Sensing the effect of body load in legs: responses of tibial campaniform sensilla to forces applied to the thorax in freely standing cockroaches

Sense organs in the legs that detect body weight are an important component in the regulation of posture and locomotion. We tested the abilities of tibial campaniform sensilla, receptors that can monitor forces in the cockroach leg, to encode variations in body load in freely standing animals. Small magnets were attached to the thorax and currents were applied to a coil below the substrate. Sensory and motor activities were monitored neurographically. The tibial sensilla could show vigorous discharges to changing forces when animals stood upon their legs and actively supported the body weight. Firing of individual afferents depended upon the orientation of the receptors cuticular cap: proximal sensilla (oriented perpendicular to the leg axis) discharged to force increases while distal receptors (parallel to the leg) fired to decreasing forces. Proximal sensillum discharges were prolonged and could encode the level of load when increases were sustained. Firing of the trochanteral extensor motoneuron was also strongly modulated by changing load. In some postures, sensillum discharges paralleled changes in motor frequency consistent with a known interjoint reflex. These findings demonstrate that tibial campaniform sensilla can monitor the effects of body weight upon the legs and may aid in generating support of body load.     

Common motor mechanisms support body load in serially homologous legs of cockroaches in posture and walking

We studied the mechanisms underlying support of body load in posture and walking in serially homologous legs of cockroaches. Activities of the trochanteral extensor muscle in the front or middle legs were recorded neurographically while animals were videotaped. Body load was increased via magnets attached to the thorax and varied through a coil below the substrate. In posture, tonic firing of the slow trochanteral extensor motoneuron (Ds) in each leg was strongly modulated by changing body load. Rapid load increases produced decreases in body height and sharp increments in extensor firing. The peak of extensor activity more closely approximated the maximum velocity of body displacement than the body position. In walking, extensor bursts in front and middle legs were initiated during swing and continued into the stance phase. Moderate tonic increases in body load elicited similar, specific, phase dependent changes in both legs: extensor firing was not altered in swing but was higher after foot placement in stance. These motor adjustments to load are not anticipatory but apparently depend upon sensory feedback. These data are consistent with previous findings in the hind legs and support the idea that body load is countered by common motor mechanisms in serially homologous legs.     

Encoding of forces by cockroach tibial campaniform sensilla: implications in dynamic control of posture and locomotion

Forces exerted by a leg in support and propulsion can vary considerably when animals stand upon or traverse irregular terrains. We characterized the responses of the cockroach tibial campaniform sensilla, mechanoreceptors which encode force via strains produced in the exoskeleton, by applying forces to the leg at controlled magnitudes and rates. We also examined how sensory responses are altered in the presence of different levels of static load. All receptors exhibit phasico-tonic discharges that reflect the level and rate of force application. Our studies show that: (1) tonic discharges of sensilla can signal the level of force, but accurate encoding of static loads may be affected by substantial receptor adaptation and hysteresis; (2) the absolute tonic sensitivities of receptors decrease when incremental forces are applied at different initial load levels; (3) phasic discharges of sensilla accurately encode the rate of force application; and (4) sensitivities to changing rates of force are strictly preserved in the presence of static loads. These findings imply that discharges of the sensilla are particularly tuned to the rate of change of force at all levels of leg loading. This information could be utilized to adapt posture and walking to varying terrains and unexpected perturbations. Accepted: 8 January 2000     

Body segments decoupling in sitting: control of body posture from automatic chair adjustments

Background

Individuals who cannot functionally reposition themselves adopt a passive body posture and suffer from physical discomfort in long-term sitting. To regulate body load and to prevent sitting related mobility problems, proper posture control is important. The inability to reposition underlines the importance for seating interventions that control body posture from automatic chair adjustments. We developed an adjustable simulator chair that allows the alignment of the trunk, pelvis and thighs to be controlled independently. This study describes the system for decoupled body segments adjustment and develops a predictive model that computes angular chair configuration for desired body postures.

Methods

Eighteen healthy male subjects participated in this study. The experiment involved a protocol of five trials, each investigating the effect of individual chair segment angle adjustment on body segments rotation. Quasi-static chair adjustments were performed, in which angular chair configuration and body segments orientation were measured using an infrared motion capturing system and an inertia sensor attached on the pelvis.

