Concerning neuromodulation as treatment of neurological and neuropsychiatric disorder: Insights gained from selective targeting of the subthalamic nucleus, para-subthalamic nucleus and zona incerta in rodents

Neuromodulation such as deep brain stimulation (DBS) is advancing as a clinical intervention in several neurological and neuropsychiatric disorders, including Parkinson´s disease, dystonia, tremor, and obsessive-compulsive disorder (OCD) for which DBS is already applied to alleviate severely afflicted individuals of symptoms. Tourette syndrome and drug addiction are two additional disorders for which DBS is in trial or proposed as treatment. However, some major remaining obstacles prevent this intervention from reaching its full therapeutic potential. Side-effects have been reported, and not all DBS-treated individuals are relieved of their symptoms. One major target area for DBS electrodes is the subthalamic nucleus (STN) which plays important roles in motor, affective and associative functions, with impact on for example movement, motivation, impulsivity, compulsivity, as well as both reward and aversion. The multifunctionality of the STN is complex. Decoding the anatomical-functional organization of the STN could enhance strategic targeting in human patients. The STN is located in close proximity to zona incerta (ZI) and the para-subthalamic nucleus (pSTN). Together, the STN, pSTN and ZI form a highly heterogeneous and clinically important brain area. Rodent-based experimental studies, including opto- and chemogenetics as well as viral-genetic tract tracings, provide unique insight into complex neuronal circuitries and their impact on behavior with high spatial and temporal precision. This research field has advanced tremendously over the past few years. Here, we provide an inclusive review of current literature in the pre-clinical research fields centered around STN, pSTN and ZI in laboratory mice and rats; the three highly heterogeneous and enigmatic structures brought together in the context of relevance for treatment strategies. Specific emphasis is placed on methods of manipulation and behavioral impact.

Vagus nerve damage increases alcohol intake and preference in a nonpreferring rat line: Relationship to vagal regulation of the hypothalamic-pituitary-adrenal axis

BACKGROUND

Clinical and preclinical research indicates that gastric weight loss surgeries, such as Roux-en-Y gastric bypass surgery, can induce alcohol use disorder (AUD). While numerous mechanisms have been proposed for these effects, one relatively unexplored potential mechanism is physical damage to the gastric branch of the vagus nerve, which can occur during bypass surgery. Therefore, we hypothesized that direct damage to the gastric branch of the vagus nerve, without altering other aspects of gastric anatomy, could result in increased alcohol intake.

METHODS

To test this hypothesis, we compared alcohol intake and preference in multiple models in male Sprague-Dawley rats that received selective gastric branch vagotomy (VX) with rats who underwent sham surgery. Because the vagus nerve regulates hypothalamic-pituitary-adrenal (HPA) axis function, and alterations to HPA function are critical to the escalation of non-dependent alcohol intake, we also tested the hypothesis that gastric VX increases HPA function.

RESULTS

We found that VX increases alcohol intake and preference in the every-other-day, two-bottle choice test and increases preference for 1 g/kg alcohol in the conditioned place preference test. The effects were selective for alcohol, as sucrose intake and preference were not altered by VX. We also found that VX increases corticotropin releasing factor (CRF) mRNA in the paraventricular nucleus of the hypothalamus (PVN), increases putative PVN CRF neuronal action potential firing, and increases corticosterone levels.

CONCLUSIONS

Overall, these findings suggest that the vagus nerve may play a critical role in regulating HPA axis function via modulation of PVN CRF mRNA expression and putative PVN CRF neuronal activity. Furthermore, disruptions to vagal regulation of HPA axis function may increase alcohol intake and preference.

Use of Post-mortem Brain Tissue in Investigations of Obsessive- Compulsive Disorder: A Systematic Review

BACKGROUND

Post-mortem examination of the brain is a key strategy to increase our understanding of the neurobiology of mental disorders. While extensive post-mortem research has been undertaken on some mental disorders, others appear to have been relatively neglected.

OBJECTIVE

The objective of the study was to conduct a systematic review of post-mortem research on obsessive-compulsive disorder (OCD).

METHODS

A systematic review was performed in accordance with PRISMA guidelines to provide an overview of quantitative, qualitative, or mixed methods primary research studies on OCD. Search platforms included NCBI Pubmed, SCOPUS, and Web of Science.

RESULTS

A total of 52 publications were found, and after the removal of works not meeting the inclusion criteria, six (6) peer-reviewed publications remained. These post-mortem studies have provided data on DNA methylation, cellular and molecular alterations, and gene expression profiling in brain areas associated with OCD.

DISCUSSION AND CONCLUSION

Included studies highlight the potential value of post-mortem brains from well-characterized individuals with OCD and suggest the need for additional work in this area.

Role of the postinspiratory complex in regulating swallow-breathing coordination and other laryngeal behaviors

Breathing needs to be tightly coordinated with upper airway behaviors, such as swallowing. Discoordination leads to aspiration pneumonia, the leading cause of death in neurodegenerative disease. Here, we study the role of the postinspiratory complex (PiCo) in coordinating breathing and swallowing. Using optogenetic approaches in freely breathing anesthetized ChATcre:Ai32, Vglut2cre:Ai32 and intersectional recombination of ChATcre:Vglut2FlpO:ChR2 mice reveals PiCo mediates airway protective behaviors. Activation of PiCo during inspiration or the beginning of postinspiration triggers swallow behavior in an all-or-nothing manner, while there is a higher probability for stimulating only laryngeal activation when activated further into expiration. Laryngeal activation is dependent on stimulation duration. Sufficient bilateral PiCo activation is necessary for preserving the physiological swallow motor sequence since activation of only a few PiCo neurons or unilateral activation leads to blurred upper airway behavioral responses. We believe PiCo acts as an interface between the swallow pattern generator and the preBötzinger complex to coordinate swallow and breathing. Investigating PiCo's role in swallow and laryngeal coordination will aid in understanding discoordination with breathing in neurological diseases.

