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Biomedical subjects

M M Henson

Publications and source records attributed to M M Henson.

At least 37 records · Page 2Linked to original sources
PubMed1994

Doppler-shift compensation by the mustached bat: quantitative data.

Quantitative data for Doppler-shift compensation by Pteronotus parnellii parnellii were obtained with a device which propelled the bats at constant velocities over a distance of 12 m. The bats compensated for Doppler shifts at all velocities tested (0.1-5.0 ms-1). The main findings were (1) that compensation was usually accomplished by a progressive lowering of the approximately 61 kHz second harmonic constant-frequency component of emitted sounds in small frequency steps (93 +/- 72 Hz); (2) that the time needed to reach a steady compensation level averaged 514 +/- 230 ms and the number of pulses required to reach full compensation averaged 10.78 +/- 5.16; (3) that the animals compensated to hold the echo (reference) frequency at a value that was slightly higher than the resting frequency and slightly lower than the cochlear resonance frequency; (4) that reference frequency varied as a function of velocity, the higher the velocity of the animal, the higher was the reference frequency (slope 55 Hz m-1s-2); and (5) that the mean reference frequency was always an undercompensation. The average amount of undercompensation was 15.8%. There was a significant difference (P < or = 0.005) in Doppler-shift compensation data collected at velocities that differed by 0.1 ms-1. A velocity difference of 0.1 ms-1 corresponds to a Doppler-shift difference of about 35 Hz in the approximately 61 kHz signals reaching the ear.

Acoustics↗
PubMed1993

Efferent terminals in the cochlea of the mustached bat: quantitative data.

Efferent terminals in the cochlea of the mustached bat were stained for acetylcholinesterase (AChE) and quantitative data were obtained for the number and size of the endings on the outer hair cells (OHCs) in each row, from base to apex. From TEM micrographs and AChE-stained, surface preparations it was determined that every OHC had a single, large terminal. The mean size of the terminals was significantly different in each row, with the largest occurring in the first row (7.1 microns 2); the mean size in the second and third rows was 5.7 and 5.0 microns 2 respectively. In specific frequency processing regions, the largest mean size (8.4 microns 2) for first row OHCs was consistently found in the distal densely innervated (DDI) area. This region has afferent neurons that are sharply tuned to the second harmonic, constant frequency component of the bat's biosonar signals. Sudden changes in the size of the terminals were observed exactly at the boundaries of the DDI with adjacent sparsely innervated regions. Similar, but less striking, size changes also occurred in and adjacent to the proximal densely innervated (PDI) region, a harmonically related, sharply tuned region, which processes the bat's 91.5 kHz, third harmonic, constant frequency signals. The region of the cochlea with the smallest first row terminals (mean 5.3 microns 2) was the large, sparsely innervated region of the basal turn, a region that does not appear to process biosonar signals. Although the significance of differences in efferent terminal size is not known, the data suggest a possible correlation between OHC stimulation and sharp tuning. The potentially greater influence of the efferent fibers on the first row of OHCs, compared to other rows, is consistent with observations made on other mammals; in the latter, however, the greater influence has been suggested more by number than size. Unlike other mammals, the OHC efferents in the mustached bat have no clear base-to-apex gradient in the number or size of the efferent terminals. It is suggested that this might reflect the high frequency nature of the ear (6-120 kHz) and absence of low frequency hearing.

Acetylcholinesterase↗
PubMed1992

Contractile proteins in the hyaline cells of the chicken cochlea.

