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M Frotscher

Publications and source records attributed to M Frotscher.

At least 91 records · Page 5Linked to original sources
PubMed1996

Sprouting of crossed entorhinodentate fibers after a unilateral entorhinal lesion: anterograde tracing of fiber reorganization with Phaseolus vulgaris-leucoagglutinin (PHAL).

Fibers from the contralateral entorhinal cortex (EC) to the dentate gyrus partially replace the input lost after an ipsilateral EC lesion. To study the morphology and course of single sprouted crossed entorhinodentate fibers, the anterograde tracer Phaseolus vulgaris-leucoagglutinin (PHAL) was used. Rats that survived for 4 to 8 weeks after a unilateral entorhinal lesion received PHAL deposits into the entorhinal cortex contralateral to the lesion. Control animals received a similar PHAL deposit. Single PHAL-labeled fibers in the molecular layer of the contralateral (EC lesion) fascia dentata were drawn with a camera lucida, and an axon-branching index (branch points/100 microns axon length) was calculated for these crossed entorhinodentate fibers in controls and operated animals. In animals with EC lesions, the density of PHAL-labeled crossed entorhinodentate fibers had increased remarkably. Single crossed entorhinodentate axons showed significantly more axon branch points in experimental than in control animals. In addition, some axon segments displayed high densities of small axonal extensions. Frequently, tanglelike structures were observed in the denervated outer molecular layer. These tangles consisted of one or more PHAL-labeled axons that intertwined and formed an axon tangle filled completely with branches, extensions, and boutons. Our data indicate that crossed EC fibers sprout by forming additional collaterals, axonal extensions, and tangles. Abnormal neurite formations are a characteristic feature of plaques in Alzheimer's disease. Future studies must be done to show whether or not there is a close relationship between axonal tangles and plaques in Alzheimer's disease, which, like the present lesion paradigm, severely affects entorhinal projection neurons.

Acetylcholinesterase↗
PubMed1996

Synthesis and evaluation of azole-substituted tetrahydronaphthalenes as inhibitors of P450 arom, P450 17, and P450 TxA2.

In search of potential drugs for the treatment of estrogen- and androgen-dependent cancer as well as the prophylaxis of metastases, tetralones, tetralins, and dihydronaphthalenes bearing a OCH3 substituent at the benzene nucleus and an imidazol-4-yl, imidazol-1-yl, or 1,2,4-triazol-1-yl substituent in 2-position were synthesized with and without C1-spacer between the rings (compounds 2-26). The compounds were tested in vitro for inhibition of the three targets enzymes P450 arom (human placental microsomes), P450 17 (rat testicular microsomes), and P450 TxA2 (citrated human whole blood). To examine selectivity, some compounds were further tested in vitro for inhibition P450 18 (bovine adrenal mitochondria), P450 scc (bovine adrenal mitochondria) and corticoid formation (aldosterone, corticosterone; ACTH stimulated rat adrenal tissue). In vitro, selected compounds were examined in Sprague Dawley rats regarding P450 TxA2 inhibition, reduction of plasma testosterone concentration, antiuterotrophic activity (inhibition of the uterotrophic activity of androstenedione), reduction of plasma estradiol concentration (pregnant mares' serum gonadotropin-primed rats), and mammary tumor inhibiting activity (dimethylbenzanthracene-induced tumor; pre-and postmenopausal model). In the series of imidazol-4-yl compounds, which represent a novelty in the field of azole inhibitors of steroidogenic P450 enzymes, strong inhibitors of P450 arom and/or P450 17 were found; 7-OCH3-2-(imidazol-4-ylmethylene)-1-tetralone (4) and 7-OCH3-2-(imidazol-4-ylmethyl)-tetralin (12) are among the most potent inhibitors of P450 arom in vitro known so far. Compound 4 is a selective inhibitor, whereas 12 shows in addition strong inhibition of P450 17. In contrast to 12, the 6-OCH3 derivative (compound 11) is a selective inhibitor of P450 17, being 50 times more potent than ketoconazole. Some imidazol-1-yl compounds show a marked inhibition of P450 TxA2: 2-(imidazol-1-ylmethyl)-1-tetralone (13) is a selective inhibitor of P450 TxA2, whereas 7-OCH3-2-(imidazol-1-ylmethyl)-tetralin (17) as well 2-(imidazol-1-ylmethyl)-tetralin (16) and 7-OCH3-2-imidazol-1-yl-3, 4-dihydronaphthalene (25) additionally show strong inhibition of P450 arom and P450 17. Regarding the other steroidogenic P450 enzymes as well as corticosterone formation, the compounds show only little inhibitory activity. Aldosterone formation, however, is inhibited at low concentrations. Nevertheless, 4 and 12 are more selective, i.e. inhibit aldosterone synthesis less than the well known inhibitor of P450 arom fadrozole. The compounds show activity in the aforementioned in vivo tests.

