PubMed Health⌕ Search

Biomedical subjects

C K Henkel

Publications and source records attributed to C K Henkel.

At least 19 recordsLinked to original sources
PubMed1999

Organization of the disynaptic pathway from the anteroventral cochlear nucleus to the lateral superior olivary nucleus in the ferret.

The medial nucleus of the trapezoid body (MNTB) is one of three major nuclei of the superior olivary complex and provides an important inhibitory input from the contralateral ear to the lateral superior olivary nucleus (LSO) in the initial binaural pathway for coding interaural intensity differences. The major input to the MNTB from the contralateral anteroventral cochlear nucleus (AVCN) involves giant, calyx-like endings that have a one-to-one relationship with cells in the MNTB as confirmed in the ferret in this study. The main objective of the present study was to define the subsequent organization of projections from cells receiving these calyx-like endings. Several anatomical tracers (Phaseolus vulgaris leucoagglutinin, dextran-biotin, and biocytin) were used that are transported both anterogradely and retrogradely within neuronal projections in order to define the organization of MNTB connections with the LSO in the adult ferret. Analysis focused on determining the topography in both the transverse and longitudinal planes of the projections. Focal tracer injections in the LSO resulted in retrograde labeling of a long, narrow column of cells in the MNTB. The orientation and location of labeled cells was dependent on the medial-lateral position of the injection site. In the rostral-caudal dimension of MNTB, there was no such topographic relation between the injection site and the position of labeled cells. Labeled cells in the MNTB were distributed more or less evenly in a longitudinal column regardless of whether the injection site was restricted to the rostral, middle or caudal part of the LSO. In keeping with this pattern, tracer injections in the MNTB resulted in bands of labeled axons that distributed endings throughout the rostral-caudal axis of the LSO. These bands or sheets varied in medial-lateral position relative to the location of the injection site, but lacked any such rostral-caudal gradient. Thus, overall the MNTB-LSO projections have a convergent-divergent pattern of organization. While MNTB cells receive singular calyx-like endings from the AVCN, LSO cells receive projections from a long column of cells in the MNTB. Implications for processing interaural intensity differences are discussed.

Animals↗
PubMed1998

Calcium-binding proteins and GABA reveal spatial segregation of cell types within the developing lateral superior olivary nucleus of the ferret.

Chemical characteristics of developing neurons in the superior olivary complex of the ferret were analyzed using immunohistochemical methods. The present report of calcium-binding proteins in the developing and adult superior olivary complex shows distinct distribution patterns for parvalbumin, calbindin, and calretinin in the lateral superior olivary nucleus (LSO) of the developing ferret that correspond to distribution patterns for different projection cell types and neurotransmitters. In the neonate, there was an initial complementary distribution of calcium-binding proteins between the shell and core of the body of the developing LSO. Parvalbumin and calbindin-immunoreactive cells were present in the shell, whereas calretinin-immunoreactive cells were restricted to the core of the LSO. Gamma amino butyric acid (GABA), but not glycine, immunoreactive cells were distributed similarly in the shell of the LSO in the neonate. There were, in addition, reciprocal medial-to-lateral gradients of parvalbumin and calbindin-immunoreactive cells in the LSO shell of the neonate. These complementary patterns in the LSO were transient, however, and by the end of the second postnatal week, each calcium-binding protein differed markedly in its cellular distribution in the superior olive, including the LSO. GABA-immunoreactive cells also were restricted transiently to the shell of the LSO in neonates. The radial segregation of transient calcium-binding expression in LSO cells was orthogonal to the medial-to-lateral axis in the LSO and, therefore, parallels fibrodendritic layers and presumed isofrequency planes of the LSO. The early postnatal segregation of calcium-binding proteins in the isofrequency axis was congruent with the gradients of contralateral and ipsilateral projection cell types in adult LSO. It seems likely that developmental mechanisms regulate expression of calcium-binding protein and neurotransmitter phenotypes and that these mechanisms operate in development within the isofrequency axis as well as along the tonotopic axis of this auditory nucleus.

