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Many developmental disorders are diagnosed based on symptoms, which may result in lumping together multiple causes. This is thought to be a factor that complicates the research and treatment of developmental disorders. The purpose of this study is to provide hypotheses on the causes of brain functions in developmental dyslexia (DD) by constructing and analyzing a simple computational model of visual information processing using a deep generative model. We then analyze three symptoms observed in DD and investigate their functions and causes.

Insects have a sophisticated ability to navigate real environments. Virtual reality (VR) is a powerful tool for analyzing animal navigation in laboratory studies and is the most successful when used in the study of visually guided behaviors. However, the use of VR with non-visual sensory information, such as sound, on which nocturnal insects rely, for analyzing animal navigation has not been fully studied. We developed an auditory VR for the study of auditory navigation in crickets, Gryllus bimaculatus. The system consisted of a spherical treadmill on which a tethered female cricket walked. Sixteen speakers were placed around the cricket for auditory stimuli. The two optical mice attached to the treadmill measured the cricket’s locomotion, and the sound pressure and direction of the auditory stimuli were controlled at 100 Hz based on the position and heading of the cricket relative to a sound source in a virtual arena. We demonstrated that tethered female crickets selectively responded to the conspecific male calling song and localized the sound source in a virtual arena, which was similar to the behavior of freely walking crickets. Further combinations of our system with neurophysiological techniques will help understand the neural mechanisms for insect auditory navigation.

A comparative analysis of animal behavior (e.g., male vs. female groups) has been widely used to elucidate behavior specific to one group since pre-Darwinian times. However, big data generated by new sensing technologies, e.g., GPS, makes it difficult for them to contrast group differences manually. This study introduces DeepHL, a deep learning-assisted platform for the comparative analysis of animal movement data, i.e., trajectories. This software uses a deep neural network based on an attention mechanism to automatically detect segments in trajectories that are characteristic of one group. It then highlights these segments in visualized trajectories, enabling biologists to focus on these segments, and helps them reveal the underlying meaning of the highlighted segments to facilitate formulating new hypotheses. We tested the platform on a variety of trajectories of worms, insects, mice, bears, and seabirds across a scale from millimeters to hundreds of kilometers, revealing new movement features of these animals., Comparative analysis of animal behaviour using locomotion data such as GPS data is difficult because the large amount of data makes it difficult to contrast group differences. Here the authors apply deep learning to detect and highlight trajectories characteristic of a group across scales of millimetres to hundreds of kilometres.

Recent advances in robotics and measurement technologies have enabled biologists to record the trajectories created by animal movements. In this paper, we convert time series of animal traj...

To survive a predator's attack, prey animals must exhibit escape responses that are appropriately regulated in terms of their moving speed, distance, and direction. Insect locomotion is considered to be controlled by an interaction between the brain, which is involved in behavioral decision-making, and the thoracic ganglia (TG), which are primary motor centers. However, it remains unknown which descending and ascending signals between these neural centers are involved in the regulation of the escape behavior. We addressed the distinct roles of the brain and TG in the wind-elicited escape behavior of crickets by assessing the effects of partial ablation of the intersegmental communications on escape responses. We unilaterally cut the ventral nerve cord (VNC) at different locations, between the brain and TG, or between the TG and terminal abdominal ganglion (TAG), a primary sensory center of the cercal system. The partial ablation of ascending signals to the brain greatly reduced the jumping response rather than running, indicating that sensory information processing in the brain is essential for the choice of escape responses. The ablation of descending signals from the brain to the TG impaired loco motor performance and directional control of the escape responses, suggesting that locomotion in the escape behavior largely depends on the descending signals from the brain. Finally, the extracellular recording from the cervical VNC indicated a difference in the descending activities preceding the escape responses between running and jumping. Our results demonstrated that the brain sends the descending signals encoding the behavioral choice and locomotor regulation to the TG, while the TG seem to have other specific roles, such as in the preparation of escape movement.

