1
|
Levic S. SK Current, Expressed During the Development and Regeneration of Chick Hair Cells, Contributes to the Patterning of Spontaneous Action Potentials. Front Cell Neurosci 2022; 15:766264. [PMID: 35069114 PMCID: PMC8770932 DOI: 10.3389/fncel.2021.766264] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/28/2021] [Accepted: 11/29/2021] [Indexed: 11/30/2022] Open
Abstract
Chick hair cells display calcium (Ca2+)-sensitive spontaneous action potentials during development and regeneration. The role of this activity is unclear but thought to be involved in establishing proper synaptic connections and tonotopic maps, both of which are instrumental to normal hearing. Using an electrophysiological approach, this work investigated the functional expression of Ca2+-sensitive potassium [IK(Ca)] currents and their role in spontaneous electrical activity in the developing and regenerating hair cells (HCs) in the chick basilar papilla. The main IK(Ca) in developing and regenerating chick HCs is an SK current, based on its sensitivity to apamin. Analysis of the functional expression of SK current showed that most dramatic changes occurred between E8 and E16. Specifically, there is a developmental downregulation of the SK current after E16. The SK current gating was very sensitive to the availability of intracellular Ca2+ but showed very little sensitivity to T-type voltage-gated Ca2+ channels, which are one of the hallmarks of developing and regenerating hair cells. Additionally, apamin reduced the frequency of spontaneous electrical activity in HCs, suggesting that SK current participates in patterning the spontaneous electrical activity of HCs.
Collapse
Affiliation(s)
- Snezana Levic
- Center for Neuroscience, University of California, Davis, Davis, CA, United States
- Sensory Neuroscience Research Group, School of Pharmacy and Biomolecular Sciences, University of Brighton, Brighton, United Kingdom
- Brighton and Sussex Medical School, University of Sussex, Brighton, United Kingdom
- *Correspondence: Snezana Levic,
| |
Collapse
|
2
|
McGee J, Nelson PB, Ponder JB, Marr J, Redig P, Walsh EJ. Auditory performance in bald eagles and red-tailed hawks: a comparative study of hearing in diurnal raptors. J Comp Physiol A Neuroethol Sens Neural Behav Physiol 2019; 205:793-811. [PMID: 31520117 DOI: 10.1007/s00359-019-01367-9] [Citation(s) in RCA: 6] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/03/2019] [Revised: 07/26/2019] [Accepted: 08/28/2019] [Indexed: 12/19/2022]
Abstract
Collision with wind turbines is a conservation concern for eagles with population abundance implications. The development of acoustic alerting technologies to deter eagles from entering hazardous air spaces is a potentially significant mitigation strategy to diminish associated morbidity and mortality risks. As a prelude to the engineering of deterrence technologies, auditory function was assessed in bald eagles (Haliaeetus leucocephalus), as well as in red-tailed hawks (Buteo jamaicensis). Auditory brainstem responses (ABRs) to a comprehensive battery of clicks and tone bursts varying in level and frequency were acquired to evaluate response thresholds, as well as suprathreshold response characteristics of wave I of the ABR, which represents the compound potential of the VIII cranial nerve. Sensitivity curves exhibited an asymmetric convex shape similar to those of other avian species, response latencies decreased exponentially with increasing stimulus level and response amplitudes grew with level in an orderly manner. Both species were responsive to a frequency band at least four octaves wide, with a most sensitive frequency of 2 kHz, and a high-frequency limit of approximately 5.7 kHz in bald eagles and 8 kHz in red-tailed hawks. Findings reported here provide a framework within which acoustic alerting signals might be developed.
Collapse
Affiliation(s)
- JoAnn McGee
- Department of Speech-Language-Hearing Sciences and the Center for Applied and Translational Sensory Science, University of Minnesota, 164 Pillsbury Dr. SE, Minneapolis, MN, 55455, USA.