Age Factors↗
PubMed1997

Axonal morphology in fibrodendritic laminae of the dorsal nucleus of the lateral lemniscus: afferent projections from the medial superior olivary nucleus.

The distribution and morphology of axons projecting from the medial superior olivary nucleus to the dorsal nucleus of the lateral lemniscus were studied in the adult cat. Injections of Phaseolus vulgaris-leucoagglutinin, biocytin, or dextran-rhodamine in the medial superior olivary nucleus labeled axons that ascended in the lateral lemniscus. Before entering the inferior colliculus, collateral branches of these labeled axons ended in the dorsal nucleus of the lateral lemniscus in thin, horizontal bands forming laminae that extended throughout the rostral-caudal length of the dorsal nucleus of the lateral lemniscus. A dorsal-ventral topography was apparent in the position of the lamina with respect to the injection site, but no relation between the rostral-caudal location of labeled endings and the injection site was observed. There was a divergent pattern of connections within the horizontal laminae rather than a point-to-point organization. The terminal branches of the collateral axons exhibited round or oval boutons en passant and terminaux. Individual arbors reconstructed from serial sections distributed varicosities in circumscribed domains that were only a subcomponent of the area of the afferent laminae in which they were distributed. The spatial relationships of axonal domains of several axons labeled from a single injection in the medial superior olivary nucleus suggest a mosaic pattern in the laminar connections with the dorsal nucleus of the lateral lemniscus.

Afferent Pathways↗
PubMed1995

Fiber outgrowth and pathfinding in the developing auditory brainstem.

In order to study the initial outgrowth of cochlear nucleus fibers, the lipophilic carbocyanine dye DiI was used to label these neurites in rats at E13 and E15. At E13, prior to leaving the ventricular zone, cochlear neurons have already extended axons along the marginal edge of the hindbrain and a few fibers have reached the midline. By E15, many more fibers have entered the midline region and some appear to contact glial cells at the midline. Based on axon trajectory and growth cone morphology it does not appear likely that there are significant intermediate decision points for trapezoid body fibers at these early stages of development. Contact between growth cones and glial cells at the midline is consistent with these cells playing a role in providing guidance cues for developing auditory fibers.

Animals↗
PubMed1995

Development of glycinergic cells and puncta in nuclei of the superior olivary complex of the postnatal ferret.

The distribution of glycine-immunopositive cells and axonal endings was studied in the adult and early postnatal ferret superior olive. As in other species, the most prominent glycine-immunopositive cell group in the adult ferret superior olive was the medial nucleus of the trapezoid body. Other darkly immunostained cells were present, although more scattered, in most periolivary regions, including the lateral and ventral trapezoid body nuclei. In the lateral superior olivary nuclei, glycine-immunopositive cells were intermingled with immunonegative cells. A comparable population of cells in the ipsilateral lateral superior olivary nucleus was retrogradely labeled in cases with unilateral injections of tritiated glycine in the inferior colliculus. Glycine-immunopositive puncta were widely distributed in the neuropil in most periolivary regions, including dense accumulations in the dorsomedial periolivary region and ventral and lateral nuclei of the trapezoid body. In the lateral and medial superior olivary nuclei, immunopositive puncta were distributed around the principal cells in characteristic perisomatic halos. In postnatal ferrets, immunopositive cell bodies were first observed by postnatal day 7 and were distributed in regions comparable to regions in the adult, with the exception that immunopositive cells in the lateral superior olivary nucleus did not appear until about postnatal day 28. There was diffuse staining in the neuropil in principal and periolivary nuclei by postnatal day 7. During the third postnatal week, the immunostaining in the neuropil began to take on a more granular appearance and immunopositive puncta could be seen by postnatal day 35. In the lateral and medial superior olivary nuclei, the earliest distribution of immunostaining in the neuropil was nonuniform, being greater in the high-frequency, medial, and ventral regions, respectively. The density gradient in these areas was gradually eliminated over the next 2 postnatal weeks as immunostained processes and endings appeared over greater portions of the nuclei.

