Desde la corteza auditiva a la cóclea: progresos en el sistema eferente auditivo / From auditory cortex to cochlea: progress in the auditory efferent system

El sistema eferente auditivo está constituido por el sistema olivococlear y por vías descendentes que provienen de la corteza auditiva y se dirigen a la cóclea. El sistema olivococlear se divide en una porción medial y una lateral, con neuronas que inervan a las células ciliadas externas y a fibras del nervio auditivo respectivamente. El principal neurotransmisor de las sinapsis olivococleares es acetilcolina, y tanto las células ciliadas externas como las fibras del nervio auditivo poseen receptores para esta molécula. El sistema eferente córtico-coclear se origina en la capa V y VI de la corteza auditiva y proyecta a los colículos inferiores y complejo olivar superior, donde a través del sistema olivococlear se conecta con el órgano receptor auditivo. En este artículo se revisan importantes hallazgos obtenidos en los últimos años que involucran (i) nuevos neurotransmisores y receptores del sistema eferente auditivo; (ii) vías descendentes de la corteza auditiva y su rol fisiológico sobre las respuestas cocleares y (iii) rol del sistema eferente auditivo en patologías audiológicas y neuropsiquiátricas.

The auditory efferent system is composed by the olivocochlear fibers and descending projections that originate in the auditory cortex and end in the cochlea. The olivocochlear system is divided into a medial and lateral division, with fibers directed to the outer hair cells and to the auditory nerve fibers respectively. It is known that acetylcholine is the main neurotransmitter of the olivocochlear synapses and that outer hair cells and auditory nerve fibers have receptors to this molecule. The cortico-cochlear efferent system originates in layers V and VI of the auditory cortex. These descending projections are directed to the inferior colliculus and superior olivary complex, a site in which the olivocochlear fibers emerge and connect the brain with the cochlear receptor. In this article recent discoveries obtained in the last years are reviewed: (i) new neurotransmitters and receptors of the olivocochlear system; (ii) anatomy and physiology of descending pathways from the auditory cortex to the cochlea and, (iii) clinical role of auditory efferents in audiological and neuropsychiatric pathologies.

The brainstem localization of gastric preganglionic parasympathetic neurons in the Agouti (Dasyprocta leporina) / Localización del tronco encefálico de las neuronas parasimpáticas preganglionares gástricas en el agutí (Dasyprocta leporina)

This study was designed to determine qualitatively, the source of gastric vagal nerve fibres in the Agouti. A total of 18 male and female adult agoutis were used for the present investigation. Following anaesthesia, laparotomy was performed and the stomach exteriorized. Multiple intramuscular injections of wheat germ agglutinin-horseradish peroxidase (WGA-HRP) were then made into different areas of the stomach in the experimental animals. The control animals were divided into four groups of two animals each. The first group had intraperitoneal injection of the tracer, the second had intramuscular injection of normal saline, the third group had injection of tracer into the hepatic portal vein and the last group had injection of the tracer into the gastric walls followed immediately by bilateral vagotomy. Following a survival period offive to seven days, the animals were sacrificed by transcardial perfusion, first with normal saline followed by fixative and finally with 20% buffered sucrose. Following perfusion, the brainstem was extracted from the brain, immersed in 20% buffered sucrose and kept refrigerated overnight for cryoprotection. The brainstems were subsequently sectioned serially, processed for WGA-HRP neurohistochemistry and then analysed under light and dark-field illuminations. The analysis of the sections taken from the experimental animals revealed bilateral presence of WGA-HRP labelled neurons in the dorsal motor nucleus of the vagus nerve (DMNV) and the nucleus ambiguus (nA) of the medulla oblongata. No labelled neurons were seen in any of the sections taken from the control animals. The implications of the findings are discussed.

