Papers by John Ramcharitar
The costs of publication of this article were defrayed in part by the payment of page charges. Th... more The costs of publication of this article were defrayed in part by the payment of page charges. The article must therefore be hereby marked ''advertisement'' in accordance with 18 U.S.C. Section 1734 solely to indicate this fact.
Chemical Ototoxicity of the Fish Inner Ear and Lateral Line
Advances in Experimental Medicine and Biology, 2016
Hair cell-driven mechanosensory systems are crucial for successful execution of a number of behav... more Hair cell-driven mechanosensory systems are crucial for successful execution of a number of behaviors in fishes, and have emerged as good models for exploring questions relevant to human hearing. This review focuses on ototoxic effects in the inner ear and lateral line system of fishes. We specifically examine studies where chemical ototoxins such as aminoglycoside antibiotics have been employed as tools to disable the lateral line. Lateral line ablation results in alterations to feeding behavior and orientation to water current in a variety of species. However, neither behavior is abolished in the presence of additional sensory cues, supporting the hypothesis that many fish behaviors are driven by multisensory integration. Within biomedical research, the larval zebrafish lateral line has become an important model system for understanding signaling mechanisms that contribute to hair cell death and for developing novel pharmacological therapies that protect hair cells from ototoxic damage. Furthermore, given that fishes robustly regenerate damaged hair cells, ototoxin studies in fishes have broadened our understanding of the molecular and genetic events in an innately regenerative system, offering potential targets for mammalian hair cell regeneration. Collectively, studies of fish mechanosensory systems have yielded insight into fish behavior and in mechanisms of hair cell death, protection, and regeneration.
Marine and Freshwater Research, 2005
Otoliths are of interest to investigators from several disciplines including systematics, auditor... more Otoliths are of interest to investigators from several disciplines including systematics, auditory neuroscience, and fisheries. However, there is often very little sharing of information or ideas about otoliths across disciplines despite similarities in the questions raised by different groups of investigators. A major purpose of this paper is to present otolith-related questions common to all disciplines and then demonstrate that the issues are not only similar but also that more frequent interactions would be mutually beneficial. Because otoliths evolved as part of the inner ear to serve the senses of balance and hearing, we first discuss the basic structure of the ear. We then raise several questions that deal with the structure and patterns of otolith morphology and how changes in otoliths with fish age affect hearing and balance. More specifically, we ask about the significance of otolith size and how this might affect ear function; the growth of otoliths and how hearing and ba...
Bioacoustics of Fishes of the Family Sciaenidae (Croakers and Drums)
Transactions of the American Fisheries Society, 2006
Abstract The teleost family Sciaenidae, collectively known as the croakers and drums because of t... more Abstract The teleost family Sciaenidae, collectively known as the croakers and drums because of their propensity for making sound, includes roughly 70 genera and 270 species worldwide. Although many other groups of fish also communicate using sound, the ...
Masked auditory thresholds in sciaenid fishes: A comparative study
The Journal of the Acoustical Society of America, 2004
Western Atlantic sciaenids comprise a taxonomically diverse teleost family with significant varia... more Western Atlantic sciaenids comprise a taxonomically diverse teleost family with significant variations in the relationship between the swim bladder and the otic capsule. In this study, the auditory brainstem response (ABR) was used to test the hypothesis that fishes with different peripheral auditory structures (black drum, Pogonias chromis and Atlantic croaker, Micropogonias undulatus) show differences in frequency selectivity. In a black drum the swim bladder is relatively distant from the otic capsule while the swim bladder in Atlantic croaker possesses anteriorly-directed diverticulas that terminate relatively near the otic capsule. Signals were pure tones in the frequency range, 100 Hz to 1.5 kHz, and thresholds were determined both with and without the presence of simultaneous white noise at two intensity levels (124 dB and 136 dB, re: 1 microPa). At the 124 dB level of white noise background, both the black drum and Atlantic croaker showed similar changes in auditory sensitivity. However, in the presence of the 136 dB white noise masker, black drum showed significantly greater shifts in auditory thresholds between 300 and 600 Hz. The results indicate that the two species differ in frequency selectivity since the Atlantic croaker was less susceptible to auditory threshold shifts, particularly at the higher level of masking. This difference may be linked to peripheral auditory mechanisms.
