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C Avendano

Publications and source records attributed to C Avendano.

7 recordsLinked to original sources
PubMed2001

Delayed inner ear maturation and neuronal loss in postnatal Igf-1-deficient mice.

Insulin-like growth factor-1 (IGF-1) has been shown to play a key role during embryonic and postnatal development of the CNS, but its effect on a sensory organ has not been studied in vivo. Therefore, we examined cochlear growth, differentiation, and maturation in Igf-1 gene knock-out mice at postnatal days 5 (P5), P8, and P20 by using stereological methods and immunohistochemistry. Mutant mice showed reduction in size of the cochlea and cochlear ganglion. An immature tectorial membrane and a significant decrease in the number and size of auditory neurons were also evident at P20. IGF-1-deficient cochlear neurons showed increased caspase-3-mediated apoptosis, along with aberrant expression of the early neural markers nestin and Islet 1/2. Cochlear ganglion and fibers innervating the sensory cells of the organ of Corti presented decreased levels of neurofilament and myelin P(0) in P20 mouse mutants. In addition, an abnormal synaptophysin expression in the somata of cochlear ganglion neurons and sensory hair cells suggested the persistence of an immature pattern of synapses distribution in the organ of Corti of these animals. These results demonstrate that lack of IGF-1 in mice severely affects postnatal survival, differentiation, and maturation of the cochlear ganglion cells and causes abnormal innervation of the sensory cells in the organ of Corti.

Aging↗
PubMed2001

Elevation localization and head-related transfer function analysis at low frequencies.

Monaural spectral features due to pinna diffraction are the primary cues for elevation. Because these features appear above 3 kHz where the wavelength becomes comparable to pinna size, it is generally believed that accurate elevation estimation requires wideband sources. However, psychoacoustic tests show that subjects can estimate elevation for low-frequency sources. In the experiments reported, random noise bursts low-pass filtered to 3 kHz were processed with individualized head-related transfer functions (HRTFs), and six subjects were asked to report the elevation angle around four cones of confusion. The accuracy in estimating elevation was degraded when compared to a baseline test with wideband stimuli. The reduction in performance was a function of azimuth and was highest in the median plane. However, when the source was located away from the median plane, subjects were able to estimate elevation, often with surprisingly good accuracy. Analysis of the HRTFs reveals the existence of elevation-dependent features at low frequencies. The physical origin of the low-frequency features is attributed primarily to head diffraction and torso reflections. It is shown that simple geometrical approximations and models of the head and torso explain these low-frequency features and the corresponding elevations cues.

Adult↗
PubMed1999

Syllable intelligibility for temporally filtered LPC cepstral trajectories.

The intelligibility of syllables whose cepstral trajectories were temporally filtered was measured. The speech signals were transformed to their LPC cepstral coefficients, and these coefficients were passed through different filters. These filtered trajectories were recombined with the residuals and the speech signal reconstructed. The intelligibility of the reconstructed speech segments was then measured in two perceptual experiments for Japanese syllables. The effect of various low-pass, high-pass, and bandpass filtering is reported, and the results summarized using a theoretical approach based on the independence of the contributions in different modulation bands. The overall results suggest that speech intelligibility is not severely impaired as long as the filtered spectral components have a rate of change between 1 and 16 Hz.

Adult↗
PubMed1994

Cytoarchitecture and responsiveness of the medial ansate region of the cat primary somatosensory cortex.

