Biomedical subjects

R H Helfert

Publications and source records attributed to R H Helfert.

At least 19 recordsLinked to original sources

PubMed2001

Age-related changes in levels of tyrosine kinase B receptor and fibroblast growth factor receptor 2 in the rat inferior colliculus: implications for neural senescence.

Brain-derived neurotrophic factor and fibroblast growth factor 2, and their respective binding sites, tyrosine kinase B receptor and fibroblast growth factor receptor 2, are known to regulate neurite outgrowth and antioxidant enzyme activity. Several studies suggest that brain-derived neurotrophic factor and fibroblast growth factor are contained in the inferior colliculus. Previous work in our laboratories revealed dendritic and synaptic losses in the inferior colliculus of aged Fischer-344 rats, along with coincident increases in lipid peroxidation possibly linked to a decrease in activity of antioxidant enzymes. In an effort to identify potential causal mechanisms underlying age-related synaptic and dendritic losses that occur in the inferior colliculus, the present study attempted to determine if inferior colliculus levels of tyrosine kinase B receptor and fibroblast growth factor receptor 2 expression are altered with age. Immunocytochemistry was performed in the inferior colliculus, hippocampus and cerebellum of 3-month-old F344 rats to study distributions of the full-length and truncated isoforms of tyrosine kinase B receptor, and fibroblast growth factor receptor 2. The latter two brain regions served as positive controls. For all three antigens, immunolabeling was localized primarily in somata and proximal dendrites in all subdivisions of the inferior colliculus, and in the dentate gyrus and Ammon's horn of the hippocampus. In the cerebellum, the somata and dendrites of the Purkinje cells were also immunolabeled.A significant reduction in levels of the full-length form of tyrosine kinase B receptor in 18- and 25-month-old rats (respectively, approximately 20% and 30% relative to 3-month-olds) was revealed using western blot analyses. Inferior colliculus and hippocampal levels of the truncated form were modestly decreased ( approximately 7%) as well in the two older age groups. In contrast, levels of fibroblast growth factor receptor 2 in the inferior colliculus and hippocampus were elevated by approximately 35% in the two older age groups when compared to 3-month-olds. Changes in cerebellar levels of tyrosine kinase B receptor and fibroblast growth factor receptor 2, while similar to those in the inferior colliculus and hippocampus among the age groups, did not achieve statistical significance in this study. These findings give rise to the possibility that age-related reductions in tyrosine kinase B receptor levels could be a causal factor in the degenerative changes observed in the inferior colliculus of aged animals, including mitochondrial damage and dendritic regression. The observed increases in fibroblast growth factor receptor 2 levels may be compensatory to the increased oxidative stress. The effectiveness of the fibroblast growth factor receptor 2 response is questionable given the damage that occurs in the inferior colliculus and hippocampus of aged animals. However, the deficits could worsen in the absence of an increase in fibroblast growth factor receptor 2.

Aging↗

PubMed1999

Age-related synaptic changes in the central nucleus of the inferior colliculus of Fischer-344 rats.

The central nucleus of the inferior colliculus (ICc) is a major processing center for the ascending auditory pathways. Gamma-aminobutyric acid (GABA) and excitant amino acids (EAAs) are essential for coding many auditory tasks in the IC. Recently, a number of neurochemical and immunocytochemical studies have suggested an age-related decline in GABAergic inhibition in the ICc, and possibly excitant-amino-acid-mediated excitation as well. The objective of this study was to compare quantitatively changes in the synaptic organization of the ICc among three age groups (3, 19, and 28 months) of Fischer-344 rats. Immunogold electron microscopic methods were used to determine if there were age-related changes in the density, distribution, or morphology of GABA-immunoreactive (+) and GABA-immunonegative (-) synapses in the ICc. The data suggest similar losses of excitatory and inhibitory synapses in the ICc. There were significant reductions in the densities of GABA+ and GABA- synaptic terminals (approximately 30% and approximately 24%, respectively) and synapses (approximately 33% and approximately 26%, respectively) in the ICc of 28-month-old rats relative to 3-month-olds. The numeric values, which were adjusted to consider changes in volume of the IC with age, depict similar effects, although the effect magnitude for the adjusted values was reduced by approximately 9%. For both types of synapses, the decreases did not differ significantly from each other. The reductions in synaptic numbers appeared, to be related to a similar numeric decline in dendrites, in particular those with calibers of between 0.5 and 1.5 microm. The number and distribution of synaptic terminals on the remaining dendrites of GABA- neurons appeared not to undergo major age-related changes. GABA+ neurons, on the other hand, may have evolved patterns of synaptic and dendritic change during aging in which the distribution of synaptic terminals shifts to dendrites of larger caliber. In the 19-month group, the synaptic areas were elevated in terminals apposed to dendrites with calibers of 1.5 microm or less. However, this increase in synaptic size did not persist in the aged animals. No neuronal losses were detectable among the three age groups. Thus, the decrease in GABA and EAAs identified in the IC by previous studies may be attributable to synaptic and dendritic declines, rather than cell loss.