Animals↗
PubMed1994

Terminal types on ipsilaterally and contralaterally projecting lateral superior olive cells.

The lateral superior olive (LSO) in ferret contains two distinct populations of principal cells, one population projecting to the ipsilateral and the other projecting to the contralateral inferior colliculus. In addition, these populations have been shown to be distinct from each other on the basis of tonotopic and isofrequency distribution within LSO, of dendritic morphology, and of neurotransmitter within the somata. The present study compared the two populations on the basis of the type of synaptic input. Laterality of projection was established using horseradish peroxidase histochemistry. Synaptic terminals contacting LSO somata identified as projecting ipsilaterally or contralaterally were quantified as round (R) or nonround (NR), representing presumptive excitatory and inhibitory input, respectively. Results indicate that the vast majority of somatic terminals contacting both projection populations are NR and, furthermore, that R terminals are significantly more likely to contact ipsilaterally than contralaterally projecting LSO cells. There is no significant difference in number of NR terminals or total number of terminals between ipsilaterally and contralaterally projecting LSO cells. These findings provide additional support to the notion that the LSO is comprised of two distinct cell populations. Moreover, they indicate a difference in the balance of somatic inhibition and excitation which may have an impact on the nature of the response properties of the two populations.

Animals↗
PubMed1993

Laterality of superior olive projections to the inferior colliculus in adult and developing ferret.

The laterality of projections from the lateral superior olivary nucleus (LSO) to the inferior colliculus was studied in adult and immature postnatal ferrets. In the adult ferret, large unilateral injections of horseradish peroxidase (HRP) in the inferior colliculus labeled about equal proportions of cells in the ipsilateral and contralateral lateral superior olivary nuclei. The contralateral labeled cells consistently were more densely labeled than those on the ipsilateral side. Double labeling experiments using fluorescent dyes indicated that only about 3% of LSO cells in the adult give rise to collaterals ending in the inferior colliculus on both sides. As expected, the distribution of labeled cells varied topographically in the LSO as a function of the injection site in the inferior colliculus. Dorsolateral inferior collicular injections labeled cells in the lateral limb of the LSO, whereas ventromedial injections labeled cells in the medial limb of the LSO. The proportion of ipsilateral and contralateral labeled cells also varied across the lateral-medial axis of the LSO in some cases. A gradient in laterality was observed in these cases with the lateral limb of the LSO containing the highest proportion of contralateral labeled cells, and the medial limb, the highest proportion of ipsilateral labeled cells. Larger inferior collicular injections resulted in greater proportions of ipsilateral labeling in LSO than smaller injections. Finally, ipsilateral labeled cells tended to be in the marginal region of the LSO, whereas contralateral labeled cells were more common within the core region of the LSO, irrespective of the location along the lateral-medial axis of LSO. The contralateral predominance of labeled cells, greater density of labeling in contralateral cells, different topographic distribution, and regional segregation of ipsilateral and contralateral labeled cells were typical of the LSO in ferret kits by birth, one month before the onset of hearing. Nevertheless, the relative proportion of ipsilateral and contralateral projection cells appears to change during postnatal development.

Animals↗
PubMed1992

Ultrastructural development of the medial superior olive (MSO) in the ferret.