The enigma of fish ear diversity
The Journal of the Acoustical Society of America, 2001
Page 1. TUESDAY MORNING, 4 DECEMBER 2001 ROOM 316, 8:00 TO 11:40 AM Session 2aAB Animal Bioacoust... more Page 1. TUESDAY MORNING, 4 DECEMBER 2001 ROOM 316, 8:00 TO 11:40 AM Session 2aAB Animal Bioacoustics: Fish Audition and Sound Production Mardi C. Hastings, Chair Biomedical Engineering Center, The Ohio ...
The Journal of the Acoustical Society of America, 2006
We investigated how morphological differences in the auditory periphery of teleost fishes may rel... more We investigated how morphological differences in the auditory periphery of teleost fishes may relate to hearing capabilities. Two species of western Atlantic sciaenids were examined: weakfish Í‘Cynoscion regalis, Block and SchneiderÍ’ and spot Í‘Leiostomus xanthurus, LacepedeÍ’. These species differ in the anatomical relationship between the swim bladder and the inner ear. In weakfish, the swim bladder has a pair of anterior horns that terminate close to the ear, while there are no extensions of the swim bladder in spot. Thus, the swim bladder in spot terminates at a greater distance from the ear when compared to weakfish. With the use of the auditory brainstem response technique, Cynoscion regalis were found to detect frequencies up to 2000 Hz, while Leiostomus xanthurus detected up to 700 Hz. There were, however, no significant interspecific differences in auditory sensitivity for stimuli between 200 and 700 Hz. These data support the hypothesis that the swim bladder can potentially expand the frequency range of detection.
Journal of Neurophysiology, 2006
Eigenmannia, a genus of weakly electric fish, exhibits a specialized behavior known as the jammin... more Eigenmannia, a genus of weakly electric fish, exhibits a specialized behavior known as the jamming avoidance response (JAR). The JAR results in a categorical difference between Eigenmannia that are in groups of conspecifics and those that are alone. Fish in groups exhibit the JAR behavior and thereby experience ongoing, global synchronous 20- to 50-Hz electrosensory oscillations, whereas solitary fish do not. Although previous work has shown that these ongoing signals do not significantly degrade electrosensory behavior, these oscillations nevertheless elicit short-term synaptic depression in midbrain circuits. Because short-term synaptic depression can have profound effects on the transmission of information through synapses, we examined the differences in intracellularly recorded responses of midbrain neurons in awake, behaving fish to moving electrosensory images under electrosensory conditions that mimic solitary fish and fish in groups. In solitary conditions, moving objects el...
Patterns of saccular afferent innervation in sciaenids
Journal of Fish Biology, 2013
In this study, saccular afferent arborization patterns in Atlantic croaker Micropogonias undulatu... more In this study, saccular afferent arborization patterns in Atlantic croaker Micropogonias undulatus, red drum Sciaenops ocellatus and spot Leiostomus xanthurus were characterized. Leiostomus xanthurus showed the simplest configuration while M. undulatus displayed the most complex. In addition, hair-cell densities at sites sampled along the rostro-caudal axis of the saccular epithelia correlated with the observed patterns of arborization.
