Descending projections from auditory brainstem nuclei to the cochlea and cochlear nucleus of the guinea pig

Projections from auditory brainstem nuclei to the cochlea and cochlear nuclei in the guinea pig were studied by injection of two retrograde fluorescent neuronal tracers. For seven experiments fast blue was injected into the scala tympani of one cochlea and diamidino yellow was injected into dorsal or anteroventral cochlear nucleus of the same side. The results show that the efferent projections to the cochlea and cochlear nucleus generally form two separate neuronal systems even though they share many common nuclei of origin. The largest projections to the cochlear nucleus come bilaterally from the lateral and ventral nuclei of the trapezoid body. Other nuclei, the lateral superior olive, the ventral nucleus of the lateral lemniscus, the dorsomedial periolivary nuclei, and the medial nucleus of the trapezoid body showed an ipsilateral bias in their projections to the cochlear nucleus. An upper limit of 3.5% of the medial system olivocochlear efferent neurones projecting to the cochlea were labelled with both diamidino yellow and fast blue, suggesting that few efferent neurones projecting to the cochlea send collaterals to the cochlear nucleus in this species. However, the site of medial system olivocochlear efferent collateral terminations is the granule cell area for the cat, mouse, and gerbil. When diamidino yellow was injected in the superficial layers of the cochlear nucleus, including the superficial granule cell layer of the ventral cochlear nucleus, approximately 3.6% of medial system olivocochlear efferents projecting to the cochlea sent collaterals to the cochlear nucleus. In three animals fast blue was injected into the cochlear nucleus and diamidino yellow into the cochlea. These experiments revealed a greater proportion of the medial system olivocochlear efferents projecting to the cochlea sending collaterals to the cochlear nucleus, but this proportion was still less than 10%. These results were confirmed by the extracellular injection of horseradish peroxidase into the intraganglionic spiral bundle. Only three medial system olivocochlear efferents were observed to send collaterals to the cochlear nucleus. This number was less than 10% of all labelled medial system fibres. Although these experiments suggest that in the guinea pig the number of olivocochlear efferents sending collaterals to the cochlear nucleus is considerably smaller than is found for the cat, mouse, and gerbil, it is not possible with the current experimental procedures to conclude whether the results are due to species or methodological differences.     

Targets of olivocochlear collaterals in cochlear nucleus of rat and guinea pig

Descending auditory pathways can modify afferent auditory input en route to cortex. One component of these pathways is the olivocochlear system which originates in brainstem and terminates in cochlea. Medial olivocochlear (MOC) neurons also project collaterals to cochlear nucleus and make synaptic contacts with dendrites of multipolar neurons. Two broadly distinct populations of multipolar cells exist: T-stellate and D-stellate neurons, thought to project to inferior colliculus and contralateral cochlear nucleus, respectively. It is unclear which of these neurons receive direct MOC collateral input due to conflicting results between in vivo and in vitro studies. This study used anatomical techniques to identify which multipolar cell population receives synaptic innervation from MOC collaterals. The retrograde tracer Fluorogold was injected into inferior colliculus or cochlear nucleus to label T-stellate and D-stellate neurons, respectively. Axonal branches of MOC neurons were labeled by biocytin injections at the floor of the fourth ventricle. Fluorogold injections resulted in labeled cochlear nucleus multipolar neurons. Biocytin abundantly labeled MOC collaterals which entered cochlear nucleus. Microscopic analysis revealed that MOC collaterals made some putative synaptic contacts with the retrogradely labeled neurons but many more putative contacts were observed on unidentified neural targets. This suggest that both T- and D-stellate neurons receive synaptic innervation from the MOC collaterals on their somata and proximal dendrites. The prevalence of these contacts cannot be stated with certainty because of technical limitations, but the possibility exists that the collaterals may also make contacts with neurons not projecting to inferior colliculus or the contralateral cochlear nucleus.     