Animals perceive their surroundings by using various modalities of sensory inputs to navigate their locomotion. Nocturnal insects such as crickets use mechanosensory inputs mediated by their antennae to navigate under dark conditions. Active sensing with voluntary antennal movements improves spatial information, but it remains unclear how accurately the insects can perceive the surrounding space by using their antennal system. Crickets exhibit escape behavior in response to a short air-puff, which is detected by the abdominal mechanosensory organ called cerci and is perceived as a “predator approach” signal. We placed objects of different shapes at different locations with which the cricket actively made contact using its antenna. We then examined the effects on wind-elicited escape. The crickets changed their movement trajectory depending on the shape and location of the objects so that they could avoid collision with these obstacles even when the escape behavior was triggered by another modality of stimulus. For instance, when a wall was placed in front of the crickets so that it was detected by one side of their antenna, the escape trajectory in response to a stimulus from behind was significantly biased toward the side opposite the wall. However, if the antenna on the free side without the wall was ablated, this modulation to avoid collision diminished, suggesting that the antenna on the free side provided information of “absence” of obstacles. This study demonstrated that crickets were able to perceive spatial information, including the presence or absence of objects by active sensing with their antennal system.Summary StatementCrickets can acquire spatial information such as shape, location and orientation of objects through active sensing by antennal mechanosensory system, which also provides information about the absence of objects.

Animals employ multiple behavioral strategies for exploring food and mating partners based on both their internal state and external environment. Here, we examined how cricket phonotaxis, which was considered an innate reactive behavior of females to approach the calling song of conspecific males, depended on these internal and external conditions. Our observation revealed that the phonotaxis process consisted of two distinctive phases: wandering and approaching. In the latter phase, crickets moved directly towards the sound source. The transition into this phase, referred to as the 'approach phase', was based on changes in the animal's internal state. Moreover, retention of the approach phase required recognition of the calling song, while song loss downregulated cricket mobility and induced frequent stopping. This is a typical movement in local search behaviors. Our results indicate that phonotaxis is not only a reactive response but a complicated process including multiple behavioral strategies.

Animals employ multiple behavioral strategies for exploring food and mating partners based on both their internal state and external environment. Here, we examined how cricket phonotaxis, which was considered an innate reactive behavior of females to approach the calling song of conspecific males, depended on these internal and external conditions. Our observation revealed that the phonotaxis process consisted of two distinctive phases: wandering and approaching. In the latter phase, crickets moved straightly and directly toward the sound source. The transition into this phase, referred to as the ‘approach phase’, was based on changes in animal's internal state. Moreover, retention of the approach phase required recognition of the calling song while song loss downregulated cricket mobility and induced frequent stopping. This is a typical movement in local search behaviors. Our results indicate that phonotaxis is not only a reactive response but a complicated process including multiple behavioral strategies.

Arthropods including insects grow through several developmental stages by molting. The abrupt changes in their body size and morphology accompanying the molting are responsible for the developmental changes in behavior. While in holometabolous insects, larval behaviors are transformed into adult-specific behaviors with drastic changes in nervous system during the pupal stage, hemimetabolous insects preserve most innate behaviors whole life long, which allow us to trace the maturation process of preserved behaviors after the changes in body. Wind-elicited escape behavior is one of these behaviors and mediated by cercal system, which is a mechanosensory organ equipped by all stages of nymph in orthopteran insects like crickets. However, the maturation process of the escape behavior after the molt is unclear. In this study, we examined time-series of changes in the wind-elicited escape behavior just after the imaginal molt in the cricket. The locomotor activities are developed over the elapsed time, and matured 24h after the molt. In contrast, a stimulus-angle dependency of moving direction was unchanged over time, meaning that the cercal sensory system detecting airflow direction was workable immediately after the molt, independent from the behavioral maturation. The post-molting development of the wind-elicited behavior was considered to result not simply from maturation of the exoskeleton or musculature because the escape response to heat-shock stimulus did not change after the molt. No effect of a temporal immobilization after the imaginal molt on the maturation of the wind-elicited behavior also implies that the maturation may be innately programmed without experience of locomotion.

Double-sides of aluminum sheet were anodized; at first, one side (front-side) of aluminum sheet was anodized, and the pores were filled with nickel using electroplating technique. Next, the other side (back side) of aluminum sheet was anodized. After formation of electrodes on both sides of anodic porous alumina, the current–voltage characteristics were examined, and reversible change in the resistance between metallic and insulating states was measured during mono-polar operation. This switching behavior could be measured for the sample with the depth of backside pores of about 100 μm. The bias voltage, at which the resistance state changed into the lower-resistance state from the higher-resistance state, decreased with decreasing the depth of backside pores, and the bias voltage was about 1 V in the case of the backside pores of about 10 μm.