Neurocircuitry of Personality Traits and Intent in Decision-Making

Even though most personality features are moderately stable throughout life, changes can be observed, which influence one's behavioral patterns. A variety of subjective assessments can be performed to track these changes; however, the subjective characteristic of these assessments may lead to questions about intentions and values. The use of neuroimaging techniques may aid the investigation of personality traits through a more objective lens, overcoming the barriers imposed by confounders. Here, neurocircuits associated with changes in personality domains were investigated to address this issue. Cortical systems involved in traits such as extraversion and neuroticism were found to share multiple components, as did traits of agreeableness and conscientiousness, with these four features revolving around the activation and structural integrity of the medial prefrontal cortex (mPFC). The attribute of openness appears scattered throughout cortical and subcortical regions, being discussed here as a possible reflection of intent, at the same time modulating and being governed by other traits. Insights on how systems operate on personality may increase comprehension on factors acting on the evolution, development, and consolidation of personality traits through life, as in neurocognitive disorders.

Alcohol consumption modulates prelimbic cortex response to cocaine following sequential cocaine and alcohol polysubstance use in the rat

Polysubstance use (PSU), involves the consumption of more than one drug within a period of time and is prevalent among cocaine users. Ceftriaxone, a beta-lactam antibiotic, reliably attenuates reinstatement of cocaine seeking in pre-clinical models by restoring glutamate homeostasis following cocaine self-administration but fails to do so when rats consume both cocaine and alcohol (cocaine + alcohol PSU). We previously found that cocaine + alcohol PSU rats reinstate cocaine seeking similarly to cocaine-only rats, but demonstrate differences in reinstatement-induced c-Fos expression throughout the reward system, including a lack of change upon ceftriaxone treatment. Here, we used this model to determine if previous findings were caused by tolerance or sensitization to the pharmacological effects of cocaine. Male rats underwent intravenous cocaine self-administration immediately followed by 6 h of home cage access to water or unsweetened alcohol for 12 days. Rats subsequently underwent 10 daily instrumental extinction sessions, during which time they were treated with either vehicle or ceftriaxone. Rats then received a non-contingent cocaine injection and were perfused for later immunohistochemical analysis of c-Fos expression in the reward neurocircuitry. c-Fos expression in the prelimbic cortex correlated with total alcohol intake in PSU rats. There were no effects of either ceftriaxone or PSU on c-Fos expression in the infralimbic cortex, nucleus accumbens core and shell, basolateral amygdala, or ventral tegmental area. These results support the idea that PSU and ceftriaxone alter the neurobiology underlying drug-seeking behavior in the absence of pharmacological tolerance or sensitization to cocaine.

Hypothalamic GABAergic neurocircuitry in the regulation of energy homeostasis and sleep/wake control

Gamma-aminobutyric acid (GABAergic) neuron, as one of important cell types in synaptic transmission, has been widely involved in central nervous system (CNS) regulation of organismal physiologies including cognition, emotion, arousal and reward. However, upon their distribution in various brain regions, effects of GABAergic neurons in the brain are very diverse. In current report, we will present an overview of the role of GABAergic mediated inhibitory neurocircuitry in the hypothalamus, underlying mechanism of feeding and sleep homeostasis as well as the characteristics of latest transcriptome profile in order to call attention to the GABAergic system as potentially a promising pharmaceutical intervention or a deep brain stimulation target in eating and sleep disorders.

Epigenetic Signatures of Smoking in Five Brain Regions

(1) Background: Epigenome-wide association studies (EWAS) in peripheral blood have repeatedly found associations between tobacco smoking and aberrant DNA methylation (DNAm), but little is known about DNAm signatures of smoking in the human brain, which may contribute to the pathophysiology of addictive behavior observed in chronic smokers. (2) Methods: We investigated the similarity of DNAm signatures in matched blood and postmortem brain samples (n = 10). In addition, we performed EWASs in five brain regions belonging to the neurocircuitry of addiction: anterior cingulate cortex (ACC), Brodmann Area 9, caudate nucleus, putamen, and ventral striatum (n = 38-72). (3) Results: cg15925993 within the LOC339975 gene was epigenome-wide significant in the ACC. Of 16 identified differentially methylated regions, two (PRSS50 and LINC00612/A2M-AS1) overlapped between multiple brain regions. Functional enrichment was detected for biological processes related to neuronal development, inflammatory signaling and immune cell migration. Additionally, our results indicate the association of the well-known AHRR CpG site cg05575921 with smoking in the brain. (4) Conclusion: The present study provides further evidence of the strong relationship between aberrant DNAm and smoking.