Este estudio fue diseñado para determinar cualitativamente el origen de las fibras gástricas del nervio vago en el agutí. Un total de 18 agutíes adultos masculinos y femeninos fueron utilizados para la presente investigación. Después de la anestesia, se realizó una laparotomía y se sacó el estómago al exterior. Luego se hicieron múltiples inyecciones intramusculares de aglutinina de germen de trigo con peroxidasa de rábano (WGA-HRP) en diferentes áreas del estómago de los animales experimentales. Los animales del control fueron divididos en cuatro grupos de dos animales cada uno. Al primer grupo se le puso una inyección intraperitoneal del marcador; al segundo se le administró una inyección intramuscular de solución salina normal; al tercer grupo se le inyectó el marcador en la vena porta hepática; y al último grupo se le puso la inyección del marcador en las paredes gástricas, seguida inmediatamente por una vagotomía bilateral. Tras un periodo de supervivencia de cinco a siete días, los animales fueron sacrificados por perfusión transcardíaca, primero con solución salina normal, seguida de fijador, y finalmente con sacarosa tamponada al 20%. Después de la perfusión, el tronco encefálico fue extraído del cerebro, inmerso en sacarosa tamponada al 20%, y mantenido en refrigeración durante la noche para su crioprotección. Los tronos encefálicos fueron luego seccionados en serie, procesados para para el análisis neuro-histoquímico mediante aglutinina de germen de trigo con peroxidasa de rábano, y analizados entonces bajo iluminaciones de campo de luz y campo oscuro. El análisis de las secciones tomadas de animales experimentales reveló la presencia bilateral de neuronas etiquetadas WGA-HRP en el núcleo motor dorsal del nervio vago (DMNV) y en el núcleo ambiguo (nA) de la médula oblonga. No se observaron neuronas etiquetadas en ninguna de las secciones tomadas de los animales de control. Se discuten las implicaciones de los hallazgos.

Mechanism of Efferent Inhibition in Cochlear Hair Cell / 대한이비인후과학회지

Efferent neurons release acetylcholine to inhibit sensory hair cells of the inner ear. The alpha9alpha10 nicotinic acetylcholine receptor (nAChR) mediates efferent inhibition of hair cell function within the auditory sensory organ. Gating of the nAChR triggers inward calcium current, and leads to activation of calcium dependent, small-conductance potassium (SK) potassium channels to hyperpolarize the hair cell. Through SK channels, large potassium outflow occurred, and outer hair cell was hyperpolarized. Thus, amplification of sound and sensitivity of hearing was reduced or modulated by efferent inhibition. In efferent system, main calcium providers to SK channel are nAChR and synaptic cistern, which contribution to efferent inhibition is different between avian and mammalian species. Calcium permeation is more effective in nAChRs of mammalian cochlea than avian cochlea, and mammalian calcium permeability of nAChRs is about 3 times more than avian hair cell. Thus, nAChRs is a main component of efferent inhibition in mammalian cochlear hair cell system.

Ultrastructural analysis of the dorsal body gland of the terrestrial snail Megalobulimus abbreviatus (Becquaert, 1948) / Análise ultraestrutural da glândula corpo dorsal do caracol terrestre Megalobulimus abbreviatus (Becquaert, 1948)

The ultrastructure of the reproductive gland, dorsal body (DB), of Megalobulimus abbreviatus was analysed. Electron microscope immunohistochemistry was used to detect FMRFamide-like peptides in the nerve endings within this gland. Nerve backfilling was used in an attempt to identify the neurons involved in this innervation. In M. abbreviatus, the DB has a uniform appearance throughout their supraesophageal and subesophageal portions. Dorsal body cells have several features in common with steroid-secreting gland cells, such as the presence of many lipid droplets, numerous mitochondria with tubular cristae and a developed smooth endoplasmic reticulum cisternae. Throughout the DB in M. abbreviatus numerous axonal endings were seen to be in contact with the DB cells exhibiting a synaptic-like structure. The axon terminals contained numerous electron-dense and scanty electron-lucid vesicles. In addition, the DB nerve endings exhibited FMRFamide immunoreactive vesicles. Injection of neural tracer into the DB yielded retrograde labelling of neurons in the metacerebrum lobe of the cerebral ganglia and in the parietal ganglia of the subesophageal ganglia complex. The possibility that some of these retrograde-labelled neurons might be FMRFamide-like neurons that may represent a neural control to the DB in M. abbreviatus is discussed.