Aging↗

PubMed1999

Age-related changes in [3H]strychnine binding in the vestibular nuclei of rats.

Glycine plays an important role as a neurotransmitter in the four vestibular nuclei (VN). The objective of this study was to determine if the levels of glycine-receptor binding in the VN change as a function of age. Quantitative receptor autoradiography was performed on brainstem sections from three age groups (3, 18 and 26 months) of Fischer 344 rats to assess binding in the VN. Glycine receptors were localized using [3H]strychnine binding. Strychnine binding declined monotonically with increasing age, such that the level of strychnine binding in each of the VN in the 28-month-old animals was approximately one-half that in the 3-month-olds. The age-related decrease in levels of strychnine binding suggest altered glycinergic function in the VN, which may in turn contribute to disturbances in equilibrium observed in the elderly.

Aging↗

PubMed1999

Age-related reductions in the activities of antioxidant enzymes in the rat inferior colliculus.

The inferior colliculus (IC) is a major relay and processing center of auditory signals in the midbrain and receives inputs from most other auditory nuclei. A number of studies have indicated age-related declines in the GABAergic and excitatory amino acid systems in the IC, including losses in both GABA immunoreactive (+) and GABA immunonegative (-) synapses. The goal of this project was to identify potential biochemical and morphological changes in the IC that may contribute to deficits in the functions of these neurotransmitters, using three age groups of Fischer-344 rats. Homogenates obtained from the IC showed age-dependent reductions in activities of the antioxidant enzymes, superoxide dismutase (SOD) and catalase (CAT), with a concomitant increase in lipid peroxidation. Dephosphorylation of IC homogenates with alkaline phosphatase reduced the activities of SOD and CAT in all age groups, which could be restored by protein kinase C (PKC)-dependent phosphorylation. Restoration of enzyme activity was specific to the PKC-alpha isozyme, but not to the beta1, beta2, delta or gamma forms. No age-dependent change in the levels of PKC isoforms (alpha, beta1, beta2 and gamma) was detectable in IC homogenates. Morphological analyses indicate decreases in mitochondrial density in the somata of both GABA+ and GABA- IC neurons in 19- and 28-month-old rats when compared to 3-month-olds, along with significantly higher matricial abnormalities. These data indicate age-related increases in oxidative stress in the IC, which could be partially restored by PKC. The progressive increase in oxidative stress with age may underlie changes in neuronal morphology and function of the IC.

Aging↗

PubMed1998

Age-related glycine receptor subunit changes in the cochlear nucleus of Fischer-344 rats.

Previous studies have shown that levels of binding for the strychnine-sensitive glycine receptor in the cochlear nucleus (CN) of Fischer (F344) rats decrease with age. Given the major role glycine plays in normal CN function, changes in glycine-receptor activity may contribute to central presbycusis. To further evaluate the impact of age on glycine receptors, in situ hybridization was used to assess, in three age groups of F344 rats, changes in levels of gene expression for four of its subunits. When compared with the 3-month-old rats, expression of mRNAs for alpha1 and beta subunits in the anteroventral CN decreased significantly in the 18- and 27-month-old age groups, while mRNA expression for the alpha2 subunit increased. If protein expressions are similar, these subunit changes may alter the function of glycine receptors, thereby affecting binding to its ligands.

