Effects of Unilateral High Frequency Stimulation of the Subthalamic Nucleus on Risk-avoidant Behavior in a Partial 6-hydroxydopamine Model of Parkinson's Disease.

BACKGROUND: Deep brain stimulation (DBS) of the subthalamic nucleus (STN) is a well-established treatment for the motor symptoms of Parkinson's disease (PD). While PD is primarily characterized by motor symptoms such as tremor, rigidity, and bradykinesia, it also involves a range of non-motor symptoms, and anxiety is one of the most common. The relationship between PD and anxiety is complex and can be a result of both pathological neural changes and the psychological and emotional impacts of living with a chronic progressive condition. Managing anxiety in PD is critical for improving the patients' quality of life. However, patients undergoing STN DBS can occasionally experience increased anxiety. METHODS: This study investigates changes in risk-avoidant behavior following STN DBS in a pre-motor animal model of PD under chronic and acute unilateral high frequency stimulation. RESULTS: No significant changes in risk-avoidant behaviors were observed in rats who underwent STN DBS compared with sham stimulation controls. Chronic stimulation prevented sensitization in the elevated zero maze. CONCLUSIONS: These results suggest that unilateral stimulation of the STN may have minimal effects on risk-avoidant behaviors in PD. However, additional research is required to fully understand the mechanisms responsible for changes in anxiety during STN DBS for PD.

The Duration and Intensity of High Frequency Alternating Current Influences the Degree and Recovery of Nerve Conduction Block.

OBJECTIVE: The purpose of this paper is to investigate the persistence of nerve blockade beyond the duration of applying high frequency alternating current (HFAC) to thinly myelinated and non-myelinated fibers, also termed a "carry-over effect". METHODS: In this study, we used electrically-evoked compound action potentials from isolated rat vagus nerves to assess the influence of 5 kHz HFAC amplitude and duration on the degree of the carry-over effect. Current amplitudes from 1-10 mA and 5 kHz durations from 10-120 seconds were tested. RESULTS: By testing 20 different combinations of 5 kHz amplitude and duration, we found a significant interaction between 5 kHz amplitude and duration on influencing the carry-over effect. CONCLUSION: The degree of carry-over effect was dependent on 5 kHz amplitude, as well as duration. SIGNIFICANCE: Utilizing the carry-over effect may be useful in designing energy efficient nerve blocking algorithms for the treatment of diseases influenced by nerve activity.

Combining Celiac and Hepatic Vagus Nerve Neuromodulation Reverses Glucose Intolerance and Improves Glycemic Control in Pre- and Overt-Type 2 Diabetes Mellitus.

Neurological disorders and type 2 diabetes mellitus (T2DM) are deeply intertwined. For example, autonomic neuropathy contributes to the development of T2DM and continued unmanaged T2DM causes further progression of nerve damage. Increasing glycemic control has been shown to prevent the onset and progression of diabetic autonomic neuropathies. Neuromodulation consisting of combined stimulation of celiac vagal fibers innervating the pancreas with concurrent electrical blockade of neuronal hepatic vagal fibers innervating the liver has been shown to increase glycemic control in animal models of T2DM. The present study demonstrated that the neuromodulation reversed glucose intolerance in alloxan-treated swine in both pre- and overt stages of T2DM. This was demonstrated by improved performance on oral glucose tolerance tests (OGTTs), as assessed by area under the curve (AUC). In prediabetic swine (fasting plasma glucose (FPG) range: 101-119 mg/dL) the median AUC decreased from 31.9 AUs (IQR = 28.6, 35.5) to 15.9 AUs (IQR = 15.1, 18.3) p = 0.004. In diabetic swine (FPG range: 133-207 mg/dL) the median AUC decreased from 54.2 AUs (IQR = 41.5, 56.6) to 16.0 AUs (IQR = 15.4, 21.5) p = 0.003. This neuromodulation technique may offer a new treatment for T2DM and reverse glycemic dysregulation at multiple states of T2DM involved in diabetic neuropathy including at its development and during progression.

A quadruple dissociation of reward-related behaviour in mice across excitatory inputs to the nucleus accumbens shell.

