Behavioral, neurochemical and molecular changes after acute deep brain stimulation of the infralimbic prefrontal cortex

New Advances in the Pharmacology and Toxicology of Lithium: A Neurobiologically Oriented Overview

Over the last six decades, lithium has been considered the gold standard treatment for the long-term management of bipolar disorder due to its efficacy in preventing both manic and depressive episodes as well as suicidal behaviors. Nevertheless, despite numerous observed effects on various cellular pathways and biologic systems, the precise mechanism through which lithium stabilizes mood remains elusive. Furthermore, there is recent support for the therapeutic potential of lithium in other brain diseases. This review offers a comprehensive examination of contemporary understanding and predominant theories concerning the diverse mechanisms underlying lithium's effects. These findings are based on investigations utilizing cellular and animal models of neurodegenerative and psychiatric disorders. Recent studies have provided additional support for the significance of glycogen synthase kinase-3 (GSK3) inhibition as a crucial mechanism. Furthermore, research has shed more light on the interconnections between GSK3-mediated neuroprotective, antioxidant, and neuroplasticity processes. Moreover, recent advancements in animal and human models have provided valuable insights into how lithium-induced modifications at the homeostatic synaptic plasticity level may play a pivotal role in its clinical effectiveness. We focused on findings from translational studies suggesting that lithium may interface with microRNA expression. Finally, we are exploring the repurposing potential of lithium beyond bipolar disorder. These recent findings on the therapeutic mechanisms of lithium have provided important clues toward developing predictive models of response to lithium treatment and identifying new biologic targets. SIGNIFICANCE STATEMENT: Lithium is the drug of choice for the treatment of bipolar disorder, but its mechanism of action in stabilizing mood remains elusive. This review presents the latest evidence on lithium's various mechanisms of action. Recent evidence has strengthened glycogen synthase kinase-3 (GSK3) inhibition, changes at the level of homeostatic synaptic plasticity, and regulation of microRNA expression as key mechanisms, providing an intriguing perspective that may help bridge the mechanistic gap between molecular functions and its clinical efficacy as a mood stabilizer.

Systematic review of rodent studies of deep brain stimulation for the treatment of neurological, developmental and neuropsychiatric disorders

Deep brain stimulation (DBS) modulates local and widespread connectivity in dysfunctional networks. Positive results are observed in several patient populations; however, the precise mechanisms underlying treatment remain unknown. Translational DBS studies aim to answer these questions and provide knowledge for advancing the field. Here, we systematically review the literature on DBS studies involving models of neurological, developmental and neuropsychiatric disorders to provide a synthesis of the current scientific landscape surrounding this topic. A systematic analysis of the literature was performed following PRISMA guidelines. 407 original articles were included. Data extraction focused on study characteristics, including stimulation protocol, behavioural outcomes, and mechanisms of action. The number of articles published increased over the years, including 16 rat models and 13 mouse models of transgenic or healthy animals exposed to external factors to induce symptoms. Most studies targeted telencephalic structures with varying stimulation settings. Positive behavioural outcomes were reported in 85.8% of the included studies. In models of psychiatric and neurodevelopmental disorders, DBS-induced effects were associated with changes in monoamines and neuronal activity along the mesocorticolimbic circuit. For movement disorders, DBS improves symptoms via modulation of the striatal dopaminergic system. In dementia and epilepsy models, changes to cellular and molecular aspects of the hippocampus were shown to underlie symptom improvement. Despite limitations in translating findings from preclinical to clinical settings, rodent studies have contributed substantially to our current knowledge of the pathophysiology of disease and DBS mechanisms. Direct inhibition/excitation of neural activity, whereby DBS modulates pathological oscillatory activity within brain networks, is among the major theories of its mechanism. However, there remain fundamental questions on mechanisms, optimal targets and parameters that need to be better understood to improve this therapy and provide more individualized treatment according to the patient's predominant symptoms.

Brain-derived neurotrophic factor/tropomyosin receptor kinase B signaling in spinal muscular atrophy and amyotrophic lateral sclerosis

Tropomyosin receptor kinase B (TrkB) and its primary ligand brain-derived neurotrophic factor (BDNF) are expressed in the neuromuscular system, where they affect neuronal survival, differentiation, and functions. Changes in BDNF levels and full-length TrkB (TrkB-FL) signaling have been revealed in spinal muscular atrophy (SMA) and amyotrophic lateral sclerosis (ALS), two common forms of motor neuron diseases that are characterized by defective neuromuscular junctions in early disease stages and subsequently progressive muscle weakness. This review summarizes the current understanding of BDNF/TrkB-FL-related research in SMA and ALS, with an emphasis on their alterations in the neuromuscular system and possible BDNF/TrkB-FL-targeting therapeutic strategies. The limitations of current studies and future directions are also discussed, giving the hope of discovering novel and effective treatments.

Neurochemical mechanisms of deep brain stimulation for depression in animal models

Deep brain stimulation (DBS) has emerged as a neuromodulation therapy for treatment-resistant depression, but its actual efficacy and mechanisms of action are still unclear. Changes in neurochemical transmission are important mechanisms of antidepressant therapies. Here, we review the preclinical DBS literature reporting behavioural and neurochemical data associated with its antidepressant-like effects. The most commonly studied target in preclinical models was the ventromedial prefrontal cortex (vmPFC). In rodents, DBS delivered to this target induced serotonin (5-HT) release and increased 5-HT1_B receptor expression. The antidepressant-like effects of vmPFC DBS seemed to be independent of the serotonin transporter and potentially mediated by the direct modulation of prefrontal projections to the raphe. Adenosinergic and glutamatergic transmission might have also play a role. Medial forebrain bundle (MFB) DBS increased dopamine levels and reduced D2 receptor expression, whereas nucleus accumbens (NAcc), and lateral habenula (LHb) stimulation increased catecholamine levels in different brain regions. In rodents, subthalamic nucleus (STN) DBS induced robust depression-like responses associated with a reduction in serotonergic transmission, as revealed by a decrease in serotonin release. Some of these effects seemed to be mediated by 5HT1_A receptors. In conclusion, the antidepressant-like effects of DBS in preclinical models have been well documented in multiple targets. Though variable mechanisms have been proposed, DBS-induced acute and long-term changes in neurochemical substrates seem to play an important role in the antidepressant-like effects of this therapy.

Sex differences in amygdalohippocampal oscillations and neuronal activation in a rodent anxiety model and in response to infralimbic deep brain stimulation

Introduction

Depression and anxiety are highly comorbid mental disorders with marked sex differences. Both disorders show altered activity in the amygdala, hippocampus, and prefrontal cortex. Infralimbic deep brain stimulation (DBS-IL) has anxiolytic and antidepressant effects, but the underlying mechanisms remain unclear. We aimed to contribute to understanding sex differences in the neurobiology of these disorders.

Methods

In male and female rats, we recorded neural oscillations along the dorsoventral axis of the hippocampus and the amygdala in response to an anxiogenic drug, FG-7142. Following this, we applied DBS-IL.