Plasticity of the auditory brainstem: Effects of cochlear ablation on GAP-43 immunoreactivity in the rat

In the adult brain, expression of the growth associated protein GAP-43 may serve as an indicator of synaptic remodeling. We have studied localization and time course of the re-expression of GAP-43 following deafening through cochlear ablation. As a consequence of unilateral cochlear lesioning, a substantial increase in the expression of GAP-43 was observed in the neuropil of all subnuclei of the ipsilateral cochlear nuclear complex. This expression of GAP-43 occurred in well-defined fibers and boutons. In the ventral cochlear nuclei, boutons immunoreactive for GAP-43 were often localized on cell bodies. However, they were found only on selected subpopulations of cochlear nucleus neurons, i.e., on cell bodies containing glutamate or calretinin immunoreactivity, but apparently not on GABAergic neurons. Olivocochlear neurons must have been axotomized by the operation. Following cochlear ablation, a dramatic re-expression of GAP-43 occurred in cell bodies of the ipsilateral lateral superior olive but not in the ventral nucleus of the trapezoid body. Position and number of these cells suggested that most, if not all, of them serve the lateral olivocochlear bundle. However, although axon collaterals are given off by certain types of olivocochlear neurons, a direct involvement of the immunoreactive cell bodies in the emergence of GAP-43 in the cochlear nucleus is not obvious. A transient rise of GAP-43 immunoreactivity that could not be attributed to axotomized neurons was observed in the contralateral dorsal cochlear nucleus and in the ipsilateral inferior colliculus. Given the functional significance attributed to GAP-43, we conclude that the sudden loss of spiral ganglion cells leads to a reactive synaptogenesis in complex patterns across several auditory brainstem nuclei. J. Comp. Neurol. 382:116-138, 1997. © 1997 Wiley-Liss Inc.     

Superior paraolivary nucleus in the pigmented guinea pig: separate classes of neurons project to the inferior colliculus and the cochlear nucleus.

The superior paraolivary nucleus is a large component of the superior olivary complex in rodents and a major source of input to the inferior colliculi and the cochlear nuclei. In the present study, retrograde transport of the fluorescent tracers Fluoro-Gold, Fluoro-Ruby (tetramethyl rhodamine conjugated to dextran), fluorescein-coated microspheres, and Fast Blue were used to reveal the morphology and collateral projection patterns of cells in the superior paraolivary nucleus. The ascending projections to the inferior colliculus from the superior paraolivary nucleus arise mainly from round, multipolar cells, including large cells that project exclusively to the inferior colliculi and not to the cochlear nuclei. Projections to the ipsilateral and contralateral inferior colliculi arise from cells with similar morphology and, in fact, many of the cells that project contralaterally project ipsilaterally as well. Projections to the ipsilateral and contralateral cochlear nuclei arise primarily from cells that do not have collicular projections. On average, the somas of these cells are significantly smaller and more elongated than those that project to the inferior colliculi. Overlap between these ascending and descending systems is restricted to a small percentage of cells that send collateral projections to both the ipsilateral cochlear nucleus and the ipsilateral inferior colliculus. These cells are small and moderately elongated. Thus the ascending and descending projections examined here arise largely from different cells that belong to different morphological classes.     

Parvalbumin and calbindin D-28 k immunoreactivity in dorsal root ganglia in acquired immunodeficiency syndrome

Various degrees of neuronal degeneration have been found in lumbosacral dorsal root ganglia of patients with acquired immunodeficiency syndrome (AIDS). To characterize the subpopulations of primary sensory neurons affected in AIDS. we immunostained dorsal root ganglion tissues from 11 AIDS patients and six controls using antibodies to the calcium binding proteins, parvalbumin and calbindin D-28 k. In controls, the proportion of neurons containing parvalbumin and calbindin was 18.0% and 22.4%, respectively. The majority of parvalbumin-positive neurons, which are thought to be proprioceptive neurons, were of medium to large size, while calbindin was found in both large- and small-sized neurons. The density of parvalbumin-immunoreactive neurons was reduced by 7.3% in AIDS patients, but the density of calbindin-immunoreactive neurons was preserved. Furthermore, in AIDS cases, the number of parvalbumin-positive neurons was reduced more in dorsal root ganglia in which human immunodeficiency virus (HIV) antigen was detected than in HIV-negative ganglia. These results suggest that specific subpopulations of sensory neurons positive for parvalbumin may be differentially affected over the course of AIDS, and that this could be related to peripheral neuropathy which frequently occurs in the late stages of AIDS.     

