Deep brain stimulation of the mediodorsal thalamic nucleus yields increases in the expression of zif-268 but not c-fos in the frontal cortex

Deep Brain Stimulation of the Medial Septal Nucleus Induces Expression of a Virally Delivered Reporter Gene in Dentate Gyrus

Background

Mechanisms of deep brain stimulation (DBS) remain controversial, and spatiotemporal control of brain-wide circuits remains elusive. Adeno-associated viral (AAV) vectors have emerged as vehicles for spatiotemporal expression of exogenous transgenes in several tissues, including specific nuclei in the brain. Coupling DBS with viral vectors to modulate exogenous transgene expression remains unexplored.

Objective

This study examines whether DBS of the medial septal nucleus (MSN) can regulate gene expression of AAV-transduced neurons in a brain region anatomically remote from the stimulation target: the hippocampal dentate gyrus.

Methods

Rats underwent unilateral hippocampal injection of an AAV vector with c-Fos promoter-driven expression of TdTomato (TdT), followed by MSN electrode implantation. Rodents received no stimulation, 7.7 Hz (theta), or 130 Hz (gamma) DBS for 1 h one week after surgery. In a repeat stimulation experiment, rodents received either no stimulation, or two 1 h MSN DBS over 2 weeks.

Results

No significant differences in hippocampal TdT expression between controls and acute MSN DBS were found. With repeat DBS we found c-Fos protein expression was induced and we could detect increased TdT with either gamma or theta stimulation.

Conclusion

We demonstrate that viral vector-mediated gene expression can be regulated spatially and temporally using DBS. Control of gene expression by DBS warrants further investigation into stimulation-responsive promoters for clinical applications.

Focal Suppression of Epileptiform Activity in the Hippocampus by a High-frequency Magnetic Field

Electric current has been used for epilepsy treatment by targeting specific neural circuitries. Despite its success, direct contact between the electrode and tissue could cause side effects including pain, inflammation, and adverse biological reactions. Magnetic stimulation overcomes these limitations by offering advantages over biocompatibility and operational feasibility. However, the underlying neurological mechanisms of its action are largely unknown. In this work, a magnetic generating system was assembled that included a miniature coil. The coil was positioned above the CA3 area of mouse hippocampal slices. Epileptiform activity (EFA) was induced with low Mg²⁺/high K⁺ perfusion or with 100 µM 4-aminopyridine (4-AP). The miniature coil generated a sizable electric field that suppressed the local EFA in the hippocampus in the low-Mg²⁺/high-K⁺ model. The inhibition effect was dependent on the frequency and duration of the magnetic stimulus, with high frequency being more effective in suppressing EFA. EFA suppression by the magnetic field was also observed in the 4-AP model, in a frequency and duration - dependent manner. The study provides a platform for further investigation of cellular and molecular mechanisms underlying epilepsy treatment with time varying magnetic fields.

Response to Deep Brain Stimulation in Three Brain Targets with Implications in Mental Disorders: A PET Study in Rats

Objective

To investigate metabolic changes in brain networks by deep brain stimulation (DBS) of the medial prefrontal cortex (mPFC), nucleus accumbens (NAcc) and dorsomedial thalamus (DM) using positron emission tomography (PET) in naïve rats.

Methods

43 male Wistar rats underwent stereotactic surgery and concentric bipolar platinum-iridium electrodes were bilaterally implanted into one of the three brain sites. [¹⁸F]-fluoro-2-deoxy-glucose-PET (¹⁸FDG-PET) and computed tomography (CT) scans were performed at the 7th (without DBS) and 9th day (with DBS) after surgery. Stimulation period matched tracer uptake period. Images were acquired with a small-animal PET-CT scanner. Differences in glucose uptake between groups were assessed with Statistical Parametric Mapping.

