Afferent innervation patterns of the saccule in pigeons

The innervation patterns of vestibular saccular afferents were quantitatively investigated in pigeons using biotinylated dextran amine as a neural tracer and three-dimensional computer reconstruction. Type I hair cells were found throughout a large portion of the macula, with the highest density observed in the striola. Type II hair cells were located throughout the macula, with the highest density in the extrastriola. Three classes of afferent innervation patterns were observed, including calyx, dimorph, and bouton units, with 137 afferents being anatomically reconstructed and used for quantitative comparisons. Calyx afferents were located primarily in the striola, innervated a number of type I hair cells, and had small innervation areas. Most calyx afferent terminal fields were oriented parallel to the anterior-posterior axis and the morphological polarization reversal line. Dimorph afferents were located throughout the macula, contained fewer type I hair cells in a calyceal terminal than calyx afferents and had medium sized innervation areas. Bouton afferents were restricted to the extrastriola, with multi-branching fibers and large innervation areas. Most of the dimorph and bouton afferents had innervation fields that were oriented dorso-ventrally but were parallel to the neighboring reversal line. The organizational morphology of the saccule was found to be distinctly different from that of the avian utricle or lagena otolith organs and appears to represent a receptor organ undergoing evolutionary adaptation toward sensing linear motion in terrestrial and aerial species.     

Neuronal organization of the utricular macula concerned with innervation of single vestibular neurons in the cat

We investigated whether cross-striolar inhibition, which may increase sensitivity to linear acceleration, contributed to utricular (UT) afferent innervation of single vestibular neurons (VNs). Excitatory and inhibitory postsynaptic potentials (EPSPs, IPSPs, respectively) were recorded from VNs after focal stimulation of the UT macula (M). From a total of 83 VNs, 25 (30%) neurons received inputs from both sides of the UTM, and the response patterns were opposite, i.e. cross-striolar inhibition was observed. In roughly 2/3 of these neurons, stimulation of the medial side of the UTM evoked EPSPs, while stimulation of the lateral side evoked IPSPs. In the remaining 1/3 neurons, the response patterns were opposite. Thirty-two (39%) of the 83 neurons received the identical pattern of inputs from both sides of the UTM: EPSPs in 26 neurons and IPSPs in six neurons. Twenty-six (31%) of the 83 neurons received inputs from either the medial or the lateral side of the UTM. These findings suggest that cross-striolar inhibition existed in the UT system, although it was not a dominant circuit that increased the sensitivity as in the saccular system [15].     

The vestibular nerve of the chinchilla. III. Peripheral innervation patterns in the utricular macula

1. Nerve fibers supplying the utricular macula of the chinchilla were labeled by extracellular injection of horseradish peroxidase into the vestibular nerve. The peripheral terminations of individual fibers were reconstructed and related to the regions of the end organ they innervated and to the sizes of their parent axons. 2. The macula is divided into medial and lateral parts by the striola, a narrow zone that runs for almost the entire length of the sensory epithelium. The striola can be distinguished from the extrastriolar regions to either side of it by the wider spacing of its hair cells. Calyx endings in the striola have especially thick walls, and, unlike similar endings in the extrastriola, many of them innervate more than one hair cell. The striola occupies 10% of the sensory epithelium; the lateral extrastriola, 50%; and the medial extrastriola, 40%. 3. The utricular nerve penetrates the bony labyrinth anterior to the end organ. Axons reaching the anterior part of the sensory epithelium run directly through the connective tissue stroma. Those supplying more posterior regions first enter a fiber layer located at the bottom of the stroma. Approximately one-third of the axons bifurcate below the epithelium, usually within 5-20 microns of the basement membrane. Bifurcations are more common in fibers destined for the extrastriola than for the striola. 4. Both calyx and bouton endings were labeled. Calyces can be simple or complex. Simple calyces innervate individual hair cells, whereas complex calyces supply 2-4 adjacent hair cells. Complex endings are more heavily concentrated in the striola than in the extrastriola. Simple calyces and boutons are found in all parts of the epithelium. Calyces emerge from the parent axon or one of its thick branches. Boutons, whether en passant or terminal, are located on thin collaterals. 5. Fibers can be classified into calyx, bouton, or dimorphic categories. The first type only has calyx endings; the second, only bouton endings; and the third, both kinds of endings. Calyx units make up 6% of the labeled fibers, bouton units less than 2%, and dimorphic units greater than 92%. The three fiber types differ in the macular zones they supply and in the diameters of their parent axons. Calyx units were restricted to the striola. The few bouton units were found in the extrastriola.(ABSTRACT TRUNCATED AT 400 WORDS)     

The vestibular nerve of the chinchilla. V. Relation between afferent discharge properties and peripheral innervation patterns in the utricular macula