| | - Peggy B Nelson
- Department of Speech-Language-Hearing Sciences and the Center for Applied and Translational Sensory Science, University of Minnesota, 164 Pillsbury Dr. SE, Minneapolis, MN, 55455, USA
| | - Julia B Ponder
- The Raptor Center, College of Veterinary Medicine, University of Minnesota, St. Paul, MN, 55108, USA
| | - Jeffrey Marr
- St. Anthony Falls Laboratory, University of Minnesota, Minneapolis, MN, 55414, USA
| | - Patrick Redig
- The Raptor Center, College of Veterinary Medicine, University of Minnesota, St. Paul, MN, 55108, USA
| | - Edward J Walsh
- Department of Speech-Language-Hearing Sciences and the Center for Applied and Translational Sensory Science, University of Minnesota, 164 Pillsbury Dr. SE, Minneapolis, MN, 55455, USA
| |
Collapse
|
3
|
Method for Dissecting the Auditory Epithelium (Basilar Papilla) in Developing Chick Embryos. Methods Mol Biol 2016. [PMID: 27259942 DOI: 10.1007/978-1-4939-3615-1_25] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register]
Abstract
Chickens are an invaluable model for exploring auditory physiology. Similar to humans, the chicken inner ear is morphologically and functionally close to maturity at the time of hatching. In contrast, chicks can regenerate hearing, an ability lost in all mammals, including humans. The extensive morphological, physiological, behavioral, and pharmacological data available, regarding normal development in the chicken auditory system, has driven the progress of the field. The basilar papilla is an attractive model system to study the developmental mechanisms of hearing. Here, we describe the dissection technique for isolating the basilar papilla in developing chick inner ear. We also provide detailed examples of physiological (patch clamping) experiments using this preparation.
Collapse
|
4
|
Corfield JR, Krilow JM, Vande Ligt MN, Iwaniuk AN. A quantitative morphological analysis of the inner ear of galliform birds. Hear Res 2013; 304:111-27. [DOI: 10.1016/j.heares.2013.07.004] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 04/26/2013] [Revised: 06/12/2013] [Accepted: 07/06/2013] [Indexed: 11/30/2022]
|
5
|
Origin and Development of Hair Cell Orientation in the Inner Ear. INSIGHTS FROM COMPARATIVE HEARING RESEARCH 2013. [DOI: 10.1007/2506_2013_28] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/12/2022]
|
6
|
Corfield JR, Kubke MF, Parsons S, Köppl C. Inner-ear morphology of the New Zealand kiwi (Apteryx mantelli) suggests high-frequency specialization. J Assoc Res Otolaryngol 2012; 13:629-39. [PMID: 22772440 DOI: 10.1007/s10162-012-0341-4] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/10/2012] [Accepted: 06/20/2012] [Indexed: 11/29/2022] Open
Abstract
The sensory systems of the New Zealand kiwi appear to be uniquely adapted to occupy a nocturnal ground-dwelling niche. In addition to well-developed tactile and olfactory systems, the auditory system shows specializations of the ear, which are maintained along the central nervous system. Here, we provide a detailed description of the auditory nerve, hair cells, and stereovillar bundle orientation of the hair cells in the North Island brown kiwi. The auditory nerve of the kiwi contained about 8,000 fibers. Using the number of hair cells and innervating nerve fibers to calculate a ratio of average innervation density showed that the afferent innervation ratio in kiwi was denser than in most other birds examined. The average diameters of cochlear afferent axons in kiwi showed the typical gradient across the tonotopic axis. The kiwi basilar papilla showed a clear differentiation of tall and short hair cells. The proportion of short hair cells was higher than in the emu and likely reflects a bias towards higher frequencies represented on the kiwi basilar papilla. The orientation of the stereovillar bundles in the kiwi basilar papilla showed a pattern similar to that in most other birds but was most similar to that of the emu. Overall, many features of the auditory nerve, hair cells, and stereovilli bundle orientation in the kiwi are typical of most birds examined. Some features of the kiwi auditory system do, however, support a high-frequency specialization, specifically the innervation density and generally small size of hair-cell somata, whereas others showed the presumed ancestral condition similar to that found in the emu.