Results

Surprisingly, in females, the anxiogenic drug failed to induce most of the changes observed in males. We found sex differences in slow, delta, theta, and beta oscillations, and the amygdalo-hippocampal communication in response to FG-7142, with modest changes in females. Females had a more prominent basal gamma, and the drug altered this band only in males. We also analyzed c-Fos expression in both sexes in stress-related structures in response to FG-7142, DBS-IL, and combined interventions. With the anxiogenic drug, females showed reduced expression in the nucleus incertus, amygdala, septohippocampal network, and neocortical levels. In both experiments, the DBS-IL reversed FG-7142-induced effects, with a more substantial effect in males than females.

Discussion

Here, we show a reduced response in female rats which contrasts with the higher prevalence of anxiety in women but is consistent with other studies in rodents. Our results open compelling questions about sex differences in the neurobiology of anxiety and depression and their study in animal models.

Continuous high-frequency deep brain stimulation of the anterior insula modulates autism-like behavior in a valproic acid-induced rat model

BACKGROUND

Until now, the treatment of patients with autism spectrum disorder (ASD) remain a difficult problem. The insula is involved in empathy and sensorimotor integration, which are often impaired in individuals with ASD. Deep brain stimulation, modulating neuronal activity in specific brain circuits, has recently been considered as a promising intervention for neuropsychiatric disorders. Valproic acid (VPA) is a potential teratogenic agent, and prenatal exposure can cause autism-like symptoms including repetitive behaviors and defective sociability. Herein, we investigated the effects of continuous high-frequency deep brain stimulation in the anterior insula of rats exposed to VPA and explored cognitive functions, behavior, and molecular proteins connected to autism spectrum disorder.

METHODS

VPA-exposed offspring were bilaterally implanted with electrodes in the anterior insula (Day 0) with a recovery period of 1 week. (Day 0-7). High-frequency deep brain stimulation was applied from days 11 to 29. Three behavioral tests, including three-chamber social interaction test, were performed on days 7, 13, 18, 25 and 36, and several rats were used for analysis of immediate early genes and proteomic after deep brain stimulation intervention. Meanwhile, animals were subjected to a 20 day spatial learning and cognitive rigidity test using IntelliCage on day 11.

RESULTS

Deep brain stimulation improved the sociability and social novelty preference at day 18 prior to those at day 13, and the improvement has reached the upper limit compared to day 25. As for repetitive/stereotypic-like behavior, self- grooming time were reduced at day 18 and reached the upper limit, and the numbers of burried marbles were reduced at day 13 prior to those at day 18 and day 25. The improvements of sociability and social novelty preference were persistent after the stimulation had ceased. Spatial learning ability and cognitive rigidity were unaffected. We identified 35 proteins in the anterior insula, some of which were intimately linked to autism, and their expression levels were reversed upon administration of deep brain stimulation.

CONCLUSIONS

Autism-like behavior was ameliorated and autism-related proteins were reversed in the insula by deep brain stimulation intervention, these findings reveal that the insula may be a potential target for DBS in the treatment of autism, which provide a theoretical basis for its clinical application., although future studies are still warranted.

Serotonin 5-HT1B receptors mediate the antidepressant- and anxiolytic-like effects of ventromedial prefrontal cortex deep brain stimulation in a mouse model of social defeat

BACKGROUND

Deep brain stimulation (DBS) delivered to the ventromedial prefrontal cortex (vmPFC) induces antidepressant- and anxiolytic-like responses in various animal models. Electrophysiology and neurochemical studies suggest that these effects may be dependent, at least in part, on the serotonergic system. In rodents, vmPFC DBS reduces raphe cell firing and increases serotonin (5-HT) release and the expression of serotonergic receptors in different brain regions.

METHODS

We examined whether the behavioural responses of chronic vmPFC DBS are mediated by 5-HT_1A or 5-HT_1B receptors through a series of experiments. First, we delivered stimulation to mice undergoing chronic social defeat stress (CSDS), followed by a battery of behavioural tests. Second, we measured the expression of 5-HT_1A and 5-HT_1B receptors in different brain regions with western blot. Finally, we conducted pharmacological experiments to mitigate the behavioural effects of DBS using the 5-HT_1A antagonist, WAY-100635, or the 5-HT_1B antagonist, GR-127935.

RESULTS

We found that chronic DBS delivered to stressed animals reduced the latency to feed in the novelty suppressed feeding test (NSF) and immobility in the forced swim test (FST). Though no significant changes were observed in receptor expression, 5-HT_1B levels in DBS-treated animals were found to be non-significantly increased in the vmPFC, hippocampus, and nucleus accumbens and reduced in the raphe compared to non-stimulated controls. Finally, while animals given vmPFC stimulation along with WAY-100635 still presented significant responses in the NSF and FST, these were mitigated following GR-127935 administration.

CONCLUSIONS

The antidepressant- and anxiolytic-like effects of DBS in rodents may be partially mediated by 5-HT1_B receptors.

Deep brain stimulation improved depressive-like behaviors and hippocampal synapse deficits by activating the BDNF/mTOR signaling pathway

Our previous study demonstrated that acute deep brain stimulation (DBS) in the ventromedial prefrontal cortex (vmPFC) remarkably improved the depressive-like behaviors in a rat model of chronic unpredictable mild stress (CUS rats). However, the mechanisms by which chronic DBS altered depressive-like behaviors and reversed cognitive impairment have not been clarified. Recent work has shown that deficits in brain-derived neurotrophic factor (BDNF) and its downstream proteins, including mammalian target of rapamycin (mTOR), might be involved in the pathogenesis of depression. Therefore, we hypothesized that the antidepressant-like and cognitive improvement effects of DBS were achieved by activating the BDNF/mTOR pathway. CUS rats received vmPFC DBS at 20 Hz for 1 h once a day for 28 days. After four weeks of stimulation, the rats were assessed for the presence of depressive-like behaviors and euthanized to detect BDNF/mTOR signaling using immunoblots. DBS at the vmPFC significantly ameliorated depressive-like behaviors and spatial learning and memory deficits in the CUS rats. Furthermore, DBS restored the reduced synaptic density in the hippocampus induced by CUS and increased the expression or activity of BDNF, Akt, and mTOR in the hippocampus. Thus, the antidepressant-like effects and cognitive improvement produced by vmPFC DBS might be mediated through increased activity of the BDNF/mTOR signaling pathway.

Biomarkers for Deep Brain Stimulation in Animal Models of Depression

OBJECTIVES

Despite recent advances in depression treatment, many patients still do not respond to serial conventional therapies and are considered "treatment resistant." Deep brain stimulation (DBS) has therapeutic potential in this context. This comprehensive review of recent studies of DBS for depression in animal models identifies potential biomarkers for improving therapeutic efficacy and predictability of conventional DBS to aid future development of closed-loop control of DBS systems.

