Spherical Cell Area Research Articles

Serotonin projection patterns to the cochlear nucleus

The cochlear nucleus is well known as an obligatory relay center for primary auditory nerve fibers. Perhaps not so well known is the neural input to the cochlear nucleus from cells containing serotonin that reside near the midline in the midbrain raphe region. Although the specific locations of the main, if not sole, sources of serotonin within the dorsal cochlear nucleus subdivision are known to be the dorsal and median raphe nuclei, sources of serotonin located within other cochlear nucleus subdivisions are not currently known. Anterograde tract tracing was used to label fibers originating from the dorsal and median raphe nuclei while fluorescence immunohistochemistry was used to simultaneously label specific serotonin fibers in cat. Biotinylated dextran amine was injected into the dorsal and median raphe nuclei and was visualized with Texas Red, while serotonin was visualized with fluorescein. Thus, double-labeled fibers were unequivocally identified as serotoninergic and originating from one of the labeled neurons within the dorsal and median raphe nuclei. Double-labeled fiber segments, typically of fine caliber with oval varicosities, were observed in many areas of the cochlear nucleus. They were found in the molecular layer of the dorsal cochlear nucleus, in the small cell cap region, and in the granule cell and external regions of the cochlear nuclei, bilaterally, of all cats. However, the density of these double-labeled fiber segments varied considerably depending upon the exact region in which they were found. Fiber segments were most dense in the dorsal cochlear nucleus (especially in the molecular layer) and the large spherical cell area of the anteroventral cochlear nucleus; they were moderately dense in the small cell cap region; and fiber segments were least dense in the octopus and multipolar cell regions of the posteroventral cochlear nucleus. Because of the presence of labeled fiber segments in subdivisions of the cochlear nucleus other than the dorsal cochlear nucleus, we concluded that the serotoninergic projection pattern to the cochlear nucleus is divergent and non-specific. Double-labeled fiber segments were also present, but sparse, in the superior olive, localized mainly in periolivary regions; this indicated that the divergence of dorsal and median raphe neurons that extends throughout regions of the cochlear nucleus also extended well beyond the cochlear nucleus to include at least the superior olivary complex as well.

Distribution and origin of serotoninergic afferents to guinea pig cochlear nucleus.

The distribution of serotoninergic fibers in the guinea pig cochlear nucleus was studied with serotonin immunohistochemistry. In addition, the origin of the serotoninergic fibers was determined by combining the retrograde transport of wheat germ agglutinin-apohorseradish peroxidase (gold conjugated) with serotonin immunohistochemistry. Immunoreactivity was present in varicose and nonvaricose fibers that were unevenly distributed throughout the cochlear nucleus. The fibers were most prominent in the superficial layers of the dorsal cochlear nucleus and the anterior spherical cell area of the anteroventral cochlear nucleus. Although less prominent, serotonin-positive fibers were also present in the remaining part of the anteroventral cochlear nucleus and the posteroventral cochlear nucleus. A few positive fibers were present in the auditory nerve root and the dorsal and intermediate acoustic striae. Double-labeled cells were found throughout the rostral-caudal extent of the serotoninergic system from the caudal linear nucleus to the nucleus raphe pallidus. However, most were confined to the dorsal (52%) and median (18%) raphe nuclei. Some serotoninergic cell groups contained retrogradely labeled cells that were not serotonin immunoreactive, indicating nonauditory afferents to cochlear nucleus containing other neurotransmitter substances. Serotonin may tonically modulate auditory processing within the cochlear nucleus as well as influence certain ascending auditory pathways. Most of the serotonin in the cochlear nucleus comes from superior raphe nuclei that also project to basal ganglia motor systems and limbic structures. Therefore, the effect of serotonin on the cochlear nucleus may be related to level of arousal or behavioral state.

Changes in the cat cochlear nucleus following neonatal deafening and chronic intracochlear electrical stimulation

