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Biomedical subjects

C E Ribak

Publications and source records attributed to C E Ribak.

At least 73 records · Page 4Linked to original sources
PubMed1989

Neurons containing retrogradely transported Fluoro-Gold exhibit a variety of lysosomal profiles: a combined brightfield, fluorescence, and electron microscopic study.

The advantages of axonally transported Fluoro-Gold as a retrograde fluorescent marker are numerous. The objective of the present study was to determine whether transported Fluoro-Gold is visible in either semi-thin sections for light microscopy or thin sections for electron microscopy. Rats received injections of Fluoro-Gold into either the striatum or thoracic spinal cord. After appropriate survival times, labelled neurons were observed with the fluorescence microscope in brain regions that are known to project to the injected areas. Sections that contained labelled cells were embedded in plastic and examined with a fluorescence microscope. Semi-thin sections of unosmicated tissue displayed high-resolution fluorescent labelling of somata and dendrites. In contrast, osmicated tissue did not fluoresce, but numerous dark granules were observed in the dendritic and perikaryal cytoplasm of labelled neurons in toluidine blue stained sections that were examined with brightfield optics. The unosmicated tissue did not display these granules, and this finding suggested that the granules are composed of membranes. Neurons in other brain regions that are known not to project to the injection sites did not contain these dark granules. Adjacent thin sections examined with the electron microscope displayed numerous electron-dense, lysosome-like organelles in the cytoplasm of labelled neurons. The electron density of these organelles was greater than that of lysosomes in unlabelled neurons. Three types of distinctive organelles were observed in these preparations: (1) relatively dense concentric lamellar bodies of various sizes; (2) heterogeneous or lipofuscin-like lysosomes; and (3) coarse grained lysosomes. Control sections and unlabelled neurons did not display these organelles. Therefore, these organelles appear to correlate with Fluoro-Gold localized within the somata and dendrites of retrogradely labelled neurons. It is not known if they are the Fluoro-Gold itself, or represent a physiological effect on membranes. The results of this study indicate that Fluoro-Gold may be useful for tract tracing at the electron microscopic level.

Biological Transport↗
PubMed1988

The development of GABAergic neurons in the rat hippocampal formation. An immunocytochemical study.

Recent studies have indicated that hippocampal GABAergic neurons in both the dentate gyrus and Ammon's horn are generated prenatally. Although the adult distribution of GABAergic neurons has been previously described by numerous investigators, the early postnatal appearance of these neurons has not been described. In the present study, immunocytochemical methods were used to localize GABAergic neurons with antisera to both GABA and its synthesizing enzyme, glutamate decarboxylase (GAD). The GABA-positive neurons appeared at the earliest postnatal day (PND) examined, 4 PND. In contrast, GAD-positive cells were not observed until 6 PND, and the number of these neurons remained less than that of the GABA-positive neurons until 14 PND. These findings indicated that immunocytochemically detectable amounts of GAD were not present in many young GABAergic neurons. Both GABA- and GAD-positive hippocampal neurons showed two large increases in number during the 4-8 PND and 12-16 PND time periods, and they reached about 90% of adult levels before 18 PND. The regional distribution of GABA- and GAD-positive neurons throughout the hippocampal formation was homogeneous for all ages examined except 4 PND. At this age, the GABA-positive cells appeared in clusters in the proximal CA3 and the distal CA1 relative to the dentate gyrus. In addition, the number of hippocampal neurons immunostained in adult preparations for both antisera to GABA and GAD showed a similar number and distribution. The data on the developmental appearance of GABA and GAD immunoreactivities are consistent with biochemical data for the development of GABA concentration and GAD activity in the hippocampal formation. Together, these data provide important information about the functional maturation of the hippocampal GABAergic system in the first 3 weeks of rat brain development.

Aging↗
PubMed1988

A Golgi-electron microscopic study of fusiform neurons in the hilar region of the dentate gyrus.

