A nitrergic projection from the superior olivary complex to the inferior colliculus of the rat

The present study was conducted to test whether the ascending auditory projection from the superior olivary complex (SOC) of the brainstem to the inferior colliculus (IC) may use nitric oxide (NO) as a neuroactive compound. We identified olivo-collicular projection neurons in subnuclei of the SOC by retrograde neuronal tracing with Fluoro-Gold (FG) injected into the central nucleus of the IC. Sections containing retrograde labelled neurons were subjected to immunohistochemical incubation in an antiserum directed against the enzyme responsible for NO production in nerve cells, neuronal NO synthase (nNOS). The analysis showed that FG-containing neurons as well as nNOS-immunoreactive neurons were present in the lateral superior olive (LSO), superior paraolivary nucleus (SPO), ventral nucleus of the trapezoid body (VNTB), medial superior olive (MSO) and in dorsal and ventral periolivary regions to different amounts. However, only in the LSO, SPO and VNTB double-labelled neurons were found. They made up to less than 10% of all nNOS neurons in the SOC. Considering that only about 5% of the nNOS cells in the SOC are olivocochlear neurons [Riemann and Reuss, 1999], it is still open whether the majority of nitrergic neurons of the SOC project to other sites or whether they rather have intrinsic actions in providing NO to the SOC.     

Immunoreactivity to calcitonin gene-related peptide in the superior olivary complex and cochlea of cat and rat

In both cat and rat, the cells of origin, axons, and terminals of the lateral olivocochlear system exhibit immunoreactivity to antisera to calcitonin gene-related peptide (CGRP). In the cat, immunoreactive neurons in the brainstem are located in the hilus of the lateral superior olivary nucleus and around its margins. In the rat, immunoreactive neurons are located within the lateral superior olivary nucleus proper. In both species, immunoreactivity in the cochlear duct is limited to the region beneath the inner hair cells. Immunoreactive axons in the cochlear nucleus could not be traced to their source but may arise as collaterals of the lateral olivocochlear system. No other components of the brainstem auditory system react to any extent with the antisera.     

Cytoarchitecture of the human superior olivary complex: medial and lateral superior olive

The superior olivary complex is a group of brainstem nuclei involved in hearing and includes the medial superior olive (MSO) and the lateral superior olive (LSO), surrounded by periolivary cell groups. The structure and functional roles of the MSO and LSO have been the subject of many investigations in laboratory animals and it has largely been assumed that these findings are directly transferable to humans. However, little is known conclusively regarding the detailed organization of the human superior olivary complex. The goal of this study is to provide a detailed analysis of the cytoarchitecture of the human MSO and LSO. Results from the examination of eight human brainstems confirm the existence of a conserved MSO and provide evidence of a prominent and highly ordered LSO. Unbiased stereological estimates of neuronal number indicate approximately 15,500 neurons in the MSO and 5600 neurons in the LSO. Additionally, a three-dimensional model of the MSO and LSO was constructed and provides evidence that the human LSO is composed of medial and lateral segments. Finally, an analysis of neuronal morphology, in Nissl stained and Golgi impregnated tissue, provides evidence of multiple neuronal classes within each nucleus and further that these neurons demonstrate a precise geometric arrangement (depending on the nucleus) that is suggestive of isofrequency laminae.     

The efferent cochlear projections of the superior olivary complex in the mustached bat