To understand its relationship to somatosensory areas in other species, we studied the rostral bank of the medial ansate sulcus in adult cats. Neurons in the shoulder and upper part of the sulcal wall responded to low-threshold cutaneous stimuli much like neurons on the crown of the gyrus, whereas neurons in some deeper portions of the sulcus required more intense but innocuous somatic stimuli. Because we found much of the body surface re-represented in this area, we suggest that, besides the representation in area 3b, there is another cutaneous representation of the hindlimb and trunk located on the gyral crown near the medial end of the medial ansate sulcus and of the forelimb and trunk within the medial ansate sulcus. Posterior to this second cutaneous representation, many parts of the body were also represented in regions activated by more intense stimuli and having a different cytoarchitecture, suggesting that they were part of another body representation. Area 3b and the shoulder of the gyrus were distinguished by relatively intense acetylcholinesterase staining of layers III and IV. In the wall of the sulcus, all layers except layer I were uniformly stained to a point where electrophysiological recordings showed the cortex to be unresponsive, whereupon the outer two-thirds of layer I became very pale. Neurons activated by afferents from knee joints were found only in a small area; we did not find a mediolateral band serving joint afferents as is reported in primates. These data suggest that cat somatosensory cortex differs in some ways from primates but that it contains multiple representations of the body, as do most other mammals.

Afferent Pathways↗
PubMed1989

Quantitative light-microscopic study of the nucleus medialis dorsalis of the thalamus in the intact cat, and after prefrontal cortical ablations.

The volume of the prefrontal cortex and of the thalamic nucleus medialis dorsalis, and the number of neurons in this nucleus were obtained, for adult cats of both sexes, using paraffin embedding and standard quantitative histological procedures. Changes in the nucleus medialis dorsalis after prefrontal cortical ablations were also quantified. All data were corrected for shrinkage. In the intact cat, the average volume of the prefrontal cortex was 235 mm3, the average volume of the nucleus medialis dorsalis was 24.5 mm3, and the number of neurons in this nucleus was 232,000. After cortical ablations which eliminated between 64% and 93% of the prefrontal cortex, the number of surviving neurons in the nucleus medialis dorsalis remained at 70%-55% of controls. When additional cortex (which surrounds the prefrontal cortex and is connectionally related to it) was damaged, the decrease in volume and neuron counts in the nucleus medialis dorsalis was proportional to the amount of cortex ablated. Even after large cortical ablations of this kind, over 45% of the neurons in the nucleus medialis dorsalis still survived. Some of the surviving neurons appeared in the core of maximal gliosis in the nucleus. No unquestionable side or sex differences were found.

Animals↗
PubMed1986

An experimental analysis of the origins of somatostatin-like immunoreactivity in the dentate gyrus of the rat.

In previous studies, fibers demonstrating somatostatin-like immunoreactivity were observed in the outer half of the molecular layer of the dentate gyrus in the rat and monkey. They occupy the same region as those of the perforant pathway that originates in the entorhinal cortex. Numerous somatostatin immunoreactive neuronal cell bodies were also observed in the hilar region, though stained axonal profiles could not be followed from these cells into the molecular layer. In the present study, several experimental procedures were employed to determine the origin of the somatostatin-positive fibers in the molecular layer. Transection of the perforant path fibers resulted in such characteristic changes as shrinkage of the molecular layer and sprouting of AChE-positive fibers. There was no apparent decrease, however, in the density of somatostatin-positive fibers. In fact, since the stained fibers occupied a narrower band in the shrunken molecular layer, their density appeared greater. Injections of kainic acid into the hilar region produced a lesion of hilar neurons, including those positive for somatostatin. In the region of cell loss, there was a marked reduction of somatostatin-immunoreactive fibers in the ipsilateral molecular layer, with no detectable changes in the homotopic contralateral molecular layer. The distribution of AChE fibers, which presumably have an extrinsic origin, was not altered by the treatment. In a final series of experiments, the retrograde tracer wheat germ agglutinin-horseradish peroxidase (WGA-HRP) was injected into the hilar region and sections were prepared for the simultaneous demonstration of the tracer and of somatostatin-like immunoreactivity. Somatostatin-positive neurons demonstrating WGA-HRP reaction product were observed primarily in the ipsilateral hilar region, but a few double-labeled cells were also seen in the same area of the contralateral side. These studies indicate that a population of intrinsic neurons located in the polymorphic layer of the dentate gyrus projects to the outer half of the ipsilateral molecular layer. A similar, but very much smaller, projection also extends to the contralateral dentate gyrus. Taken together, these projections appear to account for much of the somatostatin-like immunoreactivity in the molecular layer of the dentate gyrus.

Animals↗