Hyaline cells are a single layer of epithelial cells found at the inferior edge of the sensory epithelium in the chick cochlea. They rest directly above a specialized region of the basilar membrane at a point where it connects to the fibrocartilaginous skeleton of the cochlear duct. The basal cytoplasm of the hyaline cells contains a bundle of linearly aligned actin filaments that resemble stress fibers in their organization. The actin filaments are anchored in the basal plasma membranes of the cells, which are, in turn, associated with the underlying basal lamina and the extracellular matrix of the basilar membrane. We have used a combination of transmission electron microscopy, differential-interference-contrast and epifluorescence light microscopy, and confocal laser scanning microscopy to study the composition and organization of these actin bundles within the hyaline cells. The bundles are arranged into triangular wedges that are oriented radially across the basilar membrane. Each cell contains one or two actin wedges. Adjacent cells can have them aligned in opposite directions so that in a whole-mount surface preparation they appear as interdigitations. Immunofluorescent staining of the hyaline cells has shown that smooth muscle myosin and alpha-actinin are co-localized to the actin bundles. Smooth muscle myosin is also found throughout the cytoplasm of the cells. The fact that hyaline cells in the chick cochlea are contacted by efferent nerve fibers suggests that these cells may regulate tension on the basilar membrane via the specialized bundle of actin filaments.

Animals↗
PubMed1991

Course and distribution of efferent fibers in the cochlea of the mouse.

The course, distribution and termination of single efferent fibers to the cochlea has been described in only a few animals and relatively few fibers have been studied with knowledge of their ipsilateral or contralateral origin. In order to examine the efferent fibers in the mouse, the anterograde tracer Phaseolus vulgaris leucoagglutinin (PHA-L) was iontophoretically injected into one side of the brain stem near the location of known efferent nuclei. Examination of surface preparations of the cochlea revealed detailed information for both the lateral olivocochlear (LOC) and medial olivocochlear (MOC) systems. Many, but not all, fibers entered the cochlea within the intraganglionic spiral bundle (IGSB). The LOC fibers were restricted to the ipsilateral cochlea and rarely branched within the IGSB and osseous spiral lamina (OSL). In the organ of Corti, they traveled either basally or apically in the region of the inner hair cells (IHCs), spanning lengths up to 130 microns (basally) and 890 microns (apically). Terminal swellings of these fibers were ca 3.0 microns in diameter. Numerous en passant swellings were present where the fibers formed a plexus in the area of the IHCs. The MOC fibers followed a similar course in the IGSB and OSL, and within the OSL the fibers had few branches. Within the organ of Corti they traveled apically (up to 70 microns) in the nerve bundles located in the IHC area before they crossed the tunnel of Corti. In the region of the OHCs, 9% of the traceable fibers branched to innervate two to three OHCs while 91% appeared to innervate only one OHC. There was no discernible difference in the distribution of contralateral and ipsilateral MOC projections in terms of cochlear region or outer hair cell rows.

Animals↗
PubMed1991

Specializations for sharp tuning in the mustached bat: the tectorial membrane and spiral limbus.

The sense of hearing in the mustached bat, Pteronotus parnellii, is specialized for fine frequency analysis in three narrow bands that correspond to approx 30, 60 and 90 kHz constant frequency harmonics in the biosonar signals used for Doppler-shift compensation and acoustic imaging of the environment. Previous studies have identified anatomical specializations in and around the area of the cochlea that processes the dominant second harmonic component, but similar features have not been found in areas related to sharp tuning and high sensitivity for the first or third harmonics. In this report we call attention to the large size of the tectorial membrane and spiral limbus in all three areas that appear to process the harmonically related constant frequency components. These structures are especially pronounced in the regions of the cochlea that respond to the approx 61 kHz, second harmonic and 91.5 kHz, third harmonic bands; they correspond specifically to areas where the density of afferent nerve fibers is high and where very sharply tuned neurons occur. These data for cochleae with multiple specializations lend strong support to the idea that the mass of the tectorial membrane can be an important factor in establishing the response properties of the cochlea.

Animals↗
PubMed1990

Cochlear resonance in the mustached bat: behavioral adaptations.