Following the placement of horseradish peroxidase in the scala tympani, labeled neurons were found in the ipsilateral interstitial nucleus (INT) and throughout the ipsilateral and contralateral dorsomedial periolivary nuclei (DMPO). The neurons in the INT were morphologically distinct from those in the DMPO. The INT neurons formed a thin shell over the lateral superior olivary nucleus (LSO) and their dendrites extended into the body and hilar region. The DMPO neurons had long, tapering dendrites that extended in every direction. Data indicate that the crossed fibers in the floor of the ventricle arise entirely from the DMPO while uncrossed olivocochlear fibers originate in the INT and DMPO. It was estimated that 75% of the efferent fibers arise from the INT and 25% from the DMPO. Approximately 70% of the efferent neurons in each DMPO project to the contralateral cochlea via the crossed olivocochlear bundle. The number of olivocochlear neurons associated with each ear was determined to be approximately 1585. This number is similar to that found in cats and guinea pigs, but the number of neurons per unit length of the basilar membrane is considerably higher in the mustached bat than in other species examined to date. The compact, restricted locations of the neurons in the INT and DMPO in the mustached bat are different from those described for most other mammals and the arrangement in the mustached bat offers advantages over other species for future anatomical and physiological studies.     

逆行荧光标记观察猫上橄榄复合体向内耳的投射

Objective To investigate the distribution and projective feature of cat olivocochlear neurons. Methods Eleven adult cats were divided into two groups randomly. The experimental group of eight cats was injected of I% cholera toxin B (CTB) to the left cochlea, while injected of 5% fluoro gold (FG) to the right cochlea. The control group of three cats was injected of saline to bilateral cochlea. After a survival time of 7 days, serial frozen sections were cut in the cat brainstem. All the sections were processed by immunofluoreseent procedure for CTB and FG, and the labeled olivocochlear neurons were observed byfluorescent microscope. Results In the experimental group, the mean total of olivocochlear neurons labeled by CTB and FG was 3210 ± 168, including lateral olivocochlear neurons (LOC, 2298 ± 120) and medial olivocochlear neurons (MOC,913 ± 64). The labeled neurons were divided into three different types according to their feature of projection: neurons which only projected to the ipsilateral cochlea, neurons which only projected to the contralateral cochlea, and double-labeled neurons which projected both to the ipsilateral and contralateral cochlea, but the double-labeled neurons comprised 3.9% and 15. 1% in the LOC and MOC system respectively. No labeled neurons were found in the control group. Conclusions There are three types of neurons in the cat olivocochlear system. The neurons which projected to the bilateral cochlea may distribute both in the LOC and MOC system.     

逆行荧光标记观察猫上橄榄复合体向内耳的投射

Objective To investigate the distribution and projective feature of cat olivocochlear neurons. Methods Eleven adult cats were divided into two groups randomly. The experimental group of eight cats was injected of I% cholera toxin B (CTB) to the left cochlea, while injected of 5% fluoro gold (FG) to the right cochlea. The control group of three cats was injected of saline to bilateral cochlea. After a survival time of 7 days, serial frozen sections were cut in the cat brainstem. All the sections were processed by immunofluoreseent procedure for CTB and FG, and the labeled olivocochlear neurons were observed byfluorescent microscope. Results In the experimental group, the mean total of olivocochlear neurons labeled by CTB and FG was 3210 ± 168, including lateral olivocochlear neurons (LOC, 2298 ± 120) and medial olivocochlear neurons (MOC,913 ± 64). The labeled neurons were divided into three different types according to their feature of projection: neurons which only projected to the ipsilateral cochlea, neurons which only projected to the contralateral cochlea, and double-labeled neurons which projected both to the ipsilateral and contralateral cochlea, but the double-labeled neurons comprised 3.9% and 15. 1% in the LOC and MOC system respectively. No labeled neurons were found in the control group. Conclusions There are three types of neurons in the cat olivocochlear system. The neurons which projected to the bilateral cochlea may distribute both in the LOC and MOC system.     