The nucleus accumbens shell (NAcSh) is critically important for reward valuations, yet it remains unclear how valuation information is integrated in this region to drive behaviour during reinforcement learning. Using an optogenetic spatial self-stimulation task in mice, here we show that contingent activation of different excitatory inputs to the NAcSh change expression of different reward-related behaviours. Our data indicate that medial prefrontal inputs support place preference via repeated actions, ventral hippocampal inputs consistently promote place preferences, basolateral amygdala inputs produce modest place preferences but as a byproduct of increased sensitivity to time investments, and paraventricular inputs reduce place preferences yet do not produce full avoidance behaviour. These findings suggest that each excitatory input provides distinct information to the NAcSh, and we propose that this reflects the reinforcement of different credit assignment functions. Our finding of a quadruple dissociation of NAcSh input-specific behaviours provides insights into how types of information carried by distinct inputs to the NAcSh could be integrated to help drive reinforcement learning and situationally appropriate behavioural responses.

Integral methods for automatic quantification of fast-scan-cyclic-voltammetry detected neurotransmitters.

Modern techniques for estimating basal levels of electroactive neurotransmitters rely on the measurement of oxidative charges. This requires time integration of oxidation currents at certain intervals. Unfortunately, the selection of integration intervals relies on ad-hoc visual identification of peaks on the oxidation currents, which introduces sources of error and precludes the development of automated procedures necessary for analysis and quantification of neurotransmitter levels in large data sets. In an effort to improve charge quantification techniques, here we present novel methods for automatic selection of integration boundaries. Our results show that these methods allow quantification of oxidation reactions both in vitro and in vivo and of multiple analytes in vitro.

Calcium imaging in freely-moving mice during electrical stimulation of deep brain structures.

After decades of study in humans and animal models, there remains a lack of consensus regarding how the action of electrical stimulation on neuronal and non-neuronal elements - e.g. neuropil, cell bodies, glial cells, etc. - leads to the therapeutic effects of neuromodulation therapies. To further our understanding of neuromodulation therapies, there is a critical need for novel methodological approaches using state-of-the-art neuroscience tools to study neuromodulation therapy in preclinical models of disease. In this manuscript we outline one such approach combining chronic behaving single-photon microendoscope recordings in a pathological mouse model with electrical stimulation of a common deep brain stimulation (DBS) target. We describe in detail the steps necessary to realize this approach, as well as discuss key considerations for extending this experimental paradigm to other DBS targets for different therapeutic indications. Additionally, we make recommendations from our experience on implementing and validating the required combination of procedures that includes: the induction of a pathological model (6-OHDA model of Parkinson's disease) through an injection procedure, the injection of the viral vector to induce GCaMP expression, the implantation of the GRIN lens and stimulation electrode, and the installation of a baseplate for mounting the microendoscope. We proactively identify unique data analysis confounds occurring due to the combination of electrical stimulation and optical recordings and outline an approach to address these confounds. In order to validate the technical feasibility of this unique combination of experimental methods, we present data to demonstrate that 1) despite the complex multifaceted surgical procedures, chronic optical recordings of hundreds of cells combined with stimulation is achievable over week long periods 2) this approach enables measurement of differences in DBS evoked neural activity between anesthetized and awake conditions and 3) this combination of techniques can be used to measure electrical stimulation induced changes in neural activity during behavior in a pathological mouse model. These findings are presented to underscore the feasibility and potential utility of minimally constrained optical recordings to elucidate the mechanisms of DBS therapies in animal models of disease.

A Low-Cost Humidity Control System to Protect Microscopes in a Tropical Climate.

Introduction: A clean and functional microscope is necessary for accurate diagnosis of infectious diseases. In tropical climates, high humidity levels and improper storage conditions allow for the accumulation of debris and fungus on the optical components of diagnostic equipment, such as microscopes. Objective: Our objective was to develop and implement a low-cost, sustainable, easy to manage, low-maintenance, passive humidity control chamber to both reduce debris accumulation and microbial growth onto the optical components of microscopes. Methods: Constructed from easily-sourced and locally available materials, the cost of each humidity control chamber is approximately $2.35 USD. Relative humidity levels were recorded every 30 minutes over a period of 10 weeks from two chambers deployed at the Belize Vector and Ecology Center and the University of Belize. Results: The humidity control chamber deployed at the University of Belize maintained internal relative humidity at an average of 35.3% (SD = 4.2%) over 10 weeks, while the average external relative humidity was 86.4% (SD = 12.4%). The humidity control chamber deployed at the Belize Vector and Ecology Center effectively maintained internal relative humidity to an average of 54.5% (SD = 9.4%) over 10 weeks, while the average external relative humidity was 86.9% (SD = 12.9%). Conclusions: Control of relative humidity is paramount for the sustainability of medical equipment in tropical climates. The humidity control chambers reduced relative humidity to levels that were not conducive for fungal growth while reducing microscope contamination from external sources. This will likely extend the service life of the microscopes while taking advantage of low-cost, locally sourced components.