Insects have the ability to navigate through a complex environment. It has been reported that using multisensory information improves their ability to navigate. To reveal when and how insects utilize multiple sensory information, we developed a multisensory virtual reality system for crickets (Gryllus bimaculatus), which enables us to manipulate auditory and visual stimuli from every direction. We investigated how visual information influenced their phonotaxis towards a conspecific male calling song. Our results showed that crickets exhibit phonotaxis under virtual reality and that a visual target with a sound source reduced the variability of the body angle towards the source. These results suggested the possibility that crickets utilize visual cues to localize sound sources. Further investigation with our system will reveal how crickets effectively utilize multiple sensory information in complex environments.

To survive a predator’s attack successfully, animals choose appropriate actions from multiple escape responses. The motor performance of escape response governs successful survival, which implies that the action selection in escape behaviour is based on the trade-off between competing behavioural benefits. Thus, quantitative assessment of motor performance will shed light on the biological basis of decision-making. To explore the trade-off underlying the action selection, we focused on two distinct wind-elicited escape responses of crickets, running and jumping. We first hypothesized a trade-off between speed and directional accuracy. This hypothesis was rejected because crickets could control the escape direction in jumping as precisely as in running; further, jumping had advantages with regard to escape speed. Next, we assumed behavioural flexibility, including responsiveness to additional predator’s attacks, as a benefit of running. The double stimulus experiment revealed that crickets running in the first response could respond more frequently to a second stimulus and control the movement direction more precisely compared to when they chose jumping for the first response. These data suggest that not only the motor performance but also the future adaptability of subsequent behaviours are considered as behavioural benefits, which may be used for choosing appropriate escape reactions.

Detecting predators is crucial for survival. In insects, a few sensory interneurons receiving sensory input from a distinct receptive organ extract specific features informing the animal about approaching predators and mediate avoidance behaviors. Although integration of multiple sensory cues relevant to the predator enhances sensitivity and precision, it has not been established whether the sensory interneurons that act as predator detectors integrate multiple modalities of sensory inputs elicited by predators. Using intracellular recording techniques, we found that the cricket auditory neuron AN2, which is sensitive to the ultrasound-like echolocation calls of bats, responds to airflow stimuli transduced by the cercal organ, a mechanoreceptor in the abdomen. AN2 enhanced spike outputs in response to cross-modal stimuli combining sound with airflow, and the linearity of the summation of multisensory integration depended on the magnitude of the evoked response. The enhanced AN2 activity contained bursts, triggering avoidance behavior. Moreover, cross-modal stimuli elicited larger and longer lasting excitatory postsynaptic potentials (EPSP) than unimodal stimuli, which would result from a sublinear summation of EPSPs evoked respectively by sound or airflow. The persistence of EPSPs was correlated with the occurrence and structure of burst activity. Our findings indicate that AN2 integrates bimodal signals and that multisensory integration rather than unimodal stimulation alone more reliably generates bursting activity.NEW & NOTEWORTHY Crickets detect ultrasound with their tympanum and airflow with their cercal organ and process them as alert signals of predators. These sensory signals are integrated by auditory neuron AN2 in the early stages of sensory processing. Multisensory inputs from different sensory channels enhanced excitatory postsynaptic potentials to facilitate burst firing, which could trigger avoidance steering in flying crickets. Our results highlight the cellular basis of multisensory integration in AN2 and possible effects on escape behavior.

