Development of optically controlled "living electrodes" with long-projecting axon tracts for a synaptic brain-machine interface.

For implantable neural interfaces, functional/clinical outcomes are challenged by limitations in specificity and stability of inorganic microelectrodes. A biological intermediary between microelectrical devices and the brain may improve specificity and longevity through (i) natural synaptic integration with deep neural circuitry, (ii) accessibility on the brain surface, and (iii) optogenetic manipulation for targeted, light-based readout/control. Accordingly, we have developed implantable "living electrodes," living cortical neurons, and axonal tracts protected within soft hydrogel cylinders, for optobiological monitoring/modulation of brain activity. Here, we demonstrate fabrication, rapid axonal outgrowth, reproducible cytoarchitecture, and simultaneous optical stimulation and recording of these tissue engineered constructs in vitro. We also present their transplantation, survival, integration, and optical recording in rat cortex as an in vivo proof of concept for this neural interface paradigm. The creation and characterization of these functional, optically controllable living electrodes are critical steps in developing a new class of optobiological tools for neural interfacing.

Chemogenetic silencing of hippocampal neurons suppresses epileptic neural circuits.

We investigated how pathological changes in newborn hippocampal dentate granule cells (DGCs) lead to epilepsy. Using a rabies virus-mediated retrograde tracing system and a designer receptors exclusively activated by designer drugs (DREADD) chemogenetic method, we demonstrated that newborn hippocampal DGCs are required for the formation of epileptic neural circuits and the induction of spontaneous recurrent seizures (SRS). A rabies virus-mediated mapping study revealed that aberrant circuit integration of hippocampal newborn DGCs formed excessive de novo excitatory connections as well as recurrent excitatory loops, allowing the hippocampus to produce, amplify, and propagate excessive recurrent excitatory signals. In epileptic mice, DREADD-mediated-specific suppression of hippocampal newborn DGCs dramatically reduced epileptic spikes and SRS in an inducible and reversible manner. Conversely, specific activation of hippocampal newborn DGCs increased both epileptic spikes and SRS. Our study reveals an essential role for hippocampal newborn DGCs in the formation and function of epileptic neural circuits, providing critical insights into DGCs as a potential therapeutic target for treating epilepsy.

Neuronal nitric oxide synthase and affective disorders.

Affective disorders including major depressive disorder (MDD), bipolar disorder (BPD), and general anxiety affect more than 10% of population in the world. Notably, neuronal nitric oxide synthase (nNOS), a downstream signal molecule of N-methyl-D-aspartate receptors (NMDARs) activation, is abundant in many regions of the brain such as the prefrontal cortex (PFC), hippocampus, amygdala, dorsal raphe nucleus (DRN), locus coeruleus (LC), and hypothalamus, which are closely associated with the pathophysiology of affective disorders. Decreased levels of the neurotransmitters including 5-hydroxytryptamine or serotonin (5-HT), noradrenalin (NA), and dopamine (DA) as well as hyperactivity of the hypothalamic-pituitary-adrenal (HPA) axis are common pathological changes of MDD, BPD, and anxiety. Increasing data suggests that nNOS in the hippocampus play a crucial role in the etiology of MDD whereas nNOS-related dysregulation of the nitrergic system in the LC is closely associated with the pathogenesis of BPD. Moreover, hippocampal nNOS is implicated in the role of serotonin receptor 1 A (5-HTR1 A) in modulating anxiety behaviors. Augment of nNOS and its carboxy-terminal PDZ ligand (CAPON) complex mediate stress-induced anxiety and disrupting the nNOS-CAPON interaction by small molecular drug generates anxiolytic effect. To date, however, the function of nNOS in affective disorders is not well reviewed. Here, we summarize works about nNOS and its signal mechanisms implicated in the pathophysiology of affective disorders. On the basis of this review, it is suggested that future research should more fully focus on the role of nNOS in the pathomechanism and treatment of affective disorders.

The Emerging Roles for Telomerase in the Central Nervous System.