逆行荧光标记观察猫上橄榄复合体向内耳的投射

Objective To investigate the distribution and projective feature of cat olivocochlear neurons. Methods Eleven adult cats were divided into two groups randomly. The experimental group of eight cats was injected of I% cholera toxin B (CTB) to the left cochlea, while injected of 5% fluoro gold (FG) to the right cochlea. The control group of three cats was injected of saline to bilateral cochlea. After a survival time of 7 days, serial frozen sections were cut in the cat brainstem. All the sections were processed by immunofluoreseent procedure for CTB and FG, and the labeled olivocochlear neurons were observed byfluorescent microscope. Results In the experimental group, the mean total of olivocochlear neurons labeled by CTB and FG was 3210 ± 168, including lateral olivocochlear neurons (LOC, 2298 ± 120) and medial olivocochlear neurons (MOC,913 ± 64). The labeled neurons were divided into three different types according to their feature of projection: neurons which only projected to the ipsilateral cochlea, neurons which only projected to the contralateral cochlea, and double-labeled neurons which projected both to the ipsilateral and contralateral cochlea, but the double-labeled neurons comprised 3.9% and 15. 1% in the LOC and MOC system respectively. No labeled neurons were found in the control group. Conclusions There are three types of neurons in the cat olivocochlear system. The neurons which projected to the bilateral cochlea may distribute both in the LOC and MOC system.     

逆行荧光标记观察猫上橄榄复合体向内耳的投射

Objective To investigate the distribution and projective feature of cat olivocochlear neurons. Methods Eleven adult cats were divided into two groups randomly. The experimental group of eight cats was injected of I% cholera toxin B (CTB) to the left cochlea, while injected of 5% fluoro gold (FG) to the right cochlea. The control group of three cats was injected of saline to bilateral cochlea. After a survival time of 7 days, serial frozen sections were cut in the cat brainstem. All the sections were processed by immunofluoreseent procedure for CTB and FG, and the labeled olivocochlear neurons were observed byfluorescent microscope. Results In the experimental group, the mean total of olivocochlear neurons labeled by CTB and FG was 3210 ± 168, including lateral olivocochlear neurons (LOC, 2298 ± 120) and medial olivocochlear neurons (MOC,913 ± 64). The labeled neurons were divided into three different types according to their feature of projection: neurons which only projected to the ipsilateral cochlea, neurons which only projected to the contralateral cochlea, and double-labeled neurons which projected both to the ipsilateral and contralateral cochlea, but the double-labeled neurons comprised 3.9% and 15. 1% in the LOC and MOC system respectively. No labeled neurons were found in the control group. Conclusions There are three types of neurons in the cat olivocochlear system. The neurons which projected to the bilateral cochlea may distribute both in the LOC and MOC system.     

逆行荧光标记观察猫上橄榄复合体向内耳的投射

Objective To investigate the distribution and projective feature of cat olivocochlear neurons. Methods Eleven adult cats were divided into two groups randomly. The experimental group of eight cats was injected of I% cholera toxin B (CTB) to the left cochlea, while injected of 5% fluoro gold (FG) to the right cochlea. The control group of three cats was injected of saline to bilateral cochlea. After a survival time of 7 days, serial frozen sections were cut in the cat brainstem. All the sections were processed by immunofluoreseent procedure for CTB and FG, and the labeled olivocochlear neurons were observed byfluorescent microscope. Results In the experimental group, the mean total of olivocochlear neurons labeled by CTB and FG was 3210 ± 168, including lateral olivocochlear neurons (LOC, 2298 ± 120) and medial olivocochlear neurons (MOC,913 ± 64). The labeled neurons were divided into three different types according to their feature of projection: neurons which only projected to the ipsilateral cochlea, neurons which only projected to the contralateral cochlea, and double-labeled neurons which projected both to the ipsilateral and contralateral cochlea, but the double-labeled neurons comprised 3.9% and 15. 1% in the LOC and MOC system respectively. No labeled neurons were found in the control group. Conclusions There are three types of neurons in the cat olivocochlear system. The neurons which projected to the bilateral cochlea may distribute both in the LOC and MOC system.     