Results

Linear best-fit equations together with the coefficients of determination were computed. Significant relations have been found between angular chair configuration and body segments orientation leading to an algorithm that predicts chair configuration for desired body posture.

Conclusions

The predictive algorithm seems applicable to compute angular chair configuration for desired body posture when the initial body–chair configuration is known. For clinical application, future experiments must be performed on impaired individuals to validate the algorithm in terms of accuracy.     

Estimating the centre of gravity of the body on the basis of the centre of pressure in standing posture

This study proposes to estimate the horizontal positions of the body's centre of gravity (CoG) in a standing posture, on the basis of the horizontal positions of the centre of pressure (CoP). The latter were measured with a force plate, and using a low-pass filter defined by a mathematical relationship of the relative magnitude of the CoG with respect to the magnitude of the CoP, as a function of the frequency oscillations (Brenière, 1996, Journal of Motor Behaviour 28, 291–298). This relationship was computed from the angular momentum equation applied to the whole body with respect to the CoG using the inverse dynamics approach and force plate recordings, and considering the CoP and CoG oscillations as simple periodic functions. Five subjects were asked to perform voluntary oscillations along medio-lateral and antero-posterior axes, keeping their bodies straight, and without moving their feet. The CoG accelerations measured by the force plate were compared with the CoG accelerations derived from the estimated CoG positions. The average root-mean-square difference between these accelerations was very small, confirming the accuracy of this method. This simplified way to calculate the CoG positions, rarely measured in standing, allows a comparative assessment of motion performance. This method could also be applied to other kinds of movement such as walking.     

Indirect synaptic inputs from filiform hair sensory neurons contribute to the receptive fields of giant interneurons in the first-instar cockroach

The first-instar cockroach, Periplaneta americana, detects air movements using four filiform hair sensilla, which make synaptic connections to seven pairs of giant interneurons (GIs) in the terminal abdominal ganglion. The directional sensitivities of some of the GIs, predicted from their patterns of monosynaptic inputs, may not be the same as in the second instar or adult. Intracellular recordings were made to determine the contribution of polysynaptic inputs to the receptive fields of first-instar GIs. The ventral GI1, and the dorsal GI5, GI6, and GI7 were all found to have indirect synaptic inputs from filiform afferents. The indirect inputs were excitatory to GI1, GI5, and GI7, and inhibitory to GI6 and GI7. The indirect excitatory input to GI1 was predicted to alter qualitatively its receptive field, allowing it to respond to wind from the side of the animal, as in the adult. Inhibition was predicted to sharpen the receptive fields of GI6 and GI7. The inhibitory postsynaptic potentials reversed 6–8 mV below resting potential and were blocked by picrotoxin, indicating that they are GABAergic. Indirect excitation also altered the predicted receptive field of GI7, one of the inputs being an unusual “off-response” to movement of a filiform hair in its inhibitory direction. Accepted: 19 June 1998     

Responses of efferent octopaminergic thoracic unpaired median neurons in the locust to visual and mechanosensory signals

Insect thoracic ganglia contain efferent octopaminergic unpaired median neurons (UM neurons) located in the midline, projecting bilaterally and modulating neuromuscular transmission, muscle contraction kinetics, sensory sensitivity and muscle metabolism. In locusts, these neurons are located dorsally or ventrally (DUM- or VUM-neurons) and divided into functionally different sub-populations activated during different motor tasks. This study addresses the responsiveness of locust thoracic DUM neurons to various sensory stimuli. Two classes of sense organs, cuticular exteroreceptor mechanosensilla (tactile hairs and campaniform sensilla), and photoreceptors (compound eyes and ocelli) elicited excitatory reflex responses. Chordotonal organ joint receptors caused no responses. The tympanal organ (Müller's organ) elicited weak excitatory responses most likely via generally increased network activity due to increased arousal. Vibratory stimuli to the hind leg subgenual organ never elicited responses. Whereas DUM neurons innervating wing muscles are not very responsive to sensory stimulation, those innervating leg and other muscles are very responsive to stimulation of exteroreceptors and hardly responsive to stimulation of proprioceptors. After cutting both cervical connectives all mechanosensory excitation is lost, even for sensory inputs from the abdomen. This suggests that, in contrast to motor neurons, the sensory inputs to octopaminergic efferent neuromodulatory cells are pre-processed in the suboesophageal ganglion.     

