The lagena (the third otolith endorgan in vertebrates)

In this review, the structure and functions of the lagena (the third otolith organ) in an evolutionary lineage of the vertebrates are described and discussed. The lagenar macula appears first in the posterior part of the sacculus of elasmobranchs; in these animals, the lagena is considered to be involved in the balance support (orientation with respect to the gravitation force). The lagena as a separate endorgan has been described in teleost fishes; in some species, the lagena is connected with the sacculus, while in other species the interrelations of these structures can be dissimilar. The lagena supplements the functions of the sacculus; in fishes (animals with no special organ of hearing), it is involved in discrimination of sound oscillations, identification of the gravitation vector, and orientation in the course of movements within the vertical plane. In amphibians, the lagena is localized in the posterior part of the sacculus, near the auditory structures; it performs mostly vestibular and (to a much lesser extent) auditory functions. In amniotes, the lagena was first separated from the sacculus; it is localized in the cochlear canal, distally with respect to the hearing organ. Information on the functions of the lagena in amniotes is rather limited and contradictory. Central projections of this organ have been examined practically only in birds. Lagenar afferents project to the vestibular nuclei and cerebellum, while some fibers come to the auditory nuclei of the medulla. The lagena in birds can be related to their navigation abilities (birds are supposed to be capable of orienting within the magnetic field of the Earth due to the magnetic properties of the lagenar otoconia; this structure can also provide detection of movements along the vertical axis. The close proximity between the otolithic and auditory endorgans in the cochlear canal of amniotes can be indicative of the functional significance of these interrelations. This aspect, however, remains at present undiscovered. In mammals (except Monotremata), there is no lagena as an independent endorgan. Neirofiziologiya/Neurophysiology, Vol. 40, No. 2, pp. 160–178, March–April, 2008.     

Radioautographic studies on the neurohypophysial projections of the supraoptic and paraventricular nuclei in the rat

Summary The distribution of labelled axonal pathways was studied after unilateral stereotaxic injection of ³H-leucine into either supraoptic (SON) or paraventricular nuclei (PVN). In addition to extrahypothalamic projections of both nuclei, the main efferents appeared to run towards the neurohypophysis, yet with a strikingly different pattern. At the neurohypophysial level, the SO-neurohypophysial tract crossed the inner layers of the median eminence (ME) before scattering in the neural lobe. The PV-neurohypophysial pathway, by contrast, provided an exclusive innervation to the external layer of the whole neurohypophysial organ, including the median eminence, infundibular stalk and neural lobe. The functional correlates of the clear-cut anatomical distinctness between the two magnocellular neurosecretory systems are discussed.     

Sensory projections of identified coxal hair sensilla of the scorpionHeterometrus fulvipes (Scorpionidae)

The topography of long hair sensilla on the coxae of walking legs and pedipalps of the scorpionHeterometrus fulvipes is described. Identified long hair sensilla are cobalt filled, and central projections of sensory fibres are reported for the first time in the suboesophageal ganglion of this scorpion. The afferent fibres arising from each long hair sensilla segregate into ventral, dorsomedial and dorsal tracts upon their entry into the suboesophageal ganglion. These transverse tracts bifurcate towards the middle of the leg neuromere and form three ipsilateral, plurisegrnental, longitudinal sensory pathways. Filling a pair of bilaterally distributed long hair sensilla shows bilaterally arranged longitudinal afferent tracts interconnected by distinct transverse commissures. Similar patterns of sensory projections are observed when filling homologous hairs on other legs and pedipalps. Numerous fine collaterals arise from the longitudinal sensory trancts that subdivide and end in small blebs presumed to be presynaptic endings. The dorsal and dorsomedial longitudinal tracts and their respective commissures are in close association with the dendritic arborisations of pedipalpal and leg motor neurons, suggesting direct contact between them. The probable functions of these multisegmental hair afferent pathways are discussed.     

