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A Elepfandt

Publications and source records attributed to A Elepfandt.

14 recordsLinked to original sources
PubMed2003

Sexual growth dimorphism affects birth sex ratio in house mice.

We present the first empirical evidence that mammalian sex-ratio deviations result from variation in adult-weight sexual dimorphism via correlated effects on blastocyst development. Two selection lines of mice exhibiting high and low sexual dimorphism in adult weight showed correlated sexual weight differences at birth and at weaning, caused by relatively decelerated growth of males in the low line from before birth. The sex ratio at birth was significantly female-biased in the low line, and significantly lower than in the highly dimorphic line. Concomitantly, blastomere numbers were at significantly higher variance in the low than in the highly dimorphic line, owing to an increased frequency of slowly growing blastocysts. Since low-dimorphism mice produced more corpora lutea and more female pups than the high-dimorphism mice, but not more males, birth sex-ratio bias most parsimoniously resulted from the loss of slowly growing male blastocysts. This is in agreement with the observation that sex-ratio skews in mammals arise when timing of uterine responsiveness (i.e. its temporally limited capacity for implantation) varies in relation to sex-specific embryonic growth rates. Hence, natural mammalian sex-ratio variation that stems from developmental asynchrony might be a by-product of natural selection for sexual dimorphism in adult weight.

Animals↗
PubMed2000

Hearing threshold and frequency discrimination in the purely aquatic frog Xenopus laevis (Pipidae): measurement by means of conditioning.

Hearing threshold and frequency discrimination for underwater sound were measured in the clawed frog Xenopus laevis by means of conditioning. A go/no go discrimination procedure was used in which the test tone was presented concurrently with a wave on the surface of the water. The tone signalled whether or not the frog should respond to the wave. The hearing range of X. laevis was 200-4000 Hz. Similar thresholds of 92-96 dB re 1 microPa were found at 600 Hz, 1400-1800 Hz and 3200-3600 Hz. A high threshold at 1000-1300 Hz suggested that this was the frequency range between the sensitivities of the amphibian and basilar papillae. Relative frequency discrimination was approximately 5 % at 400-800 Hz, 45 % at 1000 Hz and 2.4-6 % at 1600-2500 Hz. This last range encompasses the dominant frequencies of the advertisement call of this species. High discrimination acuity at these frequencies may be used in distinguishing between calling males. The threshold for a one-third-octave bandpass noise centred at 600 Hz was 27.6 dB lower than that for a pure tone of 600 Hz, suggesting that sound intensity was integrated within this bandwidth, possibly by a critical-band mechanism.

Animals↗
PubMed1995

Biophysics of underwater hearing in the clawed frog, Xenopus laevis.

Anesthetized clawed frogs (Xenopus laevis) were stimulated with underwater sound and the tympanic disk vibrations were studied using laser vibrometry. The tympanic disk velocities ranged from 0.01 to 0.5 mm/s (at a sound pressure of 2 Pa) in the frequency range of 0.4-4 kHz and were 20-40 dB higher than those of the surrounding tissue. The frequency response of the disk had two peaks, in the range of 0.6-1.1 kHz and 1.6-2.2 kHz, respectively. The first peak corresponded to the peak vibrations of the body wall overlying the lung. The second peak matched model predictions of the pulsations of the air bubble in the middle ear cavity. Filling the middle ear cavity with water lowered the disk vibrations by 10-30 dB in the frequency range of 0.5-3 kHz. Inflating the lungs shifted the low-frequency peak downwards, but did not change the high-frequency peak. Thus, the disk vibrations in the frequency range of the mating call (main energy at 1.7-1.9 kHz) were mainly caused by pulsations of the air in the middle ear cavity; sound transmission via the lungs was more important at low frequencies (below 1 kHz). Furthermore, the low-frequency peak could be reversibly reduced in amplitude by loading the larynx with metal or tissue glue. This shows that the sound-induced vibrations of the lungs are probably coupled to the middle ear cavities via the larynx. Also, anatomical observations show that the two middle ear cavities and the larynx are connected in an air-filled recess in submerged animals.(ABSTRACT TRUNCATED AT 250 WORDS)

Acoustic Stimulation↗
PubMed1990

Sensory neglect in a frog: evidence for early evolution of attentional processes in vertebrates.

Mammalian-like 'sensory neglect' phenomena were elicited in Xenopus laevis by unilateral telencephalic lesion: after damage of the caudal striatum response rate to contralateral water waves was significantly lower than to ipsilateral ones. Response accuracy, however, was not affected. Within 6-8 weeks, animals recovered from neglect of unilateral stimuli; but simultaneous bilateral stimulation revealed an enduring neglect of contralateral stimuli. Latencies during acute neglect were significantly higher than after recovery. These results suggest that the neural mechanisms of selective attention might have evolved earlier than thought so far.

Animals↗
PubMed1988

Central organization of wave localization in the clawed frog, Xenopus laevis. I. Involvement and bilateral organization of the midbrain.

The central nervous organization of water wave localization in the clawed frog Xenopus laevis was investigated by performing behavioral tests on frogs that had various brain ablations. The criterion of localization was the orientation of response turns toward the origin of stimulus waves. After complete midbrain ablation, Xenopus still detected impinging waves but could not localize them. After thalamopretectal ablation, however, Xenopus localized waves with normal accuracy. Thus, wave localization can be accomplished in the brainstem, and the midbrain is necessary for it. After forebrain ablation, the frogs no longer responded to water waves, which shows that higher brain centers modulate localization. Tectal lesions that spared the ventrolateral tectum did not abolish localization. After unilateral extirpation of tectum and torus, all ipsilateral waves were localized, but contralateral waves were not. This indicates a functional chiasm for the determination of wave directions in the midbrain. Total localization failure after unilateral midbrain destruction demonstrates that wave localization also requires the ipsilateral motorial tegmentum. When wave localization was abolished, a residual correlation between stimulus directions and response angles remained.