The body beyond the body: expectation of a sensory event is enough to induce ownership over a fake hand

More than 100 papers have been published on the rubber hand illusion since its discovery 14 years ago. The illusion has been proposed as a demonstration that the body is distinguished from other objects by its participation in specific forms of intermodal perceptual correlation. Here, we radically challenge this view by claiming that perceptual correlation is not necessary to produce the experience of this body as mine. Each of 15 participants was seated with his/her right arm resting upon a table just below another smaller table. Thus, the real hand was hidden from the participant''s view and a life-sized rubber model of a right hand was placed on the small table in front of the participant. The participant observed the experimenter''s hand while approaching—without touching—the rubber hand. Phenomenology of the illusion was measured by means of skin conductance response and questionnaire. Both measures indicated that participants experienced the illusion that the experimenter''s hand was about to touch their hidden hand rather than the rubber hand, as if the latter replaced their own hand. This did not occur when the rubber hand was rotated by 180° or replaced by a piece of wood. This illusion indicates that our brain does not build a sense of self in a merely reactive way, via perceptual correlations; rather it generates predictions on what may or may not belong to itself.     

Lehr's fields of campaniform sensilla in beetles (Coleoptera): Functional morphology. II. Wing reduction and the sensory field

Loss of the flight ability and wing reduction has been reported for many taxa of Coleoptera. If elytra are closed, their roots are clenched between the tergum and the pleuron, forces applied to the elytra can not be transmitted to the field of campaniform sensilla situated on the root. That is why it is plausible to assume that the field becomes redundant in non-flying beetles. We examined the relationships between the hind wing reduction and characters of this mechanosensory field in beetles of six families. We measured the size of the elytron, that of the hind wing and counted the number of sensilla in the sensory field. Mesopterous non-flying beetles retain one half to one third of sensilla present in macropterous species of the same body size. Further reduction of the sensory field in brachypterous species is obvious, but sensilla are still present in insects with strongly reduced wings, as long as their elytra are separable and mesothoracic axillaries are present. Complete loss of sensilla coincides with the existence of a permanent sutural lock. However, some beetles with permanently locked elytra and absence of axillaries still retain few campaniform sensilla. A very special case of an extreme wing modification in feather-wing beetles is considered. No sensilla were revealed either on the root of the elytron or on the basal segment of such fringed wings in flying ptiliid species.     

Continuous detection of weak sensory signals in afferent spike trains: the role of anti-correlated interspike intervals in detection performance

An important problem in sensory processing is deciding whether fluctuating neural activity encodes a stimulus or is due to variability in baseline activity. Neurons that subserve detection must examine incoming spike trains continuously, and quickly and reliably differentiate signals from baseline activity. Here we demonstrate that a neural integrator can perform continuous signal detection, with performance exceeding that of trial-based procedures, where spike counts in signal- and baseline windows are compared. The procedure was applied to data from electrosensory afferents of weakly electric fish (Apteronotus leptorhynchus), where weak perturbations generated by small prey add ~1 spike to a baseline of ~300 spikes s^–1. The hypothetical postsynaptic neuron, modeling an electrosensory lateral line lobe cell, could detect an added spike within 10–15 ms, achieving near ideal detection performance (80–95%) at false alarm rates of 1–2 Hz, while trial-based testing resulted in only 30–35% correct detections at that false alarm rate. The performance improvement was due to anti-correlations in the afferent spike train, which reduced both the amplitude and duration of fluctuations in postsynaptic membrane activity, and so decreased the number of false alarms. Anti-correlations can be exploited to improve detection performance only if there is memory of prior decisions.Abbreviations B binomial - CV coefficient of variation - EOD electric organ discharge - ELL electrosensory lateral line lobe - EPSP excitatory postsynaptic potential - ISI interspike interval - M₀ Markov order zero - M₁ Markov order one - N noise - OC operating characteristic - PDF probability density function - ROC receiver operating characteristic - S signal - SNR signal-to-noise ratio - S+N signal in noise     

Synaptic inputs to the omega neuron of the cricket Teleogryllus oceanicus: differences in EPSP waveforms evoke by low and high sound frequencies