The fusiform cells of the dentate gyrus are located in a portion of the hilus within 100 micron of the granule cell layer. They have ovoid somata and bipolar dendrites that generally run parallel to the granule cell layer. The dendrites of these cells are either spiny or sparsely spiny. The spiny fusiform cell has numerous spines along its dendrites, which are contacted by terminals with the features of granule cell axon collaterals. This cell type also displays somal spines that are contacted by similar terminals. In contrast, the sparsely spiny fusiform cell displays only a few spines, which are contacted by multiple small axon terminals that synapse with both the stalk and end bulb of the spine. Most synaptic input for this cell type is made with the smooth surfaces of the soma and dendrites. A variety of terminals form synapses with the sparsely spiny fusiform cell, including terminals that resemble the fine axon collaterals of mossy fibers. The somata of these two cell types also display differences in the amount of Nissl bodies and the degree of nuclear infolding. The results indicate that spiny fusiform cells are similar to mossy cells, another hilar cell type that receives its major synaptic input from axon collaterals of mossy fibers from granule cells. The distribution of the dendrites of spiny fusiform cells and the pattern of granule cell axon collaterals suggest a high degree of convergence from granule cells. In contrast, the variety of axodendritic synapses for sparsely spiny fusiform cells suggests that more diverse inputs affect this cell's activity. Therefore, the structure and circuitry of these two hilar cell types are probably different. This study adds further evidence to indicate that the hilus contains a large variety of cell types with different neuronal connections.

Animals↗
PubMed1988

Colchicine causes intrasomatic neurofilament bundles in the mesencephalic trigeminal nucleus and intradendritic bundles in other brain regions.

The effect of a single intracerebroventricular injection of colchicine on the distribution of organelles in neurons of the mesencephalic nucleus of the trigeminal nerve, the inferior colliculus and the deep cerebellar nuclei was studied. In the mesencephalic nucleus of the trigeminal nerve colchicine produced a dramatic accumulation of neurofilament bundles in the soma of these neurons and did not produce a reduction in the number of lysosomes. In other neuronal populations studied, colchicine produced neurofilament bundles in the dendrites and a reduction of lysosomes from the soma of neurons.

Animals↗
PubMed1987

The effects of knife cuts of hippocampal pathways on epileptic activity in the seizure-sensitive gerbil.

Previous studies have shown morphological differences in the hippocampal formation of seizure-sensitive gerbils as compared to seizure-resistant gerbils. To determine the significance of these differences, lesions were made of hippocampal afferents and efferents. Seizure-sensitive gerbils with bilateral knife cuts of the perforant path, including those with bilateral fornix lesions, showed no seizure activity following surgery. However, bilateral transections of the fimbria of the fornix, unilateral lesions of the perforant path and sham surgeries had no significant effect on seizure activity. The termination of seizure activity with bilateral lesions of the perforant path suggests that this pathway, as opposed to the fornix, is required for motor seizures in this strain of gerbils.

Animals↗
PubMed1987

Hippocampus of the seizure-sensitive gerbil is a specific site for anatomical changes in the GABAergic system.

The brains of seizure-sensitive (SS) and seizure-resistant (SR) gerbils were studied with an immunocytochemical method to localize glutamic acid decarboxylase (GAD) to determine whether a defect existed in the inhibitory GABAergic system similar to that which has been reported in animal models of focal epilepsy in which GABAergic cell bodies and terminals are decreased in number. A major difference between the two strains of gerbils was found in the number of GABAergic neurons in the hippocampal formation. Specifically, a paradoxical increase occurred in the number of glutamate decarboxylase GAD-immunoreactive neurons: there were approximately 65% more GABAergic cells within the dentate gyrus and the CA3 region of the hippocampus in the SS gerbils. Furthermore, the density of GAD-immunoreactive puncta, the light microscopic correlates of synaptic boutons, was greater in the SS animals. Other histological methods were used to determine if the difference between SS and SR gerbils was specific for the GABAergic system. Nissl-stained preparations showed that the number of granule cells in the dentate gyrus was 20% greater in SS gerbils than in SR gerbils. An examination of some hippocampal afferents, efferents, and intrinsic connections with acetylcholinesterase histochemistry and the Timm's stain for heavy metals demonstrated no differences between the two strains. In addition, Golgi-stained preparations of the dentate gyrus indicated that the morphology of basket cells did not differ between the two strains nor between the gerbil and the rat. Several brain regions in addition to the hippocampus were studied to determine whether or not the increased number of GAD-immunoreactive neurons was specific for the hippocampal formation. These regions included the substantia nigra, motor cortex, and nucleus reticularis thalami and were selected because they contain large populations of GABAergic neurons and have been implicated in seizure activity. No differences between the two strains were detected in any of these regions. Therefore, a major morphological difference between the brains of SS and SR gerbils exists in the hippocampal formation of SS gerbils in which an increase occurs in the number of GABAergic neurons and granule cells. If these additional inhibitory neurons act mainly to inhibit other inhibitory neurons, the net effect would be increased disinhibition of the principal excitatory neurons of the hippocampal formation. This could lead to seizure activity within the hippocampal formation and at distant sites through multiple synaptic connections.

