COMPARISON OF PHOTON-COUNTING AND FLAT-PANEL DIGITAL MAMMMOGRAPHY FOR THE PURPOSE OF 3D IMAGING USING A NOVEL IMAGE PROCESSING METHOD.

The purpose of the present work was to compare the quality of low-dose projections from a photon-counting with a flat-panel system, and to evaluate a novel image processing method. Images were acquired of phantoms in both systems at average glandular doses ranging from ~ 0.15 to 1.4 mGy. Automated detection of low-contrast features and modulation transfer functions were evaluated in phantom images. The novel image processing method was compared with standard processing in a series of clinical cases. At low-doses (~0.15) the photon-counting system out-performed the flat-panel system with a much higher detectability of low-contrast features. The novel algorithm was superior to both manufacturers' processing in terms of conspicuity of soft-tissue lesions (p > 0.05), whereas it was not significantly different in calcification conspicuity. Photon-counting should allow more low-dose projections to be acquired at the same total dose. The novel image enhancer can help to further increase the image quality.

Plasticity of signaling and mate choice in a trilling species of the Mecopoda complex (Orthoptera: Tettigoniidae).

ABSTRACT: Males of a trilling species in the Mecopoda complex produce conspicuous calling songs that consist of two motifs: an amplitude-modulated motif with alternating loud and soft segments (AM-motif) and a continuous, high-intensity trill. The function of these song motifs for female attraction and competition between males was investigated. We tested the hypothesis that males modify their signaling behavior depending on the social environment (presence/absence of females or rival males) when they compete for mates. Therefore, we analyzed acoustic signaling of males in three different situations: (1) solo singing, (2) acoustic interaction with another male, and (3) singing in the presence of a female. In addition, the preference of females for these song motifs and further song parameters was studied in two-choice experiments. As expected, females showed a preference for conspicuous and loud song elements, but nevertheless, males increased the proportion of the AM-motif in the presence of a female. In acoustic interactions, males reduced bout duration significantly compared to both other situations. However, song bouts in this situation still overlapped more than expected by chance, which indicates intentionally simultaneous singing. A multivariate statistical analysis revealed that the proportion of the AM-motif and the duration of loud segments within the AM-motif allow a reliable prediction of whether males sing in isolation, compete with another male, or sing in the presence of a female. These results indicate that the AM-motif plays a dominant role especially in close-range courtship and that males are challenged in finding a balance between attracting females and saving energy during repeated acoustic interactions. SIGNIFICANCE STATEMENT: Males of acoustic insects often produce conspicuous calling songs that have a dual function in male-male competition and mate attraction. High signal amplitudes and signal rates are associated with high energetic costs for signal production. We would therefore predict that males adjust their signaling behavior according to their perception of the social context. Here we studied signal production and mate choice in a katydid, where males switch between loud and soft song segments in a dynamic way. Additionally, we examined the attractiveness of different song elements in female choice tests. Our results show how males of this katydid deal with the conflict of remaining attractive for females and competing with a costly signal with rivals.

Male age and female mate choice in a synchronizing katydid.

In acoustically communicating species, females often evaluate the frequency content, signal duration and the temporal signal pattern to gain information about the age of the signaller. This is different in the synchronizing bush cricket Mecopoda elongata where females select males on the basis of relative signal timing in duets. In a longitudinal approach, we recorded songs of M. elongata males produced 2 weeks (young male) and 9 weeks (old male) after their ultimate moult. Signal timing of both age categories was studied in acoustic interactions, and female preference was investigated in choice situations. Young male chirps were significantly shorter and contained less energy compared to "old chirps". In mixed-age duets younger males timed their chirps as leader significantly more often. Females preferred the young male chirp when broadcast as leader over the old male chirp, but choice was random when the old male chirp was leader. This choice asymmetry was abolished after reducing the duration of the "old chirp". Results were mirrored in response of a bilateral pair of auditory neurons, where the asymmetry in spike count and first-spike latency correlated with behaviour. We suggest that older males may compensate their disadvantage in a more complex chorus situation.

Competition and cooperation in a synchronous bushcricket chorus.

