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N Tønder

Publications and source records attributed to N Tønder.

At least 19 recordsLinked to original sources
PubMed1997

Development of microglia in the prenatal rat hippocampus.

The distribution and appearance of microglia cell precursors in the prenatal hippocampus were examined in embryonic day 14 (E14) to E21 rats by nucleoside diphosphatase histochemistry. For comparison, the differentiation of astroglial cells was analyzed from E17 by vimentin and glial fibrillary acidic protein immunohistochemistry. Based on morphologic features, nucleoside diphosphatase-positive microglial cell precursors were classified as ameboid microglial cells and primitive ramified microglial cells. Ameboid microglia were present in the hippocampal primordium on E14. As the hippocampus developed, however, ameboid microglia gradually transformed into primitive ramified microglia, first recognized at E19. Microglial cell precursors, often related to nucleoside diphosphatase-labeled blood vessels, were particularly observed next to the pial surface on days E14 and E17 and in the highly vascularized area around the hippocampal fissure from E19. Within the brain parenchyma, the microglial cell precursors tended to be located within the differentiating cell and neuropil layers rather than in the germinative zones. The late developing dentate gyrus remained almost devoid of microglial cell precursors before birth. Vimentin-positive astroglial processes with radial orientation were observed throughout the hippocampal subregions from E17. In contrast, glial fibrillary acidic protein-positive, radial processes were barely discernible in the fimbria and the dentate gyrus before E19. The results are discussed in relation to the possible interactive role of microglial cells in central nervous tissue development and histogenesis. Regarding the origin of hippocampal microglial cell precursors, the present observations support the view that these cells may well originate from different mesodermal sources depending on time and localization.

Animals↗
PubMed1996

No loss of hippocampal hilar somatostatinergic neurons after repeated electroconvulsive shock: a combined stereological and in situ hybridization study.

Electrically induced seizures with anesthesia and muscle relaxation (ECT) is commonly used in the therapy of psychotic depression in humans. Unmodified electroshock (ECS) is used as a model for epilepsy in the rat. In several seizure models of epilepsy, in particular the dentate hilar somatostatin-containing (SSergic) neurons have been found to undergo degeneration. To assess the potential loss of SSergic hilar neurons after repeated ECS, 10 rats were given 110 ECS, one per day, 5 days a week. One day after the last ECS the rats were anesthesized, perfused, the brains cut on a vibratome and prepared for nonradioactive in situ hybridization for somatostatin along with five control rats. Like rats given 10-36 ECS in earlier studies, the ECS-treated rats displayed a markedly increased neuronal hybridization labeling when compared with control rats. The total number of dentate hilar SSergic neurons of each rat was estimated using the optical disector technique. The mean number of hilar SSergic neurons in the ECS-treated rats was 12,785, compared to 12,392 in the control rats. The total number of hilar SSergic neurons in ECS-treated versus control rats was not significantly different (Student's t test; t value = .35; p = .74). We conclude that repeated ECS treatment does not cause loss of hilar SSergic neurons.

Animals↗
PubMed1995

c-JUN, KROX-24, and c-FOS expression in hippocampal grafts placed in excitotoxic hippocampal lesions of the rat.

Hippocampal transplants were examined for the expression of three specific immediate early gene encoded proteins in order to establish if grafted immature tissue maintains the basic molecular program necessary for gene transcription after grafting to excitotoxic (ibotenic acid-induced) lesions in adult host rat brains. The transplants were derived from newborn donor rats and were analyzed immunocytochemically for the presence of c-JUN, KROX-24, and c-FOS transcription factors 5 months after grafting. The expression and distribution patterns of these genes in the host hippocampus were identical to those in hippocampal neurons of normal untreated animals. c-JUN-, KROX-24-, and c-FOS-labeled neurons were also present in the transplants, where KROX-24 and c-FOS exhibited a distribution similar to host hippocampus. In contrast, c-JUN was more extensively expressed in the transplants, suggesting a molecular response to the grafting conditions and the actual graft-host brain interactions.

Animals↗
PubMed1994

Transient decrease in calbindin immunoreactivity of the rat fascia dentata granule cells after repeated electroconvulsive shocks.

