Nicotine‐mediated neuroprotection of rat spinal networks against excitotoxicity

Soft monolithic infrared neural interface for simultaneous neurostimulation and electrophysiology

Controlling neuronal activity using implantable neural interfaces constitutes an important tool to understand and develop novel strategies against brain diseases. Infrared neurostimulation is a promising alternative to optogenetics for controlling the neuronal circuitry with high spatial resolution. However, bi-directional interfaces capable of simultaneously delivering infrared light and recording electrical signals from the brain with minimal inflammation have not yet been reported. Here, we have developed a soft fibre-based device using high-performance polymers which are >100-fold softer than conventional silica glass used in standard optical fibres. The developed implant is capable of stimulating the brain activity in localized cortical domains by delivering laser pulses in the 2 μm spectral region while recording electrophysiological signals. Action and local field potentials were recorded in vivo from the motor cortex and hippocampus in acute and chronic settings, respectively. Immunohistochemical analysis of the brain tissue indicated insignificant inflammatory response to the infrared pulses while the signal-to-noise ratio of recordings still remained high. Our neural interface constitutes a step forward in expanding infrared neurostimulation as a versatile approach for fundamental research and clinically translatable therapies.

A mechanistic overview of spinal cord injury, oxidative DNA damage repair and neuroprotective therapies

Despite substantial development in medical treatment strategies scientists are struggling to find a cure against spinal cord injury (SCI) which causes long term disability and paralysis. The prime rationale behind it is the enlargement of primary lesion due to an initial trauma to the spinal cord which spreads to the neighbouring spinal tissues It begins from the time of traumatic event happened and extends to hours and even days. It further causes series of biological and functional alterations such as inflammation, excitotoxicity and ischemia, and promotes secondary lesion to the cord which worsens the life of individuals affected by SCI. Oxidative DNA damage is a stern consequence of oxidative stress linked with secondary injury causes oxidative base alterations and strand breaks, which provokes cell death in neurons. It is implausible to stop primary damage however it is credible to halt the secondary lesion and improve the quality of the patient's life to some extent. Therefore it is crucial to understand the hidden perspectives of cell and molecular biology affecting the pathophysiology of SCI. Thus the focus of the review is to connect the missing links and shed light on the oxidative DNA damages and the functional repair mechanisms, as a consequence of the injury in neurons. The review will also probe the significance of neuroprotective strategies in the present scenario. HIGHLIGHTSSpinal cord injury, a pernicious condition, causes excitotoxicity and ischemia, ultimately leading to cell death.Oxidative DNA damage is a consequence of oxidative stress linked with secondary injury, provoking cell death in neurons.Base excision repair (BER) is one of the major repair pathways that plays a crucial role in repairing oxidative DNA damages.Neuroprotective therapies curbing SCI and boosting BER include the usage of pharmacological drugs and other approaches.

The Reassessed Impact of Nicotine against Neurotoxicity in Mesencephalic Dopaminergic Cell Cultures and Neuroblastoma N18TG2 Cells

Neuroprotective effects of nicotine are still under debate, so further studies on its effectiveness against Parkinson's disease are required. In our present study, we used primary dopaminergic cell cultures and N18TG2 neuroblastoma cells to investigate the effect of nicotine and its neuroprotective potential against rotenone toxicity. Nicotine protected dopaminergic (tyrosine hydroxylase immunoreactive) neurons against rotenone. This effect was not nAChR receptor-dependent. Moreover, the alkaloid at a concentration of 5 µM caused an increase in neurite length, and at a concentration of 500 µM, it caused an increase in neurite count in dopaminergic cells exposed to rotenone. Nicotine alone was not toxic in either cell culture model, while the highest tested concentration of nicotine (500 µM) caused growth inhibition of N18TG2 neuroblastoma cells. Nicotine alone increased the level of glutathione in both cell cultures and also in rotenone-treated neuroblastoma cells. The obtained results may be helpful to explain the potential neuroprotective action of nicotine on neural cell cultures.

