Vestibular Efferent Neurons Research Articles

Bemerkungen zum Ursprung der labyrinth�ren Efferenz bei Vertebraten. Eine Evolutionshypothese

In our comparative study in all classes of vertebrates we determined the cells of origin of efferent acoustic and efferent vestibular fibers by the use of retrograde axonal transport of horseradish peroxidase (HRP). In fish we investigated the goldfish, in the amphibians the green tree frog, in reptiles a turtle and the Caiman. In birds we studied the chicken and in mammals the guinea pig. If one compares the origin of efferent labyrinthine fibers there seems to be a shift from a medial position in the brain stem (lateral to the fasciculus longitudinalis medialis) in the fish to a more lateral position in the amphibians. In reptiles the parent cells stretch more ventral in the direction of the superior olive. While in turtles efferent acoustic neurons are intermingled with efferent vestibular neurons, it is in the evolutionary stage of Crocodilia that efferent acoustic neurons separate from efferent vestibular neurons. In birds there is a similar finding as in the Caiman. In mammals, efferent vestibular neurons shift dorsally to a position lateral to the genu of the facial nerve. Efferent acoustic neurons are located throughout the superior olivary complex.

Identification of multiple groups of efferent vestibular neurons in the adult pigeon using horseradish peroxidase and DAPI

This study was designed to investigate the efferent innervation of the pigeon labyrinth. Horseradish peroxidase (HRP) was injected and confined within the endolymphatic space of one labyrinth in 9 adult pigeons. The brain was perfused by transcardiac carotid catheterization and the HRP reacted by the tetramethylbenzidine (TMB) blue reaction process. Five different groups of HRP-labeled vestibular efferent neurons were identified. Three groups were located within the confines of the ipsilateral vestibular nuclear complex (in the lateral, tangential and descending nucleus) and two additional groups, each bilateral, were located in the reticular formation. In 9 additional pigeons, 4,6-diamidino-2-phenylindole (DAPI) was also injected and confined within the endolymphatic space of one labyrinth. DAPI-labeled cells were noted in 3 of the 5 locations (tangential nucleus, and both reticular groups) which in the other animals contained HRP-labeled cells. These findings raise the possibility of different physiological roles for the efferent vestibular groups in the ipsilateral vestibular nuclear complex and bilateral reticular formation.

The origin of efferent labyrinthine fibers: A comparative study in vertebrates

Parent cells of efferent acoustic and efferent vestibular fibers were determined anatomically in all classes of vertebrates by use of retrograde axonal transport of horseradish peroxidase. These neurons were found in the brainstem, in particular in the reticular formation. In the goldfish, efferent labyrinthine neurons could be demonstrated in a medial position (lateral to the fasciculus longitudinalis medialis). In the frog, efferent neurons appeared more lateral, dorsomedial to the facial motor nucleus. In reptiles and birds, efferent acoustic neurons separate from efferent vestibular neurons. In mammals, efferent vestibular neurons are located more dorsally, lateral to the genu of the facial nerve. Efferent acoustic neurons take their origin from the superior olivary complex.

Recordings from efferent vestibular neurons in freely moving goldfish

Recordings from efferent vestibular neurons in freely moving goldfish

Acoustic and vestibular efferent neurons in the chicken (Gallus domesticus). A horseradish peroxidase study.

The origin of labyrinthine efferent fibres was investigated in the chicken. After injection of horseradish peroxidase (HRP) into the cochlear duct or into the ampulla of the horizontal semicircular canal, efferent neurons in the medulla oblongata were labelled by the granular reaction product of retrogradely transported HRP. Efferent vestibular neurons were found in the nucleus reticularis pontis caudalis bilaterally with more cells ipsilateral to the injection side, while efferent cochlear neurons could be demonstrated medial to the ventral division of the facial nucleus bilaterally with more neurons contralateral to the injection.

The origin of efferent vestibular fibres in the guinea pig. A horseradish peroxidase study.

The origin of efferent vestibular neurons was determined in the guinea pig by means of retrograde axonal transport of horseradish peroxidase. After injection of a horseradish peroxidase solution into the ampulla of the horizontal and anterior semicircular canal, efferent vestibular neurons labelled by the granular reaction product were found in the medulla oblongata bilaterally at two locations. The first is lateral to the genu of the facial nerve. It has a bilateral and symmetric origin. The second is the nucleus reticularis pontis caudalis. Here there were more labelled neurons contralateral to the injection site.