Synchronous signalling within choruses of the same species either emerges from cooperation or competition. In our study on the katydid Mecopoda elongata, we aim to identify mechanisms driving evolution towards synchrony. The increase of signal amplitude owing to synchronous signalling and the preservation of a conspecific signal period may represent cooperative mechanisms, whereas chorus synchrony may also result from the preference of females for leading signals and the resulting competition for the leader role. We recorded the timing of signals and the resulting communal signal amplitudes in small choruses and performed female choice experiments to identify such mechanisms. Males frequently timed their signals either as leader or follower with an average time lag of about 70 ms. Females selected males in such choruses on the basis of signal order and signal duration. Two-choice experiments revealed a time lag of only 70 ms to bias mate choice in favour of the leader. Furthermore, a song model with a conspecific signal period of 2 s was more attractive than a song model with an irregular or longer and shorter than average signal period. Owing to a high degree of overlap and plasticity of signals produced in 'four male choruses', peak and root mean square amplitudes increased by about 7 dB relative to lone singers. Modelling active space of synchronous males and solo singing males revealed a strongly increased broadcast area of synchronous signallers, but a slightly reduced per capita mating possibility compared with lone singers. These results suggest a strong leader preference of females as the ultimate causation of inter-male competition for timing signals as leader. The emerging synchrony increases the amplitude of signals produced in a chorus and has the potential to compensate a reduction of mating advantage in a chorus. We discuss a possible fitness benefit of males gained through a beacon effect and the possibility that signalling as follower is stabilized via natural selection.

Maintaining acoustic communication at a cocktail party: heterospecific masking noise improves signal detection through frequency separation.

We examined acoustic masking in a chirping katydid species of the Mecopoda elongata complex due to interference with a sympatric Mecopoda species where males produce continuous trills at high amplitudes. Frequency spectra of both calling songs range from 1 to 80 kHz; the chirper species has more energy in a narrow frequency band at 2 kHz and above 40 kHz. Behaviourally, chirper males successfully phase-locked their chirps to playbacks of conspecific chirps under masking conditions at signal-to-noise ratios (SNRs) of -8 dB. After the 2 kHz band in the chirp had been equalised to the level in the masking trill, the breakdown of phase-locked synchrony occurred at a SNR of +7 dB. The remarkable receiver performance is partially mirrored in the selective response of a first-order auditory interneuron (TN1) to conspecific chirps under these masking conditions. However, the selective response is only maintained for a stimulus including the 2 kHz component, although this frequency band has no influence on the unmasked TN1 response. Remarkably, the addition of masking noise at 65 dB sound pressure level (SPL) to threshold response levels of TN1 for pure tones of 2 kHz enhanced the sensitivity of the response by 10 dB. Thus, the spectral dissimilarity between masker and signal at a rather low frequency appears to be of crucial importance for the ability of the chirping species to communicate under strong masking by the trilling species. We discuss the possible properties underlying the cellular/synaptic mechanisms of the 'novelty detector'.

Acoustic signal perception in a noisy habitat: lessons from synchronising insects.

Acoustically communicating animals often have to cope with ambient noise that has the potential to interfere with the perception of conspecific signals. Here we use the synchronous display of mating signals in males of the tropical katydid Mecopoda elongata in order to assess the influence of nocturnal rainforest noise on signal perception. Loud background noise may disturb chorus synchrony either by masking the signals of males or by interaction of noisy events with the song oscillator. Phase-locked synchrony of males was studied under various signal-to-noise ratios (SNRs) using either native noise or the audio component of noise (<9 kHz). Synchronous entrainment was lost at a SNR of -3 dB when native noise was used, whereas with the audio component still 50% of chirp periods matched the pacer period at a SNR of -7 dB. Since the chirp period of solo singing males remained almost unaffected by noise, our results suggest that masking interference limits chorus synchrony by rendering conspecific signals ambiguous. Further, entrainment with periodic artificial signals indicates that synchrony is achieved by ignoring heterospecific signals and attending to a conspecific signal period. Additionally, the encoding of conspecific chirps was studied in an auditory neuron under the same background noise regimes.

Signalling plasticity and energy saving in a tropical bushcricket.

Males of the tropical bushcricket Mecopoda elongata synchronize their acoustic advertisement signals (chirps) in interactions with other males. However, synchrony is not perfect and distinct leader and follower roles are often maintained. In entrainment experiments in which conspecific signals were presented at various rates, chirps displayed as follower showed notable signal plasticity. Follower chirps were shortened by reducing the number and duration of syllables, especially those of low and medium amplitude. The degree of shortening depended on the time delay between leader and follower signals and the sound level of the entraining stimulus. The same signal plasticity was evident in male duets, with the effect that the last syllables of highest amplitude overlapped more strongly. Respiratory measurements showed that solo singing males producing higher chirp rates suffered from higher metabolic costs compared to males singing at lower rates. In contrast, respiratory rate was rather constant during a synchronous entrainment to a conspecific signal repeated at various rates. This allowed males to maintain a steady duty cycle, associated with a constant metabolic rate. Results are discussed with respect to the preference for leader signals in females and the possible benefits males may gain by overlapping their follower signals in a chorus.