Viral strategies for targeting spinal neuronal subtypes in adult wild-type rodents

Targeting specific subtypes of interneurons in the spinal cord is primarily restricted to a small group of genetic model animals. Since the development of new transgenic model animals can be expensive and labor intensive, it is often difficult to generalize these findings and verify them in other model organisms, such as the rat, ferret or monkey, that may be more beneficial in certain experimental investigations. Nevertheless, endogenous enhancers and promoters delivered using an adeno-associated virus (AAV) have been successful in providing expression in specific subtypes of neurons in the forebrain of wildtype animals, and therefore may introduce a shortcut. GABAergic interneurons, for instance, have successfully been targeted using the mDlx promoter, which has recently been developed and is now widely used in wild type animals. Here, we test the specificity and efficiency of the mDlx enhancer for robust targeting of inhibitory interneurons in the lumbar spinal cord of wild-type rats using AAV serotype 2 (AAV2). Since this has rarely been done in the spinal cord, we also test the expression and specificity of the CamKIIa and hSynapsin promoters using serotype 9. We found that AAV2-mDlx does in fact target many neurons that contain an enzyme for catalyzing GABA, the GAD-65, with high specificity and a small fraction of neurons containing an isoform, GAD-67. Expression was also seen in some motor neurons although with low correlation. Viral injections using the CamKIIa enhancer via AAV9 infected in some glutamatergic neurons, but also GABAergic neurons, whereas hSynapsin via AAV9 targets almost all the neurons in the lumbar spinal cord.

Adaptive polymer fiber neural device for drug delivery and enlarged illumination angle for neuromodulation

OBJECTIVE

Optical fiber devices constitute significant tools for the modulation and interrogation of neuronal circuitry in the mid and deep brain regions. The illuminated brain area during neuromodulation has a direct impact on the spatio-temporal properties of the brain activity and depends solely on the material and geometrical characteristics of the optical fibers. In the present work, we developed two different flexible polymer optical fibers (POFs) with integrated microfluidic channels (MFCs) and an ultra-high numerical aperture (UHNA) for enlarging the illumination angle to achieve efficient neuromodulation.

APPROACH

Three distinct thermoplastic polymers: polysulfone (PSU), polycarbonate (PC), and fluorinated ethylene propylene (FEP) were used to fabricate two step-index UHNA POF neural devices using a scalable thermal drawing process. The POFs were characterized in terms of their illumination map as well as their fluid delivery capability in phantom and adult rat brain slices.

MAIN RESULTS

A 100-fold reduced bending stiffness of the proposed fiber devices compared to their commercially available counterparts has been found. The integrated MFCs can controllably deliver dye (trypan blue) on-demand over a wide range of injection rates spanning from 10 nL/min to 1000 nL/min. Compared with commercial silica fibers, the proposed UHNA POFs exhibited an increased illumination area by 17% and 21% under 470 and 650 nm wavelength, respectively. In addition, a fluorescent light recording experiment has been conducted to demonstrate the ability of our UHNA POFs to be used as optical waveguides in fiber photometry.

SIGNIFICANCE

Our results overcome the current technological limitations of fiber implants that have limited illumination area and we suggest that soft neural fiber devices can be developed using different custom designs for illumination, collection, and photometry applications. We anticipate our work to pave the way towards the development of next-generation functional optical fibers for neuroscience.

Characterization, Cytotoxicity and Anti-Inflammatory Effect Evaluation of Nanocapsules Containing Nicotine

(1) Background: Nanotechnology is an emerging field that can be applied in the biomedical area. In this study, Eudragit nanocapsules (NCs) containing nicotine were produced. Nicotine is the main alkaloid found in tobacco and has anti-inflammatory properties. NCs containing nicotine may be used as an adjuvant therapy in the treatment of inflammation in the central nervous system. (2) Methods: Nanocapsules were prepared by the interfacial deposition of the pre-formed polymer method and characterized in terms of zeta potential, diameter, polydispersity index, pH, encapsulation efficiency (EE), stability and sustained release profile. In vitro tests with the PC12 cell line were performed, such as MTT, LIVE/DEAD and ELISA assays, to verify their cytotoxic and anti-inflammatory effects. (3) Results: The nanocapsules presented satisfactory values of the characterization parameters; however, poor encapsulation was obtained for nicotine (8.17% ± 0.47). The in vitro tests showed that the treatment with nanocapsules reduced cell viability, which suggests that the Eudragit or the amount of polymer on top of the cells may be detrimental to them, as the cells were able to survive when treated with bulk nicotine. ELISA showed an increment in the expression of IL-6 and IL-1β, corroborating the hypothesis that NCs were toxic to the cells because of the increase in the levels of these pro-inflammatory cytokines. (4) Conclusions: This study demonstrates that NCs of Eudragit present toxicity. It is therefore necessary to improve NC formulation to obtain better values for the encapsulation efficiency and reduce toxicity of these nanodevices.