The effects of chronic intracochlear electrical stimulation on the cochlear nucleus (CN) were studied in eight cats that were neonatally deafened by daily intramuscular injections of neomycin. Profound hearing loss was confirmed in each animal by auditory brainstem response (ABR) and frequency following response (500 Hz) testing. Five of the kittens were implanted unilaterally with a scala tympani electrode array at ages 8–16 weeks. These kittens were stimulated daily for four hours at 2 dB above the evoked ABR threshold, over a period of three months, and subsequently euthanized for histological analysis at 26–32 weeks of age. The three remaining deaf kittens were maintained without stimulation over prolonged periods in order to study the long-term consequences of neonatal deafening, and were euthanized at 66–133 weeks of age. This study compares the CN of these deafened experimental animals and the CN of normal adult cats. Three experimental parameters were examined: CN volume, cross-sectional area of spherical cells in the rostral anteroventral cochlear nucleus (AVCN), and spherical cell density in this same region. The CN in animals that received electrical stimulation showed significant bilateral degenerative changes in all three measured parameters. Total nuclear volume was reduced by 35–36%, spherical cell size was reduced by 20–26%, and spherical cell density decreased by 36–42%, as compared to the normal cat CN. Comparisons were also made in the stimulated animals between CN ipsilateral to the stimulated cochlea and the contralateral, unstimulated CN. Although CN volume and cell density were not significantly different between the two sides, the spherical cells ipsilateral to the stimulated cochlea were on average 6% larger than cells in the contralateral, unstimulated CN. This difference was statistically significant (paired Student's t-test, P = 0.035). After neonatal long-term deafening, there was highly significant shrinkage of about 42% in total CN volume, a 38% reduction in mean spherical cell size, and a 57% decrease in spherical cell density in the AVCN, compared to the CN of the normal adult cat. From these data it is concluded that neonatal deafening induces severe reduction in CN volume and a decrease in AVCN spherical cell area and density that are progressive over many months. The spherical cell shrinkage that was induced by deafness was mitigated slightly by chronic intracochlear electrical stimulation; however the other effects of deafening were not prevented or reversed by chronic stimulation.

Brainstem auditory evoked potentials correlate with morphological changes in Gunn rat pups

The relationship of brainstem structure and function in bilirubin encephalopathy is incompletely understood. The present experiments compare quantitative measures of brainstem structures with brainstem auditory evoked potentials (BAEPs) in infant jaundiced (jj) and nonjaundiced (Nj) Gunn rats. Ten jj's from 4 litters were injected with sulfadimethoxine at 11–12 days of age to raise their brain bilirubin concentration. Littermate controls were jj's given saline, and Nj's given sulfadimethoxine or saline. At 15–17 days of age BAEPs were recorded, and rats were prepared for histological examination, as was reported in the previous paper (Conlee and Shapiro. 1991). Significant differences between groups were seen for BAEP wave I latency ( P = 0.002), I–II interwave interval ( P = 0.001), and amplitudes of waves I, II, III, and IV (each P <0.0005) due to increased latencies and decreased amplitudes in the jj-sulfa group. Animals with the most severe BAEP abnormalities had the most severe histological abnormalities. Cochlear nucleus volume had a positive linear correlation with the amplitude of BAEP waves I. II, and IV, and an inverse correlation with wave I latency and I–II interwave interval ( P ≦ 0.001). The highest correlations were BAEP I–II interwave interval and amplitude of waves I and II with cochlear nucleus volume ( r = −0.78, 0.71 and 0.70, respectively, P < 0.0005). In the cochlear nucleus, spherical cell area correlated with wave I latency and amplitude, and wave III amplitude ( P < 0.001), the I–II interwave interval, and the amplitudes of waves II and IV ( P < 0.01). In contrast, globular cells, which were not affected anatomically, did not correlate significantly with later BAEP waves. Cell area in the nucleus of the trapezoid body correlated with amplitude of I and II ( P < 0.01). There were no significant correlations of cell area in the superior olive with any of the BAEP values. These results show that BAEPs are sensitive indicators of morphometric abnormalities in the brainstem of jaundiced Gunn rats, and help to establish the predictive validity of BAEPs in determining the specific sites of bilirubin-induced brain damage.

Effects of neonatal deafening and chronic intracochlear electrical stimulation on the cochlear nucleus in cats

Four newborn kittens were deafened by daily intramuscular injections of neomycin sulfate, beginning the day after birth and continuing for 14–16 days. At 10–16 weeks of age the deaf kittens were implanted unilaterally with a four wire intracochlear electrode array. The animals were stimulated daily (starting at 13–18 weeks of age), for a period of one hour, at 6 dB above the electrically evoked auditory brainstem response threshold. After 3 months of chronic intracochlear electrical stimulation, animals were studied in acute electrophysiological experiments and euthanized for histological studies. This study compares the stimulated and control cochlear nuclei (CN) of these deafened animals to the CN of four normal adult cats. Statistical comparisons of spherical cell densities in the anteroventral cochlear nucleus (AVCN), cross-sectional spherical cell areas, and volumes of the cochlear nucleus subdivisions were included in the analysis. The results indicate that, by all of these measures, the cochlear nuclei in neonatally deafened animals were significantly different from the cochlear nuclei of control animals. As a result of deafening, the density of spherical cells was decreased by 30%, the cross-sectional areas of spherical cells were reduced by 20%. and the volume of the cochlear nucleus was reduced by 25%. These changes were observed in both cochlear nuclei (ipsilateral to both stimulated and unstimulated ears) of the deafened animals. With the measures employed, no significant difference was demonstrated in comparisons between the deafened/unstimulated and the deafened/stimulated cochlear nuclei. That is, no reversal of the profound effects of deafening was observed in the cochlear nuclei as a consequence of chronic intracochlear electrical stimulation which was begun 11 to 16 weeks after deafening.

