Biomedical subjects

A N Popper

Publications and source records attributed to A N Popper.

At least 37 records · Page 2Linked to original sources

PubMed1996

Novel afferent terminal structure in the crista ampullaris of the goldfish, carassius auratus.

Using transmission electron microscopy, we have identified a new type of afferent terminal structure in the crista ampullaris of the goldfish Carassius auratus. In addition to the bouton-type afferent terminals previously described in the ear of this species, the crista also contained enlarged afferent terminals that enveloped a portion of the basolateral hair cell membrane. The hair cell membrane was evaginated and protruded into the afferent terminal in a glove-and-finger configuration. The membranes of the two cells were regularly aligned in the protruded region of the contact and had a distinct symmetrical electron density. The electron-dense profiles of these contacts were easily identified and were present in every crista sampled. In some cases, efferent terminals synapsed onto the afferents at a point where the hair cell protruded into the terminal. The ultrastructural similarities of the goldfish crista afferents to calyx afferents found in amniotes (birds, reptiles, and mammals) are discussed. The results of the study support the hypothesis that structural variation in the vertebrate inner ear may have evolved much earlier in evolution than previously supposed.

Afferent Pathways↗

PubMed1996

Behavioral detection of acoustic particle motion by a teleost fish (Astronotus ocellatus): sensitivity and directionality.

Behavioral detection thresholds for oscars (Astronotus ocellatus) were measured in response to linear, oscillatory motion at 100 Hz along seven axes (-90 degrees, -60 degrees, -30 degrees, 0 degree, +30 degrees, and +60 degrees in azimuth, where 0 degree is the fish longitudinal axis; and the vertical axis) using a cardiac classical conditioning paradigm. Thresholds at all selected axes ranged from -58 to -56 dB re: 1 micron, which corresponds to 1.2 to 1.6 nm displacement (RMS). Thus, oscars appear to be equally sensitive to stimulation at all axes in three dimensional space. Behavioral thresholds of the oscar are close to the neural thresholds obtained from the most sensitive auditory nerve fibers in two other species, the goldfish (Carassius auratus) and the toadfish (Opsanus tau).

Acoustic Stimulation↗

PubMed1996

Hair cell precursors are ultrastructurally indistinguishable from mature support cells in the ear of a postembryonic fish.

The ultrastructure of S-phase cells in the postembryonic fish ear was compared with that of mature support cells. S-phase cells were identified by injecting animals with [3H]thymidine and sacrificing 3 h later. Sensory epithelia (saccules, utricles, and canals) were processed for light-level autoradiography. Sections containing thymidine-labeled cells were re-embedded and re-examined using transmission electron microscopy. The results indicate that S-phase cells differ from mature support cells only in nuclear position and shape. Otherwise their cytoplasmic characteristics are indistinguishable. Both cell types, on the other hand, are readily distinguishable from hair cells. These data provide ultrastructural evidence for the ability of mature support cells to enter the cell cycle in postembryonic vertebrates.

Animals↗

PubMed1996

Cell proliferation and hair cell addition in the ear of the goldfish, Carassius auratus.

Cell proliferation and hair cell addition have not been studied in the ears of otophysan fish, a group of species who have specialized hearing capabilities. In this study we used the mitotic S-phase marker bromodeoxyuridine (BrdU) to identify proliferating cells in the ear of one otophysan species, Carassius auratus (the goldfish). Animals were sacrificed at 3 h or 5 days postinjection with BrdU and processed for immunocytochemistry. The results of the study show that cell proliferation occurs in all of the otic endorgans and results in the addition of new hair cells. BrdU-labeled cells were distributed throughout all epithelia, including the primary auditory endorgan (saccule), where hair cell phenotypes vary considerably along the rostrocaudal axis. This study lays the groundwork for our transmission electron microscopy study of proliferative cells in the goldfish ear (Presson et al., Hearing Research 100 (1996) 10-20) as well as future studies of hair cell development in this species. The ability to predict, based on epithelial location, the future phenotype of developing hair cells in the saccule of the goldfish make that endorgan a particularly powerful model system for the investigation of early hair cell differentiation.

Animals↗

PubMed1996

Effects of low-frequency underwater sound on hair cells of the inner ear and lateral line of the teleost fish Astronotus ocellatus.