Mapping the neurocircuitry of impulsive aggression through the pharmacologic review of anti-impulsive aggressive agents

Impulsive aggression, in contradistinction to premeditated aggression in humans or predatory aggression in animals, corresponds to defensive aggression in animal models. At the core of the neurocircuitry of impulsive aggression, from murine to feline to human species, it is the medial amygdala-mediobasal hypothalamus-dorsal periaqueductal gray pathway. Here, we update current knowledge on the neurocircuitry of impulsive aggression by placing the neurocircuitry and its neurophysiological substrates into the top-down/bottom-up hypothesis of impulsive aggression. We then reverse the neurotranslational approach, which applies neuroscience to developing therapeutic drugs, and apply current understanding of potential mechanisms of anti-impulsive aggression agents to further clarify, at least heuristically and hypothetically, the dynamic biochemical components of the neurocircuitry of impulsive aggression. To do this, we searched the medical literature for studies attempting to clarify the neurobiological and neurochemical effects of the five most widely studied anti-impulsive aggressive agents, particularly as they pertain to the top-down/bottom-up hypothesis. Multiple different mechanisms are discussed, all of which fitting in the hypothesis by way of either promoting the "top-down" part (i.e., enhancing inhibitory neurotransmitters), or suppressing the "bottom-up" part (i.e., decreasing excitatory neurotransmitters). The hypothesis appears consistent with the current psychopharmacological understanding of these agents, as well as to account for the likely multifactorial etiology of the condition. Limitations of the hypothesis and future directions are finally discussed.

Targeting the Salience Network: A Mini-Review on a Novel Neuromodulation Approach for Treating Alcohol Use Disorder

Alcohol use disorder (AUD) continues to be challenging to treat despite the best available interventions, with two-thirds of individuals going on to relapse by 1 year after treatment. Recent advances in the brain-based conceptual framework of addiction have allowed the field to pivot into a neuromodulation approach to intervention for these devastative disorders. Small trials of repetitive transcranial magnetic stimulation (rTMS) have used protocols developed for other psychiatric conditions and applied them to those with addiction with modest efficacy. Recent evidence suggests that a TMS approach focused on modulating the salience network (SN), a circuit at the crossroads of large-scale networks associated with AUD, may be a fruitful therapeutic strategy. The anterior insula or dorsal anterior cingulate cortex may be particularly effective stimulation sites given emerging evidence of their roles in processes associated with relapse.

Therapeutic Neurostimulation in Obsessive-Compulsive and Related Disorders: A Systematic Review

Invasive and noninvasive neurostimulation therapies for obsessive-compulsive and related disorders (OCRD) were systematically reviewed with the aim of assessing clinical characteristics, methodologies, neuroanatomical substrates, and varied stimulation parameters. Previous reviews have focused on a narrow scope, statistical rather than clinical significance, grouped together heterogenous protocols, and proposed inconclusive outcomes and directions. Herein, a comprehensive and transdiagnostic evaluation of all clinically relevant determinants is presented with translational clinical recommendations and novel response rates. Electroconvulsive therapy (ECT) studies were limited in number and quality but demonstrated greater efficacy than previously identified. Targeting the pre-SMA/SMA is recommended for transcranial direct current stimulation (tDCS) and transcranial magnetic stimulation (TMS). TMS yielded superior outcomes, although polarity findings were conflicting, and refinement of frontal/cognitive control protocols may optimize outcomes. For both techniques, standardization of polarity, more treatment sessions (>20), and targeting multiple structures are encouraged. A deep brain stimulation (DBS) 'sweet spot' of the striatum for OCD was proposed, and CBT is strongly encouraged. Tourette's patients showed less variance and reliance on treatment optimization. Several DBS targets achieved consistent, rapid, and sustained clinical response. Analysis of fiber connectivity, as opposed to precise neural regions, should be implemented for target selection. Standardization of protocols is necessary to achieve translational outcomes.

The Arcuate Nucleus of the Hypothalamus and Metabolic Regulation: An Emerging Role for Renin-Angiotensin Pathways

Obesity is a chronic state of energy imbalance that represents a major public health problem and greatly increases the risk for developing hypertension, hyperglycemia, and a multitude of related pathologies that encompass the metabolic syndrome. The underlying mechanisms and optimal treatment strategies for obesity, however, are still not fully understood. The control of energy balance involves the actions of circulating hormones on a widely distributed network of brain regions involved in the regulation of food intake and energy expenditure, including the arcuate nucleus of the hypothalamus. While obesity is known to disrupt neurocircuits controlling energy balance, including those in the hypothalamic arcuate nucleus, the pharmacological targeting of these central mechanisms often produces adverse cardiovascular and other off-target effects. This highlights the critical need to identify new anti-obesity drugs that can activate central neurocircuits to induce weight loss without negatively impacting blood pressure control. The renin–angiotensin system may provide this ideal target, as recent studies show this hormonal system can engage neurocircuits originating in the arcuate nucleus to improve energy balance without elevating blood pressure in animal models. This review will summarize the current knowledge of renin–angiotensin system actions within the arcuate nucleus for control of energy balance, with a focus on emerging roles for angiotensin II, prorenin, and angiotensin-(1–7) pathways.