Aging↗

PubMed1996

Three classes of inhibitory amino acid terminals in the cochlear nucleus of the guinea pig.

Electron microscopic postembedding immunocytochemistry was used to analyze and assess the synaptic distribution of glycine (GLY) and gamma-amino butyric acid (GABA) immunoreactivities in the guinea pig cochlear nucleus (CN). Three classes of endings were identified containing immunolabeling for glycine, GABA, or both glycine and GABA (GLY/GABA). All classes were similar in that the terminals contained pleomorphic vesicles and formed symmetric synapses with their postsynaptic targets. A fourth class, which labeled with neither antibody, contained round vesicles and formed asymmetric synapses. Glycine endings predominated in the ventral CN, while GLY/GABA endings were prevalent in the dorsal CN. GABA endings were the least common and smallest in size. Glycine, GLY/GABA, and GABA endings differed in their proportions and patterns of distribution on the different classes of projection neurons in the CN, including spherical bushy, type I stellate/multipolar, and octopus cells in the ventral CN and fusiform cells in the dorsal CN. The vast majority of anatomically-defined, putative inhibitory endings contain GLY, GABA, or both, suggesting that most of the inhibition in the cochlear nucleus is mediated by these three cytochemically and, probably, functionally distinct classes of endings. The results of this study also suggest that a large proportion of the GABA available for inhibition in the CN coexists in terminals with glycine.

Animals↗

PubMed1996

Silver intensification of immunocolloidal gold on ultrathin plastic sections applied to the study of the neuronal distribution of GABA and glycine.

A postembedding silver intensification procedure for immunogold on ultrathin sections has been used to help in the study of localization and co-localization of glycine and GABA in synaptic terminals and cell bodies in the cochlear nucleus of the auditory pathway. Intensification take place in a single step after the immunogold procedure. Intensification times vary from 2 to 6 minutes. This allows visualization of silver enhanced gold particles at low electron microscopic magnifications, which greatly facilitates the analysis of patterns of distribution of putative inhibitory ending immunolabelled for glycine, GABA or both glycine and GABA.

Animals↗

PubMed1996

Distribution of glycine and GABA immunoreactivities in the cochlear nucleus: quantitative patterns of putative inhibitory inputs on three cell types.

Postembedding immunocytochemistry was used to compare the distribution of GABA and glycine immunoreactive labelling in the cochlear nucleus, in particular the number of immunolabeled synaptic boutons apposing the cell body profiles of three major neuronal types. The proportions and absolute numbers of glycine immunoreactive puncta were greatest on fusiform cell body profiles. Glycine immunoreactive puncta also predominated on spherical cell body profiles, although GABA immunoreactive boutons were more abundant than on fusiform cells. Octopus cell body profiles were apposed by the fewest immunoreactive puncta. Puncta colabeled for glycine and GABA were frequently observed on all three cell types. These findings suggest that each major cell type possesses a distinct pattern of glycinergic and GABAergic input, with glycinergic input predominating. Since both tuberculoventral and cartwheel neurons were immunolabeled and are known to project intrinsically, it is clear that a large percentage of glycinergic and GABAergic input to cochlear nucleus neurons originates from intrinsic sources.

Animals↗

PubMed1995

Deafness induced cell size changes in rostral AVCN of the guinea pig.

The right cochleae of 250-350 g guinea pigs were lesioned by topical administration of neomycin in the middle ear cavity. Eight weeks after the lesion, the cochleae and cochlear nuclei were analyzed. Cochlear hair cell loss was assessed, and cell areas of spherical bushy cells in the rostral anteroventral cochlear nucleus (AVCN) were compared between the lesioned and normal hearing sides for each animal. In five animals with both inner and outer hair cell loss in the lesioned cochlea, the average area of neuronal somata in the rostral AVCN in the lesioned side was 22% smaller than the average area of these cells in the normal hearing side. In two animals with outer hair cell loss but inner hair cells remaining, there was no difference in cell size between the lesioned and non-lesioned AVCN. These results provide evidence that there is significant shrinkage in AVCN cell size in the mature mammal after hearing loss associated with inner hair cell loss.

