Anatomy and physiology of identified wind-sensitive local interneurons in the cricket cercal sensory system

1. A group of wind sensitive local interneurons (9DL Interneurons) in the terminal abdominal ganglion of the cricket Acheta domesticus were identified and studied using intracellular staining and recording techniques. 2. The 9DL interneurons had apparent resting potentials ranging from -38 mV to -45 mV. At this membrane potential, these cells produced graded responses to wind stimuli; action potentials were never observed at these resting potentials. However, when the 9DL interneurons were hyperpolarized to a membrane potential of approximately -60 mV, a single action potential at the leading edge of the wind stimulus response was sometimes observed. 3. The wind stimulus threshold of the 9DL interneurons to the types of stimuli used in these studies was approximately 0.01 cm/s. Above this threshold, the excitatory responses increased logarithmically with increasing peak wind velocity up to approximately 0.5 cm/s. 4. The 9DL interneurons were directionally sensitive; their response amplitudes varied with wind stimulus orientation. 9DL1 cells responded maximally when stimulated with wind directed at the front of the animal. The apparent peak in directional sensitivity of the 9DL2 interneurons varied between the side and the rear of the animal, depending upon the site of electrode penetration within the cell's dendritic arbor. 5. The locations of dendritic branches of the 9DL interneurons within the afferent map of wind direction were used to predict the excitatory receptive field of these interneurons.     

Excitatory influence of wind-sensitive local interneurons on an ascending interneuron in the cricket cercal sensory system

This study examined the effects of a set of identified wind-sensitive local interneurons (9DL interneurons) on the wind-evoked spike output and directional sensitivity of an ascending interneuron (10-3) in the cricket (Acheta domesticus) cercal sensory system. Comparison of the directional sensitivities of the 9DL interneurons and 10-3 revealed that 3 of the 9DL interneurons have a large degree of overlap in their excitatory receptive fields with that of 10-3. Photoinactivation of any one of these 3 9DL interneurons resulted in a significant decrease in the spike output of 10-3 at its optimal excitatory wind stimulus positions. However, the overall directional sensitivity of 10-3 remained essentially unchanged. Photoinactivation of the one 9DL interneuron which had no overlap in its excitatory receptive field with 10-3 did not affect 10-3's responsiveness to wind stimuli. Results from simultaneous intracellular recordings of 10-3 and one of the 9DL interneurons which had an excitatory influence on 10-3 showed that depolarization of the local interneuron produced an epsp in 10-3, and could elicit several action potentials. Comparison of the morphologies of the 9DL interneurons and 10-3 revealed that the 3 9DL interneurons which had an excitatory influence on 10-3 all had regions of dendritic overlap with this ascending interneuron.Abbreviations ANOVA analysis of variance - Contra contralateral - epsp excitatory post-synaptic potential - Ipsi ipsilateral - LGI lateral giant interneuron - MGI medial giant interneuron     

The shape of wind-receptor hairs of cricket and cockroach

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. Accepted: 24 February 1998     

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.Abbreviations TAG terminal abdominal ganglion - LSI local spiking interneuron - LNI local non-spiking interneurons - CNS central nervous system - PSP post synaptic potential - GI giant interneuron     

Synchronous firing by specific pairs of cercal giant interneurons in crickets encodes wind direction

One prominent stimulus to evoke an escape response in crickets is the detection of air movement, such as would result from an attacking predator. Wind is detected by the cercal sensory system that consists of hundreds of sensory cells at the base of filiform hairs. These sensory cells relay information to about a dozen cercal giant and non-giant interneurons. The response of cercal sensory cells depends both, on the intensity and the direction of the wind. Spike trains of cercal giant interneurons then convey the information about wind direction and intensity to the central nervous system. Extracellular recording of multiple cercal giant interneurons shows that certain interneuron pairs fire synchronously if a wind comes from a particular direction. We demonstrate here that directional tuning curves of synchronously firing pairs of interneurons are sharper than those of single interneurons. Moreover, the sum total of all synchronously firing pairs eventually covers all wind directions. The sharpness of the tuning curves in synchronously firing pairs results from excitatory and inhibitory input from the cercal sensory neurons. Our results suggest, that synchronous firing of specific pairs of cercal giant interneurons encodes the wind direction. This was further supported by behavioral analyses.     