Mustached bats, Pteronotus p. parnellii, use complex, multiharmonic biosonar signals with prominent approx. 60 kHz (CF) components. The sense of hearing is especially acute to sounds near 60 kHz and the cochlea shows a number of specializations in the 60 kHz region. Foremost is a remarkable degree of cochlear resonance. In this study it is shown that: 1) any sounds near the resonance frequency elicit a pronounced resonance that continues after the stimulus terminates; 2) Doppler-shifted echoes of the bat's own cries may cause resonance; 3) continuous resonance can be produced by stimulating the ear with broadband noise but such resonance does not interfere with the bat's ability to Doppler-shift compensate during simulated flight; 4) significant changes in the resonance frequency of the cochlea occur during and after flight; 5) the changes in resonance can be dependent or independent of body temperature changes; and 6) mustached bats continuously adjust the CF component of their pulses to keep the second harmonic echoes in a constant frequency band near the resonance frequency. Thus, mustached bats not only compensate for Doppler-shifts imposed by their movements relative to that of a target, but they cochlear resonance compensate to deal with small changes in the micromechanical properties of the cochlea.

Animals↗
PubMed1989

Evoked potential correlates of echolocation in the mustached bat, Pteronotus p. parnellii.

The biosonar signals of the greater mustached bats are characterized by a long constant frequency component that is preceded and terminated by frequency modulated components. It has generally been concluded that the terminal FM (TFM) is important for target ranging while the initial FM (IFM), or beginning of the signal, is relatively insignificant. With the aid of chronically implanted electrodes, acoustically evoked brainstem potentials were recorded from bats during simulated flight on a pendulum and when targets were placed at fixed distances from the bat's head. Distinct pulse- and echo-evoked potentials were recorded in relation to the onset of both the IFM and TFM, or the onset of the CF when no IFM was present. Echo-evoked potentials were often as high in amplitude as pulse-evoked potentials and the timing of the IFM- and TFM-pulse and echo-evoked potentials seemed to accurately reflect target distance. Data indicate that the IFM, or signal onset, must be a significant part of the echo even though it is usually faint, overlaps the intense outgoing CF component, and returns to the ear when the middle ear muscles are contracting.

Animals↗
PubMed1988

Tension fibroblasts and the connective tissue matrix of the spiral ligament.

Fibroblasts with stress fibers (tension fibroblasts) have previously been described in the marginal region of the spiral ligament of bats and mice (Henson et al., 1984, 1985). The location, structure and attachments of these cells and the fact that they contain contraction associated proteins, have suggested a role in the generation of tension within the basilar membrane-spiral ligament complex. In this study the structure of these fibroblasts and their relationships to different types of connective tissue matrices were examined in representative Marsupalia, Insectivora, Chiroptera, Rodentia, Lagomorpha, Carnivora and Primates. Tension fibroblasts occur in all species but they are remarkably different in their actin filament content, their structure and distribution, and in their association with the extracellular matrix and otic capsule. Six types of matrices are described (dense filamentous, bundled, laminated, honeycombed, trabeculated and loose filamentous). The configurations of the cells and fibers indicate that tension on the basilar membrane may be accomplished in different ways and to different degrees in different mammals. The arrangement of the matrix and cells in some animals is markedly different in the parts of the cochlea that respond to high, middle and low frequencies.

Actins↗
PubMed1988

Olivocochlear neurons in the brainstem of the mouse.

The locations of efferent auditory neurons in the white mouse were determined using retrograde transport of HRP from the cochlea. Labeled neurons were localized in the lateral superior olivary nucleus (LSO) and ventral nucleus of the trapezoid body (VNTB). The total number of efferent neurons was determined to be 475; of these 34.5% are medial group efferents and 65.4% are lateral group efferents. The ipsilateral LSO contains 99% of the lateral group neurons and the contralateral VNTB contains 75% of the medial group neurons.

Animals↗
PubMed1985

Immunocytochemical localization of contractile and contraction associated proteins in the spiral ligament of the cochlea.