Collapse
Affiliation(s)
- Jeremy R Corfield
- Department of Anatomy with Radiology, University of Auckland, Auckland, New Zealand.
| | | | | | | |
Collapse
|
7
|
Corfield J, Kubke MF, Parsons S, Wild JM, Köppl C. Evidence for an auditory fovea in the New Zealand kiwi (Apteryx mantelli). PLoS One 2011; 6:e23771. [PMID: 21887317 PMCID: PMC3161079 DOI: 10.1371/journal.pone.0023771] [Citation(s) in RCA: 24] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/01/2011] [Accepted: 07/25/2011] [Indexed: 11/18/2022] Open
Abstract
Kiwi are rare and strictly protected birds of iconic status in New Zealand. Yet, perhaps due to their unusual, nocturnal lifestyle, surprisingly little is known about their behaviour or physiology. In the present study, we exploited known correlations between morphology and physiology in the avian inner ear and brainstem to predict the frequency range of best hearing in the North Island brown kiwi. The mechanosensitive hair bundles of the sensory hair cells in the basilar papilla showed the typical change from tall bundles with few stereovilli to short bundles with many stereovilli along the apical-to-basal tonotopic axis. In contrast to most birds, however, the change was considerably less in the basal half of the epithelium. Dendritic lengths in the brainstem nucleus laminaris also showed the typical change along the tonotopic axis. However, as in the basilar papilla, the change was much less pronounced in the presumed high-frequency regions. Together, these morphological data suggest a fovea-like overrepresentation of a narrow high-frequency band in kiwi. Based on known correlations of hair-cell microanatomy and physiological responses in other birds, a specific prediction for the frequency representation along the basilar papilla of the kiwi was derived. The predicted overrepresentation of approximately 4-6 kHz matches potentially salient frequency bands of kiwi vocalisations and may thus be an adaptation to a nocturnal lifestyle in which auditory communication plays a dominant role.
Collapse
Affiliation(s)
- Jeremy Corfield
- Department of Anatomy with Radiology, University of Auckland, Auckland, New Zealand
- School of Biological Sciences, University of Auckland, Auckland, New Zealand
| | - M. Fabiana Kubke
- Department of Anatomy with Radiology, University of Auckland, Auckland, New Zealand
| | - Stuart Parsons
- School of Biological Sciences, University of Auckland, Auckland, New Zealand
| | - J. Martin Wild
- Department of Anatomy with Radiology, University of Auckland, Auckland, New Zealand
| | - Christine Köppl
- Institute for Biology and Environmental Sciences, and Research Center Neurosensory Science, Carl von Ossietzky University, Oldenburg, Germany
| |
Collapse
|
8
|
Auditory capabilities of birds in relation to the structural diversity of the basilar papilla. Hear Res 2011; 273:80-8. [DOI: 10.1016/j.heares.2010.01.009] [Citation(s) in RCA: 18] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 10/28/2009] [Revised: 01/18/2010] [Accepted: 01/22/2010] [Indexed: 11/18/2022]
|
9
|
Vergne AL, Pritz MB, Mathevon N. Acoustic communication in crocodilians: from behaviour to brain. Biol Rev Camb Philos Soc 2009; 84:391-411. [PMID: 19659884 DOI: 10.1111/j.1469-185x.2009.00079.x] [Citation(s) in RCA: 74] [Impact Index Per Article: 4.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/26/2022]
Abstract
Crocodilians and birds are the modern representatives of Phylum Archosauria. Although there have been recent advances in our understanding of the phylogeny and ecology of ancient archosaurs like dinosaurs, it still remains a challenge to obtain reliable information about their behaviour. The comparative study of birds and crocodiles represents one approach to this interesting problem. One of their shared behavioural features is the use of acoustic communication, especially in the context of parental care. Although considerable data are available for birds, information concerning crocodilians is limited. The aim of this review is to summarize current knowledge about acoustic communication in crocodilians, from sound production to hearing processes, and to stimulate research in this field. Juvenile crocodilians utter a variety of communication sounds that can be classified into various functional categories: (1) "hatching calls", solicit the parents at hatching and fine-tune hatching synchrony among siblings; (2) "contact calls", thought to maintain cohesion among juveniles; (3) "distress calls", induce parental protection; and (4) "threat and disturbance calls", which perhaps function in defence. Adult calls can likewise be classified as follows: (1) "bellows", emitted by both sexes and believed to function during courtship and territorial defence; (2) "maternal growls", might maintain cohesion among offspring; and (3) "hisses", may function in defence. However, further experiments are needed to identify the role of each call more accurately as well as systematic studies concerning the acoustic structure of vocalizations. The mechanism of sound production and its control are also poorly understood. No specialized vocal apparatus has been described in detail and the motor neural circuitry remains to be elucidated. The hearing capabilities of crocodilians appear to be adapted to sound detection in both air and water. The ear functional anatomy and the auditory sensitivity of these reptiles are similar in many respects to those of birds. The crocodilian nervous system likewise shares many features with that of birds, especially regarding the neuroanatomy of the auditory pathways. However, the functional anatomy of the telencephalic auditory areas is less well understood in crocodilians compared to birds.