Stimulus-specific adaptation (SSA) is considered to be the neural underpinning of habituation to frequent stimuli and novelty detection. However, neither the cellular mechanism underlying SSA nor the link between SSA-like neuronal plasticity and behavioral modulation is well understood. The wind-detection system in crickets is one of the best models for investigating the neural basis of SSA. We found that crickets exhibit stimulus-direction-specific adaptation in wind-elicited avoidance behavior. Repetitive air currents inducing this behavioral adaptation reduced firings to the stimulus and the amplitude of excitatory synaptic potentials in wind-sensitive giant interneurons (GIs) related to the avoidance behavior. Injection of a Ca 2+ chelator into GIs diminished both the attenuation of firings and the synaptic depression induced by the repetitive stimulation, suggesting that adaptation of GIs induced by this stimulation results in Ca 2+ -mediated modulation of postsynaptic responses, including postsynaptic short-term depression. Some types of GIs showed specific adaptation to the direction of repetitive stimuli, resulting in an alteration of their directional tuning curves. The types of GIs for which directional tuning was altered displayed heterogeneous direction selectivity in their Ca 2+ dynamics that was restricted to a specific area of dendrites. In contrast, other types of GIs with constant directionality exhibited direction-independent global Ca 2+ elevation throughout the dendritic arbor. These results suggest that depression induced by local Ca 2+ accumulation at repetitively activated synapses of key neurons underlies direction-specific behavioral adaptation. This input-selective depression mediated by heterogeneous Ca 2+ dynamics could confer the ability to detect novelty at the earliest stages of sensory processing in crickets. SIGNIFICANCE STATEMENT Stimulus-specific adaptation (SSA) is considered to be the neural underpinning of habituation and novelty detection. We found that crickets exhibit stimulus-direction-specific adaptation in wind-elicited avoidance behavior. Repetitive air currents inducing this behavioral adaptation altered the directional selectivity of wind-sensitive giant interneurons (GIs) via direction-specific adaptation mediated by dendritic Ca 2+ elevation. The GIs for which directional tuning was altered displayed heterogeneous direction selectivity in their Ca 2+ dynamics and the transient increase in Ca 2+ evoked by the repeated puffs was restricted to a specific area of dendrites. These results suggest that depression induced by local Ca 2+ accumulation at repetitively activated synapses of key neurons underlies direction-specific behavioral adaptation. Our findings elucidate the subcellular mechanism underlying SSA-like neuronal plasticity related to behavioral adaptation.

Acoustic signals trigger various behaviours in insects such as courtship or escape from predators. However, it remains unknown whether insects utilize acoustic signals to recognize environmental contexts. The cricket is a prominent model insect for neuroethological studies on acoustic behaviour because female crickets exhibit positive phonotaxis in response to male calling songs, and flying crickets display avoidance behaviour for high-frequency sounds such as echolocation call of bats. The carrier frequency of these sounds is a major factor in determining whether they initiate these acoustic behaviours. Here, we examined the impacts of different frequencies of tone sounds on cercal-mediated escape behaviour, using a 5-kHz tone corresponding to the calling song and a 15-kHz tone serving as a trigger of avoidance behaviours. Neither frequency elicited a response in the standing cricket by itself, but they had different impacts on walking responses to airflow stimuli. While the 15-kHz tone reduced response probability, extended moving distance, and enhanced turn-angle variability, the 5-kHz tone had no effect. Although both frequencies of tones facilitated walking backward, the 15-kHz tone had a larger effect than the 5-kHz tone. These frequency dependencies of behavioural modulation suggest that crickets can recognize acoustic contexts and alter their escape strategy accordingly.

In crickets, the cercal system is a mechanosensory system in which the receptor organ is a pair of antenna-like appendages called cerci located at the rear of the abdomen and covered with mechanosensory hairs, similar to the bristles on a bottlebrush. This system mediates the detection, localization, and identification of air currents surrounding the animal. Owing to the easy accessibility of the nervous system and advantages in physiological techniques, the cercal system of the cricket has been used as a model system for investigations of development, mechanoreceptor biomechanics, neural maps, and neural coding over the past few decades. In contrast, the behavioral significance of this system is still poorly understood. In early studies, the cercal system was regarded to be a simple system for triggering an escape reflex against an approaching predator. However, recent studies suggest that it is a more complex “generalist” system involved in various behaviors. In this chapter, we review studies on the cricket cercal system from a neuroethological point of view and discuss the future direction of neuroethological research on this system.

Optical recording that provides both anatomical and physiological data has become an essential research technique for neuroscience studies. In particular, Ca2+ imaging is one of the most popular and useful methods for monitoring local activity at subcellular regions of single neurons and/or visualization of spatiotemporal dynamics of neuronal population activity. In neuroethological studies on the cricket, the Ca2+ imaging is also a powerful method for optical recording of neural activity and has yielded important information on neural mechanisms in the cricket. In this chapter, we summarize some important features for the application of Ca2+ imaging in the cricket nervous system. This includes the selection of an appropriate Ca2+ indicator and the dye loading protocols, experimental designs, and optical system configurations that are required to enable the effective use of the Ca2+ imaging techniques in the cricket. As an example application, we focused on Ca2+ imaging experiments in the cricket cercal sensory system in vivo.

