Enhancement-mode ion-based transistor as a comprehensive interface and real-time processing unit for in vivo electrophysiology.

Bioelectronic devices must be fast and sensitive to interact with the rapid, low-amplitude signals generated by neural tissue. They should also be biocompatible and soft, and should exhibit long-term stability in physiologic environments. Here, we develop an enhancement-mode, internal ion-gated organic electrochemical transistor (e-IGT) based on a reversible redox reaction and hydrated ion reservoirs within the conducting polymer channel, which enable long-term stable operation and shortened ion transit time. E-IGT transient responses depend on hole rather than ion mobility, and combine with high transconductance to result in a gain-bandwidth product that is several orders of magnitude above that of other ion-based transistors. We used these transistors to acquire a wide range of electrophysiological signals, including in vivo recording of neural action potentials, and to create soft, biocompatible, long-term implantable neural processing units for the real-time detection of epileptic discharges. E-IGTs offer a safe, reliable and high-performance building block for chronically implanted bioelectronics, with a spatiotemporal resolution at the scale of individual neurons.

Pathway-Specific Control of Striatal Neuron Vulnerability by Corticostriatal Cannabinoid CB1 Receptors.

The vast majority of neurons within the striatum are GABAergic medium spiny neurons (MSNs), which receive glutamatergic input from the cortex and thalamus, and form two major efferent pathways: the direct pathway, expressing dopamine D1 receptor (D1R-MSNs), and the indirect pathway, expressing dopamine D2 receptor (D2R-MSNs). While molecular mechanisms of MSN degeneration have been identified in animal models of striatal damage, the molecular factors that dictate a selective vulnerability of D1R-MSNs or D2R-MSNs remain unknown. Here, we combined genetic, chemogenetic, and pharmacological strategies with behavioral and neurochemical analyses, and show that the pool of cannabinoid CB1 receptor (CB1R) located on corticostriatal terminals efficiently safeguards D1R-MSNs, but not D2R-MSNs, from different insults. This cell-specific response relies on the regulation of glutamatergic signaling, and is independent from the CB1R-dependent control of astroglial activity in the striatum. These findings define cortical CB1R as a pivotal synaptic player in dictating a differential vulnerability of D1R-MSNs versus D2R-MSNs, and increase our understanding of the role of coordinated cannabinergic-glutamatergic signaling in establishing corticostriatal circuits and its dysregulation in neurodegenerative diseases.

A restricted population of CB1 cannabinoid receptors with neuroprotective activity.

The CB1 cannabinoid receptor, the main molecular target of endocannabinoids and cannabis active components, is the most abundant G protein-coupled receptor in the mammalian brain. Of note, CB1 receptors are expressed at the synapses of two opposing (i.e., GABAergic/inhibitory and glutamatergic/excitatory) neuronal populations, so the activation of one and/or another receptor population may conceivably evoke different effects. Despite the widely reported neuroprotective activity of the CB1 receptor in animal models, the precise pathophysiological relevance of those two CB1 receptor pools in neurodegenerative processes is unknown. Here, we first induced excitotoxic damage in the mouse brain by (i) administering quinolinic acid to conditional mutant animals lacking CB1 receptors selectively in GABAergic or glutamatergic neurons, and (ii) manipulating corticostriatal glutamatergic projections remotely with a designer receptor exclusively activated by designer drug pharmacogenetic approach. We next examined the alterations that occur in the R6/2 mouse, a well-established model of Huntington disease, upon (i) fully knocking out CB1 receptors, and (ii) deleting CB1 receptors selectively in corticostriatal glutamatergic or striatal GABAergic neurons. The data unequivocally identify the restricted population of CB1 receptors located on glutamatergic terminals as an indispensable player in the neuroprotective activity of (endo)cannabinoids, therefore suggesting that this precise receptor pool constitutes a promising target for neuroprotective therapeutic strategies.

ß-Adrenergic receptors activate exchange protein directly activated by cAMP (Epac), translocate Munc13-1, and enhance the Rab3A-RIM1α interaction to potentiate glutamate release at cerebrocortical nerve terminals.

The adenylyl cyclase activator forskolin facilitates synaptic transmission presynaptically via cAMP-dependent protein kinase (PKA). In addition, cAMP also increases glutamate release via PKA-independent mechanisms, although the downstream presynaptic targets remain largely unknown. Here, we describe the isolation of a PKA-independent component of glutamate release in cerebrocortical nerve terminals after blocking Na(+) channels with tetrodotoxin. We found that 8-pCPT-2'-O-Me-cAMP, a specific activator of the exchange protein directly activated by cAMP (Epac), mimicked and occluded forskolin-induced potentiation of glutamate release. This Epac-mediated increase in glutamate release was dependent on phospholipase C, and it increased the hydrolysis of phosphatidylinositol 4,5-bisphosphate. Moreover, the potentiation of glutamate release by Epac was independent of protein kinase C, although it was attenuated by the diacylglycerol-binding site antagonist calphostin C. Epac activation translocated the active zone protein Munc13-1 from soluble to particulate fractions; it increased the association between Rab3A and RIM1α and redistributed synaptic vesicles closer to the presynaptic membrane. Furthermore, these responses were mimicked by the ß-adrenergic receptor (ßAR) agonist isoproterenol, consistent with the immunoelectron microscopy and immunocytochemical data demonstrating presynaptic expression of ßARs in a subset of glutamatergic synapses in the cerebral cortex. Based on these findings, we conclude that ßARs couple to a cAMP/Epac/PLC/Munc13/Rab3/RIM-dependent pathway to enhance glutamate release at cerebrocortical nerve terminals.