MATERIALS AND METHODS

A systematic search was performed in Pubmed, EMBASE, and Cochrane Review using relevant keywords. Overall, 56 animal studies satisfied the inclusion criteria.

RESULTS

Outcomes were divided into biochemical/physiological, electrophysiological, and behavioral categories. Promising biomarkers include biochemical assays (in particular, microdialysis and electrochemical measurements), which provide real-time results in awake animals. Electrophysiological tests, showing changes at both the target site and downstream structures, also revealed characteristic changes at several anatomic targets (such as the medial prefrontal cortex and locus coeruleus). However, the substantial range of models and DBS targets limits the ability to draw generalizable conclusions in animal behavioral models.

CONCLUSIONS

Overall, DBS is a promising therapeutic modality for treatment-resistant depression. Different outcomes have been used to assess its efficacy in animal studies. From the review, electrophysiological and biochemical markers appear to offer the greatest potential as biomarkers for depression. However, to develop closed-loop DBS for depression, additional preclinical and clinical studies with a focus on identifying reliable, safe, and effective biomarkers are warranted.

Galanin (1-15) Enhances the Behavioral Effects of Fluoxetine in the Olfactory Bulbectomy Rat, Suggesting a New Augmentation Strategy in Depression

BACKGROUND

Selective serotonergic reuptake inhibitors, including fluoxetine (FLX), are the most commonly used for the treatment of major depression. However, they are effective for remission in only 30% of patients. Recently, we observed that Galanin (1-15) [GAL(1-15)] enhanced the antidepressant effects of FLX in naïve animals, suggesting a new augmentation strategy in depression.

METHODS

We have analyzed in an animal model of depression, the olfactory bulbectomy (OBX) rats, the effect of GAL(1-15) on FLX-mediated responses in the forced swimming test and the sucrose preference test and the involvement of GAL receptor 2 with its antagonist, M871. We have also studied the corticosterone levels in OBX after the coadministration of GAL(1-15) with FLX. Moreover, we studied whether the effects of GAL(1-15) on FLX actions were mediated via auto- and heteroreceptor 5-HT1A (5-HT1AR), analyzing the binding characteristics, mRNA levels, and functionality of 5-HT1AR in the dorsal hippocampus.

RESULTS

GAL(1-15) enhances the antidepressant-like effects induced by FLX in OBX animals in the forced swimming test and the sucrose preference test. The involvement of the GALR2 was demonstrated with M871. Importantly, the mechanism underlying the GAL(1-15)/FLX interactions in the OBX animals involves the 5-HT1AR in the hippocampus at the plasma membrane (increase of affinity and density of 5HT1AR in the DG) and transcriptional (increase of 5HT1AR mRNA levels in DG and CA1) levels. Besides, the coadministration of GAL(1-15) and FLX also reduced OBX-increased corticosterone levels.

CONCLUSIONS

The results open the possibility to use GAL(1-15) in combination with FLX as a novel strategy for the treatment of depression.

Insufficiency of ventral hippocampus to medial prefrontal cortex transmission explains antidepressant non-response

BACKGROUND

There is extensive evidence that antidepressant drugs restore normal brain function by repairing damage to ventral hippocampus (vHPC) and medial prefrontal cortex (mPFC). While the damage is more extensive in hippocampus, the evidence of treatments, such as deep brain stimulation, suggests that functional changes in prefrontal cortex may be more critical. We hypothesized that antidepressant non-response may result from an insufficiency of transmission from vHPC to mPFC.

METHOD

Antidepressant non-responsive Wistar Kyoto (WKY) rats were subjected to chronic mild stress (CMS), then treated with chronic daily administration of the antidepressant drug venlafaxine (VEN) and/or repeated weekly optogenetic stimulation (OGS) of afferents to mPFC originating from vHPC or dorsal HPC (dHPC).

RESULTS

As in many previous studies, CMS decreased sucrose intake, open-arm entries on the elevated plus maze (EPM), and novel object recognition (NOR). Neither VEN nor vHPC-mPFC OGS alone was effective in reversing the effects of CMS, but the combination of chronic VEN and repeated OGS restored normal behaviour on all three measures. dHPC-mPFC OGS restored normal behaviour in the EPM and NOR test irrespective of concomitant VEN treatment, and had no effect on sucrose intake.

CONCLUSIONS

The synergism between VEN and vHPC-mPFC OGS supports the hypothesis that the antidepressant non-responsiveness of WKY rats results from a failure of antidepressant treatment fully to restore transmission in the vHPC-mPFC pathway.

Induced Dipoles and Possible Modulation of Wireless Effects in Implanted Electrodes. Effects of Implanting Insulated Electrodes on an Animal Test to Screen Antidepressant Activity

There is evidence that Deep Brain Stimulation (DBS) produces health benefits in patients even before initiating stimulation. Furthermore, DBS electrode insertion in rat infralimbic cortex (ILC) provokes antidepressant-like effects before stimulation, due to local inflammation and astrogliosis. Consequently, a significant effect of implanting electrodes is suspected. External fields, similar in magnitude to the brain’s endogenous fields, induce electric dipoles in conducting materials, in turn influencing neural cell growth through wireless effects. To elucidate if such dipoles influence depressive-like behavior, without external stimulation, the comparative effect of conducting and insulated electrodes along with the glial response is studied in unstressed rats. Naïve and implanted rats with electrically insulated or uninsulated steel electrodes were evaluated in the modified forced swimming test and expression of ILC-glial markers was assessed. An antidepressant-like effect was observed with conducting but not with insulated electrodes. Gliosis was detected in both groups, but astroglial reactivity was larger near uninsulated electrodes. Thus, induced dipoles and antidepressant-like effects were only observed with conducting implants. Such correlation suggests that dipoles induced in electrodes by endogenous fields in turn induce neuron stimulation in a feedback loop between electrodes and neural system. Further research of the effects of unwired conducting implants could open new approaches to regulating neuronal function, and possibly treat neurological disorders.

A narrative review on invasive brain stimulation for treatment-resistant depression

While most patients with depression respond to pharmacotherapy and psychotherapy, about one-third will present treatment resistance to these interventions. For patients with treatment-resistant depression (TRD), invasive neurostimulation therapies such as vagus nerve stimulation, deep brain stimulation, and epidural cortical stimulation may be considered. We performed a narrative review of the published literature to identify papers discussing clinical studies with invasive neurostimulation therapies for TRD. After a database search and title and abstract screening, relevant English-language articles were analyzed. Vagus nerve stimulation, approved by the U.S. Food and Drug Administration as a TRD treatment, may take several months to show therapeutic benefits, and the average response rate varies from 15.2-83%. Deep brain stimulation studies have shown encouraging results, including rapid response rates (> 30%), despite conflicting findings from randomized controlled trials. Several brain regions, such as the subcallosal-cingulate gyrus, nucleus accumbens, ventral capsule/ventral striatum, anterior limb of the internal capsule, medial-forebrain bundle, lateral habenula, inferior-thalamic peduncle, and the bed-nucleus of the stria terminalis have been identified as key targets for TRD management. Epidural cortical stimulation, an invasive intervention with few reported cases, showed positive results (40-60% response), although more extensive trials are needed to confirm its potential in patients with TRD.