Animals↗
PubMed1996

Organization of identified fiber tracts in the rat fimbria-fornix: an anterograde tracing and electron microscopic study.

The fimbria is a major route for afferent and efferent fibers of the hippocampal formation. However, little is known about the intrinsic organization of the fimbria-fornix complex. In this study, the anterograde tracer Phaseolus vulgaris-leucoagglutinin (PHAL) was used to analyze the ultrastructure and topography of identified fiber tracts within the fimbria-fornix. Septo-hippocampal fibers are loosely distributed throughout the fimbria-fornix. Commissural fibers cross the midline in the ventral hippocampal commissure and form a tight fiber bundle in the fimbria. Crossed entorhino-hippocampal fibers cross the midline in the ventral hippocampal commissure rostral to the commissural fiber bundle, and crossed entorhino-entorhinal fibers pass through the dorsal hippocampal commissure. This suggests a topographical organization of fiber tracts within the fimbria-fornix that reflects the laminar organization of the hippocampal target structure: fibers of the diffusely terminating septohippocampal projection are loosely distributed throughout the fimbria-fornix, while those projections that are known to terminate in specific laminae of the hippocampal formation (commissural projection, crossed entorhino-hippocampal projection) form fiber bundles within the fimbria and the ventral hippocampal commissure.

Animals↗
PubMed1996

The alvear pathway of the rat hippocampus.

Neurons of the entorhinal cortex project to the hippocampus proper and dentate gyrus. This projection is called the "perforant pathway" because it perforates the subiculum; current usage applies this term to all entorhino-hippocampal fibers. However, entorhinal fibers also reach Ammon's horn via the alveus ("alvear pathway"), an alternative route first described by Cajal. The anterograde tracer Phaseolus vulgaris leucoagglutinin (PHAL) was used in order to analyze the contribution of this pathway to the temporo-ammonic projection. In the temporal portion of the rat hippocampus, most of the entorhinal fibers reach Ammon's horn after perforating the subiculum (classical perforant pathway). At more septal levels, the number of entorhinal fibers that take the alvear pathway increases; in the septal portion of the hippocampal formation, most of the entorhinal fibers to hippocampal subfield CA1 reach this subfield via the alveus. These fibers make sharp right-angle turns in the alveus, perforate the pyramidal cell layer, and finally terminate in the stratum lacunosum-moleculare. The crossed temporo-ammonic fibers reach their termination area in the stratum lacunosum-moleculare of CA1 almost exclusively via the alveus. These data indicate that the alveus is a major route by which entorhinal fibers reach their targets in CA1.

Animals↗
PubMed1996

Spine loss in experimental epilepsy: quantitative light and electron microscopic analysis of intracellularly stained CA3 pyramidal cells in hippocampal slice cultures.

The sequence of neuronal alterations resulting from epileptic activity is poorly understood. In the hippocampus of some epileptic patients, there is a loss of certain neuronal types in the hilar region and in CA3. The neuronal alterations preceding this degeneration probably affect synaptic structures. Here we have estimated the number of dendritic spines, major postsynaptic elements of hippocampal neurons, in defined dendritic segments of identified (intracellularly stained) CA3 pyramidal neurons in "epileptic" slice cultures of hippocampus and in control cultures. Slice cultures were prepared from five- or six-day-old rat pups and maintained in vivo for 23 days before epileptic activity was induced by application of the convulsants bicuculline and picrotoxin for three days. Individual CA3 pyramidal neurons were then intracellularly injected with horseradish peroxidase, and the number of dendritic spines was counted in proximodistal dendritic segments by applying the Sholl method. In addition, the total dendritic length was measured and the branching index evaluated. The number of spines on CA3 pyramidal cell dendrites in the "epileptic" cultures was found to be decreased by 40%. This spine loss affected proximal and peripheral dendritic segments of the CA3 pyramidal neurons to a similar extent. No significant differences were observed between control and "epileptic" cultures in dendritic length or in the branching index. Quantitative electron microscopic analysis did not reveal differences between "epileptic" cultures and control cultures in the spine area of the labelled CA3 pyramidal cells, indicating that there was a real spine loss, not just a reduction in the size of the spines. We conclude that epileptic activity causes morphological alterations in defined postsynaptic compartments of hippocampal pyramidal cells surviving under these conditions.

