Biomedical subjects

J R Wolff

Publications and source records attributed to J R Wolff.

At least 55 records · Page 3Linked to original sources

PubMed1993

Pre- and postnatal development of the primary visual cortex of the common marmoset. II. Formation, remodelling, and elimination of synapses as overlapping processes.

During ontogenesis changes in the numerical density of synapses are usually assumed to depend essentially on variations in the formation of synapses. Only the final adjustment to adult synapse densities is thought to include the elimination of synapses in some brain regions of certain species. Here, we focus attention on quantitative aspects of synapse elimination throughout development of area 17 of marmoset monkeys (Callithrix jacchus). Mature synapses, various precursor forms, and indicators of lysosomal degradation of synapses were quantitatively analysed by electron microscopy and morphometric methods. A total number of about 135 x 10(9) synapses was calculated for area 17 in each adult hemisphere corresponding to a volume density of 600 x 10(6) synapses/mm3. At 3 months of age, the respective values were 508 x 10(9)/area and 1,159 x 10(6)/mm3, while at birth these values were 69 x 10(9)/area and 328 x 10(6)/mm3. Consequently, at least three out of four synapses are eliminated between 3 months and adulthood. However, the real number of synapses being eliminated during development is probably much larger if the time course of lysosomal degradation is additionally taken into account. The frequency of lysosomes in presynaptic endings is highest before net-elimination of synapses occurs, i.e., between 1 and 3 months. This suggests that lysosomal degradation is not directly responsible for the majority of synapses removed during ontogenesis but apparently represents a second mechanism for synapse remodelling and elimination. Thus, it appears from this study that remodelling and elimination of synapses are quantitatively as important as their formation, and accompany synaptogenesis from its very onset onwards.

Animals↗

PubMed1993

Facial nerve lesions lead to increased immunostaining of the astrocytic gap junction protein (connexin 43) in the corresponding facial nucleus of rats.

After peripheral transection of the facial nerve, immunostaining of astrocytic gap junction protein changed in the corresponding brainstem nucleus of the rat. Enhanced connexin-43 immunoreactivity was restricted to the ipsilateral facial nucleus and to astrocytes surrounding lesioned motoneurons. This reaction is focally distinct, and marks only a part of the astrocytic network indicating a local plasticity of intercellular coupling. These results suggest that astrocytes work as sensors of signals which either depend on the integrity of neighboring neurons or inform about neuronal disorders.

Animals↗

PubMed1993

Perineuronal nets provide a polyanionic, glia-associated form of microenvironment around certain neurons in many parts of the rat brain.

The nature and function of previously described perineuronal nets are still obscure. In the present study their polyanionic components were demonstrated in the rat brain using colloidal iron hydroxide (CIH) staining. In subcortical regions, such as the red nucleus, cerebellar, and vestibular nuclei, most neurons were ensheathed by CIH-binding material. In the cerebral cortex perineuronal nets were seen around numerous nonpyramidal neurons. Biotinylated hyaluronectin revealed that hyaluronan occurs in perineuronal nets. Two plant lectins [Wisteria floribunda agglutinin (WFA) and Vicia villosa agglutinin (VVA)] with affinity for N-acetylgalactosamine visualized perineuronal nets similar to those rich in anionic components. Glutamic acid decarboxylase (GAD)-immunoreactive synaptic boutons were shown to occupy numerous meshes of perineuronal VVA-positive nets. Electron microscopically, VVA binding sites were scattered throughout perisynaptic profiles, but accumulated at membranes and in the extracellular space except not in synaptic clefts. To investigate the spatial relationship between glial cell processes and perineuronal nets, two astrocytic markers (S100-protein and glutamine synthetase) were visualized at the light and electron microscopic level. Two methods to detect microglia by the use of Griffonia simplicifolia agglutinin (GSA I-B4) and the monoclonal antibody, OX-42, were also applied. Labelled structures forming perineuronal nets were observed with both astrocytic, but not with microglial, markers. It is concluded that perineuronal nets are composed of a specialized type of glia-associated extracellular matrix rich in polyanionic groups and N-acetylgalactosamine. The net-like appearance is due to perisynaptic arrangement of the astrocytic processes and these extracellular components. Similar to the ensheathment of nodes of Ranvier, perineuronal nets may provide a special ion buffering capacity required around various, perhaps highly active, types of neurons.

Acetylgalactosamine↗

PubMed1993

Modulation by GABA of neuroplasticity in the central and peripheral nervous system.

