastic approach showed that the probabilities of the behaviors converged in a series of responses obtained from one cricket and in mass response data collected from 48 crickets. These probabilities, the values calculated from the different populations, were the same. The statistical analysis, using the probabilities, revealed that the probabilities of these wind-evoked behaviors were affected by the intensity of the wind stimulus. The escape and “no action” were dominant, together constituting more than 60% of the total responses. The stimulus method and the animal conditions determining a high probability of escape are also discussed.

Analysis of neural spike trains with interspike interval reconstruction.

Abstract. As a method for the analysis of neural spike trains, we examine fundamental characteristics of interspike interval (ISI) reconstruction theoretically with a leaky-integrator neuron model and experimentally with cricket wind receptor cells. Both the input to the leaky integrator and the stimulus to the wind receptor cells are the time series generated from the Rössler system. By numerical analysis of the leaky integrator, it is shown that, even if ISI reconstruction is possible, sometimes the entire structure of the Rössler attractor may not be reconstructed with ISI reconstruction. For analysis of the in vivo physiological responses of cricket wind receptor cells, we apply ISI reconstruction, nonlinear prediction and the surrogate data method to the experimental data. As a result of the analysis, it is found that there is a significant deterministic structure in the spike trains. By this analysis of physiological data, it is also shown that, even if ISI reconstruction is possible, the entire attractor may not be reconstructed.

A fixed time-interval between two behavioural elements in the mating behaviour of male crickets, Gryllus bimaculatus

Abstract In the sequence of mating behaviours of male crickets there is a fixed time-interval between two behaviours: spermatophore protrusion and courtship stridulation. During the fixed time-interval, courtship activities are specifically suppressed and self-maintenance activities such as feeding, drinking and aggressive stridulation appear. This paper reports on an experiment to investigate an interval timing mechanism controlling behavioural time sharing. Isolation experiments revealed that the presence of a female was necessary as a releaser for a male to stridulate the courtship song. However, the presence or absence of a female did not affect the length of the interval between the two behaviours. Even when spermatophore protrusion was postponed or the spermatophore was removed, the time-interval from spermatophore protrusion to courtship stridulation was unaffected. The interval seemed to depend on an internal mechanism, because (1) sensory feedbacks from genital organs were not necessary, (2) the interval length was about 1 h, and (3) the temperature coefficient Q10 was 2·0.

Change of Motion and Localization of Cholesterol Molecule during Lα-HII Transition

Abstract Formation of the inverted hexagonal (H II ) phase from the lamellar (L α ) phase of bovine brain-extracted phosphatidylcholine (BBPC) and phosphatidylethanolamine (BBPE) was investigated using 31 P-NMR with or without cholesterol. When the ratio of BBPC to BBPE was 1:1, the H II formation was observed in the presence of 33mol% cholesterol (i.e., BBPC:BBPE:cholesterol=1:1:1) at 47°C. The fraction of the H II phase in the BBPC/BBPE/cholesterol system could be controlled by the addition of dioleoylglycerol. The change of molecular motion of cholesterol affected by the H II formation was measured at various ratios of the L α to H II phase with the time-resolved fluorescence depolarization method, using dehydroergosterol as a fluorescent probe. It is observed that the motion of cholesterol became vigorous in the mixture state of the L α and the H II phases compared to that in the L α or the H II phase only. These facts show that cholesterol has the strong ability to induce the H II phase, probably by special molecular motion, which includes change of its location from the headgroup area to the acyl-chain area.