Properties of cochlear nucleus neurons in primary culture

Isolation and culture of adult mouse vestibular nucleus neurons

Background/aim: Isolated cell cultures are widely used to study neuronal properties due to their advantages. Although embryonic animals are preferred for culturing, their morphological or electrophysiological properties may not reflect adult neurons, which may be important in neurodegenerative diseases. This paper aims to develop a method for preparing isolated cell cultures of medial vestibular nucleus (MVN) from adult mice and describe its morphological and electrophysiological properties.Materials and methods: Vestibular nucleus neurons were mechanically and enzymatically isolated and cultured using a defined medium with known growth factors. Cell survival was measured with propidium iodide, and electrophysiological properties were investigated with current-clamp recording.Results: Vestibular neurons grew neurites in cultures, gaining adult-like morphological properties, and stayed viable for 3 days in culture. Adding bovine calf serum, nerve growth factor, or insulin-like growth factor into the culture medium enhanced neuronal viability. Current-clamp recording of the cultured neurons revealed tonic and phasic-type neurons with similar input resistance, resting membrane potential, action potential amplitude, and duration. Conclusion: Vestibular neurons from adult mice can be cultured, and regenerate axons in a medium containing appropriate growth factors. Culturing adult vestibular neurons provides a new method to study age-related pathologies of the vestibular system.

Multiple Sclerosis Patient-Specific Primary Neurons Differentiated from Urinary Renal Epithelial Cells via Induced Pluripotent Stem Cells

As multiple sclerosis research progresses, it is pertinent to continue to develop suitable paradigms to allow for ever more sophisticated investigations. Animal models of multiple sclerosis, despite their continuing contributions to the field, may not be the most prudent for every experiment. Indeed, such may be either insufficient to reflect the functional impact of human genetic variations or unsuitable for drug screenings. Thus, we have established a cell- and patient-specific paradigm to provide an in vitro model within which to perform future genetic investigations. Renal proximal tubule epithelial cells were isolated from multiple sclerosis patients’ urine and transfected with pluripotency-inducing episomal factors. Subsequent induced pluripotent stem cells were formed into embryoid bodies selective for ectodermal lineage, resulting in neural tube-like rosettes and eventually neural progenitor cells. Differentiation of these precursors into primary neurons was achieved through a regimen of neurotrophic and other factors. These patient-specific primary neurons displayed typical morphology and functionality, also staining positive for mature neuronal markers. The development of such a non-invasive procedure devoid of permanent genetic manipulation during the course of differentiation, in the context of multiple sclerosis, provides an avenue for studies with a greater cell- and human-specific focus, specifically in the context of genetic contributions to neurodegeneration and drug discovery.

Effects of the neurotrophic factors BDNF, NT-3, and FGF2 on dissociated neurons of the cochlear nucleus

The cochlear nucleus is the first relay station for acoustic information in the auditory pathway and its cellular integrity is affected by hearing loss. Neurotrophic factors, which are known to regulate fundamental processes in the brain, are expressed in the cochlear nucleus and are regulated by the changes in the stimulation. The aim of this study was to evaluate the effect of the neurotrophins Brain derived neurotrophic factor (BDNF) and Neurotrophin 3 (NT-3) and the neurotrophic factor Fibroblast growth factor 2 (FGF2) on primary cultured cells of the mouse cochlear nucleus. No effect on overall cell growth was detected after 8 days in culture by the factors applied. NT-3 had a strong impact on enhancement of neuronal survival, whereas BDNF stimulated neuronal survival and axonal outgrowth. Axonal branching was negatively affected by the administration of BDNF. FGF2 did not show any effect. The results presented represent fundamental research on auditory neurons, but might be one step toward defining novel therapeutic strategies in the future to prevent cochlear nucleus degeneration induced by hearing loss.

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.

Growth behavior of cochlear nucleus neuronal cells on semiconductor substrates

Auditory brainstem implants provide sound information by direct stimulation of the cochlear nucleus to patients with dysfunctional or absent cranial nerve VIII. In contrast to patients with cochlear implants, the use of the auditory brainstem implants is less successful. This cannot be fully explained by the difference location of stimulation but a rather unspecific neuronal stimulation. The aim of this study was to further examine neuronal cells of the cochlear nucleus and to test their interactions with semiconductor substrates as a potential electrode material for improved auditory brainstem implants. The cochlear nuclei of postnatal day 7 rats were microsurgically dissected. The tissue was dissociated enzymatically and plated on coverslips as control and on the semiconductor substrates silicon or silicon nitride. After 4 days in culture the morphology and growth of dissociated cells was determined by fluorescence and scanning electron microscopy. Dissociated cells of the cochlear nucleus showed reduced cell growth on semiconductor substrates compared with controls. SEM analysis demonstrated close contact of neurons with supporting cells in culture and good adherence of neuronal growth cones on the used materials. These findings present basic knowledge for the development of neuron-electrode interfaces for future auditory brainstem implants.

