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Biomedical subjects

F J Seil

Publications and source records attributed to F J Seil.

At least 37 records · Page 2Linked to original sources
PubMed1994

Reduced cortical inhibitory synaptogenesis in organotypic cerebellar cultures developing in the absence of neuronal activity.

Organotypic cerebellar cultures derived from newborn mice were continuously exposed to medium containing tetrodotoxin and elevated levels of magnesium to block all electrical activity. After 2 weeks in vitro, no activity was evident during the first 15-20 minutes following transfer to a recording medium without blocking agents. Thereafter, cortical discharge rates increased until a state of sustained hyperactivity was reached. Ultrastructural examination of such cultures revealed a reduction of inhibitory Purkinje cell somatic synapses to half the control value along with an even greater reduction of axodendritic synapses (largely inhibitory) in the cortical neuropil. No loss of axospinous synapses (excitatory) was evident. These results support the concept that spontaneous neuronal activity is necessary for the full development of inhibitory circuitry.

Action Potentials↗
PubMed1994

Dystrophic dendrites induced in cultured Purkinje cells by exposure to vinblastine.

Organotypic cerebellar cultures were exposed to the mitotic spindle inhibitor, vinblastine, and examined by light and electron microscopy, and electrophysiologically. Purkinje cells in exposed cultures had stunted, varicose dendrites when observed in preparations reacted with antibody to nonphosphorylated neurofilament protein. Ultrastructurally, microtubules were selectively reduced in Purkinje cell dendrites, which contained disarrayed excess smooth endoplasmic reticulum, but no large accumulations of densely packed neurofilaments. Spontaneous cortical discharges were initially increased in vinblastine treated cultures and then ceased, at which time the cultures became unresponsive to electrical stimulation. The vinblastine-induced changes were attributed to impaired intracellular transport secondary to disruption of Purkinje cell dendritic microtubules.

Animals↗
PubMed1994

Morphological correlates of altered neuronal activity in organotypic cerebellar cultures chronically exposed to anti-GABA agents.

Organotypic cerebellar cultures derived from newborn mice were chronically exposed to medium containing picrotoxin or bicuculline from explanation until they were recorded from extracellularly or fixed for morphological studies. Cultures exposed to anti-GABA agents for 13-18 days in vitro had decreased spontaneous cortical discharge rates when compared with sister control cultures and prolonged inhibitory responses to cortical stimulation. Electron microscopic examination of exposed cultures after 14-16 days in vitro revealed a hyperinnervation of Purkinje cell somata by inhibitory terminals predominantly of basket cell origin. The sprouted terminals penetrated otherwise intact Purkinje cell astrocytic sheaths. These changes represent a departure from the usual developmental pattern, a departure induced by exposure to anti-GABA agents that increased neuronal activity early in the development of the cerebellar circuitry in vitro. The precise signals that initiated the changes are unknown, but the altered development is most likely in response to increased Purkinje cell activity.

6-Cyano-7-nitroquinoxaline-2,3-dione↗
PubMed1994

Plastic changes in Ara C-treated and "transplanted" coeruleocerebellar cultures.

Locus coeruleus axons project to cerebellar cortex in coeruleocerebellar cultures, where they make functional contacts, and also appear as fine fibers in the outgrowth zones. The predominant catecholamine of locus coeruleus neurons in culture is dopamine. When coeruleocerebellar cultures are exposed to cytosine arabinoside to destroy cerebellar granule cells and functionally compromise glia, there is a resultant increase of Purkinje cell survival and a sprouting of Purkinje cell recurrent axon collaterals, plus an increase of catecholaminergic axons accompanied by a doubling of tissue dopamine content. If such reorganized cultures are transplanted with granule cells and glia, a second round of plastic changes ensues in which the Purkinje cell population and the recurrent axon collaterals are reduced to control levels, but catecholaminergic axons and dopamine content remain increased. The maintenance of catecholaminergic axons does not appear to depend on the persistence of target neurons.

Animals↗
PubMed1994

Persistence of heterotypical synapses in transplanted cerebellar cultures in the absence of functional glia.