Discrete TrkB-expressing neurons of the dorsomedial hypothalamus regulate feeding and thermogenesis

Mutations in the TrkB neurotrophin receptor lead to profound obesity in humans, and expression of TrkB in the dorsomedial hypothalamus (DMH) is critical for maintaining energy homeostasis. However, the functional implications of TrkB-fexpressing neurons in the DMH (DMHTrkB) on energy expenditure are unclear. Additionally, the neurocircuitry underlying the effect of DMHTrkB neurons on energy homeostasis has not been explored. In this study, we show that activation of DMHTrkB neurons leads to a robust increase in adaptive thermogenesis and energy expenditure without altering heart rate or blood pressure, while silencing DMHTrkB neurons impairs thermogenesis. Furthermore, we reveal neuroanatomically and functionally distinct populations of DMHTrkB neurons that regulate food intake or thermogenesis. Activation of DMHTrkB neurons projecting to the raphe pallidus (RPa) stimulates thermogenesis and increased energy expenditure, whereas DMHTrkB neurons that send collaterals to the paraventricular hypothalamus (PVH) and preoptic area (POA) inhibit feeding. Together, our findings provide evidence that DMHTrkB neuronal activity plays an important role in regulating energy expenditure and delineate distinct neurocircuits that underly the separate effects of DMHTrkB neuronal activity on food intake and thermogenesis.

Glutamate and GABA Homeostasis and Neurometabolism in Major Depressive Disorder

Major depressive disorder (MDD) is a leading cause of distress, disability, and suicides. As per the latest WHO report, MDD affects more than 260 million people worldwide. Despite decades of research, the underlying etiology of depression is not fully understood. Glutamate and γ-aminobutyric acid (GABA) are the major excitatory and inhibitory neurotransmitters, respectively, in the matured central nervous system. Imbalance in the levels of these neurotransmitters has been implicated in different neurological and psychiatric disorders including MDD. ¹H nuclear magnetic resonance (NMR) spectroscopy is a powerful non-invasive method to study neurometabolites homeostasis in vivo. Additionally, ¹³C-NMR spectroscopy together with an intravenous administration of non-radioactive ¹³C-labeled glucose or acetate provides a measure of neural functions. In this review, we provide an overview of NMR-based measurements of glutamate and GABA homeostasis, neurometabolic activity, and neurotransmitter cycling in MDD. Finally, we highlight the impact of recent advancements in treatment strategies against a depressive disorder that target glutamate and GABA pathways in the brain.

Grant Report on the Effects of Childhood Maltreatment on Neurocircuitry in Adolescent Depression

This report describes the protocol for an ongoing project funded by the National Institutes of Health (R01MH108155) that is focused on effects of childhood maltreatment (MALTX) on neurocircuitry changes associated with adolescent major depressive disorder (MDD). Extant clinical and neuroimaging literature on MDD is reviewed, which has relied on heterogeneous samples that do not parse out the unique contribution of MALTX on neurobiological changes in MDD. Employing a 2 × 2 study design (controls with no MALTX or MDD, MALTX only, MDD only, and MDD + MALTX), and based on a cohesive theoretical model that incorporates behavioral, cognitive and neurobiological domains, we describe the multi-modal neuroimaging techniques used to test whether structural and functional alterations in the fronto-limbic and fronto-striatal circuits associated with adolescent MDD are moderated by MALTX. We hypothesize that MDD + MALTX youth will show alterations in the fronto-limbic circuit, with reduced connectivity between the amygdala (AMG) and the prefrontal cortex (PFC), as the AMG is sensitive to stress/threat during development. Participants with MDD will exhibit increased functional connectivity between the AMG and PFC due to self-referential negative emotions. Lastly, MDD + MALTX will only show changes in motivational/anticipatory aspects of the fronto-striatal circuit, and MDD will exhibit changes in motivational and consummatory/outcome aspects of reward-processing. Our goal is to identify distinct neural substrates associated with MDD due to MALTX compared to other causes, as these markers could be used to more effectively predict treatment outcome, index treatment response, and facilitate alternative treatments for adolescents who do not respond well to traditional approaches.

Involvement of Centrally Projecting Edinger-Westphal Nucleus Neuropeptides in Actions of Addictive Drugs

The centrally-projecting Edinger-Westphal nucleus (EWcp) is a brain region distinct from the preganglionic Edinger-Westphal nucleus (EWpg). In contrast to the EWpg, the EWcp does not send projections to the ciliary ganglion and appears not to regulate oculomotor function. Instead, evidence is accumulating that the EWcp is extremely sensitive to alcohol and several other drugs of abuse. Studies using surgical, genetic knockout, and shRNA approaches further implicate the EWcp in the regulation of alcohol sensitivity and self-administration. The EWcp is also known as the site of preferential expression of urocortin 1, a peptide of the corticotropin-releasing factor family. However, neuroanatomical data indicate that the EWcp is not a monotypic brain region and consists of several distinct subpopulations of neurons. It is most likely that these subpopulations of the EWcp are differentially involved in the regulation of actions of addictive drugs. This review summarizes and analyzes the current literature of the EWcp's involvement in actions of drugs of abuse in male and female subjects in light of the accumulating evidence of complexities of this brain region.