Analysis of Variance↗

PubMed1995

Regional induction of fos immunoreactivity in the brain by anticonvulsant stimulation of the vagus nerve.

Electrical stimulation of the vagus nerve exerts an antiepileptic effect on human partial-onset epilepsy, but little is known about the brain structures that mediate this phenomenon. Fos is a nuclear protein that is expressed under conditions of high neuronal activity. We utilized fos immunolabeling techniques on Sprague-Dawley rat brains to identify regions that are activated by antiepileptic stimulation of the left vagus nerve. Vagus nerve stimulation (VNS) induced specific nuclear fos immunolabeling in several forebrain structures, including the posterior cortical amygdaloid nucleus, cingulate and retrosplenial cortex, ventromedial and arcuate hypothalamic nuclei. In the brainstem, there was specific immunolabeling in vagus nerve nuclei, in the A5 and locus ceruleus noradrenergic nuclei, and in the cochlear nucleus. No labeling of these structures occurred in sham-operated, unstimulated control animals. Intense labeling also occurred in habenular nucleus of thalamus after vagus nerve stimulation, whereas only mild staining occurred in unstimulated animals. Several of the brain structures activated by VNS are important for genesis or regulation of seizures in the forebrain. These structures may mediate the antiepileptic effect of VNS.

Animals↗

PubMed1994

Distribution of GABAA and GABAB binding sites in the cochlear nucleus of the guinea pig.

We compared the distribution of GABAA and GABAB binding sites in the cochlear nucleus using quantitative receptor autoradiography with [3H]GABA. To visualize GABAA binding sites, GABAB binding sites were blocked with +/- baclofen. To visualize GABAB binding sites, isoguvacine was used to block GABAA binding sites. GABAA binding sites predominated over GABAB, although there were marked regional differences in the distribution of binding. In the ventral cochlear nucleus, GABAA and GABAB binding sites were concentrated in the peripheral granule cell cap, with low binding levels in the central region. In the dorsal cochlear nucleus, binding was concentrated in the superficial (fusiform and molecular) layers, with a distinct laminar pattern. GABAA binding sites predominated in the fusiform cell layer. The molecular layer contained the highest level of GABAB binding sites in the entire cochlear nucleus. These results suggest that GABAergic inhibition in the cochlear nucleus is mediated both by GABAA and GABAB receptors, particularly in the dorsal cochlear nucleus. However, low levels of binding in areas such as the magnocellular regions of the ventral cochlear nucleus, known to contain abundant GABAergic synapses, suggest heterogeneity of GABA receptors in this auditory nucleus.

Animals↗

PubMed1994

Scanning electron microscopic evaluation of age-related changes in the rat vestibular epithelium.

An ultrastructural study was performed to assess age-related changes in the vestibular end organs of Fischer 344 rats. The surfaces of the maculae and cristae from 3-, 12-, and 24-month-old Fischer 344 rats were observed by use of scanning electron microscopy. Age-related changes in the morphology of the vestibular neuroepithelium included a substantial loss of hair cells, as well as a reduction in the number of kinocilia and stereocilia on those that remained. These changes were greatest in the central upper regions of the three ampullae. In aged animals a greater area of the neuroepithelial surface was covered with microvilli, and in some instances, giant cilia were found among the microvillous surfaces. In contrast, there were few differences among the three age groups in the number and condition of hair cells in the saccules and utricles. The changes observed in the cristae may contribute to the age-associated impairment of vestibular function. If similar changes occur in human beings, these could in part account for the presbycusis observed in the elderly.

Acoustic Maculae↗

PubMed1992

Patterns of glutamate, glycine, and GABA immunolabeling in four synaptic terminal classes in the lateral superior olive of the guinea pig.