Telomerase, a specialized ribonucleoprotein enzyme complex, maintains telomere length at the 3' end of chromosomes, and functions importantly in stem cells, cancer and aging. Telomerase exists in neural stem cells (NSCs) and neural progenitor cells (NPCs), at a high level in the developing and adult brains of humans and rodents. Increasing studies have demonstrated that telomerase in NSCs/NPCs plays important roles in cell proliferation, neuronal differentiation, neuronal survival and neuritogenesis. In addition, recent works have shown that telomerase reverse transcriptase (TERT) can protect newborn neurons from apoptosis and excitotoxicity. However, to date, the link between telomerase and diseases in the central nervous system (CNS) is not well reviewed. Here, we analyze the evidence and summarize the important roles of telomerase in the CNS. Understanding the roles of telomerase in the nervous system is not only important to gain further insight into the process of the neural cell life cycle but would also provide novel therapeutic applications in CNS diseases such as neurodegenerative condition, mood disorders, aging and other ailments.

Engineered Axonal Tracts as "Living Electrodes" for Synaptic-Based Modulation of Neural Circuitry.

Brain-computer interface and neuromodulation strategies relying on penetrating non-organic electrodes/optrodes are limited by an inflammatory foreign body response that ultimately diminishes performance. A novel "biohybrid" strategy is advanced, whereby living neurons, biomaterials, and microelectrode/optical technology are used together to provide a biologically-based vehicle to probe and modulate nervous-system activity. Microtissue engineering techniques are employed to create axon-based "living electrodes", which are columnar microstructures comprised of neuronal population(s) projecting long axonal tracts within the lumen of a hydrogel designed to chaperone delivery into the brain. Upon microinjection, the axonal segment penetrates to prescribed depth for synaptic integration with local host neurons, with the perikaryal segment remaining externalized below conforming electrical-optical arrays. In this paradigm, only the biological component ultimately remains in the brain, potentially attenuating a chronic foreign-body response. Axon-based living electrodes are constructed using multiple neuronal subtypes, each with differential capacity to stimulate, inhibit, and/or modulate neural circuitry based on specificity uniquely afforded by synaptic integration, yet ultimately computer controlled by optical/electrical components on the brain surface. Current efforts are assessing the efficacy of this biohybrid interface for targeted, synaptic-based neuromodulation, and the specificity, spatial density and long-term fidelity versus conventional microelectronic or optical substrates alone.

Growth Associated Protein 43 (GAP-43) as a Novel Target for the Diagnosis, Treatment and Prevention of Epileptogenesis.

We previously showed increased growth associated protein 43 (GAP-43) expression in brain samples resected from patients with cortical dysplasia (CD), which was correlated with duration of epilepsy. Here, we used a rat model of CD to examine the regulation of GAP-43 in the brain and serum over the course of epileptogenesis. Baseline GAP-43 expression was higher in CD animals compared to control non-CD rats. An acute seizure increased GAP-43 expression in both CD and control rats. However, GAP-43 expression decreased by day 15 post-seizure in control rats, which did not develop spontaneous seizures. In contrast, GAP-43 remained up-regulated in CD rats, and over 50% developed chronic epilepsy with increased GAP-43 levels in their serum. GAP-43 protein was primarily located in excitatory neurons, suggesting its functional significance in epileptogenesis. Inhibition of GAP-43 expression by shRNA significantly reduced seizure duration and severity in CD rats after acute seizures with subsequent reduction in interictal spiking. Serum GAP-43 levels were significantly higher in CD rats that developed spontaneous seizures. Together, these results suggest GAP-43 as a key factor promoting epileptogenesis, a possible therapeutic target for treatment of progressive epilepsy and a potential biomarker for epilepsy progression in CD.

Treatment with lacosamide impedes generalized seizures in a rodent model of cortical dysplasia.