Optogenetic and chemogenetic insights into the neurocircuitry of depression-like behaviour: A systematic review

Major depressive disorder (MDD) and its treatment are challenges for global health. Optogenetics and chemogenetics are driving MDD research forward by unveiling causal relations between cell-type-specific control of neurons and depressive-like behaviour in rodents. Using a systematic search process, in this review, a set of 43 original studies applying optogenetic or chemogenetic techniques in rodent models of depression was identified. Our aim was to provide an examination of all available studies elucidating central neuronal mechanisms leading to depressive-like behaviour in rodents and thereby unveiling the most promising routes for future research. A complex interacting network of relevant structures, in which central circuitries causally related to depressive-like behaviour are implicated, has been identified. As most relevant structures emerge: medial prefrontal cortex, anterior cingulate cortex, amygdala, nucleus accumbens, ventral tegmental area, hippocampus and raphe nuclei. Further evidence, though examined by only few studies, emerges for structures like the lateral habenula, or medial dorsal thalamus. Most of the identified brain areas have previously been associated with MDD neuropathology, but now evidence can be provided for causal pathological mechanisms within a complex cortico-limbic reward circuitry. However, the studies also show conflicting results concerning the mechanisms underlying the causal involvement of specific circuitries. Comparability of studies is partly limited since even small deviations in methodological approaches lead to different outcomes. Factors influencing study outcomes were identified and need to be considered in future studies (e.g. frequency used for stimulation, time and duration of stimulation, limitations of applied animal models of MDD).

Regional complexity in enteric neuron wiring reflects diversity of motility patterns in the mouse large intestine

The enteric nervous system controls a variety of gastrointestinal functions including intestinal motility. The minimal neuronal circuit necessary to direct peristalsis is well-characterized but several intestinal regions display also other motility patterns for which the underlying circuits and connectivity schemes that coordinate the transition between those patterns are poorly understood. We investigated whether in regions with a richer palette of motility patterns, the underlying nerve circuits reflect this complexity. Using Ca²⁺ imaging, we determined the location and response fingerprint of large populations of enteric neurons upon focal network stimulation. Complemented by neuronal tracing and volumetric reconstructions of synaptic contacts, this shows that the multifunctional proximal colon requires specific additional circuit components as compared to the distal colon, where peristalsis is the predominant motility pattern. Our study reveals that motility control is hard-wired in the enteric neural networks and that circuit complexity matches the motor pattern portfolio of specific intestinal regions.

Compartmentalized Devices as Tools for Investigation of Human Brain Network Dynamics

Neuropsychiatric disorders have traditionally been difficult to study due to the complexity of the human brain and limited availability of human tissue. Induced pluripotent stem (iPS) cells provide a promising avenue to further our understanding of human disease mechanisms, but traditional 2D cell cultures can only provide a limited view of the neural circuits. To better model complex brain neurocircuitry, compartmentalized culturing systems and 3D organoids have been developed. Early compartmentalized devices demonstrated how neuronal cell bodies can be isolated both physically and chemically from neurites. Soft lithographic approaches have advanced this approach and offer the tools to construct novel model platforms, enabling circuit-level studies of disease, which can accelerate mechanistic studies and drug candidate screening. In this review, we describe some of the common technologies used to develop such systems and discuss how these lithographic techniques have been used to advance our understanding of neuropsychiatric disease. Finally, we address other in vitro model platforms such as 3D culture systems and organoids and compare these models with compartmentalized models. We ask important questions regarding how we can further harness iPS cells in these engineered culture systems for the development of improved in vitro models. Developmental Dynamics 248:65-77, 2019. © 2018 Wiley Periodicals, Inc.

The Role of Cholinergic Midbrain Neurons in Startle and Prepulse Inhibition

One of the two major cholinergic centers of the mammalian brain is located in the midbrain, i.e., the pedunculopontine tegmentum (PPTg) and the adjacent laterodorsal tegmentum. These cholinergic neurons have been shown to be important for e.g., arousal, reward associations, and sleep. They also have been suggested to mediate sensorimotor gating, measured as prepulse inhibition of startle (PPI). PPI disruptions are a hallmark of schizophrenia and are observed in various other psychiatric disorders, where they are associated with, and often predictive of, other cognitive symptoms. PPI has been proposed to be mediated by a short midbrain circuitry including inhibitory cholinergic projections from PPTg to the startle pathway. Although the data indicating the involvement of the PPTg is very robust, some more recent evidence challenges that there is a cholinergic contribution to PPI. We here use transient optogenetic activation of specifically the cholinergic PPTg neurons in male and female rats to address their role in startle modulation in general, and in PPI specifically. Although we could confirm the crucial role of PPTg cholinergic neurons in associative reward learning, validating our experimental approach, we found that activation of cholinergic PPTg neurons did not inhibit startle responses. In contrast, activation of cholinergic PPTg neurons enhanced startle, which is in accordance with their general role in arousal and indicate a potential involvement in sensitization of startle. We conclude that noncholinergic PPTg neurons mediate PPI in contrast to the longstanding hypothetical view that PPI is mediated by cholinergic PPTg neurons.SIGNIFICANCE STATEMENT Activation of cholinergic neurons in the midbrain has been assumed to mediate prepulse inhibition of startle (PPI), a common measure of sensorimotor gating that is disrupted in schizophrenia and other psychiatric disorders. We here revisit this long-standing hypothesis using optogenetic activation of these specific neurons combined with startle testing in rats. In contrast to the hypothetical role of these neurons in startle modulation, we show that their activation leads to an increase of baseline startle and to prepulse facilitation. This supports recent data by others that have started to cast some doubt on the cholinergic hypothesis of PPI, and calls for a revision of the theoretical construct of PPI mechanisms.