This paper proposes a thermal design procedure for micro- and nanosatellites that can be completed in one year. Two thermal design concepts keep components within their design temperature range, reducing the temperature change by using the whole structure for heat storage and reducing the temperature change of the inner structure where the most temperature-sensitive components are mounted. One- and two-nodal analysis methods are used for the former and latter concepts, respectively, to clarify the combinations of optical properties for the structures and components to keep within the design temperature range of the components. Finally, multinodal analysis is performed for detail design based on the optical properties clarified from the one- and two-nodal analyses. This thermal design procedure was applied to the Hodoyoshi-1 satellite, which is a cube about 50cm on a side, has two inner plates and has solar cells on the body, is on a sun-synchronous orbit at an altitude of about 500km, and is pointing to Earth. The thermal design of the Hodoyoshi-1 satellite was completed in about 10 months.

We used FM imaging to identify neurons that receive sensory feedback from the body wall in a circuit for octopamine (OA)-evoked rhythmic locomotion in the earthworm, Eisenia fetida. We visualized synapses in which postsynaptic neurons receive the sensory feedback, by using FM1-43 dye to label the synapses of both motor and sensory pathways that are associated with locomotion, then clearing the motor pathway synapse labeling, and finally identifying the target synapses by distinguishing physiologically functional synapses through destaining using a high-K(+) solution. A pair of synaptic regions associated with the sensory feedback was found to be located two or three cell body-widths away from the midline, between the anterior parts of the roots of the second lateral nerves (LNs) at the segmental ganglia (SGs). Using conventional intracellular recording and dye loading of the cell bodies surrounding these synaptic regions, we identified a pair of bilateral neurons with cell bodies larger than those of other cells in these regions, and named them "Oscillatory firing neurons Projecting to Peripheral nerves" (OPPs). These had a bipolar shape and projected neurites to the ipsilateral first and third LNs, fired rhythmically, and had a burst timing synchronized with the motor pattern bursts from the ipsilateral first LNs. Current injection into an OPP caused firing in the ipsilateral first LNs, supporting the hypothesis that OPPs functionally project to the peripheral nerves. OPPs also sent neurites to the adjacent anterior and posterior SGs, suggesting connections with the adjacent segments. We conclude that FM imaging can be used to identify neurons involved in specific functions, and that OPPs are the first neurons to be associated with OA-induced locomotion in the earthworm.

The cricket (Gryllus bimaculatus) is a hemimetabolous insect that is emerging as a model organism for the study of neural and molecular mechanisms of behavioral traits. However, research strategies have been limited by a lack of genetic manipulation techniques that target the nervous system of the cricket. The development of a new method for efficient gene delivery into cricket brains, using in vivo electroporation, is described here. Plasmid DNA, which contained an enhanced green fluorescent protein (eGFP) gene, under the control of a G. bimaculatus actin (Gb'-act) promoter, was injected into adult cricket brains. Injection was followed by electroporation at a sufficient voltage. Expression of eGFP was observed within the brain tissue. Localized gene expression, targeted to specific regions of the brain, was also achieved using a combination of local DNA injection and fine arrangement of the electroporation electrodes. Further studies using this technique will lead to a better understanding of the neural and molecular mechanisms that underlie cricket behaviors.

Two types of mechanosensitive proprioceptor organ are present on the stinging apparatus of the honeybee: campaniform sensilla and mechanosensory hairplates. The campaniform sensilla are located on the surface of the tapering sting-shaft, which comprises an unpaired stylet and paired lancets. Each sensillum on the lancet differs from that on the stylet in terms of their topography and external morphology. The sensory afferents of the campaniform sensilla display slow-adapted firing responses to deformation of the cuticle that would be caused by the action of inserting the sting into a substrate, and their afferent signals induce and/or prolong the stinging response. By contrast, the mechanosensory hairplates are located at basal cuticular plates and on the posterior surface of the lancet valves. Two fields of hairplates on the second ramus at the ventral edge of the groove and on the antero-lateral edge of the oblong plate respond synchronously to protraction of the lancet. During the stinging response, these hairplates are likely to detect any sliding movement of the lancet and its position relative to the stylet. Afferent signals produced by them are likely to provide important information to the neuronal circuit for the generation and modulation of the stinging motor pattern.