Acetylcholinesterase↗
PubMed1987

GABAergic neurons and axon terminals in the brainstem auditory nuclei of the gerbil.

The anatomical localization of glutamic acid decarboxylase (GAD), the synthesizing enzyme for GABA, was analyzed in the brainstem auditory nuclei of the adult gerbil. GAD-positive terminals and somata were present in the cochlear nucleus, superior olivary complex, lateral lemniscus, and inferior colliculus in varying concentrations and patterns. One of the highest densities of GAD-positive terminals is found in the superficial layers of the dorsal cochlear nucleus (DCN), whereas the ventral cochlear nucleus (VCN) has somewhat fewer terminals that are arranged in pericellular plexuses. GAD-positive neurons occur mainly in the superficial and fusiform layers of the DCN and are scattered throughout the VCN. Within the superior olivary complex, the highest concentration of immunoreactive terminals and neurons occurs in the ventral and lateral nuclei of the trapezoid body. In contrast, the medial nucleus of the trapezoid body and the medial superior olive contain fewer GAD-positive puncta and probably no immunoreactive somata. The lateral superior olive and superior periolivary nucleus contain a few immunoreactive puncta but a large number of immunoreactive somata. In the midbrain, the nuclei of the lateral lemniscus contain a moderate number of GAD-positive puncta and a large number of different types of GAD-positive neurons. The inferior colliculus also contains a heterogeneous population of labeled somata, most of which are multipolar neurons. In addition, a high concentration of immunoreactive puncta occurs in this region. These data demonstrate a diverse distribution of GAD-positive neurons and puncta throughout the brainstem auditory nuclei and suggest that GABA might be an important neurotransmitter in the processing of auditory information.

Animals↗
PubMed1987

An electron microscopic study of GABAergic neurons and terminals in the central nucleus of the inferior colliculus of the rat.

Neurons and terminals in the ventral lateral portion of the central nucleus of the inferior colliculus (ICCN) of the rat were labelled immunocytochemically with antisera to GABA or to its synthesizing enzyme, glutamic acid decarboxylase. Four types of GABAergic neuron are described: small, medium-sized and large multipolar neurons, as well as medium-sized bipolar neurons. All sizes of GABAergic multipolar neurons are characterized by highly infolded nuclei, many mitochondria and both asymmetric and symmetric axosomatic synapses. A dense plexus of terminals occurs on the proximal dendrites of GABAergic neurons, and most of these terminals form asymmetric axodendritic contacts. Small GABAergic neurons (diameter less than 15 microns) are multipolar, and have a large nucleus to cytoplasm ratio, prominent nucleoli and usually two to five axosomatic synapses per thin section, with the majority of these contacts being symmetric. Medium-sized GABAergic neurons (15-25 microns in diameter) display both multipolar and fusiform shaped somata, have a more abundant cytoplasm than the small neurons and show about ten axosomatic contacts per thin section. Large GABAergic neurons (diameters greater than 25 microns) have eccentrically located, highly infolded nuclei, abundant cytoplasm and a denser plexus of terminals that form axosomatic synapses than the other cell types. These results indicate that four of the six major cell types in the ICCN are probably GABAergic inhibitory neurons. The axon initial segments of GABAergic neurons in the ICCN all have similar features in that they are contacted by only one or two terminals that form symmetric synapses on their proximal portions and are invested by a glial sheath from 3 to 20 microns from the cell body. Many immunoreactive myelinated axons (approximately 0.5 micron in diameter) are observed and some terminals that arise from these axons form synapses with small neuronal somata. Both these and other labelled terminals are shown to form symmetric synapses. These data suggest a complex circuitry for the GABAergic neurons within the ICCN.

Animals↗
PubMed1987

Electron microscopic localization of acetylcholinesterase in the dentate gyrus of young and adult rats.