Neonatal mouse cerebellar cultures depleted of granule cells and functional glia by exposure to cytosine arabinoside were transplanted with either granule cells and glia or with granule cells in the absence of functional glia. Myelination was evident in cultures transplanted with granule cells and glia, excess sprouted cortical neurites were reduced, Purkinje cells acquired astrocytic sheaths and had a near normal complement of axosomatic synapses, and homotypical parallel fiber-Purkinje cell dendritic spine synapses were present in a 2.4:1 ratio to heterotypical recurrent axon collateral-Purkinje cell dendritic spine synapses. Cultures transplanted with granule cells were not myelinated, sprouted cortical neurites were not reduced. Purkinje cells lacked astrocytic sheaths and their somata remained hyperinnervated, and the ratio of homotypical to heterotypical dendritic spine synapses was 1.4:1. In the absence of functional glia there was a greater persistence of heterotypical recurrent axon collateral-Purkinje cell dendritic spine synapses. These results are consistent with a previously described astrocytic role in the regulation of axosomatic synapse density on glially ensheathed neurons, and suggest astrocytic participation in the reduction of heterotypical axospinous synapses. Astrocyte-mediated synapse reduction may be an important mechanism for circuit reorganization after transplantation or during development.

Animals↗
PubMed1992

Tyrosine hydroxylase expression in non-catecholaminergic cells in cerebellar cultures.

Organotypic cerebellar cultures, some with incorporated portions of brainstem, were immunostained after 12-19 days in vitro with three different antibodies to tyrosine hydroxylase. Similar cultures were reacted with glyoxylic acid and examined for catecholamine histofluorescence. Locus coeruleus and other subcortical neurons were positive for tyrosine hydroxylase, as were Purkinje cells and outgrowth zone astrocytes. By contrast, only locus coeruleus neurons and their axons exhibited catecholamine histofluorescence after reaction with glyoxylic acid. These results confirm previously reported in vivo developmental studies indicating that tyrosine hydroxylase can be expressed in the absence of its normal biosynthetic products, and suggest that tyrosine hydroxylase cannot be considered to be a specific marker for catecholaminergic neurons in vitro, as well as during development in vivo.

Animals↗
PubMed1992

Induction of dendritic spine proliferation by an astrocyte secreted factor.

A number of neuron-supporting functions have been ascribed to astrocytes. In this study we found that a proliferation of Purkinje cell dendritic spines, a target site for presynaptic axon terminals, was induced in cytosine arabinoside-treated cerebellar cultures by exposure to astrocyte-conditioned medium. This result suggests that astrocytes may instigate the elaboration of postsynaptic neuronal elements prior to the appearance of axons. This may be an important mechanism in neural development, postdevelopmental neuroplastic change, or regeneration.

Animals↗
PubMed1992

Cytosine arabinoside effects in mouse cerebellar cultures in the presence of astrocytes.

Organotypic cerebellar cultures derived from neonatal mice were exposed to recent preparations of cytosine arabinoside that destroyed oligodendrocytes and drastically reduced granule cells, but did not reduce the astrocyte population. The cultures were analysed by light and electron microscopy, and by extracellular electrophysiological recording. Purkinje cells survived in greater numbers than in untreated explants and sprouted excess recurrent axon collaterals that formed heterotypical synapses with Purkinje cell dendritic spines. These changes were similar to those found in earlier studies with a cytosine arabinoside preparation that did reduce the astrocyte population, in addition to destroying oligodendrocytes and granule cells. Results with recent cytosine arabinoside preparations that differed from those obtained previously included astrocytic ensheathment of Purkinje cells and apposition of many unattached dendritic spines, encasement of heterotypical synapses by astroglial processes, a loss of Purkinje cell somatic spines, and a lack of somatic hyperinnervation of Purkinje cells by sprouted recurrent axon collateral terminals. All of these differences were attributed to the presence of adequate numbers of competent astrocytes. Heterotypical synapses formed by sprouted recurrent axon collateral terminals and Purkinje cell dendritic spines were functional, as indicated by cortical inhibition in response to antidromic Purkinje cell activation in the absence of somatic hyperinnervation. These results give further definition to the role of astrocytes in cerebellar development and plasticity.

Animals↗
PubMed1991

Reorganization of organotypic cultures of mouse cerebellum exposed to cytosine arabinoside: a timed ultrastructural study.