mTOR Knockdown in the Infralimbic Cortex Evokes A Depressive-like State in Mouse

Fast and sustained antidepressant effects of ketamine identified the mammalian target of rapamycin (mTOR) signaling pathway as the main modulator of its antidepressive effects. Thus, mTOR signaling has become integral for the preclinical evaluation of novel compounds to treat depression. However, causality between mTOR and depression has yet to be determined. To address this, we knocked down mTOR expression in mice using an acute intracerebral infusion of small interfering RNAs (siRNA) in the infralimbic (IL) or prelimbic (PrL) cortices of the medial prefrontal cortex (mPFC), and evaluated depressive- and anxious-like behaviors. mTOR knockdown in IL, but not PrL, cortex produced a robust depressive-like phenotype in mice, as assessed in the forced swimming test (FST) and the tail suspension test (TST). This phenotype was associated with significant reductions of mTOR mRNA and protein levels 48 h post-infusion. In parallel, decreased brain-derived neurotrophic factor (BDNF) expression was found bilaterally in both IL and PrL cortices along with a dysregulation of serotonin (5-HT) and glutamate (Glu) release in the dorsal raphe nucleus (DRN). Overall, our results demonstrate causality between mTOR expression in the IL cortex and depressive-like behaviors, but not in anxiety.

The Oscillatory Profile Induced by the Anxiogenic Drug FG-7142 in the Amygdala-Hippocampal Network Is Reversed by Infralimbic Deep Brain Stimulation: Relevance for Mood Disorders

Anxiety and depression exhibit high comorbidity and share the alteration of the amygdala–hippocampal–prefrontal network, playing different roles in the ventral and dorsal hippocampi. Deep brain stimulation of the infralimbic cortex in rodents or the human equivalent—the subgenual cingulate cortex—constitutes a fast antidepressant treatment. The aim of this work was: (1) to describe the oscillatory profile in a rodent model of anxiety, and (2) to deepen the therapeutic basis of infralimbic deep brain stimulation in mood disorders. First, the anxiogenic drug FG-7142 was administered to anaesthetized rats to characterize neural oscillations within the amygdala and the dorsoventral axis of the hippocampus. Next, deep brain stimulation was applied. FG-7142 administration drastically reduced the slow waves, increasing delta, low theta, and beta oscillations in the network. Moreover, FG-7142 altered communication in these bands in selective subnetworks. Deep brain stimulation of the infralimbic cortex reversed most of these FG-7142 effects. Cross-frequency coupling was also inversely modified by FG-7142 and by deep brain stimulation. Our study demonstrates that the hyperactivated amygdala–hippocampal network associated with the anxiogenic drug exhibits an oscillatory fingerprint. The study contributes to comprehending the neurobiological basis of anxiety and the effects of infralimbic deep brain stimulation.

Clinical applications of neurochemical and electrophysiological measurements for closed-loop neurostimulation

The development of closed-loop deep brain stimulation (DBS) systems represents a significant opportunity for innovation in the clinical application of neurostimulation therapies. Despite the highly dynamic nature of neurological diseases, open-loop DBS applications are incapable of modifying parameters in real time to react to fluctuations in disease states. Thus, current practice for the designation of stimulation parameters, such as duration, amplitude, and pulse frequency, is an algorithmic process. Ideal stimulation parameters are highly individualized and must reflect both the specific disease presentation and the unique pathophysiology presented by the individual. Stimulation parameters currently require a lengthy trial-and-error process to achieve the maximal therapeutic effect and can only be modified during clinical visits. The major impediment to the development of automated, adaptive closed-loop systems involves the selection of highly specific disease-related biomarkers to provide feedback for the stimulation platform. This review explores the disease relevance of neurochemical and electrophysiological biomarkers for the development of closed-loop neurostimulation technologies. Electrophysiological biomarkers, such as local field potentials, have been used to monitor disease states. Real-time measurement of neurochemical substances may be similarly useful for disease characterization. Thus, the introduction of measurable neurochemical analytes has significantly expanded biomarker options for feedback-sensitive neuromodulation systems. The potential use of biomarker monitoring to advance neurostimulation approaches for treatment of Parkinson's disease, essential tremor, epilepsy, Tourette syndrome, obsessive-compulsive disorder, chronic pain, and depression is examined. Further, challenges and advances in the development of closed-loop neurostimulation technology are reviewed, as well as opportunities for next-generation closed-loop platforms.

Perspectives for therapy of treatment-resistant depression

A high proportion of depressed patients fail to respond to antidepressant drug treatment. Treatment-resistant depression (TRD) is a major challenge for the psychopharmacology of mood disorders. Only in the past decade have novel treatments, including deep brain stimulation (DBS) and ketamine, been discovered that provide rapid and sometimes prolonged relief to a high proportion of TRD sufferers. In this review, we consider the current status of TRD from four perspectives: the challenge of developing an appropriate regulatory framework for novel rapidly acting antidepressants; the efficacy of non-pharmacological somatic therapies; the development of an animal model of TRD and its use to understand the neural basis of antidepressant non-response; and the potential for rapid antidepressant action from targets (such as 5-HT_1A receptors) beyond the glutamate receptor.

Early-life stress effects on BDNF DNA methylation in first-episode psychosis and in rats reared in isolation

Stressful events during early-life are risk factors for psychiatric disorders. Brain-derived neurotrophic factor (BDNF) is implicated in psychosis pathophysiology and deficits in BDNF mRNA in animal models of psychiatric disease are reported. DNA methylation can control gene expression and may be influenced by environmental factors such as early-life stress. We investigated BDNF methylation in first-episode psychosis (FEP) patients (n = 58), their unaffected siblings (n = 29) and community-based controls (n = 59), each of whom completed the Childhood Trauma Questionnaire (CTQ); BDNF methylation was also tested in male Wistar rats housed isolated or grouped from weaning. DNA was extracted from human blood and rat brain (prefrontal cortex and hippocampus), bisulphite-converted and the methylation of equivalent sequences within BDNF exon IV determined by pyrosequencing. BDNF methylation did not differ significantly between diagnostic groups; however, individuals who had experienced trauma presented higher levels of methylation. We found association between the mean BDNF methylation and total CTQ score in FEP, as well as between individual CpG sites and subtypes of trauma. No significant correlations were found for controls or siblings with child trauma. These results were independent of age, gender, body mass index, BDNF genotype or LINE-1, a measure of global methylation, which showed no significant association with trauma. Isolation rearing resulted in increased BDNF methylation in both brain regions compared to group-housed animals, a correlate of previously reported changes in gene expression. Our results suggest that childhood maltreatment may result in increased BDNF methylation, providing a mechanism underlying the association between early-life stress and psychosis.

