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

[Mental burden, resilience and tendency towards absenteeism among healthcare personnel in Germany during the first wave of the COVID-19 pandemic in spring 2020 : An ad hoc survey]

Hintergrund

Die COVID-19(„coronavirus disease 2019“)-Pandemie geht mit tiefgreifenden Änderungen im öffentlichen wie privaten Leben in Deutschland einher. Gesundheitspersonal ist dabei zusätzlich besonderen Belastungen ausgesetzt.

Ziel der Arbeit

In einer anonymen Querschnittsbefragung sollten die psychische Belastung, Resilienz, Absentismusneigung sowie assoziierte Faktoren in der COVID-19-Pandemie identifiziert werden.

Methoden

Unter einer nichtzufallsverteilten Stichprobe von Mitarbeitenden des Gesundheitswesens im Frühjahr 2020 (06.04. bis 07.05.2020) wurden Daten zu Soziodemographie, beruflicher Situation, Kontakt zu COVID-19-Patient*innen, psychischen Belastungen, Stressoren, Resilienz sowie Risiko- und Schutzfaktoren erhoben. Ein Vergleich mit Daten der Allgemeinbevölkerung in Deutschland vor und während der COVID-19-Pandemie wurde durchgeführt.

Ergebnisse

Nach der Auswertung 650 beantworteter Fragebögen fand sich im Vergleich zur deutschen Allgemeinbevölkerung vor der Pandemie eine höhere, im Vergleich zur Allgemeinbevölkerung während der Pandemie eine geringere psychische Belastung. Die Resilienz wurde etwas höher als in der Allgemeinbevölkerung vor und während der Pandemie eingeschätzt. COVID-19-bezogene Stressoren und Sorgen waren die wichtigsten Risikofaktoren, Selbstwirksamkeit und Optimismus die wichtigsten Schutzfaktoren. Die psychische Belastung korrelierte moderat mit dem Wunsch nach Berufswechsel und der Absentismusneigung.

Diskussion

Psychische Belastung von Gesundheitspersonal während der COVID-19-Pandemie geht mit einer verstärkten Neigung einher, sich krank zu melden. Um Gesundheitspersonal zu unterstützen, sollten besonders belasteten Gruppen Interventionen angeboten werden, die Schutzfaktoren wie Selbstwirksamkeit und Optimismus trainieren.

Zusatzmaterial online

Die Onlineversion dieses Beitrags (10.1007/s00115-021-01132-x) enthält umfangreiches Zusatzmaterial sowie weiterführende Literatur. Beitrag und Zusatzmaterial stehen Ihnen auf www.springermedizin.de zur Verfügung. Bitte geben Sie dort den Beitragstitel in die Suche ein, das Zusatzmaterial finden Sie beim Beitrag unter „Ergänzende Inhalte“.

The changeable nervous system: studies on neuroplasticity in cerebellar cultures

Circuit reorganization after injury was studied in a cerebellar culture model. When cerebellar cultures derived from newborn mice were exposed at explantation to a preparation of cytosine arabinoside that destroyed granule cells and oligodendrocytes and compromised astrocytes, Purkinje cells surviving in greater than usual numbers were unensheathed by astrocytic processes and received twice the control number of inhibitory axosomatic synapses. Purkinje cell axon collaterals sprouted and many of their terminals formed heterotypical synapses with other Purkinje cell dendritic spines. The resulting circuit reorganization preserved inhibition in the cerebellar cortex. Following this reorganization, replacement of the missing granule cells and glia was followed by a restitution of the normal circuitry. Most of these developmental and reconstructive changes were not dependent on neuronal activity, the major exception being inhibitory synaptogenesis. The full complement of inhibitory synapses did not develop in the absence of neuronal activity, which could be mitigated by application of exogenous TrkB receptor ligands. Inhibitory synaptogenesis could also be promoted by activity-induced release of endogenous TrkB receptor ligands or by antibody activation of the TrkB receptor.