This study was designed to examine the sequential changes in the developing granuloprival cerebellar culture. In this model of anomalous cerebellar development, organotypic cultures derived from newborn Swiss-Webster mice were exposed to the DNA synthesis inhibitor, cytosine arabinoside, at explantation and were fixed for electron microscopic examination on successive days in vitro. Similar developmental stages were compared in control explants. Granule cell destruction began early, and was widespread by 2 days in vitro, when oligodendrocyte destruction also began in treated cultures. A few granule cells survived, but no recognizable oligodendrocytes remained by 7 days in vitro, at a time when myelin was initially evident in control explants. Purkinje cell recurrent axon collateral sprouting began at 3 days in vitro in cultures exposed to cytosine arabinoside, and the sprouted terminals initially synapsed with Purkinje cell somata, somatic spines and dendritic shafts. Synapses with Purkinje cell dendritic spines developed later, at approximately the same time as parallel fiber-Purkinje cell dendritic spine synapses formed in control cultures. Astrocytic ensheathment of control Purkinje cells was well underway by 6 days in vitro and Purkinje cell somata were relatively rounded and almost completely ensheathed by 9 days in vitro. Glial ensheathment did not occur in cytosine arabinoside treated cultures, and Purkinje cell somata were scalloped at 7 days in vitro by excess impinging recurrent axon collateral terminals, and never developed the smooth contours characteristic of control Purkinje cells. Purkinje cell somatic spines persisted in treated explants, and reduction of excess extracellular space was delayed until 12 days in vitro, when most of the developmental changes had been completed. The earlier development of synapses by excess recurrent axon collateral terminals with Purkinje cell somata, somatic spines and dendritic shafts, followed by the later development of heterotypical synapses with dendritic spines, in parallel with synapse formation by normal presynaptic elements, suggests that the sequence of development of synapses is a function of the maturational state of the postsynaptic components.

Animals↗
PubMed1991

Myelination and glial ensheathment of Purkinje cells in cerebellar cultures are not inhibited by antibodies to the neural cell adhesion molecule, N-CAM.

Mouse cerebellar cultures were exposed to anti-N-CAM antibodies throughout their in vitro development. Some cultures were stripped of myelinating oligodendrocytes and functionally competent astrocytes by treatment with cytosine arabinoside (Ara C), while others were left untreated and were potentially capable of forming myelin around axons and astrocytic sheaths around Purkinje cell somata and dendrites. As expected, the antibodies inhibited axonal fasciculation in the Ara C treated cultures. However, the same antibodies had no discernible effect on formation of myelin or astrocytic sheaths in cultures not treated with Ara C. N-CAM is expressed on the surfaces of neurons, oligodendroglia and astrocytes, and has been proposed as the signal molecule governing both kinds of neuron-glia interactions. The observations of the present study strongly suggest, however, that N-CAM does not have an indispensable role in such interactions.

Animals↗
PubMed1989

Myelination of axons within cytosine arabinoside treated mouse cerebellar explants by cultured rat oligodendrocytes.

Cell suspensions of cultured purified rat oligodendrocytes prepared by the differential substrate adhesion method were applied to neonatal mouse cerebellar explant cultures in which myelination and oligodendrocyte maturation had been irreversibly inhibited by exposure to cytosine arabinoside. Myelination of Purkinje cell axons within 92% of the host explants was observed 2-5 days after oligodendrocyte application. Ultrastructurally, mature oligodendrocytes and axons surrounded by compact myelin, as well as spherules of compact myelin membranes without axons, were present within the cerebellar explants. It is evident that cultured dissociated purified oligodendrocytes retain the ability to myelinate appropriate axons. Such oligodendrocytes may be hyperreactive with regard to myelin membrane formation, as suggested by the presence of spheres of compact myelin without axons.

Animals↗
PubMed1989

Antisera to the ganglioside GM1 do not have anti-myelin or anti-axon activities in vitro.

Four antisera to the ganglioside GM1 were tested for effects on myelin and axons when applied to mouse spinal cord-dorsal root ganglia explant cultures. None of the antisera to GM1 caused myelination inhibition or demyelination, while an antiserum to galactocerebroside caused both. Antisera to GM1 did not inhibit axonal outgrowth or destroy mature outgrowth zone axons, while an antiserum to a rat brain axolemma-enriched fraction did both. These results suggest that antibodies to GM1 do not have significant anti-myelin or anti-axon activity.