AMPA receptors mediate the pro-cognitive effects of electrical and optogenetic stimulation of the medial prefrontal cortex in antidepressant non-responsive Wistar-Kyoto rats

BACKGROUND

The chronic mild stress (CMS) procedure is a widely used animal model of depression, and its application in Wistar-Kyoto (WKY) rats has been validated as a model of antidepressant-refractory depression. While not responding to chronic treatment with antidepressant drugs, WKY rats do respond to acute deep brain stimulation (DBS) of the medial prefrontal cortex (mPFC). In antidepressant-responsive strains there is evidence suggesting a role for AMPA subtype of glutamate receptor in the action mechanism of both antidepressants and DBS.

METHODS

Animals were subjected to CMS for 6 to 8 weeks; sucrose intake was monitored weekly and novel object recognition (NOR) test was conducted following recovery from CMS. Wistars were treated chronically with venlafaxine (VEN), while WKY were treated acutely with either DBS, optogenetic stimulation (OGS) of virally-transduced (AAV5-hSyn-ChR2-EYFP) mPFC or ventral hippocampus, or acute intra-mPFC injection of the AMPA receptor positive allosteric modulator CX-516. The AMPA receptor antagonist NBQX was administered, at identical sites in mPFC, immediately following the exposure trial in the NOR.

RESULTS

Sucrose intake and NOR were suppressed by CMS, and restored by VEN in Wistars and by DBS, OGS, or CX-516 in WKY. However, OGS of the ventral hippocampal afferents to mPFC was ineffective. A low dose of NBQX selectively blocked the procognitive effect of VEN, DBS and OGS.

CONCLUSIONS

These results suggest that activation of AMPA receptors in the mPFC represents a common pathway for the antidepressant effects of both conventional (VEN) and novel (DBS, OGS) antidepressant modalities, in both antidepressant responsive (Wistar) and antidepressant-resistant (WKY) rats.

Low-intensity pulsed ultrasound ameliorates depression-like behaviors in a rat model of chronic unpredictable stress

Introduction

There is an unmet need for better nonpharmaceutical treatments for depression. Low‐intensity pulsed ultrasound (LIPUS) is a novel type of neuromodulation that could be helpful for depressed patients.

Objective

The goal of this study was to investigate the feasibility and potential mechanisms of LIPUS in the treatment of depression.

Methods

Chronic unpredictable stress (CUS) was used to generate rats with depression‐like features that were treated with four weeks of LIPUS stimulation of the ventromedial prefrontal cortex. Depression‐like behaviors were assessed with the sucrose preference, forced swim, and open field tests. BDNF/mTORC1 signaling was examined by Western blot to investigate this potential molecular mechanism. The safety of LIPUS was evaluated using hematoxylin‐eosin and Nissl staining.

Results

Four weeks of LIPUS stimulation significantly increased sucrose preference and reduced forced swim immobility time in CUS rats. LIPUS also partially reversed the molecular effects of CUS that included decreased levels of BDNF, phosphorylated tyrosine receptor kinase B (TrkB), extracellular signal‐regulated kinase (ERK), mammalian target of rapamycin complex 1 (mTORC1), and S6 kinase (S6K). Moreover, histological staining revealed no gross tissue damage.

Conclusions

Chronic LIPUS stimulation can effectively and safely improve depression‐like behaviors in CUS rats. The underlying mechanisms may be related to enhancement of BDNF/ERK/mTORC1 signaling pathways in the prefrontal cortex (PFC). LIPUS is a promising noninvasive neuromodulation tool that merits further study as a potential treatment for depression.

A Decade of Progress in Deep Brain Stimulation of the Subcallosal Cingulate for the Treatment of Depression

Major depression contributes significantly to the global disability burden. Since the first clinical study of deep brain stimulation (DBS), over 446 patients with depression have now undergone this neuromodulation therapy, and 29 animal studies have investigated the efficacy of subgenual cingulate DBS for depression. In this review, we aim to provide a comprehensive overview of the progress of DBS of the subcallosal cingulate in humans and the medial prefrontal cortex, its rodent homolog. For preclinical animal studies, we discuss the various antidepressant-like behaviors induced by medial prefrontal cortex DBS and examine the possible mechanisms including neuroplasticity-dependent/independent cellular and molecular changes. Interestingly, the response rate of subcallosal cingulate Deep brain stimulation marks a milestone in the treatment of depression. DBS achieved response and remission rates of 64–76% and 37–63%, respectively, from clinical studies monitoring patients from 6–24 months. Although some studies showed its stimulation efficacy was limited, it still holds great promise as a therapy for patients with treatment-resistant depression. Overall, further research is still needed, including more credible clinical research, preclinical mechanistic studies, precise selection of patients, and customized electrical stimulation paradigms.

Gestational poly(I:C) attenuates, not exacerbates, the behavioral, cytokine and mTOR changes caused by isolation rearing in a rat 'dual-hit' model for neurodevelopmental disorders

Many psychiatric illnesses have a multifactorial etiology involving genetic and environmental risk factors that trigger persistent neurodevelopmental impairments. Several risk factors have been individually replicated in rodents, to understand disease mechanisms and evaluate novel treatments, particularly for poorly-managed negative and cognitive symptoms. However, the complex interplay between various factors remains unclear. Rodent dual-hit neurodevelopmental models offer vital opportunities to examine this and explore new strategies for early therapeutic intervention. This study combined gestational administration of polyinosinic:polycytidylic acid (poly(I:C); PIC, to mimic viral infection during pregnancy) with post-weaning isolation of resulting offspring (to mirror adolescent social adversity). After in vitro and in vivo studies required for laboratory-specific PIC characterization and optimization, we administered 10 mg/kg i.p. PIC potassium salt to time-mated Lister hooded dams on gestational day 15. This induced transient hypothermia, sickness behavior and weight loss in the dams, and led to locomotor hyperactivity, elevated striatal cytokine levels, and increased frontal cortical JNK phosphorylation in the offspring at adulthood. Remarkably, instead of exacerbating the well-characterized isolation syndrome, gestational PIC exposure actually protected against a spectrum of isolation-induced behavioral and brain regional changes. Thus isolation reared rats exhibited locomotor hyperactivity, impaired associative memory and reversal learning, elevated hippocampal and frontal cortical cytokine levels, and increased mammalian target of rapamycin (mTOR) activation in the frontal cortex - which were not evident in isolates previously exposed to gestational PIC. Brains from adolescent littermates suggest little contribution of cytokines, mTOR or JNK to early development of the isolation syndrome, or resilience conferred by PIC. But notably hippocampal oxytocin, which can protect against stress, was higher in adolescent PIC-exposed isolates so might contribute to a more favorable outcome. These findings have implications for identifying individuals at risk for disorders like schizophrenia who may benefit from early therapeutic intervention, and justify preclinical assessment of whether adolescent oxytocin manipulations can modulate disease onset or progression.