Amygdala lesions eliminate viewing preferences for faces in rhesus monkeys

In free-viewing experiments, primates orient preferentially toward faces and face-like stimuli. To investigate the neural basis of this behavior, we measured the spontaneous viewing preferences of monkeys with selective bilateral amygdala lesions. The results revealed that when faces and nonface objects were presented simultaneously, monkeys with amygdala lesions had no viewing preference for either conspecific faces or illusory facial features in everyday objects. Instead of directing eye movements toward socially relevant features in natural images, we found that, after amygdala loss, monkeys are biased toward features with increased low-level salience. We conclude that the amygdala has a role in our earliest specialized response to faces, a behavior thought to be a precursor for efficient social communication and essential for the development of face-selective cortex.

Interpersonal violence in posttraumatic women: brain networks triggered by trauma-related pictures

Interpersonal violence (IPV) is one of the most frequent causes for the development of posttraumatic stress disorder (PTSD) in women. Trauma-related triggers have been proposed to evoke automatic emotional responses in PTSD. The present functional magnetic resonance study investigated the neural basis of trauma-related picture processing in women with IPV-PTSD (n = 18) relative to healthy controls (n = 18) using a newly standardized trauma-related picture set and a non-emotional vigilance task. We aimed to identify brain activation and connectivity evoked by trauma-related pictures, and associations with PTSD symptom severity. We found hyperactivation during trauma-related vs neutral picture processing in both subcortical [basolateral amygdala (BLA), thalamus, brainstem] and cortical [anterior cingulate cortex (ACC), medial prefrontal cortex (mPFC), insula, occipital cortex] regions in IPV-PTSD. In patients, brain activation in amygdala, ACC, insula, occipital cortex and brainstem correlated positively with symptom severity. Furthermore, connectivity analyses revealed hyperconnectivity between BLA and dorsal ACC/mPFC. Results show symptom severity-dependent brain activation and hyperconnectivity in response to trauma-related pictures in brain regions related to fear and visual processing in women suffering from IPV-PTSD. These brain mechanisms appear to be associated with immediate responses to trauma-related triggers presented in a non-emotional context in this PTSD subgroup.

Compromised Neurocircuitry in Chronic Blast-Related Mild Traumatic Brain Injury

The aim of this study was to apply recently developed automated fiber segmentation and quantification methods using diffusion tensor imaging (DTI) and DTI-based deterministic and probabilistic tractography to access local and global diffusion changes in blast-induced mild traumatic brain injury (bmTBI). Two hundred and two (202) male active US service members who reported persistent post-concussion symptoms for more than 6 months after injury were recruited. An additional forty (40) male military controls were included for comparison. DTI results were examined in relation to post-concussion and post-traumatic stress disorder (PTSD) symptoms. No significant group difference in DTI metrics was found using voxel-wise analysis. However, group comparison using tract profile analysis and tract specific analysis, as well as single subject analysis using tract profile analysis revealed the most prominent white matter microstructural injury in chronic bmTBI patients over the frontal fiber tracts, that is, the front-limbic projection fibers (cingulum bundle, uncinate fasciculus), the fronto-parieto-temporal association fibers (superior longitudinal fasciculus), and the fronto-striatal pathways (anterior thalamic radiation). Effects were noted to be sensitive to the number of previous blast exposures, with a negative association between fractional anisotropy (FA) and time since most severe blast exposure in a subset of the multiple blast-exposed group. However, these patterns were not observed in the subgroups classified using macrostructural changes (T2 white matter hyperintensities). Moreover, post-concussion symptoms and PTSD symptoms, as well as neuropsychological function were associated with low FA in the major nodes of compromised neurocircuitry. Hum Brain Mapp 38:352-369, 2017. © 2016 Wiley Periodicals, Inc.

The impact of cultural differences in self-representation on the neural substrates of posttraumatic stress disorder

A significant body of literature documents the neural mechanisms involved in the development and maintenance of posttraumatic stress disorder (PTSD). However, there is very little empirical work considering the influence of culture on these underlying mechanisms. Accumulating cultural neuroscience research clearly indicates that cultural differences in self-representation modulate many of the same neural processes proposed to be aberrant in PTSD. The objective of this review paper is to consider how culture may impact on the neural mechanisms underlying PTSD. We first outline five key affective and cognitive functions and their underlying neural correlates that have been identified as being disrupted in PTSD: (1) fear dysregulation; (2) attentional biases to threat; (3) emotion and autobiographical memory; (4) self-referential processing; and (5) attachment and interpersonal processing. Second, we consider prominent cultural theories and review the empirical research that has demonstrated the influence of cultural variations in self-representation on the neural substrates of these same five affective and cognitive functions. Finally, we propose a conceptual model that suggests that these five processes have major relevance to considering how culture may influence the neural processes underpinning PTSD.

Childhood Poverty Predicts Adult Amygdala and Frontal Activity and Connectivity in Response to Emotional Faces

Childhood poverty negatively impacts physical and mental health in adulthood. Altered brain development in response to social and environmental factors associated with poverty likely contributes to this effect, engendering maladaptive patterns of social attribution and/or elevated physiological stress. In this fMRI study, we examined the association between childhood poverty and neural processing of social signals (i.e., emotional faces) in adulthood. Fifty-two subjects from a longitudinal prospective study recruited as children, participated in a brain imaging study at 23–25 years of age using the Emotional Faces Assessment Task. Childhood poverty, independent of concurrent adult income, was associated with higher amygdala and medial prefrontal cortical (mPFC) responses to threat vs. happy faces. Also, childhood poverty was associated with decreased functional connectivity between left amygdala and mPFC. This study is unique, because it prospectively links childhood poverty to emotional processing during adulthood, suggesting a candidate neural mechanism for negative social-emotional bias. Adults who grew up poor appear to be more sensitive to social threat cues and less sensitive to positive social cues.