When ferrets are born, four weeks before the onset of hearing, few synapses are evident in the medial superior olive (MSO). The synapses present are immature and almost exclusively found in the neuropil. The MSO somata are virtually devoid of synaptic contacts but are contacted by fine glial processes that increasingly ensheathe the somata during the first postnatal week. By P12, somatic synaptogenesis in the MSO is evident. Initially the terminals contain vesicles of irregular shape, size, and distribution. The glial lamellae appear to withdraw as the synaptic contacts form but continue to cover the asynaptic portions of the cell surface. The lamellae frequently extend from ensheathing the soma to encapsulate the immature terminals. During the next two weeks, synaptic density and terminal encapsulation proceed until the somata is surrounded by encapsulated synaptic terminals as in the adult ferret MSO. While most immature terminals contain round vesicles, during the first postnatal week some terminals with nonround vesicles can be distinguished. The first distinction between types of nonround vesicle-containing terminals, i.e., pleiomorphic and ovoid, is in the second postnatal week. This distinction becomes increasingly clear and by the end of the first postnatal month, terminal types can be reliably categorized. These observations indicate that: (1) synapses are present in the MSO neuropil one month prior to the onset of hearing, (2) the major period of synaptogenesis begins approximately two weeks prior to the onset of hearing, and (3) glial lamellae ensheathe MSO somata prior to the onset of somatic synaptogenesis, withdraw as synapses form, and subsequently re-extend to encapsulate newly formed synapses.

Animals↗
PubMed1991

Dendritic morphology and development in the ferret lateral superior olivary nucleus.

The dendritic morphology of cells in the lateral superior olivary nucleus was studied with the Golgi method in adult and postnatal ferrets. The lateral superior olivary nucleus in the adult ferret is a convoluted structure with an M-shape in frontal sections. The major cell type appears to have disk-shaped dendritic trees. Most dendritic trees appear to be approximately orthogonal to the curved medial-lateral axis of the nucleus. Depending on their position in the limb and on the plane of section with respect to the dendritic tree, the disk-shaped cells are either bipolar or radiate in orientation. One subclass of disk-shaped cells has secondary dendritic branches that end as tufts of tendril-like processes. In a second subclass of cells, the dendrites exhibit several orders of dichotomous branching and lack obvious tufts of terminal processes. Marginal cells are observed at the border of the nucleus and have dendrites restricted to the margins of the cell plate. The bipolar orientation of disk-shaped cells orthogonal to the axis of the limbs is already apparent by the time of birth. Transient spines and other appendages are abundant on somata and dendrites during the first postnatal week. By the end of the first postnatal month only distal appendages are found. Tufts of fine tendril-like processes appear at the ends of dendrites between postnatal days 28 and 56.

Animals↗
PubMed1991

Dendritic and axonal morphology of HRP-injected neurons in the inferior colliculus of the cat.

The dendritic and axonal morphology of neurons in the inferior colliculus of the cat was investigated after intracellular injection of HRP, in vivo. All injected axons gave off local collaterals, and most showed a widespread distribution and lacked a specific orientation. In contrast, the dendrites of injected neurons were distinguished by their degree of orientation and the direction of the longest axis of orientation. Dendrites showed a high, moderate, or low degree of orientation. Most highly oriented cells had their longest axis in the rostrocaudal direction with fewer in the mediolateral direction. In the central nucleus, only the rostrocaudally oriented cells correspond to the disc-shaped cells identified in Golgi preparations. Unlike most cells in our sample, the two cells that were disc-shaped had axons that were parallel to the orientation of the dendritic tree. In the dorsal cortex, rostrocaudally oriented cells also were found, but they had unoriented axons. In both the central nucleus and dorsal cortex, cells with a mediolateral axis of orientation or no specific orientation correspond to stellate cells and had axons with widespread local collaterals. These results suggest that an extensive network of local axon collaterals may contribute to neural processing within the inferior colliculus. In the central nucleus, local axons may establish connections within or across the fibrodendritic laminae. In the dorsal cortex, the local and afferent axons may form a complex reticular network. Finally, some injected cells had axons terminating locally and also entering the brachium of the inferior colliculus. This suggests that cells in the inferior colliculus may function as both interneurons and projection neurons.

Animals↗
PubMed1990

Dendritic morphology and development in the ferret medial superior olivary nucleus.