Animals↗
PubMed1988

Central organization of wave localization in the clawed frog, Xenopus laevis. II. Midbrain topology for wave directions.

The organization of water wave localization within the midbrain of the clawed frog Xenopus was investigated by performing behavioral tests on frogs that had partial midbrain ablations. The criterion of localization was the orientation of turns toward the origin of impinging waves. All lesion effects became apparent as localization failure within an angular sector of wave direction. The sectors were contralateral to the lesion and of various sizes, some comprising the complete hemifield. Localization outside of the sectors was not affected. Thus, wave localization is topologically organized with respect to wave direction. Two topological projections were found. Lesions of the first projection resulted in unoriented responses to the affected wave directions. After lesions of the other projection, the frog responded to waves from the affected directions by lunges without turns. It is suggested that the two types of localization failures are due to impairment of the sensory wave direction detection and of the sensorimotor transfer, respectively. The essential midbrain areas are presumably the magnocellular nucleus of the torus magnocellularis and the ventrolateral tectum, but a considerable part of the localization might be done in the medulla.

Animals↗
PubMed1988

Processing of wave patterns in the lateral line system parallels to auditory processing.

Processing of wave patterns in the lateral line system is reviewed with particular reference to similarities with auditory processing. Four levels are considered: the receptor cell, stimulus parameter encoding in the afferent nerve, the neural organization of stimulus localization, and analysis of complex waves. The high degree of parallelism at all these levels to auditory processing is considered as a strong evidence for a common evolutionary origin of these two systems.

Acoustic Stimulation↗
PubMed1983

Cell responses in dorsal layers of macaque lateral geniculate nucleus as a function of intensity and wavelength.

We studied the relationship between light intensity and cell response to various wavelengths and wavelength combinations in the dorsal, parvocellular layers of the macaque lateral geniculate nucleus. When response is plotted as a function of the logarithm of stimulus intensity, the slope and shape of curves depends on wavelength. For wavelengths near the crossover point between excitatory and suppressive responses, nonmonotonic curves are common. Consequently, the form of spectral-response functions depends on stimulus intensity. Responses to combined stimuli made up of wavelengths close together near one spectral extreme are approximately additive. If one wavelength is near the crossover point, responses are nonadditive so that a midspectral wavelength, only producing a weak excitatory response, is able to occlude more vigorous responses to wavelengths near the spectral ends. Responses of parvocellular layer cells are consistent with their being a result of linear interaction of opponent cone mechanisms, the response of each of which follows a modified hyperbolic tangent function (22). Responses to all wavelength combinations, even those showing strikingly nonadditive effects, could be predicted from the additive opponent model described above.

Animals↗
PubMed1979

A quantitative study of chromatic organisation and receptive fields of cells in the lateral geniculate body of the rhesus monkey.

The responses of neurones in the lateral geniculate nucleus (LGN) were investigated in anaesthetised rhesus monkeys. A new classification for cells in the parvocellular layers (PCL) is proposed, based on their spectral response curve and their response to white stimuli: (A) narrow-band, short wavelength (NS) excited cells, activity suppressed by white stimuli; (B) wide-band, short-wavelength (WS) excited cells, excited by white stimuli; (C) wide-band, long-wavelength (WL) excited cells, (D) narrow-band, long-wavelength (NL) excited cells, activity suppressed by white stimuli; (E) light suppressed (LI) cells, activity suppressed by all wavelengths, usually with some concealed excitatory input at extreme short or long wavelengths. Responses to moving bars and to spots of various diameters (area response curves) were determined for various wavelengths. It was found that the receptive fields from which wavelength-dependent excitatory or suppressive effects could be elicited are concentrically superimposed. The spectral responsiveness of the excitatory inputs to individual cell types corresponds to the absorption curves of single cones (S-, M- or L-cone for NS, WS and WL cells respectively), the spectral distribution of the suppressive mechanisms of all cells was panchromatic and approximately fitted to a sum of all cones. The excitatory input to NL-cells cannot be related to any of the known cone absorption curves, and a simple (L-M) subtraction model is questioned. Neurones in the magnocellular layers (MCL) can be divided into on- and off-centre cells as in the cat's LGN and give qualitatively similar responses over the whole spectrum. In contrast to the tonic responses of PCL cells, MCL cells respond phasically to chromatic and white flashed spots, even with the smallest stimuli. Implications of these findings for colour processing in the LGN are discussed.

Animals↗
PubMed1979

The responses of magno- and parvocellular cells of the monkey's lateral geniculate body to moving stimuli.

The responses to moving stimuli of single cells in the parvo- and magnocellular layers (PCL and MCL) of the macaque lateral geniculate nucleus (LGN) have been studied. PCL cells respond with a monophasic increase or decrease in firing when a bar passes across the receptive field, according to the wavelength composition of the stimulus. MCL cells respond with a biphasic sequence of excitation and suppression or vice versa dependent on whether a cell is on-centre or off-centre and on stimulus contrast direction. With large stimuli, PCL cells respond as long as the stimulus covers the receptive field while MCL cells respond only at the contrast borders. MCL cell responses are maximal with bars just long enough to cover the field centre, while PCL cell responses show a variable relation with bar length, depending on stimulus wavelength and receptive field structure. PCL cells show broad velocity tuning while at least some MCL cells were more sharply tuned. Many cells in the macaque LGN show weak orientation or direction preference.

Animals↗