Temporary sensory deprivation changes calcium-binding proteins levels in the auditory brainstem

Auditory brainstem neurons probably depend on afferent input to maintain calcium homeostasis within a narrow range. These neurons are endowed with high concentrations of the calcium-binding proteins parvalbumin, calretinin, and calbindin D28k that are presumed to buffer cytosolic calcium transients. To determine the effects of functional deafferentation on these proteins in the auditory brainstem of adult guinea pigs, we have manipulated the sensory input with an intracochlear perfusion of the glutamate agonist α-amino-3-hydroxy-5-methyl-4-isoxazole propionic acid (AMPA), which is known to transiently disconnect inner hair cells and primary auditory dendrites. Semiquantitative measures of immunostaining intensities showed rapid and reversible changes in calcium-binding protein levels. By 24 hours after AMPA treatment, calretinin immunostaining was reduced in deafferented neurons of the cochlear nuclei and their axons in the superior olivary nuclei. In contrast, calbindin D28k immunoreactivity levels by this time were higher in deafferented neurons of the medial nucleus of the trapezoid body and their axons in the lateral superior olivary nucleus (LSO). Parvalbumin immunostaining was also generally increased in deafferented neurons, but changes were less evident and more complex. The changes in all three immunoreactivities disappeared with the progressive restoration of afferent input. Normal levels were reestablished by 5 days after AMPA treatment, when afferent activity had almost completely recovered. These results show that calcium-binding protein immunostaining in auditory neurons is functionally responsive to afferent activity. The increased buffering capacity in deafferented neurons as shown by the rises in parvalbumin and calbindin D28k immunostaining may be part of mechanisms promoting neuronal survival after loss of sensory input. This input, on the other hand, may be necessary for maintaining the high calretinin levels normally present in cochlear nucleus neurons. J. Comp. Neurol. 378:1–15, 1997. © 1997 Wiley-Liss, Inc.     

ERK and SAPK signaling in auditory brainstem neurons after unilateral cochlear ablation

Unilateral cochlear ablation (UCA) in adults deafferented one cochlear nucleus (CN) and induced several plasticities in central auditory pathways. To assess whether signal transduction could contribute to these changes, we determined if UCA induced activity in the extracellular signal-regulated kinase (ERK) and the stress-activated protein kinase (SAPK) signal transduction pathways. Using Western blots, we measured phosphorylated ERK1 (ERK1-P), ERK2 (ERK2-P), p46 and p54 SAPK (SAPK-P) and c-Jun (c-Jun-P) levels in the major subdivisions of the CN, the principal nuclei of the superior olivary complex (SOC) and the central nucleus of the inferior colliculus (ICc) for up to 145 days postablation. ERK1-P and ERK2-P were typically elevated at 7 and 145 days but depressed at 30 days, 60 days, or both. In addition, ERK1-P and ERK2-P were elevated at 3 days in the anteroventral (AVCN) and posteroventral CN (PVCN). Immunohistochemical labeling indicated that after 5 days, most ERK1/2-P in the CN was in neuronal nuclei. Only minor changes were evident in total ERK1 and ERK2 levels. Several correlations were evident between the postablation plasticities observed previously and altered ERK1-P and ERK2-P levels. Few changes were found in SAPK-P and c-Jun-P levels. Concomitant elevations of SAPK-P and c-Jun-P were not evident, except in the superficial dorsal CN (DCN) at postablation day 3, consistent with a cell-stress response. These findings suggest that signals induced as a consequence of UCA are transduced mainly through the neuronal ERK pathway. This activity probably influenced gene expression and cytoplasmic regulatory mechanisms that contributed to the plasticities induced by UCA.     

Pre- and postnatal development of efferent connections of the cochlear nucleus in the rat

