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J K Brunso-Bechtold

Publications and source records attributed to J K Brunso-Bechtold.

At least 19 recordsLinked to original sources
PubMed1999

Alterations in insulin-like growth factor-1 gene and protein expression and type 1 insulin-like growth factor receptors in the brains of ageing rats.

Ageing in mammals is characterized by a decline in plasma levels of insulin-like growth factor-1 that appears to contribute to both structural and functional changes in a number of tissues. Although insulin-like growth factor-1 has been shown to provide trophic support for neurons and administration of insulin-like growth factor-1 to ageing animals reverses some aspects of brain ageing, age-related changes in insulin-like growth factor-1 or type 1 insulin-like growth factor receptors in brain have not been well documented. In this series of studies, insulin-like growth factor-1 messenger RNA and protein concentrations, and type 1 insulin-like growth factor receptor levels were analysed in young (three to four- and 10-12-month-old), middle-aged (19-20-month-old) and old (29-32-month-old) Fisher 344 x Brown Norway rats. Localization of insulin-like growth factor-1 messenger RNA throughout the lifespan revealed that expression was greatest in arteries, arterioles, and arteriolar anastomoses with greater than 80% of these vessels producing insulin-like growth factor-1 messenger RNA. High levels of expression were also noted in the meninges. No age-related changes were detected by either in situ hybridization or quantitative dot blot analysis of cortical tissue. However, analysis of insulin-like growth factor-1 protein levels in cortex analysed after saline perfusion indicated a 36.5% decrease between 11 and 32 months-of-age (P<0.05). Similarly, analysis of type 1 insulin-like growth factor receptor messenger RNA revealed no changes with age but levels of type 1 insulin-like growth factor receptors indicated a substantial decrease with age (31% in hippocampus and 20.8 and 27.3% in cortical layers II/III and V/VI, respectively). Our results indicate that (i) vasculature and meninges are an important source of insulin-like growth factor-1 for the brain and that expression continues throughout life, (ii) there are no changes in insulin-like growth factor-1 gene expression with age but insulin-like growth factor-1 protein levels decrease suggesting that translational deficiencies or deficits in the transport of insulin-like growth factor-1 through the blood-brain barrier contribute to the decline in brain insulin-like growth factor-1 with age, and (iii) type 1 insulin-like growth factor receptor messenger RNA is unchanged with age but type 1 insulin-like growth factor receptors decrease in several brain regions. We conclude that significant perturbations occur in the insulin-like growth factor-1 axis with age. Since other studies suggest that i.c.v. administration of insulin-like growth factor-1 reverses functional and cognitive deficiencies with age, alterations within the insulin-like growth factor-1 axis may be an important contributing factor in brain ageing.

Aging↗
PubMed1998

Distribution and levels of insulin-like growth factor I mRNA across the life span in the Brown Norway x Fischer 344 rat brain.

Previous studies have reported changes in insulin-like growth factor I (IGF-I) mRNA expression during early postnatal development of the rat brain. Although changes in IGF-I gene expression have been documented in a wide range of central nervous system structures during early development and investigated in the hippocampus during aging, no study has compared changes in IGF-I gene expression in different brain regions across the life span. The present study assessed the distribution of IGF-I gene expression using in situ hybridization in rats aged 2-30 months. Dot blots were used as a quantitative assessment of cortical IGF-I mRNA. Results indicate that both the distribution and levels of brain IGF-I mRNA do not change significantly between 2 and 30 months of age in the rat. However, in spite of relatively constant levels of mRNA, other studies from our laboratory have demonstrated that cortical IGF-I protein levels decrease 36.6% between 11 and 32 months of age, suggesting that IGF-I function is decreased with increasing age.

Aging↗
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↗
PubMed1998

Directed outgrowth from a subset of cochlear nucleus fibers in a collagen-gel matrix.

We have employed a collagen-gel co-culture system to evaluate the influence of the hindbrain floor-plate on initial axon outgrowth from the cochlear nucleus. After 2 days in vitro, cochlear nucleus explants exhibited directed outgrowth towards co-cultured floor plate explants. Comparisons with co-cultures of cochlear nucleus/forebrain or cochlear nucleus/midbrain explants or with cochlear nucleus explants cultured alone suggest that the floor-plate has a specific chemoattractant effect on the outgrowth of the pioneer fibers of the hindbrain auditory commissure. Fiber outgrowth was not directed towards a recombinant source of the chemoattractant molecule netrin suggesting that floor plate directed outgrowth in the cochlear nucleus is not solely dependent on netrin. In the present report, we present evidence for the first time that the floor-plate is a chemotropic source in pathfinding of second-order auditory fibers from the cochlear nucleus in the hindbrain.

Animals↗
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.

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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↗
PubMed1994

Cellular origins of tenascin in the developing nervous system.

We have used in situ hybridization and reverse transcriptase polymerase chain reaction (PCR) to study the origins of the extracellular matrix glycoprotein tenascin during the development of the central and peripheral nervous systems. Previous studies have shown that neural crest cells migrate along pathways that are lined with tenascin. In situ hybridization, PCR, and western blotting reveal that these cells themselves are a major source of tenascin both in vitro and in the embryo. Thus, tenascin is probably not acting as a guidance molecule but is more likely to be promoting neural crest cell motility in a more general way. Similarly, subpopulations of proliferating and migrating glia make tenascin in the developing central nervous system, as do the radial glia that are used as a substratum for migrating neuronal cell bodies. In the adult, tenascin continues to be expressed in the cerebellum by Golgi epithelial cells. This expression, as well as the expression of tenascin in connective tissue, indicates that this molecule may also be playing a role in regulating differentiation. Finally, the distribution of tenascin transcripts in the developing brain and spinal cord is similar to the distribution of mRNAs encoding receptors for platelet-derived growth factor-AA and basic fibroblast growth factor. In vitro studies indicate that both of these factors are potential regulators of tenascin expression.