Effects of Total Cochlear Haircell Loss on Integrity of Cochlear NucleusA Quantitative Study

In cochleas of chincillas treated with amikacin, cochlear sensory cells were totally destroyed in all new-born animals. In animals treated as adults some occasional haircells remained in apical turns. In the neonatally treated animals, the resulting auditory deprivation significantly affected the volume of the ventral cochlear nucleus and large-dark spherical cell area. The density of large-dark spherical cells increased significantly from normal in both neonatally and adult treated groups. Our results suggest that the VCN is more dependent on auditory stimulation for proper development than the DCN. In adult chinchillas treated with amikacin there was a significant change in large-dark spherical cell density without a change in total cell numbers or large-dark spherical cell area volume. Our study indicates that the mature cochlear nucleus is much more resistant to the effects of auditory deprivation than the developing cochlear nucleus and that the maintenance of the mature auditory system is not as dependent on auditory stimulation. Studies such as this examining the morphological effects of profound cochlear deafness on higher levels of the auditory system are essential in cochlear implant research.

The distribution of spherical cells in the anteroventral cochlear nucleus of the guinea pig.

Several types of neuron are found in Nissl-stained sections of the anteroventral cochlear nucleus (AVCN). From these one group, the spherical cells (Osen, 1969), can be readily distinguished from the remaining small and multipolar forms. The rostral pole of the AVCN has previously been subdivided into the large and the small spherical cell areas (in several mammals). In the present study of the guinea pig AVCN, spatial distributions of cell density, size, and shape have been investigated. These have been used to test whether the subdivision made on the basis of morphological differences in the spherical cells is valid, or whether there is a gradual gradient in these features. This analysis has shown that although variations in cell size and shape are observed, the spherical cell area cannot be partitioned on these grounds. There is, however, a graded increase in spherical cell packing density towards the rostral pole of the AVCN, with proportionately fewer of the other cell types present.

Cochlear nuclear complex of mice.

Using serial sections stained with luxol fast blue-cresyl violet, the cochlear nuclei of CBA/J mice were parcellated into the same cytoarchitectonic areas and layers that Osen (1969) used in cats. Within the spherical cell areas, the distribution of Nissl substance is more reliable than soma shape in identifying the spherical cells. The area of large spherical cells is extremely small in CBA/J mice but does contain significantly larger neurons than the small spherical cell area. In Golgi preparations, bushy cells are found in all areas of the ventral cochlear nucleus except in the octopus cell area and granule cell layer. They are more numerous anteriorly than posteriorly and details of their morphology are quite variable. Stellate cells are found throughout the ventral cochlear nuclei but are present in greatest numbers in the multipolar cell area; they are rare in the large spherical cell area and octopus cell area. Because size, soma morphology, and dendritic arborization vary on a continuum rather than in discrete steps, we have not subcategorized these neurons. Octopus cells are restricted to the posterior, dorsomedial area of the ventral cochlear nucleus. In the central region of the dorsal cochlear nucleus, stellate cells abound and are categorized as vertical, elongate, or radiate cells. In the granule layer of the dorsal cochlear nucleus there are both fusiform and Purkinje-like neurons, so named because of their resemblance to cerebellar Purkinje cells. These Purkinje-like cells differ from fusiform cells in having 1) a smaller cell body, spherical in shape, 2) no basal dendrites, 3) a sagittal dendritic orientation, 4) elaborate dendritic branching, and 5) abundant dendritic spines.