Central projections of fibers in the auditory and tensor nerves of cicadas (Homoptera: Cicadidae)

Summary The auditory and tensor nerves of cicadas are mixed nerves containing both afferent and efferent elements. In 17-year cicadas, and in Okanagana rimosa, the auditory nerve contains afferents from body hairs, from the detensor tympani-chordotonal organ, and some 1300–1500 afferents from the hearing organ. Within the fused metathoracic-abdominal ganglionic complex the receptors from both the auditory and tensor nerves form a neuropilar structure that reveals the metameric organization of this complex. A few fibers run anteriorly, projecting into the meso and prothoracic ganglia. Within the ganglionic complex a division of auditory nerve afferents into a dense intermediate and a more diffuse ventral neuropile is observed. In addition, a dorsal motor neuropile is outlined by arborizations of the timbal motor neuron. This neuron is one of several efferent cell types associated with the auditory nerve, and there is an indication that several efferent fibers innervate the timbal muscle. There is anatomical evidence for a possible neuronal coupling between the bilaterally symmetrical large timbal motor neurons. In general, central projections from the auditory and tensor nerves support evidence of a structural layering within the CNS of insects.     

Intra‐ and Intersexual swim bladder dimorphisms in the plainfin midshipman fish (Porichthys notatus): Implications of swim bladder proximity to the inner ear for sound pressure detection

The plainfin midshipman fish, Porichthys notatus , is a nocturnal marine teleost that uses social acoustic signals for communication during the breeding season. Nesting type I males produce multiharmonic advertisement calls by contracting their swim bladder sonic muscles to attract females for courtship and spawning while subsequently attracting cuckholding type II males. Here, we report intra‐ and intersexual dimorphisms of the swim bladder in a vocal teleost fish and detail the swim bladder dimorphisms in the three sexual phenotypes (females, type I and II males) of plainfin midshipman fish. Micro‐computerized tomography revealed that females and type II males have prominent, horn‐like rostral swim bladder extensions that project toward the inner ear end organs (saccule, lagena, and utricle). The rostral swim bladder extensions were longer, and the distance between these swim bladder extensions and each inner‐ear end organ type was significantly shorter in both females and type II males compared to that in type I males. Our results revealed that the normalized swim bladder length of females and type II males was longer than that in type I males while there was no difference in normalized swim bladder width among the three sexual phenotypes. We predict that these intrasexual and intersexual differences in swim bladder morphology among midshipman sexual phenotypes will afford greater sound pressure sensitivity and higher frequency detection in females and type II males and facilitate the detection and localization of conspecifics in shallow water environments, like those in which midshipman breed and nest.     

A model for energy flow in the inner ear of the bullfrog (Rana catesbeiana)

We present a quantitative mathematical model that represents the main features of the bullfrog inner ear. Calculated responses based on this model predict the observed frequency separation between the amphibian papilla and basilar papilla responses. The origin of this separation can be traced to the effect of the contact membranes on the impedance of the respective paths. Additionally, we calculated the input impedance of the periotic canal and showed that at low frequencies it acts as a bypass for most of the energy entering the ear, shunting it away from the amphibian-basilar papilla complex. As this shunting decreases with increasing frequency, we propose that the periotic canal functions as a protection mechanism to prevent overload of the amphibian papilla and basilar papilla during ventilation and for quasi-static pressure equalization. Our model explains the main features of the empirical data obtained from direct measurement of the amphibian papilla and basilar papilla contact membranes reported in an accompanying paper (this issue). Accepted: 9 March 2000     

Regeneration of the visual system in gastropods (Mollusca)

Abstract. The topic of tissue and organ regeneration has been of interest to life scientists ever since the phenomenon was noticed. The reason for this is obvious: if one can learn what drives and controls regeneration, i.e., how lost or damaged structures can be replaced, one not only has a better chance to understand an animal's embryogenesis and evolutionary relationship with other taxa, but one would also be in a better position to treat organ loss or tissue damage in humans. In this context, the possible restitution of individual sensory neurons or nerve projections has been of special interest to us. We identified central visual projections in several gastropod species and found that: (1) projections are very extensive across the brain and (2) they have connections with other systems and organs (including, most likely, non-ocular skin photoreceptors) that may be involved in the integration of signals from different sensors. Investigations of afferent and efferent visual elements at a morphological level should help reveal the neuronal basis of a gastropod's behavioral reactions.     

