Biomedical subjects

A Stumpner

Publications and source records attributed to A Stumpner.

8 recordsLinked to original sources

PubMed2004

Processing of auditory information in insects.

Insects exhibit an astonishing diversity in the design of their ears and the subsequent processing of information within their auditory pathways. The aim of this review is to summarize and compare the present concepts of auditory processing by relating behavioral performance to known neuronal mechanisms. We focus on three general aspects, that is frequency, directional, and temporal processing. The first part compares the capacity (in some insects high) for frequency analysis in the ear with the rather low specificity of tuning in interneurons by looking at Q10dB values and frequency dependent inhibition of interneurons. Since sharpening of frequency does not seem to be the prime task of a set of differently tuned receptors, alternative hypotheses are discussed. Moreover, the physiological correspondence between tonotopic projections of receptors and dendritic organization of interneurons is not in all cases strong. The second part is concerned with directional hearing and thus with the ability for angular resolution of insects. The present concepts, as derived from behavioral performances, for angular resolution versus lateralization and serial versus parallel processing of directional and pattern information can be traced to the thoracic level of neuronal processing. Contralateral inhibition, a mechanism for enhancing directional tuning, appears to be most effective in parallel pathways, whereas in serial processing it may have detrimental effects on pattern processing. The third part, after some considerations of signal analysis in the temporal domain, demonstrates that closely related species often use different combinations of temporal parameters in their recognition systems. On the thoracic level, analysis of temporal modulation functions and effects of inhibition on spiking patterns reveals relatively simple processing, whereas brain neurons may exhibit more complex properties.

Acoustic Stimulation↗

PubMed2002

A species-specific frequency filter through specific inhibition, not specific excitation.

Many bushcrickets produce specific song spectra for acoustic communication. Song detection and/ or recognition may make use of such specificity. Where in the nervous system are the filters for song frequency situated? A peripheral tuning for song frequency typically does not exist. Auditory receptor cells of bushcrickets connect to local and ascending neurons in the prothoracic ganglion. One of the ascending neurons (1) may function as a frequency filter in a group of four related bushcrickets (genera Ancistrura, Barbitistes). The frequency response of ascending neuron 1 is species-specific roughly corresponding to the frequency of the conspecific male song. The species-specific tuning of the neuron is not brought about by specific excitation, but by specific inhibition. By eliminating this frequency-dependent and species-specific inhibition the former filter neuron is transformed into an unspecific broad-band neuron in all four species. Its tuning then does not differ from omega neuron 1, a local neuron which is rather unspecific for frequency. Also, the supra-threshold responses of ascending neuron 1, which are different in intact animals, are similar to each other and similar to omega neuron 1 following elimination of inhibition. Only ascending neuron 1 of Ancistrura retains some species-specific features at low frequencies. In conclusion, evolution changed inhibition, not excitation of a species-specific neuron.

Action Potentials↗

PubMed2001

Evolution and function of auditory systems in insects.

While the sensing of substrate vibrations is common among arthropods, the reception of sound pressure waves is an adaptation restricted to insects, which has arisen independently several times in different orders. Wherever studied, tympanal organs were shown to derive from chordotonal precursors, which were modified such that mechanosensitive scolopidia became attached to thin cuticular membranes backed by air-filled tracheal cavities (except in lacewings). The behavioural context in which hearing has evolved has strongly determined the design and properties of the auditory system. Hearing organs which have evolved in the context of predator avoidance are highly sensitive, preferentially in a broad range of ultrasound frequencies, which release rapid escape manoeuvres. Hearing in the context of communication does not only require recognition and discrimination of highly specific song patterns but also their localisation. Typically, the spectrum of the conspecific signals matches the best sensitivity of the receiver. Directionality is achieved by means of sophisticated peripheral structures and is further enhanced by neuronal processing. Side-specific gain control typically allows the insect to encode the loudest signal on each side. The filtered information is transmitted to the brain, where the final steps of pattern recognition and localisation occur. The outputs of such filter networks, modulated or gated by further processes (subsumed by the term motivation), trigger command neurones for specific behaviours. Altogether, the many improvements opportunistically evolved at any stage of acoustic information-processing ultimately allow insects to come up with astonishing acoustic performances similar to those achieved by vertebrates.

Animals↗

PubMed1999

An interneurone of unusual morphology is tuned to the female song frequency in the bushcricket Ancistrura nigrovittata (Orthoptera, Phaneropteridae).