Neuronal differentiation of the early embryonic auditory hindbrain of the chicken in primary culture

Neurons in the auditory hindbrain pathway of the chicken are physiologically and morphologically highly specialized. It remains unclear to what extent independent differentiation vs. activity-dependent mechanisms determines the development of this system. To address this question we established a primary culture system of the early auditory hindbrain neurons. Primary cultures of neurons from nucleus magnocellularis and nucleus laminaris were prepared from embryonic day 6.5 chicken. These cells developed in culture under serum-free conditions for up to 15 days. Immunocytochemical staining and whole-cell patch recordings were used to characterize the development of the neurons. A stable expression of the calcium-binding protein calretinin, which serves as a characteristic marker of the auditory pathway, was found at all stages. A voltage-gated potassium channel (Kv3.1b) with a specific function in the auditory system was also expressed after about 1 week in culture. Electrophysiological recordings showed a general maturation of the neuronal phenotype as reflected by an increase in the mean resting membrane potential, a decrease in the mean input resistance as well as a maturation of action potential parameters. Four groups of neurons that generate action potentials could be distinguished. One of these showed the phasic firing pattern of auditory brainstem neurons known from slice preparations. In older cultures we demonstrated functional synaptogenesis in vitro by recording postsynaptic activity elicited by extracellular stimulation and styryl dye loading of vesicles. Thus, isolated neurons from the auditory region of the avian brainstem differentiate to specific neuronal subtypes and autonomously develop synaptic connections in vitro.

Selective cultivation of N-cadherin expressing cells from the optic tectum of the chick

Dissociated primary cell cultures of the nervous system are usually composed of many different cell types, which makes it difficult to investigate a specific cell type and to describe its development in vitro without direct or indirect influence of other cell types. Although various methods have been published to specifically separate either neurons or glial cells, there is still a need for simple protocols to isolate distinct neuronal subpopulations. Here we describe a method to purify specific neuronal subtypes from the chick embryonic midbrain. Embryonic (E10) optic tecta were dissociated and a cell suspension was produced. Cells were separated by magnetic cell sorting (MACS) based on their specific expression of somatic N-cadherin. After cultivation on poly-D-lysine coated dishes in serum-free culture medium supplemented with B27, cells were fixed and analyzed with immuncytochemistry. Enriched primary cultures contained about 70% of N-cadherin positive cells compared to 46% before sorting. 7 days after cultivation, N-cadherin expression and its co-localization with synapses was demonstrated.

Morphology of neurons cultured from subdivisions of the mouse cochlear nucleus

This study was designed to characterize the dendritic organization of cochlear nucleus (CN) cells grown in primary cell culture and to assess differences among cultures grown from different regions of CN. Cultures were prepared from postnatal mice and processed using microtubule-associated protein 2 (MAP2) or gamma-aminobutyric acid (GABA) immunohistochemistry. CN neurons were successfully cultured from preparations grown from either the anteroventral subdivision of the nucleus (AVCN), the posterior region [posteroventral (PVCN) and dorsal (DCN) subnuclei], or the whole CN, although the cultured neurons did not exhibit complex dendritic patterns characteristic of CN neurons in vivo. Neurons cultured from the entire nucleus exhibited an increased rate of survival compared to those cultured from either the anterior or posterior regions, although similar types of cells were observed in all preparations. The majority of cultured CN neurons were GABA-positive and had soma areas that were similar to the areas of immature GABAergic neurons measured in CN sections. Small cells (soma areas <or=60 microm(2)) with one to three symmetrically organized dendrites and large non-GABAergic cells (>or=120 microm(2)) were also present in significant numbers. Overall, CN cultures consisted of a heterogeneous population of neurons that had less elaborate dendritic organizations than cells of corresponding size that have been described in adult animals in vivo.

Survival and differentiation of neurons cultured from the mouse cochlear nucleus on extracellular matrix components

This study was designed to determine the effects of several extracellular matrix (ECM) proteins on the survival and differentiation of cochlear nucleus (CN) neurons grown in primary cell culture. CN neurons were successfully grown on laminin, collagen and fibronectin, but neuronal survival was significantly decreased on all three substrates relative to poly-D-lysine controls. In addition, analysis of dendrite organization patterns indicated that CN neurons branched more extensively when grown on poly-D-lysine than on any of the ECM components tested. Although dendrite growth has been shown to depend strongly on the presence of ECM components in other neuronal systems, the data from these experiments do not support the hypothesis that laminin, collagen or fibronectin is necessary for the survival and differentiation of CN neurons.

Effects of deafferentation on the electrophysiology of ventral cochlear nucleus neurons

When cochlear pathology impairs the afferent innervation of the ventral cochlear nucleus (VCN), electrical responses of the auditory brainstem are altered and changes in cell and synaptic morphology are observed. However, the impact of deafferentation on the electrical properties of cells in the VCN is unknown. We examined the electrical properties of single neurons in the anterior and posterior VCN following bilateral cochlear removal in young rats. In control animals, two populations of cells were distinguished: those with a linear subthreshold current-voltage relationship and repetitive firing of action potentials with regular interspike intervals (type I), and those with rectifying subthreshold current-voltage relationships and phasic firing of 1-3 action potentials (type II). Measures of action potential shape further distinguished these two groups. Two weeks following cochlear removal, both electrical response patterns were still seen. Type I cells showed a higher input resistance. Deafferented single-spiking type II cells were slightly more depolarized, had smaller action potentials, smaller afterhyperpolarizations and shorter membrane time constants, whereas multiple-spiking type II cells were apparently unaffected. These changes in the electrical properties of VCN neurons following cochlear injury may adversely affect central processing of sounds presented acoustically or electrically by prostheses.