Altered neuronal and endothelial nitric oxide synthase expression in the bladder and urethra of cyclophosphamide-treated rats.

Increased nitric oxide (NO) production seems to play a key role in cyclophosphamide (CYP)-induced cystitis, although the underlying mechanisms and the relative involvement of the different NO synthase (NOS) isoforms remain to be elucidated. Moreover, the role of the urethra in this process is also unclear. In this study, we have analyzed the changes in the expression and distribution of the inducible (iNOS), endothelial (eNOS) and neuronal (nNOS) isoforms of NOS, and the alterations in nerve-mediated contractility in the bladder and urethra of CYP-treated rats. Accordingly, Wistar rats were treated with 150 mg kg(-1) CYP for 4 (acute treatment) or 48 h (intermediate treatment), or with 70 mg kg(-1) CYP every 3 days for 10 days (chronic treatment), and the changes in protein expression were assessed by immunohistofluorescence and in Western blots, while mRNA expression was assessed by conventional and quantitative PCR. Similarly, nerve-mediated contractility was analyzed in vitro. Unexpectedly, no iNOS expression was detected in CYP-treated animals, while a transient downregulation of nNOS expression and a progressive upregulation of eNOS was observed, although the eNOS accumulated was not in the active phosphorylated form. Qualitative changes in mRNA expression were also observed in the bladder and urethra, although contractility only diminished in the bladder and this change was not dependent on NOS activity. These findings suggest that spatiotemporal alterations in NO production by constitutive NOS may be involved in the pathogenicity of CYP. Further studies will be necessary to understand the contribution of eNOS to the increases in NO associated with bladder inflammation, or that of free radicals.

Closed-loop electrical stimulation to prevent focal epilepsy progression and long-term memory impairment.

Interictal epileptiform discharges (IEDs) are ubiquitously expressed in epileptic networks and disrupt cognitive functions. It is unclear whether addressing IED-induced dysfunction could improve epilepsy outcomes as most therapeutics target seizures. We show in a model of progressive hippocampal epilepsy that IEDs produce pathological oscillatory coupling which is associated with prolonged, hypersynchronous neural spiking in synaptically connected cortex and expands the brain territory capable of generating IEDs. A similar relationship between IED-mediated oscillatory coupling and temporal organization of IEDs across brain regions was identified in human subjects with refractory focal epilepsy. Spatiotemporally targeted closed-loop electrical stimulation triggered on hippocampal IED occurrence eliminated the abnormal cortical activity patterns, preventing spread of the epileptic network and ameliorating long-term spatial memory deficits in rodents. These findings suggest that stimulation-based network interventions that normalize interictal dynamics may be an effective treatment of epilepsy and its comorbidities, with a low barrier to clinical translation. One-Sentence Summary: Targeted closed-loop electrical stimulation prevents spread of the epileptic network and ameliorates long-term spatial memory deficits.

Large-scale, closed-loop interrogation of neural circuits underlying cognition.

Cognitive functions are increasingly understood to involve coordinated activity patterns between multiple brain regions, and their disruption by neuropsychiatric disorders is similarly complex. Closed-loop neurostimulation can directly modulate neural signals with temporal and spatial precision. How to leverage such an approach to effectively identify and target distributed neural networks implicated in mediating cognition remains unclear. We review current conceptual and technical advances in this area, proposing that devices that enable large-scale acquisition, integrated processing, and multiregion, arbitrary waveform stimulation will be critical for mechanistically driven manipulation of cognitive processes in physiological and pathological brain networks.

Chronic electrical stimulation of peripheral nerves via deep-red light transduced by an implanted organic photocapacitor.

Implantable devices for the wireless modulation of neural tissue need to be designed for reliability, safety and reduced invasiveness. Here we report chronic electrical stimulation of the sciatic nerve in rats by an implanted organic electrolytic photocapacitor that transduces deep-red light into electrical signals. The photocapacitor relies on commercially available semiconducting non-toxic pigments and is integrated in a conformable 0.1-mm3 thin-film cuff. In freely moving rats, fixation of the cuff around the sciatic nerve, 10 mm below the surface of the skin, allowed stimulation (via 50-1,000-µs pulses of deep-red light at wavelengths of 638 nm or 660 nm) of the nerve for over 100 days. The robustness, biocompatibility, low volume and high-performance characteristics of organic electrolytic photocapacitors may facilitate the wireless chronic stimulation of peripheral nerves.

Translational Organic Neural Interface Devices at Single Neuron Resolution.

Recording from the human brain at the spatiotemporal resolution of action potentials provides critical insight into mechanisms of higher cognitive functions and neuropsychiatric disease that is challenging to derive from animal models. Here, organic materials and conformable electronics are employed to create an integrated neural interface device compatible with minimally invasive neurosurgical procedures and geared toward chronic implantation on the surface of the human brain. Data generated with these devices enable identification and characterization of individual, spatially distribute human cortical neurons in the absence of any tissue penetration (n = 229 single units). Putative single-units are effectively clustered, and found to possess features characteristic of pyramidal cells and interneurons, as well as identifiable microcircuit interactions. Human neurons exhibit consistent phase modulation by oscillatory activity and a variety of population coupling responses. The parameters are furthermore established to optimize the yield and quality of single-unit activity from the cortical surface, enhancing the ability to investigate human neural network mechanisms without breaching the tissue interface and increasing the information that can be safely derived from neurophysiological monitoring.