Effects of monaural and binaural sound deprivation on cell development in the anteroventral cochlear nucleus of rats

The sizes of large spherical and fusiform cells of the anteroventral cochlear nucleus were studied in rats reared after unilateral middle ear ossicle removal on postnatal days 10 or 16, or after bilateral removal on postnatal day 16. In animals deprived monaurally from 10 days after birth, large spherical cell areas of the deprived side were reduced by 21% compared to the nondeprived side; the deprived cells were 17% smaller than cells of control animals. Large spherical cells contralateral to the deprived ear were slightly larger than those of controls. Large spherical cells monaurally deprived from the 16th day showed effects similar to those deprived from the onset of hearing, although cell reduction on the deprived side was only 10% relative to controls. In contrast to the consequences of monaural sound deprivation, binaural deprivation from the 16th day resulted in no reduction in size of large spherical cells. Fusiform cells of animals in monaurally and binaurally deprived groups were not significantly smaller than the fusiform cells of controls. Ear histologies confirmed that each cochlea and spiral ganglion was normal in experimental and control animals. Because large spherical cells receive unilateral input directly from the acoustic nerve and are known to project bilaterally to the medial superior olive, the bilateral differences observed in large spherical cell area following rearing under monaural deprivation conditions may reflect a form of imbalanced binaural interactions between axon terminals of spherical cells.

Projections of the trapezoid body and the superior olivary complex of the Kangaroo rat (Dipodomys merriami).

Glass micropipettes filled with 2 M sodium cyanide were used to physiologically locate and iontophoretically damage the nucleus of the trapezoid body (NTB), the medial superior olive (MSO), and the lateral superior olive (LSO). Mechanical lesions were made in the trapezoid body as it leaves the cochlear nuclei. After a 3- to 10-day survival time the projections and terminal degeneration were traced with the Fink-Heimer and Nauta-Gygax stains. The ventral cochlear nucleus (VCN) projects via the trapezoid body to ipsilateral LSO, ipsilateral preolivary nuclei, ipsilateral lateral and a contralateral medial dendritic fields of MSO, and contralateral NTB; there is also a small ipsilateral projection to the ventral nucleus of the lateral lemniscus (VNLL) and the central nucleus of the inferior colliculus (CNIC). Some trapezoid body fibers ascend via the contralateral lateral lemniscus to VNLL, DNLL (dorsal nucleus of the lateral lemniscus), and CNIC. There is no projection from the ventral cochlear nucleus to the ipsilateral NTB and contralateral preolivary nuclei. All portions of NTB project ipsilaterally to LSO (ventral NTB to dorsomedial LSO, dorsal NTB to ventral LSO) and to the retro-olivary nucleus. In two animals with NTB lesions there is also degeneration in the ventromedial portion of the ipsilateral facial nucleus. NTB projects contralaterally by way of the stria of Monakow to the pyramidal and molecular cell layers of the dorsal cochlear nucleus (DCN). The NTB does not project ipsilaterally to MSO, preolivary nuclei, VNLL, DNLL and CNIC. Contralaterally there are no projections to any of the nuclei of the auditory pathway except the DCN. Most MSO projections are ipsilateral. The densest goes by way of the lateral lemniscus to the lateral aspect of the ipsilateral CNIC, terminating throughout its dorsoventral axis. MSO also projects bilaterally to the pyramidal and molecular cell layers of dorsal cochlear nucleus (DCN), and ipsilaterally to the ventral portion of the motor nucleus of V and to the facial nucleus. MSO does not project ipsilaterally to the LSO, NTB, preolivary, VCN and retro-olivary nuclei. On the contralateral side, all structures except the DCN are free of projection patterns from axons originating in the MSO. LSO projects bilaterally to the central and ventral portions of CNIC and to the nuclei of the lateral lemnisci, and ipsilaterally to the large and small spherical cell areas of anterior ventral cochlear nucleus (AVCN) and to all portions of DCN. The LSO does not project ipsilaterally to the NTB, MSO, preolivary and retro-olivary nuclei. On the side opposite, this nucleus does not project to NTB, MSO, retro-olive, VCN, preolivary and LSO. For all lesions regardless of the site, there is no degeneration found rostral to the CNIC. The medial geniculate body or other structures in the diencephalon or cortex are free of any fields of terminal degeneration.

Anatomical projection of the cochlea to the cochlear nuclei of the guinea pig.