Serial changes in granuloprival cerebellar cultures after transplantation with granule cells and glia: a timed ultrastructural study

Granuloprival cerebellar cultures derived from neonatal mice were transplanted at nine days in vitro with granule cells and glia, and the changes induced in the host explants were examined daily with the electron microscope from one to nine days post-transplantation. Granule cells and astrocytes had migrated into the host cultures within 24 h, and astrocytic processes began to ensheath Purkinje cells and to interpose themselves between axon terminals and Purkinje cell somata, reducing the number of axosomatic synapses. Occasional degenerating Purkinje cells were present. At two days post-transplantation, synapse formation between parallel fibre terminals and Purkinje cell dendritic spines was initially evident, and Purkinje cells began to proliferate dendritic spines near astrocytic processes. Degenerating Purkinje cells were more frequently encountered. Myelin was first observed in host cultures at three days after transplantation, and astrocytes continued to ensheath Purkinje cells and reduce the population of axosomatic synapses, a process that began to stabilize at four days post-transplantation. At this time astrocytic ensheathment had extended to Purkinje cell dendrites and dendritic spine synapses. Proliferation of Purkinje cell dendritic spines accelerated, and occasional synapses with presumptive parallel fibre terminals were present among clusters of proliferated spines. At five days after transplantation, contours of Purkinje cells were rounded, and there was a decrease of somatic spines and of synapses with somatic spines. Purkinje cells were fully ensheathed by astrocytic processes by six days post-transplantation and had assumed a mature appearance. Homotypical parallel fibre-Purkinje cell dendritic spine synapses were predominant in more developed areas of cortical neuropil as heterotypical recurrent axon collateral-Purkinje cell dendritic spine synapses were reduced. Increasing synapse formation was evident among clusters of proliferated spines, which continued at seven days post-transplantation, as the spine clusters became less frequent. At eight days after transplantation, space between Purkinje cells had increased and the cortical neuropil resembled that of comparably aged control cultures. Occasional degenerating Purkinje cells were still evident at nine days post-transplantation, at which time residual clusters of proliferated unattached dendritic spines were scarce. The sequence of changes after transplantation was consistent with the specific roles of the transplanted elements. Astrocytes were involved with the regulation of synapse density, including reduction of some heterotypical synapses, and induced proliferation of Purkinje cell dendritic spines. Granule cell axons synapsed with Purkinje cell dendritic spines, further reducing heterotypical synapses and restoring cortical circuitry to a near control state. The loss of heterotypical synapses was associated with programmed cell death of excess Purkinje cells, reducing the Purkinje cell population to control levels.

Neural plasticity in cerebellar cultures

Cerebellar granule cells and oligodendrocytes are destroyed and astrocytes are functionally compromised by exposure of organotypic cerebellar cultures derived from newborn mice to cytosine arabinoside for the first 5 days in vitro. Consequently, myelin does not form and Purkinje cells survive in increased numbers, but without astrocytic ensheathment. In the absence of glial sheaths, Purkinje cells have altered membrane properties and reduced input resistance. Their inhibitory recurrent axon collaterals sprout enormously and hyperinnervate the unensheathed somata of other Purkinje cells and form heterotypical synapses with Purkinje cell dendritic spines normally occupied by homotypical excitatory parallel fiber (granule cell axon) terminals. This reorganization of the cortical circuitry, in which recurrent axon collaterals are the dominant inhibitory elements, allows retention of some inhibition in the absence of parallel fiber excitation of the inhibitory interneurons. In the absence of neuronal activity, the full complement of inhibitory synapses is not developed and the cultures exhibit sustained cortical hyperactivity after recovery from the blockade. If granule cells and glia are replaced, a second round of reorganization ensues, in the direction of restoration of the normal cortical circuitry. The cultures are myelinated and the number of recurrent axon collaterals is reduced. Astrocytes ensheath Purkinje cell somata and strip excess axosomatic synapses, as well as eliminate some of the heterotypical synapses in the cortical neuropil. Parallel fibers synapse with already present Purkinje cell dendritic spines and with newly proliferated spines, the latter induced by an astrocyte secreted factor. As homotypical synapses develop and heterotypical synapses decline, Purkinje cells undergo apoptosis and their population is reduced to control levels. With the restoration of parallel fiber excitation, recurrent axon collaterals are no longer the dominant cortical inhibitory elements. If neuronal activity is blocked as the granule cells and glia are replaced, there is incomplete formation of inhibitory synapses, and cortical discharges are hyperactive after recovery from activity blockade.

The cerebellar model of neural grafting: structural integration and functional recovery

A synopsis is presented of the recent history of cerebellar tissue transplantation over the past 25 years. The properties of growth and differentiation of cerebellar grafts placed intraocularly or intracranially are reviewed, as well as the interaction of heterotopic and orthotopic grafts with the host brain. Particular emphasis is placed on the use of ataxic mouse mutants as recipients of donor cerebellar tissue for the correction of their structural deficits and the functional recovery of behavioural responses.