Growth behavior of cochlear nucleus neuronal cells on semiconductor substrates

Different Neurogenic Potential in the Subnuclei of the Postnatal Rat Cochlear Nucleus

In patients suffering from hearing loss, the reduced or absent neural input induces morphological changes in the cochlear nucleus (CN). Neural stem cells have recently been identified in this first auditory relay. Afferent nerve signals and their impact on the immanent neural stem and progenitor cells already impinge upon the survival of early postnatal cells within the CN. This auditory brainstem nucleus consists of three different subnuclei: the anteroventral cochlear nucleus (AVCN), the posteroventral cochlear nucleus (PVCN), and the dorsal cochlear nucleus (DCN). Since these subdivisions differ ontogenetically and physiologically, the question arose whether regional differences exist in the neurogenic niche. CN from postnatal day nine Sprague-Dawley rats were microscopically dissected into their subnuclei and cultivated in vitro as free-floating cell cultures and as whole-mount organ cultures. In addition to cell quantifications, immunocytological and immunohistological studies of the propagated cells and organ preparations were performed. The PVCN part showed the highest mitotic potential, while the AVCN and DCN had comparable activity. Specific stem cell markers and the ability to differentiate into cells of the neural lineage were detected in all three compartments. The present study shows that in all subnuclei of rat CN, there is a postnatal neural stem cell niche, which, however, differs significantly in its potential. The results can be explained by the origin from different regions in the rhombic lip, the species, and the various analysis techniques applied. In conclusion, the presented results provide further insight into the neurogenic potential of the CN, which may prove beneficial for the development of new regenerative strategies for hearing loss.

Advantageous environment of micro-patterned, high-density complementary metal-oxide-semiconductor electrode array for spiral ganglion neurons cultured in vitro

This study investigated micro-patterned, high-density complementary metal–oxide–semiconductor (CMOS) electrode array to be used as biologically permissive environment for organization, guidance and electrical stimulation of spiral ganglion neurons (SGN). SGNs extracted and isolated from cochleae of P5-P7 rat pups and adult guinea pigs were cultured 1, 4 and 7 days in vitro on glass coverslips (control) and CMOS electrode array. The cultures were analyzed visually and immunohistochemically for SGN presence, outgrowth, neurite alignment, neurite length, neurite asymmetry as well as the contact of a neuronal soma and neurites with the micro-electrodes. Our findings indicate that topographical environment of CMOS chip with micro-patterned pillars enhanced growth, survival, morphology, neural orientation and alignment of SGNs in vitro compared to control. Smaller spacing (0.8–1.6 µm) between protruding pillars on CMOS led SGNs to develop structured and guided neurites oriented along three topographical axes separated by 60°. We found morphological basis for positioning of the micro-electrodes on the chip that was appropriate for direct contact of SGNs with them. This configuration allowed CMOS electrode array to electrically stimulate the SGN whose responses were observed with live Fluo 4 calcium imaging.

Patterned semiconductor structures modulate neuronal outgrowth: Implication for the development of a neurobionic interface

Auditory implants stimulate the neurons by broad electrical fields, which leads to a low number of spectral channels. A reduction in the distance between the electrode and the neuronal structures might lead to better electrical transduction. The use of microstructured semiconductors offers a large number of contacts, which could attract neurons and stimulate them individually. To investigate the interaction between neurons and semiconductors, differentiated neuronal precursor cells were cultured on silicon wafers. Different structures were added on the wafers by electron beam lithography, and deep reactive ion etching in different depths (2 and 7 µm). Grooved surfaces guided the neurons and resulted in straight oriented axons, but neuronal outgrowth was impaired by the 7 µm grooves. Within the 7 µm structures, the neuronal cell body was totally encased and the nuclei were deformed from a round to an elliptical shape. On both square and cylindrical structures neuronal bridging could be detected in different forms, either between the tops of the structures or between the bottom and the top. Furthermore, neuronal bridges were established on the lateral part of the structures, and change in direction of neuronal growth was induced by the structure. Finally, it could be shown that neuronal growth cones were particularly attracted by the top of the cylinders, which might allow for the stimulation of neurons via this structure. In conclusion, study results indicate that structured semiconductors can modulate neuronal growth and its direction, offering a novel method for the development of new implants with improved neuronal stimulation. © 2017 Wiley Periodicals, Inc. J Biomed Mater Res Part A: 106A: 65-72, 2018.