Journal of Comparative Physiology A, 2005
Wave-type weakly electric fish such as Eigenmannia produce continuous sinusoidal electric fields.... more Wave-type weakly electric fish such as Eigenmannia produce continuous sinusoidal electric fields. When conspecifics are in close proximity, interaction of these electric fields can produce deficits in electrosensory function. We examined a neural correlate of such jamming at the level of the midbrain. Previous results indicate that neurons in the dorsal layers of the torus semicircularis can (1) respond to jamming signals, (2) respond to moving electrosensory stimuli, and (3) receive convergent information from the four sensory maps of the electrosensory lateral line lobe (ELL). In this study we recorded the intracellular responses of both tuberous and ampullary neurons to moving objects. Robust Gaussian-shaped or sinusoidal responses with half-height durations between 55 ms and 581 ms were seen in both modalities. The addition of ongoing global signals with temporal-frequencies of 5 Hz attenuated the responses to the moving object by 5 dB or more. In contrast, the responses to the moving object were not attenuated by the addition of signals with temporal frequencies of 20 Hz or greater. This occurred in both the ampullary and tuberous systems, despite the fact that the ampullary afferents to the torus originate in a single ELL map whereas the tuberous afferents emerge from three maps.
Form and function in the unique inner ear of a teleost: The silver perch (Bairdiella chrysoura)
The Journal of Comparative Neurology, 2004
Members of the teleost family Sciaenidae show significant variation in inner ear and swim bladder... more Members of the teleost family Sciaenidae show significant variation in inner ear and swim bladder morphology as well as in the relationship between the swim bladder and the inner ear. In the silver perch (Bairdiella chrysoura), a Stellifer-group sciaenid, both the saccular and utricular otoliths are enlarged relative to those in other teleosts. Additionally, its swim bladder is two-chambered, and the anterior chamber surrounds the otic capsule and terminates lateral to the saccules. Structure and function of the auditory system of the silver perch were explored by using gross dissections, scanning electron microscopy, CT scan reconstruction, and auditory brainstem response approach. Several morphological specializations of the auditory system of the silver perch were found, including expansion of the utricular and lagenar otoliths, close proximity between the saccules and the utricles, deeply grooved sulci on the saccular otoliths, two-planar saccular sensory epithelia, and a unique orientation pattern of sensory hair cell ciliary bundles on the saccular sensory epithelium. It was determined that the silver perch can detect up to 4 kHz, with lowest auditory thresholds between 600 Hz and 1 kHz. Audition in the silver perch is comparable to that in the goldfish (Carassius auratus), a hearing "specialist." The morphological specializations of the inner ear and swim bladder of the silver perch may be linked to its enhanced hearing capabilities. The findings of this study support the proposal that sciaenids are excellent model species for investigating structure-function relations in the teleost auditory system.
Journal of Clinical Neuroscience, 2012
In zebrafish neuromast hair cells, the process of programmed cell death ototoxic damage is striki... more In zebrafish neuromast hair cells, the process of programmed cell death ototoxic damage is strikingly similar to that of degenerating hair cells of the mammalian organ of Corti. Therefore, in vivo zebrafish assays involving the lateral line have been developed for drug ototoxicity screening. This is accomplished by examination of canal neuromast morphology in treated larvae using fluorescent dyes. To-date however, physiological confirmation of lateral line dysfunction resulting from such ototoxins has not been reported in the scientific literature-neither for larval nor adult zebrafish. Here we describe a rapid, non-invasive far-field electrophysiological method for assessing lateral line function. We suggest that ototoxic and otoprotective agents identified in larval studies may be assessed using this tool in adult fish. In this way, potential drug candidates can be further screened en route to testing in mammalian models, before potential clinical trials begin.
Journal of Clinical Neuroscience, 2010
Pharmaceutical agents known to be toxic to the human auditory system also impair sensory hair cel... more Pharmaceutical agents known to be toxic to the human auditory system also impair sensory hair cells of teleosts, and this supports the use of fish models for the screening of such compounds. However, previous investigations have focused almost exclusively on anatomical changes after drug administration without assessing macro-level physiological effects. Using the goldfish (Carassius auratus), we demonstrate that the acquisition of auditory evoked potentials offers a rapid and non-invasive means for tracking ototoxin-induced shifts in auditory thresholds. Gentamicin (100 mg/mL) was the agent of choice as it is an extensively-studied human ototoxin. Significant shifts (p < 0.05) in hearing sensitivity were observed between 300 Hz and 600 Hz and these shifts depended on acoustic pressure, but not particle motion. This differential elevation of auditory thresholds may be caused by impairment of specific populations of auditory sensory hair cells.