1. The relation between the discharge properties of utricular afferents and their peripheral innervation patterns was studied in the chinchilla by the use of intra-axonal labeling techniques. Fifty-three physiologically characterized units were injected with horseradish peroxidase (HRP) or lucifer yellow CH (LY) and their labeled processes were traced to the utricular macula. For most labeled neurons, the discharge regularity, background discharge, and sensitivity to externally applied galvanic currents were determined, as were the gain (g2 Hz) and phase (phi 2 Hz) of the response to 2-Hz sinusoidal linear forces. Terminal fields were reconstructed and fibers were classified as calyx (n = 13) or dimorphic units (n = 40). No bouton units were recovered. Calyx units were confined to the striola. Dimorphic units were located in the striola (n = 8), the juxtastriola (n = 7), or the peripheral extrastriola (n = 25). 2. To determine whether the intra-axonal sample was representative, the physiological properties of labeled utricular units were compared with those of a larger sample of extracellularly recorded units. A comparison was also made between the morphology of intra-axonally labeled units and those labeled by the extracellular injection of HRP into the vestibular nerve. Most of the discrepancies between the intra-axonal and either extracellular sample can be explained by assuming that small-diameter fibers are underrepresented in the former sample. Dimorphic fibers labeled intra-axonally had more bouton endings and larger terminal trees than did those labeled extracellularly. The latter differences may reflect a sampling bias in the extracellular material. 3. Calyx units were irregularly discharging. The discharge regularity of dimorphic units was related to their macular locations. Only 1/8 dimorphic units in the striola was regularly discharging. The ratio increases to 3/7 in the juxtastriola and to 23/25 in the peripheral extrastriola. Among dimorphic units, there is a tendency for irregularly discharging afferents to have fewer bouton endings. The trend is far from perfect because it is possible to pick a subsample of dimorphic units that have similar numbers of boutons and, yet, have discharge patterns that range from regular to irregular. 4. Published morphological polarization maps can be used to predict the excitatory tilt directions of a unit from its macular location. Predictions were confirmed in 39/41 labeled afferents. 5. The galvanic sensitivity (beta *) of an afferent, irrespective of its peripheral innervation pattern or its epithelial location, was strongly correlated with a normalized coefficient of variation (CV*).(ABSTRACT TRUNCATED AT 400 WORDS)     

Afferent innervation of the guinea-pig's ureter

The electrical activity of 41 mechanosensitive afferent units was recored using anin vitro preparation of the guinea-pig's ureter. The conduction velocities of these fibres were found to be in the C-fibre range. Only 4 of them responded to contractions of the ureter. The activation threshold of the units to intraluminal (i.l.) pressure varied between 3 and 50 mm Hg. It is concluded that some of these afferent fibres might be involved in the signalling of nociceptive events.     

Zebrafish pax5 regulates development of the utricular macula and vestibular function.

The zebrafish otic vesicle initially forms with only two sensory epithelia, the utricular and saccular maculae, which primarily mediate vestibular and auditory function, respectively. Here, we test the role of pax5, which is preferentially expressed in the utricular macula. Morpholino knockdown of pax5 disrupts vestibular function but not hearing. Neurons of the statoacoustic ganglion (SAG) develop normally. Utricular hair cells appear to form normally but a variable number subsequently undergo apoptosis and are extruded from the otic vesicle. Dendrites of the SAG persist in the utricle but become disorganized after hair cell loss. Hair cells in the saccule develop and survive normally. Otic expression of pax5 requires pax2a and fgf3, mutations in which cause vestibular defects, albeit by distinct mechanisms. Thus, pax5 works in conjunction with fgf3 and pax2a to establish and/or maintain the utricular macula and is essential for vestibular function.     

Afferent and efferent innervation of the rat esophagus

Summary The technique of retrograde labeling of nerve cells with HRP and nuclear yellow as well as transganglionic anterograde HRP-tracing of sensory projections into the CNS were used to establish the motor and sensory innervation pattern of two parts of the rat esophagus: the cervical and the abdominal segment. For comparison, also the innervation of the anterior wall of the stomach was studied.Application of HRP to the cervical part of the esophagus resulted in bilateral labeling of neurons in the nucleus ambiguns exclusively, while application of the tracer to the abdominal part was followed by labeling of cells in both the nucleus ambiguus and the dorsal motor nucleus of the vagus. Application of tracer to the wall of the stomach caused labeling of cells in the dorsal motor nucleus of the vagus exclusively. Labeling appeared always bilaterally.In all experiments there was a profuse labeling of primary afferent neurons with cell bodies in both nodose ganglia and endings in certain subnuclei of the solitary nucleus. Endings related to the cervical esophagus projected into the ventral subnuclei, projections from the abdominal esophagus were located in the ventral and medial subnuclei, those from the stomach in the medial subnucleus solely. The area postrema and the commissural nucleus received afferents from both organs, the esophagus and the stomach.Double labeling experiments with HRP and nuclear yellow provided no signs of overlap of sensory innervation areas of the sites investigated in this study. Within the wall of the esophagus no labeled intramural cells nor nerve fibers were found in sections beyond the injection sites.     