Fish (Astronotus ocellatus, the oscar) were subject to pure tones in order to determine the effects of sound at levels typical of man-made sources on the sensory epithelia of the ear and the lateral line. Sounds varied in frequency (60 or 300 Hz), duty cycle (20% or continuous), and intensity (100, 140, or 180 dB re: 1 muPa). Fish were allowed to survive for 1 or 4 days posttreatment. Tissue was then evaluated using scanning electron microscopy to assess the presence or absence of ciliary bundles on the sensory hair cells on each of the otic endorgans and the lateral line. The only damage that was observed was in four of five fish stimulated with 300-Hz continuous tones at 180 dB re: 1 muPa and allowed to survive for 4 days. Damage was limited to small regions of the striola of the utricle and lagena. There was no damage in any other endorgan, and the size and location of the damage varied between specimens. No damage was observed in fish that had been allowed to survive for 1 day poststimulation, suggesting that damage may develop slowly after exposure.

Acoustic Stimulation↗

PubMed1995

Damage and recovery of hair cells in fish canal (but not superficial) neuromasts after gentamicin exposure.

Recent evidence demonstrating the presence of two types of sensory hair cell in the ear of a teleost fish (Astronotus ocellatus, the oscar) indicates that hair cell heterogeneity may exist not only in amniotic vertebrates but also in anamniotes. Here we report that a similar heterogeneity between hair cell types may also occur in the other mechanosensory organ of the oscar, the lateral line. We exposed oscars to the aminoglycoside (ototoxic) antibiotic gentamicin sulfate and found damaged sensory hair cells in one class of the lateral line receptors, the canal neuromasts, but not in the other class, the superficial neuromasts. This effect was not due to the canal environment. Moreover, new ciliary bundles on hair cells of the canal neuromasts were found after, and during, gentamicin exposure. The pattern of hair cell destruction and recovery in canal neuromasts is similar to that of type I-like hair cells found in the striolar region of the utricle and lagena of the oscar after gentamicin treatment. These results suggest that the hair cells in the canal and superficial neuromasts may be similar to type I-like and type II hair cells, respectively, in the fish ear.

Animals↗

PubMed1995

Hair cell orientation patterns on the saccules of juvenile and adult toadfish, Opsanus tau.

Saccules from 10 adult (five female, five male) toadfish (Opsanus tau) 13.5-26 cm standard length, were examined for individual/sexual variation in the hair cell orientation pattern. In addition, saccules from two juveniles (5 and 6 cm standard length) were compared with those of the adults to determine whether maturational differences exist in the hair cell orientations. The hair cell orientation pattern is unlike any reported previously for this species or its congener, O. beta. There are no major differences between the hair cell orientations of males and females, nor between the juveniles and the adults. A slight individual variation is present in the proportion of hair cells oriented in a particular direction in a specific area of the sensory epithelium. Potential ramifications of this hair cell orientation pattern are discussed with regard to development and auditory processing.

Age Factors↗

PubMed1995

The octavolateralis system and Mauthner cell: interactions and questions.

This paper is an overview of some of the major points to arise in the accompanying contributions of this special symposium issue. The symposium papers arose out of discussions among investigators interested in the inner ear and Mauthner cell, with the focus on hydrodynamic components that activate the Mauthner cell through the octavolateralis system. The intention of the symposium was to investigate the possibility of using our knowledge of the Mauthner system to help understand acoustic processing by the ear, and of using our knowledge of fish hearing to better understand Mauthner cell function. This is the first attempt to take a broad look at both systems to see how they might function together. As such, these proceedings can serve as a mini-tutorial for investigators interested in one system or the other. In this summary paper we also identify some of the major uncertainties in our understanding of the ear-Mauthner connection. These include questions about: (1) the identity of the acoustic stimuli that are neuroethologically relevant to the Mauthner system; (2) the relative importance of the various octavolateralis inputs (acoustic, vestibular, or lateral line); (3) the contribution of the different various acoustic endorgans to the Mauthner system; (4) whether the Mauthner system can distinguish sound source location, and (5) whether Mauthner neurobiology is compatible with the prevailing model (the phase model) for determining sound source location by fishes. We believe these issues provide potentially useful avenues of future investigation that should give important insights in both acoustic processing by fish and the function of the mauthner system.

Animals↗

PubMed1995

Structural diversity in the inner ear of teleost fishes: implications for connections to the Mauthner cell.