Changes in hippocampal calbindin immunoreactivity were investigated after repeated electroconvulsive shocks. Adult rats were subjected to 10, 20, or 36 electroconvulsive shocks (50 mA, 0.5 seconds), given as on shock per day, 5 days a week. The rats were sacrificed and processed for calbindin immunohistochemistry 1, 2, and 30 days after the last electroconvulsive shock. In the rats receiving 10 or 20 electroconvulsive shocks, a selective reduction of the calbindin immunoreactivity of the dentate granule cell bodies, dendrites, and mossy fibers was noted 1 and 2 days after the last electroconvulsive shock. After 36 electroconvulsive shocks there was an almost complete loss of calbindin immunoreactivity from the granule cell bodies and dendrites, and the calbindin immunoreactivity of the mossy fibers was markedly reduced. Thirty days after the last of 36 electroconvulsive shocks, the calbindin immunoreactivity was back to normal. Besides demonstrating pronounced changes associated with repeated electroconvulsive shocks, the results confirm the transient nature of these changes.

Animals↗
PubMed1994

Repeated electroconvulsive shocks cause transient changes in rat hippocampal somatostatin and neuropeptide Y immunoreactivity and mRNA in situ hybridization signals.

Increased levels of somatostatin (SS) and neuropeptide Y (NPY) have been demonstrated in the hippocampal formation after kindling. The increase might be specifically associated with kindling, or be an effect of repeated seizures per se. In order to separate these two components we studied the effects of repeated electroconvulsive shocks (ECS) on hippocampal SS-like and NPY-like immunoreactivity and SS mRNA and NPY mRNA in situ hybridization. ECS elicit seizures without having a demonstrable kindling effect. Rats were subjected to 10, 20, or 36 ECS (50 mA, 0.5 s), given as one shock per day, 5 days per week. One, 2 and 30 days after the last ECS, the rats were killed, together with sham-treated control rats, and processed for immunocytochemistry and non-radioactive in situ hybridization. There was a bilateral increase in SS-like and NPY-like immunoreactivity 1 and 2 days after the last ECS in the outer part of the dentate molecular layer. This is the terminal field of the hilar SS-containing and NPY-containing neurons, which displayed both increased immunoreactivity and hybridization signal of the cell bodies. There was also a bilateral de novo expression of NPY-like immunoreactivity in the mossy fiber system, but this was not accompanied by the appearance of a detectable NPY hybridization signal over the parent dentate granule cell bodies. The increase in SS-like immunoreactivity and hybridization signal was most pronounced in the rats that had received the largest number of ECS. This was not observed for the NPY-like immunoreactivity and hybridization signal, where the increase appeared similar after 10, 20 and 36 ECS.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1994

The susceptibility of CA1 pyramidal cells to cerebral ischemia is maintained after neonatal, lesion-induced reorganization of the hippocampal circuitry.

Acute lesions of hippocampal pathways have been shown previously to ameliorate CA1 pyramidal cell loss after subsequent transient cerebral ischemia. In this study, we examined the effect of chronic neonatal lesion with reorganization of hippocampal circuitry on adult postischemic neuron loss in the hippocampus. Newborn rats were subjected to unilateral knife-cut lesions at various positions along the trisynaptic entorhino-dentato-hippocampal pathway. Seven months later, the rats were subjected to transient cerebral ischemia using the four-vessel occlusion technique. At the time of killing 4 days later, a Nissl stain was used to demonstrate neuronal degeneration, while connective reorganization resulting from the neonatal lesions was monitored by Timm staining. In one group of rats, neonatal lesions had caused severe depletion of entorhinal projections to the septodorsal fascia dentata and hippocampus (CA1 and CA3), without any direct damage to the dorsal hippocampus itself. Another group had extensive damage of the dorsal CA3, with removal of the Schaffer collaterals from these levels to CA1, and variable damage to the entorhinal afferents. In both groups, the extent and pattern of ischemia-induced degeneration of CA1 pyramidal cells were the same on the lesioned and nonlesioned sides of the brain, demonstrating that neonatal lesions and the subsequent connective reorganization did not have a sparing effect. Seen in relationship to previous observations in adult rats of the neuroprotective actions of acute, preischemic lesions of the trisynaptic hippocampal pathway, it is concluded that CA1 pyramidal cell loss requires the presence of intact excitatory afferents rather than an intact hippocampal circuitry.

Afferent Pathways↗
PubMed1993

Biocytin pellets: an alternative technique for massive anterograde labeling of neuronal pathways in vivo and in vitro.

The present study demonstrates that biocytin suspended in pellets of either coagulated chicken plasma (plasmaclot) or gelatine, produces intense anterograde axonal and terminal labeling and dense retrograde Golgi like labeling of neurons when injected into the brain parenchyma of young adult rats. The technique worked perfectly on hippocampal pathways like the mossy fiber system, the hilodentate associational and commissural fiber systems, CA3 Schaffer collaterals, the entorhinal perforant path to fascia dentata and hippocampus, as well as frontal motor cortical efferent and afferent fiber tracts. This pellet tracer delivery technique also proved very useful when applied on hippocampal slice cultures, where small pellets of plasmaclot embedded biocytin resulted in very discrete uptake sites with dense labeling of small groups of neurons and their projections.