Vestibular efferent neurons and catecholamine cell groups in the reticular formation of the pigeon

This study was designed to investigate the relationship between vestibular efferent neurons and catecholamine cell groups within the reticular formation of the pigeon. Horseradish peroxidase (HRP) was injected into the endolymphatic space of one labyrinth. The brain was perfused with glyoxylic acid and serial sections were examined with a fluorescence microscope. After documentation of the location of fluorescent cells the sections were reacted for HRP with tetramethylbenzidine. Fluorescent cells were noted intermingled among the HRP-labeled vestibular efferent neurons in the nucleus reticularis pontis caudalis. No neurons were both fluorescent and HRP-positive. Fluorescent cells were also noted bilaterally in locus ceruleus, raphe nucleus, and in close proximity to the abducent, facial, hypoglossal and ambiguus nuclei.

Efferent vestibular neurons: a study employing retrograde tracer methods in the pigeon (Columba livia).

Efferent neurons innervating the vestibular labyrinth and cochlea of the pigeon have been identified by means of a variety of retrograde tracers: [3H]-adenosine (Ad), horseradish peroxidase (HRP), Evan's Blue (EB) and Bisbenzimide (Bb). Discrete injections into individual cristae ampullares of the semicircular canals, into the macula utriculi, or into several of these end organs resulted in similar patterns of neuronal labelling. Efferent vestibular neurons were always found within a small portion of the nucleus reticularis pontis caudalis (RP), ventrolateral to the abducens nucleus on both sides. No systemic difference in the locations of labelled cells was found following injection into different sensory epithelia. Cell counts following injections into individual cristae did not differ significantly from those following injections into all three cristae. The injections into all cristae in both labyrinths yielded cell counts that were much lower than twice the number of cells labelled by injections into the three cristae on one side only. When HRP was injected into the right lateral canal crista and Ad into the right posterior canal crista, a high proportion of neurons was labelled with both compounds (61% of the HRP-labelled cells and 67% of the Ad-labelled cells). Injections of EB into all three cristae on the right side and Bb into all three cristae on the left side produced a smaller percentage of doubly labelled cells (10% of the EB-labelled cells and 6% of the Bb-labelled cells). It is concluded, therefore, that there is a considerable degree of collateralization within one labyrinth. Fewer collaterals of efferent neurons are directed to both labyrinths. Since each semicircular canal represents head rotation in one direction and one plane, it is unlikely that efferents which contact several different movement sensors can provide sensory motor control that is specific for directions and planes of head movements. Control injections of these tracers into the cochlea yielded labelled cells in a different reticular structure, the nucleus reticularis paragigantocellularis lateralis (Pgc), on both sides, as well as in the RP. It is proposed that the Pgc cells represent cochlear efferents, while the RP neurons are related to the macula lagenae, an otolithic organ of balance in the pigeon.

Efferent vestibular neurons. Electrophysiological evidence for axon collateralization to cristae ampullares in the pigeon (Columba livia).

Extracellular spikes were recorded under general anaesthesia from the cell bodies of efferent vestibular neurons located in the caudal pontine reticular nucleus of the pigeon. Discrete electrical stimuli, applied directly to the three ampullary nerve branches in one labyrinth and to the anterior ramus of the vestibular nerve trunk in the other labyrinth, evoked antidromic spikes which served to identify efferent neurons. Most cells could be antidromically driven only by stimuli to the vestibular nerve trunk (anterior ramus). The majority of cells exhibiting direct axonal connections to one individual semicircular canal crista ampullaris showed axon collateralization to one or two other cristae as well. Sixty percent of the efferent neurons responded with antidromic spikes to ipsilateral labyrinthine stimuli, 34% to contralateral stimuli, and 6% to both. Synaptic activation was observed in a few efferent and adjacent unidentified neurons. It is concluded that efferent neurons often send collaterals to various cristae in one labyrinth, and less frequently, to both labyrinths. Such projections are incompatible with the assumption that vestibular efferents provide a simple control mechanism which is related to the direction of head movement.