A body of literature suggests that the Mauthner cell startle response can be elicited by stimulation of the ear. While we know that there are projections to the M-cell from the ear, the specific endorgan(s) of the ear projecting to the M-cell are not known. Moreover, there are many reasons to question whether there is one pattern of inner ear to M-cell connection or whether the endorgan(s) projection to the M-cell varies in species that have different hearing capabilities of hearing structures. In this paper, we briefly review the structure of fish ears, with an emphasis on structural regionalization within the ear. We also review the central projections of the ear, along with a discussion of the limited data on projections to the M-cell.

Animals↗

PubMed1995

Hair cell heterogeneity in the goldfish saccule.

A set of cytological studies performed in the utricle and saccule of Astronotus ocellatus (Teleostei, Percomorphi, Cichlidae) identified two basic types of hair cells and others with some intermediate characteristics. This paper reports on applying the same techniques to the saccule of Carassius auratus (Teleostei, Otophysi, Cyprinidae) and demonstrates similar types of hair cells to those found in Astronotus. Since Carassius and Astronotus are species of extreme taxonomic distance within the Euteleostei, two classes of mechanoreceptive hair cells are likely to represent the primitive condition for sensory receptors in the euteleost inner ear and perhaps in all bony fish ears.

Animals↗

PubMed1994

Quantitative analyses of postembryonic hair cell addition in the otolithic endorgans of the inner ear of the European hake, Merluccius merluccius (Gadiformes, Teleostei).

Bony fishes add sensory hair cells to the saccule and lagena of the ear for at least several years after hatching. However, it is not known whether hair cell proliferation occurs for the whole lifetime of an animal, whether proliferation occurs in all endorgans of the ear, or whether the rate of proliferation is the same in all of the endorgans. To obtain answers to these questions, the extent of postembryonic hair-cell proliferation was determined in the saccule, lagena, and utricle of the ear in the European hake, Merluccius merluccius, for fish ranging from 7 to 75 cm in total length (6 months to 9 years of age). Results demonstrated that hair-cell addition continued throughout this period in all three otic endorgans, although endorgan size was proportionally greatest in smaller animals. Of the three endorgans, cell addition was greatest in the saccule. Moreover, far more cells were added to the caudal end of the saccule than to the rostral end. Each saccule of the largest hake had over 900,000 hair cells. It is estimated that each saccule adds approximately 110,000 new hair cells each year (or 302 cells/day) over the life span of the fish studied. A significant number of small ciliary bundles, thought to represent newly proliferated hair cells, was found throughout each endorgan, and the number of such bundles declined as the rate of hair cell proliferation decreased. The results demonstrate that extensive proliferation occurs in all three otolithic endorgans of the ears in a fish and that such proliferation continues for virtually the whole life of the animal. The functional significance of this addition is not known.

Animals↗

PubMed1993

Acoustic intensity discrimination by the cichlid fish Astronotus ocellatus (Cuvier).

The acoustic intensity discrimination ability of the oscar (Astronotus ocellatus), a cichlid fish, was investigated using an automated positive reward method. Intensity discrimination thresholds (delta I, in dB) for 7-s continuous pure tone signals were measured both as functions of sound intensity above thresholds, i.e., sensation levels, (SL)(+10 dB, +20 dB and +30 dB) and frequency (200 Hz, 500 Hz, and 800 Hz). delta I at 500 Hz for +10 dB, +20 dB, and +30 dB SLs are 8.9, 5.5, and 3.3 dB, respectively. delta I (at +20 dB SL) for 200 Hz, 500 Hz, and 800 Hz are 4.5, 5.5, and 9.3 dB, respectively. Despite having poor auditory sensitivity (narrow frequency range and high thresholds), the intensity discrimination ability of the oscar follows the general trends of previously studied fish species, however, with higher thresholds.

Acoustic Stimulation↗

PubMed1993

Modes of neuronal arbor enlargement in the ear of a postembryonic fish, Astronotus ocellatus.