Dendritic morphology and development in the medial superior olivary nucleus of the ferret were studied using the Golgi method. In the adult ferret most medial superior olivary neurons had disk-shaped dendritic fields. These dendritic fields were oriented such that cells in a coronal plane of section appeared bipolar with major lateral and medial dendritic axes. In the horizontal plane the dendrites radiated about the soma. Dendrites of principal cells branched distally into tufts of numerous, tertiary processes that were beaded and thin. Peripheral cells in the fiber mantle encircling the nucleus were generally spindle-shaped or tripolar and lacked the tufted dendrites of principal cells. The dendrites of these peripheral cells coursed parallel to the nucleus both dorsoventrally and rostrocaudally. Horizontally oriented dendrites were observed even at birth for some cells in the medial superior olivary nucleus and bipolar dendritic fields were typical of most cells by the end of the second postnatal week. Dendrites of immature cells varied in caliber and radiated in all directions from the soma. Around postnatal days 8-10 transient appendages appeared on the soma and dendrites, first proximally and then more distally. These appendages persisted until the first postnatal month. Cell size and dendritic radius increased markedly during this same period. Postnatal days 28-30 were marked by the first appearance of tufts of tertiary dendritic branches. The tendril-like processes continued to increase in length until about the end of the second postnatal month.

Aging↗
PubMed1990

Synaptic organization in the adult ferret medial superior olive.

The ultrastructure of the medial superior olive (MSO) was studied in the adult ferret. The synaptic terminals were categorized on the basis of morphology and their distribution determined. There are three types of synaptic terminals: R terminals, containing round vesicles; Ov terminals, containing ovoid vesicles; and P terminals, containing vesicles of varying morphologies. R terminals are the dominant terminal type on both the somata and dendrites. Ov and P terminals are equally prevalent on the dendrites; however, P terminals are significantly more common than Ov terminals on the somata. Furthermore, P terminals are significantly more common on the somata than on the dendrites. These results suggest that there is some segregation of types of afferent synapses on MSO cells.

Animals↗
PubMed1988

Connections of the dorsal nucleus of the lateral lemniscus: an inhibitory parallel pathway in the ascending auditory system?

This study examines the dorsal nucleus of the lateral lemniscus (DNLL) and its afferent and efferent connections. In Nissl-stained material, DNLL has three parts: dorsal, ventral, and lateral. Although each part contains neurons with similar Nissl patterns, the subdivisions may be distinguished by the size, shape, and orientation of the cells. The lateral DNLL contains a mixture of DNLL neurons and cells from the sagulum. Afferent connections to DNLL were investigated with anterograde axonal transport techniques. Bilateral inputs to DNLL arise from the anteroventral cochlear nucleus and lateral superior olive, while unilateral inputs are provided by the ipsilateral medial superior olive and the contralateral DNLL. The inputs appear to have a tonotopic organization. Afferent fibers to DNLL form horizontal bands that are continuous both mediolaterally and rostrocaudally. All parts of DNLL do not share the same inputs, and a medial-to-lateral gradient in the labeling of some pathways is evident. To study the efferent connections of DNLL, both retrograde and anterograde axonal transport techniques were used. The DNLL projects to the inferior colliculus and the contralateral DNLL. The topography of these projections suggests that areas of similar tonotopic organization are connected. In the inferior colliculus, the projection is heaviest to the central nucleus and extends to the adjacent dorsal and caudal cortex, the rostral pole nucleus, and the ventrolateral nucleus. Axons from DNLL terminate along the fibrodendritic laminae of the central nucleus as bands that are prominent on the contralateral side, whereas those on the ipsilateral colliculus are more diffuse. The afferent and efferent connections of DNLL constitute a multisynaptic pathway, parallel to the other ascending pathways to the inferior colliculus. The other ascending pathways include the direct pathways from the cochlear nucleus to the inferior colliculus and the indirect pathways via the superior olivary complex. Ascending pathways are discussed as to their relationship to the subdivisions of the inferior colliculus, the laterality of their projections, and their banding patterns in the central nucleus. In contrast to the excitatory pathways to the inferior colliculus, the neurons in DNLL may use GABA as a neurotransmitter. Axons from the DNLL terminate in the inferior colliculus as bands that could have a unique inhibitory function. Thus, the multisynaptic, DNLL pathway may provide feed-forward inhibitory inputs to the inferior colliculus, bilaterally, and to the contralateral DNLL.

