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M Frotscher

Publications and source records attributed to M Frotscher.

At least 199 records · Page 11Linked to original sources
PubMed1986

Non-pyramidal neurons in the guinea pig hippocampus. A combined Golgi-electron microscope study.

Morphological characteristics of non-pyramidal neurons in the guinea pig hippocampus (regions CA1 and CA3) were analyzed by a correlated light and electron microscopic approach. Following Golgi impregnation, the cells were first studied under the light microscope and classified according to the location of their cell bodies and the distribution of their dendrites in the different hippocampal layers. Next, the Golgi impregnated non-pyramidal neurons were gold-toned and deimpregnated, allowing an electron microscopic analysis of the identified structures. With regard to cell body location and dendritic pattern, non-pyramidal cells are a rather heterogeneous group of neurons. Their perikarya were found in all hippocampal layers and their dendrites had a less regular orientation when compared to pyramidal neurons and granule cells. Two basic types, i.e., "vertical" and "horizontal" non-pyramidal neurons are described. Many cells were of an intermediate type with dendrites extending in all directions. Non-pyramidal cell dendrites were mostly devoid of spines but exhibited numerous varicosities. Non-pyramidal cell axons could sometimes be seen extending towards the pyramidal cell layer. A surprising uniformity was observed when the impregnated, identified non-pyramidal neurons were studied in the electron microscope. Their perikarya exhibited a well-developed endoplasmic reticulum and indented nuclei. Both the cell bodies and the varicose dendrites were densely covered with synaptic boutons which mainly formed asymmetric synaptic contacts. Only occasionally were symmetric synaptic contacts observed. Non-pyramidal cell dendrites extending into the stratum lucidum of CA3 were found to be contacted by the giant boutons of mossy fiber axons. In addition to synaptic contacts, the dendrites of gold-toned non-pyramidal neurons formed gap junctions with neighboring dendrites. The results are discussed in relation to recent immunocytochemical studies which have shown non-pyramidal neurons in the hippocampus to contain gamma-aminobutyric acid and/or various neuropeptides.

Animals↗
PubMed1986

Late development of intrinsic excitation in the rat neostriatum: an in vitro study.

Functional maturation of intrinsic circuitry in the neostriatum was studied by intracellular recording and intracellular staining with Lucifer yellow in slices obtained from rat pups at postnatal days (P)1-20 and from adult rats. The most striking observation was that intrastriatal stimulation elicited predominantly inhibitory responses in slices obtained from animals of P1-6. In contrast, intrastriatally evoked responses in slices obtained after P10 were predominantly excitatory. The inhibitory postsynaptic potentials (IPSPs) recorded in slices obtained from pups were blocked by bicuculline (50 microM) and exhibited a reversal potential at about -60 mV which shifted in depolarizing direction when intracellular Cl- activity increased. Thus, these IPSPs correspond to IPSPs observed in adult animals. It is concluded that maturation of excitatory synapses is the main change during postnatal development. The changes of postsynaptic potentials were paralleled by the appearance of spines on dendrites around P7 as revealed by intracellular staining. The apparent input resistances and time constants of young neurons were very high and responses to large current injections were often distorted by humps which could not be observed in adult neurons. Only young neurons responded with bursts to synaptic activation in the presence of bicuculline (50 microM). It appears that dendritic conductances have a stronger influence on somatic discharge in the electrotonically compact young neurons than in adult neurons.

Animals↗
PubMed1986

Postsynaptic-GABAergic inhibition of non-pyramidal neurons in the guinea-pig hippocampus.