We studied age-related sexual dimorphism of the terminal abdominal ganglion in the cricket, Gryllus bimaculatus using osmium/ethyl-gallate staining and GABA immunohistochemistry. We determinedthat the volume of the terminal abdominal ganglion increases with increasing body size. The growth ratio between longitude and width in the terminal abdominal ganglion is the same in all nymph stages and sexes. However, the longitudinal growth of the male terminal abdominal ganglion ceases in the 8th instar and the adult stage. Therefore, in the adult stage, sexual dimorphism is observed in ganglion morphology. Additionally, sexual dimorphism is also observed in numbers of neuronal somata and GABA-like immunoreactive neurons in the terminal abdominal ganglion. At the beginning of the 8th instar, the number of somata is greater in female crickets than in males. GABA-like immunoreactive neurons, which were classified into eight clusters, increased between the 8th instar and adult in both sexes, but their numbers were sexually dimorphic in the 7th and 8th instars, and in the adult. Females had a greater number of GABA-like immunoreactive neurons than males. These differences occurred mainly in the 8th neuromere cluster, as well as the anterior region of the 9-11th neuromeres.

The distribution of potential nitric oxide (NO) donor neurons and NO-responsive target neurons was revealed in the terminal abdominal ganglion (TAG) of the cricket. The expression of nitric oxide synthase (NOS) in the nervous system was examined by Western blotting using universal nitric oxide synthase (uNOS) antibody that gave about a 130 kDa protein band. Immunohistochemistry using the uNOS antibody detected neurons whose cell bodies are located at the lateral region of the TAG. These neurons expanded their neuronal branches into the dorsal-median region or the dorsal-lateral region of the TAG. NADPH-diaphorase histochemistry was performed to confirm the distribution of NOS-containing neurons. The distributions of cell bodies and stained neuronal branches were similar to those revealed by uNOS immunohistochemistry. NO-induced cGMP immunohistochemistry was performed to reveal NO-responsive target neurons. Most of the cell bodies stained by immunohistochemistry appeared at the dorsal side of the TAG. At the dorsal-median region, some unpaired neuronal cell bodies were strongly stained. Some efferent neurons whose axon innervate into each nerve root were strongly stained. The generation of NO in the TAG was detected by NO electrode. We found that NO is generally produced to maintain a basal concentration of 70 nM. Hemoglobin scavenged released NO from the ganglion. The concentration of NO was partly recovered when hemoglobin was replaced by normal saline. Application of 10 microM L-arginine that is a substrate of NOS increased NO release by approximately 10 nM. Furthermore, an excitatory neurotransmitter acetylcholine (ACh) also increased NO generation by approximately 40-50 nM in concentration in addition to the basal level of 70 nM. Optical imaging with fluorescent NO-indicator demonstrated that ACh-induced enhancement of NO release was transiently observed in the outer-edge region of TAG, where cell bodies of NOS-immunoreactive neurons were located. These results suggest that ACh accelerates NO production via neuronal events activated by ACh in the TAG.

We numerically minimized the Landau-de Gennes free energy to investigate the layer structure of the twist-grain boundary (TGB) phase of chiral liquid crystals. We compare the obtained structure with Scherk's minimial surface. For large twist angles, an unlocking of the director and the layer orientation reduces the effective layer bending rigidity, which causes a large deviation of the mean curvature from zero. At temperatures close to the TGB-cholesteric transition, we find a melting of the smectic layers in the whole grain boundary.

The spatial dynamics of action potentials, including their propagation and the location of spike initiation zone (SIZ), are crucial for the computation of a single neuron. Compared with mammalian central neurons, the spike dynamics of invertebrate neurons remain relatively unknown. Thus, we examined the spike dynamics based on single spike-induced Ca(2+) signals in the dendrites of cricket mechanosensory projection neurons, known as giant interneurons (GIs). The Ca(2+) transients induced by a synaptically evoked single spike were larger than those induced by an antidromic spike, whereas subthreshold synaptic potentials caused no elevation of Ca(2+). These results indicate that synaptic activity enhances the dendritic Ca(2+) influx through voltage-gated Ca(2+) channels. Stimulation of the presynaptic sensory afferents ipsilateral to the recording site evoked a dendritic spike with higher amplitude than contralateral stimulation, thereby suggesting that alteration of the spike waveform resulted in synaptic enhancement of the dendritic Ca(2+) transients. The SIZ estimated from the spatial distribution of the difference in the Ca(2+) amplitude was distributed throughout the right and left dendritic branches across the primary neurite connecting them in GIs.