Animals↗
PubMed1988

Nucleus sagulum: projections of a lateral tegmental area to the inferior colliculus in the cat.

The nucleus sagulum, an area of the midbrain tegmentum, has been considered a component of a lateral tegmental system within the ascending auditory pathway to the thalamus. In this study, connections of the nucleus sagulum within the midbrain were investigated in adult cats. Tracing methods using anterograde and retrograde axonal transport of markers were employed. The nucleus sagulum was identified as a region of principally small neurons (261 +/- 79 micron2) at the margin of the midbrain and neighboring the nuclei of the lateral lemniscus. Injections of tritiated leucine in the nucleus sagulum labeled axons that ended in dense patches within the superficial layers of the caudal portion of the dorsal cortex of the inferior colliculus on the ipsilateral side. Retrograde experiments confirmed this connection. Other axonal projections labeled in the anterograde studies included fibers ending in the dorsomedial nucleus, the superficial layers of the dorsal cortex, and the rostral nucleus of the inferior colliculus with some bilateral distribution. Outside of the inferior colliculus, sagulum injections labeled other axons ending in the ventral intercollicular tegmentum on both sides and in a dorsal and rostral region of the contralateral nucleus sagulum that appeared contiguous with the dorsal nucleus of the lateral lemniscus. The latter region included a population of larger neurons (340-540 micron2) and had different connections with the inferior colliculus. The distribution of axonal labeling after injections in the nucleus sagulum was contrasted with the distribution of projections from several neighboring areas of the lateral tegmentum, including the dorsal nucleus of the lateral lemniscus. None of these areas exhibited connections with the superficial layers of the caudal cortex of the inferior colliculus, which was the major target in the inferior colliculus of the nucleus sagulum. Thus, the results indicated that the nucleus sagulum is distinguished from adjacent regions of the lateral tegmentum by its connectivity. Its association with midbrain auditory pathways is supported by these connections as well as ascending ones to the auditory thalamus.

Animals↗
PubMed1987

Banding of lateral superior olivary nucleus afferents in the inferior colliculus: a possible substrate for sensory integration.

In this study the organization of the projection from the lateral superior olivary nucleus (LSO) to the inferior colliculus was investigated in the cat by using anterograde tract-tracing techniques. The findings indicated that LSO projected bilaterally to the central nucleus of the inferior colliculus as well as to the ventrolateral and rostral pole nuclei. In the central nucleus a larger medial component of the projection ended in pars medialis and centralis. A smaller lateral component ended in the region of the pars lateralis. Both components of the projection appeared to be topographically organized, but in the lateral component the low-frequency part of LSO appeared to have greater representation. The uncrossed and crossed LSO projections to the inferior colliculus exhibited several important differences in their distribution. First, periodic bands of dense labeling were more prominent in the distribution of the uncrossed projection. The bands measured 150-200 micron in thickness and in some cases interruptions or gaps were present along the length of the bands. The distribution of the crossed projection was more diffuse, but some banding was also apparent. Second, the positions of the bands of dense labeling on the two sides were not homotopic as determined by labeling projections from the ipsilateral and contralateral LSO in the same tissue. The dense bands labeled with WGA-HRP from an injection in LSO on one side and bands labeled with 3H-leucine from an injection in LSO on the other side either were interdigitating or were only partially overlapping. Finally, the area over which the uncrossed projection distributed endings varied in size with respect to that of the crossed projection. The variation in size of the area of the projections was a function of the frequency representation. A model based on the three-dimensional reconstruction of bands as projection sheets is proposed as a substrate for selective integration of afferents in the inferior colliculus.