Prelimbic cortex and ventral tegmental area modulate synaptic plasticity differentially in nucleus accumbens during cocaine-reinstated drug seeking

Addictive drug use causes long-lasting changes in synaptic strength and dendritic spine morphology in the nucleus accumbens that might underlie the vulnerability to relapse. Although activity in mesocorticolimbic circuitry is required for reinstating cocaine seeking, its role in reinstatement-associated synaptic plasticity is not well characterized. Using rats extinguished from cocaine self-administration, we found potentiated synaptic strength (assessed as the AMPA/NMDA current amplitude ratio) and increased spine head diameter in medium spiny neurons in the accumbens core (NAcore). The basal changes in synaptic strength and morphology in cocaine-extinguished animals were further augmented during cocaine-induced reinstatement. Two NAcore afferents contributing to cocaine reinstatement are glutamatergic inputs from the prelimbic prefrontal cortex (PL) and dopamine from the ventral tegmental area (VTA). Pharmacological inhibition of either PL or VTA prevented cocaine-primed reinstatement. However, inhibiting the PL further potentiated AMPA/NMDA and spine head diameter, while inactivating the VTA or the combined systemic administration of dopamine D1 and D2 antagonists prevented the increase in AMPA/NMDA and spine diameter induced by cocaine priming. These data indicate that neuronal activity in the VTA and associated dopamine receptor stimulation is necessary for the synaptic potentiation in the NAcore during cocaine-induced reinstatement. Although activity in the PL was necessary for reinstatement, it inhibited synaptic potentiation initiated by an acute cocaine injection. Thus, although the PL and VTA differentially regulate the direction of synaptic plasticity induced by a cocaine-priming injection, coordinated synaptic potentiation by both NAcore afferents is necessary for cocaine-induced relapse.

Postconcussional disorder and PTSD symptoms of military-related traumatic brain injury associated with compromised neurocircuitry

Traumatic brain injury (TBI) is a common combat injury, often through explosive blast, and produces heterogeneous brain changes due to various mechanisms of injury. It is unclear whether the vulnerability of white matter differs between blast and impact injury, and the consequences of microstructural changes on neuropsychological function are poorly understood in military TBI patients. Diffusion tensor imaging (DTI) techniques were used to assess the neurocircuitry in 37 U.S. service members (29 mild, 7 moderate, 1 severe; 17 blast and 20 nonblast), who sustained a TBI while deployed, compared to 14 nondeployed, military controls. High-dimensional deformable registration of MRI diffusion tensor data was followed by fiber tracking and tract-specific analysis along with region-of-interest analysis. DTI results were examined in relation to post-concussion and post-traumatic stress disorder (PTSD) symptoms. The most prominent white matter microstructural injury for both blast and nonblast patients was in the frontal fibers within the fronto-striatal (corona radiata, internal capsule) and fronto-limbic circuits (fornix, cingulum), the fronto-parieto-occipital association fibers, in brainstem fibers, and in callosal fibers. Subcortical superior-inferiorly oriented tracts were more vulnerable to blast injury than nonblast injury, while direct impact force had more detrimental effects on anterior-posteriorly oriented tracts, which tended to cause heterogeneous left and right hemispheric asymmetries of white matter connectivity. The tractography using diffusion anisotropy deficits revealed the cortico-striatal-thalamic-cerebellar-cortical (CSTCC) networks, where increased post-concussion and PTSD symptoms were associated with low fractional anisotropy in the major nodes of compromised CSTCC neurocircuitry, and the consequences on cognitive function were explored as well.

Maturation of the adolescent brain

Adolescence is the developmental epoch during which children become adults - intellectually, physically, hormonally, and socially. Adolescence is a tumultuous time, full of changes and transformations. The pubertal transition to adulthood involves both gonadal and behavioral maturation. Magnetic resonance imaging studies have discovered that myelinogenesis, required for proper insulation and efficient neurocybernetics, continues from childhood and the brain's region-specific neurocircuitry remains structurally and functionally vulnerable to impulsive sex, food, and sleep habits. The maturation of the adolescent brain is also influenced by heredity, environment, and sex hormones (estrogen, progesterone, and testosterone), which play a crucial role in myelination. Furthermore, glutamatergic neurotransmission predominates, whereas gamma-aminobutyric acid neurotransmission remains under construction, and this might be responsible for immature and impulsive behavior and neurobehavioral excitement during adolescent life. The adolescent population is highly vulnerable to driving under the influence of alcohol and social maladjustments due to an immature limbic system and prefrontal cortex. Synaptic plasticity and the release of neurotransmitters may also be influenced by environmental neurotoxins and drugs of abuse including cigarettes, caffeine, and alcohol during adolescence. Adolescents may become involved with offensive crimes, irresponsible behavior, unprotected sex, juvenile courts, or even prison. According to a report by the Centers for Disease Control and Prevention, the major cause of death among the teenage population is due to injury and violence related to sex and substance abuse. Prenatal neglect, cigarette smoking, and alcohol consumption may also significantly impact maturation of the adolescent brain. Pharmacological interventions to regulate adolescent behavior have been attempted with limited success. Since several factors, including age, sex, disease, nutritional status, and substance abuse have a significant impact on the maturation of the adolescent brain, we have highlighted the influence of these clinically significant and socially important aspects in this report.