Intracellular recording and staining was applied to study non-pyramidal neurons in the guinea-pig hippocampus. To avoid accidental impalement of pyramidal or granule cells, two hippocampal regions known to be devoid of pyramidal or granule cells were chosen. In transverse and longitudinal slices, neurons of the deep hilar region (zone 4 of Amaral3), and in transverse slices, neurons of the stratum lacunosum-moleculare (CA3) were impaled. The intracellular staining with Lucifer Yellow revealed that of 20 neurons stained in these zones all were non-pyramidal neurons. Hilar neurons, situated just below the granular layer, differed from granule cells and CA3 neurons with respect to their action potential waveform and their current/voltage relationship. In contrast to granule cells, hilar neurons exhibited spontaneous bursts in the presence of bicuculline (25 microM). In all neurons impaled in the hilar region and the stratum lacunosum-moleculare (n = 42), inhibitory postsynaptic potentials could be elicited. These inhibitory postsynaptic potentials were blocked by bicuculline. In transverse slices, perforant path stimulation elicited inhibition preceding excitation in hilar neurons and excitation preceding inhibition in granule cells. Since non-pyramidal neurons are likely to be inhibitory neurons, our data suggest that GABAergic neurons in the hilus or in the stratum lacunosum-moleculare are controlled by inhibitory GABAergic synapses. This was verified by immunocytochemistry using antibodies against glutamate decarboxylase, the gamma-aminobutyric acid synthetizing enzyme. In both hippocampal regions studied, glutamate decarboxylase-positive synaptic terminals on glutamate decarboxylase-positive cells were observed. It is concluded that disinhibition is an important feature of information processing in the hippocampus, and that disinhibition is mediated by GABAergic synapses on GABAergic neurons.

Action Potentials↗
PubMed1985

Neurogenesis of GABAergic neurons in the rat dentate gyrus: a combined autoradiographic and immunocytochemical study.

Neurogenesis of GABAergic neurons in the rat area dentata was studied combining [3H]thymidine autoradiography with immunostaining for glutamate decarboxylase (GAD), the gamma-aminobutyric acid (GABA) synthesizing enzyme. GAD immunocytochemistry stained many neurons located mainly in the hilar region but also in the granular and molecular layers. Granule cells were not immunoreactive. On embryonic day (E) 14, [3H]thymidine injection labelled 12.8% of GAD-positive (+) neurons in sections of the area dentata processed at an age of 40 days postnatally. This proportion decreased to 1.8% on E17 and to 1% on E18. No GAD (+) neurons were labelled by thymidine injection on E19, while non-immunoreactive granule cells and CA4 pyramids were still labelled, indicating persisting neurogenesis of those cells.

Age Factors↗
PubMed1985

Cholinergic innervation of the rat hippocampus as revealed by choline acetyltransferase immunocytochemistry: a combined light and electron microscopic study.

The cholinergic innervation of the rat hippocampus proper and fascia dentata was investigated by using a monoclonal antibody against choline acetyltransferase (ChAT). At the light microscopic level, thin varicose ChAT-immunoreactive fibers were observed mainly in the vicinity of the pyramidal and granular layers where they formed a fine network around proximal dendrites of pyramidal and granule cells. In addition, many ChAT-immuno-reactive fibers were found in the hilar region and in stratum oriens, radiatum, and lacunosum-moleculare of all hippocampal sectors. Electron microscopic analysis revealed ChAT immunoreactivity in thin unmyelinated varicose axons and terminals which established synaptic contacts. Asymmetric contacts of ChAT-immunoreactive terminals were found on small spines in the dendritic layers of the hippocampus proper and in the molecular layer of the fascia dentata. Symmetric synaptic contacts were formed on the cell bodies of pyramidal and granule cells. Both symmetric and asymmetric synaptic contacts occurred on dendritic shafts. The analysis of serial thin sections, which allows identification of postsynaptic elements, suggests that pyramidal cells, granule cells, and nonpyramidal neurons of the hippocampus receive a cholinergic input.

Animals↗
PubMed1985

Mossy fibres form synapses with identified pyramidal basket cells in the CA3 region of the guinea-pig hippocampus: a combined Golgi-electron microscope study.

Mossy fibres, i.e. the axons of dentate granule cells, terminate with characteristic giant boutons on large spines or excrescences of the pyramidal cells in regio inferior of the hippocampus. In addition to pyramidal cells there are several types of non-pyramidal neuron which extend their dendrites into the termination zone of mossy fibres. By using the combined Golgi-electron microscope technique mossy fibre terminals were found, which established asymmetric synaptic contacts with both spines of pyramidal cells and smooth dendrites of identified (Golgi-stained) pyramidal basket cells in the CA3 region of the guinea-pig hippocampus. The observed synaptic connection with pyramidal basket cells suggests an involvement of the mossy fibre system in feed-forward inhibition of the hippocampal pyramidal neurons.