Afferent Pathways↗
PubMed1987

Descending projections from the superior olivary complex to the cochlear nucleus of the cat.

Subdivisions of the cochlear nuclear complex give rise to a number of discrete projections to certain cell groups of the superior olivary complex and also received substantial descending projections from the periolivary nuclei. In the present study, we sought to determine by means of retrograde transport of horseradish peroxidase (HRP), and anterograde transport of radiolabeled protein, if the periolivary nuclei give rise to discrete projections to the various subdivisions of the cochlear nuclear complex. Following medium to large injections of HRP into the cochlear nucleus, irrespective of location, labeled cells were found in all periolivary nuclei bilaterally. In every case more than 40% of the labeled cells were found in the lateral nucleus of the trapezoid body on the same side and the ventral nucleus of the trapezoid body of both sides. Other periolivary nuclei contributing more than 5% of the total number of cells in individual cases were the contralateral lateral nucleus of the trapezoid body and the ipsilateral anterolateral and dorsal periolivary nuclei. Injections of tritiated leucine into periolivary nuclei gave rise to axonal labeling to the trapezoid body and the dorsal acoustic stria, usually bilaterally, and to terminal labeling that was widely distributed within the cochlear nuclear complex. In several cases with small injections, particularly in the lateral nucleus of the trapezoid body, the projections from the periolivary nuclei to the anteroventral and dorsal cochlear nuclei connected areas described as having similar best-frequency representation. The autoradiographic data corroborated the main results from the HRP experiments and provided additional information permitting these conclusions: the projections from the periolivary nuclei to the cochlear nuclear complex are organized tonotopically, at least in part; each periolivary nucleus (and perhaps individual cells), projects widely throughout the cochlear nuclear complex; the pattern of termination of projections from different periolivary nuclei to a given region of the cochlear nuclear complex are similar, as seen in autoradiograms, and the lateral and dorsal periolivary nuclei project mainly ipsilaterally, while the medial periolivary nuclei project bilaterally with a contralateral bias. The magnitude of these projections and their widespread distribution within the cochlear nuclear complex would suggest an important role for the descending projections in the normal functioning of the cochlear nucleus.

Acetylcholinesterase↗
PubMed1985

The projections of principal cells of the medial nucleus of the trapezoid body in the cat.

Previous studies suggest that the principal cells of the medial nucleus of the trapezoid body (MNTB) give rise to the projection from MNTB to the lateral superior olivary nucleus (LSO) of the same side, where they mediate rapid inhibitory effects of contralateral sound stimulation. In the present study, we explored certain morphological features of this connection as well as several other projections of the MNTB by using anterograde and retrograde axonal tracing methods. Following injections of tritiated leucine into MNTB, labeled axons reached LSO by passing ventral to, dorsal to, and through the medial superior olivary nucleus, and gave rise to labeling around the somata and proximal dendrites of LSO fusiform cells. As measured in autoradiograms of 2 micron plastic sections, these axons had a modal diameter of 5-6 micron. Terminal labeling, tentatively attributed to principal cell axons, was also seen in the ventral nucleus of the lateral lemniscus (VNLL) and the dorsomedial and ventromedial periolivary nuclei. HRP injections into the LSO and the VNLL showed that the principal cell projected to both of these nuclei and revealed a topographic arrangement of the projection to the LSO which is consistent with tonotopic maps determined electrophysiologically. Control HRP injections demonstrated that other minor projections of the MNTB arose from minor cell populations in this nucleus. The findings provide a morphological correlate of certain physiological findings and suggest a wider role for the MNTB in the ascending auditory system than previously has been supposed.

Animals↗