The morphology and fine structure of the giant interneurons of the wood cricket Nemobius sylvestris

The structural and ultrastructural characteristics of giant interneurons in the terminal abdominal ganglion of the cricket Nemobius sylvestris were investigated by means of cobalt and fluorescent dye backfilling and transmission electron microscopy.The projections of the 8 eight pairs of the biggest ascending interneurons (giant interneurons) are described in detail. The somata of all interneurons analyzed are located contralateral to their axons, which project to the posterior region of the terminal ganglion and arborise in the cercal glomerulus. Neuron 7-1a is an exception, because its arborisation is restricted to the anterior region of the ganglion. The fine structure of giant interneurons shows typical features of highly active cells. We observed striking indentations in the perineural layer, enabling the somata of the giant interneurons to be very close to the haemolymph. The cercal glomerulus exhibits a high diversity of synaptic contacts (i.e. axo-dendritic, axo-axonic, dendro-axonic, and dendro-dendritic), as well as areas of tight junctions. Electrical synapses seem to be present, as well as mixed synapses. The anatomical organization of the giant interneurons is finally discussed in terms of functional implications and on a comparative basis.     

White noise analysis of graded response in a wind-sensitive,nonspiking interneuron of the cockroach

1. A novel approach using a Gaussian white noise as stimulus is described which allowed quantitative analysis of neuronal responses in the cercal system of the cockroach, Periplaneta americana. Cerci were stimulated by air displacement which was modulated by a sinusoidal and a white noise signal. During the stimulation, intracellular recordings were made from a uniquely identifiable, nonspiking, local interneuron which locates within the terminal abdominal ganglion. The white noise stimulation was cross-correlated with the evoked response to compute first- and second-order kernels that could define the cell's response dynamics. 2. The interneuron, cell 101, has an exceptionally large transverse neurite that connects two asymmetrical dendritic arborizations located on both sides of the ganglion. 3. The first-order Wiener kernels in cell 101 were biphasic (differentiating). The waveforms of the kernels produced by the ipsilateral and contralateral stimulations were roughly mirror images of each other: the kernels produced by wind stimuli on the side ipsilateral to the cell body of the interneuron are initially depolarized and then hyperpolarized, whereas those on the other side are initially hyperpolarized. The polarity reversal occurred along the midline of the animal's body, and no well-defined kernel was produced by a stimulus directed head on or from the tail. 4. Mean square error (MSE) between the actual response and the model prediction suggests that the linear component in cell 101 comprises half of the cell's total response (MSEs for the linear models were about 50% at preferred directions), whereas the second-order, non-linear component is insignificant. The linear component of the wind-evoked response was bandpass with the preferred frequency of 70-90 Hz. 5. Accounting for a noise, we reasonably assumed that at high frequencies the graded response in cell 101 is linearly related to a modulation of the air displacement and sensitive to the rate of change of the signal (i.e., wind velocity) and the direction of its source. It is suggested that the dynamics of the first-order kernel simply reflect the dynamics of sensory receptors that respond linearly to wind stimulation.     

Response properties of wind-sensitive giant interneurons in the fourth-instar nymphs of the cricket, Gryllus bimaculatus

The response properties of four wind-sensitive giant interneurons (GIs) 8-1, 9-1, 9-2 and 9-3 in the fourth-instar nymphs of the cricket Gryllus bimaculatus were investigated to clarify the differences and/or similarities of the escape eliciting neural system between nymphs and adults. Air current was presented to the animal from 12 different directions in the horizontal plane, and the intensity-response curves for each GI were obtained at each stimulus direction. The intensity-response curves showed that the response magnitudes of GI 8-1 in the fourth-instar crickets increased with stimulus velocity up to 300 mm/s regardless of the stimulus direction. The response magnitudes of GI 9-1 in the nymphs reached a plateau at a stimulus velocity of 30 mm/s in most stimulus directions. The response magnitudes of GIs 9-2 and 9-3 increased with stimulus velocity up to 300 mm/s regardless of the stimulus direction. The directional sensitivity curves plotted on the basis of threshold velocities revealed that the preferential directions of the GIs were the ipsilateral-side in GI 8-1, the ipsilateral-front and contralateral-rear in GI 9-1, the ipsilateral-rear in GI 9-2 and the ipsilateral-front in GI 9-3, designated with respect to the side of the ventral nerve cord containing the axons. Although the GIs in nymphs occasionally showed higher threshold velocities and larger response magnitudes, the directional sensitivities, i.e., the preferred directions, of the GIs were basically the same with those of adults.     

Directional sensitivity of wind-sensitive giant interneurons in the cave cricket Troglophilus neglectus.

Unlike the situation in most cockroach and cricket species studied so far, the wind-sensitive cerci of the cave cricket Troglophilus neglectus Krauss (Rhaphidophoridae, Orthoptera) are not oriented parallel to the body axis but perpendicular to it. The effects of this difference on the morphology, and directional sensitivity of cercal giant interneurons (GIs), were investigated. In order to test the hypothesis that the 90 degrees change in cercal orientation causes a corresponding shift in directional sensitivity of GIs, their responses in both the horizontal and vertical planes were tested. One ventral and four dorsal GIs (corresponding to GIs 9-1a and 9-2a, 9-3a, 10-2a, 10-3a of gryllid crickets) were identified. The ventral GI 9-1a of Troglophilus differed somewhat from its cricket homologue in its dendritic arborisation and its directional sensitivity in the horizontal plane. The morphology and horizontal directionality of the dorsal GIs closely resembled that of their counterparts in gryllids. In the vertical plane, the directionality of all GIs tested was similar. They were all excited mainly by wind puffs from the axon-ipsilateral quadrant. The results suggest that directional sensitivity to air currents in the horizontal plane is maintained despite the altered orientation of the cerci. This is presumably due to compensatory modifications in the directional pReferences of the filiform hairs.     