The goal of this study was to correlate synaptic ultrastructure with transmitter specificity and function in the lateral superior olive (LSO), a nucleus that is thought to play a major role in sound localization. This was accomplished by means of postembedding immunogold immunocytochemistry. Four classes of synaptic terminals were identified in the LSO. They were distinguishable from one another both morphologically and on the basis of their different patterns of immunolabeling for glutamate, glycine, and gamma-aminobutyric acid (GABA). The highest level of glutamate immunoreactivity was found in terminals that contained round vesicles (R) and formed synaptic contacts with asymmetric synaptic junctions. Round-vesicle terminals predominated on small caliber dendrites by a ratio of at least 2:1 over the other classes combined. The thinnest dendrites were typically contacted by R terminals only. The ratio of R terminals to the other types decreased as the caliber of the dendritic profiles they apposed increased so that on the soma, R terminals were outnumbered by at least 2:1 by the other types. Terminals containing flattened vesicles (F) exhibited intense immunoreactivity for both glycine and glutamate, although the glutamate immunolabeling was not as high as that in the R terminals. Flattened-vesicle terminals formed symmetric synaptic contacts with their targets and their distribution was the reverse of that described for R terminals; i.e., they were most abundant on LSO perikarya and fewest on small caliber dendrites. Two terminal types, both containing pleomorphic vesicles and forming symmetric synaptic junctions, were found in far fewer numbers. One group contained large pleomorphic vesicles (LP) and was immunoreactive for both glycine and GABA. The other group contained small pleomorphic vesicles (SP) along with a few dense-core vesicles and labeled for GABA only. The LP terminals were preferentially distributed on somata and large-caliber dendrites, while the SP terminals most often contacted smaller dendrites. Previous work suggests that a large percentage of the R terminals arise from spherical cells in the ipsilateral cochlear nucleus and are excitatory in action. This pathway may use glutamate as a transmitter. Many of the F terminals are thought to originate from the ipsilateral medial nucleus of the trapezoid body and appear to be the inhibitory (glycinergic) terminals from a pathway that originates from the contralateral ear. The origins and functions of LP and SP terminals are unknown, but a few possibilities are discussed along with the significance of cocontainment of neuroactive substances in specific terminal types.

Animals↗

PubMed1992

Connections between the cochlear nuclei in guinea pig.

This study provides a detailed analysis of the appearances and distributions of neurons projecting from one cochlear nucleus to the other. Injections of wheatgerm agglutinin conjugated to horseradish peroxidase were made into ventral or dorsal cochlear nucleus of the guinea pig. Retrogradely labeled cells in the opposite cochlear nucleus were examined and quantified. Three major categories of labeled cells were discerned on the basis of their soma shape: elongate, round-to-oval, and polygonal. All injections resulted in widespread labeling of cells in all of these categories, but especially round-to-oval cells, in the opposite ventral cochlear nucleus and sparse labeling in the dorsal cochlear nucleus. The results suggest that there is a significant cochlear nucleus commissural projection involving heterogeneous cell types which could have diverse functions in binaural auditory signal processing.

Animals↗

PubMed1991

Descending projections to the dorsal and ventral divisions of the cochlear nucleus in guinea pig.

The origins of extrinsic projections to the guinea pig dorsal and ventral cochlear nuclei were identified by examining the retrograde transport of horseradish peroxidase conjugated to wheatgerm agglutinin following its injection into each of these divisions. Major projections originated in periolivary regions of the superior olivary complex, the contralateral cochlear nucleus and the inferior colliculus. There was no contribution from the nuclei of the lateral lemniscus to these pathways. The heaviest projection from the periolivary regions to both divisions of the cochlear nucleus arose bilaterally in the ventral nucleus of the trapezoid body. The ipsilateral lateral nucleus of the trapezoid body also projected heavily to dorsal and ventral cochlear nucleus. In addition, the ventral cochlear nucleus received a substantial projection from the dorsal aspect of the ipsilateral dorsomedial periolivary nucleus. Projections originating bilaterally in the central nucleus of the inferior colliculus terminated in the deep layers of dorsal cochlear nucleus. These projections appear to be more strongly ipsilateral and specific than those reported in the cat.