Animals↗
PubMed1996

Layer-specific sprouting of commissural fibres to the rat fascia dentata after unilateral entorhinal cortex lesion: a Phaseolus vulgaris leucoagglutinin tracing study.

After unilateral entorhinal cortex lesion commissural fibres to the inner molecular layer of the rat fascia dentata are said to sprout into the former termination zone of entorhinal afferents. This sprouting process has not yet been demonstrated at the level of individual fibres. In the present study, Phaseolus vulgaris leucoagglutinin tracing was used to analyse the commissural projection to the inner molecular layer in rats with longstanding entorhinal cortex lesions. In comparison with controls, the commissural fibre plexus in the inner molecular layer had expanded by 20-45 microns outwards on the side of the entorhinal lesion. Unexpectedly, only a small number of axons arising from the bulk of commissural fibres in the inner molecular layer left the main fibre plexus and entered the outer molecular layer. Thus, there was still a clearly recognizable border between the Phaseolus vulgaris leucoagglutinin-labelled commissural fibre plexus in the inner molecular layer and the unstained outer molecular layer. The few commissural axons invading the outer molecular layer rarely branched but formed multiple en passant boutons, and occasionally exhibited growth cones. The data indicate that only few commissural fibres appear to be able to sprout beyond the border of their appropriate layer suggesting that the characteristic laminar specificity of hippocampal afferents is largely retained following deafferentation.

Animals↗
PubMed1996

Regeneration of the GABAergic septohippocampal projection in vitro.

The formation of the GABAergic septohippocampal projection was studied in vitro. Slice cultures of the septal complex from young postnatal rats were prepared and co-cultivated with hippocampal slices for up to four weeks. Then, the anterogradely transported tracer Phaseolus vulgaris leucoagglutinin was injected into the septal culture and the labeled fibers were traced into the hippocampal culture. Some fibers were identified as originating from GABAergic septal cells by double-labeling with an antiserum against GABA using the postembedding immunogold procedure. Our results showed that double-labeled terminals of GABAergic septohippocampal neurons established symmetric synapses exclusively with GABA-positive dendrites in one out of five co-cultures, but also contacted numerous GABA-negative structures in the remaining four co-cultures. These findings, together with light microscopic data from sections double-stained for Phaseolus and parvalbumin, indicate that the high target selectivity of the GABAergic septohippocampal pathway for GABAergic interneurons in vivo is lost in most cases, at least under the present in vitro conditions. It is hypothesized that this may be due to an immaturity of the connection, the lack of axon-guiding factors or an expansion of the septohippocampal GABAergic fibers in the absence of many extrinsic afferents, including GABAergic fibers. The simultaneous occurrence of anterogradely labeled, but GABA-negative, septohippocampal terminals in the hippocampal target culture also suggests that the septohippocampal cholinergic projection developed in vitro, as was shown before in other studies. Since most septohippocampal neurons have to be axotomized for culture preparation, the present results indicate that GABAergic septohippocampal neurons from young postnatal rats survive axotomy and are capable of regenerating a septohippocampal projection, including the formation of characteristic GABAergic synapses on co-cultured hippocampal neurons. However, the characteristic target selectivity is rarely preserved.

Animals↗
PubMed1996

Heterogeneity of the commissural projection to the rat dentate gyrus: a Phaseolus vulgaris leucoagglutinin tracing study.

The commissural and associational projections to the rat dentate gyrus are believed to be anatomically homologous fiber systems. They are often referred to as the so-called commissural/ associational system of the dentate gyrus. However, whereas characteristic laminar termination patterns within the molecular layer of the dentate gyrus have been described for the different cells of origin of the associational projection, the axons of the different cell types of commissural neurons have long been believed to terminate exclusively within the inner molecular layer. Only recently, a previously unknown commissural projection to the outer molecular layer of the dentate gyrus was described and the question was raised whether the commissural fibers could exhibit a heterogeneity similar to that of the associational projections. Using the anterograde tracer Phaseolus vulgaris leucoagglutinin, which labels individual axons and their collaterals, we have studied the termination pattern of commissural axons in the dentate gyrus of the septal hippocampus. At least four different commissural fiber types could be revealed on the basis of their laminar termination pattern: fibers to the inner molecular layer (type 1), fibers to the outer molecular layer (type 2), fibers terminating throughout the molecular layer (type 3), and fibers terminating in both the granule cell layer and the molecular layer (type 4). These observations demonstrate a previously underestimated heterogeneity of the commissural projection. In addition, there is a great deal of parallelism between the different commissural and associational fibers, pointing to a coordinated action of the two systems in the two hippocampi.