Most of the extracellular fibers of the spiral ligament are associated with a distinct band of 'anchoring' cells which occur at the boundary between the spiral ligament and the otic capsule. These cells are characterized by parallel arrays of intracellular filaments which, along with the extracellular fibers, insert into electron dense, conical adhesion plaques. The intracellular filaments show a close morphological resemblance to the 'stress fibers' of cultured fibroblasts (Henson et al., 1984). In the present study we have demonstrated by immunofluorescence techniques that the anchoring cells, unlike adjacent cells of the spiral ligament, contain a complement of proteins that is typically associated with stress fibers and with contractile systems. In addition to actin, the cells contain myosin, tropomyosin, alpha-actinin and talin. These results lend further support to the hypothesis that the anchoring cells have the capacity to create and/or maintain tension on the spiral ligament-basilar membrane complex and to influence the mechanical properties of the basilar membrane.

Actinin↗
PubMed1984

The attachment of the spiral ligament to the cochlear wall: anchoring cells and the creation of tension.

The spiral ligament of the cochlea contains an array of criss-crossing extracellular fibers which are anchored to the bony wall of the cochlea and into the outer margin of the basilar membrane. In certain areas there is an accumulation of unusual sponge-shaped cells which are clearly involved in anchoring the extracellular fibers to the bony wall and possibly in maintaining or applying radial tension on the spiral ligament-basilar membrane complex. The latter is suggested by the occurrence of a large number of intracellular fibers which have many of the characteristics of the so-called 'stress fibers' of cultured fibroblasts. Where these cells occur the fibers of the spiral ligament bend sharply, presumably due to tension applied on them. This paper provides transmission and scanning electron micrographs of the 'anchoring' cells in the mouse and two species of bats. In the horseshoe bat, the anchoring cells provide the sole mode of attachment of most of the spiral ligament to the otic capsule. Marked differences occur not only among species but also in different regions of the spiral ligament. A diagram is provided to show how the system of cells and fibers might create or maintain tension on the basilar membrane.

Animals↗
PubMed1983

Ultrastructure of the lining of the scala tympani of the bat, Pteronotus parnellii.

The cells lining the scala tympani of the cochlea of Pteronotus p. parnellii were studied in whole mount preparations and with light and scanning and transmission electron microscopy. On the basis of structure and location three different cell types were recognized: (1) those lying on the undersurface of the basilar membrane; (2) those covering the internal surface of most of the otic capsule; and (3) those associated with a thick layer of osmiophilic substance and restricted to a specific region in the basal turn. The cells associated with the osmiophilic substance were strikingly different from the other cells; they were relatively rich in organelles and had a Golgi complex which appeared to produce granules which coalesced both intracellularly and extracellularly to form the osmiophilic layer. The function and composition of the osmiophilic substance is unknown but it seems to be unique to Pteronotus parnellii and related subspecies known to have greatly enlarged perilymphatic scalae and unusual hearing capacities associated with Doppler shift compensation sonar.

Animals↗
PubMed1983

Sustentacular cells of the organ of Corti--the tectal cells of the outer tunnel.

The cells which form the roof of the outer tunnel of the organ of Corti were studied by light microscopy and scanning and transmission electron microscopy. In the mustache bat, Pteronotus p. parnellii, the cells are characterized by: (1) a unique position in the roof and along the lateral wall of the outer tunnel; (2) no contact with the basilar membrane; (3) isolation of adjacent cell bodies; (4) an extensive endolymphatic surface with a sparse population of short microvilli; (5) a loose association with the adjacent mat of polypous surface projections on the outer tunnel surface of the first row of Hensen's cells; and (6) a darkly staining cytoplasm. These cells occur in certain other mammals (cats and mice) and have been classified previously as Hensen's or Deiters' cells, but since they lack the distinct morphological characteristics of either of these types of cells, it is suggested that they be recognized as a distinct cell type, the tectal cells of the outer tunnel.

Animals↗
PubMed1982

Cochlear microphonic potentials elicited by biosonar signals in flying bats, Pteronotus p. parnellii.