Existence of manserin, a secretogranin II-derived neuropeptide, in the rat inner ear: relevance to modulation of auditory and vestibular system

Manserin is a 40-amino acid neuropeptide derived from rat brain. Manserin has been shown to distribute in the neuroendocrine system, such as the pituitary and adrenal glands, but it has been little studied in other organs. In this study, the authors examined localization of manserin in the inner ear of the adult Wistar rat using immunohistochemical analyses. Manserin immunoreactivity was detected in the neuronal terminals of the organ of Corti and type II spiral ganglion cells. In addition to being identified in the auditory system, manserin was detected at the synapses of the vestibular system, such as saccule, utricle, and semicircular canal. These results suggest that inner ear manserin may be involved in the function of peripheral auditory and vestibular systems.     

Bony labyrinth morphometry reveals hidden diversity in lungless salamanders (Family Plethodontidae): Structural correlates of ecology,development, and vision in the inner ear

Lungless salamanders (Family Plethodontidae) form a highly speciose group that has undergone spectacular adaptive radiation to colonize a multitude of habitats. Substantial morphological variation in the otic region coupled with great ecological diversity within this clade make plethodontids an excellent model for exploring the ecomorphology of the amphibian ear. We examined the influence of habitat, development, and vision on inner ear morphology in 52 plethodontid species. We collected traditional and 3D geometric morphometric measurements to characterize variation in size and shape of the otic endocast and peripheral structures of the salamander ear. Phylogenetic comparative analyses demonstrate structural convergence in the inner ear across ecologically similar species. Species that dwell in spatially complex microhabitats exhibit robust, highly curved semicircular canals suggesting enhanced vestibular sense, whereas species with reduced visual systems demonstrate reduced canal curvature indicative of relaxed selection on the vestibulo‐ocular reflex. Cave specialists show parallel enlargement of auditory‐associated structures. The morphological correlates of ecology among diverse species reveal underlying evidence of habitat specialization in the inner ear and suggest that there exists physiological variation in the function of the salamander ear even in the apparent absence of selective pressures on the auditory system to support acoustic behavior.     

The Lateral Hypothalamus Is Involved in the Pathway Mediating the Hypotensive Response to Cingulate Cortex-Cholinergic Stimulation

1. The injection of acetylcholine (ACh) into the medial prefrontal cortex (MPFC) caused marked hypotensive response in either unanesthetized or anesthetized rats.2. The present experiment was designed to investigate anatomical connections of the ACh injection site in the MPFC with putative autonomic-related brain nuclei, as well as their possible involvement in the mediation of the hypotensive response to ACh.3. For the above purpose, the bidirectional neuronal tracer biotinylated dextran amine (BDA) was injected into Cg1 and Cg3 areas, within the MPFC of male Wistar rats. Five days later the animals were sacrificed and brain slices were processed and analyzed to determine neuronal projections efferent from as well afferent to the MPFC.4. Neuronal staining was more prominent in regions ipsilateral to the BDA injection site. Prominent efferent projections of the MPFC were observed in the contralateral MPFC; ipsi- and contralateral amygdala and hypothalamus; ipsilateral septal area, diagonal band, and zona incerta.5. Similar but not equal patterns of neuronal labeling were observed when BDA injections were performed within the two adjacent MPFC areas. BDA injections centered in the ACh injection site in the Cg3 area caused strong labeling in the septal area and diagonal band as well as an overall hypothalamic labeling. Within the hypothalamus an intense cortical projection was observed in the lateral hypothalamus (LH). BDA injections into the Cg1 area caused a more evident labeling of the amygdaloid complex.6. Neuronal cell bodies were evident throughout the MPFC as well as in the sensory-motor cortex when BDA was injected into the LH, thus indicating a massive ipsilateral cortical projection from the Cg3 to the LH.7. Bilateral NMDA-induced lesions within the LH caused a significant attenuation of the depressor responses to ACh injection in the MPFC, whereas unilateral lesions were marginally effective. These results indicate the involvement of the LH in the mediation of the hypotensive response to ACh injection into the MPFC as well as the bilateral distribution of the hypotensive pathway.     

