Diversity of intersegmental auditory neurons in a bush cricket

Various auditory interneurons of the duetting bush cricket Ancistrura nigrovittata with axons ascending to the brain are presented. In this species, more intersegmental sound-activated neurons have been identified than in any other bush cricket so far, among them a new type of ascending neuron with posterior soma in the prothoracic ganglion (AN4). These interneurons show not only morphological differences in the prothoracic ganglion and the brain, but also respond differently to carrier frequencies, intensity and direction. As a set of neurons, they show graded differences for all of these parameters. A response type not described among intersegmental neurons of crickets and other bush crickets so far is found in the AN3 neuron with a tonic response, broad frequency tuning and little directional dependence. All neurons, with the exception of AN3, respond in a relatively similar manner to the temporal patterns of the male song: phasically to high syllable repetitions and rhythmically to low syllable repetitions. The strongest coupling to the temporal pattern is found in TN1. In contrast to behavior the neuronal responses depend little on syllable duration. AN4, AN5 and TN1 respond well to the female song. AN4 (at higher intensities) and TN1 respond well to a complete duet.     

Effects of pharmacological treatment and photoinactivation on the directional responses of an insect neuron

Soma-ipsilateral branches of the large segmental omega neuron of the phaneropterid bush cricket Ancistrura nigrovittata have smooth endings, which extend through most of the auditory neuropile. Correspondingly, it shows a broad frequency tuning. Large excitatory postsynaptic potentials (EPSPs) and inhibitory postsynaptic potentials (IPSPs) are observed when recording from soma-ipsilateral branches. Stimulation from the soma-ipsilateral side leads to a strong excitation. Soma-contralateral branches have a strong, beaded appearance. IPSPs, which seem to be of soma-contralateral origin, can be recorded from these branches. Stimulation from the soma-contralateral side leads to a strong inhibition of the omega neuron. Soma-contralateral stimulation must be 30-40 dB more intense than soma-ipsilateral stimulation to evoke similar spike numbers in the omega neuron. The side-to-side difference is reduced to 10-15 dB after cutting the input from the soma-contralateral leg (tympanic nerve). The thresholds for eliciting IPSPs by soma-contralateral stimulation correspond roughly to excitatory thresholds of the mirror-image omega with the same stimuli. Pharmacological treatment with picrotoxin (PTX) or photoinactivation of the Lucifer Yellow filled mirror-image omega neuron reduces contralateral inhibition considerably and eliminates all visible IPSPs. Nevertheless, an additional contralateral inhibition survives both procedures and is only eliminated after cutting the soma-contralateral tympanic nerve. These results demonstrate that the mirror-image partners of the omega neuron mutually inhibit each other in bush crickets--as in crickets. This mutual inhibition is PTX-sensitive. At least one additional element exerts contralateral PTX-insensitive inhibition on the omega neuron.     

Sound localisation in crickets

Intracellular recordings were made in the brain of the cricket Gryllus bimaculatus from an ascending auditory interneuron (AN1). Acoustic stimuli with calling song temporal pattern were delivered via earphones in a preparation with the acoustic trachea cut (attenuation of crossing sound > 30 dB). The input-output function of this cell was then determined by recording its responses to stimulation of the ipsilateral ear alone, of the contralateral ear alone and to stimulation of both ears simultaneously with the same or different carrier frequencies and intensities.This interneuron was excited by the ear ipsilateral to its axon and dendritic field and unresponsive to stimuli presented to the axon-contralateral ear alone. However, in binaural stimulation experiments, the response to a constant ipsilateral stimulus was progressively reduced as the intensity of a simultaneous contralateral stimulus was increased, above a threshold intensity.Tuning curves for threshold of this inhibition, determined in binaural stimulation experiments, indicated significant inhibition in the range 3–20 kHz with lowest threshold at 4–5 kHz. The inhibition was unaffected by sectioning of the contralateral circumoesophageal or neck connective, indicating that the inhibitory influence crosses the midline at the level of the prothoracic ganglion. Intracellular recordings from AN1 in the prothoracic ganglion confirmed that it was indeed neurally inhibited by inputs from the contralateral ear.Tuning curves for excitation of an omega neuron (ON1) by the ear ipsilateral to its soma and also the tuning of inhibition of ON1 by its contralateral ON1 partner, closely match the tuning of inhibition of AN1 and to a lesser extent, of AN2. This was taken as evidence that each AN1 is inhibited by the contralateral ON1. The significance of this interaction for directional hearing and phonotaxis is discussed.Abbreviations AP/CHP action potentials per chirp - AN1, AN2 ascending auditory interneurons 1, 2 - ON1 omega neuron 1 - ipsi ipsilateral contra contralateral - PTG prothoracic ganglion loc lateral ocellar nerve - On optic nerve an antennal nerve - coc circum-oesophageal connective so sound off     