Collapse
Affiliation(s)
- A L Vergne
- Université de Saint-Etienne, Ecologie & Neuro-Ethologie Sensorielles EA3988, Saint-Etienne, France.
| | | | | |
Collapse
|
10
|
Abstract
The sensory end organs of the inner ear of the lungfish, Protopterus, were examined using scanning and transmission electron microscopy. The utricle has a structure and hair cell orientation pattern that are typical for vertebrates, although the hair cells are unusually large. There are the typical three semicircular canals extending from the utricle, with the typical hair cell orientations, but the lateral canal sensory crista looks like the "hemicrista" of some amphibians and amniotes, lacking a saddle-shaped flare on one wall of the ampulla. Unlike most vertebrates that have the saccule and lagena as two separate pouches ventral to the utricle, the lungfish has a single large ventral pouch that contains a single large pasty otoconial mass. This mass covers two hair cell patches, each like a striola with prominent hair cell ciliary bundles, that are presumed to represent saccular and lagenar maculae. However, these two major sensory patches are not completely separate maculae because they lie within a less densely populated field of smaller hair cells, which forms an extrastriolar region that surrounds and fills the region between the two striolae of higher hair cell density. The more caudal lagenar striola is a vertically elongated stripe with hair cell orientation vectors facing antiparallel on either side of a midline drawn vertically along the macula, resembling the macula lagena of some bony fishes but not of tetrapods. The more rostral saccular striola is a curving band with hair cell orientation vectors facing away from its midline, but because this macula curves in three dimensions, the vectors at the rostral end of this striola are oriented mediolaterally, whereas the vectors on the caudal half of this striola are oriented dorsoventrally. The presence of a macula neglecta was confirmed near the posterior canal as a tiny single patch of a few dozen hair cells with all the cell orientations directed caudally. The ciliary bundles on the cells in the striolar-like regions of all of three otolithic organs average over 80 cilia, a number far greater than for any other fish studied to date. The features of the single sacculolagenar pouch with separate striolar-like regions, the cellular orientation in the otolith organs, and the large cells and ciliary bundles in Protopterus also were observed in specimens of the other extant lungfish genera, Lepidosiren and Neoceratodus.
Collapse
Affiliation(s)
- Christopher Platt
- Department of Biology, University of Maryland, College Park, Maryland 20742, USA
| | | | | |
Collapse
|
11
|
Eisen MD, Spassova M, Parsons TD. Large releasable pool of synaptic vesicles in chick cochlear hair cells. J Neurophysiol 2004; 91:2422-8. [PMID: 14749306 DOI: 10.1152/jn.01130.2003] [Citation(s) in RCA: 26] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
Hearing requires the hair cell synapse to maintain notable temporal fidelity (< or =1 ms) while sustaining neurotransmitter release for prolonged periods of time (minutes). Here we probed the properties and possible anatomical substrate of prolonged neurotransmitter release by using electrical measures of cell surface area as a proxy for neurotransmitter release to study hair cell exocytosis evoked by repetitive stimuli. We observed marked depression of exocytosis by chick tall hair cells. This exocytic depression cannot be explained by calcium current inactivation, presynaptic autoinhibition by metabotropic glutamate receptors, or postsynaptic receptor desensitization. Rather, cochlear hair cell exocytic depression resulted from the exhaustion of a functional vesicle pool. This releasable vesicle pool is large, totaling approximately 8,000 vesicles, and is nearly 10 times greater than the number of vesicles tethered to synaptic ribbons. Such a large functional pool suggests the recruitment of cytoplasmic vesicles to sustain exocytosis, important for maintaining prolonged, high rates of neural activity needed to encode sound.