The directionality of the ear of the pigeon (Columba livia)

Summary The directionality of cochlear microphonic potentials in the azimuthal plane was investigated in the pigeon (Columba livia), using acoustic free-field stimulation (pure tones of 0.25–6 kHz).At high frequencies in the pigeon's hearing range (4–6 kHz), changing azimuth resulted in a maximum change of the cochlear microphonic amplitude by about 20 dB (SPL). The directionality decreased clearly with decreasing frequency.Acoustic blocking of the contralateral ear canal could reduce the directional sensitivity of the ipsilateral ear by maximally 8 dB. This indicates a significant sound transmission through the bird's interaural pathways. However, the magnitude of these effects compared to those obtained by sound diffraction (maximum > 15 dB) suggests that pressure gradients at the tympanic membrane are only of subordinate importance for the generation of directional cues.The comparison of interaural intensity differences with previous behavioral results confirms the hypothesis that interaural intensity difference is the primary directional cue of azimuthal sound localization in the high-frequency range (2–6 kHz).Abbreviations CM cochlear microphonic potential - IID interaural intensity difference - IID-MRA minimum resolvable angle calculated from interaural intensity difference - MRA minimum resolvable angle - OTD interaural ongoing time difference - RMS root mean square - SPL sound pressure level     

Retinal projections in the caecilian Ichthyophis kohtaoensis (Amphibia,Gymnophiona)

Summary The retinal projections of the caecilian Ichthyophis kohtaoensis were investigated by anterograde transport of HRP. The optic tract forms two bundles in the diencephalon, a narrow medial bundle in the optic tectum, and a basal optic tract consisting of few fibres. Terminal fields are in the thalamus, pretectum, tectum, and as a circum-scribed basal optic neuropile in the tegmentum. Thalamic, pretectal and tectal projections are contralateral as well as ipsilateral. The reduced but existing visual projection corresponds to a reduced but existing visually guided behaviour.     

A Golgi study of the isthmic nuclei in the pigeon (Columba Iivia)

Summary The isthmic nuclei of the pigeon were studied with the use of three different Golgi techniques. The nucleus isthmo-opticus (IO) consists of a single cell type in which all dendrites of one neuron take the same direction and ramify at identical distances from the perikaryon to form dense dendritic arborizations. The cell bodies of the IO neurons form two parallel layers. The dendrites of these neurons always extend to the area between the two layers so that the dendritic arborizations of opposite neurons overlap. A model of the cellular organization of the IO was constructed based upon these morphological characteristics. The neurons of the n. isthmi/pars parvocellularis (Ipc) have oval perikarya and long, smooth, infrequently branching dendrites. All neurons except those at the borders of the nucleus show the same dorsoventral orientation in their dendritic arborizations and together with their afferents seem to have a columnar organization. The dendrites of the neurons located at the margin of the nucleus ramify within the Ipc along its border. The n. semilunaris (Slu) consists of neurons with round somata that have on an average three dendrites with small spines. The axons leave the nucleus from the medial side and join the lemniscus lateralis. The neurons of the n. isthmi/pars magnocellularis (Imc) comprise a generalized isodendritic type resembling the cells of the reticular formation. Axons from the tectum penetrate the nucleus, making numerous en-passant contacts with several neurons.     