Cochlear microphonic (CM) potentials were recorded from the bat, Pteronotus p. parnellii during tethered flight and during simulated flight on a pendulum. For each emitted signal the frequency of the ca. 61 kHz constant frequency (CF) component was compared with the frequency response characteristics of the animals's ear. The majority of "resting pulses' had CF components with the maximum frequency approximately 200 Hz below the best frequency (BF) of the CM audiogram. Doppler shift compensation occurred only during forward swings of the pendulum and in such a way that the echo CF components were always maintained near the BF, but on the low frequency slope of the CM audiogram. CM responses to emitted pulses were usually small in amplitude and in some animals no responses were seen. Echoes Doppler shifted upward, however, evoked high amplitude potentials. Echo CF components estimated to be at least 43 dB fainter than the emitted pulses evoked higher amplitude CM potentials than the loud emitted pulses. Echoes from large surfaces up to 4.5-5.0 meters away evoked CM potentials as high in amplitude as those elicited by emitted pulses, even when there was no Doppler shift. Beats in the CM were observed on many occasions and occurred as a result of pulse-echo and echo-echo interactions.

Animals↗
PubMed1982

The cells of Boettcher in the bat, Pteronotus p. parnellii.

The structural characteristics, distribution and intercellular relationships of the cells of Boettcher were studied in the mustache bat, Pteronotus P. parnellii. The cells of Boettcher have many structural features similar to those described in other mammals, but in Pteronotus they are distributed throughout the cochlea and are associated with relatively large amounts of secretory and/or absorptive material. Much of this material seems to be derived from or contribute to, a darkly staining upper layer of the basilar membrane. This material accumulates in elaborate microvillus-filled intercellular channels which are restricted to an area near the basilar membrane. The channels communicate with the basilar membrane surface through wide intercellular spaces and through small canals. The microvillus-filled channels are confluent with large extracellular spaces between Boettcher's cells and a single row of cells which form the floor of the outer tunnel. The latter have irregular shaped nuclei, contain many vacuoles and like Boettcher's cells, are associated with large amounts of basilar membrane-like material. Observations on Pteronotus, as well as other species of bats, do not support concepts relating Boettcher's cells to hair cell innervation patterns or to high frequency hearing.

Animals↗
PubMed1979

Some aspects of structural organization in the cochlea of the bat, Pteronotus parnellii.

The scanning electron microscope was used to study some specific features of the organ of Corti in the bat, Pteronotus parnellii parnellii. The region of the outer tunnel and the external sulcus were analyzed in detail. Good visualization of the geometric arrangement of the external sulcus cells and the deep channels for their root processes was obtained by digestion of fixed material with 1% trypsin. Processes of the cellular elements forming the roof of the outer tunnel are very thin and appear to be weakly attached to the heads of the phalangeal processes of the third row of Deiters' cells. In much of the overstimulated and trypsin digested material the weak junction was broken and the outer tunnel elements exposed. Two distinct cellular elements occur along the outer wall of the tunnel. One type has a surface with numerous projections on tis outer tunnel surface. The other has a smooth surface and an expanded fanshaped extremity which forms at least part of the roof of the tunnel. With trypsin digestion some of the more deeply situated cells were exposed.

Animals↗
PubMed1978

The basilar membrane of the bat, Pteronotus p. parnellii.

The basilar membrane of Pteronotus p. parnellii was studied by light and scanning electron microscopy in order to examine the relationship of membrane structure to the sharply tuned sense of hearing in this bat. The basilar membrane was found to differ from those of other mammals and other bats by showing virtually no change in width except at the extreme ends. Thickenings of the pars pectinata and pars tecta are well developed in Pteronotus; they show no sudden changes in their dimensions and in this way differ from the thickenings found in the European horseshoe bat whose sharply tuned sense of hearing seems at least partially dependent on sudden, marked changes in the structure of the basilar membrane. In Pteronotus the greater part of the basilar membrane, 7.5 mm or approximately 58%, lies within the enormous basal turn and within this turn there are steeply banked curves and one small 0.5-mm region where the membrane is straight. The straight portion is associated with a region of the cochlea where there is a marked change in the density of nerve fibers and where the stria vascularis, spiral ligament and fluid-filled spaces of the ear are enlarged.

Animals↗