OBJECTIVE: Epilepsy is a common neurologic disorder resulting in spontaneous, recurrent seizures. About 30-40% of patients are not responsive to pharmacologic therapies. This may be due to the differences between individual patients such as etiology, underlying pathophysiology, and seizure focus, and it highlights the importance of new drug discovery and testing in this field. Our goal was to determine the efficacy of lacosamide (LCM), a drug approved for the treatment of focal seizures, in a model of generalized epilepsy with cortical dysplasia (CD). We sought to compare LCM to levetiracetam (LEV), a drug that is currently used for the treatment of both partial and generalized epilepsy and to test its proficiency. METHODS: Pregnant rats were irradiated to produce pups with malformed cortices in a model of CD, which will be referred to as the "first hit." Adult animals, developed normally (NL) and irradiated (XRT), were surgically implanted with electroencephalography (EEG) electrodes. Baseline EEG was recorded on all rats prior to pretreatments with either LCM, LEV, or placebo (PBO). After 30 min, all rats were injected with a subconvulsive dose of pentylenetetrazole (PTZ), a γ-aminobutyric acid receptor A (GABAA ) antagonist used to provoke generalized seizures as a "second hit." RESULTS: LCM and LEV were both effective against seizures induced by PTZ. XRT rats had a higher seizure incidence with longer and more severe seizures than NL rats. Seizure duration was decreased with both LCM and LEV in all animals. In XRT rats, there was a significant reduction in acute seizure incidence and severity with both LCM and LEV after PTZ injection. SIGNIFICANCE: Our results suggest that LCM could be used as a potential treatment option for generalized epilepsy with CD as the underlying pathology.

Underlying Cortical Dysplasia as Risk Factor for Traumatic Epilepsy: An Animal Study.

Traumatic brain injury (TBI) is a significant risk factor for development of epilepsy in humans. It is unclear, however, why some persons are at an increased risk of becoming epileptic, while others recover from the TBI seizure-free. We previously showed that the presence of a proepileptic pathology increases the risk of epilepsy in an animal model of cortical dysplasia (CD) after a secondary insult, which we described as the "second hit". Here we sought to evaluate the prevalence of epileptic activity and seizures in CD after a moderate TBI to determine the influence of dysplastic pathology on TBI-induced epileptogenesis. CD was generated in rats through in utero irradiation (the "first hit"). Nondysplastic and CD rats were surgically implanted with EEG electrodes. Craniotomies were performed over the pre-central cortex, and rats were given a moderate TBI using the lateral fluid percussion injury device. Rats were monitored with chronic EEG and video. EEG data were analyzed for the occurrence of interictal spikes and epileptic EEG seizure patterns. Brains were harvested and evaluated histologically. Spontaneous seizures are more prominent and occur earlier in rats with CD after a moderate TBI compared with nondysplastic control rats. All of the CD animals exhibited interictal spiking after TBI, while only a portion of nondysplastic animals produced spikes. These results suggest that the presence of a proepileptic pathology may increase the risk for the development of epilepsy after TBI. Diagnosis and treatment of TBI may depend on underlying pathologies contributing to epilepsy after a brain injury.

Growth-associated protein 43 and progressive epilepsy in cortical dysplasia.

OBJECTIVE: To investigate growth-associated protein 43 (GAP-43), a marker for axonal growth and synaptic plasticity, as potential substrate for progressive epilepsy and potential predictor of postsurgical seizure outcome in patients with focal cortical dysplasia (FCD). METHODS: GAP-43 immunohistochemistry was performed on cortical specimens from 21 patients with FCD: 12 with FCD type II (IIA or IIB) and nine with FCD type IA. Twenty normal anterior temporal lobe specimens from patients with mesial temporal lobe epilepsy due to hippocampal sclerosis (mTLE/HS) were used as controls. Semiquantitative analysis of GAP-43 staining patterns was performed. Additionally, GAP-43 immunoblotting was performed on resected tissue from three patients with FCD type IIA/B; GAP-43 protein levels in electroencephalography-verified epileptic, and distal nonepileptic, areas were compared within each patient. Two outcome categories were used: completely seizure free (Engel IA) versus not seizure free. We examined the relationship of GAP-43 scores with epilepsy duration and seizure-free outcome for each of the three pathologies. RESULTS: Within-patient GAP-43 expression is selectively increased in the epileptic as compared to nonepileptic cortex. GAP-43 immunoreactivity (IRs) patterns were seen on the cell surface and tubular punctate structures intercellularly only in FCD cortex. Higher GAP-43 scores were correlated (P < 0.0001) with longer epilepsy duration only in FCD IIA/B. Lower GAP-43 scores were associated with better surgical outcome in the same group. No such relationship was observed in FCD IA. INTERPRETATION: GAP-43 proteins are not only associated with intrinsic epileptogenicity but may be markers of progressive epilepsy and predictors of postoperative seizure outcome in patients with pharmacoresistant epilepsy due to FCD IIA/B.