Evaluation of silicon nitride as a substrate for culture of PC12 cells: an interfacial model for functional studies in neurons

Silicon nitride is a biocompatible material that is currently used as an interfacial surface between cells and large-scale integration devices incorporating ion-sensitive field-effect transistor technology. Here, we investigated whether a poly-L-lysine coated silicon nitride surface is suitable for the culture of PC12 cells, which are widely used as a model for neural differentiation, and we characterized their interaction based on cell behavior when seeded on the tested material. The coated surface was first examined in terms of wettability and topography using contact angle measurements and atomic force microscopy and then, conditioned silicon nitride surface was used as the substrate for the study of PC12 cell culture properties. We found that coating silicon nitride with poly-L-lysine increased surface hydrophilicity and that exposing this coated surface to an extracellular aqueous environment gradually decreased its roughness. When PC12 cells were cultured on a coated silicon nitride surface, adhesion and spreading were facilitated, and the cells showed enhanced morphological differentiation compared to those cultured on a plastic culture dish. A bromodeoxyuridine assay demonstrated that, on the coated silicon nitride surface, higher proportions of cells left the cell cycle, remained in a quiescent state and had longer survival times. Therefore, our study of the interaction of the silicon nitride surface with PC12 cells provides important information for the production of devices that need to have optimal cell culture-supporting properties in order to be used in the study of neuronal functions.

Dissociated neurons and glial cells derived from rat inferior colliculi after digestion with papain

The formation of gliosis around implant electrodes for deep brain stimulation impairs electrode–tissue interaction. Unspecific growth of glial tissue around the electrodes can be hindered by altering physicochemical material properties. However, in vitro screening of neural tissue–material interaction requires an adequate cell culture system. No adequate model for cells dissociated from the inferior colliculus (IC) has been described and was thus the aim of this study. Therefore, IC were isolated from neonatal rats (P3_5) and a dissociated cell culture was established. In screening experiments using four dissociation methods (Neural Tissue Dissociation Kit [NTDK] T, NTDK P; NTDK PN, and a validated protocol for the dissociation of spiral ganglion neurons [SGN]), the optimal media, and seeding densities were identified. Thereafter, a dissociation protocol containing only the proteolytic enzymes of interest (trypsin or papain) was tested. For analysis, cells were fixed and immunolabeled using glial- and neuron-specific antibodies. Adhesion and survival of dissociated neurons and glial cells isolated from the IC were demonstrated in all experimental settings. Hence, preservation of type-specific cytoarchitecture with sufficient neuronal networks only occurred in cultures dissociated with NTDK P, NTDK PN, and fresh prepared papain solution. However, cultures obtained after dissociation with papain, seeded at a density of 2×10⁴ cells/well and cultivated with Neuro Medium for 6 days reliably revealed the highest neuronal yield with excellent cytoarchitecture of neurons and glial cells. The herein described dissociated culture can be utilized as in vitro model to screen interactions between cells of the IC and surface modifications of the electrode.

Highly conductive carbon nanotube matrix accelerates developmental chloride extrusion in central nervous system neurons by increased expression of chloride transporter KCC2

Exceptional mechanical and electrical properties of carbon nanotubes (CNT) have attracted neuroscientists and neural tissue engineers aiming to develop novel devices that interface with nervous tissues. In the central nervous system (CNS), the perinatal chloride shift represents a dynamic change that forms the basis for physiological actions of γ-aminobutyric acid (GABA) as an inhibitory neurotransmitter, a process of fundamental relevance for normal functioning of the CNS. Low intra-neuronal chloride concentrations are maintained by a chloride-extruding transporter, potassium chloride cotransporter 2 (KCC2). KCC2's increasing developmental expression underlies the chloride shift. In neural injury, repressed KCC2 expression plays a co-contributory role by corrupting inhibitory neurotransmission. Mechanisms of Kcc2 up-regulation are thus pertinent because of their medical relevance, yet they remain elusive. Here, it is shown that primary CNS neurons originating from the cerebral cortex, cultured on highly-conductive few-walled-CNT (fwCNT) have a strikingly accelerated chloride shift caused by increased KCC2 expression. KCC2 upregulation is dependent on neuronal voltage-gated calcium channels (VGCC) and, furthermore, on calcium/calmodulin-dependent kinase II, which is linked to VGCC-mediated calcium-influx. It is also demonstrated that accelerated Kcc2 transcription in brain-slices prepared from genetically-engineered reporter mice, in which Kcc2 promoter drives luciferase, when the cerebral cortex of these mice is exposed to fwCNT-coated devices. Based on these findings, whether fwCNT can enhance neural engineering devices for the benefit of neural injury conditions associated with elevated neuronal intracellular chloride concentration-such as pain, epilepsy, traumatic neural injury and ischemia-can now be addressed. Taken together, our novel insights illustrate how fwCNTs can promote low neuronal chloride in individual neurons and thus inhibitory transmission in neural circuits.