The cercal sensory system of the cricket mediates the detection and analysis of low velocity air currents in the animal's immediate environment, and is implemented around an internal representation of air current direction that demonstrates the essential features of a continuous neural map. Previous neurophysiological and anatomical studies have yielded predictions of the global spatio-temporal patterns of activity that should be evoked in the sensory afferent map by air current stimuli of different directions. We tested those predictions by direct visualization of ensemble afferent activity patterns using Ca2+ -sensitive indicators. The AM ester of the fluorescent Ca2+ indicator (Oregon Green 488 BAPTA-1 AM) was injected under the sheath of a cercal sensory nerve containing all of the mechanosensory afferent axons from one cercus. Optical signals were recorded with a digital intensified CCD camera. Control experiments using direct electrical stimulation of stained and unstained nerves demonstrated that the observed Ca2+ signals within the terminal abdominal ganglion (TAG) were due to activation of the dye-loaded sensory afferent neurons. To visualize the spatial patterns of air-current-evoked ensemble activity, unidirectional air currents were applied repeatedly from eight different directions, and the optically recorded responses from each direction were averaged. The dispersion of the optical signals by the ganglion limited the spatial resolution with which these ensemble afferent activity patterns could be observed. However, resolution was adequate to demonstrate that different directional stimuli induced different spatial patterns of Ca2+ elevation in the terminal arbors of afferents within the TAG. These coarsely- resolved, optically-recorded patterns were consistent with the anatomy-based predictions.

As a neurotransmitter and neuromodulator, serotonin (5-HT) influences neuronal outgrowth in the nervous systems of several species. In PC12 cells, 5-HT is known to have neuritogenic effects, although the signal transduction pathway responsible for these effects is not understood. In this study, we hypothesized that a 5-HT-induced increase in intracellular Ca(2+) concentration ([Ca(2+)](i)) could be involved in mediating the effects of 5-HT. Application of 5-HT to PC12 cells enhanced nerve growth factor (NGF)-induced neurite outgrowth in a dose-dependent manner, and the sensitivity of this neuritogenic effect was increased in differentiated PC12 cells. In accordance, an increase in [Ca(2+)](i) was observed following application of 5-HT in differentiated PC12 cells. This increase was amplified by further NGF treatment. 5-HT-induced increases in [Ca(2+)](i) were inhibited by MDL 72222, a selective 5-HT(3) receptor antagonist, and nifedipine, an L-type calcium channel blocker, but not by ketanserin, a 5-HT(2) receptor antagonist, or thapsigargin, a specific inhibitor of endoplasmic reticulum Ca(2+)-ATPase. These pharmacological tests indicated that 5-HT-induced increases in [Ca(2+)](i) are mediated by activation of voltage-gated calcium channels via 5-HT(3) receptors and that 5-HT-induced increases in [Ca(2+)](i) are likely to be independent of activation of 5-HT(2) receptors in PC12 cells. Furthermore, the neuritogenic effect of 5-HT was suppressed by MDL 72222, nifedipine, calmodulin (CaM) inhibitor, and calcineurin inhibitors. Taken together, our results indicate that 5-HT-induced increases in [Ca(2+)](i), which are mediated via 5-HT(3) receptors and L-type calcium channels in PC12 cells, and subsequent activation of CaM and calcineurin enhance NGF-induced neurite outgrowth.

We examined dendritic activity in identified mechanosensory interneurons in the cricket cercal sensory system using Ca2+ imaging and intracellular recording techniques. Different dendritic branches of the interneurons displayed distinct directional sensitivity profiles to air-current stimuli. The amplitude of evoked spikes was larger at the dendritic branches in which the Ca2+ elevation was larger. Dual-site recordings of the dendritic spikes indicate that the spike-initiation site shifts depending on the location of the site of synaptic activation. We propose that a difference in spike-propagation direction could change the spike waveform at the distal dendrite and could produce synaptic activity-dependent Ca2+ dynamics.

We examined directional sensitivities in the dendritic activity of the identified giant interneurons (GIs) in the cricket, using in vivo Ca(2+) imaging during different directional air-current stimuli. Air current stimulus evoked action potential burst and quick Ca(2+) increase in GI. The stimulus direction of the maximal Ca(2+) responses corresponded to that of the maximal voltage response. However, the shapes of the directional tuning curves based on the Ca(2+) responses for each dendritic branch were different from the overall tuning curve based on spike counts for the cell. Moreover, different dendritic branches displayed distinct directional sensitivity profiles to the air-current stimuli. We propose that postsynaptic activities will influence the local Ca(2+) signals in the distal dendrites, and produce the difference in directional sensitivity of the dendritic Ca(2+) response.