Animals↗
PubMed1989

Tissue culture models of myelination after oligodendrocyte transplantation.

Studies of myelination after transplantation of mature oligodendrocytes to cerebellar cultures in which oligodendrocyte maturation and myelination had been irreversibly inhibited by exposure to cytosine arabinoside were reviewed. Transplanted oligodendrocytes were derived from three sources, including cerebellar explants treated with kainic acid, dissociated oligodendrocyte cultures, and optic nerve fragments. Oligodendrocytes from all sources migrated into the host explants and myelinated appropriate axons. The time of appearance of myelin and the percentage of host cultures myelinated differed for the three sources of oligodendrocytes, however. Myelin was visible earliest and in the highest percentage of host explants transplanted with cultured dissociated oligodendrocytes, which were presumably the most free to migrate into the host tissue, and latest and in the lowest percentage of host cultures transplanted with optic nerve, from which oligodendrocytes were presumably least free to migrate. Some myelin-like membranes unassociated with axons appeared in cerebellar cultures transplanted with cultured dissociated oligodendrocytes, and not in cerebellar explants transplanted with oligodendrocytes from other sources. The formation of such myelin-like membranes was interpreted as a manifestation of oligodendrocyte hyperreactivity induced by culture in isolation.

Animals↗
PubMed1988

Differential effects of granule cell transplantation on two sprouted axonal systems in granuloprival coeruleocerebellar cultures.

Exposure of coeruleocerebellar cultures to cytosine arabinoside for the first 5 days in vitro destroyed granule cells and induced sprouting of cortical neurites (Purkinje cell recurrent axon collaterals) and catecholaminergic fibers. Transplantation of such granuloprival cultures with kainic acid-treated cerebellar explants as a source of granule cells resulted in a reduction of silver-positive cortical neurites, but not of histofluorescent catecholaminergic axons. Tissue levels of catecholamines were similar in transplanted and nontransplanted cultures. Differences in types of contacts made with target Purkinje cells in vitro may account for the difference in response to granule cell transplantation by the two axonal groups.

Animals↗
PubMed1988

Transplanted astrocytes reduce synaptic density in the neuropil of cerebellar cultures.

Cytosine arabinoside-treated neonatal mouse cerebellar cultures, devoid of granule cells and mature glia, demonstrate heterologous synapses between sprouted Purkinje cell recurrent axon collaterals and dendritic spines in the neuropil. Such cultures were transplanted with optic nerve as a source of glia, and the effect on neuropil synapses was investigated. There was a significant reduction in the number of synapses in the neuropil and an increase in the number of free dendritic spines. Many of these spines occurred in clusters, unapposed by glial processes. The effect on the synapse density was not due to a comparable increase in the area occupied by the added astrocytes or an increase in nerve terminal diameter. The results suggest that astrocytes alter the density of neuropil synapses and may also induce the sprouting of dendritic spines.

Animals↗
PubMed1988

Serum anti-myelin antibodies in chronic relapsing experimental allergic encephalomyelitis.

To investigate the role of anti-myelin antibodies in chronic relapsing experimental allergic encephalomyelitis (CR-EAE), sera from SJL/J mice with CR-EAE actively induced by inoculation with spinal cord homogenate in complete Freund's adjuvant (CFA) were compared with sera from mice to whom CR-EAE was passively transferred by lymph node cells (LNC) stimulated with myelin basic protein (BP). Sera were obtained serially from mice during both remissions and relapses of disease and were evaluated for the presence of anti-myelin antibodies using an avidin-biotin-immunoperoxidase technique. Four of six mice with CR-EAE induced with cord-CFA were positive for anti-myelin antibodies 15-124 days after inoculation, with 16 of 18 sera positive in these four mice. Two mice inoculated with cord-CFA did not have detectable serum anti-myelin antibodies, despite a clinical and histopathological picture indistinguishable from the antibody-positive mice. None of seven mice with CR-EAE passively transferred by BP-stimulated LNC had detectable anti-myelin antibodies in 30 sera obtained 7-141 days after cell transfer. We conclude that serum anti-myelin antibodies probably do not play a significant role in the pathogenesis of CR-EAE in SJL/J mice.

Animals↗