Afferent Pathways↗
PubMed1996

Survival, regeneration and sprouting of central neurons: the rat septohippocampal projection as a model.

The septohippocampal projection was used to study the survival following axotomy, axonal regeneration, and sprouting of a defined group of central neurons. Septohippocampal projection neurons in adult rats were axotomized by bilateral lesions of the fimbria-fornix. Using prelabeling prior to axotomy, intracellular staining, electron microscopy, and immunocytochemical and in situ hybridization techniques, we were able to demonstrate that the majority of septohippocampal neurons survived after axotomy. At least in young postnatal rats, these axotomized neurons have the capacity to regenerate an axonal process that reinnervates its appropriate target tissue, the hippocampus. We demonstrated this by axotomizing young septohippocampal neurons and co-culturing them with sections of hippocampus. Septohippocampal neurons appear to retain their capacity for axonal growth in adulthood, since they are able to sprout within hippocampal layers partially denervated by removing entorhinal afferents. In this paradigm the terminals of septohippocampal neurons themselves were not lesioned. Our results point to a previously underestimated capacity of septohippocampal neurons for survival following axotomy, regeneration, and sprouting.

Acetylcholinesterase↗
PubMed1995

Fate of GABAergic septohippocampal neurons after fimbria-fornix transection as revealed by in situ hybridization for glutamate decarboxylase mRNA and parvalbumin immunocytochemistry.

Many septohippocampal neurons are GABAergic and are affected by transection of the fimbria-fornix, like the septohippocampal cholinergic cells. Here we have studied the changes that occur in GABAergic septohippocampal neurons following fimbria-fornix transection. For labeling of septohippocampal projection neurons, adult Sprague-Dawley rats received injections of the fluorescent tracer Fluoro-Gold into the hippocampus 1 week prior to bilateral transection of the fimbria-fornix. After axotomy, rats were allowed to survive for varying periods ranging from 3 weeks to 18 months. Following fixation of the animals, sections through the septal region were either stained by in situ hybridization for glutamate decarboxylase (GAD) mRNA or immunostained for parvalbumin (PARV), which is known to be present in GABAergic septohippocampal neurons. In situ hybridization for GAD mRNA revealed no statistically significant changes in cell number 3 weeks and 6 months postlesion. In contrast, PARV-immunoreactive neurons were reduced to 35% of control 3 weeks postlesion. This value increased to 66% after 6 months of survival. As seen in the electron microscope, axotomized PARV-positive neurons exhibited characteristics of vital cells. Most neurons contained lysosomes associated with Fluoro-Gold, resulting from retrograde labeling prior to fimbria-fornix transection. We conclude that mainly PARV-containing GABAergic neurons in the medial septal nucleus (MS) project to the hippocampus and are thus heavily affected by the lesion but are able to survive and restore the synthesis of PARV. The lack of significant changes in the number of GAD mRNA-expressing cells is explained by the presence of numerous GABAergic MS neurons not projecting to the hippocampus.

Animals↗
PubMed1995

Developmental upregulation of the neural cell adhesion molecule VASE exon in slice cultures of rat hippocampus.

The factors limiting axonal growth in the mature CNS are poorly understood. It has been shown that the neural cell adhesion molecule VASE exon (variable alternative spliced exon) is one of the factors that may account for the downregulation of neurite outgrowth. Here we demonstrate that the developmental upregulation of the VASE exon is preserved in slice cultures of hippocampus, making these cultures a useful model to study the regulation of VASE and age-dependent growth processes in an organotypic environment.

Animals↗
PubMed1995

Phaseolus vulgaris-leucoagglutinin tracing of commissural fibers to the rat dentate gyrus: evidence for a previously unknown commissural projection to the outer molecular layer.