逆行荧光标记观察猫上橄榄复合体向内耳的投射

Objective To investigate the distribution and projective feature of cat olivocochlear neurons. Methods Eleven adult cats were divided into two groups randomly. The experimental group of eight cats was injected of I% cholera toxin B (CTB) to the left cochlea, while injected of 5% fluoro gold (FG) to the right cochlea. The control group of three cats was injected of saline to bilateral cochlea. After a survival time of 7 days, serial frozen sections were cut in the cat brainstem. All the sections were processed by immunofluoreseent procedure for CTB and FG, and the labeled olivocochlear neurons were observed byfluorescent microscope. Results In the experimental group, the mean total of olivocochlear neurons labeled by CTB and FG was 3210 ± 168, including lateral olivocochlear neurons (LOC, 2298 ± 120) and medial olivocochlear neurons (MOC,913 ± 64). The labeled neurons were divided into three different types according to their feature of projection: neurons which only projected to the ipsilateral cochlea, neurons which only projected to the contralateral cochlea, and double-labeled neurons which projected both to the ipsilateral and contralateral cochlea, but the double-labeled neurons comprised 3.9% and 15. 1% in the LOC and MOC system respectively. No labeled neurons were found in the control group. Conclusions There are three types of neurons in the cat olivocochlear system. The neurons which projected to the bilateral cochlea may distribute both in the LOC and MOC system.     

逆行荧光标记观察猫上橄榄复合体向内耳的投射

目的 探讨猫橄榄耳蜗神经元的分布和向内耳的投射特征.方法 11只成年猫随机分为两组,实验组8只,左侧耳蜗鼓阶内注射1%霍乱毒素B亚单位,右侧耳蜗鼓阶注射5%荧光金,对照组3只,双侧耳蜗均注射生理盐水.动物饲养7 d后处死,脑干连续冰冻切片,免疫荧光处理,荧光显微镜观察被标记的橄榄耳蜗神经元.结果 实验组每只动物被霍乱毒素B亚单位和荧光金标记的橄榄耳蜗神经元平均总数为(3210±168)个,分为外侧橄榄耳蜗神经元[(2298±120)个]和内侧橄榄耳蜗神经元[(913±64)个].根据投射特征可将被标记的神经元分为三种不同类型:只投射到同侧耳蜗的神经元,只投射到对侧耳蜗的神经元,既向同侧又向对侧耳蜗投射的双标记神经元,其中双标记神经元在外侧橄榄耳蜗神经元和内侧橄榄耳蜗神经元中分别占3.9%和15.1%.对照组未观察到被标记的檄榄耳蜗神经元.结论猫的橄榄耳蜗系统中存在三种不同投射特征的神经元,其中双侧投射的神经元在外侧橄榄耳蜗神经元和内侧橄榄耳蜗神经元中均有分布.     

逆行荧光标记观察猫上橄榄复合体向内耳的投射

Objective To investigate the distribution and projective feature of cat olivocochlear neurons. Methods Eleven adult cats were divided into two groups randomly. The experimental group of eight cats was injected of I% cholera toxin B (CTB) to the left cochlea, while injected of 5% fluoro gold (FG) to the right cochlea. The control group of three cats was injected of saline to bilateral cochlea. After a survival time of 7 days, serial frozen sections were cut in the cat brainstem. All the sections were processed by immunofluoreseent procedure for CTB and FG, and the labeled olivocochlear neurons were observed byfluorescent microscope. Results In the experimental group, the mean total of olivocochlear neurons labeled by CTB and FG was 3210 ± 168, including lateral olivocochlear neurons (LOC, 2298 ± 120) and medial olivocochlear neurons (MOC,913 ± 64). The labeled neurons were divided into three different types according to their feature of projection: neurons which only projected to the ipsilateral cochlea, neurons which only projected to the contralateral cochlea, and double-labeled neurons which projected both to the ipsilateral and contralateral cochlea, but the double-labeled neurons comprised 3.9% and 15. 1% in the LOC and MOC system respectively. No labeled neurons were found in the control group. Conclusions There are three types of neurons in the cat olivocochlear system. The neurons which projected to the bilateral cochlea may distribute both in the LOC and MOC system.     