Afferent Pathways↗
PubMed1984

Concentration of F-actin in synaptic formations of the hippocampus as visualized by staining with fluorescent phalloidin.

Polymerized actin (F-actin) was localized in the guinea pig hippocampus by fluorescent staining with rhodamine-labeled phalloidin. Phalloidin displayed a preferential affinity for the main synaptic areas where the fluorescence was confined to 0.5-1 micron particles, roughly the size of synaptic structures (dendritic spines and presynaptic terminals). These particles appeared to stud the surface of dendrites. Particularly large and strongly fluorescent particles mainly 1-3 micron in diameter were found in the termination zone of mossy fibres which form the largest synapses of the hippocampus. The apparent high concentration of F-actin in synaptic formations suggests a role for actin in synaptic function.

Actins↗
PubMed1984

Identification of projecting neurons in rat neostriatal slices.

Spiny neurons projecting to substantia nigra (SN) were identified by combining retrograde transport of tracers in vivo with intracellular staining in vitro. First, neostriatal projection neurons were retrogradely labeled by the injection of fluorescent tracers into the ipsilateral SN. Then, slices were taken from the neostriata containing the retrogradely labeled cells. Cells were impaled for intracellular recording and stained by intracellular dye injection. All cells were of the spiny type and 75% contained both dyes, the intracellularly injected dye as well as the retrogradely transported tracer. Thus, most intracellular recordings in neostriatal slices are obtained from spiny neurons projecting to SN.

Animals↗
PubMed1984

Commissural afferents innervate glutamate decarboxylase immunoreactive non-pyramidal neurons in the guinea pig hippocampus.

The innervation of GABAergic hippocampal neurons by commissural fibers was investigated in the guinea pig by a combined anterograde degeneration - immunocytochemical technique. Presumed GABAergic neurons were identified by immunocytochemistry for glutamate decarboxylase (GAD) and the commissural fibers by electron-dense degeneration following contralateral transection of the fimbria. Commissural afferents were found to establish asymmetric synaptic contacts with non-pyramidal GAD-immunoreactive neurons located in subpyramidal and suprapyramidal zones of region CA1. The observed connection suggests that inhibition of pyramidal cells may occur in a feed-forward manner as postulated by electrophysiological studies.

Animals↗
PubMed1984

Ultrastructure and synaptic connections of vasoactive intestinal polypeptide-like immunoreactive non-pyramidal neurons and axon terminals in the rat hippocampus.

In the hippocampus, antibody raised against vasoactive intestinal polypeptide (VIP) labeled perikarya and processes of non-pyramidal neurons whereas these structures remained unlabeled in pyramidal cells and granule cells. In the present study, VIP-immunostaining was used to investigate the fine structure and synaptic connections of identified non-pyramidal neurons and of immunoreactive axon terminals in the CA1 region of the rat hippocampus by means of electron microscopic immunocytochemistry. From a number of cells studied, two VIP-like immunoreactive non-pyramidal neurons in the regio superior were selected for an electron microscopic analysis of serial thin sections. These cells were different with regard to the location of their cell bodies and the orientation of their dendrites. One cell was located in the stratum lacunosum-moleculare with dendritic processes oriented parallel to the hippocampal fissure. The second neuron was found in the inner one-third of the stratum radiatum. The dendrites of this cell ran nearly parallel to the ascending apical dendrites of the pyramidal cells. Both cells had a round or ovoid perikaryon and an infolded nucleus. The aspinous dendrites of both neurons were densely covered with synaptic boutons. These terminals were small, filled with spherical vesicles, and established asymmetric synaptic contacts. No variations in the fine structure of the presynaptic boutons were found along the course of the labeled dendrites through the various hippocampal layers, although different afferents are known to terminate in these layers. Vasoactive intestinal polypeptide-like immunopositive axon terminals course through all layers of the hippocampus. In the stratum pyramidale they established symmetric synaptic contacts with the perikarya of pyramidal cells. In the stratum radiatum they made symmetric contacts with the shafts of apical dendrites of pyramidal cells but never contacted dendritic spines. The symmetric contacts with pyramidal cell perikarya suggest an involvement of the VIP-like immunoreactive axon terminals in pyramidal cell inhibition.