Central projections of labellar taste hairs in the blowfly,Phormia regina Meigen

Summary We have traced the central projections of the receptor neurons associated with each of the eleven largest taste hairs on the labellum of the blowfly, Phormia regina (Meigen), by staining them with cobaltous lysine. The eleven hairs fall into three groups which reflect their peripheral locations and their branching patterns in the subesophageal ganglion. Group 1, consisting of the anterior hairs (numbers 1 and 2) and Group 3, consisting of the posterior hairs (numbers 9–11) project bilaterally, while Group 2, consisting of the middle hairs (numbers 3–8) projects primarily ipsilaterally. The central projections of the hairs within a single group are similar. Each hair houses four chemoreceptors, which have differing chemical sensitivities and behavioral roles, and one mechanoreceptor. In some cases, there were indications that the different cells within a single hair have different central branching patterns. For some hairs, however, it was clear that a single central branching region and pattern was shared by more than one receptor cell. We failed to find either a continuous somatotopic representation of a hair's position on the periphery, or an anatomical segregation of receptors coding for different modalities. Behavioral experiments indicate that the fly is informed both of the identity of the hair stimulated and of the chemical nature of the stimulus. Our results suggest that this information is not represented on a gross anatomical level.     

An in vitro mouse model of congenital cytomegalovirus‐induced pathogenesis of the inner ear cochlea

Congenital human cytomegalovirus (CMV) infection is the leading nongenetic etiology of sensorineural hearing loss (SNHL) at birth and prelingual SNHL not expressed at birth. The paucity of temporal bone autopsy specimens from infants with congenital CMV infection has hindered the critical correlation of histopathology with pathogenesis. Here, we present an in vitro embryonic mouse model of CMV‐infected cochleas that mimics the human sites of viral infection and associated pathology. There is a striking dysplasia/hyperplasia in mouse CMV‐infected cochlear epithelium and mesenchyme, including organ of Corti hair and supporting cells and stria vascularis. This is concomitant with significant dysregulation of p19, p21, p27, and Pcna gene expression, as well as proliferating cell nuclear antigen (PCNA) protein expression. Other pathologies similar to those arising from known deafness gene mutations include downregulation of KCNQ1 protein expression in the stria vascularis, as well as hypoplastic and dysmorphic melanocytes. Thus, this model provides a relevant and reliable platform within which the detailed cell and molecular biology of CMV‐induced deafness may be studied. Birth Defects Research (Part A), 2013. © 2012 Wiley Periodicals, Inc.     

Central nervous projections of mechanoreceptors in the spider Cupiennius salei Keys.

Summary The basic organization of sensory projections in the suboesophageal central nervous system of a spider (Cupiennius salei Keys.) was analyzed with anterograde cobalt fills and a modified Golgi rapid method. The projections of three lyriform slit sense organs and of tactile hairs located proximally on the legs are described and related to central nerve tracts. There are five main longitudinal sensory tracts in the central region of the suboesophageal nervous mass arranged one above the other. Whereas the three dorsal ones contain fibers from the lyriform organs, the two ventral ones contain axons from the hair receptors. Axons from all three lyriform organs have typical shapes and widely arborizing ipsilateral intersegmental branches and a few contralateral ones. The terminal branches of the afferent projections from identical lyriform organs on each leg form characteristic longitudinal pathways, typical of each organ: U-shaped, O-shaped, or two parallel bundles. The terminations of the hair sensilla are ipsilateral and intersegmental. Two large bilaterally arranged longitudinal sensory association tracts receive inputs from all legs including the dense arborizations from tactile hairs, lyriform organs, and other sense organs. These tracts may serve as important integrating neuropils of the suboesophageal central nervous system.     