Nicotine Neurotoxicity Involves Low Wnt1 Signaling in Spinal Locomotor Networks of the Postnatal Rodent Spinal Cord

The postnatal rodent spinal cord in-vitro is a useful model to investigate early pathophysiological changes after injury. While low dose nicotine (1 µM) induces neuroprotection, how higher doses affect spinal networks is unknown. Using spinal preparations of postnatal wild-type Wistar rat and Wnt1Cre2:Rosa26Tom double-transgenic mouse, we studied the effect of nicotine (0.5–10 µM) on locomotor networks in-vitro. Nicotine 10 µM induced motoneuron depolarization, suppressed monosynaptic reflexes, and decreased fictive locomotion in rat spinal cord. Delayed fall in neuronal numbers (including motoneurons) of central and ventral regions emerged without loss of dorsal neurons. Conversely, nicotine (0.5–1 µM) preserved neurons throughout the spinal cord and strongly activated the Wnt1 signaling pathway. High-dose nicotine enhanced expression of S100 and GFAP in astrocytes indicating a stress response. Excitotoxicity induced by kainate was contrasted by nicotine (10 µM) in the dorsal area and persisted in central and ventral regions with no change in basal Wnt signaling. When combining nicotine with kainate, the activation of Wnt1 was reduced compared to kainate/sham. The present results suggest that high dose nicotine was neurotoxic to central and ventral spinal neurons as the neuroprotective role of Wnt signaling became attenuated. This also corroborates the risk of cigarette smoking for the foetus/newborn since tobacco contains nicotine.

Dataset on inflammation induced after lumbar puncture

Neuroinflammation is evident and one of the primary induced responses after central nervous system (CNS) injury, lumbar puncture and CNS surgery. In rare cases, complications could arise after the lumbar puncture or CNS surgery leading to inflammation, bleeding or other problems such as cerebrospinal fluid (CSF) leakage. The present dataset describes the occurrence of such a condition after the dura breakage or postoperative complication leading to the development of neuroinflammation in the adult Wistar rats. Therefore, objective of the study is to report such a rare condition and detect the most reliable glial proteins upregulated 2-3 weeks after the lumbar puncture which may help the neuroscience community to a better understanding their cause of action. In response to neuroinflammation, glial cells leak into the extracellular space, where they can be identified in the CSF or serum and may act as diagnostic biomarkers.

Laminectomy was performed at the thoraco-lumbar (T12-L1) region and the dura was punctured. After that, the exposed part was covered with silica gel and adhesive followed by dental cement. The skin was closed using sterile sutures. After, the rats were given buprenorphine (0.05 mg/kg, every 8 h for 3 days) and carprofen (5 mg/kg, once a day for 5 days) as analgesic and anti-inflammatory and baytril (5 mg/kg, once a day for 10 days) as antibiotic drugs. Note, the buprenorphine and lidocaine were also given before starting the procedure. After the laminectomy, the functional outcomes of the rats were tested (starting from the day of surgery to the last day) and the rats which were locomoting normally using all the limbs were included in the study. In case of any decompression, the functional outcomes showing any kind of laming or partial paralysis of hindlimbs were excluded from the study. Unexpected neuroinflammation has occurred 2-3 weeks after performing the given procedure.

Data presented in the article implicate active microglia measured by using protein biomarker such as Iba-1 [1, 3] and astrocytes measured by using Glial fibrillary acidic protein (GFAP) [2, 3] and S100 (strongly targets S100B and weakly A1) [7, 8] in the CSF collected two-three weeks after the laminectomy and dura breakage from the adult rats. Later paraformaldehyde (PFA) fixed spinal cord slices were also collected from the animals and immunolabelled with the same biomarkers. Western blots were performed with the collected CSF which showed high expression of glial markers such as GFAP, Iba-1 and S100 which has shown to target S100B with no expression of A1 (or A2, play an important role in neuroprotection) astrocytes which have recently been shown to be produced by microglia at the site of injury [9]. However, S100B [10] and GFAP [2] are known to be adequately discharged by the distinct cells in stress conditions which seems to occur in the present report. In addition, the spinal slices immunolabelled with the same biomarkers also showed increased expression of glia. Cross-talk between microglia-astrocyte in CNS stress is crucial for the neurons to survive and function after the injury. Reactive microglia (shown by high Iba-1 expression) leading to microgliosis comprise the first line of defense to phagocytose the dead cells [11]. Astrocytes act as the second line of defense leading to a process known as astrogliosis and upregulate GFAP and S100B to limit the damage [12]. Further studies are needed to explain the molecular mechanism/s of different astrocytes release such as A2 and their interaction with microglia after the lumbar puncture.