Acetylcholinesterase (AChE) histochemical staining occurred in neurons of the dentate gyrus at the day of birth and steadily increased in intensity and distribution during the first 3 postnatal weeks until the adult pattern was reached. Granule cells failed to display AChE staining; however, the somata of most non-principal cells in these regions showed AChE activity. It is interesting that most hilar neurons in the dentate gyrus were AChE-positive, but molecular layer local circuit neurons and pyramidal basket cells associated with the granule cell layer did not display AChE staining. AChE reaction product was localized to the nuclear envelope and cisternae of the granular endoplasmic reticulum in the labeled neuronal somata. In addition, the neuropil in the dentate gyrus displayed AChE staining associated with membranes. The possible cholinoceptive role of the AChE somata in the hilus is discussed.

Acetylcholinesterase↗
PubMed1986

Anatomical changes of the GABAergic system in the inferior colliculus of the genetically epilepsy-prone rat.

The number of GABAergic neurons as determined by GAD immunocytochemistry and total neurons as determined from Nissl preparations were counted and classified at the light microscopic level in the inferior colliculus (IC) of the genetically epilepsy prone rat (GEPR) and the non-epileptic Sprague-Dawley (SD) strain of rat. GAD-positive neurons are abundant in the IC and a significant increase in the number of GAD-positive neurons occurs in the GEPR as compared to the SD in all three subdivisions. However, the most pronounced difference occurs in the ventral lateral portion of the central nucleus, where there is a selective increase in the small (200%) and medium-sized (90%) GABAergic somata (10-15 microns in diameter and 15-25 microns in diameter, respectively). As determined from Nissl preparations an increase in total numbers of neurons also occurs. Thus, a 100% increase in the number of small neurons and a 30% increase in the number of medium-sized neurons occur in the adult GEPR as compared to the SD rat. A statistically significant increase in the numbers of small neurons also occurred in the IC of the young GEPR. At 4 days of age, a 55% increase in the number of small neurons was found, and at 10 days of age this increase was 105%. The numbers of the medium and large neurons were similar in the older group of rats. These data suggest that the increase in cell number observed in the adult GEPR is not compensatory to the seizure activity, but may either be genetically programmed or be a failure of cell death. Based on other studies of genetic models of epilepsy, we propose that the additional GABAergic neurons may disinhibit excitatory projection neurons in the IC.

Acoustic Stimulation↗
PubMed1986

A decrease in the number of GABAergic somata is associated with the preferential loss of GABAergic terminals at epileptic foci.

Previous studies have indicated that a loss of GABAergic terminals occurs at epileptic foci. The present study was undertaken to investigate if this loss is associated with a loss of GABAergic neuronal somata. Seven juvenile monkeys (M. mulatta) received alumina gel injections to the pre-central gyrus of the left cerebral hemisphere to produce epileptic foci. Four of these monkeys were chosen for further quantitative study. One was sacrificed prior to seizure onset ('pre-seizure'), one had seizures for 3 days ('acute'), and two had a seizure record of one month ('chronic'). Sections of tissue from the epileptic cortex and from the contralateral, non-epileptic cortex were processed for glutamate decarboxylase (GAD) immunocytochemistry at the light microscopic level. Quantitative analysis revealed that a loss of GAD-positive neuronal somata ranging from 24 to 52% occurred at epileptic foci for all monkeys. This decrease was significant (P less than 0.01) for the two chronic monkeys. There was also a slight decrease in GAD-positive neurons 1 cm distal to the focus ('parafocus') in the chronic monkeys, but not in the acute or pre-seizure animals. In addition, small GAD-positive somata (50-150 micron2) were more severely decreased in number at epileptic foci than larger ones (200-250 micron2). As an experimental control, an additional monkey was given a surgical lesion in area 4 of one cerebral hemisphere. It did not display seizure activity prior to sacrifice and did not show a loss of GAD-positive neurons proximal to the control lesions. The results of this study indicate that a loss of GABAergic neuronal somata is associated with a loss of GABAergic terminals at epileptic foci, and that this loss may be more specific for the small GABAergic neurons.

Animals↗
PubMed1986

Effects of neonatal monocular enucleation on the number of GAD-positive puncta in rat visual cortex.