Temporal processing of vibratory communication signals at the level of ascending interneurons in Nezara viridula (Hemiptera: Pentatomidae)

During mating, males and females of N. viridula (Heteroptera: Pentatomidae) produce sex- and species-specific calling and courtship substrate-borne vibratory signals, grouped into songs. Recognition and localization of these signals are fundamental for successful mating. The recognition is mainly based on the temporal pattern, i.e. the amplitude modulation, while the frequency spectrum of the signals usually only plays a minor role. We examined the temporal selectivity for vibratory signals in four types of ascending vibratory interneurons in N. viridula. Using intracellular recording and labelling technique, we analyzed the neurons' responses to 30 pulse duration/interval duration (PD/ID) combinations. Two response arrays were created for each neuron type, showing the intensity of the responses either as time-averaged spike counts or as peak instantaneous spike rates. The mean spike rate response arrays showed preference of the neurons for short PDs (below 600 ms) and no selectivity towards interval duration; while the peak spike rate response arrays exhibited either short PD/long ID selectivity or no selectivity at all. The long PD/short ID combinations elicited the weakest responses in all neurons tested. No response arrays showed the receiver preference for either constant period or duty cycle. The vibratory song pattern selectivity matched the PD of N. viridula male vibratory signals, thus pointing to temporal filtering for the conspecific vibratory signals already at level of the ascending interneurons. In some neurons the responses elicited by the vibratory stimuli were followed by distinct, regular oscillations of the membrane potential. The distance between the oscillation peaks matched the temporal structure of the male calling song, indicating a possible resonance based mechanism for signal recognition.     

Cricket phonotaxis: localization depends on recognition of the calling song pattern

Summary Calling song with a carrier frequency of 5 kHz evokes positive phonotaxis in female crickets,Gryllus bimaculatus, when presented at an azimuth. In contrast, a continuous tone of 4.7 kHz in the same position when paired with calling song from above leads to negative phonotaxis. Under open-loop conditions, when a tethered animal runs on a paired tread wheel, characteristic curves are produced with the stable equilibrium point towards or away from the stimulus, respectively (Fig. 3).In order to understand this sign reversal at the neuronal level, directional characteristics of the ascending acoustic inter neurons AN1 and AN2 were measured using extracellular recordings from the cervical connectives.Taking the mean spike rate of the interneurons as a measure for their excitation, the function relating response magnitude to stimulus direction for calling song corresponds well to the behavioural characteristic curve (Fig. 5). The response function obtained using a continuous tone with simultaneous presentation of calling song from above is similar (Fig. 5) and hence does not correspond to the inverse behavioural characteristic curve.However, consideration of the extent to which the temporal parameters of the calling song (syllables and chirps) are reflected in the neuronal response (amplitudes of the Fourier components) leads to characteristic curves for AN1 and AN2 which are in good agreement with the behaviour for stimulation with calling song as well as for the continuous tone experiment (Fig. 8). In addition, the neural response curves correspond to the behaviour in showing smaller amplitudes when a continuous tone rather than the calling song is presented on the horizon (Fig. 8).From these data we conclude that the activity in interneurons AN1 and AN2 does not directly guide orientation in mating behaviour but first is filtered by a mechanism tuned to the frequency of syllables and/or chirps. According to this hypothesis recognition of conspecific song and localization proceed sequentially inGryllus.     