In 16 guinea pigs restricted lesions of the cochlea and the resulting degeneration in the cochlear nerve and in the cochlear nuclei were confirmed by Bodian and Schultze-Gros methods, to study the relationships of central projection of single cochlear turns with the cytoarchitectural areas of the cochlear nucleus complex. The ascending branches of the basal turn terminate in the medial part of the anteroventral cochlear nucleus (AVCN) including the globular cell area, the small spherical cell area and the caudal portion of the large spherical cell area. The descending branches of the basal turn project onto the dorsomedial two-thirds of the posteroventral nucleus (PVCN) with globular cell and octopus cell areas, and terminate in the dorsomedial portion of the central region of the dorsal cochlear nucleus (DCN). Terminals of the apical turn are associated with globular, small spherical and large spherical cells in the ventrolateral part of the AVCN, with globular cells, multipolar cells and a few octopus cells in the ventral PVCN, and with cells of the lateroventral extreme of the central region in the DCN. Lesions of the second and third turns result in degeneration in correspondingly intermediate regions of the cochlear nuclei. There is a predominance of the basal and second turn representation in the three major subdivisions of the cochlear nuclei except the anterior pole of the AVCN.

Projection of the cochlea to cochlear nuclei in Merriam's kangaroo rat.

AbstractProjection of the cochlea onto the cochlear nuclei was studied by lesioning the spiral ganglion and tracing degenerating fibers and terminals by the Nauta‐Gygax and Fink‐Heimer methods. Basal turn lesions result in degeneration in the medial portion of anterior ventral cochlear nucleus (AVCN) including globular cell area, small spherical cell area, and a small portion of the large spherical cell area; in dorsomedial portion of posterior ventral cochlear nucleus (PVCN) including globular cell area and octopus cell area; and in the medial extreme of the central region of dorsal cochlear nucleus (DCN). Apical turn lesions result in degeneration in the lateral portion of AVCN including globular cell area, small spherical cell area, and a substantial amount of the large spherical cell area; in the ventrolateral portion of PVCN including globular cell area and multipolar cell area; and in the lateral extreme of the central region of DCN. Lesions in intermediate turns of the cochlea result in degeneration in correspondingly intermediate regions of the cochlear nuclear complex. The basal portion of the cochlea (high frequency) projects most strongly to the small spherical cell area and the octopus cell area. The apical turns (low frequency) project most strongly to the large spherical cell area and the multipolar cell area.

Coding and Cytoarchitecture in the Kangaroo Rat Cochlear Nuclei

Eighty-four neurons were recorded from and correlated with cytoarchitectural fields: 21 were located in the globular cell area, 19 in the multipolar cell area, 17 in the small spherical cell area, 11 in the octopus cell area, 8 in the dorsal cochlear nucleus, and 6 in the large spherical cell area. Eight neurons were successfully marked by intracellular injection of procion yellow. Units in small spherical cell area (best frequencies, 0.475–11.500 kHz) rarely display tight phase locking and show a characteristic “onset” response followed by decreased activity. Neurons in the multipolar cell area (best frequencies, 0.10–1.45 kHz) are mostly low-frequency phase lockers. There is great physiological and cellular diversity in globular cell area (best frequencies, 0.24–34.10 kHz). Units in the octopus cell area (best frequencies, 1.4–21.5 kHz) typically display high rates of spontaneous and driven activity. Neurons in large spherical cell area (best frequencies, 0.8–14.5 kHz) have interspike interval histograms of spontaneous activity with short modes and rapid decay. Long modes and a high degree of symmetry characterize neurons in dorsal cochlear nucleus (best frequencies, 0.5–10.9 kHz). [Supported by NIH grants.]

Histochemical localization of cholinesterases in the cochlear nuclei of the cat, with notes on the origin of acetylcholinesterase-positive afferents and the superior olive

This study was carried out in order to correlate the distribution of cholinesterases in the cat cochlear nuclei with the cytoarchitecture and terminal areas of afferent fiber tracts. Formaldehyde-fixed frozen sections were stained by the thiocholine method using acetylthiocholine and butyrylthiocholine iodides as substrates and Mipafox as a specific inhibitor of butyrylcholinesterase (BuChE). The acetylcholinesterase (AChE) activity appeared to be associated with neurons while the BuChE reaction probably was confined to glial elements. Short incubation revealed only a few AChE positive structures which appeared to form a continuous pathway leading from certain cells in the superior olivary complex via the olivocochlear bundle to the molecular and granular cell layers of the cochlear nuclei. The probable role of this AChE-positive pathway in the central control of the pyramidal cell activity in the cochlear nuclei is discussed. Prolonged incubation resulted in a more widespread AChE reaction, and in these sections most cell areas of the cochlear nuclei could be defined by their staining properties. The AChE-positive plexus of the large and small spherical cell areas may represent the terminal arborization of the facilitatory cholinergic pathway found physiologically by Whitfield and Comis 50,51 to arise in the lateral superior olive on the same side.