In the ventral nervous system of the earthworm, a central pattern generator and motor neurons are activated during locomotion. We have previously reported that bath application of octopamine (OA) induces fictive locomotion in the earthworm, and the burst frequency of electrical activity from the first lateral nerves increases with OA concentration. However, there are no reports concerning locomotor neural networks in the earthworm. To identify neural networks involved in fictive locomotion, we optically monitored activity-dependent fluorescent staining in the earthworm ventral nerve cord (VNC) with a styryl dye, N-(3-triethylammoniumpropyl)-4-(4-(dibutylamino)styryl)pyridinium dibromide (FM1-43), and a confocal laser scanning microscope. OA induces FM1-43 fluorescence in a dose-dependent manner, with bright fluorescent spots of 3-10 microm in diameter observed to be localized around specified neurons in the segmental ganglion of the VNC. We compared OA dose-response curves for FM1-43 fluorescence with the bursting frequency for fictive locomotion, and found that two types of curves could be identified: one fluorescence response shows a similar dose-dependency to that of the burst frequency, while another response has a higher sensitivity to OA. From these results, we suggest that OA acts as one of the neuromodulators for the earthworm locomotion. This is the first attempt to record motor and inter-neuronal activities simultaneously in a locomotor network in the earthworm.

To understand the relationship between the propagation direction of action potentials and dendritic Ca(2+) elevation, simultaneous measurements of intracellular Ca(2+) concentration ([Ca(2+)](i)) and intradendritic membrane potential were performed in the wind-sensitive giant interneurons of the cricket. The dendritic Ca(2+) transients induced by synaptically-evoked action potentials had larger amplitudes than those induced by backpropagating spikes evoked by antidromic stimulation. The amplitude of the [Ca(2+)](i) changes induced by antidromic stimuli combined with subthreshold synaptic stimulation was not different from that of the Ca(2+) increases evoked by the backpropagating spikes alone. This result means that the synaptically activated Ca(2+) release from intracellular stores does not contribute to enhancement of Ca(2+) elevation induced by backpropagating spikes. On the other hand, the synaptically evoked action potentials were also increased at distal dendrites in which the Ca(2+) elevation was enhanced. When the dendritic and axonal spikes were simultaneously recorded, the delay between dendritic spike and ascending axonal spike depended upon which side of the cercal nerves was stimulated. Further, dual intracellular recording at different dendritic branches illustrated that the dendritic spike at the branch arborizing on the stimulated side preceded the spike recorded at the other side of the dendrite. These results suggest that the spike-initiation site shifts depending on the location of the activated postsynaptic site. It is proposed that the difference of spike propagation manner could change the action potential waveform at the distal dendrite, and could produce synaptic activity-dependent Ca(2+) dynamics in the giant interneurons.

Crickets (Gryllus bimaculatus) use the cercal sensory system at the rear of the abdomen to detect air currents and direct predator avoidance behavior. Sensory information regarding the direction and dynamic properties of air currents is processed within the terminal abdominal ganglion, and conveyed by ascending giant interneurons (GIs) to higher centers including the brain. However, the brain region responsible for decoding cercal sensory information has not yet been identified, nor the response properties within the brain characterized. In this study, we performed in vivo Ca(2+) imaging to investigate wind-evoked neural activities within the cricket protocerebrum. Ca(2+) responses to air current stimuli were observed at peripheral regions of the ventrolateral neuropile (VLNP) where projection of GIs' axon terminals has been observed in larvae. The wind-evoked Ca(2+) response had temporal dynamics and directional sensitivity that varied with different recorded regions displaying transient or sustained Ca(2+) increases. Individual cells showed Ca(2+) elevation in response to air currents from a specific angle, while stimuli from a different angle evoked decreased signals. Removing the antennae reduced the air-current-evoked responses in VLNP, suggesting contribution of sensory inputs from antennae in addition to the cercal inputs. The VLNP is presumably an integrative center for mechanosensory processing from antennae and cerci where directional information is primarily decoded by protocerebral neurons.