An Injectable Neural Stimulation Electrode Made from an In-Body Curing Polymer/Metal Composite.

Implanted neural stimulation and recording devices hold vast potential to treat a variety of neurological conditions, but the invasiveness, complexity, and cost of the implantation procedure greatly reduce access to an otherwise promising therapeutic approach. To address this need, a novel electrode that begins as an uncured, flowable prepolymer that can be injected around a neuroanatomical target to minimize surgical manipulation is developed. Referred to as the Injectrode, the electrode conforms to target structures forming an electrically conductive interface which is orders of magnitude less stiff than conventional neuromodulation electrodes. To validate the Injectrode, detailed electrochemical and microscopy characterization of its material properties is performed and the feasibility of using it to stimulate the nervous system electrically in rats and swine is validated. The silicone-metal-particle composite performs very similarly to pure wire of the same metal (silver) in all measures, including exhibiting a favorable cathodic charge storage capacity (CSCC ) and charge injection limits compared to the clinical LivaNova stimulation electrode and silver wire electrodes. By virtue of its simplicity, the Injectrode has the potential to be less invasive, more robust, and more cost-effective than traditional electrode designs, which could increase the adoption of neuromodulation therapies for existing and new indications.

Synaptic Depotentiation and mGluR5 Activity in the Nucleus Accumbens Drive Cocaine-Primed Reinstatement of Place Preference.

Understanding the neurobiological processes that incite drug craving and drive relapse has the potential to help target efforts to treat addiction. The NAc serves as a critical substrate for reward and motivated behavior, in part due to alterations in excitatory synaptic strength within cortical-accumbens pathways. The present studies investigated a causal link between cocaine-induced reinstatement of conditioned place preference and rapid reductions of cocaine-dependent increases in NAc shell synaptic strength in male mice. Cocaine-conditioned place preference behavior and ex vivo whole-cell electrophysiology showed that cocaine-primed reinstatement and synaptic depotentiation were disrupted by inhibiting AMPAR internalization via intra-NAc shell infusion of a Tat-GluA23Y peptide. Furthermore, reinstatement was driven by an mGluR5-dependent reduction in AMPAR signaling. Intra-NAc shell infusion of the mGluR5 antagonist MTEP blocked cocaine-primed reinstatement and corresponding depotentiation, whereas infusion of the mGluR5 agonist CHPG itself promoted reinstatement and depotentiated synaptic strength in the NAc shell. Optogenetic examination of circuit-specific plasticity showed that inhibition of infralimbic cortical input to the NAc shell blocked cocaine-primed reinstatement, whereas low-frequency stimulation (10 Hz) of this pathway in the absence of cocaine triggered a reduction in synaptic strength akin to that observed with cocaine, and was sufficient to promote reinstatement in the absence of a cocaine challenge. These data support a model in which mGluR5-mediated reduction in GluA2-containing AMPARs at NAc shell synapses receiving input from the infralimbic cortex is a critical factor in triggering reinstatement of cocaine-primed conditioned approach behavior.SIGNIFICANCE STATEMENT These studies identified a sequence of neural events whereby reexposure to cocaine activates a signaling cascade that alters synaptic strength in the NAc shell and triggers a behavioral response driven by a drug-associated memory.

Design Choices for Next-Generation Neurotechnology Can Impact Motion Artifact in Electrophysiological and Fast-Scan Cyclic Voltammetry Measurements.