Collapse
Affiliation(s)
- Marc D Eisen
- Department of Clinical Studies, New Bolton Center, University of Pennsylvania School of Veterinary Medicine, 382 West Street Road, Kennett Square, PA 19348, USA
| | | | | |
Collapse
|
12
|
Gleich O, Fischer FP, Köppl C, Manley GA. Hearing Organ Evolution and Specialization: Archosaurs. EVOLUTION OF THE VERTEBRATE AUDITORY SYSTEM 2004. [DOI: 10.1007/978-1-4419-8957-4_8] [Citation(s) in RCA: 23] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/06/2023]
|
13
|
Hossler FE, Olson KR, Musil G, McKamey MI. Ultrastructure and blood supply of the tegmentum vasculosum in the cochlea of the duckling. Hear Res 2002; 164:155-65. [PMID: 11950535 DOI: 10.1016/s0378-5955(01)00427-0] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
The tegmentum vasculosum of the duckling consists of a highly folded epithelium which extends over the dorsal and lateral walls of the cochlear duct, separating the scala media from the scala vestibuli. This epithelium consists of two distinct cell types, dark cells and light cells, and is well vascularized. The surface of the epithelium is formed by a mosaic of alternating dark and light cells. The goblet-shaped dark cells have an electron-dense, organelle-rich cytoplasm, and are expanded basally by extensive basolateral plasma membrane infoldings, within which are numerous mitochondria. Dark cells are isolated from each other and from the capillaries within the epithelium by intervening light cells. In contrast, columnar light cells exhibit an electron-lucent, organelle-poor cytoplasm and may extend from the underlying capillaries to the endolymphatic surface. Light cells contain abundant, coated endocytic vesicles on their apical surfaces and are bound, apically, to other light cells or to dark cells by tight junctions and desmosomes. Laterally, light cells are linked to each other either by complex, fluid-filled membrane interdigitations or by extensive gap junctions. Plasma membrane interdigitations and obvious, fluid-filled intercellular spaces characterize the lateral borders between light and dark cells. Vascular corrosion casting reveals the three-dimensional anatomy of the cochlear vasculature. A continuous arteriolar loop fed by anterior and posterior cochlear arterioles encircles the cochlear duct. The rich capillary beds of the tegmentum vasculosum are supplied by arching arterioles arising from this loop. These capillaries are the continuous type and are situated primarily within the core of the epithelium or along its border with the scala vestibuli. The structure and blood supply of the tegmentum vasculosum are characteristic of an epithelium involved in active transport.
Collapse
Affiliation(s)
- Fred E Hossler
- Department of Anatomy and Cell Biology, J.H. Quillen College of Medicine, Box 70582, East Tennessee State University, Johnson City 37614, USA.
| | | | | | | |
Collapse
|
14
|
Abstract
The sensory hair cells of the inner ear receive both afferent and efferent innervation. The efferent supply to the auditory organ has evolved in birds and mammals into a separate complex system, with several types of neurons of largely unknown function. In this study, the efferent axons in four different species of birds (chicken, starling, barn owl and emu) were examined anatomically. Total numbers of efferents supplying the cochlear duct (auditory basilar papilla and the vestibular lagenar macula) were determined; separate estimates of the efferents to the lagenar macula only were also derived and subtracted. The numbers for auditory efferents thus varied between 120 (chicken) and 1068 (barn owl). Considering the much larger numbers of hair cells in the basilar papilla, each efferent is predicted to branch extensively. However, pronounced species-specific differences as well as regional differences along the tonotopic gradient of the basilar papilla were documented. Myelinated and unmyelinated axons were found, with mean diameters of about 1 microm and about 0.5 microm, respectively. This suggests two basic populations of efferents, however, they did not appear to be distinguished sharply. Evidence is presented that some efferents lose their myelination at the transition from central oligodendrocyte to peripheral Schwann cell myelin. Finally, a comparison of the four bird species evaluated suggests that the efferent population with smaller, unmyelinated axons is the phylogenetically more primitive one. A new population probably arose in parallel with the evolution and differentiation of the specialized hair-cell type it innervates, the short hair cell.