Although the connections of the auditory brainstem nuclei are well described in adult mammals, almost nothing is known concerning how and when these connections develop. The purpose of the present study was to describe the development of the efferent projections of the cochlear nucleus (CN), the first central relay station in the ascending auditory pathway of mammals. We used two tracers in rats aged between embryonic day 15 (E15) and postnatal day 14 (P14; birth in the rat is at E22 = P0). The carbocyanine dye DiI was applied into the CN in aldehyde-fixed tissue. The second tracer, biocytin, was applied into the ventral acoustic stria in an in vitro slice preparation. The ontogeny of the efferent projections from the CN could be divided into three periods. The first period (E15–E17) is characterized by axonal outgrowth. Axons traverse nuclei in the superior olivary complex and the lateral lemniscus and finally grow up into the inferior colliculus, but axon collaterals do not from during this period. The second period (E18–P5) is marked by pronounced collateral branching of CN fibers in auditory brainstem nuclei. Collateralisation in the contralateral inferior colliculus starts shortly before that in the ipsilateral superior olivary complex. The remaining auditory nuclei become successively innervated, as indicated by collaterals found in them. During the third period (P5–P14) terminal structures mature further, as shown by the morphological changes of the calyces of Held in the medial nucleus of the trapezoid body. In conclusion, our results show that the efferent connections from the cochlear nucleus form over a period of almost two weeks and are laid down without forming aberrant internuclear connections. On a nuclear level, an adult-like projection pattern is already achieved one week prior to the onset of physiological hearing. © 1993 Wiley-Liss, Inc.     

Selective retrograde labeling of lateral olivocochlear neurons in the brainstem based on preferential uptake of 3H-D-aspartic acid in the cochlea

We have previously shown that perfusion of the gerbil cochlea with probe concentrations of 3H-D-aspartic acid (D-ASP) results in immediate, selective labeling of 50-60% of the efferent terminals under the inner hair cells, presumably by high-affinity uptake. The present study was undertaken to determine the origin of these endings. Twenty-four hours after cochlear perfusion with D-ASP, labeled neurons were observed in the ipsilateral, and to a much lesser extent in the contralateral, lateral superior olivary nucleus (LSO). The cells were small, primarily fusiform, and showed fewer synaptic contacts than other LSO cells. Combined transport of D-ASP and horseradish peroxidase indicated that all olivocochlear neurons within the LSO that projected to the injected cochlea were labeled by D-ASP. Labeled fibers coursed dorsally from the LSO, joined contralateral fibers that had passed under the floor of the fourth ventricle, and entered the VIIIth nerve root at its ventromedial edge. Adjacent to the ventral cochlear nucleus (VCN), densely labeled collateral fibers crossed the nerve root to enter the VCN. Labeled fibers and terminals were prominent in the central VCN. Neither retrograde transport of D-ASP by medial olivocochlear and vestibular efferents nor anterograde transport by VIIIth nerve afferents was observed. The D-ASP-labeled cells and fibers are clearly lateral olivocochlear efferents. Retrograde transport of D-ASP thus allows the cells, axons, and collaterals of the lateral olivocochlear system to be studied, morphologically, in isolation from other cells that project to the cochlea. Since the olivocochlear neurons are almost certainly cholinergic, retrograde amino acid transport does not necessarily identify the primary neurotransmitter of a neuron. Rather, it indicates the presence of selective uptake by the processes of that neuron at the site of amino acid injection. Retrograde labeling appears to be markedly enhanced by the use of metabolically inert compounds such as d-isomer amino acids.     

GABA- and glycine-immunoreactive projections from the superior olivary complex to the cochlear nucleus in guinea pig

Retrograde transport of horseradish peroxidase was combined with immunocytochemistry to identify the origins of potential γ-aminobutyric acid (GABA) -ergic and glycinergic inputs to different subdivisions of the cochlear nucleus. Projection neurons in the inferior colliculus, superior olivary complex, and contralateral cochlear nucleus were examined, but only those from the superior olivary complex contained significant numbers of GABA- or glycine-immunoreactive neurons. The majority of these were in periolivary nuclei ipsilaterally, with a sizeable contribution from the contralateral ventral nucleus of the trapezoid body. Overall, 80% of olivary neurons projecting to the cochlear nucleus were immunoreactive for GABA, glycine, or both. Most glycine-immunoreactive projection neurons were located ipsilaterally, in the lateral and ventral nuclei of the trapezoid body and the dorsal periolivary nucleus. This suggests that glycine is the predominant neurotransmitter used by ipsilateral olivary projections. Most GABA-immunoreactive cells were located bilaterally in the ventral nuclei of the trapezoid body. The contralateral olivary projection was primarily GABA-immunoreactive and provided almost half the GABA-immunoreactive projections to the cochlear nucleus. This suggests that GABA is the predominant neurotransmitter used by contralateral olivary projections. The present results suggest that the superior olivary complex is the most important extrinsic source of inhibitory inputs to the cochlear nucleus. Individual periolivary nuclei differ in the strength and the transmitter content of their projections to the cochlear nucleus and may perform different roles in acoustic processing in the cochlear nucleus. J. Comp. Neurol. 381:500-512, 1997. © 1997 Wiley-Liss, Inc.     

