The lack of classical lymph vessels within brain tissue complicates immune surveillance of the CNS, and therefore, cellular emigration out of the CNS parenchyma requires alternate pathways. Whereas invasion of blood-derived mononuclear cells and their transformation into ramified, microglia-like cells in areas of axonal degeneration across an intact BBB have been demonstrated, it still remained unclear whether these cells reside permanently, undergo apoptosis, or leave the brain to present antigen in lymphoid organs. With the use of ECL of mice and injection of GFP-expressing monocytes, we followed the appearance of injected cells in spleen and LNs and the migratory pathways in whole-head histological sections. Monocytes migrated from the lesion site to deep CLNs, peaking in number at Day 7, but they were virtually absent in spleen and in superficial CLNs and inguinal LNs until Day 21 after lesion/injection. In whole-head sections, GFP monocytes were found attached to the olfactory nerves and located within the nasal mucosa at 48 hpi. Thus, monocytes are capable of migrating from lesioned brain areas to deep CLNs and use the cribriform plate as an exit route.

Studies of axonal outgrowth and regeneration after spinal cord injury are hampered by the complexity of the events involved. Here, we present a simple and improved in vitro approach to investigate outgrowth, regeneration of the corticospinal tract, and intrinsic parenchymal responses. We prepared organotypic co-cultures using explants from the motor cortex of postnatal donor mice ubiquitously expressing green fluorescent protein and cervical spinal cord from wild type pups of the same age. Our data show that: a) motor-cortical outgrowth is already detectable after 1 d in culture and is source specific; b) treatment with neurotrophin-3 and C3 transferase from Clostridium botulinum significantly enhances axonal outgrowth during the course of cultivation; c) outgrowing axons form synaptic connections, as demonstrated by immunohistochemistry and calcium imaging; and d) migrating cells of motor-cortical origin can be reliably identified without previous tracing and are mostly neural precursors that survive and mature in the spinal cord parenchyma. Thus, our model is suitable for screening for candidate substances that enhance outgrowth and regeneration of the corticospinal tract and for studying the role of endogenous neural precursors after lesion induction.

The mechanical properties of cells are important for many biological processes, including wound healing, cancers, and embryogenesis. Currently, our understanding of cell mechanical properties remains incomplete. Different techniques have been used to probe different aspects of the mechanical properties of cells, among them microplate rheology, optical tweezers, micropipette aspiration, and magnetic twisting cytometry. These techniques have given rise to different theoretical descriptions, reaching from simple Kelvin-Voigt or Maxwell models to fractional such as power law models, and their combinations. Atomic force microscopy (AFM) is a flexible technique that enables global and local probing of adherent cells. Here, using an AFM, we indented single retinal pigmented epithelium cells adhering to the bottom of a culture dish. The indentation was performed at two locations: above the nucleus, and towards the periphery of the cell. We applied creep compliance, stress relaxation, and oscillatory rheological tests to wild type and drug modified cells. Considering known fractional and semi-fractional descriptions, we found the extracted parameters to correlate. Moreover, the Young’s modulus as obtained from the initial indentation strongly correlated with all of the parameters from the applied power-law descriptions. Our study shows that the results from different rheological tests are directly comparable. This can be used in the future, for example, to reduce the number of measurements in planned experiments. Apparently, under these experimental conditions, the cells possess a limited number of degrees of freedom as their rheological properties change.

Superparamagnetic iron oxide nanoparticles (SPIO) are applied as contrast media for magnetic resonance imaging (MRI) and treatment of neurologic diseases despite the fact that important information concerning their local interactions is still lacking. Due to their small size, SPIO have great potential for magnetically labeling different cell populations, facilitating their MRI tracking in vivo. Before SPIO are applied, however, their effect on cell viability and tissue homoeostasis should be studied thoroughly. We have previously published data showing how citrate-coated very small superparamagnetic iron oxide particles (VSOP) affect primary microglia and neuron cell cultures as well as neuron-glia cocultures. To extend our knowledge of VSOP interactions on the three-dimensional multicellular level, we further examined the influence of two types of coated VSOP (R1 and R2) on murine organotypic hippocampal slice cultures. Our data show that 1) VSOP can penetrate deep tissue layers, 2) long-term VSOP-R2 treatment alters cell viability within the dentate gyrus, 3) during short-term incubation VSOP-R1 and VSOP-R2 comparably modify hippocampal cell viability, 4) VSOP treatment does not affect cytokine homeostasis, 5) microglial depletion decreases VSOP uptake, and 6) microglial depletion plus VSOP treatment increases hippocampal cell death during short-term incubation. These results are in line with our previous findings in cell coculture experiments regarding microglial protection of neurite branching. Thus, we have not only clarified the interaction between VSOP, slice culture, and microglia to a degree but also demonstrated that our model is a promising approach for screening nanoparticles to exclude potential cytotoxic effects.