EPSP waveforms were recorded from the omega neuron of Teleogryllus oceanicus for 5 kHz and ultrasonic sound stimuli. EPSPs in response to 5 kHz stimuli were smooth in shape and increased in amplitude with increasing stimulus intensity, while responses to ultrasound consisted of series' of large, discrete, unitary EPSPs, which increased in frequency with stimulus intensity.The hypothesis that a few, synaptically potent receptors might account for ultrasound sensitivity was tested by examining temporal coupling between ultrasound responses of the omega neuron and of another ultrasound-sensitive neuron, INT-1. INT-1 spikes were temporally correlated both to omega neuron spikes and to the large EPSPs recorded in the omega neuron. Coupling was not apparent for 5 kHz stimuli.The omega neuron encodes the intensity of 5 kHz and ultrasonic stimuli with similar resolution. Response latencies are markedly shorter for ultrasonic stimuli.These findings suggest that 5 kHz information is carried by a relatively large number of receptors, each of which has only a small effect on central neurons, while ultrasound information is carried by a few, synaptically potent, receptors.     

DUM neurons in locust flight: a model system for amine-mediated peripheral adjustments to the requirements of a central motor program

In both vertebrates and invertebrates, multiple effects of biogenic amines on neuromuscular transmission, muscle contraction kinetics and metabolism have been described. Nevertheless, it is not yet known whether and how these different effects work in concert during the performance of a specific behavior. In the locust flight system, the biogenic amine octopamine is released as a neurohormone into the haemolymph, and also delivered directly onto specific target muscles by individually identified dorsal unpaired median neurons. Determining the connectivity of these neurons and their activation during behavior, we show for the first time that different types of dorsal unpaired median neurons are differentially connected to certain components of the flight circuitry. During flight, all types of pterothoracic dorsal unpaired median neurons innervating flight muscles receive inhibitory inputs from tegula proprioceptive afferents and from the central flight circuitry, whereas all other types of dorsal unpaired median neurons are excited by wind-sensitive pathways and by the central pattern generator. Considering the results of other studies which investigated metabolic effects of octopamine, we propose a model in which the differential activation of dorsal unpaired median neurons during flight may lead to an adequately controlled release or removal of octopamine to adjust metabolic processes to the requirements of a specific motor program. Accepted: 24 February 1999     

Synaptic specificity in the first instar cockroach: patterns of monosynaptic input from filiform hair afferents to giant interneurons

Summary Direct evidence for monosynaptic connections between filiform hair sensory axons and giant interneurons (GIs) in the first instar cockroach, Periplaneta americana, was obtained using intracellular recording and HRP injection followed by electron microscopy. GIs 1–6 all receive monosynaptic input from at least one filiform afferent axon. GI1, GI2 and GI5 receive input only from the medial (M) axon, while GI3, GI4 and GI6 receive input from both M and lateral (L) axons. The dendrites of GI3 and GI6 which are contralateral to the cell bodies receive input from both axons whereas the smaller ipsilateral dendritic fields have synapses only from the L axon. GI5 has M axon input only onto its contralateral dendrites. In 50% of preparations GI7 receives weak input from the ipsilateral L axon. There is no obvious relationship between the morphology of the giant interneurons and the pattern of input they receive from the filiform afferents.Abbreviations GI giant interneuron - HRP horseradish peroxidase - L lateral axon - M medial axon     

Development of the subsoephageal body cells and the pericardiac cells during embryogenesis with diapause in Locusta migratoria (Linnaeus 1758) (Orthoptera: Acrididae)

During Locusta migratoria embryogenesis, the yolk is progressively degraded and the resulting metabolites are released in the haemolymph. We researched the organs possibly involved in the uptake of haemolymphatic proteins. Among organs originated from mesoderm, the SOB (suboesophageal bodies) situated in the embryonic head are remarkable by a very early acquisition of differentiated cytological characters, while most other cells of the embryo are undifferentiated. The SOB quite disappear before hatching. Just before katatrepsis stage, the other organs derived from mesoderm begin to differentiate, including the PC (pericardial cells) which take over from the SOB. These cells, situated in thorax and abdomen, are developed during the dorsal close of embryo. The development and the ultrastructural changes of the SOB cells and of the PC were studied during an embryogenesis with diapause. The morphology of embryos which enter diapause is comparable with that of a continuous development at the beginning of katatrepsis. However, the cells of SOB and PC cells suffer from remarkable changes not only physiologically but cytologically. At the beginning of diapause, the proteosynthetic activity practically disappears in the SOB cells and the lysis areas appear. Nevertheless, the exchanges between these cells and the haemolymph still remain important. For the period of cold, which is necessary to the resumption of development, the aspect of the SOB cells changes and in particular the areas of lysis become less wide. When the embryo reopens its development, the SOB cells show a proteosynthetic activity and the areas of lysis disappear. The changes of the SOB cells and of the PC cells are regularized during the resumption of the development: the SOB cells which had again taken a normal activity start to regress from the stage VII on, while the PC cells take over.     