Nitric oxide regulates the firing rate of neuronal subtypes in the guinea pig ventral cochlear nucleus

The gaseous free radical, nitric oxide (NO) acts as a ubiquitous neuromodulator, contributing to synaptic plasticity in a complex way that can involve either long term potentiation or depression. It is produced by neuronal nitric oxide synthase (nNOS) which is presynaptically expressed and also located postsynaptically in the membrane and cytoplasm of a subpopulation of each major neuronal type in the ventral cochlear nucleus (VCN). We have used iontophoresis in vivo to study the effect of the NOS inhibitor L‐NAME (L‐NG‐Nitroarginine methyl ester) and the NO donors SIN‐1 (3‐Morpholinosydnonimine hydrochloride) and SNOG (S‐Nitrosoglutathione) on VCN units under urethane anaesthesia. Collectively, both donors produced increases and decreases in driven and spontaneous firing rates of some neurones. Inhibition of endogenous NO production with L‐NAME evoked a consistent increase in driven firing rates in 18% of units without much effect on spontaneous rate. This reduction of gain produced by endogenous NO was mirrored when studying the effect of L‐NAME on NMDA(N‐Methyl‐D‐aspartic acid)‐evoked excitation, with 30% of units showing enhanced NMDA‐evoked excitation during L‐NAME application (reduced NO levels). Approximately 25% of neurones contain nNOS and the NO produced can modulate the firing rate of the main principal cells: medium stellates (choppers), large stellates (onset responses) and bushy cells (primary‐like responses). The main endogenous role of NO seems to be to partly suppress driven firing rates associated with NMDA channel activity but there is scope for it to increase neural gain if there were a pathological increase in its production following hearing loss.     

Projections from the posteroventral cochlear nucleus to the superior olivary complex in guinea pig: light and EM observations with the PHA-L method.

The efferent neural projections from posteroventral cochlear nucleus to the superior olivary complex in guinea pig were examined with the Phaseolus vulgaris-leucoagglutinin anterograde tract-tracing method. Light microscopic analysis demonstrated that the posteroventral cochlear nucleus of guinea pig bilaterally projects to the superior para-olivary nucleus and the rostral, medioventral, and lateroventral peri-olivary regions. Ipsilaterally, the posteroventral cochlear nucleus projects to the lateral superior olive, the caudal peri-olivary region, and areas immediately surrounding the capsule of the lateral superior olive. Contralaterally, the posteroventral cochlear nucleus projects to the medial nucleus of the trapezoid body. All of these projection axons travel in the trapezoid body and their terminals make, primarily, en passant endings upon their targets. Exclusively within the contralateral medial nucleus of the trapezoid body, some neurons terminate also in calyceal endings. The assumption that immunolabeled structures observed with light microscopy made actual synaptic contact in their respective target areas was confirmed with electron microscopy. With postembedding immunocytochemical procedures applied to thin sections, the electron microscope revealed labeled synaptic vesicles and pre- and postsynaptic membrane specializations. The projection pattern from posteroventral cochlear nucleus was found to be topographically organized in three distinct regions. The more dorsally located neurons of the posteroventral cochlear nucleus terminated dorsomedially in the ipsilateral lateral superior olive, ventromedially in the contralateral superior para-olivary nucleus, and medially in the contralateral medioventral peri-olivary region. The more ventrally located neurons of the posteroventral cochlear nucleus terminated dorsolaterally in the ipsilateral lateral superior olive, dorsolaterally in the contralateral superior para-olivary nucleus, and laterally in the contralateral medioventral peri-olivary region.     