Hippocampus Metabolic Disturbance and Autophagy Deficiency in Olfactory Bulbectomized Rats and the Modulatory Effect of Fluoxetine

An olfactory bulbectomy (OBX) rodent is a widely-used model for depression (especially for agitated depression). The present study aims to investigate the hippocampus metabolic profile and autophagy-related pathways in OBX rats and to explore the modulatory roles of fluoxetine. OBX rats were given a 30-day fluoxetine treatment after post-surgery rehabilitation, and then behavioral changes were evaluated. Subsequently, the hippocampus was harvested for metabonomics analysis and Western blot detection. As a result, OBX rats exhibited a significantly increased hyperemotionality score and declined spatial memory ability. Fluoxetine reduced the hyperemotional response, but failed to restore the memory deficit in OBX rats. Sixteen metabolites were identified as potential biomarkers for the OBX model including six that were rectified by fluoxetine. Disturbed pathways were involved in amino acid metabolism, fatty acid metabolism, purine metabolism, and energy metabolism. In addition, autophagy was markedly inhibited in the hippocampus of OBX rats. Fluoxetine could promote autophagy by up-regulating the expression of LC3 II, beclin1, and p-AMPK/AMPK, and down-regulating the levels of p62, p-Akt/Akt, p-mTOR/mTOR, and p-ULK1/ULK1. Our findings indicated that OBX caused marked abnormalities in hippocampus metabolites and autophagy, and fluoxetine could partly redress the metabolic disturbance and enhance autophagy to reverse the depressive-like behavior, but not the memory deficits in OBX rats.

Induction of reversible bidirectional social approach bias by olfactory conditioning in male mice

Social avoidance is a common component of neuropsychiatric disorders that confers substantial functional impairment. An unbiased approach to identify brain regions and neuronal circuits that regulate social avoidance might enable development of novel therapeutics. However, most paradigms that alter social avoidance are irreversible and accompanied by multiple behavioral confounds. Here we report a straightforward behavioral paradigm in male mice enabling the reversible induction of social avoidance or approach with temporal control. C57BL/6J mice repeatedly participated in both negative and positive social experiences. Negative social experience was induced by brief social defeat by an aggressive male CD-1 mouse, while positive social experience was induced by exposure to a female mouse, each conducted daily for five days. Each social experience valence was conducted in a specific odorant context (i.e. negative experience in odorant A, positive experience in odorant B). Odorants were equally preferred pre-conditioning. However, after conditioning, mice sniffed positive experience-paired odorants more than negative experience-paired odorants. Furthermore, positive- or negative-conditioned odorant contexts increased or decreased, respectively, the approach behavior of conditioned mice toward conspecifics. Because individual mice undergo both positive and negative conditioning, this paradigm may be useful to examine neural representations of social approach or avoidance within the same subject.

The role of prefrontal cortex dopamine D2 and D3 receptors in the mechanism of action of venlafaxine and deep brain stimulation in animal models of treatment-responsive and treatment-resistant depression

AIMS

The Wistar-Kyoto rat has been validated as an animal model of treatment-resistant depression. Here we investigated a role of dopamine D2 and D3 receptors in the ventro-medial prefrontal cortex in the mechanism of action of deep brain stimulation in Wistar-Kyoto rats and venlafaxine in Wistar rats.

METHODS

Wistar or Wistar-Kyoto rats were exposed chronically to chronic mild stress. Wistar rats were treated chronically with venlafaxine (10 mg/kg) beginning after two weeks of chronic mild stress; Wistar-Kyoto rats received two sessions of deep brain stimulation before behavioural tests. L-742,626 (1 µg), a D2 receptor agonist, or 7-OH DPAT (3 µg), a D3 receptor antagonist, were infused into the ventro-medial prefrontal cortex immediately following the exposure trial in the Novel Object Recognition Test, and discrimination between novel and familiar object was tested one hour later.

RESULTS

Chronic mild stress decreased sucrose intake and impaired memory consolidation; these effects were reversed by venlafaxine in Wistar rats and deep brain stimulation in Wistar-Kyoto rats. In control animals, L-742,626 and 7-OH DPAT also impaired memory consolidation. In Wistar rats, venlafaxine reversed the effect of L-742,626 in controls, but not in the chronic mild stress group, and venlafaxine did not reverse the effect of 7-OH DPAT in either group. In Wistar-Kyoto rats, deep brain stimulation reversed the effect of both L-742,626 and 7-OH DPAT in both control and chronic mild stress groups.

CONCLUSIONS

We conclude that the action of venlafaxine to reverse the impairment of memory consolidation caused by chronic mild stress in Wistar rats involves D2 receptors in the ventro-medial prefrontal cortex; but the effect of deep brain stimulation to reverse the same effect in Wistar-Kyoto rats does not.

Chronic antidepressant-like effect of EMD386088, a partial 5-HT6 receptor agonist, in olfactory bulbectomy model may be connected with BDNF and/or CREB signalling pathway

BACKGROUND

The removal of the olfactory bulbs has been attributed to behavioral changes and neuroplasticity manifesting themselves among others like increases in brain neurotrophin expression and neurogenesis. Earlier data presented that EMD386088, a 5-HT6 receptor partial agonist, exerts antidepressant-like properties after chronic administration in olfactory bulbectomy (OB) model as was it compared with amitriptyline (AMI). The aim of this study was to compare acute and chronic biochemical effects of EMD386088, administered in its antidepressant active (2.5mg/kg) and non-active (1.25mg/kg) doses, found in the open field test in OB rats, with those of AMI (10mg/kg). The levels of 5-HT6 receptor protein and selected neurotrophins in prefrontal cortex (PFC) and hippocampus (Hp) of rats have been examined.

METHODS

5-HT6 receptor protein and selected neurotrophins: brain-derived neurotrophic factor (BDNF), cAMP-response element binding protein (CREB), the product of the immediate early gene c-fos (cFos) protein levels were assessed using a Western blot analysis in PFC and Hp of bulbectomized rats after acute or chronic (14-day) EMD386088 or AMI intraperitoneal (ip) treatment.

RESULTS

The acute treatment with EMD386088 caused significant increases in CREB and BDNF protein levels in PFC, and an increase in BDNF in Hp of OB rats, while AMI injection decreased CREB and did not change BDNF levels. After the chronic administration of EMD386088, the increasing levels of BDNF and CREB were still observed in PFC and Hp.

CONCLUSIONS

The antidepressant-like effect of EMD386088 may be associated with the neuroplasticity activation in PFC and Hp in rats.