Animals↗
PubMed1983

Commissural afferents to the rat hippocampus terminate on vasoactive intestinal polypeptide-like immunoreactive non-pyramidal neurons. An EM immunocytochemical degeneration study.

In the rat hippocampus, bipolar non-pyramidal neurons in stratum radiatum and stratum oriens and multipolar neurons in stratum lacunosum-moleculare react for vasoactive intestinal polypeptide (VIP) immunostaining, but pyramidal cells do not. Such bipolar VIP-like immunoreactive neurons in strata radiatum and oriens of regio superior were studied by electron microscopy for synaptic contacts with commissural afferents. The commissural fibers were identified by their anterograde degeneration induced by contralateral fimbria transections 2 days before sacrifice. Electron-dense degenerated boutons of commissural origin were found in synaptic contact with the cell bodies and dendrites of the VIP-like immunoreactive non-pyramidal cells.

Afferent Pathways↗
PubMed1983

Retrograde labeling of striato-nigral neurons in the rat by three different tracers.

The three tracers horseradish peroxidase (HRP), 4',6-diamidino-2-phenylindol-2HCl (DAPI) and Fast Blue (FB) differ in retrograde labeling of striato-nigral neurons. After a 24 h survival, injection of DAPI into the ventral tegmentum labeled numerous cells throughout the neostriatum, whereas an identical amount of HRP only labeled cells in circumscribed areas of the neostriatum. Injections of FB labeled a substantial number of neostriatal neurons after a survival time of 4 days, but not after 24 h. In addition, differences between retrograde staining of striato-nigral neurons and layer V pyramidal cells of the ipsilateral neocortex, also labeled in these experiments, were found.

Amidines↗
PubMed1983

Commissural fibers terminate on non-pyramidal neurons in the guinea pig hippocampus -- a combined Golgi/EM degeneration study.

The combined Golgi/EM method was applied to guinea pig hippocampi with acute anterograde degeneration of the commissural afferents in order to identify possible synaptic contacts between commissural terminals and non-pyramidal neurons. Degenerating, electron-dense terminals of commissural origin were found in synaptic contact with both perikarya and dendrites of two identified non-pyramidal neurons in regio superior, namely a basket cell and a bipolar neuron in stratum oriens. The observed connection may form the morphological basis for the physiologically observed feed-forward inhibition of the pyramidal cells.

Animals↗
PubMed1983

Lesion-induced mossy fibers to the molecular layer of the rat fascia dentata: identification of postsynaptic granule cells by the Golgi-EM technique.

The axons of the dentate granule cells, the hippocampal mossy fibers, sprout "backward" into the dentate molecular layer when this is heavily denervated. Using the combined Golgi-electron microscopy (EM) technique we now demonstrate that these aberrant supragranular mossy fibers at least in part terminate on granule cell dendrites. Sprouting of mossy fibers into the dentate molecular layer was induced in adult rats by simultaneous surgical removal of the commissural and entorhinal afferents to the fascia dentata. After at least 7 weeks survival, the presence of mossy fiber terminals in the inner part of the dentate molecular layer was demonstrated by light microscopy. In the electron microscope the mossy fiber terminals were identified by their unique structural characteristics, namely, the unusually large size of the terminals, the dense packing of clear synaptic vesicles with a few dense core vesicles intermingled, the presence of asymmetric synaptic contacts with spines and desmosome-like contacts with dendritic shafts, and the continuity with a thin unmyelinated preterminal axon. Golgi-stained granule cells were first identified in the light microscope, and then, after deimpregnation, the same cells were examined in the electron microscope. In ultrathin, serial sections lesion-induced mossy fiber terminals were found in synaptic contact with spines on proximal dendritic segments of such identified Golgi-impregnated granule cells. From this we conclude that the aberrant, supragranular mossy fibers can innervate dendrites of the parent cell group, the dentate granule cells. The results, moreover, provide an example of reactive synaptogenesis where both the sprouted afferents and its postsynaptic element have been identified.