Apart from being a prominent (inhibitory) neurotransmitter that is widely distributed in the central and peripheral nervous system, gamma-aminobutyric acid (GABA) has turned out to exert trophic actions. In this manner GABA may modulate the neuroplastic capacity of neurons and neuron-like cells under various conditions in situ and in vitro. In the superior cervical ganglion (SCG) of adult rat, GABA induces the formation of free postsynaptic-like densities on the dendrites of principal neurons and enables implanted foreign (cholinergic) nerves to establish functional synaptic contacts, even while preexisting connections of the preganglionic axons persist. Apart from postsynaptic effects, GABA inhibits acetylcholine release from preganglionic nerve terminals and changes, at least transiently, the neurochemical markers of cholinergic innervation (acetylcholinesterase and nicotinic receptors). In murine neuroblastoma cells in vitro, GABA induces electron microscopic changes, which are similar in principle to those seen in the SCG. Both neuroplastic effects of GABA, in situ and in vitro, could be mimicked by sodium bromide, a hyperpolarizing agent. In addition, evidence is available that GABA via A- and/or B-receptors may exert direct trophic actions. The regulation of both types of trophic actions (direct, receptor-mediated vs. indirect, bioelectric activity dependent) is discussed.

Acetylcholine↗

PubMed1993

Distinct subsets of neuropeptide Y-negative principal neurons receive basket-like innervation from enkephalinergic and gabaergic axons in the superior cervical ganglion of adult rats.

The distributions of axons immunoreactive for [Leu]- or [Met]enkephalin and GABA were studied in the superior cervical ganglion of adult rats. The antigens were visualized separately and in combination with neuropeptide Y by the immunoperoxidase technique, using reaction end-products of different colors. Similarities and differences were found in the light-microscopic innervation patterns of enkephalin- and GABA-immunoreactive nerve fibers. Both fiber systems were heterogeneously distributed within the superior cervical ganglion, forming denser networks in its rostral part than elsewhere in the ganglion. The appearance of labeled nerve fibers differed in the two systems. Enkephalin-immunoreactive axons exhibited dotted profiles due to a strong immunoreaction in the axonal varicosities as compared with that in the intervaricose segments, whereas GABA-positive fibers were evenly labeled in both parts of the axons. The most marked difference between the innervation patterns from enkephalin- and GABA-immunoreactive axons was the presence of bundles of varicose axons in conjunction with the basket-like aggregation of enkephalin-immunoreactive nerve terminals. The possibility that enkephalins and GABA are co-localized in certain axons was excluded in double-labeling studies, silver intensification being used for the first antigen and the nickel-enhanced diaminobenzidine reaction for the second antigen. Different subsets of principal neurons were richly innervated in a basket-like manner by axons immunoreactive for enkephalins and GABA. Additionally, combined staining with antisera against either enkephalin and neuropeptide Y or GABA and neuropeptide Y revealed that both subsets of principal neurons richly innervated either by enkephalin-immunoreactive or by GABA-immunoreactive axons were devoid of neuropeptide Y immunoreactivity. Thus, the enkephalinergic and GABAergic axons have different subpopulations of neuropeptide Y-negative principal neurons as targets in the superior cervical ganglion. These results provide further evidence that sympathetic ganglion cells can be classified on the basis of their receiving input from different sources.

Animals↗

PubMed1993

Calcium/calmodulin-stimulated protein kinase II is present in primary cultures of cerebral endothelial cells.

Calcium/calmodulin-stimulated protein kinase II (CaM-PK II), a major kinase in brain, has been established to play an important role in neurotransmitter release and organization of postsynaptic receptors, and it is known to be involved in long-term potentiation and memory. Less is known about the function of this enzyme in nonneural cells. Here we report on the production, presence, and phosphorylation of the alpha-subunit of CaM-PK II in primary cultures of cerebral endothelial cells. These results raise the possibility that alpha-CaM-PK II can act as one of the key enzymes of calcium-mediated intracellular signaling in the cerebral endothelial cells and suggest that alpha-CaM-PK II may participate in such basic cellular processes as permeability in physiological and pathological conditions.

Animals↗

PubMed1993

In situ hybridization with digoxigenin labeled oligonucleotide probes: detection of CAMK-II gene expression in primary cultures of cerebral endothelial cells.