Results

DBS induced site-specific metabolic changes, although a common increased metabolic activity in the piriform cortex was found for the three brain targets. mPFC-DBS increased metabolic activity in the striatum, temporal and amygdala, and reduced it in the cerebellum, brainstem (BS) and periaqueductal gray matter (PAG). NAcc-DBS increased metabolic activity in the subiculum and olfactory bulb, and decreased it in the BS, PAG, septum and hypothalamus. DM-DBS increased metabolic activity in the striatum, NAcc and thalamus and decreased it in the temporal and cingulate cortex.

Conclusions

DBS induced significant changes in ¹⁸FDG uptake in brain regions associated with the basal ganglia-thalamo-cortical circuitry. Stimulation of mPFC, NAcc and DM induced different patterns of ¹⁸FDG uptake despite interacting with the same circuitries. This may have important implications to DBS research suggesting individualized target selection according to specific neural modulatory requirements.

Multimodal 7T Imaging of Thalamic Nuclei for Preclinical Deep Brain Stimulation Applications

Precise neurosurgical targeting of electrode arrays within the brain is essential to the successful treatment of a range of brain disorders with deep brain stimulation (DBS) therapy. Here, we describe a set of computational tools to generate in vivo, subject-specific atlases of individual thalamic nuclei thus improving the ability to visualize thalamic targets for preclinical DBS applications on a subject-specific basis. A sequential nonlinear atlas warping technique and a Bayesian estimation technique for probabilistic crossing fiber tractography were applied to high field (7T) susceptibility-weighted and diffusion-weighted imaging, respectively, in seven rhesus macaques. Image contrast, including contrast within thalamus from the susceptibility-weighted images, informed the atlas warping process and guided the seed point placement for fiber tractography. The susceptibility-weighted imaging resulted in relative hyperintensity of the intralaminar nuclei and relative hypointensity in the medial dorsal nucleus, pulvinar, and the medial/ventral border of the ventral posterior nuclei, providing context to demarcate borders of the ventral nuclei of thalamus, which are often targeted for DBS applications. Additionally, ascending fiber tractography of the medial lemniscus, superior cerebellar peduncle, and pallidofugal pathways into thalamus provided structural demarcation of the ventral nuclei of thalamus. The thalamic substructure boundaries were validated through in vivo electrophysiological recordings and post-mortem blockface tissue sectioning. Together, these imaging tools for visualizing and segmenting thalamus have the potential to improve the neurosurgical targeting of DBS implants and enhance the selection of stimulation settings through more accurate computational models of DBS.

Merging DBS with viral vector or stem cell implantation: "hybrid" stereotactic surgery as an evolution in the surgical treatment of Parkinson's disease

Parkinson’s disease (PD) is a complex neurodegenerative disorder that is currently managed using a broad array of symptom-based strategies. However, targeting its molecular origins represents the potential to discover disease-modifying therapies. Deep brain stimulation (DBS), a highly successful treatment modality for PD symptoms, addresses errant electrophysiological signaling pathways in the basal ganglia. In contrast, ongoing clinical trials testing gene and cell replacement therapies propose to protect or restore neuronal-based physiologic dopamine transmission in the striatum. Given promising new platforms to enhance target localization—such as interventional MRI-guided stereotaxy—the opportunity now exists to create hybrid therapies that combine DBS with gene therapy and/or cell implantation. In this mini-review, we discuss approaches used for central nervous system biologic delivery in PD patients in previous trials and propose a new set of strategies based on novel molecular targets. A multifaceted approach, if successful, may not only contribute to our understanding of PD pathology but could introduce a new era of disease modification.