Postembryonic development of mating behavior in the male cricket Gryllus bimaculatus DeGeer

Summary The intact male nymph cricket, Gryllus bimaculatus DeGeer, was found to show mating-like behavior, that is, courtship-like behavior (CSLB) and copulation-like behavior (CPLB), in the 7th and 8th (last) instars. The 8th instar nymph exhibited less CSLB and CPLB than the adult but much more than the 7th instar nymph. The movement patterns of CSLB and CPLB were essentially the same as those of adults except for motor acts requiring the use of the genitalia. CSLB was short and often ceased spontaneously before it switched to CPLB. CPLB also ended earlier than in adults. The occurrence of CSLB and CPLB was almost zero the few days around ecdysis. The nymph was very sensitive to disturbance, so that he often stopped courtship for more than 30 min after stimulation. CSLB was similarly induced in the male nymph (8th instar) by pairing with a female adult, male adult, female nymph (8th) and male nymph (8th). The female nymph (8th) was observed to mount not only the male adult but also the male nymph (8th). A fixed time sexual refractoriness forming a basis of cyclical mating activity was not present after CPLB in the nymph. It appeared in association with the emergence of spermatophore protrusion behavior around day 3 after the imaginal molt. In fledglings, there were some transitions during the sexual maturation process, such as failures in hook hanging, spermatophore extrusion, and spermatophore transfer to the female. The decerebration experiments on nymphs and fresh adults agreed with behavioral observations. These results suggest that the development of mating behavior in the male cricket is a process of enhancement of basic motor patterns but not a process of addition of new movements by changes in pattern generation circuits in the central nervous system.Abbreviations CPLB copulation-like behavior - CPPT interval between copulation and spermatophore protrusion - CSCP interval between calling song and copulation - CSLB courtship-like behavior - CSS courtship song - PTCS interval between spermatophore protrusion and calling song - SPE spermatophore extrusion     

Cartesian representation of stimulus direction: Parallel processing by two sets of giant interneurons in the cockroach

The cockroachPeriplaneta americana responds to wind puffs by turning away, both on the ground and when flying. While on the ground, the ventral giant interneurons (ventrals) encode the wind direction and specify turn direction, whereas while flying the dorsal giant interneurons (dorsals) appear to do so. We report here on responses of these cells to controlled wind stimuli of different directions. Using improved methods of wind stimulation and of positioning the animal revealed important principles of organization not previously observed.All six cells of largest axonal diameter on each side respond preferentially to ipsilateral winds. One of these cells, previously thought to respond non-directionally (giant interneuron 2), was found to have a restricted directional response (Fig. 3). The organization of directional coding among the ventral giant interneurons is nearly identical to that among the dorsals (Fig. 2). Each group contains, on each side, one cell that responds primarily to wind from the ipsilateral front, another primarily in the ipsilateral rear, and a third responding more broadly to ipsilateral front and rear.These results are discussed in terms of the mechanisms of directional localization by the assembly of giant interneurons.Abbreviations GI giant interneuron - vGI ventral giant interneuron - dGI dorsal giant interneuron - CF 5-carboxyfluorescein - A6 6th abdominal ganglion - TI thoracic interneuron - BED best excitatory direction     

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.     

Postembryonic changes in circadian photo-responsiveness rhythms of optic lobe interneurons in the cricket Gryllus bimaculatus

The photo-responsiveness of 2 groups of interneurons responding to light in the protocerebrum was investigated at 2 developmental stages, the last instar nymphs and adults, in the cricket Gryllus bimaculatus. The cricket is diurnally active during the nymphal stage but becomes nocturnal as an adult. In both adults and nymphs, light-induced responses of optic lobe light-responding interneurons that conduct light information from the optic medulla to the lobula and the cerebral lobe showed a circadian rhythm peaking during the subjective night. Amplitudes of the rhythms were not significantly different between adults and nymphs, but adults showed more stable day and night states than did nymphs. The medulla bilateral neurons that interconnect the bilateral medulla areas of the optic lobe also showed circadian rhythms in their light-induced responses in both adults and nymphs. The rhythm had a clear peak and a trough in adults, and its amplitude was significantly greater than that of nymphs. These results suggest that the 2 classes of interneurons are differentially controlled by the circadian clock. The difference might be related to their functional roles in the animal's circadian behavioral organization.     