Medial Forebrain Bundle Deep Brain Stimulation Reverses Anhedonic-Like Behavior in a Chronic Model of Depression: Importance of BDNF and Inflammatory Cytokines

Deep brain stimulation (DBS) of the medial forebrain bundle (MFB) displays a promising antidepressant effects in patients with treatment-refractory depression; however, a clear consensus on underlying mechanisms is still enigmatic. Herein, we investigated the effects of MFB-DBS on anhedonic-like behavior using the Froot Loops® consumption in a chronic unpredictable mild stress (CUS) model of depression, biochemical estimation of peripheral and central inflammatory cytokines, stress hormone, and brain-derived neurotrophic factor (BDNF). Seven days of MFB-DBS significantly reversed the 42-day CUS-generated anhedonic-like phenotype (p < 0.02) indicated by an increase in Froot Loops® consumption. Gross locomotor activity and body weight remained unaffected across the different groups. A dramatic augmentation of adrenocorticotropic hormone levels was seen in the plasma and cerebrospinal fluid (CSF) samples of CUS rats, which significantly reduced following MFB-DBS treatment. However, C-reactive protein levels were found to be unaffected. Interestingly, decreased levels of BDNF in the CUS animals were augmented in the plasma, CSF, and hippocampus following MFB-DBS, but remained unaltered in the nucleus accumbens (NAc). While multiplex assay revealed no change in the neuronal levels of inflammatory cytokines including IL-1α, IL-4, IL-10, IL-12, IL-13, and IL-17 in the neuroanatomical framework of the hippocampus and NAc, increased levels of IL-1β, IL-2, IL-5, IL-6, IL-7, IL-18, TNF-α, and INF-γ were seen in these brain structures after CUS and were differentially modulated in the presence of MFB stimulation. Here, we show that there is dysregulation of BDNF and neuroimmune mediators in a stress-driven chronic depression model, and that chronic MFB-DBS has the potential to undo these aberrations.

Enriched Environment Facilitates Anxiolytic Efficacy Driven by Deep-Brain Stimulation of Medial Prefrontal Cortex

Deep brain stimulation (DBS) is a widely used treatment for neurodegenerative disorders like Parkinson’s disease. Recently, several studies have used preclinical animal models to suggest that DBS has a potential to improve emotional symptoms in mental disorders such as treatment-resistant depression and post-traumatic stress disorder. An important difference between neurodegenerative and emotional disorders is the crucial role of environment in the ontogeny of the latter. Thus, it is important to understand the effects of DBS in the context of environmental variation. In this study, we show that DBS of ventromedial prefrontal cortex reduces anxiety in rats when it is coupled with simultaneous exposure to an enriched environment (EE). In contrast, effects of DBS on anxiety-like behaviors remained equivocal when animals were housed in standard laboratory conditions. These results suggest that the ability of DBS to treat anxiety and related phenotypes can be significantly enhanced by EE opportunities.

Glutamine has antidepressive effects through increments of glutamate and glutamine levels and glutamatergic activity in the medial prefrontal cortex

Emerging evidence has shown the low levels of glutamate (Glu) and glutamine (Gln) and the hypoactivity in the cortex of patients with depression. The hypoactivity is closely related with low frequency of glutamatergic signaling that is affected by the levels of Glu and Gln. Thus, we hypothesized that there might be a causality among low levels of Glu and Gln, hypoactive glutamatergic neurotransmissions, and depressive behaviors. Here, we found low Glu and Gln levels and low frequency of spontaneous excitatory postsynaptic current (sEPSC) of glutamatergic neurons in the medial prefrontal cortex (mPFC) of chronic immobilization stress (CIS)-induced depressed mice. The depressed mice also showed hypoactive Gln synthetase (GS). Inhibition of GS by methionine sulfoximine (MSO) decreased Glu and Gln levels and increased depressive behaviors with low frequency of sEPSC in the mPFC, indicating that Glu and Gln decrements cause hypoactive glutamatergic neurotransmissions and depressive behaviors. Both Glu and Gln could increase sEPSC of glutamatergic neurons in the mPFC on slice patch, but only Gln overcame MSO to increase sEPSC, suggesting that exogenous Gln would recover CIS-induced low frequency of sEPSC caused by hypoactive GS and act as an antidepressant. Expectedly, Gln supplementation showed antidepressant effects against CIS; it increased glutamatergic neurotransmissions with Glu and Gln increment in the mPFC and attenuated depressive behaviors. Moreover, selective glutamatergic activation in the mPFC by optogenetics decreased depressive behavior. In conclusion, depressive behaviors evoked by chronic stress were due to hypoactive glutamatergic neurons in the mPFC caused by low levels of Glu and Gln, and exogenous Gln can be used as an alternative antidepressant to increase glutamatergic neurotransmission.

Deep Brain Stimulation Modified Autism-Like Deficits via the Serotonin System in a Valproic Acid-Induced Rat Model

Deep brain stimulation (DBS) is known to be a promising treatment for resistant depression, which acts via the serotonin (5-hydroxytryptamine, 5-HT) system in the infralimbic prefrontal cortex (ILPFC). Previous study revealed that dysfunction of brain 5-HT homeostasis is related to a valproate (VPA)-induced rat autism spectrum disorder (ASD) model. Whether ILPFC DBS rescues deficits in VPA-induced offspring through the 5-HT system is not known. Using VPA-induced offspring, we therefore explored the effect of DBS in autistic phenotypes and further investigated the underlying mechanism. Using combined behavioral and molecular approaches, we observed that applying DBS and 5-HT_1A receptor agonist treatment with 8-hydroxy-2-(di-n-propylamino)tetralin (8-OH-DPAT) reversed sociability deficits, anxiety and hyperactivity in the VPA-exposed offspring. We then administered the selective 5-HT_1A receptor antagonist N-[2-[4-(2-Methoxyphenyl)-1-piperazinyl]ethyl]-N-2-pyridinylcyclohexanecarboxamide maleate (WAY 100635), following which the effect of DBS in terms of improving autistic behaviors was blocked in the VPA-exposed offspring. Furthermore, we found that both 8-OH-DPAT and DBS treatment rescued autistic behaviors by decreasing the expressions of NR2B subunit of N-methyl-D-aspartate receptors (NMDARs) and the β₃ subunit of γ-aminobutyric acid type A receptors (GABA_AR) in the PFC region. These results provided the first evidence of characteristic behavioral changes in VPA-induced offspring caused by DBS via the 5-HT system in the ILPFC.

Deep brain stimulation for treatment-resistant depression: an integrative review of preclinical and clinical findings and translational implications

Although deep brain stimulation (DBS) is an established treatment choice for Parkinson's disease (PD), essential tremor and movement disorders, its effectiveness for the management of treatment-resistant depression (TRD) remains unclear. Herein, we conducted an integrative review on major neuroanatomical targets of DBS pursued for the treatment of intractable TRD. The aim of this review article is to provide a critical discussion of possible underlying mechanisms for DBS-generated antidepressant effects identified in preclinical studies and clinical trials, and to determine which brain target(s) elicited the most promising outcomes considering acute and maintenance treatment of TRD. Major electronic databases were searched to identify preclinical and clinical studies that have investigated the effects of DBS on depression-related outcomes. Overall, 92 references met inclusion criteria, and have evaluated six unique DBS targets namely the subcallosal cingulate gyrus (SCG), nucleus accumbens (NAc), ventral capsule/ventral striatum or anterior limb of internal capsule (ALIC), medial forebrain bundle (MFB), lateral habenula (LHb) and inferior thalamic peduncle for the treatment of unrelenting TRD. Electrical stimulation of these pertinent brain regions displayed differential effects on mood transition in patients with TRD. In addition, 47 unique references provided preclinical evidence for putative neurobiological mechanisms underlying antidepressant effects of DBS applied to the ventromedial prefrontal cortex, NAc, MFB, LHb and subthalamic nucleus. Preclinical studies suggest that stimulation parameters and neuroanatomical locations could influence DBS-related antidepressant effects, and also pointed that modulatory effects on monoamine neurotransmitters in target regions or interconnected brain networks following DBS could have a role in the antidepressant effects of DBS. Among several neuromodulatory targets that have been investigated, DBS in the neuroanatomical framework of the SCG, ALIC and MFB yielded more consistent antidepressant response rates in samples with TRD. Nevertheless, more well-designed randomized double-blind, controlled trials are warranted to further assess the efficacy, safety and tolerability of these more promising DBS targets for the management of TRD as therapeutic effects have been inconsistent across some controlled studies.