Animals↗

PubMed1990

Immunocytochemical and lesion studies support the hypothesis that the projection from the medial nucleus of the trapezoid body to the lateral superior olive is glycinergic.

Pre- and postembedding immunocytochemical techniques were used to study the distribution of glycine immunoreactivity in the superior olivary complex of guinea pigs following kainic acid (KA) lesions of the medial nucleus of the trapezoid body (MNTB). Destruction of the MNTB by injecting 50-100 nl of 10 mM KA virtually abolished labeled neurons in the MNTB at the site of the lesion. This resulted in a marked decrease in the number of labeled fibers projecting to the ipsilateral lateral superior olive (LSO) and in the number of labeled fibers and presynaptic terminals in the neuropil of the LSO. Smaller volumes (20 nl) of KA produced similar but more restricted changes that conformed to the topographic organization of the MNTB projection to the LSO. The results support the hypothesis that the MNTB to LSO pathway is glycinergic.

Animals↗

PubMed1989

Immunocytochemical localization of the GABAA/benzodiazepine receptor in the guinea pig cochlear nucleus: evidence for receptor localization heterogeneity.

Immunocytochemistry with a monoclonal antibody against the GABAA/benzodiazepine receptor showed labeled axo-dendritic synapses in the anteroventral cochlear nucleus. In the dorsal cochlear nucleus, label was seen apposing both axo-somatic and axo-dendritic terminals. The results suggest a heterogeneous distribution of GABA receptors, together with a possible segregation of receptor subtypes between somata and dendrites in certain neurons. The presence of cytoplasmic labeling in some neurons might reflect a higher receptor turnover rate in these neurons.

Animals↗

PubMed1989

GABA and glycine immunoreactivity in the guinea pig superior olivary complex.

Immunoperoxidase immunocytochemistry was employed to examine the distribution of gamma-aminobutyric acid (GABA)-and glycine (GLY)-immunoreactive cells, fibers, and terminals in the guinea pig superior olivary complex. The nuclei studied were the lateral superior olive (LSO), medial superior olive (MSO), superior paraolivary nucleus (SPN), and the medial, ventral, and lateral nuclei of the trapezoid body (MNTB, VNTB, and LNTB, respectively). The majority of LSO neurons exhibited GABA-immunoreactive (+) labeling. These same neurons were also lightly GLY+. Extensive perisomatic punctate GLY + labeling was observed on most LSO neurons; these puncta most likely correspond to synaptic terminals. A very small number of MSO fusiform neurons were GABA +, and none were GLY +. The GLY positive perisomatic punctate labeling around most MSO neurons, although abundant, was not as profuse as that observed in the LSO. The MNTB neurons corresponding to the principal and elongate types were intensely GLY + and were contacted by small numbers of GLY + puncta. There was extensive GLY + punctate labeling in the SPN that surrounded the cell bodies of most of its large, radiate neurons and many of the smaller, fusiform neurons. The few large, radiate neurons that were lightly GLY + possessed far fewer GLY + puncta on their perikarya. The distribution of GABA + puncta was generally diffuse and scattered throughout the nuclei described above. In the VNTB and LNTB, several large neurons of various shapes were GLY + as were the small, oval neurons. The extent of GLY + punctate labeling was quite variable in both nuclei. The majority of perikarya in the VNTB and LNTB were GABA +. A light distribution of GABA + puncta was observed on most cell bodies in both nuclei. Peridendritic GABA + punctate labeling was dense in the VNTB neuropil. Two small populations of GLY + neurons were observed outside of the named nuclei of the SOC; one was located dorsal to the LSO, near its dorsal hilus, and the other was identified near the medial pole of the LSO. The somata of both populations possessed extremely sparse GLY + punctate labeling. In general, these results agree with and expand on findings in rodents from previous studies. There appears, however, to be differences between the guinea pig and cat with regard to the proportions of GABA + neurons in the LSO and GLY + punctate labeling in the MSO.

Animals↗