Animals↗
PubMed1993

Zinc-positive afferents to the rat septum originate from distinct subpopulations of zinc-containing neurons in the hippocampal areas and layers. A combined fluoro-gold tracing and histochemical study.

The purpose of the present study was to examine whether zinc-positive and zinc-negative hippocampal neurons in rats differed with respect to their projections to the septum. By combining retrograde axonal transport of the fluorescent tracer Fluoro-Gold with histochemical demonstration of zinc selenide complexes in zinc-containing neurons after intraperitoneal injection of sodium selenite, we were able to visualize the distribution of retrogradely Fluoro-Gold labeled neurons and zinc-containing neurons in the same sections. After unilateral injection of Fluoro-Gold into the rat septum a few retrogradely labeled cells were observed in layer IV of the ipsilateral medial entorhinal area, and numerous labeled cells were observed mainly in the superficial layers of the ipsilateral subicular areas and throughout the CA1 and CA3 pyramidal cell layers, as well as in the contralateral CA3 pyramidal cell layer. Zinc-containing neurons were observed in layers IV-VI of the medial entorhinal area, layers II and III of the parasubiculum, layers II, III and V of presubiculum, and in the superficial CA1 and deep CA3 pyramidal cell layers. Cells double-labeled with Fluoro-Gold and zinc selenide complexes were primarily located in distal (relative to the area dentata) parts of the superficial CA1 pyramidal cell layer and distal parts of the deep CA3 pyramidal cell layer and in layers II and III of presubiculum. Only a very few double-labeled cells were seen in the contralateral CA3. The result demonstrates that the hippocampo-septal projection of rats is a mixture of zinc-positive and zinc-negative fibers.(ABSTRACT TRUNCATED AT 250 WORDS)

Afferent Pathways↗
PubMed1993

A developmental study of lactate dehydrogenase isozyme and aspartate aminotransferase activity in organotypic rat hippocampal slice cultures and primary cultures of mouse neocortical and cerebellar neurons.

The development of enzyme activity and isozyme distribution of lactate dehydrogenase (LDH) was studied in murine organotypic hippocampal slice cultures and dissociated cultures of neocortical neurons and cerebellar granule cells and compared with that of the respective brain regions in vivo. In the hippocampal slice cultures and the hippocampus in vivo, the activity of aspartate aminotransferase (AAT) was also measured. During development in culture the specific activity of LDH increased in all types of cultures reaching values similar to that found in the corresponding brain areas in vivo. However, significant differences in the isozyme distribution were observed between the preparations in vitro and in vivo. During development in vivo, the LDH isozyme pattern changed from a preferential M-subunit composition to a preferential H-subunit composition regardless of the brain area. This shift was not observed in the respective cultures where the M4-isozyme prevailed at all culture periods examined accounting for 30-45% of the total LDH activity. The cultured cerebellar granule cells did not express the H4-isozyme at all, while in the hippocampal slice cultures and the cultured neo-cortical neurons this isozyme accounted for about 5% of the total LDH activity. The activity of AAT in the hippocampal organotypic slice cultures increased considerably during the culture period in parallel with the increase in AAT activity during postnatal development of hippocampus in vivo. The activity of AAT in the slice cultures was, however, consistently lower than the corresponding activity in vivo.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1993

Time course of hippocampal glucose utilization and persistence of parvalbumin immunoreactive neurons after ibotenic acid-induced lesions of the rat dentate area.

The effects of ibotenic acid induced lesions of the dentate gyrus on hippocampal glucose utilization and parvalbumin-positive neurons were evaluated in male Wistar rats. Ibotenic acid was injected in the right dorsal dentate gyrus. Quantification of glucose utilization was performed 3 days, 3 weeks, or 3 months after the lesion using the 14C-2-deoxyglucose method. Nissl-stained sections and sections stained for acetylcholinesterase were used as references for anatomical delineation of the hippocampal cytoarchitecture. Additional sections were stained for parvalbumin. The results revealed widespread reductions of glucose utilization in all layers and sectors of the hippocampus in the ipsilateral lesioned hemisphere and also in the nonlesioned contralateral hemisphere. The reductions occurred as early as 3 days after the lesion and persisted up to 3 months. In neither hippocampal structure did glucose utilization return to control levels. Immunohistochemical visualization of parvalbumin-containing neurons revealed that these putatively inhibitory neurons persisted in the otherwise granule-cell-depleted area. The data show that interruption of the excitatory trisynaptic pathway from the entorhinal cortex to the CA1 at the level of the dentate gyrus affects hippocampal glucose utilization irreversibly and uniformly. Since some inhibitory neurons seem to survive the ibotenic acid lesion, we suggest that the reductions of hippocampal glucose utilization reflect an imbalance in favor of inhibitory neurons in the ipsilateral hippocampus after the lesion, which manifests also in the contralateral hemisphere via the commissural pathways.