The interneurone AN5-AG7 of the duetting bushcricket Ancistrura nigrovittata has its soma in the seventh (penultimate) abdominal ganglion. Its major postsynaptic arborizations with dense thin branches of smooth appearance are found in the prothoracic ganglion. The branches terminate in the auditory neuropile, predominantly at the same location as those auditory receptors that respond best to the female song frequency. Correspondingly, AN5-AG7 responds preferentially to frequencies between 24 and 28 kHz, thereby matching the carrier frequency of the female response song quite well. At frequencies below 24 kHz, AN5-AG7 receives inhibition, which is sometimes seen as clear inhibitory postsynaptic potentials. At these frequencies, thresholds of excitatory postsynaptic potentials are considerably lower than spike thresholds. In contrast, above 20 kHz, the two thresholds match and they correspond to the behavioural threshold. The AN5-AG7 interneurone is more sensitive to soma-contralateral stimuli and it receives predominantly inhibition, but also some excitation, from the soma-ipsilateral ear. Response strength is not greatly affected by stimulus duration but shows prominent habituation. This habituation depends only weakly on intensity and frequency. Some AN5-AG7 interneurones show very small graded potentials and no spiking responses to any acoustic stimuli.

Animals↗

PubMed1998

Tonotopic organization of auditory receptors of the bushcricket pholidoptera griseoaptera (Tettigoniidae, decticinae)

The peripheral and central tonotopy of auditory receptors of the bushcricket Pholidoptera griseoaptera is described. Out of 24 auditory receptor cells of the crista acustica 18 were identified by single-cell recordings in the prothoracic ganglion and complete staining with neurobiotin. Proximal receptor cells of the crista acustica were most sensitive to 6 kHz, with medial cells being sensitive to 20-30 kHz, whereas distal cells were most sensitive to frequencies higher than 50 kHz. Projection areas within the auditory neuropile in the prothoracic ganglion were to- notopically arranged. Proximal cells projected anteriorly, medial cells ventrally and posteriorly, and distal cells to more dorsal regions. Identified receptor cells revealed an interindividual variability of tuning and central projections. Receptor cells from the intermediate organ of a bushcricket were identified for the first time. Receptors of the distal intermediate organ were broadly tuned and less sensitive than those of the crista acustica. Receptor cells of the proximal intermediate organ were most sensitive to frequencies below 10 kHz. They projected in anterior portions of the auditory neuropile, whereas cells of the distal intermediate organ had terminations spread over almost the whole auditory neuropile.

Journal Article↗

PubMed1998

Picrotoxin eliminates frequency selectivity of an auditory interneuron in a bushcricket.

AN1, an auditory interneuron in the bushcricket Ancistrura nigrovittata, is narrowly tuned to the male song frequency ( approximately 15 kHz). It receives pronounced inhibitory input at frequencies below and, more prominently, above this fundamental frequency. It is also subject to side-dependent inhibition producing asymmetric response functions for left- and right-side stimulation. In addition, intensity-response functions of AN1 peak as stimulus intensities increase. Application of the GABAA channel-blocker picrotoxin eliminates all subthreshold inhibitory postsynaptic potentials, revealing underlying excitation that is particularly obvious in the high-frequency range. Excitatory thresholds close to the song frequency remain unchanged by picrotoxin. Thus a specifically tuned neuron is shown to become broadly tuned after elimination of frequency-dependent inhibition. Although average maximum response strength is increased by 150% after picrotoxin application, at male song frequencies a slight reduction of the responses is still present at high intensities. Side-dependent inhibition remains largely unaffected by picrotoxin, suggesting that side- and frequency-dependent inhibitions are caused by different transmitters from different neurons.

Animals↗

PubMed1997

An auditory interneurone tuned to the male song frequency in the duetting bushcricket Ancistrura nigrovittata (Orthoptera, Phaneropteridae)

An auditory interneurone (AN1) of the bushcricket Ancistrura nigrovittata is described; it has a soma and dendrites in the prothoracic ganglion, an ascending axon and axon collaterals in the protocerebrum. As judged from morphological and physiological similarity, it is probably homologous to AN1 described in Tettigonia viridissima and to AN1 described in Gryllus bimaculatus. The occurrence and physiology of AN1 are not sex-specific. It receives predominant excitation between 12 and 16 kHz (male song frequency) and inhibition at lower frequencies and more strongly at higher frequencies. It shows optimum-type intensity/response curves. Frequency tuning and intensity-dependence compare well with female behaviour. Lesion experiments demonstrate that AN1 receives excitation and frequency-dependent inhibition from the soma-contralateral ear and inhibition from the soma-ipsilateral ear. The latter contributes to the clear leftright difference in its responses. AN1 does not obviously discriminate between temporal patterns of different behavioural effectivity. Its spiking, however, is coupled to the temporal pattern. It is hypothesized that AN1 may be involved in frequency processing by female A. nigrovittata.

Journal Article↗

PubMed1994

A new biophysical method to determine the gain of the acoustic trachea in bushcrickets.

A method is described for measuring the gain (i.e., the change of amplitude and phase angle) for sounds that propagate to the internal surface of the tympana in ears working as pressure difference receivers. The gain of the acoustic trachea has been measured in two similarly sized and closely related species of bushcrickets, in which the acoustic spiracles and tracheae differ markedly in size. The amplitude part of the gain is much larger in the species with the larger acoustic spiracle, whereas the phase part is very similar in the two species. The method is compared with other methods, which in the past have been used for estimating the gain of sound pathways inside animal bodies.

Animals↗