逆行荧光标记观察猫上橄榄复合体向内耳的投射

Objective To investigate the distribution and projective feature of cat olivocochlear neurons. Methods Eleven adult cats were divided into two groups randomly. The experimental group of eight cats was injected of I% cholera toxin B (CTB) to the left cochlea, while injected of 5% fluoro gold (FG) to the right cochlea. The control group of three cats was injected of saline to bilateral cochlea. After a survival time of 7 days, serial frozen sections were cut in the cat brainstem. All the sections were processed by immunofluoreseent procedure for CTB and FG, and the labeled olivocochlear neurons were observed byfluorescent microscope. Results In the experimental group, the mean total of olivocochlear neurons labeled by CTB and FG was 3210 ± 168, including lateral olivocochlear neurons (LOC, 2298 ± 120) and medial olivocochlear neurons (MOC,913 ± 64). The labeled neurons were divided into three different types according to their feature of projection: neurons which only projected to the ipsilateral cochlea, neurons which only projected to the contralateral cochlea, and double-labeled neurons which projected both to the ipsilateral and contralateral cochlea, but the double-labeled neurons comprised 3.9% and 15. 1% in the LOC and MOC system respectively. No labeled neurons were found in the control group. Conclusions There are three types of neurons in the cat olivocochlear system. The neurons which projected to the bilateral cochlea may distribute both in the LOC and MOC system.     

逆行荧光标记观察猫上橄榄复合体向内耳的投射

Objective To investigate the distribution and projective feature of cat olivocochlear neurons. Methods Eleven adult cats were divided into two groups randomly. The experimental group of eight cats was injected of I% cholera toxin B (CTB) to the left cochlea, while injected of 5% fluoro gold (FG) to the right cochlea. The control group of three cats was injected of saline to bilateral cochlea. After a survival time of 7 days, serial frozen sections were cut in the cat brainstem. All the sections were processed by immunofluoreseent procedure for CTB and FG, and the labeled olivocochlear neurons were observed byfluorescent microscope. Results In the experimental group, the mean total of olivocochlear neurons labeled by CTB and FG was 3210 ± 168, including lateral olivocochlear neurons (LOC, 2298 ± 120) and medial olivocochlear neurons (MOC,913 ± 64). The labeled neurons were divided into three different types according to their feature of projection: neurons which only projected to the ipsilateral cochlea, neurons which only projected to the contralateral cochlea, and double-labeled neurons which projected both to the ipsilateral and contralateral cochlea, but the double-labeled neurons comprised 3.9% and 15. 1% in the LOC and MOC system respectively. No labeled neurons were found in the control group. Conclusions There are three types of neurons in the cat olivocochlear system. The neurons which projected to the bilateral cochlea may distribute both in the LOC and MOC system.     

逆行荧光标记观察猫上橄榄复合体向内耳的投射

Objective To investigate the distribution and projective feature of cat olivocochlear neurons. Methods Eleven adult cats were divided into two groups randomly. The experimental group of eight cats was injected of I% cholera toxin B (CTB) to the left cochlea, while injected of 5% fluoro gold (FG) to the right cochlea. The control group of three cats was injected of saline to bilateral cochlea. After a survival time of 7 days, serial frozen sections were cut in the cat brainstem. All the sections were processed by immunofluoreseent procedure for CTB and FG, and the labeled olivocochlear neurons were observed byfluorescent microscope. Results In the experimental group, the mean total of olivocochlear neurons labeled by CTB and FG was 3210 ± 168, including lateral olivocochlear neurons (LOC, 2298 ± 120) and medial olivocochlear neurons (MOC,913 ± 64). The labeled neurons were divided into three different types according to their feature of projection: neurons which only projected to the ipsilateral cochlea, neurons which only projected to the contralateral cochlea, and double-labeled neurons which projected both to the ipsilateral and contralateral cochlea, but the double-labeled neurons comprised 3.9% and 15. 1% in the LOC and MOC system respectively. No labeled neurons were found in the control group. Conclusions There are three types of neurons in the cat olivocochlear system. The neurons which projected to the bilateral cochlea may distribute both in the LOC and MOC system.     