New hair cells are added during postembryonic life in several species of fishes and birds. The production of new hair cells appears to require enlargement of eighth nerve arbors during growth since, at least in fish, eighth nerve neurons are added more slowly than hair cells or not at all. This situation provides an intriguing opportunity to study the mechanisms of growth of the neuronal arbors. In this paper, we report the results of studies on the postembryonic growth of eighth nerve dendritic arbors in the saccular epithelium of the cichlid fish Astronotus ocellatus. Arbor sizes and shapes were compared in small and large fish using the axonal tracer cobaltous lysine. Our data suggest that postembryonic eighth nerve arbors enlarge in 2 ways. First, arbors add new terminal endings to their distal ends. Second, whole new branches appear to be added at locations up to hundreds of micrometers proximal to the terminal endings. These 2 modes of growth suggest that more than one mechanism may be operative in controlling arbor enlargement.

Animals↗

PubMed1993

Damage and regeneration of hair cell ciliary bundles in a fish ear following treatment with gentamicin.

Sensory hair cells in the striolar regions of the utricle and lagena of a teleost fish, the oscar (Astronotus ocellatus), were damaged following intramuscular injections of gentamicin sulfate. In order to determine whether fish can regenerate hair cells, the time course of damage and recovery was followed over a period of four weeks by scanning electron microscopy. Maximum loss of ciliary bundles occurred at about day 10 after the first of four daily injections of gentamicin (20 mg/kg) in 4-6 cm long fish. The striolar regions were almost totally denuded of ciliary bundles, and there was evidence of considerable hair cell loss. The time course for damage was longer in larger fish, but the recovery of the ciliary bundles appeared to be complete about 10 days after maximal damage was seen in both the smaller and larger fish. These data indicate that Astronotus is able to repair damage to hair cells for an extended period of time post-embryonically.

Analysis of Variance↗

PubMed1993

Two types of sensory hair cell in the saccule of a teleost fish.

Previous investigations have demonstrated significant ultrastructural differences in hair cells located in various regions of the utricle of the oscar, Astronotus ocellatus. In this study, we used TEM and SEM to examine cells from the central and marginal regions of the saccule to determine if similar hair cell ultrastructural differences exist in this endorgan. Based upon ultrastructural characteristics, central saccular cells closely resemble utricular striolar cells while marginal cells are intermediate in ultrastructure between striolar and extrastriolar cells of the utricle.

Animals↗

PubMed1993

Sound detection and processing by fish: critical review and major research questions.

The literature on fish hearing has increased significantly since our last critical review in 1973. The purpose of the current paper is to review the more recent literature and to identify those questions that need to be asked to develop a fuller understanding of the auditory capabilities and processing mechanisms of fishes. We conclude that while our understanding of fish hearing has increased substantially in the past years, there are still major gaps in what we know. In particular, the comparative functional literature is extremely limited, and we do not yet know whether different species, and particularly hearing specialists as compared to hearing nonspecialists, have fundamentally different auditory capabilities and mechanisms.

Animals↗

PubMed1992

Heterogeneity of sensory hair cells in a fish ear.

The ultrastructure of sensory hair cells in the utricle of the cichlid fish, Astronotus ocellatus, the oscar, was studied by transmission electron microscopy of serial ultrathin sections from different regions of the epithelium. Two distinctly different types of hair cell were found, one located in the striolar region of the epithelium and the other in the extrastriolar region. Striolar hair cells have a well-defined perinuclear cisterna located just below the nucleus, and large perinuclear mitochondria. Synaptic bodies of striolar cells are small and located in clusters, while those in extrastriolar cells are relatively large and individually dispersed. The extrastriolar hair cell closely resembles the amniote type II hair cell. On the basis of these data, and consistent with earlier studies, it appears that the striolar hair cells closely resemble amniote type I hair cells in many significant ways. Thus we have called them type I-like cells. The extrastriolar hair cells appear to be typical of eighth nerve mechanoreceptors commonly described for fish and closely resemble the amniote type II hair cell.

Animals↗

PubMed1992

Auditory sensitivity of the cichlid fish Astronotus ocellatus (Cuvier).

Auditory sensitivity was determined for the oscar, Astronotus ocellatus, a cichlid fish that has no known structural specializations to enhance hearing. Trained A. ocellatus behaviorally responded to sound stimuli from 200 Hz to 800 Hz with best sensitivity of 18 dB (re: 1 mubar) to 21 dB for frequencies between 200 and 400 Hz. This is significantly poorer than hearing sensitivity for fish classified as hearing specialists, but well within the range of hearing capabilities reported for non-specialist teleost species.

Acoustic Stimulation↗