Animals↗
PubMed1982

Dependence of the viability of neurons in hippocampal slices on oxygen supply.

Hippocampal slices were tested for their viability by recording monosynaptic responses in granule cell and CA3 pyramidal cell layer. Subsequently, they were studied by light and electron microscopy. Cross sections through the slices contained intact cells clustered in the central part, while the rims consisted of swollen neurons. Electrophysiological and morphological findings indicated that a greater number of granule cells than of CA3 neurons was preserved. This difference was not due to different sensitivity of the neurons to hypoxia, since synaptic responses disappeared within 3-5 min in both cell layers, when the slices were incubated in N2/CO2 instead of O2/CO2. The block of synaptic transmission during hypoxia was caused by hyperpolarization, decrease of EPSP/IPSP amplitudes and increase of membrane conductance as revealed by intracellular recording. Synaptic potentials recorded extracellularly recovered even after 20 min of hypoxia. Morphologically these slices were not different from control slices. After 1 hr of hypoxia no recovery of electrical potentials was seen. In cross sections of these slices, swollen neurons outnumbered intact cells.

Aerobiosis↗
PubMed1981

Ultrastructure of mossy fiber endings in in vitro hippocampal slices.

0.2 to 0.4 mm thick slices of guinea pig hippocampus were studied morphologically after varying periods of incubation at 36 degrees C in Krebs-Ringer solution. Prior to fixation, the slices were tested for the presence of synaptically driven discharges of CA 3 neurons following mossy fiber (mf) stimulation because tissue preservation was satisfactory only in slices in which electrical responses were obtained. The fine structure of the MF layer in slices was compared with the ultrastructure of this region in hippocampal tissue fixed by transcardial perfusion or immersion of the tissue in the fixative. In the central part of the slices many intact neuronal structures of the mf layer could be seen even after 4 h of incubation. In the outer parts of the slices, neurons were swollen and vacuolated. These alterations were not observed in hippocampal tissue fixed by transcardial perfusion or by immersion. In all parts of the slices dark neurons and processes were found. Since dark neurons were also numerous in tissue blocks immersed in the fixative but were rare in perfused material, these changes were obviously caused by damage to unfixed tissue and fixation by immersion.

Animals↗
PubMed1981

Termination of cortical afferents on identified neurons in the caudate nucleus of the cat. A combined Golgi-EM degeneration study.

A combined Golgi/electron microscopic technique was used to investigate tne fine structure and synaptology of Golgi-stained spiny neurons in the caudate nucleus of the cat. In order to study the termination sites of cortical afferents on Golgi-stained spiny neurons, cortical fibres were caused to degenerate by making extensive cortical lesions 3 days prior to fixation of the animals. When examined in the electron microscope, perikarya of labelled spiny neurons have a round nucleus, a few mitochondria and microtubules, and a poorly developed Golgi apparatus and rough endoplasmic reticulum. Only rarely are axo-somatic contacts seen. Labelled dendrites exhibit a moderate number of microtubules and sometimes elongated mitochondria. Numerous labelled spines are seen in the vicinity of their parent dendrites. They are contacted by smaller type I and type III boutons and larger type IV boutons (Hassler et al. 1978). Large boutons filled with clear round vesicles establish symmetric contacts with labelled dendritic shafts. Degenerating boutons of cortical afferents are seen in contact with spines and, more rarely, with dendritic shafts of Golgi-stained spiny neurons. All degenerating boutons synapsing with labelled structures are found some distance from the cell body. No contacts of degenerating cortical boutons with the soma or with stem dendrites of Golgi-stained spiny neurons are found.

Afferent Pathways↗