Neuronal correlates of a preference for leading signals in the synchronizing bushcricket Mecopoda elongata (Orthoptera, Tettigoniidae).

Acoustically interacting males of the tropical katydid Mecopoda elongata synchronize their chirps imperfectly, so that one male calls consistently earlier in time than the other. In choice situations, females prefer the leader signal, and it has been suggested that a neuronal mechanism based on directional hearing may be responsible for the asymmetric, stronger representation of the leader signal in receivers. Here, we investigated the potential mechanism in a pair of interneurons (TN1 neuron) of the afferent auditory pathway, known for its contralateral inhibitory input in directional hearing. In this interneuron, conspecific signals are reliably encoded under natural conditions, despite high background noise levels. Unilateral presentations of a conspecific chirp elicited a TN1 response where each suprathreshold syllable in the chirp was reliably copied in a phase-locked fashion. Two identical chirps broadcast with a 180 deg spatial separation resulted in a strong suppression of the response to the follower signal, when the time delay was 20 ms or more. Muting the ear on the leader side fully restored the response to the follower signal compared with unilateral controls. Time-intensity trading experiments, in which the disadvantage of the follower signal was traded against higher sound pressure levels, demonstrated the dominating influence of signal timing on the TN1 response, and this was especially pronounced at higher sound levels of the leader. These results support the hypothesis that the female preference for leader signals in M. elongata is the outcome of a sensory mechanism that originally evolved for directional hearing.

Chirp rate is independent of male condition in a synchronising bushcricket.

Males of the bushcricket Mecopoda elongata synchronise their chirps with neighbouring males, but because synchrony is imperfect, one male's chirp preceeds the other by some 50-200 ms. Since a male's intrinsic chirp rate is critical for the establishment of the leader role in a duet, and females prefer the leader in a choice situation, we investigated a possible condition dependence of this male trait. In a duet leader males are usually those calling at a higher intrinsic rate; therefore, we investigated whether calling at a higher rate indicates male condition. The calling metabolism was quantified in a respirometer; the factorial slope of males calling at a high rate was three times higher compared to males calling at lower rates. Males produce on average 3.4 singing bouts/per night, and there is a significant increase in chirp periods (CPs) with successive singing bouts. Call properties were investigated throughout a male's life; chirp period increases significantly with age. Two groups of males were reared on either a low- or a high-nutrition diet, and the influence of male condition on different song parameters was investigated. CPs in two feeding regimes did not differ significantly, although males of the low-nutrition diet group were significantly affected by nutrition with respect to mortality, a delayed last moult and reduced weight as adults. We therefore conclude that solo chirp rates do not reflect phenotypic male condition properly.

Antiapoptotic effects of the peptidergic drug cerebrolysin on primary cultures of embryonic chick cortical neurons.

Cerebrolysin (EBEWE Arzneimittel, Austria, Europe) is a widely used drug relieving the symptoms of a variety of neurological disorders, particularly of neurodegenerative dementia of the Alzheimer's type. It consists of approximately 25% of low molecular weight peptides (<10k DA) and a mixture of approximately 75% free amino acids, this being based on the total nitrogen content. In this study we used a low serum (2% serum supplement) cell stress in-vitro model to assess drug effectiveness on neuronal viability and programmed cell death (PCD). In this in-vitro model the type of cell death was previously shown to be primarly apoptotic, which was verified by DNA-laddering and TUNEL-staining. For evaluation of neuronal viability a MTT-reduction assay was performed after 4 DIV and 8 DIV and the percentage of apoptotic neurons was determined by bis-benzimide staining of nuclear chromatin. To differentiate between possible effects of the free amino acids and the peptide fraction of Cerebrolysin an artificial amino acid mixture (AA-mix) was used as a control. Cerebrolysin, the AA-mix and 10% foetal calf serum (FCS) caused a similar increase in viability after 4 DIV, whereas the effects of the growth factors BDNF and FGF-2 were less pronounced. After 8 DIV Cerebrolysin, but not the AA-mix, was able to ameliorate neuronal viability, which could reflect a neuro-protective effect or an increased activity of the mitochondrial dehydrogenase measured in a MTT-reduction assay. The percentage of cells showing apoptotic chromatin changes was significantly reduced (p < 0.01) in cultures treated with Cerebrolysin, whereas the AA-mix failed to decrease the percentage of cells showing apoptotic chromatin changes. These findings ascertain an anti-apoptotic effect of the peptide fraction of Cerebrolysin and reveal a transient viability promoting effect of the amino acid fraction, which is most likely due to improved nutritional supply.