Rats that had one eye removed on the day of birth were examined at various postnatal ages with immunocytochemical methods to determine the effect on the development of the GABAergic axonal plexus in the visual cortex. The monocular segment of visual cortex contralateral to the enucleated orbit had 20-30% fewer GABAergic axon terminals than the monocular segment of visual cortex contralateral to the normal eye. Other cortical areas did not show any significant changes. These findings suggest that sensory deprivation of the visual cortex interferes with the normal development of GABAergic neurons.

Animals↗
PubMed1986

The ultrastructure of the central nucleus of the inferior colliculus of the Sprague-Dawley rat.

Previous studies from this laboratory have indicated that increased numbers of GABAergic neurons, as well as total neurons, occur in the central nucleus of the inferior colliculus (IC) of genetically epilepsy-prone rats (GEPRs) as compared to non-seizuring Sprague-Dawley rats. Since electron microscopic studies of the IC have not been reported for rats, we wanted to determine the ultrastructure of neurons and their processes in this brain region to serve as a basis for future studies on neuronal circuitry in the GEPRs. Both disc-shaped and stellate types were found for each of three size categories: large, medium and small. Thus, six types of neuron were distinguished by differences in somatic size, shape, organelles and dendritic orientation. Large neurons (longest diameter greater than 25 micron), which are the least frequent cell type, contained vast perikaryal cytoplasm, eccentrically located nuclei and abundant granular endoplasmic reticulum (GER) adjacent to the nucleus as well as clustered in the cytoplasm; many axosomatic, symmetric synapses were present. Medium-sized neuronal somata (15-25 micron in diameter) had smooth as well as infolded nuclear membranes and clusters of GER in their cytoplasm but no GER adjacent to the nucleus; synapses were sparse along the surface of their somata. Small neurons (10-15 micron in diameter), which are the most frequent cell type, had scant perikaryal cytoplasm, usually infolded nuclei, frequently two nucleoli, and few or no stacked cisternae of GER in the perikaryal cytoplasm; only infrequent axosomatic synapses were found. Based on previous retrograde and immunocytochemical studies, most large disc-shaped and stellate cells project to the medial geniculate body and are probably excitatory, but some large stellate neurons have been shown to be GABAergic and it is doubtful that such neurons participate in this projection. A dense plexus of terminals that form symmetric synapses covers the soma and proximal dendrites of large neurons, and may provide a strong GABAergic inhibition of this type of projection neuron. Small and medium-sized disc-shaped cells also project to the thalamus but they lack this dense axosomatic plexus. The stellate cells from these same two size categories probably do not project to the thalamus and may be GABAergic local circuit neurons. Other ultrastructural features of IC neurons that were analysed include dendrites, dendritic spines, axon hillocks, initial segments and terminals, as well as the laminae of myelinated axons. Dendrites were either beaded or smooth and few spines were observed.(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗
PubMed1986

A GABAergic inhibitory component within the hippocampal commissural pathway.

Previous results from immunocytochemical and retrograde transport studies indicated that some GABAergic neurons in the hilus of the dentate gyrus may have axonal projections through the hippocampal commissure. This study has utilized a combined immunocytochemical and retrograde transport method as well as 2 anterograde electron-microscopic methods to determine the existence of this projection in rats. Combined tracer and immunofluorescence studies showed several double-labeled GABAergic neurons in the hilus contralateral to the injection site. The electron-microscopic studies revealed both degenerating and HRP-labeled commissural axons that formed symmetric synapses, the type shown to be formed by GABAergic terminals in the hippocampus. These data demonstrate a GABAergic component within the hippocampal commissural pathway and add further evidence that cortical GABAergic terminals are not derived exclusively from intrinsic neurons.

Animals↗
PubMed1986

Contemporary methods in neurocytology and their application to the study of epilepsy.

