Suppression of excitotoxicity and foreign body response by memantine in chronic cannula implantation into the rat brain

Local Administrations of Iron Oxide Nanoparticles in the Prefrontal Cortex and Caudate Putamen of Rats Do Not Compromise Working Memory and Motor Activity

Iron oxide nanoparticles (IONPs) have come into focus for their use in medical applications although possible health risks for humans, especially in terms of brain functions, have not yet been fully clarified. The present study investigates the effects of IONPs on neurobehavioural functions in rats. For this purpose, we infused dimercaptosuccinic acid-coated IONPs into the medial prefrontal cortex (mPFC) and caudate putamen (CPu). Saline (VEH) and ferric ammonium citrate (FAC) were administered as controls. One- and 4-week post-surgery mPFC-infused animals were tested for their working memory performance in the delayed alternation T-maze task and in the open field (OF) for motor activity, and CPu-infused rats were tested for their motor activity in the OF. After completion of the experiments, the brains were examined histologically and immunohistochemically. We did not observe any behavioural or structural abnormalities in the rats after administration of IONPs in the mPFC and the CPu. In contrast, administration of FAC into the CPu resulted in decreased motor activity and increased the number of microglia in the mPFC. Perls' Prussian blue staining revealed that FAC- and IONP-treated rats had more iron-containing ramified cells than VEH-treated rats, indicating iron uptake by microglia. Our results demonstrate that local infusions of IONPs into selected brain regions have no adverse impact on locomotor behaviour and working memory.

Effects of Local Administration of Iron Oxide Nanoparticles in the Prefrontal Cortex, Striatum, and Hippocampus of Rats

Iron oxide nanoparticles (IONPs) are used for diverse medical approaches, although the potential health risks, for example adverse effects on brain functions, are not fully clarified. Several in vitro studies demonstrated that the different types of brain cells are able to accumulate IONPs and reported a toxic potential for IONPs, at least for microglia. However, little information is available for the in vivo effects of direct application of IONPs into the brain over time. Therefore, we examined the cellular responses and the distribution of iron in the rat brain at different time points after local infusion of IONPs into selected brain areas. Dispersed IONPs or an equivalent amount of low molecular weight iron complex ferric ammonium citrate or vehicle were infused into the medial prefrontal cortex (mPFC), the caudate putamen (CPu), or the dorsal hippocampus (dHip). Rats were sacrificed 1 day, 1 week, or 4 weeks post-infusion and brain sections were histologically examined for treatment effects on astrocytes, microglia, and neurons. Glial scar formation was observed in the mPFC and CPu 1 week post-infusion independent of the substance and probably resulted from the infusion procedure. Compared to vehicle, IONPs did not cause any obvious additional adverse effects and no additional tissue damage, while the infusion of ferric ammonium citrate enhanced neurodegeneration in the mPFC. Results of iron staining indicate that IONPs were mainly accumulated in microglia. Our results demonstrate that local infusions of IONPs in selected brain areas do not cause any additional adverse effects or neurodegeneration compared to vehicle.

High-density microfibers as a potential optical interface to reach deep brain regions

OBJECTIVE

Optical techniques for recording and manipulating neural activity have traditionally been constrained to superficial brain regions due to light scattering. New techniques are needed to extend optical access to large 3D volumes in deep brain areas, while retaining local connectivity.

APPROACH

We have developed a method to implant bundles of hundreds or thousands of optical microfibers, each with a diameter of 8 μm. During insertion, each fiber moves independently, following a path of least resistance. The fibers achieve near total internal reflection, enabling optically interfacing with the tissue near each fiber aperture.

MAIN RESULTS

At a depth of 3 mm, histology shows fibers consistently splay over 1 mm in diameter throughout the target region. Immunohistochemical staining after chronic implants reveals neurons in close proximity to the fiber tips. Models of photon fluence indicate that fibers can be used as a stimulation light source to precisely activate distinct patterns of neurons by illuminating a subset of fibers in the bundle. By recording fluorescent beads diffusing in water, we demonstrate the recording capability of the fibers.

SIGNIFICANCE

Our histology, modeling and fluorescent bead recordings suggest that the optical microfibers may provide a minimally invasive, stable, bidirectional interface for recording or stimulating genetic probes in deep brain regions-a hyper-localized form of fiber photometry.

Extracting individual neural activity recorded through splayed optical microfibers

Previously introduced bundles of hundreds or thousands of microfibers have the potential to extend optical access to deep brain regions, sampling fluorescence activity throughout a three-dimensional volume. Each fiber has a small diameter ( 8    μ m ) and follows a path of least resistance, splaying during insertion. By superimposing the fiber sensitivity profile for each fiber, we model the interface properties for a simulated neural population. Our modeling results suggest that for small ( < 200 ) bundles of fibers, each fiber will collect fluorescence from a small number of nonoverlapping neurons near the fiber apertures. As the number of fibers increases, the bundle delivers more uniform excitation power to the region, moving to a regime where fibers collect fluorescence from more neurons and there is greater overlap between neighboring fibers. Under these conditions, it becomes feasible to apply source separation to extract individual neural contributions. In addition, we demonstrate a source separation technique particularly suited to the interface. Our modeling helps establish performance expectations for this interface and provides a framework for estimating neural contributions under a range of conditions.