Deep brain stimulation and fluoxetine exert different long-term changes in the serotonergic system

Both selective serotonin reuptake inhibitors (SSRIs) and ventromedial prefrontal cortex (vmPFC) deep brain stimulation (DBS) modulate serotonergic activity. We compared the acute (1 day) and long-term (12 days) effects of vmPFC stimulation and fluoxetine on serotonin (5-HT) release and receptor expression in rats. Samples to measure serotonin levels were collected from the hippocampus using microdialysis. Serotonin transporter (SERT), 5-HT_1A and 5-HT_1B mRNA were measured using in situ hybridization. [³H]8-OH-DPAT and [¹²⁵I]cyanopindolol autoradiography were used to measure 5-HT_1A and 5-HT_1B binding. Our results show that after fluoxetine injections serotonin levels were approximately 150% higher than at baseline. Twelve days later, pre-injection 5-HT extracellular concentration was substantially higher than on day 1. In contrast, serotonin levels following DBS were only 50% higher than at baseline. While pre-stimulation 5-HT on day 12 was significantly higher than on treatment day 1, no stimulation-induced 5-HT peak was recorded. SERT expression in the dorsal raphe was increased after acute fluoxetine and decreased following a single day of DBS. Neither fluoxetine nor DBS administered acutely substantially changed 5-HT_1A or 5-HT_1B binding. Chronic fluoxetine treatment, however, was associated with a decrease in [³H]8-OH-DPAT prefrontal cortex and hippocampus expression. In contrast, chronic DBS induced a significant increase in [¹²⁵I]cyanopindolol binding in the prefrontal cortex, globus pallidus, substantia nigra and raphe nuclei. mRNA expression of 5-HT_1A and 5-HT_1B in raphe nuclei was not altered by either treatment. These results suggest that fluoxetine and DBS modulate activity of the serotonergic system but likely exert their effects through different mechanisms.

Deep brain stimulation of the subcallosal cingulate gyrus in patients with treatment-resistant depression: A double-blinded randomized controlled study and long-term follow-up in eight patients

BACKGROUND

Deep brain stimulation (DBS) of the subcallosal cingulate gyrus (SCG) is an experimental approach in treatment-resistant depression (TRD). Short-term results of efficacy in DBS are incongruent and studies investigating long-term effects are warranted.

METHODS

We assessed efficacy of SCG-DBS in eight patients randomized into a delayed-onset group (sham-DBS four weeks) and a non-delayed-onset group. The primary outcome measure was improvement on the Hamilton Depression Rating-Scale (HAMD-24-item-version). Response was defined as HAMD-24 reduction of at least 50% compared to baseline. Assessment was double-blind for a period of eight weeks and after 6,- 12,- 24,- and 28,- months open-label.

RESULTS

The average improvement in HAMD-24 scores after 6,- 12,- and 24-months were 34%, 25%, and 37%. After 6 months, HAMD-24 revealed a significant difference (P = .022) and 37.5% of the patients were responders. After 12 months, HAMD-24 scores dropped, but no significant difference was observed. After 24 months, a significant improvement was found (P = .041). After the four weeks lasting sham vs. DBS-ON period, there was no group difference (P = .376) in HAMD-24 and patients did not improve during sham stimulation. Patients were followed until 28 months and two up to 4 years under SCG-DBS and average response rate was 51%, whereas two patients were remitters (33,3%).

LIMITATIONS

The small sample size limited the statistical power and external validity.

CONCLUSIONS

Long-term improvement after SCG-DBS revealed a stable effect. There was no significant difference in response rates between the delayed and non-delayed-onset group. DBS for TRD remains experimental and longitudinal investigations of large samples are needed.

Deep brain stimulation induces antidepressant-like effects in serotonin transporter knockout mice

BACKGROUND

Some of the antidepressant-like effects of ventromedial prefrontal cortex (vmPFC) deep brain stimulation (DBS) in rodents have been attributed to the modulation of prefrontal-raphe pathways. This is largely different from selective serotonin reuptake inhibitors (SSRIs), which increase serotonin (5-HT) levels by inhibiting the serotonin transporter (SERT). SSRIs have limited efficacy when given to SERT knockout (KO) mice, or patients with mutations in the serotonin transporter promoter gene (5-HTTLPR).

HYPOTHESIS

vmPFC DBS will induce antidepressant-like effects and serotonin release in SERT KOs.

RESULTS

DBS-treated wild-type and SERT KO mice had a significant 22-26% decrease in immobility in the forced swim test. DBS delivered to either group was associated with 33-55% increase in 5-HT levels.

CONCLUSIONS

DBS induced a significant antidepressant-like effect in KO mice. This suggests that it may be reasonable to consider DBS in states where SERT is not fully operational.

Cellular and molecular mechanisms triggered by Deep Brain Stimulation in depression: A preclinical and clinical approach

Deep Brain Stimulation (DBS) was originally developed as a therapeutic approach to manage movement disorders, in particular Parkinson's Disease. However, DBS also seems to be an effective treatment against refractory depression when patients fail to respond satisfactorily to conventional therapies. Thus, DBS targeting specific brain areas can produce an antidepressant response that improves depressive symptomatology, these areas including the subcallosal cingulate region, nucleus accumbens, ventral capsule/ventral striatum, medial forebrain bundle, the inferior thalamic peduncle and lateral habenula. Although the efficacy and safety of this therapy has been demonstrated in some clinical trials and preclinical studies, the intrinsic mechanisms underlying its antidepressant effect remain poorly understood. This review aims to provide a comprehensive overview of DBS, focusing on the molecular and cellular changes reported after its use that could shed light on the mechanisms underpinning its antidepressant effect. Several potential mechanisms of action of DBS are considered, including monoaminergic and glutamatergic neurotransmission, neurotrophic and neuroinflammatory mechanisms, as well as potential effects on certain intracellular signaling pathways. Although future studies will be necessary to determine the key molecular events underlying the antidepressant effect of DBS, the findings presented provide an insight into some of its possible modes of action.