锐化蝙蝠听皮层神经元频率调谐的柱特征

用双声刺激和多管电极方法在 6只大棕蝠 (bigbrownbat,Eptesicusfuscus)的 98个神经元上研究了锐化 (sharpening)蝙蝠听皮层 (primaryauditorycortex ,AC)神经元频率调谐的柱特征。结果发现 ,电极直插在 1个电极通道内连续记录到多个神经元时 ,它们锐化频率调谐的抑制性调谐曲线或抑制区基本相似。电极与AC表面呈 45°斜向推入使其跨越多个功能柱时 ,可观察到锐化频率调谐的抑制区构成也随电极进入不同的功能柱而发生相应的改变。两种不同的电极插入方式均证明锐化AC神经元频率调谐的神经抑制呈柱状组构。这些神经元组合起来排列在同一听觉功能柱内 ,构成AC频率分析的基本功能组构单位“微频率处理器”。实验中还观察到多峰频率调谐曲线神经元 ,它们在声通讯和声定位中不同波谱区域的时间匹配中起作用。此外 ,也有理由认为多峰调谐神经元亦被用于作为复杂波谱信息的“高级调谐预处理器” ,从而极大地提高了神经元对频率分析的能力。为研究锐化频率调谐的神经抑制机制 ,用多管电极电泳γ -氨基丁酸 (γ aminobutyricacid ,GA BA)能a受体拮抗剂荷包牡丹碱 (bicuculline ,Bic)至所记录的神经元 ,发现能大部分或几乎全部取消抑制区 ,从而表明在正常情况下GABA能抑制参与构成锐化AC神经元频率调谐的抑制区 ,     

Influence of different envelope maskers on signal recognition and neuronal representation in the auditory system of a grasshopper

Background

Animals that communicate by sound face the problem that the signals arriving at the receiver often are degraded and masked by noise. Frequency filters in the receiver''s auditory system may improve the signal-to-noise ratio (SNR) by excluding parts of the spectrum which are not occupied by the species-specific signals. This solution, however, is hardly amenable to species that produce broad band signals or have ears with broad frequency tuning. In mammals auditory filters exist that work in the temporal domain of amplitude modulations (AM). Do insects also use this type of filtering?

Principal Findings

Combining behavioural and neurophysiological experiments we investigated whether AM filters may improve the recognition of masked communication signals in grasshoppers. The AM pattern of the sound, its envelope, is crucial for signal recognition in these animals. We degraded the species-specific song by adding random fluctuations to its envelope. Six noise bands were used that differed in their overlap with the spectral content of the song envelope. If AM filters contribute to reduced masking, signal recognition should depend on the degree of overlap between the song envelope spectrum and the noise spectra. Contrary to this prediction, the resistance against signal degradation was the same for five of six masker bands. Most remarkably, the band with the strongest frequency overlap to the natural song envelope (0–100 Hz) impaired acceptance of degraded signals the least. To assess the noise filter capacities of single auditory neurons, the changes of spike trains as a function of the masking level were assessed. Increasing levels of signal degradation in different frequency bands led to similar changes in the spike trains in most neurones.

Conclusions

There is no indication that auditory neurones of grasshoppers are specialized to improve the SNR with respect to the pattern of amplitude modulations.     

Microelectrophoretic application of antagonists of putative neurotransmitters onto various types of bulbar respiratory neurons.