Rodent Behavioral Testing to Assess Functional Deficits Caused by Microelectrode Implantation in the Rat Motor Cortex

Medical devices implanted in the brain hold tremendous potential. As part of a Brain Machine Interface (BMI) system, intracortical microelectrodes demonstrate the ability to record action potentials from individual or small groups of neurons. Such recorded signals have successfully been used to allow patients to interface with or control computers, robotic limbs, and their own limbs. However, previous animal studies have shown that a microelectrode implantation in the brain not only damages the surrounding tissue but can also result in functional deficits. Here, we discuss a series of behavioral tests to quantify potential motor impairments following the implantation of intracortical microelectrodes into the motor cortex of a rat. The methods for open field grid, ladder crossing, and grip strength testing provide valuable information regarding the potential complications resulting from a microelectrode implantation. The results of the behavioral testing are correlated with endpoint histology, providing additional information on the pathological outcomes and impacts of this procedure on the adjacent tissue.

Microelectrode implantation in motor cortex causes fine motor deficit: Implications on potential considerations to Brain Computer Interfacing and Human Augmentation

Intracortical microelectrodes have shown great success in enabling locked-in patients to interact with computers, robotic limbs, and their own electrically driven limbs. The recent advances have inspired world-wide enthusiasm resulting in billions of dollars invested in federal and industrial sponsorships to understanding the brain for rehabilitative applications. Additionally, private philanthropists have also demonstrated excitement in the field by investing in the use of brain interfacing technologies as a means to human augmentation. While the promise of incredible technologies is real, caution must be taken as implications regarding optimal performance and unforeseen side effects following device implantation into the brain are not fully characterized. The current study is aimed to quantify any motor deficit caused by microelectrode implantation in the motor cortex of healthy rats compared to non-implanted controls. Following electrode insertion, rats were tested on an open-field grid test to study gross motor function and a ladder test to study fine motor function. It was discovered that rats with chronically indwelling intracortical microelectrodes exhibited up to an incredible 527% increase in time to complete the fine motor task. This initial study defines the need for further and more robust behavioral testing of potential unintentional harm caused by microelectrode implantation.

Reduction of the foreign body response and neuroprotection by apyrase and minocycline in chronic cannula implantation in the rat brain

Implantation of electrodes or cannulae into the brain is accompanied by a tissue response referred to as foreign body response. Adenosine triphosphate (ATP) is one of the signalling molecules released by injured cells which mediate the chemoattraction of microglial cells. The constitutive release of pro-inflammatory and cytotoxic substances by microglial cells in chronic implants exacerbates neuronal cell death and the immune response. This study aimed to interfere with the initial events of the foreign body response in order to mitigate neurotoxicity and inflammation. For this purpose, the ATP-hydrolysing enzyme apyrase and the antibiotic minocycline with a broad range of anti-inflammatory, anti-apoptotic and glutamate-antagonist properties were locally infused during cannula implantation in the caudal forelimb area of the motor cortex in Lister Hooded rats. The rats' motor performance was assessed in a skilled reaching task and the distribution of neurons and glial cells in the vicinity of the implant was examined 2 and 6 weeks post-implantation. Apyrase as well as minocycline increased the number of surviving neurons and reduced microglial activation. Moreover, minocycline improved the motor performance and, additionally, caused a temporary reduction in astrogliosis, suggesting it as a possible therapeutic candidate to improve the biocompatibility of chronic brain implants.

The gene BRAF is underexpressed in bipolar subject olfactory neuroepithelial progenitor cells undergoing apoptosis

BACKGROUND

Bipolar disorder is a devastating psychiatric condition that frequently results in various degrees of brain tissue loss, cognitive decline, and premature death. The documentation of brain tissue loss implicates apoptosis as the likely underlying degenerative process, but direct experimental demonstration is lacking.

METHODS

Olfactory neuroepithelial biopsies from individuals with and without bipolar I disorder yielded olfactory neuroepithelial progenitor cells (ONPs), which spontaneously differentiate into neurons and glia. Glutamate, 0.1M, for 3 and 6h was used to induce apoptosis. Genes involved in the apoptotic pathway were interrogated with micro-array analysis before and after glutamate treatment for 6h. Confirmation was accomplished with real-time PCR. Total and phospho-B-Raf protein levels were measured using Western blot analysis.

RESULTS

ONPs from bipolar individuals demonstrated significantly greater apoptosis than cells from non-bipolar subjects. Microarray results revealed 12 differentially expressed genes. Five genes were further examined. BRAF mRNA and protein levels were significantly reduced in bipolar ONPs.

CONCLUSIONS

ONPs with the genetic heritage of bipolar I disorder were more sensitive to glutamate induced apoptosis. Under expression of the BRAF gene and protein, which plays a role in regulating the pro-survival MEK/ERK signaling pathway, may contribute to this apoptotic sensitivity.