A better understanding of the regulation of gene expression under physiological and experimental conditions is one of the most important goals of today's neurobiology. In order to accomplish this task a number of in-situ hybridization methods have been elaborated. In the past few years the use of nonradioactive procedures have gained more and more space among these efforts. One of the most promising methods in this field is the application of digoxigenin-labeled probes, which have been used successfully in several laboratories. Here we present a rapid method providing good spatial resolution and low background labeling for the detection of messenger RNAs in various cell culture systems using digoxigenin-labeled probes. By using oligonucleotides complementary to the alpha and beta subunit of the calcium/calmodulin dependent protein kinase II (CAMK-II) we were able to demonstrate the presence of this enzyme in cultured cerebral endothelial cells, an enzyme that plays an important role in mediating the effects of extracellular signals.

Animals↗

PubMed1993

Deep sensibility of the mystacial pad in the rat and its cortical representation.

The cortical representation of the rat's mystacial pad was examined with the aid of evoked field potentials and recording of single cell activity. Mechanical bending of the vibrissae activated the well-known area within the somato-sensory cortex. Electrical stimulation of the mystacial pad with inserted needle electrodes, bi- and monopolarly, caused a widespread activation extending practically to the whole exposed cortex, including visual, acoustic and motor areas (MSS potentials). The evoked field potentials were accompanied by well-recordable unit activity, mainly in the upper 1000 microns of the cortical depth. Capsaicin, injected into the mystacial pad on the 8th-10th postnatal day heavily impaired the MSS potentials as recorded at 2 months of age, and only moderately acted on the mechanically evoked potentials. So did also the acutely injected capsaicin. Peak latency of the MSS potentials seemed to be in correlation with the distance from the punctum maximum. The latencies of unit potentials, however, did not show such dependence, they were between 8 and 10 ms. MSS potentials are thought to represent cortical projection mainly of thermo- and nociceptive fibers, which play an important role in the early postnatal life.

Animals↗

PubMed1993

Synaptic remodelling and elimination as integral processes of synaptogenesis.

It has become increasingly clear that the development and maintenance of synaptic connectivity patterns in the central and peripheral nervous system are not only based on the formation of synapses but include the selective elimination of synaptic subpopulations. Synaptic remodeling and elimination apparently also play a key role in the specification of neuronal connections during ontogenesis of the neocortex in various species. At least three types of synapse elimination have been demonstrated until now, i.e. physiological cell death of synaptically connected neurons, synaptic disconnection and lysosomal degradation, predominantly of presynaptic elements. Occurrence of different elimination types appears to depend on (1) whether the presynaptic or postsynaptic element induces the synaptic reorganization and (2) whether or not the neuron inducing the synapse elimination survives. The same type of synapse elimination may be seen during normal development and under pathological conditions. Factors inducing mental retardation may then either retard synapse formation or interfere with the process of synapse removal. In order to undergo plastic changes in synaptic connections, neurons may respond to exogenous factors such as lack of trophic factors or sensitivity for them (e.g. NGF), long-lasting changes in neuronal activity (e.g. due to drug application or sensory deprivation), hormonal influences (e.g. thyroxin or sexual hormones), learning conditions, or lesions (partial deafferentation and axotomy). The neurons, in turn, may change their responsiveness to exogenous stimuli by inducing synaptic reorganisation.

Age Factors↗

PubMed1992

Neonatal enucleation induces correlated modification in sensory responsive areas and pial angioarchitecture of the parietal and occipital cortex of albino rats.

This study was carried out to investigate whether correlations existing in normal adult rats (Ambach et al., '86) between functional characteristics of neocortical areas and their pial angioarchitecture can be correspondingly modified under pathological conditions. The right eyes of albino rats were enucleated on the 1st, 8th, 15th and 30th day after birth, respectively. At the age of 3 to 4 months, the responsiveness of the parieto-occipital cortex to sensory stimuli was studied in enucleated animals and age matched controls. After the mapping of visually and somatosensorily evoked potentials, the vascular system was filled with dye. Monocular enucleation at birth induced bilateral modifications in sensory responsiveness and corresponding changes in pial angioarchitecture, especially in the venous drainage fields. In comparison with the controls, a considerable expansion was observed in the overlapping zone between visually and somatosensorily responsive areas. In contrast, borders of the visual cortex toward the auditory and retrosplenial areas were essentially stable. Corresponding changes were found in the pial distribution patterns of cerebral veins but not of arteries. The major effect of neonatal enucleation on angioarchitecture was a change in the subdivision of the parieto-occipital veins drainage fields. This was due to a significant enlargement of the anterior accessory occipital (O3) vein, which compressed the drainage fields of the parietal and occipital veins and completely separated them from one another. The results suggest that during ontogenesis: (1) alterations in the formation of sensory input may interfere with neocortical angiogenesis, especially the structuring of veins, (2) after monocular enucleation this influence is prominent in parietal and occipital cerebral veins, and (3) these angiogenetic processes are vulnerable only during the perinatal and early postnatal period.