Flexible Use of Predictive Cues beyond the Orbitofrontal Cortex: Role of the Submedius Thalamic Nucleus

The orbitofrontal cortex (OFC) is known to play a crucial role in learning the consequences of specific events. However, the contribution of OFC thalamic inputs to these processes is largely unknown. Using a tract-tracing approach, we first demonstrated that the submedius nucleus (Sub) shares extensive reciprocal connections with the OFC. We then compared the effects of excitotoxic lesions of the Sub or the OFC on the ability of rats to use outcome identity to direct responding. We found that neither OFC nor Sub lesions interfered with the basic differential outcomes effect. However, more specific tests revealed that OFC rats, but not Sub rats, were disproportionally relying on the outcome, rather than on the discriminative stimulus, to guide behavior, which is consistent with the view that the OFC integrates information about predictive cues. In subsequent experiments using a Pavlovian contingency degradation procedure, we found that both OFC and Sub lesions produced a severe deficit in the ability to update Pavlovian associations. Altogether, the submedius therefore appears as a functionally relevant thalamic component in a circuit dedicated to the integration of predictive cues to guide behavior, previously conceived as essentially dependent on orbitofrontal functions. Significance statement: In the present study, we identify a largely unknown thalamic region, the submedius nucleus, as a new functionally relevant component in a circuit supporting the flexible use of predictive cues. Such abilities were previously conceived as largely dependent on the orbitofrontal cortex. Interestingly, this echoes recent findings in the field showing, in research involving an instrumental setup, an additional involvement of another thalamic nuclei, the parafascicular nucleus, when correct responding requires an element of flexibility (Bradfield et al., 2013a). Therefore, the present contribution supports the emerging view that limbic thalamic nuclei may contribute critically to adaptive responding when an element of flexibility is required after the establishment of initial learning.

Critical review of the responsive neurostimulator system for epilepsy

Patients with medically refractory epilepsy have historically had few effective treatment options. Electrical brain stimulation for seizures has been studied for decades and ongoing technological refinements have made possible the development of an implantable electrical brain stimulator. The NeuroPace responsive neurostimulator was recently approved by the FDA for clinical use and the initial reports are encouraging. This device continually monitors brain activity and delivers an electric stimulus when abnormal activity is detected. Early reports of efficacy suggest that the device is well tolerated and offers a reduction in seizure frequency by approximately half at 2 years.

Lower expression of glutamic acid decarboxylase 67 in the prefrontal cortex in schizophrenia: contribution of altered regulation by Zif268

OBJECTIVE

Cognitive deficits of schizophrenia may be due at least in part to lower expression of the 67-kDa isoform of glutamic acid decarboxylase (GAD67), a key enzyme for GABA synthesis, in the dorsolateral prefrontal cortex of individuals with schizophrenia. However, little is known about the molecular regulation of lower cortical GAD67 levels in schizophrenia. The GAD67 promoter region contains a conserved Zif268 binding site, and Zif268 activation is accompanied by increased GAD67 expression. Thus, altered expression of the immediate early gene Zif268 may contribute to lower levels of GAD67 mRNA in the dorsolateral prefrontal cortex in schizophrenia.

METHOD

The authors used polymerase chain reaction to quantify GAD67 and Zif268 mRNA levels in dorsolateral prefrontal cortex area 9 from 62 matched pairs of schizophrenia and healthy comparison subjects, and in situ hybridization to assess Zif268 expression at laminar and cellular levels of resolution. The effects of potentially confounding variables were assessed in human subjects, and the effects of antipsychotic treatments were tested in antipsychotic-exposed monkeys. The specificity of the Zif268 findings was assessed by quantifying mRNA levels for other immediate early genes.

RESULTS

GAD67 and Zif268 mRNA levels were significantly lower and were positively correlated in the schizophrenia subjects. Both Zif268 mRNA-positive neuron density and Zif268 mRNA levels per neuron were significantly lower in the schizophrenia subjects. These findings were robust to the effects of the confounding variables examined and differed from other immediate early genes.

CONCLUSIONS

Deficient Zif268 mRNA expression may contribute to lower cortical GAD67 levels in schizophrenia, suggesting a potential mechanistic basis for altered cortical GABA synthesis and impaired cognition in schizophrenia.