Seven antagonists of putative neurotransmitters were applied to bulbar respiratory neurons and, for comparison, also to unspecific cells. The antagonists exerted distinct effects when released alone, permitting to draw conclusions about receptor properties of the various cell types. With strychnine, specific antagonist of glycine, excitation prevailed in EI, I and E neurons. With bicuculline, specific antagonist of GABA, excitation preponderated in EI and E cells. About half of the unspecific neurons were activated and the remainder were unresponsive. GDEE (glutamatediethylester), antagonist of glutamate, excited part of the IE neurons and inhibited part of the E units, while the remainder of both types as well as 2 EI cells tested were not affected. With flupentixol, antagonist of dopamine, excitation prevailed in I neurons. About half of the IE and E units remained unaffected, while in the remainder E cells inhibition preponderated over excitation. With yohimbine, an alpha-adrenoceptor blocker, inhibition prevailed in E units. The two EI as well as the majority of the I neurons remained unaffected, with two cells of the latter type being activated. Propranolol, a beta-adrenoceptor blocker, inhibited about half of the E neurons, while the remainder as well as most IE and the 2 EI cells tested were not affected. Cyproheptadine, an antagonist of 5-HT, excited most E neurons. As concerns NE-receptors, those of the alpha-type might be involved in activation of part of the E cells only, whereas all other NE effects (inhibition or activation) are mediated by CNS-specific receptors different from the alpha- and beta-type. 5-HT effects apparently are mediated by two different receptor types.     

Behavioral detection of acoustic particle motion by a teleost fish (Astronotus ocellatus): sensitivity and directionality

The physiology and morphology of auditory interneurons of a fly, the parasitoid Therobia leonidei, are described for the first time. 1. The hearing threshold has been determined with summed recordings of the neck connective. Females are most sensitive in a frequency range from 16 to 40 kHz (thresholds: around 45 dB SPL). This broad hearing range matches with the peak frequencies of the song spectra of host bushcricket species. Male flies are 10–20 dB less sensitive than females. 2. The sensory cells of the prosternal tympanal organ of T. leonidei project into the thoracico-abdominal ganglion complex with arborizations in all three thoracic neuromeres. 3. Three types of ascending auditory interneurons were identified by their morphology and response properties. These have arborizations in all three thoracic neuromeres and terminate soma-contralaterally in the brain. At least three other neuron types were also identified according to response properties alone. The neurons show similar spectral tuning but different sensitivities.     

Lateral sharpening of cortical frequency tuning by approximately balanced inhibition

Cortical inhibition plays an important role in shaping neuronal processing. The underlying synaptic mechanisms remain controversial. Here, in vivo whole-cell recordings from neurons in the rat primary auditory cortex revealed that the frequency tuning curve of inhibitory input was broader than that of excitatory input. This results in relatively stronger inhibition in frequency domains flanking the preferred frequencies of the cell and a significant sharpening of the frequency tuning of membrane responses. The less selective inhibition can be attributed to a broader bandwidth and lower threshold of spike tonal receptive field of fast-spike inhibitory neurons than nearby excitatory neurons, although both types of neurons receive similar ranges of excitatory input and are organized into the same tonotopic map. Thus, the balance between excitation and inhibition is only approximate, and intracortical inhibition with high sensitivity and low selectivity can laterally sharpen the frequency tuning of neurons, ensuring their highly selective representation.     

A bio-inspired visual collision detection mechanism for cars: combining insect inspired neurons to create a robust system

The lobula giant movement detector (LGMD) of locusts is a visual interneuron that responds with an increasing spike frequency to an object approaching on a direct collision course. Recent studies involving the use of LGMD models to detect car collisions showed that it could detect collisions, but the neuron produced collision alerts to non-colliding, translating, stimuli in many cases. This study presents a modified model to address these problems. It shows how the neurons pre-synaptic to the LGMD show a remarkable ability to filter images, and only colliding and translating stimuli produce excitation in the neuron. It then integrates the LGMD network with models based on the elementary movement detector (EMD) neurons from the fly visual system, which are used to analyse directional excitation patterns in the biologically filtered images. Combining the information from the LGMD neuron and four directionally sensitive neurons produces a robust collision detection system for a wide range of automotive test situations.     

Resonant neurons and bushcricket behaviour

The resonant properties of the intrinsic dynamics of single neurons could play a direct role in behaviour. One plausible role is in the recognition of temporal patterns, such as that seen in the auditory communication systems of Orthoptera. Recent behavioural data from bushcrickets suggests that this behaviour has interesting resonance properties, but the underlying mechanism is unknown. Here we show that a very simple and general model for neural resonance could directly account for the different behavioural responses of bushcrickets to different song patterns.     