Energy expenditure during flight in relation to body mass: effects of natural increases in mass and artificial load in Rose Coloured Starlings

Rose Coloured Starlings (Sturnus roseus) flew repeatedly for several hours in a wind tunnel while undergoing spontaneous variation in body mass. The treatments were as follows: flying unrestrained (U), with a control harness of 1.2% of their body mass (C), or with a harness of 7.4% of their body mass, which was either applied immediately before the flight (LS) or at least 9 days in advance (LL). Energy expenditure during flight (ef in W) was measured with the Doubly Labelled Water method. Flight costs in L(S) and LL were not significantly different and therefore were pooled (L). The harness itself did not affect ef, i.e. U and C flights were not different. ef was allometrically related with body mass m (in g). The slopes were not significantly different between the treatments, but ef was increased by 5.4% in L compared to C flights (log10(ef) = 0.050 + 0.47 x log10(m) for C, and log10(ef) = 0.073 + 0.47 x log10(m) for L). The difference in ef between C, LS and LL was best explained by taking the transported mass m transp (in g) instead of m into account (log10(ef) = -0.08 + 0.54 x log10(m transp)). Flight costs increased to a lesser extent than expected from interspecific allometric comparison or aerodynamic theory, regardless of whether the increase in mass occurred naturally or artificially. We did not observe an effect of treatment on breast muscle size and wingbeat frequency. We propose that the relatively low costs at a high mass are rather a consequence of immediate adjustments in physiology and/or flight behaviour than of long-term adaptations.     

Directional and anteroposterior asymmetry of common white markings in the legs of the Arabian horse: response to selection

Arabian bay horses manifest, on the average, more common white markings in their hind legs than their forelegs (anteroposterior asymmetry) and more common white markings in their left legs than their right legs (directional asymmetry). To determine if genetic variation exists for these types of asymmetry, the phenotypic response was studied in bay foals when their dams and sires were selected for the directions of fore-hind and left-right differences. In the fore-hind studies, the quantitative shifts in the bay foals were in the direction specified by the selection scheme and the observed deviations were all statistically significant. The shifts were also consistently in the direction favored by selection in the left-right studies, but only two of six observed deviations were statistically significant using a one-tailed test of significance. Thus, only marginal statistical evidence is available to support the observed consistent responses to selection in the left-right studies. These differential responses are reflected in the magnitudes of the heritability estimates. Based on the overall results, it is concluded that both types of asymmetry have a genetic basis in the Arabian horse, but much more genetic variation is present for anteroposterior asymmetry than for directional asymmetry. This revised version was published online in July 2006 with corrections to the Cover Date.     

A morphometric study of the midgut in resistant and non-resistant Anticarsia gemmatalis (Hübner) (Lepidoptera: Noctuidae) larvae to its nucleopolyhedrovirus (AgMNPV)

In this investigation, the anterior and posterior regions of the midgut of resistant (RL) and non-resistant (SL) Anticarsia gemmatalis larvae were analyzed morphometrically to characterize different regions along their length. Also, this investigation compares the results between SL and RL to improve the understanding of the resistance mechanisms to the virus. Histological sections were analyzed in a computerized system and the data were statistically analyzed by the Kruskal-Wallis test and by multivariate analysis. The midguts are morphometrically different in the two larval populations; we observed higher values in RL. The morphometric analysis of the epithelial cells showed that only columnar and goblet cells were distinct along the midgut, in both larvae, with the higher values found in the anterior region. Comparing the results between the two larval populations, all the epithelial cells presented significant differences, with RL showing the higher morphometric values. We concluded that there are regional differences along the length of midgut in SL and RL that confirm the idea of two morpho-functional distinct regions. The consistently morphometric superior values in RL indicate that this variability can be related with the resistance of A. gemmatalis to its AgMNPV.