Transformations in processing interaural time differences between the superior olivary complex and inferior colliculus: beyond the Jeffress model

Interaural time differences (ITDs) are used to localize sounds and improve signal detection in noise. Encoding ITDs in neurons depends on specialized mechanisms for comparing inputs from the two ears. Most studies have emphasized how the responses of ITD-sensitive neurons are consistent with the tenets of the Jeffress model. The Jeffress model uses neuronal coincidence detectors that compare inputs from both sides and delay lines so that different neurons achieve coincidence at different ITDs. Although Jeffress-type models are successful at predicting sensitivity to ITDs in humans, in many respects they are a limited representation of the responses seen in neurons. In the superior olivary complex (SOC), ITD-sensitive neurons are distributed across both the medial (MSO) and lateral (LSO) superior olives. Similar response types are found in neurons sensitive to ITDs in two signal types: low-frequency sounds and envelopes of high-frequency sounds. Excitatory-excitatory interactions in the MSO are associated with peak-type responses, and excitatory-inhibitory interactions in the LSO are associated with trough-type responses. There are also neurons with responses intermediate between peak- and trough-type. In the inferior colliculus (IC), the same basic types remain, presumably due to inputs arising from the MSO and LSO. Using recordings from the SOC and IC, we describe how the response types can be described within a continuum that extends to very large values of ITD, and compare the functional organization at the two levels.     

Development and influence of inhibition in the lateral superior olivary nucleus

While studies of neuronal development and plasticity have focused on excitatory pathways, the inhibitory projection from the MNTB to the LSO provides a favorable model for studies of synaptic inhibition. This review covers recent studies from our laboratories indicating that inhibitory connections are quite dynamic during development. These findings suggest that there are two phases inhibitory transmission. During an initial depolarizing phase is growth and branching of pre- and postsynaptic elements in the LSO. During a second hyperpolarizing phase there is refinement of inhibitory afferent arborizations and the LSO dendrites that they innervate.     

Uptake of gentamicin by vestibular efferent neurons and superior olivary complex after transtympanic administration in guinea pigs

Transtympanic administration of gentamicin is a widely accepted and effective approach for treating patients with intractable vertigo. Previous studies have demonstrated the uptake, distribution and effects of gentamicin in peripheral vestibular and cochlear structures after transtympanic injection. However, little is known about whether transtympanically administered gentamicin is trafficked into more central auditory and vestibular structures and its effect on these structures. In this study, we used immunofluorescence to determine the distribution of gentamicin within the auditory and vestibular brainstem. We observed gentamicin immunolabeling bilaterally in the vestibular efferent neurons, and in the superior olivary complex, and ipsilaterally in the cochlear nucleus 24h after transtympanic administration of gentamicin, and that the drug could still be detected in these locations 30 days after injection. In contrast, no gentamicin labeling was detected in the vestibular nuclear complex. In the vestibular efferent neurons and superior olivary complex, gentamicin labeling was detected in the cytoplasm and cell processes, while in the cochlear nucleus gentamicin is mainly localized outside and adjacent to the cell bodies of neurons. Nerve fibers in cochlear nucleus, root of eighth nerve, as well as descending pathways from the superior olivary complex, are also immunolabeled with gentamicin continuously. Based on these data, we hypothesize that retrograde axonal transport of gentamicin is responsible for the distribution of gentamicin in these efferent nuclei including vestibular efferent neurons and superior olivary complex and anterograde axonal transport into the ipsilateral cochlear nucleus.