Implantable devices to measure neurochemical or electrical activity from the brain are mainstays of neuroscience research and have become increasingly utilized as enabling components of clinical therapies. In order to increase the number of recording channels on these devices while minimizing the immune response, flexible electrodes under 10 µm in diameter have been proposed as ideal next-generation neural interfaces. However, the representation of motion artifact during neurochemical or electrophysiological recordings using ultra-small, flexible electrodes remains unexplored. In this short communication, we characterize motion artifact generated by the movement of 7 µm diameter carbon fiber electrodes during electrophysiological recordings and fast-scan cyclic voltammetry (FSCV) measurements of electroactive neurochemicals. Through in vitro and in vivo experiments, we demonstrate that artifact induced by motion can be problematic to distinguish from the characteristic signals associated with recorded action potentials or neurochemical measurements. These results underscore that new electrode materials and recording paradigms can alter the representation of common sources of artifact in vivo and therefore must be carefully characterized.

Medium- and high-intensity rTMS reduces psychomotor agitation with distinct neurobiologic mechanisms.

Definitive data are lacking on the mechanism of action and biomarkers of repetitive transcranial magnetic stimulation (rTMS) for the treatment of depression. Low-intensity rTMS (LI-rTMS) has demonstrated utility in preclinical models of rTMS treatments but the effects of LI-rTMS in murine models of depression are unknown. We examined the behavioral and neurobiologic changes in olfactory bulbectomy (OB) mice with medium-intensity rTMS (MI-rTMS) treatment and fluoxetine hydrochloride. We then compared 10-Hz rTMS sessions for 3 min at intensities (measured at the cortical surface) of 4 mT (LI-rTMS), 50 mT (medium-intensity rTMS [MI-rTMS]), or 1 T (high-intensity rTMS [HI-rTMS]) 5 days per week over 4 weeks in an OB model of agitated depression. Behavioral effects were assessed with forced swim test; neurobiologic effects were assessed with brain levels of 5-hydroxytryptamine, brain-derived neurotrophic factor (BDNF), and neurogenesis. Peripheral metabolomic changes induced by OB and rTMS were monitored through enzyme-linked immunosorbent assay and ultrapressure liquid chromatography-driven targeted metabolomics evaluated with ingenuity pathway analysis (IPA). MI-rTMS and HI-rTMS attenuated psychomotor agitation but only MI-rTMS increased BDNF and neurogenesis levels. HI-rTMS normalized the plasma concentration of α-amino-n-butyric acid and 3-methylhistidine. IPA revealed significant changes in glutamine processing and glutamate signaling in the OB model and following MI-rTMS and HI-rTMS treatment. The present findings suggest that MI-rTMS and HI-rTMS induce differential neurobiologic changes in a mouse model of agitated depression. Further, α-amino-n-butyric acid and 3-methylhistidine may have utility as biomarkers to objectively monitor the response to rTMS treatment of depression.

Multifunctional System for Observing, Measuring and Analyzing Stimulation-Evoked Neurochemical Signaling.

The ability to measure neurotransmitter activity using implanted electrochemical sensors offers researchers a potent technique for analyzing neural activity across specific neural circuitry. We have developed a wirelessly controlled device, WINCS Harmoni, to observe and measure neurotransmitter dynamics at up to four separate sensors, with high temporal and spatial resolution. WINCS Harmoni also incorporates a versatile neurostimulator that can be synchronized with electrochemical recording. The WINCS Harmoni platform is thus optimally suited for probing the neurochemical effects of neurostimulation, and may in turn enable the development of personalized therapies for multiple brain disorders.

Reversal of morphine-induced cell-type-specific synaptic plasticity in the nucleus accumbens shell blocks reinstatement.

Drug-evoked plasticity at excitatory synapses on medium spiny neurons (MSNs) of the nucleus accumbens (NAc) drives behavioral adaptations in addiction. MSNs expressing dopamine D1 (D1R-MSN) vs. D2 receptors (D2R-MSN) can exert antagonistic effects in drug-related behaviors, and display distinct alterations in glutamate signaling following repeated exposure to psychostimulants; however, little is known of cell-type-specific plasticity induced by opiates. Here, we find that repeated morphine potentiates excitatory transmission and increases GluA2-lacking AMPA receptor expression in D1R-MSNs, while reducing signaling in D2-MSNs following 10-14 d of forced abstinence. In vivo reversal of this pathophysiology with optogenetic stimulation of infralimbic cortex-accumbens shell (ILC-NAc shell) inputs or treatment with the antibiotic, ceftriaxone, blocked reinstatement of morphine-evoked conditioned place preference. These findings confirm the presence of overlapping and distinct plasticity produced by classes of abused drugs within subpopulations of MSNs that may provide targetable molecular mechanisms for future pharmacotherapies.