Animals↗

PubMed1992

Glutamate decarboxylase in developing rat neocortex: does it correlate with the differentiation of GABAergic neurons and synapses?

Postnatal development of glutamate decarboxylase was studied in the rat cerebral cortex. Two methods were used: estimation of the enzymatic activity of glutamate decarboxylase in homogenates of developing cortical tissue and visualization of structures containing glutamate decarboxylase-like immunoreactivity. Glutamate decarboxylase-like immunoreactivity appeared first in perikarya and dendrites and only later in axons and axon varicosities. The most rapid increase in the glutamate decarboxylase activity took place during the second postnatal week and this coincided with a rapid increase in the density of axon varicosities containing glutamate decarboxylase-like immunoreactivity but preceded the most rapid phase in the formation of GABAergic synapses by several days. However, there was a change in the characteristics of glutamate decarboxylase which correlated with GABA synaptogenesis: two fractions of glutamate decarboxylase with different sensitivities to the activating effects of Triton X-100 could be distinguished as from about the time when most of the GABAergic synapses are formed.

Animals↗

PubMed1992

Termination pattern and fine structural characteristics of GABA- and [Met]enkephalin-containing nerve fibers and synapses in the superior cervical ganglion of adult rat.

Morphological features of nerve fibers and synapses containing GABA and [Met]enkephalin were studied at the light and electron microscopic levels in the superior cervical ganglia of rats by pre- and postembedding immunohistochemistry. Both GABA and [Met]enkephalin immunoreactivities were found in varicose nerve fibers, forming diffuse networks which were denser in the rostral than in the caudal part of each ganglion. For both antigens rich and basket-like innervation was observed around some of the principal neurons. The GABA-immunoreactive fibers were evenly stained, while in case of [Met]enkephalin-positive nerve fibers the varicosities showed intensive immunopositivity only. Postembedding immunochemistry revealed that both inhibitory substances were located in axon varicosities which established asymmetric synapses of Gray I type. Fine structural investigation revealed that GABA-like immunoreactivity was confined in the nerve endings to the clear synaptic vesicles of 40 nm diameter, whereas the immunogold particles, indicating the occurrence of [Met]enkephalin, were located over the large dense-cored vesicles of 120 nm diameter. The clear and dense-cored vesicles were, however, mixed in the nerve endings labeled by either neurotransmitter substance. Interestingly, the [Met]enkephalin-immunopositive axon terminals were found, consequently, in synaptic contacts with dendrites containing dense bodies in a row underlying the postsynaptic membrane thickening. Since nerve terminals with GABA-like immunoreactivity established synapses of Gray I type without such subjunctional bodies, one can reasonably assume that, in spite of similarities in termination pattern, there is no co-existence of GABA and enkephalin in the axons in the superior cervical ganglion.

Animals↗

PubMed1992

Synaptic reorganization in developing and adult nervous systems.

Evidence is accumulating that synapse reorganization already starts during development, soon after first synapses appear. Although remodeling continues throughout ontogenesis, there are apparently (critical) periods which are characterized by enhanced synaptic reorganization. In certain parts of the peripheral and central nervous system, synapses may undergo remodeling which leads to changes in their transmission efficiency or complete elimination of the synaptic junctions, even in adulthood. Synaptic reorganization includes progressive and regressive changes on branches of dendritic and/or axonal processes that accompany the formation and elimination of synapses. Three modes of elimination are presently known: Physiological cell death of synaptically connected neurons is involved, especially during certain developmental periods, during hormonally induced metamorphosis and in the olfactory bulb. Synaptic disconnection ("stripping") and lysosomal degradation predominantly of presynaptic elements occur under different conditions. In order to undergo plastic changes, neurons seem to respond to exogenous or intrinsic factors such as lesions (partial deafferentation and axotomy), long-lasting changes in neuronal activity (e.g. drug application and sensory deprivation), hormonal influences (e.g. sexual hormones) or learning conditions.

Aging↗

PubMed1992

GABA-immunoreactive structures in rat kidney.