Axonal projections from the lateral and medial superior olive to the inferior colliculus of the cat: A study using electron microscopic autoradiography

The superior olivary complex is the first site in the central auditory system where binaural interactions occur. The output of these nuclei is direct to the central nucleus of the inferior colliculus, where binaural inputs synapse with monaural afferents such as those from the cochlear nuclei. Despite the importance of the olivary pathways for binaural information processing, little is known about their synaptic organization ir the colliculus. The present study investigates the structure of the projections from the lateral and medial superior olivary nuclei to the inferior colliculus at the electron microscopic level. Stereotaxic placement and electrophysi ological responses to binaural sounds were used to locate the superior olive. Anterograde axonal transport of 3H-leucine was combined with light and electron microscopic autoradiography to reveal the location and morphology of the olivary axonal endings. The results show that the superior olivary complex contributes different patterns of synaptic input to the central nucleus of the inferior colliculus. Each projection from the superior olivary complex to the colliculus differs in the number and combinations of endings. Axonal endings from the ipsilateral medial superior olive were exclusively the round (R) type that contain round synaptic vesicles and make asymmetrical synaptic junctions. This morpholo is usually associated with excitatory synapses and neurotransmitters such as glutamate. Endings from medial superior olive terminate densely in the central nucleus. The projection from the contralateral lateral superior olive also terminates primarily as R endings. This projection also includes small numbers of pleomorphic (PL) endings that contain pleomorphic synaptic vesicles and usually make symmetrical synaptic junctions. The PL morpholo is associated with inhibitory synapses and transmitters such as gamma-aminobutyric acid and glycine. All endings from the contralateral lateral superior olive terminate much less densely than endings from the medial olive. In contrast, the projection from the ipsilateral lateral superior olive contributes both R and PL endings in roughly equal proportions. These ipsilateral afferents are heterogeneous in density and can terminate in lower or higher concentrations than endings from the contralateral side. These data show that the superior olive is a major contributor to the synaptic organization of the centr nucleus of the inferior colliculus. The ipsilateral projections of the medial and lateral superior olive may produce higher concentrations of R endings than other inputs to the central nucleus. Such endings may participate in excitatory synapses. The highest concentra tions of PL endings come from the ipsilateral lateral superior olive. In combination with inputs from the contralateral dorsal nucleus of the lateral lemniscus, PL endings from the superior olive may participate in many inhibitory synapses found in the central nucleus. These different patterns of synaptic input from the superior olivary complex will influence how binaural information is transmitted to the inferior colliculus. © 1995 Wiley-Liss, Inc.     

Morphology and physiology of cells in slice preparations of the dorsal cochlear nucleus of mice

Horseradish peroxidase (HRP) was injected into cells from which intracellular recordings were made in slices of the dorsal cochlear nucleus (DCN) in order to correlate physiology with morphology. In general, the morphology of cells labeled intracellularly with HRP corresponded to those made with Golgi impregnations in mice and other mammals. The following cells were labeled: one granule cell, four cartwheel cells, eight fusiform cells, two other cells in the fusiform cell layer, and two tuberculoventral association cells in the deep layers of the DCN. The axon of the granule cell runs parallel to isofrequency laminae with collaterals branching perpendicularly and running along the tonotopic axis. The cartwheel cells have dendrites in the molecular layer that are densely covered with spines. The axon of one cell terminates just dorsally to the cell body. Fusiform cells have the characteristic spiny, apical and smooth, basal dendrites. The basal dendrites are conspicuously oriented parallel to isofrequency laminae. Axons of the fusiform cells exit through the dorsal acoustic stria without branching. The two tuberculoventral association cells in the deep DCN have axons that terminate both in the deep DCN, within the same isofrequency lamina that contains the cell body, and in the ventral cochlear nucleus (VCN). Intracellular recordings from 11 of these cells show that they cannot be distinguished on the basis of their responses to intracellularly injected current. All cell types fired large action potentials that were followed by a fast and a slower undershoot, distinguishing them from cells of the VCN but not from one another. Most cells responded to shocks of the auditory nerve root with early EPSPs and later IPSPs. The latencies of EPSPs show that some were monosynaptic and others polysynaptic. That there was no systematic relationship between the latencies of EPSPs and the cell types from which they were recorded shows that shocks to the nerve root may have activated more than just the large, myelinated, auditory nerve fibers.     

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.     