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.     

Effects of GABA-mediated inhibition on direction-dependent frequency tuning in the frog inferior colliculus

Earlier studies from our laboratory have shown that the frequency selectivity of neurons in the frog inferior colliculus is direction dependent. The goal of this study was to test the hypotheses that gamma-aminobutyric acid or GABA (but not glycine)-mediated synaptic inhibition was responsible for the direction-dependence in frequency tuning, and that GABA acted through creation of binaural inhibition. We performed single unit recordings and investigated the unit's free-field frequency tuning, and/or the unit's response to the interaural level differences (under dichotic stimulation), before and during local applications of antagonists specific to gamma-aminobutyric acid a and glycine receptors. Our results showed that application of bicuculline produced a broadening of free-field frequency tuning, and differential changes in free-field frequency tuning depending on sound direction, i.e., more pronounced at azimuths at which the unit exhibited narrower frequency tuning under the pre-drug condition, thereby typically abolishing direction dependence in tuning. Application of strychnine produced no change in frequency tuning. The results from dichotic stimulation further revealed that bicuculline typically elevated and/or flattened the unit's interaural-level-difference response function, indicating a reduction in the strength of binaural inhibition. Our study provides evidence that gamma-aminobutyric acid-mediated binaural inhibition is important for direction dependence in frequency tuning. Accepted: 24 July 1998     

Prolonged response to calling songs by the L3 auditory interneuron in female crickets (Acheta domesticus): possible roles in regulating phonotactic threshold and selectiveness for call carrier frequency

L3, an auditory interneuron in the prothoracic ganglion of female crickets (Acheta domesticus) exhibited two kinds of responses to models of the male's calling song (CS): a previously described, phasically encoded immediate response; a more tonically encoded prolonged response. The onset of the prolonged response required 3-8 sec of stimulation to reach its maximum spiking rate and 6-20 sec to decay once the calling song ceased. It did not encode the syllables of the chirp. The prolonged response was sharply selective for the 4-5 kHz carrier frequency of the male's calling songs and its threshold tuning matched the threshold tuning of phonotaxis, while the immediate response of the same neuron was broadly tuned to a wide range of carrier frequencies. The thresholds for the prolonged response covaried with the changing phonotactic thresholds of 2- and 5-day-old females. Treatment of females with juvenile hormone reduced the thresholds for both phonotaxis and the prolonged response by equivalent amounts. Of the 3 types of responses to CSs provided by the ascending L1 and L3 auditory interneurons, the threshold for L3's prolonged response, on average, best matched the same females phonotactic threshold. The prolonged response was stimulated by inputs from both ears while L3's immediate response was driven only from its axon-ipsilateral ear. The prolonged response was not selective for either the CS's syllable period or chirp rate.     

Microelectrophoretic application of metabolic modifiers of the phosphofructokinase-hexosediphosphatase-system onto various types of bulbar respiratory neurons

Three metabolic modifiers of the PFK-HDPase system were applied to bulbar respiratory neurons and, for comparison, also to unspecific cells. F-6-P did not alter the spike density of the majority of the respiratory and about half of the unspecific neurons. When responding, IE units were activated and unspecific cells were inhibited. Citrate did not alter the spike density of about half of all neurons tested. When responding, excitation prevailed in IE and E units, while unspecific cells were inhibited. AMP did not alter the spike density of the majority of the respiratory and about half of the unspecific cells. When responding, I neurons were activated, inhibition preponderated in IE units and both effects occurred in unspecific cells. The large number of zero effects suggests that the activity of only part of the cells is governed by the PFK-HDPase system.     