We examined the distribution of gamma-aminobutyric acid-like immunoreactivity (GABA-LI) in the rat kidney by light and electron microscopy. In vibratome sections, GABA-LI was present in both the renal medulla and cortex. The inner stripe of the outer medulla was most heavily and almost homogeneously labeled, whereas GABA-LI in the cortex was mainly confined only to some tubules. GABA-positive structures involved the epithelial cells of the thin and the thick ascending limbs of the loop of Henle, the connecting tubules, and the collecting ducts. In GABA-positive connecting tubules and collecting ducts the immunoreactivity was present in the cytoplasm of about half of the epithelial cells. As revealed by electron microscopy, the labeled cells in the collecting tubules were the light (principal) cells. No GABA-LI occurred in neuronal structures. These findings are consistent with the presence of a non-neuronal GABA system in the rat kidney. Furthermore, the specific distribution of GABA in the tubular epithelium suggests a functional significance of this amino acid in tubular transport processes.

Animals↗

PubMed1992

Developmental biology of the common marmoset: proposal for a "postnatal staging".

The published knowledge on neurobiological, psychological, and ethological aspects of development in Callithrix jacchus is still limited. We have collected published and unpublished data from several Callithrix colonies and pooled information on criteria for developmental progress and maturation using a questionnaire sent to numerous experts in the field. The data suggest that developmental stages can be defined not only for the embryonic and fetal but also for the postnatal period. Based on multifactorial definitions, using criteria selected from maturational changes in the motor and visual systems and behavioral features, we propose to subdivide postnatal development of the common marmoset into seven periods ("stages").

Animals↗

PubMed1992

Phagocytosis of latex beads by rabbit retinal Müller (glial) cells in vitro.

The ability of rabbit retinal Müller (glial) cells to perform phagocytosis was studied in vitro. Müller cells were feed with various kinds of latex beads either shortly after enzymatical isolation from adult retinae or in monolayer cell cultures derived from neonatal retinae and kept 14 days in vitro. Both types of Müller cell preparations showed intense phagocytosis of latex beads. Moreover, when entire retinae were isolated and exposed (sclerad side up) to latex beads in vitro for 30 min, Müller cells had picked up fluorescent beads and showed, after fixation, intense labeling in radial sections of such retinae. Effective phagocytosis by Müller cells was demonstrated 1.) by transmission electron microscopy, 2.) by bright-field light microscopy of unstained large beads (diameter 660 nm), or 3.) by fluorescence microscopy of small (diameter about 60 nm) and large latex beads labeled with rhodamine. These results suggest that both labeled and unlabeled latex beads are suitable tools to study the phagocytotic activity of retinal glial cells in vitro, thus providing information on important processes occurring in situ during ontogenesis, physiological renewal of retinal receptor cells, and pathological events. We found that movements of cells or cytoplasmic excrescences, and cell-cell interactions, play important roles in removal of foreign particles out of the fluid environment. Engulfed latex beads move through the elongated cells with velocities similar to slow axoplasmic transport.

Animals↗

PubMed1991

Releasable GABA in tubular epithelium of rat kidney.

The distribution of gamma-aminobutyric acid (GABA) in the rat kidney was examined by immunocytochemical techniques. GABA-like immunoreactivity (GABA-LI) was predominantly confined to the renal tubules, including the ascending parts of the distal tubules, and the loops of Henle, the collecting tubules and ducts, and the connective parts of the convoluted tubules. In GABA-positive cortical tubules, about half of the epithelial cells were labelled. The labelled cell type showed the ultrastructural features of principal cells. Depolarizing stimulation by ouabain and high K+ concentration evoked the efflux of endogenous GABA from kidney slices. The present findings, along with previous results, suggest that GABA released from renal tubular epithelium, and transported with the urine, might be involved in the modulation of contractility in the urinary tract.

Animals↗

PubMed1991

GABA accelerates excitotoxic cell death in cortical cultures: protection by blockers of GABA-gated chloride channels.

The effects of gamma-aminobutyric acid (GABA) and related agonists and antagonists on the excitatory cell death were examined in dispersed primary cultures of the rat cerebral cortex. The cytotoxic effects evoked by kainic acid, quisqualic acid and N-methyl-D-aspartic acid were evaluated by phase contrast microscopy and quantified by the measurement of lactic dehydrogenase release into the culture medium. GABA accelerated the cell death in a concentration-dependent fashion, but did not influence the amount of cells dying with 24 h after the treatment. This effect of GABA could be mimicked by GABAA rather than GABAB receptor agonists. Blockers acting at different sites of the GABAA receptor/chloride channel complex not only reduced the GABA-induced acceleration of cell death, but also showed a significant protection against the excitotoxic cell death in the absence of exogenous GABA. Blockers of chloride channels unrelated to GABA receptors produced similar protection. Our findings indicate that GABA-gated chloride channels may be effective in modulating excitotoxic vulnerability of cerebrocortical cells.

Animals↗