Afferent innervation patterns of the pigeon horizontal crista ampullaris

The vestibular semicircular canals are responsible for detection of rotational head motion although the precise mechanisms underlying the transduction and encoding of movement information are still under study. In the present investigation, we utilized neural tracers and immunohistochemistry to quantitatively examine the topology and afferent innervation patterns of the horizontal semicircular canal crista (HCC) in pigeons (Columba livia). Two hundred and eighty-six afferents from five horizontal canal organs were identified of which 92 units were sufficiently labeled and isolated to perform anatomical reconstructions. In addition, a three-dimensional contour map of the crista was constructed. Bouton afferents were located only in the peripheral regions of the receptor epithelium. Bouton afferents had the most complex innervation patterns with significantly longer and more numerous branches as well as a higher branch order than any other fiber type. Bouton fibers also contained significantly more bouton terminals than did dimorph afferents. Calyx afferents were located only in the apex and central planar regions. Calyx fibers had the largest axonal diameters yet the smallest fiber lengths and innervation areas, the fewest number of branches, the lowest branch order, and the fewest total number of terminals of all fiber types. Dimorph afferents were located throughout the central crista with afferent terminations that were larger and more complex than calyx fibers but less so than bouton fibers. Overall, the pigeon HCC morphology and innervation shares many common features with those of other animal classes.     

Afferent innervation in the cervical region of the esophagus and trachea in early postnatal ontogenesis

Method of retrograde axonal transport of horseradish peroxidase was used to study the afferent innervation of trachea and esophagus cervical portion in the neonatal, 10-, 20- and 30-days old kittens. Labeled neurons in all the animals were localized in the vagal caudal sensory ganglion and CI-CVI spinal ganglia both in right and left sides. The major role in the innervation of trachea and esophagus cervical portion in kittens from the moment of their birth till postnatal day 20, is played by the cells of spinal ganglia, while at day 30 these are neurocytes of the vagal ganglia. No significant differences were found in the number of neurocytes, innervating the trachea and the esophagus.     

Efferent innervation of the larynx in domestic pigeons (Columba livia domestica L

The motoneurons innervating the larynx of the pigeon were localized with the horseradish peroxidase (HRP)-method (Mesulam 1978). After injection of HRP into the laryngeal muscles the exact position of the Nucleus ambiguous could be determined, which lays in the region of 600 micron rostral to 1,000 micron caudal of the obex.     

Afferent innervation of extraocular muscles in the rat studied by retrograde and anterograde horseradish peroxidase transport

After injection of horseradish peroxidase (HRP) into extraocular muscles of rat perikarya were labeled mainly along the medial edge of the ophthalmic subdivision of the trigeminal ganglion but not in the mesencephalic nucleus of the trigeminal nerve. Injections of HRP into the trigeminal ganglion labeled simple as well as branching and meandering free fiber endings in extraocular muscles. No evidence for muscle spindles was found, but the meandering endings may be considered as candidates for stretch receptors.     

Afferent and efferent innervation of the guinea-pig cochlea: a light microscopic and histochemical study.

The pattern of innervation of the normal and de-efferented guinea-pig cochlea has been studied from sections prepared without dehydration or decalcification procedures. This technique has given very good preservation of fine structure, thus enabling us to observe the existence of fibre routes not before described. Tissue was treated by various techniques: osmic acid fixation alone, formalin followed by either Holmes or Bielschowsky-Gros silver stains, or by Karnovsky-Roots acetylcholinesterase or a modified Maillet zinc iodide histochemical reaction. We have been able to visualize two routes which efferent fibres take to the Hensen cells, as well as connections to the efferent network under the three rows of outer hair cells. The tunnel fibres are shown to cross to three levels of a plaque on the outer hair cell-1/Deiters' cell-1 surface. The medial tunnel fibres degenerate rapidly after olivocochlear bundle section; the ‘efferent’ stained basilar fibres remain intact. ‘Efferent’ fibres are seen among the outer spiral bundle and which can take a different route from the afferent component. These newly described routes to the Deiters' and Hensen cells now pose the question whether the role of these ‘supporting’ cells is really a passive one, as has been assumed in the past.     

The distinctive central utricular projections in the herring

The utriculus of the inner ear of clupeid fishes comprises three maculae, each separately innervated. The three nerves were labelled with horseradish peroxidase in the herring and were found to project ipsilaterally to the cerebellum and octavus area and bilaterally to the lateralis zone of the brainstem. The anterior macular nerve terminates dorsally in the octavus area and exclusively in a rostral portion of the anterior octavus nucleus, whereas the middle and posterior macular nerves end ventrally in the octavus area and in the reticular formation. Large middle macular fibers synapse on the Mauthner-cell lateral dendrite.     