Parvalbumin and calbindin D-28k in the entopeduncular nucleus,subthalamic nucleus,and substantia nigra of the rat as revealed by double-immunohistochemical methods

The cellular localization of calbindin D-28k (CB) and parvalbumin (PV) was analyzed by means of double-immunohistochemical techniques applied to single sections in the entopeduncular nucleus (EP), the subthalamic nucleus (STh), and the substantia nigra (SN) of the rat. In EP, PV-positive cells abounded centrally, where CB immunostaining was minimal. The medial and ventral sectors of EP were markedly enriched with CB neurophil but devoid of PV-positive cells. CB-positive neurons abounded particularly in the rostral pole of EP. In STh, PV-positive neurons and neuropil were concentrated in the lateral two thirds of this nucleus. Only a few PV-positive cells were detected in sectors of STh devoid of PV-positive neuropil. The STh was completely devoid of CB immunostaining. In the rostral two thirds of SN, PV-positive neurons were largely confined to the lateral half of the pars reticulata (SNR), and occurred more ventrally and medially in the caudal third. Intense CB-immunoreactive neuropil was found in medial and dorsal parts of rostral SNR, and CB-positive cells were observed in the SN pars compacta and the ventral tegmental area. PV and CB cells were also observed in the pars lateralis of SN. The markedly heterogeneous pattern of distribution of PV and CB in EP, STh, and SN suggests that these two calcium-binding proteins may label distinct functional domains in each of these three components of the rat basal ganglia. Synapse 25:359–367, 1997. © 1997 Wiley-Liss, Inc.     

Postnatal development of GAP-43 immunoreactivity in the auditory brainstem of the rat

Extensive data link the growth associated protein GAP-43 to axonal elongation and synapse formation during development and in plastic responses of nervous tissue. We have studied the changing levels of GAP-43 expression in the auditory brainstem nuclei of the developing rat by applying immunocytochemical techniques. By the first postnatal day (P1), GAP-43 was expressed at high concentrations in all subdivisions of the cochlear nuclear complex and the superior olivary complex. At this stage, neuropil structures recognized by the antibody did not show any varicosities on cellular processes in all these regions. By P8, the texture of the stain has turned markedly more granular, a pattern likely to reflect the formation of presynaptic endings. A predominantly granular distribution of GAP-43 has developed by P12. At that time, the staining intensity is markedly reduced compared to the levels of the newborn. By P16, the auditory brainstem nuclei have lost most of their GAP-43 immunoreactivity, but a distinct level of staining persisted into adulthood in all of them. This staining was restricted to boutons, which are thought to be presynaptic terminals. We conclude that a moderate but apparently relevant potential for plasticity is retained in these auditory structures. Should the patterns of neural signals, mediated by the inner ear, change during adulthood, the central structures appear to be able to respond with the formation of altered synaptic connectivity. J. Comp. Neurol. 382:104-115, 1997. © 1997 Wiley-Liss Inc.     

Parvalbumin,calbindin D-28k,and calretinin immunoreactivity in the ascending auditory pathway of horseshoe bats

In the subcortical auditory system of Rhinolophus rouxi, antibodies directed against the calcium-binding proteins parvalbumin, calbindin D-28k, and calretinin yield partly overlapping and partly complementary labeling patterns which are described in detail for each nucleus. The most general features of the labeling patterns are that: (1) Parvalbumin is a potent marker for large and heterogenous populations of cells and puncta (presumed axon terminals) throughout the auditory pathway. (2) Immunostaining with the monoclonal calbindin-antiserum was typically absent or sparse in most auditory brainstem centers, but prominent in auditory nerve fibers and in cells of the medial geniculate body (MGB). (3) Calretinin label is abundant but more restricted to subsets of auditory nuclei or subpopulations of cells than parvalbumin. (4) Calcium-binding proteins are useful markers to define particular subregions or cell types in auditory nuclei: for example, (i) different labeling patterns are obtained within the nuclei of the lateral lemniscus and adjacent tegmental zones; (ii) in the inferior colliculus both calbindin- and calretinin-antisera yield similar regional specific staining patterns, but label different cell types; (iii) subregions of the medial geniculate body have characteristic profiles of calcium-binding proteins; and (iv) analyses of different nuclei showed that there is no simple common denominator for cells characterized by the expression of particular calcium-binding proteins, nor does labeling correspond in a straightforward way with specific functional systems. (5) there are profound differences between the calbindin labeling patterns seen in Rhinolophus and those in other mammals.