Animals↗
PubMed1993

Area specific functional activity in organotypic hippocampal slice cultures. A 2-deoxyglucose study.

Slices of hippocampus from 5 day old rats were cultured by the roller-tube technique. After 4 weeks [14C]-2-deoxyglucose (2-DG) was added to the medium for 45 min, whereafter the cultures were frozen and cut on a cryostat. The sections were thawed onto coverslips and processed for autoradiography. Image analysis of the resulting autoradiographs showed a higher uptake of 2-DG in CA3 than in CA1 and fascia dentata, whereas CA1 and fascia dentata did not differ significantly with respect to 2-DG uptake. The study demonstrates, that organotypic hippocampal slice cultures display an area specific glucose utilization, and thus functional activity, which is similar to that observed in adult conscious rats. We therefore anticipate that the method can be used to examine the integrated activity of the whole neuronal network in these cultures under various manipulations, like hypoxia or additions of various drugs.

Animals↗
PubMed1992

Somatostatin and neuropeptide Y in organotypic slice cultures of the rat hippocampus: an immunocytochemical and in situ hybridization study.

The neuronal distributions of somatostatin and neuropeptide Y and their respective mRNAs in hippocampal slice cultures were examined by immunohistochemical staining and in situ hybridization. For the in situ hybridization we used an alkaline phosphatase-labelled oligodeoxynucleotide probe for somatostatin mRNA and an 35S-labelled oligodeoxynucleotide probe for neuropeptide Y mRNA. For both neuropeptides the immunostained and hybridized neurons displayed a comparable, organotypic distribution. Most labelled neurons were located in the dentate hilus and stratum oriens of CA3 and CA1. Additional neurons were found in stratum radiatum and pyramidale of CA3, but very few in the corresponding layers of CA1. In all locations the density of somatostatin- and neuropeptide Y-reactive cells exceeded that observed in vivo. Also, the hybridization signal of the individual neurons appeared enhanced in the slice cultures. Methodologically it was noted that the non-radioactive alkaline phosphatase-labelled oligodeoxynucleotide probe gave excellent in situ hybridization results with detailed cellular resolution and no apparent problems of tissue penetration, even when used on whole-mount explants. These results demonstrate that somatostatin and neuropeptide Y-immunoreactive and mRNA containing neurons retain their organotypic distribution and basic morphological characteristics in the slice cultures. The supernormal density of these neurons and their hybridization signals indicate that a transient developmental increase in neuropeptide expression may persist in vitro.

Animals↗
PubMed1992

Neuroactive amino acids in organotypic slice cultures of the rat hippocampus: an immunocytochemical study of the distribution of GABA, glutamate, glutamine and taurine.

Antisera raised against protein-glutaraldehyde-amino acid conjugates were used to study the light and electron microscopic distribution of GABA, glutamate, glutamine and taurine in organotypic slice cultures of rat hippocampi. In the stratum oriens and radiatum, glutamate-like immunoreactivity was particularly concentrated in nerve endings establishing asymmetric junctions with dendritic spines. Mossy fiber terminals in CA3 and the dentate hilus were also strongly labeled. A quantitative immunogold analysis of the glutamate-immunolabelled profiles showed a pattern that was highly reminiscent of that previously observed in perfusion-fixed hippocampi, including a correspondingly sparse labeling of glial processes and of presynaptic elements in symmetric synapses. GABA-like immunoreactivity was localized predominantly in interneurons and in presynaptic terminals contacting dendritic shafts and neuronal cell bodies, while immunoreactivities for glutamine and taurine were found mainly in astroglial cells and pyramidal cells, respectively. Our data indicate that the major intrinsic fiber systems of the cultured hippocampi have retained their normal transmitter phenotypes.

Animals↗
PubMed1992

Ultrastructure of neurons containing somatostatin in the dentate hilus of the rat hippocampus after cerebral ischaemia, and a note on their commissural connections.