Numerous studies have shown a lamina-specific termination of commissural fibers to the dentate gyrus in the inner molecular layer. However, the exact course and arborization pattern of individual fibers remained unknown. In this study, the commissural fiber tract to the dentate gyrus of the rat has been studied using the anterograde tracer Phaseolus vulgaris-leucoagglutinin (PHA-L), which labels individual axons and their collaterals. Following iontophoretic application of the tracer, anterogradely labeled fibers were followed through the posterior basal fornix and medial fimbria where they formed a dense fiber bundle. Labeled fibers then entered the dentate gyrus close to the medial blade of the granule cell layer where they separated and traversed the hilus. Only in those cases where the injection also involved CA3 pyramidal cells could axons arborizing in the hilus be observed. Typically, fibers that continued into the molecular layer did not arborize in the hilus. Upon their entrance into the molecular layer, these fibers changed direction, gave off several collaterals, and followed a new path parallel to the granule cell layer where they preferentially formed en passant contacts. These commissural fibers to the inner molecular layer terminated in a wide septotemporal (longitudinal) extension. However, a considerable number of fibers reached the outer molecular layer where some of them formed extensive arborizations. Moreover, these commissural fibers to the outer molecular layer appeared to be restricted to the hippocampal lamella, corresponding to the level of the contralateral injection site. These data suggest the existence of three commissural projections to the rat dentate gyrus: (1) commissural fibers to the hilus arising from CA3 neurons, (2) commissural fibers to the inner molecular layer, and, (3) commissural fibers to the outer molecular layer.

Animals↗
PubMed1995

Development of the hippocamposeptal projection in the rat.

We analyzed the development of the hippocamposeptal projection and the morphology of the neurons giving rise to this projection. The fluorescent tracer Dil was injected into the septal region or the hippocampus in fixed brains of embryonic and early postnatal rats. Anterogradely labeled hippocampal axons first reached the septal region at E16. They ran along the midline of the brain, thereby approaching the medial septum. Axons to the lateral septum were first observed around E18/19. The lateral septum is partly innervated by collaterals of axons that travel to the medial septum. The projection to the lateral septal nuclei becomes more massive during early postnatal stages, whereas that to the medial septum becomes smaller. Cells in the medial septum retrogradely labeled by injection into the hippocampus were first observed at E18. Thus, the hippocamposeptal projection is established earlier than the septohippocampal projection. The first hippocampal projection neurons are nonpyramidal neurons that appear to pioneer the pathway to the septum. Pyramidal cell axons follow this first cohort of axons into the medial septum. Pyramidal cells could be retrogradely labeled from the medial septum during the perinatal period but then diminished in number. At P10, only nonpyramidal cells were labeled by medial septal injections. This indicates that the pyramidal component of this projection is transient and is removed shortly after birth. However, as is known from other studies, hippocampal pyramidal cells give rise to a powerful projection to the lateral septum in adult animals. Our results show that there is a considerable remodeling of the projection from the hippocampus to the septum during ontogenetic development.

Animals↗
PubMed1995

Lamina-specific synaptic connections of hippocampal neurons in vitro.

By using slice cultures as a model, we demonstrate here that different target selectivities exist among the various afferent fibers to the hippocampus. As in intact animals, septohippocampal cholinergic fibers, provided by a slice culture of septum, innervate a co-cultured slice of hippocampus diffusely, that is, without forming distinct layers of termination. As in vivo, the septal cholinergic fibers establish synapses with a variety of target cells. Conversely, fibers from an entorhinal slice co-cultured to a hippocampal slice display their normal laminar specificity. They preferentially terminate in the outer molecular layer of the fascia dentata, thereby selectively contacting peripheral dendrites of the granule cells. This preferential termination on peripheral dendritic segments is remarkable, since these fibers do not have to compete with commissural fibers, hypothalamic fibers, and septal afferents for dendritic space under these culture conditions. Moreover, in triplet cultures in which first two hippocampal slices were co-cultured and then, with a delay of 5 days, an entorhinal slice was added, the fibers from the entorhinal slice and those from the hippocampal culture terminated in their appropriate layers in the hippocampal target culture. However, in this approach the normal sequence of ingrowth of these two afferents was reversed. In normal ontogenetic development, entorhinal afferents arrive in the hippocampus before the commissural fibers. The results show that there are different degrees of target selectivity of hippocampal afferents and that the characteristic lamination of certain afferent fibers in the hippocampus is not determined by their sequential ingrowth during development.

Afferent Pathways↗
PubMed1995

Axonal regeneration of identified septohippocampal projection neurons in vitro.

Previous studies have shown that the septohippocampal projection develops in vitro. It remained unclear, however, whether this in vitro projection resulted from axonal regeneration of septal neurons transected by the culture preparation, or from a priori outgrowth of undamaged cells that had not yet sent an axonal process to the hippocampus at the time of tissue preparation. Here we have prepared slice cultures of identified septohippocampal projection neurons that were retrogradely labeled by hippocampal tracer injection prior to slice preparation. We demonstrate that these identified projection neurons survive axotomy caused by culture preparation, are able to regrow an axonal process in vitro, and innervate a co-cultured hippocampal slice.

Animals↗