Avian efferent vestibular neurons identified by axonal tranpoort of [ 3H]adenosine and horseradish peroxidase

Avian efferent vestibular neurons identified by axonal tranpoort of [ 3H]adenosine and horseradish peroxidase

Cat efferent vestibular system: Weak suppression of primary afferent activity

Efferent vestibular neurons identified electrophysiologically in the brain stem do not receive a short latency synaptic input from the ipsilateral labyrinth. Central electric stimulation of these neurons influenced the resting discharge of only 8% of the primary afferent vestibular neurons. Caloric or electric stimulation of the vestibular input was ineffective in changing the spontaneous activity of contralateral primary afferent vestibular neurons.

Functional characterization of primary vestibular afferents in the frog.

1. In order to more accurately identify the nature of the vestibular input to central neurons, the response properties of single semicircular canal and otolith units in the frog VIIth nerve were studied in curarized preparations. 2. An equation describing the response plane was calculated for each canal on the basis of null point measurements. These results show that the ipsilateral canal planes are orthogonal within 2-5 degrees, and the pairs of right-left synergists are essentially coplanar. A head position of 10-20 degrees maxilla nose up produces optimal horizontal canal and minimal vertical canal activation with horizontal rotation. 3. The frequency response of the horizontal canal was examined in the range 0.025-0.5 Hz. Comparatively shorter phase-lags and a 10 fold greater acceleration gain in this frequency range distinguish the frog from the mammalian species studied. 4. Otolithic responses were tonic, phasic-tonic, and phasic in nature. The preponderance of the latter two groups is stressed (94%). Tonic responses were proportional to the gravitational vector change. Phasic responses were proportional to velocity during transitions in head position and phase-led displacement (30-80%) with sinusoidal acceleration in roll and pitch. 5. Efferent vestibular neurons respond to rotation in the horizontal (usually Type III) as well as vertical planes. Responses in the vertical planes result from canal and/or otolithic input to these neurons indicating that the vestibular efferent system receives extensive multi-labyrinthine convergence.

Olivocochlear and vestibular efferent neurons of the feline brain stem: their location, morphology and number determined by retrograde axonal transport and acetylcholinesterase histochemistry.

Anterograde degeneration studies have shown that the cochlear and vestibular receptor organs receive an efferent innervation from neurons in the brain stem. This pathway may provide a mechanism by which the CNS could modulate its own afferent input. The neurons which provide this innervation have so far escaped positive identification with methods which depend on retrograde cell changes after axotomy. In the present study, horseradish peroxidase (HRP) was injected into the labryinths of kittens and after allowing 24 hours for the retrograde axonal transport of this tracer, its presence in neurons of the brain stem was demonstrated histochemically. Because there is evidence that the efferent innervation of the labyrinth is cholinergic, acetylcholinesterase (AChE) was also demonstrated histochemically in the same or in adjacent tissue sections. Neurons labelled with HRP were found bilaterally in most periolivary cell groups of the superior olivary complex (cochlear efferents) and in the parvocellular reticular nucleus lateral to the abducens nucleus (vestibular efferents). Counts of labelled neurons yielded estimated totals of 1,700-1,800 cochlear and 400-500 vestibular efferent neurons. Approximately 60% of the neurons in each total were located on the side ipsilateral to the injection. The distribution of HRP-labelled neurons was virtually identical to that of AChE-positive neurons found in adjacent sections, and in those regions with predominantly ipsilateral or contralateral projections, there was an approximate correspondence in number of HRP- and AChE-positive neurons. In tissue sections processed successively for demonstration of HRP and AChE, virtually all HRP-labelled neurons were found to be AChE-positive. These findings suggest that a number of current conceptions regarding labyrinthine efferent systems may need revision.

The localization of vestibular efferent neurons in the kitten with horseradish peroxidase.

The location of efferent vestibular neurons in the brainstem of newborn kittens was determined by means of horseradish peroxidase used as a tracer of retrograde protein transport. Two to three milligrams of horseradish peroxidase were injected into the vestibule of 8 kittens. After survival for 24 hours, the animals were fixed by perfusion and the brainstems sectioned. Stains for peroxidase demonstrated the labelled neurons lateral to the abducens nucleus bilaterally.