Foi analisada a ultraestrutura da glândula reprodutiva corpo dorsal (CD) de Megalobulimus abbreviatus. Imunoistoquímica para microscopia eletrônica foi utilizada para detectar peptídeos relacionados ao tetrapeptídeo FMRFamida nas terminações axonais existentes nessa glândula. Foi utilizada marcação neuronal retrógada com o intuito de localizar os neurônios envolvidos nesta inervação. O CD de M. abbreviatus possui um aspecto uniforme em toda sua extensão, tanto na porção supraesofágica como subesofágica. As células do CD possuem várias características de glândulas esteroidogênicas, tais como a presença de inúmeras gotículas lipídicas, numerosas mitocôndrias com cristas tubulares e cisternas bem desenvolvidas de retículo endoplasmático liso. Por toda a extensão do CD de M. abbreviatus foram encontradas numerosas terminações axonais fazendo contatos estruturalmente semelhantes a sinapses com as células do CD. As terminações axonais continham grande número de vesículas eletrodensas e esparsas vesículas eletrolúcidas. As terminações axonais no CD apresentavam vesículas com conteúdo imunorreativo à FMRFamida. A injeção de traçador neural no CD resultou em marcação retrógrada de neurônios no metacérebro dos gânglios cerebrais e nos gânglios parietais do complexo ganglionar subesofágico de M. abbreviatus. É discutida a possibilidade de que estes neurônios identificados por marcação retrógrada possam representar a via de controle neural do CD de M. abbreviatus, cujo mediador químico seria um neuropeptídeo relacionado à FMRFamida.

[ effect of contralateral noise stimulation on difference limen for intensity]

Contralateral stimulation with noise can improve auditory intensity discrimination. This may be related to function of the efferent system. The purpose of this study was to determine the relationship between the auditory intensity discrimination and the efferent system function. Twenty students with normal hearing were included in this descriptive-analytic study. We examined Difference Limen for Intensity [DLI], Otoacoustic Emissions suppression and Speech In Noise. DLI was evaluated with and without contralateral noise stimulation at two different stimulus levels [20, 70 dB SL]. There was significant difference between mean DLI scores of with contralateral masking comparing to without it, which was more prominent as frequency increased. Mean DLI score while masking with white noise was more than scores when masking with narrow band noise [p<0.05]. Transient evoked otoacoustic emissions responses decreased significantly in amplitude with contralateral masking. [p<0.05]. These results suggest that medial olivocochlear bundle functions as a key role in auditory intensity discrimination

Distribution of projection neurons of the superior olivary complex in the auditory brainstem in cats / 中南大学学报(医学版)

OBJECTIVE@#To investigate the distribution and morphology of olivocochlear neurons of superior olivary complex in cats.@*METHODS@#Eight adult cats were divided into 2 groups randomly. Cholera toxin B subunit was injected to the left cochlea and fluoro-gold was injected to the right cochlea in the experimental group (n=5). Saline was injected to bilateral cochlea in the control group (n=3). Brainstem tissue was sectioned serially. All of the sections were immunohistochemically treated with ABC and stained with DAB, and then the labelled olivocochlear neurons were observed.@*RESULTS@#The labelled olivocochlear neurons in the experimental group were 2 518 in total. Of them, the number of lateral olivocochlear (LOC) neurons was 1 738 (69.0%), mainly located in the middle of the pons, predominantly projected ipsilaterally. The total of medial olivocochlear (MOC) neurons was 780 (31%), mainly located in dorsomedial periolivary nucleus, medial nucleus of the trapezoid body and ventral nucleus of the trapezoid body, mainly distributed in the rostral extent of the pons, predominantly projected contralaterally.@*CONCLUSION@#In the distribution of olivocochlear neurons in cats, LOC neurons mainly project to the ipsilateral. While the projection of MOC neurons is predominantly contralateral, the distribution of MOC neurons is more adjacent to the rostral extent of the pons than LOC neurons.

Basic science review on circadian rhythm biology and circadian sleep disorders

The sleep-wake cycle displays a characteristic 24-hour periodicity, providing an opportunity to dissect the endogenous circadian clock through the study of aberrant behaviour. This article surveys the properties of circadian clocks, with emphasis on mammals. Information was obtained from searches of peer-reviewed literature in the PUBMED database. Features that are highlighted include the known molecular components of clocks, their entrainment by external time cues and the output pathways used by clocks to regulate metabolism and behaviour. A review of human circadian rhythm sleep disorders follows, including recent discoveries of their genetic basis. The article concludes with a discussion of future approaches to the study of human circadian biology and sleep-wake behaviour.

Uso combinado de resonancia magnética funcional (fMRI) y tractografía para seleccionar tractos específicos de sustancia blanca: experiencia preliminar / Combined use of functional magnetic resonance imaging (FMRI) and tractography to select specific white matter fibers: a preliminary study

Tractography is a magnetic resonance imaging post processing technique, that reveals white matter tracts. The selection of specific tracts is a current research topic in medical imaging. Fibers of a male patient were chosen by using a ROÍ selection generated by activation of the primary motor cortex area (SM1) of the left hand (fMRI), and fiber tracts related to that cortex area (efferent fibers) were obtained. Fibers obtained through this procedure present the typical arrangement of the corticospinal tract motor fibers: originated from the motor cortex, they descend through the posterior limb ofthe internal capsule to converge to the cerebral peduncle until the pons. We have concluded that it is possible to select the corticospinal tract by using a functional Magnetic Resonance Imaging to generate ROÍ selection.