The contemporary neuroanatomist has a number of available methods to analyze epileptic brain tissue. Many studies have utilized Nissl- and Golgi-stained preparations to determine that gliosis and neuronal loss occur at epileptic foci as well as a decrease in the dendritic spine density. These structural changes did not reveal any specific basic mechanism that may cause epileptic activity. In contrast, the relatively newer techniques in neurocytology provide functional data that relate to the physiology and chemistry of the brain tissue. The use of immunocytochemical, histochemical, and receptor ligand-binding autoradiographic methods have aided in the understanding of cellular neurochemistry in both normal and epileptic tissue. In addition, the use of intracellular horseradish peroxidase and recording and quantitative morphological methods at both light- and electron-microscopic levels has helped gain insights into the functional state of synapses and neurons. Together, these methods have been utilized to help unravel the mystery of epilepsy. Our laboratory has utilized immunocytochemical and quantitative light- and electron-microscopic methods to analyze four models of epilepsy; two resemble posttraumatic focal epilepsy, and the other two are genetic models of epilepsy. Our data indicate that a preferential loss of cortical GABAergic, inhibitory terminals occurs at posttraumatic epileptic foci. In contrast, the genetic models of epilepsy did not display a loss of GABAergic terminals. Instead, specific brain regions of epileptic animals had an increased number of GABAergic neurons and terminals. These data indicate that two different neuronal circuits may provide the anatomical substrate for epileptic activity: loss of inhibition and disinhibition.

Animals↗
PubMed1986

Polyribosomes associated with synaptic specializations on axon initial segments: localization of protein-synthetic machinery at inhibitory synapses.

Previous studies have revealed a selective association between polyribosomes and axospinous synapses in a variety of brain regions. The present study evaluates whether polyribosomes are also associated with the symmetrical and presumably inhibitory synaptic connections found on the initial segment of axons of some neurons in the CNS. The initial segments of pyramidal neurons in the sensorimotor cortex of the monkey and of granule cells in the hippocampus of the rat were examined. The initial segments of these cell types are contacted by GABAergic terminals that form symmetrical synaptic connections. In the present study, these initial segments were found to contain polyribosomes that tended to be selectively localized beneath the synaptic specializations. Both the synaptic connections and the polyribosomes were localized to the initial segment; after the point at which the axon became myelinated, neither synapses nor polyribosomes were found. The association between polyribosomes and synapses was also suggested by the position of the polyribosomes with respect to the synapse. In each cell type, the majority of the polyribosomes that were present in the initial segments appeared to be localized preferentially beneath synaptic sites, although some polyribosomes were also present in the core of the axon. These data reveal that polyribosomes are not peculiar to spine synapses, but rather are ubiquitous components of the subsynaptic region of many types of synapses. We propose that neurons may regulate their innervation by positioning protein-synthetic machinery (and appropriate mRNA molecules) at particular locations in order to construct particular types of synapses at defined positions on the postsynaptic cells' receptive surface.

Animals↗
PubMed1985

Increased numbers of GABAergic neurons occur in the inferior colliculus of an audiogenic model of genetic epilepsy.

The numbers of GABAergic neurons as determined by GAD immunocytochemistry and total neurons as determined from Nissl preparations were counted and classified at the light microscopic level in the inferior colliculus (IC) of the genetically epilepsy-prone rat (GEPR) and the non-epileptic Sprague-Dawley (SD) strain of rat. GAD-positive neurons are abundant in the IC in all 3 subdivisions. Several sizes of multipolar neurons as well as medium-sized bipolar or fusiform neurons are GAD-positive. GAD-positive punctate structures that were interpreted to be axon terminals and transversely-sectioned dendrites and preterminal axons are abundant in the IC of both the GEPR and SD. A dramatic increase in the number of GAD-positive neurons occurs in the GEPR as compared to the SD. This increase is most evident in the middle of the rostrocaudal extent of the IC. Although the increase is statistically significant in all subdivisions of the IC, it is most pronounced in the central nucleus, especially the ventral lateral portion. Within the central nucleus, the increase in the number of GAD-positive neurons is due to a selective increase in the small (200%) and medium (90%) cell body size populations (10-15 micron and 15-25 micron in diameter, respectively). Concomitant with this increase in the number of GAD-positive neurons, an increase in total numbers of neurons occurs as determined from Nissl preparations. A 100% increase in the number of small neurons and a 30% increase in the number of medium-sized neurons occur in the GEPR as compared to the SD rat. The proportion of GAD-positive neurons to total neurons is also increased in the GEPR. Approximately 25% of the neurons in the IC in SD rat are GAD-positive, while about 35% of the neurons in the GEPR are GAD-positive. These data demonstrate an anatomical difference in the IC of the GEPR as compared to the SD which appears to be preferential for the GABAergic system.

Acoustic Stimulation↗