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     

Spike‐triggered dendritic calcium transients depend on synaptic activity in the cricket giant interneurons

The relationship between electrical activity and spike‐induced Ca²⁺ increases in dendrites was investigated in the identified wind‐sensitive giant interneurons in the cricket. We applied a high‐speed Ca²⁺ imaging technique to the giant interneurons, and succeeded in recording the transient Ca²⁺ increases (Ca²⁺ transients) induced by a single action potential, which was evoked by presynaptic stimulus to the sensory neurons. The dendritic Ca²⁺ transients evoked by a pair of action potentials accumulated when spike intervals were shorter than 100 ms. The amplitude of the Ca²⁺ transients induced by a train of spikes depended on the number of action potentials. When stimulation pulses evoking the same numbers of action potentials were separately applied to the ipsi‐ or contra‐lateral cercal sensory nerves, the dendritic Ca²⁺ transients induced by these presynaptic stimuli were different in their amplitude. Furthermore, the side of presynaptic stimulation that evoked larger Ca²⁺ transients depended on the location of the recorded dendritic regions. This result means that the spike‐triggered Ca²⁺ transients in dendrites depend on postsynaptic activity. It is proposed that Ca²⁺ entry through voltage‐dependent Ca²⁺ channels activated by the action potentials will be enhanced by excitatory synaptic inputs at the dendrites in the cricket giant interneurons. © 2002 Wiley Periodicals, Inc. J Neurobiol 50: 234–244, 2002; DOI 10.1002/neu.10032     

爪鲵呼吸器官的胚后发育

应用石蜡切片和扫描电镜技术,对爪鲵(Onychodactylus fischeri)幼体、亚成体和成体3个不同发育阶段的皮肤、外鳃、咽等呼吸器官进行了显微观察与比较分析,旨在揭示爪鲵不同发育阶段各呼吸器官的演化规律.结果表明,爪鲵的皮肤随年龄的增长而逐渐增厚,幼体阶段其背腹皮肤厚度相差不大,亚成体及成体背部皮肤明显厚于腹部;外鳃是幼体和亚成体爪鲵呼吸器官的重要组成部分,随着发育外鳃逐渐完善,到亚成体阶段达到顶峰,随后逐步退化;咽部是爪鲵的重要呼吸器官,幼体期口腔和咽发育不完善,亚成体咽部逐渐发育,至成体时发育完善.     

Biogenic amines modulate synaptic transmission between identified giant interneurons and thoracic interneurons in the escape system of the cockroach

In the escape system of the cockroach, Periplaneta americana, a population of uniquely identifiable throacic interneurons (type A or TI_As) receive information about wind via chemical synapses from a population of ventral giant interneurons (vGIs). The TI_As are involved in the integration of sensory information necessary for orienting the animal during escape. It is likely that there are times in an animal's life when it is advantageous to modify the effectiveness of synaptic transmission between the vGIs and the TI_As. Given the central position of the TI_As inthe escape system, this would greatly alter associated motor outputs. We tested the ability of octopamine, serotonin, and dopamine to modulate synaptic transmission between vGIs and TI_As. Both octopamine and dopamine significantly increased the amplitude of vGI-evoked excitatory postsynaptic potentials (EPSPs) in TI_As at 10^?4?10^?2 M, and 10^?3 M, respectively. On the other hand, serotonin significantly decreased the vGI-evoked EPSPs in TI_As at 10^?4?10^?3 M. These results indicate that octopamine, serotonin, and dopamine are capable of modulating the efficacy of transmission of important neural connections within this circuit. © 1992 John Wiley & Sons, Inc.     

Electrophysiological and morphological characterization of the medulla bilateral neurons that connect bilateral optic lobes in the cricket,Gryllus bimaculatus

The medulla bilateral neurons (MBNs) in the cricket brain directly connect two optic lobes and have been suggested to be involved in mutual coupling between the bilateral optic lobe circadian pacemakers. Single unit analysis with intracellular recording and staining with Lucifer Yellow was carried out to reveal morphology and physiology of the MBNs. Neurons having a receptive field in the rostral part of the compound eye showed greater response and a higher sensitivity to light than those having receptive fields in the ventro-caudal or dorsal portions. The MBN showed diurnal change in their responsiveness to light; the light-induced response in the night was about 1.3, 5 and 2 times of that in the day in MBN-1s, -3s and -4s, respectively. These results suggest that the MBNs mainly encode the temporal information by the magnitude of light-induced responses. The differences in magnitude of light-induced responses and of daily change in photo-responsiveness among MBNs may suggest that each group of MBNs plays different functional role in visual and/or circadian systems.     

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