Unilateral testing of utricular function

A modified rotatory chair test is reported in which radial acceleration, generated by eccentric displacement of the subject during constant angular velocity, is exploited as a unilateral stimulation to the otolith organs. During constant angular rate rotation, the test subject is displaced laterally on the rotating turntable by 3.5 cm, so that one labyrinth becomes aligned with the rotatory axis while the second – eccentric – labyrinth is solely exposed to the altered gravito-inertial acceleration (GIA). Previously reported results showed that the direction of the response is independent of the direction of turntable rotation, ruling out any canal influence, and indicated that in a normal population the response, measured in one eye, was symmetrical for displacement of the left and right labyrinths. This mode of stimulus thus appears to elicit a unilateral otolith-ocular response (OOR). Examination of this unilateral OOR was extended in the present study; comparative testing with head-tilt to gravity, i.e. involving bilateral stimulation to the otolith organs, was carried out. Movements of both eyes were recorded (by three-dimensional video-oculography), in order to examine response conjugacy. To verify the specificity of the unilateral stimulus, tests were performed with patients who had previously undergone unilateral section of the vestibular nerve as treatment for acoustic neuroma. The eccentric displacement profile (EDP) and head-tilt stimulus each included ten cycles of left-right oscillation in order to permit signal averaging. In the normal subjects (n=12) the torsional component of the OOR proved to be both labyrinth-symmetrical and conjugate, during both bilateral and unilateral otolith stimulation. OOR gain (ocular torsion/GIA tilt) was higher for bilateral than unilateral stimulation. Bilateral OORs, obtained from three of the five unilaterally deafferented patients, proved less symmetrical and conjugate than in the normals. Unilateral OORs in all five patients were characteristically asymmetrical, with little or no response during stimulation of the diseased labyrinth. Received: 28 July 1997 / Accepted: 3 February 1998     

Studies on the functional significance of efferent innervation in the auditory system: Afferent neuronal activity as influenced by contralaterally applied sound

Summary Recordings were made using stereotaxic techniques from single neurons of the cochlear nucleus of cats in very light barbiturate anesthesia (supplemented by local anesthesia). The responses of afferent neurons to ipsilateral acoustic stimulation were recorded and compared with the responses following binaural stimulation. The sound pressure levels in both ears were kept low enough to avoid interaural cross-talk. It was shown that contralateral stimulation reduced the response of an afferent neuron to ipsilateral stimulation. This inhibition was dependent, on the frequency of the sound presented to the contralateral ear. Adjacent frequencies inhibited more strongly than the characteristic frequency itself or more widely removed frequencies. The dependency of the inhibition on frequency took the form of a W-shaped curve. From this frequency dependent behavior it is concluded that this inhibition leads to an increase of pitch discrimination. This effect can only be explained as resulting from the efferent innervation.Preliminary report of this work was presented at the 34 th Meeting of the Deutsche Physiologische Gesellschaft (March 27–29, 1968, Mainz, Germany).     

Statoacoustic properties of utricular afferents.

1. We classified the utricular afferents on the basis of their spontaneous acitivity and responses to tilts and vibrations. 2. Type I afferents fire spontaneously in a regular pattern; their responses to tilts consist of a phasic-tonic change in firing rate. They may respond to vibrations by increasing or decreasing their rate and show no adaptation. 3. The spontaneous activity and the responses to tilts of type II are similar to those observed in type I afferents. The differences become apparent when the preparation is subjected to a vibrational stimulus, since type II neurons increase their firing rate regardless of the stimulus frequency and show adaptation. 4. Type III neurons have no spontaneous activity. They respond to tilts by firing during the transition from one position to the other. They respond to a vibrational stimulus with maintained firing and show no adaptation. 5. We studied the dynamic responses of each type of neuron. We used sensitivity curves for the study of type III afferents and proposed a statistical method to define gain curves for the study of the other types. 6. The gain curves generated by type I neurons reach their maximum at frequencies of stimulation close to the spontaneous rate of firing. 7. In the gain curves of type II afferents the maximum corresponds to frequencies higher than their spontaneous activity. 8. Sensitivity curves and gain curves give similar results for type III fibers. The sensitivity curves of these afferents were classified into four subtypes. 9. We studied the responses of the three types of afferents to bursts of sinusoidal vibrations. 10. We concluded that the properties of types I and II fibers are fit to carry information about movements and position of the head, but also transmit acoustical information. Type III fibers are more adapted to provide information about acoustical stimuli, but can also convey information about head movements.