In a light microscopical study, we previously showed that more than 80% of somatostatin (SS) immunoreactive (-i) neurons in the hilus of the dorsal part of the rat dentate gyrus are lost 4 days after ischemia. In order to verify that the loss of SS immunostaining is due to an actual loss of the SS-i neurons and not merely a loss in expression of SS immunoreactivity, we have now performed an ultrastructural study of these neurons before and 40 h after 20 min of global cerebral ischaemia in adult rats. The normal SS-i neurons were multipolar and fusiform in shape. The SS-i product was associated with the endoplasmic reticulum and occasionally the Golgi apparatus. The cell nuclei had indentations of the nucleolemma and contained intranuclear rods. After ischaemia, many SS-i neurons in the dentate hilus showed increased electron density of both the cell nucleus and the cytoplasm. In addition the cytoplasm was heavily vacuolated with the SS-i associated with some of these vacuoles. Other SS-i neurons had, in addition to the vacuoles a more homogeneous, and abnormal electron lucent nucleus and cytoplasm. These ultrastructural changes correspond to previously reported irreversible, ischaemic cell changes of neurons. Based on this we conclude that the SS immunoreactivity in the dentate hilus of the dorsal hippocampus is lost after ischaemia because of neuronal necrosis. As a minor part of this study, we examined whether the ischaemia-susceptible SS-i neurons in dentate hilus had commissural axonal projections. This was done utilizing double fluorescence microscopy of retrograde axonal transport of the fluorescent dye, Fluoro-Gold, and the observation that vulnerable SS-i neurons display homogeneously dispersed immunostaining 40 h after ischaemia. Fluoro-Gold was injected unilaterally into the dorsal dentate gyrus 5 days prior to ischaemia. Then, 40 h after ischaemia, sections were stained for SS immunofluorescence, and examined, in the dentate hilus contralateral to the injection, for neuronal co-localization of both events. Cell counts revealed double-labelling of 13% of all neurons which displayed one of the events. This observation suggests that at least some of the ischaemia-susceptible SS-i neurons in dentate hilus do project commissurally. The pathophysiological significance of ischaemic loss of commissurally projecting SS-i neurons in dentate hilus remains to be determined.

Animals↗
PubMed1990

Short-term changes of parvalbumin and calbindin immunoreactivity in the rat hippocampus following cerebral ischemia.

The calcium-binding proteins, parvalbumin (PV) and calbindin (CaBP), were used as immunocytochemical markers for two different interneuron populations in the rat hippocampus shortly after transient cerebral ischemia. Besides in interneurons, CaBP immunoreactivity (-i) is located in hippocampal CA1 pyramidal cells and dentate granule cells. Shortly after ischemia, the PV-i and CaBP-i were unchanged but, around the 4th postischemic day, PV-i disappeared from somata and fibers located in CA1, CA3c, and the dentate hilus. Terminal PV-i was unchanged. Within days, the PV-i gradually reappeared, first in somata and then in fibers. The transient loss of PV-i was, on a time scale, closely accompanied by a permanent loss of CaBP-i in CA1 pyramidal cells. CaBP-i in interneurons was unchanged. In order to examine the effect of an increased intracellular calcium concentration on the PV-i and CaBP-i, the calcium ionophore A23187 was stereotaxically injected into CA1. In rats killed 30 min later and processed for PV-i and CaBP-i, both PV-i and CaBP-i had disappeared around the A23187 injection sites. Based on this observation and the changes observed after ischemia, it is suggested that the hippocampal PV-i interneurons suffer from a delayed and reversible calcium accumulation in the days after ischemia. Concomitantly, there could be a decreased synthesis or increased destruction of PV after ischemia.

Animals↗
PubMed1990

Possible role of zinc in the selective degeneration of dentate hilar neurons after cerebral ischemia in the adult rat.

The fluorescent dye 6-methoxy-8-p-toluene sulfonamide quinoline (TSQ) was used to monitor the distribution of zinc in the hippocampus and fascia dentata of adult rats subjected to 20 min of cerebral ischemia. In normal brains TSQ stains only neuropil, in particular the mossy fiber layers in the dentate hilus (CA4) and CA3, but within 2 h after ischemia, TSQ-fluorescent cells were observed in the dentate hilus. At longer survival times TSQ-positive cells stained positively with acid fuchsin, a sign of cellular degeneration. At the same time a decrease in the TSQ fluorescence of the mossy fiber terminals in the dentate hilus (CA4) and the CA3 mossy fiber layer was noted. The observations suggest that zinc many play a role in the selective death of dentate hilar neurons after cerebral ischemia.

Aminoquinolines↗