Collapse
Affiliation(s)
- C Köppl
- Zoologie, Technische Universität München, Lichtenbergstrasse 4, 85747 Garching, Germany
| |
Collapse
|
15
|
Abstract
This paper is a comparative study of auditory-nerve morphology in birds. The chicken (Gallus gallus), the emu (Dromaius novaehollandiae) and the starling (Sturnus vulgaris) were chosen as unspecialised birds that have already been used in auditory research. The data are discussed in comparison to a similar earlier study on the barn owl, a bird with highly specialised hearing, in an attempt to separate general avian patterns from species specialisations. Average numbers of afferent fibres from 8775 (starling) to 12¿ omitted¿406 (chicken) were counted, excluding fibres to the lagenar macula. The number of fibres representing different frequency ranges showed broad maxima in the chicken and emu, corresponding to hearing ranges of best sensitivity and/or particular behavioural relevance. Mean axon diameters were around 2 microm in the chicken and starling, and around 3 microm in the emu. Virtually all auditory afferents were myelinated. The mean thickness of the myelin sheaths was between 0.33 microm (starling) and 0.4 microm (emu). There was a consistent pattern in the diameters of axons deriving from different regions. Axons from very basal, i.e. highest-frequency, parts of the basilar papilla were always the smallest. In the emu and the chicken, axons from the middle papillar regions were, in addition, larger than axons innervating apical regions.
Collapse
Affiliation(s)
- C Köppl
- Institut für Zoologie, Technische Universität München, Lichtenbergstrasse 4, 85747, Garching, Germany.
| | | | | | | |
Collapse
|
16
|
|
17
|
Köppl C, Gleich O, Schwabedissen G, Siegl E, Manley GA. Fine structure of the basilar papilla of the emu: implications for the evolution of avian hair-cell types. Hear Res 1998; 126:99-112. [PMID: 9872138 DOI: 10.1016/s0378-5955(98)00156-7] [Citation(s) in RCA: 20] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/25/2022]
Abstract
The morphology of the basilar papilla of the emu was investigated quantitatively with light and scanning electron microscopical techniques. The emu is a member of the Paleognathae, a group of flightless birds that represent the most primitive living avian species. The comparison of the emu papilla with that of other, more advanced birds provides insights into the evolution of the avian papilla. The morphology of the emu papilla is that of an unspecialised bird, but shows the full range of features previously shown to be typical for the avian basilar papilla. For example, the orientation of the hair cells' sensitive axes varied in characteristic fashion both along and across the papilla. Many of the quantitative details correlate well with the representation of predominantly low frequencies along the papilla. The most distinctive features were an unusually high density of hair cells and an unusual tallness of the hair-cell bodies. This suggests that the evolution of morphologically very short hair cells, which are a hallmark of avian papillae, is a recent development in evolution. The small degree of differentiation in hair-cell size contrasts with the observation that a significant number of hair cells in the emu lack afferent innervation. It is therefore suggested that the development of functionally different hair-cell types in birds preceded the differentiation into morphologically tall and short hair cells.
Collapse
Affiliation(s)
- C Köppl
- Institut für Zoologie der Technischen Universität München, Garching, Germany. Christine.
| | | | | | | | | |
Collapse
|
18
|
Abstract
The emu, being a member of the rather primitive bird group of the palaeognathid Ratitae, may reveal primitives features of the avian basilar papilla. There are, however, no qualitative differences with the papillae of other birds such as the chicken or the starling. There are only quantitative differences in the continuous morphological gradients (such as hair cell height, stereovillar height) from neural to abneural, and from the base to the apex of the papilla. Only few (about two in the emu) afferent terminals and on average one efferent fiber contact each hair cell. Along the abneural edge, there is a population of hair cells that lack afferent innervation (short hair cells), suggesting that their function must lie in the papilla itself. There is thus a general pattern in the structures of the avian basilar papilla. In detail, however, a number of primitive characters were observed in the emu, as compared to advanced birds such as the starling and the barn owl. The hair cells are very densely packed and comparatively tall (up to 40 microm in the apex). This anatomy correlates well with the good lower-frequency hearing (see Köppl and Manley, J. Acoust. Soc. Am. 101 (1997) 1574 1584). The afferent nerve fibers contacting the hair cells within the basilar papilla are rather thick, and there are a large number of afferent fibers that contact more than one hair cell. The zone of hair cells without afferent innervation (short hair cells) along the abneural edge of the basilar papilla is rather narrow in the emu.
Collapse
Affiliation(s)
- F P Fischer
- Institut für Zoologie, Technische Universität München, Garching, Germany.
| |
Collapse
|