La tractografía es una técnica de postprocesamiento de imágenes de resonancia magnética, que permite visualizar tractos de sustancia blanca. La selección de tractos específicos es un tema actual de investigación a nivel mundial. En un paciente se seleccionaron las fibras utilizando ROÍ generada mediante activación del área motora primaria de la mano izquierda (fMRI), obteniéndose asilas fibras del tracto motor específicas de esta área (fibras eferentes). Las fibras obtenidas presentan la disposición clásica de las fibras motoras en el tracto corticoespinal: se inician en la corteza motora, descienden por el brazo posterior de la cápsula interna integrándose al pedúnculo cerebral y visualizándose hasta la parte del tronco cerebral. Se concluye que es posible seleccionar el tracto corticoespinal mediante ROÍ generado con resonancia magnética funcional.

Location of somatic sensory neurons of the skin and dorsal nerve of the penis in rabbits / 中华男科学杂志

<p><b>OBJECTIVE</b>To trace the segmental distribution of somatic sensory neurons of the skin and dorsal nerve in the rabbitś penis.</p><p><b>METHODS</b>The experiment was performed on 8 adult male rabbits with the nerve tracing method of retrograde axonal transport of horseradish peroxidase (HRP), which was injected into the dermis around the penis and the dorsal nerve of the penis. The rabbits were sacrificed five days later to harvest the spinal cord segments and the dorsal root ganglia of lumbosacral segments for histological study.</p><p><b>RESULTS</b>The HRP tracing showed that a number of labeled HRP positive neurons appeared in spinal ganglia (S2 - S4) in all the rabbits, and distributed segmentally. The counts of the positive neurons different segments were: S2 (215.0 +/- 10.2) , S3 (242.2 +/- 8.3) and S4 (109.7 +/- 8.4) respectively, with statistically significant difference between the two groups.</p><p><b>CONCLUSION</b>The rabbit's sensory nerve fibers in both the skin and the dorsal nerve of the penis are rooted in the S2-S4 segments of spinal ganglia, which distribute regularly.</p>

Análise das emissões otoacústicas - produto de distorção - após a aplicação de toxina botulínica A (botox®) sobre a janela redonda de chinchilas / Analysis of otoacustic emissions - distortion product - after the use of botulinum toxin A (botox®) on the round window of chinchillas

Através das emissões otoacústicas pré e pós operatória foi avaliada a inativação da contração das células ciliadas externas pela ação da toxina botulínica A. No grupo de estudo aplicou-se uma unidade de toxina botulínica sobre a janela redonda de oito chinchilas. O grupo controle usou soro fisiológico. As emissões otoacústicas estiveram ausentes nos exames pós operatórios de todas as orelhas do grupo de estudo e estiveram presentes em todos os exames pós-operatórios do grupo controle. Esses resultados sugerem que a toxina botulínica pode ser uma eficiente ferramenta para o estudo das vias eferentes cocleares, pois a cirurgia é de fácil realização e não requer a intervenção intracerebral.The action of botulinum toxin A inactivating the contraction of the outer hair cells was evaluated by pre and postoperative otoacoustic emissions exams. In the study group, one unit of toxin was applied onto the round window of eight chinchillas. The control group was submitted to saline solution. Otoacoustic emissions were absent in all postoperative exams of the study group, in contrast to the control group. Those results suggest that botulinum toxin can be an efficient tool for the study of efferent auditory pathways. The surgery can be easily done without an intracranial intervention...