The neuroprotective effects of activated α7 nicotinic acetylcholine receptor against mutant copper-zinc superoxide dismutase 1-mediated toxicity

Amyotrophic lateral sclerosis (ALS) is a fatal neurodegenerative disease characterized by the selective and progressive loss of motor neurons. Although many drugs have entered clinical trials, few have shown effectiveness in the treatment of ALS. Other studies have shown that the stimulation of α7 nicotinic acetylcholine receptor (nAChR) can have neuroprotective effects in some models of neurodegenerative disease, as well as prevent glutamate-induced motor neuronal death. However, the effect of α7 nAChR agonists on ALS-associated mutant copper-zinc superoxide dismutase 1 (SOD1) aggregates in motor neurons remains unclear. In the present study, we examined whether α7 nAChR activation had a neuroprotective effect against SOD1^G85R-induced toxicity in a cellular model for ALS. We found that α7 nAChR activation by PNU282987, a selective agonist of α7 nAChR, exhibited significant neuroprotective effects against SOD1^G85R-induced toxicity via the reduction of intracellular protein aggregates. This reduction also correlated with the activation of autophagy through the AMP-activated protein kinase (AMPK)-mammalian target of rapamycin (mTOR) signaling pathway. Furthermore, the activation of α7 nAChRs was found to increase the biogenesis of lysosomes by inducing translocation of the transcription factor EB (TFEB) into the nucleus. These results support the therapeutic potential of α7 nAChR activation in diseases that are characterized by SOD1^G85R aggregates, such as ALS.

Assessment of nicotine release from nicotine-loaded chitosan nanoparticles dry powder inhaler formulations via locomotor activity of C57BL/6 mice

PURPOSE

This study aimed to assess the activity of controlled release nicotine from dry powder inhaler formulation via locomotor activity of C57BL/6 mice.

METHODS

To achieve this we built a nose-only inhalation device for pulmonary administration of nicotine to mice and determined the optimal operational parameters. We used the locomotor activity test to compare the effects of the inhaled nicotine hydrogen tartrate-loaded chitosan nanoparticles (NHT-CS) with NHT in C57BL/6 mice. The minimum inhaled dose of NHT-CS required to alter locomotor activity was compared with inhaled and subcutaneously (s.c) injected NHT. Finally, histological examination of lung tissues was performed to ensure inhalation of NHT-CS did not cause lung damage.

RESULTS

We found a flow rate of 0.9 L/min and an exposure time of 5 min achieved optimal delivery of nicotine. A minimum of 0.88 mg inhaled of NHT-CS or 0.59 mg inhaled of NHT was required to alter locomotor activity similarly to injection of 0.5 mg/kg nicotine, suggesting the reformulation process did not alter the activity of NHT-CS. No differences between untreated and NHT-CS treated lung tissue upon histological examination were observed.

CONCLUSIONS

The results indicated the inhaled NHT-CS is a viable preclinical option for developing novel inhalation formulations as a potential anti-smoking therapeutic.

Pharmacological induction of Heat Shock Protein 70 by celastrol protects motoneurons from excitotoxicity in rat spinal cord in vitro

The secondary phase of spinal cord injury arising after the primary lesion largely extends the damage severity with delayed negative consequences for sensory-motor pathways. It is, therefore, important to find out if enhancing intrinsic mechanisms of neuroprotection can spare motoneurons that are very vulnerable cells. This issue was investigated with an in vitro model of rat spinal cord excitotoxicity monitored for up to 24 hr after the primary injury evoked by kainate. This study sought to pharmacologically boost the expression of heat shock proteins (HSP) to protect spinal motoneurons using celastrol to investigate if the rat spinal cord can upregulate HSP as neuroprotective mechanism. Despite its narrow range of drug safety in vitro, celastrol was not toxic to the rat spinal cord at 0.75 μM concentration and enhanced the expression of HSP70 by motoneurons. When celastrol was applied either before or after kainate, the number of dead motoneurons was significantly decreased and the nuclear localization of the cell death biomarker AIF strongly inhibited. Nevertheless, electrophysiological recording showed that protection of lumbar motor networks by celastrol was rather limited as reflex activity was impaired and fictive locomotion largely depressed, suggesting that functional deficit persisted, though the networks could express slow rhythmic oscillations. While our data do not exclude further recovery at later times beyond the experimental observations, the present results indicate that the upregulated expression of HSP in the aftermath of acute injury may be an interesting avenue for early protection of spinal motoneurons.