Ethanol modifies zebrafish responses to abrupt changes in light intensity
Journal of Clinical Neuroscience, 2013
Zebrafish exhibit a preference for dark areas and this behavior has been used to characterize anx... more Zebrafish exhibit a preference for dark areas and this behavior has been used to characterize anxiety. Their responses to light may also be modified by ethanol. Using high-speed video recordings, we demonstrated that untreated animals were relatively more active immediately after a bright-dim transition compared to animals exposed to low dose ethanol (2%). Additionally, ethanol-treated larvae were more prone to initiating behavioral responses following abrupt changes of light intensity. In conclusion, the larval zebrafish is an excellent model for investigating locomotory kinetics as well as drugs with anxiolytic properties. High-speed video recordings of behavioral responses in this species are indeed very promising for high-throughput screening.
Journal of Applied Toxicology, 2010
In recent years, fish models have become popular for investigations of ototoxic agents. However, ... more In recent years, fish models have become popular for investigations of ototoxic agents. However, the vast majority of such studies have focused on anatomical changes in lateral line hair cells after drug adminitration. Using the goldfish (Carassius auratus), we confirm that the acquisition of auditory evoked potentials offers a rapid and non-invasive method for quantifying ototoxin-induced changes in hearing sensitivity. Gentamicin (100 mg ml-1) was the drug of choice as it is a well-studied human ototoxin. Auditory threshold elevation was observed between 300 and 600 Hz and was accompanied by significant reductions in hair cell ciliary bundle densities in specific regions of the utricle and saccule. The correlations between structure and function suggest that differential susceptibility of sensory hair cells to acute gentamicin treatment underlies the frequency-specific elevation of auditory thresholds. We propose that fish auditory systems should be used alongside the lateral line, for the assessment of ototoxicity in new-developed drugs.
Brain, Behavior and Evolution, 2001
Sciaenid fishes (Family Sciaenidae) could potentially serve as models for understanding the relat... more Sciaenid fishes (Family Sciaenidae) could potentially serve as models for understanding the relationship between structure and function in the teleost auditory system, as they show a broad range of variation in not only the structure of the ear but also in the relationship between the ear and swim bladder. In this study, scanning electron microscopy (SEM) was used to investigate inner ear ultrastructure of the Atlantic croaker (Micropogonias undulatus), spotted seatrout (Cynoscion nebulosus), kingfish (Menticirrhusamericanus) and spot (Leiostomus xanthurus). These species reflect the diversity of otolith and swim bladder morphology in sciaenids. The distribution of different hair cell bundle types, as well as hair cell orientation patterns on the saccular and lagenar maculae of these fishes were similar to one another. The rostral ends of the saccular sensory epithelia (maculae) were highly expanded in a dorsal-ventral direction in the Atlantic croaker and spotted seatrout as compar...
Unique Ear Structure of Silver Perch Bairdiella Chrysoura
Bioacoustics, 2002
... Am. Mus. Novit. 2428, 1-25. UNIQUE EAR STRUCTURE OF SILVER PERCH BAIRD/ELLA CHRYSOURA JOHN RA... more ... Am. Mus. Novit. 2428, 1-25. UNIQUE EAR STRUCTURE OF SILVER PERCH BAIRD/ELLA CHRYSOURA JOHN RAMCHARITAR Department of Biology, University of Maryland, College Park, MD 20742, USA. jramch@wam.umd.edu INTRODUCTION ...
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Papers by John Ramcharitar