The Effect of Acethylcholine on the Slow Motility Induced by High Potassium Ion and Increased Intracellular Calcium in Outer Hair Cells / 대한이비인후과학회지

BACKGROUND AND OBJECTIVES: It has been known that the motility of the outer hair cell controls the physiological characteristics of the organ of Corti. Motility can be divided into two different types: fast and slow motility. Slow motility can be induced by high concentration of KCl and increase of intracellular Ca2+ concentration. In this study, authors aimed to define the effect of acetylcholine, one of the efferent neurotransmitters, on the slow motility of the outer hair cells of guinea pig. MATERIALS AND METHOD: Outer hair cells were isolated from guinea pigs by enzymatic and mechanical dissociation. The length of the hair cells was recorded by CCD camera equipped on an inverted microscope. Slow motility was induced by 10 (micro)M of ionomycin and 150 mM of KCl. Carbamylcholine (1 mM), a non-hydrolyzable derivative of acetylcholine, was used to observe the effect of acetylcholine and choline chloride (1 mM) was used as control. RESULTS: The length of outer hair cell was decreased after adding 150 mM of KCl and increased after adding 10 (micro)M of ionomycin. Stimulation of carbamylcholine (1 mM) did not induce the length change of the outer hair cells. Preincubation of 1 mM of carbamylcholine also did not affect the length change induced by ionomycin or KCl in outer hair cells. CONCLUSION: We could suggest that carbamylcholine does not have an effect on the slow motility of outer hair cell induced by the change of osmotic pressure which was elicited by high potassium, or intracellular Ca2+ increase.

Amantadine as Treatment for Levodopa-Induced Dyskinesia

BACKGROUND: Dyskinesia is a common side effect complicating long-term levodopa therapy for Parkinson's disease. However, the pathogenesis of dyskinesia has not been completely understood. In recent animal studies, it has been reported that a NMDA (N-methyl-D-aspartate) antagonist reduced levodopa-induced dyskinesia. These findings suggest that the hyperfunction of NMDA receptors on striatal efferent neurons contributed to the pathogenesis of dyskinesia. Amantadine has also been recently shown to antagonize central NMDA receptors. In the present study, we observed amantadine efficacy in levodopa-induced dyskinesia in parkinsonian patients. METHODS:Twenty-two parkinsonian patients with levodopa-induced dyskinesia participated in a placebo-controlled, cross-over study. We prescribed 100 mg amantadine daily as a starting dose, which was built up every four days and titrated up to 400 mg a day. After two weeks of a wash-out period, a placebo was given with the same schedule. The doses of levodopa and other antiparkinsonian drugs were unchanged during this period. We assessed the duration and disability of dyskinesia (UPDRS part IV, item 32 and 33) based on diary and interview. RESULTS: Amantadine was superior to placebo in reducing the duration of dyskinesia in 9 patients (42.9%) and the disability of dyskinesia in 11 patients (52.4%). The reduction of the duration and disability of dyskinesia was correlated with the dose of amantadine. CONCLUSIONS These findings suggest that amantadine can improve levodopa induced dyskinesia and supports the view that the hyperfunction of NMDA receptors contributes to the pathogenesis of levodopa induced dyskinesia.

Identification of efferent-stimulus-responding neurons in the earthwoem 3rd segmental nerve by Lucifer yellow-ch backfilling

The objective of the present study was to identifify the mechanism for the decreased efferent reflex response recorded extracellulary from an earthworm 3rd segmental nerve after the nerve had been cut. Four neurons which showed a correlated decrease in their efferent responses were identified in the ventral nerve cord by the broken-microelectrode-backfilling method using Lucifer Yellow-CH. The long processes of these neurons extended into the 3 rd nerve trunk.Thus teses neurons may neurons mayrepresent an efferent link in the this complicated reflex are

The projection of GABAergic neurons of the medial terminal accessory optic nucleus to the pretectum in the rat

Large numbers of neurons were retrogradely labeled in both the dorsal and ventral medial terminal nucleous (MTN) after fluoro-gold injections into the rat pretectal nucleus of the optic tract/dorsal terminal nucleus (NOT/DTN). Fluorescence immunocytochemistry for GABA in the same brains revealed GABA-positive neurons distributed mainly in the dorsal MTN. Approximately half of all the GABAergic neurons in the MTN were double-labeled. Therefore, GABAergic neurons comprise a significant component of the MTN-NOT-DTN projection which most likely inhibits the pretectal pathway mediating horizontal optokinetic nystagmus

Bilateral asymmetry in conduction velocity in the efferent fibres of the median nerve andits relationship to handedness.

The conduction velocity in the efferent fibres of the median nerve has been compared in the right and left forelimbs of 38 human subjects. Six independent estimates were made for each limb. Estimates on the right and left limb of a subject were made at the same sitting. Conduction velocity was faster on the right side in the majority of right handed subjects; and on the left side in the majority of left handed subjects. The mean conduction velocity was greater on the right side in right handed subjects (P less than 0.02).