Immunohistochemical localization of two otolith matrix proteins in the otolith and inner ear of the rainbow trout,<Emphasis Type="Italic"> Oncorhynchus mykiss</Emphasis>: comparative aspects between the adult inner ear and embryonic otocysts

The fish otolith consists mainly of calcium carbonate and organic matrices, the latter of which may play important roles in the process of otolith formation. We previously identified two otolith matrix proteins, named otolith matrix protein-1 (OMP-1) and otolin-1, from the rainbow trout, Oncorhynchus mykiss, and the chum salmon, O. keta. In this study, recombinant proteins corresponding to OMP-1 and otolin-1 were synthesized using yeast and bacterial expression systems, respectively, to produce specific antibodies against each protein. Immunohistochemical analysis using these antisera revealed that in the otoliths of adult fish, OMP-1 and otolin-1 were colocalized along the daily rings possibly formed by alternate deposition of calcium carbonate and organic matrices. In the adult inner ear, OMP-1 was produced at most of the saccular epithelium, while otolin-1 was produced at a limited part of cylindrical cells located at the marginal zone of the sensory epithelium. In the embryonic inner ear, these proteins had already existed in the otolith primordia when calcification had commenced. In addition, otolin-1 was localized in the fibrous materials connecting otolith primordia and sensory epithelium at this stage. These results indicate that these proteins are required as essential components for otolith formation and calcification.     

中华稻蝗全消化道内壁显微结构观察

本文采用扫描仪和扫描电镜对中华稻蝗消化道内壁的细微结构进行了系统观察和研究。结果表明,中华稻蝗食道内壁由纵行脊组成,前端有齿。嗉囊包括两段,前段的一个小的膨大部分,由V-形区和两侧的V-形脊组成,只在前端内壁有齿;后段为一个大的膨大部分,由柳叶脊、扇形脊和不规则脊组成,脊的上缘有齿。前肠内壁的齿主要为单生齿,除贲门瓣上齿的齿尖指向前方外,全部齿的齿尖指向后方。后肠的前端为12个幽门瓣,内壁有齿。回肠和结肠由6条纵行脊组成,结肠内壁有齿。直肠的齿在除直肠垫外的直肠内壁上。后肠的齿主要为丛生齿,后肠除直肠内壁齿的齿尖指向附着环外,全部齿的齿尖指向后方。根据我们的观察,对前肠提出了新的分区。     

Sparc (Osteonectin) functions in morphogenesis of the pharyngeal skeleton and inner ear

Sparc (Osteonectin), a matricellular glycoprotein expressed by many differentiated cells, is a major non-collagenous constituent of vertebrate bones. Recent studies indicate that Sparc expression appears early in development, although its function and regulation during embryogenesis are largely unknown. We cloned zebrafish sparc and investigated its role during development, using a mo rpholino antisense oligonucleotide-based knockdown approach. Consistent with its strong expression in the otic vesicle and developing pharyngeal cartilages, knockdown of Sparc function resulted in specific inner ear and cartilage defects that are highlighted by changes in gene expression, morphology and behavior. We rescued the knockdown phenotypes by co-injecting sparc mRNA, providing evidence that the knockdown phenotype is due specifically to impairment of Sparc function. A comparison of the phenotypes of Sparc knockdown and known zebrafish mutants with similar defects places Sparc downstream of sox9 in the genetic network that regulates development of the pharyngeal skeleton and inner ear of vertebrates.     

Retinofugal and retinopetal projections in the teleost Channa micropeltes (Channiformes)

Summary Retinofugal and retinopetal projections were investigated in the teleost fish Channa micropeltes (Channiformes) by means of the cobaltous lysine and horseradish peroxidase (HRP) tracing techniques. Retinofugal fibers cross completely in the optic chiasma. A conspicious lamination is present in those parts of the optic tract that give rise to the marginal branches of the optic tract. This layering of optic fibers continues in the marginal branches to mesencephalic levels. Retinal projections to the preoptic and hypothalamic regions are sparse; they are more pronounced in the area of pretectal nuclei. The medial pretectal complex and the cortical pretectal nucleus are more fully differentiated than in other teleostean species. Further targets include the thalamus and the optic tectum. The course of major optic sub-tracts and smaller fascicles is described. Retinopetal neurons are located contralaterally in a rostral and a caudal part of the nucleus olfactoretinalis, and in a circumscribed nucleus thalamoretinalis. The present findings are compared with reports on other teleost species.