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↗
PubMed1993

Dendritic development in the dorsal lateral geniculate nucleus of ferrets in the postnatal absence of retinal input: a Golgi study.

In order to determine the ongoing role of retinal fibers in the development of dorsal lateral geniculate nucleus (dLGN) neurons during postnatal development, the development of dLGN neurons in the postnatal absence of retinal input was studied in pigmented ferrets using the Golgi-Hortega technique. The development of four dLGN cell classes, defined on the basis of somatic and dendritic morphology, was described previously in normal ferrets (Sutton and Brunso-Bechtold, 1991, J. Comp. Neurol. 309:71-85). The present results indicate that the morphological development of dLGN neurons is strikingly similar in normal and experimental ferrets. The exuberant dendritic appendages that appear after eye opening in normal ferrets are overproduced and eliminated in the postnatal absence of retinal input; however, the final reduction of these transient appendages is delayed. Because exuberant appendages develop in the absence of retinal input, their production cannot depend upon visual experience. Differences in cell body size between normal and experimental ferrets are apparent only after neurons can be classified at the end of the first postnatal month. Cell body size is markedly reduced for class 1 neurons; class 2 cells also are reduced in size but to a far lesser extent. As there is a general trend for class 1 neurons to have the functional properties of Y-cells, it is likely that the dLGN neurons most affected by the absence of retinal input also are Y-cells.

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↗
PubMed1992

Immunohistochemical evidence for transient expression of fibronectin in the developing dorsal lateral geniculate nucleus of the ferret.

In recent years, the important role of the extracellular matrix in neural development has been increasingly recognized. In order to begin to examine what role might be played by the extracellular matrix in the developing dorsal lateral geniculate nucleus (dLGN), the present study used immunocytochemistry to assess the distribution of a recognized extracellular matrix molecule, fibronectin (FN), during postnatal development of the ferret dLGN. Prior to the segregation of cell layers, no clear pattern of FN distribution can be distinguished within the dLGN. By P16, when layers A and A1 are separated by an interlaminar space, FN is localized in that space. By P24, FN is present not only between layers A and A1, but also within layers A and A1 as bands parallel to the laminar borders. These bands appear to correspond spatially and temporally to the development of sublaminar boundaries in the ferret (Hahm and Sur, Neurosci Abstr 14:460, 1988). By the end of the first postnatal month, immunoreactivity is diminished but still present. FN is no longer present at P44 or in the adult. Adjacent sections were incubated with antiserum to glial fibrillary acid protein (GFAP). When a laminar pattern of GFAP can be distinguished, it coincides with the interlaminar distribution of FN. The findings described here are consistent with a role for FN in the development of a laminar organization in the dLGN.

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

A Golgi study of dendritic development in the dorsal lateral geniculate nucleus of normal ferrets.

The development of neurons in the dorsal lateral geniculate nucleus (dLGN) of pigmented ferrets was studied by using the Golgi-Hortega technique. In adult ferrets, four dLGN cell classes were defined on the basis of somatic and dendritic morphology. Classes 1 and 2 were divided into stellate and oriented subtypes. Class 1 and 4 cells are characterized by filiform appendages, class 2 cells by club-like appendages, and class 3 cells by stalked appendages. At birth, dLGN neurons have simple dendritic arbors. During the first postnatal week, dendritic length and proximal branching density increase markedly. By postnatal day 21 (P21), dendritic morphology begins to take on mature characteristics and by the time of eye opening (P30-P35), most neurons can be classified. Also by that time, dLGN cells are covered with abundant filiform appendages. Developmental changes in appendage density were quantified for class 1 stellate cells. These data reveal that appendage density reaches a peak at P56, decreases sharply until P90, and then gradually declines to mature levels by P180. Elaboration and elimination of transient appendages occurs centrifugally; at maturity appendage density remains greater distally.

Aging↗
PubMed1990

An ultrastructural and morphometric study of the effect of removal of retinal input on the development of the dorsal lateral geniculate nucleus.

In normal development, cell layers in the dorsal lateral geniculate nucleus (dLGN) segregate from a relatively homogeneous cell group. If all retinal input is removed prior to this segregation, the layers fail to form. In the present study, we used ultrastructural and morphometric analyses to study dLGN development in the tree shrew following neonatal removal of retinal input. The goal of the present study was to determine whether there are differences between normal animals and enucleates in the development of dLGN cells and their interrelationships with each other and/or with the surrounding glia, which might explain the failure of cellular lamination in enucleated animals. The results indicate that although the development in enucleated animals may take place somewhat more slowly, by P90 cell size and density are not significantly different from normal. These results, coupled with the observation that the dLGN in enucleates is smaller than in normals, suggest that the removal of retinal input results in dLGN cell loss. At both the light and electron microscopic level, cells in the developing normal dLGN are arranged in bands of immediately adjacent cells. In enucleates, dLGN cells are less frequently in immediate contact and are arranged in small groups or clumps which may be separated by degenerating cells. The present data suggest that the presence of retinal input may be necessary to allow dLGN cells to maintain the intercellular relationships necessary for laminar segregation to take place.

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↗