Neuron loss and addition in developing zebra finch song nuclei are independent of auditory experience during song learning

In zebra finches early auditory experience is critical for normal song development. Young males first listen to and memorize a suitable song model and then use auditory feedback from their own vocalizations to mimic that model. During these two phases of vocal learning, song-related brain regions exhibit large, hormone-induced changes in volume and neuron number. Overlap between these neural changes and auditory-based vocal learning suggests that processing and acquiring auditory input may influence cellular processes that determine neuron number in the song system. We addressed this hypothesis by measuring neuron density, nuclear volume, and neuron number within the song system of normal male zebra finches and males deafened prior to song learning (10 days of age). Measures were obtained at 25, 50, 65, and 120 days of age, and included four song nuclei: the hyperstriatum ventralis pars caudalis or higher vocal center (HVc), Area X, the robust nucleus of the archistriatum (RA), and the lateral magnocellular nucleus of the anterior neostriatum (IMAN). In both HVc and Area X, nuclear volume and neuron number increased markedly with age in both normal and deafened birds. The volume of RA also increased with age and was not affected by early deafening. In IMAN, deafening also did not affect the overall age-related loss of neurons, although at 25 days neuron number was slightly less in deafened than in normal birds. We conclude that while the addition and loss of neurons in the developing song system may provide plasticity essential for song learning, these changes do not reflect learning.(ABSTRACT TRUNCATED AT 250 WORDS)     

Sex-dependent loss of projection neurons involved in avian song learning.

In zebra finches, only males sing, and the neural regions controlling song exhibit prominent, hormone-induced sex differences in neuron number. In order to understand how sexual differentiation regulates neuron number within one song nucleus, the lateral magnocellular nucleus of the anterior neostriatum (IMAN), we studied the development of sex differences among IMAN neurons that project to the robust nucleus of the archistriatum (RA). The IMAN is implicated in song learning, and previous ontogenetic studies have indicated that males lose over 50% of their IMAN neurons during the juvenile song learning period. Based on developmental changes in both the extent of androgen accumulation within the IMAN and its appearance in Nissl-stained tissue, it had been hypothesized that IMAN neuron loss was even greater in young females, resulting in sex differences in neuron number. However, this hypothesis has not been tested directly because the Nissl-stained boundaries of the IMAN sometimes are ambiguous in young animals, and are not evident at all in adult females. To circumvent these problems, we employed the retrograde tracer fast blue to study the development of IMAN neurons defined on the basis of their projections to the RA. We find that the number of these IMAN-RA projection neurons is much greater in adult males than in females, and that this sex difference develops during the juvenile period of sexual differentiation and song learning because a significant number of these neurons are lost in females but not in males. With respect to sexual differentiation, we conclude that masculinization (which is stimulated by the hormone estradiol) promotes the retention of IMAN-RA projection neurons. In addition, our results indicate that any loss of IMAN neurons that may occur in young males does not include cells projecting to the RA.     

Sex-dependent loss of projection neurons involved in avian song learning

In zebra finches, only males sing, and the neural regions controlling song exhibit prominent, hormone-induced sex diffences in neuron number. In order to understand how sexual differentiation regulates neuron number within one song nucleus, the lateral magnocellular nucleus of the anterior neostriatum (IMAN), we studied the development of sex differences among IMAN neurons that project to the robust nucleus of the archistriatum (RA). The IMAN is implicated in song learning, and previous ontogenetic studies have indicated that males lose over 50% of their IMAN neurons during the juvenile song learning period. Based on developmental changes in both the extent of androgen accumulation within the IMAN and its appearance in Nissl-stained tissue, it had been hypothesized that IMAN neuron loss was even greater in young females, resulting in sex differences in neuron number. However, this hypothesis has not been tested directly because the Nissl-stained boundaries of the IMAN sometimes are ambiguous in young animals, and are not evident at all in adult females. To circumvent these problems, we employed the retrograde tracer fast blue to study the development of IMAN neurons defined on the basis of their projections to the RA. We find that the number of these IMAN-RA projection neurons is much greater in adult males than in females, and that this sex difference develops during the juvenile period of sexual differentiation and song learning because a significant number of these neurons are lost in females but not in males. With respect to sexual differentiation, we conclude that masculinization (which is stimulated by the hormone estradiol) promotes the retention of IMAN-RA projection neurons. In addition, our results indicate that any loss of IMAN neurons that may occur in young males does not include cells projecting to the RA. © 1992 John Wiley & Sons, Inc.