Effects of Cerebrolysin on the outgrowth and protection of processes of cultured brain neurons.

Cerebrolysin (Cere, EBEWE Arzneimittel, Austria), a peptidergic drug produced by a standardised enzymatic breakdown of porcine brain proteins, consists of a mixture of 75% free amino acids and 25% low molecular weight peptides (<10 k DA). Cerebrolysin was shown to protect against MAP2 loss in primary embryonic chick neuronal cultures after brief histotoxic hypoxia and in a rat model of acute brain ischemia. Since MAP2 is involved in processes like neuronal growth, plasticity and dendritic branching, we address the question whether Cere is protecting processes against degeneration in a chronic low serum (2% FCS) cell stress model and whether the spontaneous outgrowth of axon-like processes is influenced. This was accomplished by quantification of the neurite lengths of embryonic chicken telencephalon neurons after 4 and 8 days. Additionally, time-lapse video microscopy was performed to study a possible influence of Cere on the growth cone behaviour of axon-like processes. To distinguish between effects caused by the peptide fraction and the effects related to free amino acids, we used an artificial amino acid solution (AA-mix). Results demonstrate a process outgrowth promoting effect of the AA-mix and Cere after 4 DIV. After 8 days neuronal network degeneration occurred in the AA-mix treated cultures, whereas Cere treated cultures still presented a well differentiated neuronal network. Dying neurons could release factors possibly impeding neurite outgrowth and Cere was shown to increase the viability of chicken cortical neurons. Neither the addition of BDNF nor serum supplementation (5% and 10% FCS) could protect the neuronal network against degeneration after 8 DIV, although these treatments were shown to ameliorate the viability of chicken telencephalon neurons. This result together with the finding obtained using the artificial amino acid solution points to the peptide fraction of Cere to be responsible for the protection of processes against degeneration. Time-lapse studies of Cere treated cultures revealed a significant decrease of the velocities characterising random growth cone movements, which is thought to be responsible for an increase in the length of axon-like processes after 4 DIV.

Cross-talk reduction in confocal images of dual fluorescence labelled cell spheroids.

Dual fluorescence labelling is an advanced method to separate two individual specimens in a biological system using confocal microscopy. An inherent problem of this method is fluorescence channel cross-talk, which causes problems for the exact spatial determination and separation of the specimens. Using a parallel fluorescence detection and an image processing technique, based on an image subtraction method, we have developed a very straight forward method for correcting the dual channel fluorescence images. We successfully applied this method to a 3-dimensional cancer spheroid invasion assay and controlled the cross-talk compensation efficiency by a quality parameter.

Flecainide alters the cardiac microscopic activation pattern. An in-vitro study using voltage sensitive dyes.

In order to evaluate whether flecainide may alter microscopic activation patterns, isolated guinea pig papillary muscles (paced at a rate of 1 Hz or 3 Hz respectively, superfused with saline Tyrode solution at 37 degrees C) were exposed to 1.5 mumol l-1 flecainide. The muscles were stained with the voltage sensitive dye di-4-ANEPPS and excited with argon ion laser light at 514 nm. Fluorescence (F) was measured through a OG 570 filter by a 16*16 photodiode array (spatial resolution 180 microns). Activation times were determined the minimum -dF/dt. From these data on activation sequence could be determined. From the activation times of a given photodiode and of the surrounding diodes, which were activated later, vectors were calculated giving direction and velocity of the local activation wave. The isochrones under control conditions and under treatment were compared directly in a qualitative manner. For quantification the percentage of vectors with similar direction (deviation < 5 degrees) under control conditions and after treatment were determined. Under the influence of flecainide, the percentage of similar vectors decreased from 34% to 24% (1 Hz) or from 27% to 17% (3 Hz) (n = 6). Analysis of the isochrones showed that the propagation velocities were altered inhomogeneously. The total activation time (TAT) of the papillary muscles (calculated from the delay between the end of the stimulus and the activation of the last photodiode) was increased from 10.2 to 11.5 ms at 3 Hz, but was only slightly prolonged at the lower frequency (from 10.9 to 11.1 ms at 1 Hz). These results demonstrate that (a) flecainide can alter the microscopic activation patterns (b) that this effect has a use-dependent component and (c) the total activation time is slowed by flecainide. These effects may be linked to the proarrhythmic and antiarrhythmic activity of the drug.