Deep brain stimulation in obsessive-compulsive disorder: neurocircuitry and clinical experience

The last decade has seen a significant rise in interest in the use of deep brain stimulation (DBS) for the management of obsessive-compulsive disorder (OCD), one of psychiatry's most challenging conditions. The prominent role of both thought (obsessions) and motor (compulsions) dysfunction in OCD place the condition at the border between the neurological and the psychiatric. This is supported by a growing body of literature that implicates structures in decision-making, reward, and action-selection circuits in the disorder. Here, we provide an overview of the neurocircuitry of OCD while reviewing the DBS literature to date for the condition. Results of DBS trials in treatment- resistant OCD have been remarkably similar, with clinical response rates in the range of 40-60%, despite the use of a diverse range of targets. These results imply that a common underlying circuit is being modulated, and moreover that there is room for improvement, and debate, in the development of an evidence-driven DBS treatment for this chronic, debilitating illness.

Neurobiological mechanisms of repetitive transcranial magnetic stimulation on the underlying neurocircuitry in unipolar depression

For nearly two decades now, transcranial magnetic stimulation (TMS) has been available as a noninvasive clinical tool to treat patients suffering from major depression. In this period, a bulk of animal and human studies examined TMS parameters to improve clinical outcome. However, the neurobiological mechanisms underlying mood changes remain an important focus of research. In addition to having an effect on neuroendocrinological processes, neurotransmitter systems, and neurotrophic factors, TMS may not only affect the stimulated cortical regions, but also those connected to them. Therefore, we will review current human data on possible neurobiological mechanisms of repetitive (r) TMS implicated in the deregulated neurocircuitry present in unipolar depression. Furthermore, as the rTMS application can be considered as a "top-down" neuronal intervention, we will focus on the neuronal pathways linked with the stimulated area and we will present an integrative model of action.

Inactivation of the bed nucleus of the stria terminalis in an animal model of relapse: effects on conditioned cue-induced reinstatement and its enhancement by yohimbine

RATIONALE

Drug-associated cues and stress increase craving and lead to greater risk of relapse in abstinent drug users. Animal models of reinstatement of drug seeking have been utilized to study the neural circuitry by which either drug-associated cues or stress exposure elicit drug seeking. Recent evidence has shown a strong enhancing effect of yohimbine stress on subsequent cue-elicited reinstatement; however, there has been no examination of the neural substrates of this interactive effect.

OBJECTIVES

The current study examined whether inactivation of the bed nucleus of the stria terminalis (BNST), an area previously implicated in stress activation of drug seeking, would affect reinstatement of cocaine seeking caused by conditioned cues, yohimbine stress, or the combination of these factors.

METHODS

Male rats experienced daily IV cocaine self-administration, followed by extinction of lever responding in the absence of cocaine-paired cues. Reinstatement of responding was measured during presentation of cocaine-paired cues, following pretreatment with the pharmacological stressor, yohimbine (2.5 mg/kg, IP), or the combination of cues and yohimbine.

RESULTS

All three conditions led to reinstatement of cocaine seeking, with the highest responding seen after the combination of cues and yohimbine. Reversible inactivation of the BNST using the gamma-aminobutyric acid receptor agonists, baclofen + muscimol, significantly reduced all three forms of reinstatement.

CONCLUSION

These results demonstrate a role for the BNST in cocaine seeking elicited by cocaine-paired cues, and suggest the BNST as a key mediator for the interaction of stress and cues for the reinstatement of cocaine seeking.

Structural equation modeling and principal component analysis of gray matter volumes in major depressive and bipolar disorders: differences in latent volumetric structure

Abnormalities of the cortico-striatal-thalamic-cortical (CSTC) and the limbic-cortico-striatal-thalamic-cortical (LCSTC) circuits have been hypothesized in mood disorders. We performed principal component analysis (PCA) to identify latent volumetric systems on regional brain volumes and correlated these patterns with clinical characteristics; further, we performed exploratory structural equation modeling (SEM) to test a priori hypotheses about the organization among the structures comprising the CSTC and LCSTC circuits, and to investigate differences among subjects with bipolar disorder (BD), major depressive disorder (MDD), and healthy controls (HC). Participants included 45 BD and 31 MDD patients, and 72 HC. Regional MR brain volumes were used to calculate patterns of volumetric covariance. The identified latent volumetric systems were related to the depression severity and the duration of illness. BD differed from HC on the estimated parameters describing the paths of cortico-striatal, thalamo-striatal and intrastriatal loops of the CSTC circuit, and the paths between anterior and posterior cingulate cortex (PCC), and hippocampus to amygdala of the LCSTC circuit. MDD differed from HC on the paths between putamen and thalamus, and PCC to hippocampus. This study provides evidence to suggest different organizational patterns among structures within the CSTC and LCSTC circuits for BD, MDD, and HC, which may point to structural abnormalities underlying mood disorders.

Environmental living conditions introduced during forced abstinence alter cocaine-seeking behavior and Fos protein expression

Environmental enrichment (EE) introduced during abstinence from cocaine self-administration is protective in reducing cue-elicited incentive motivation for cocaine in rats. This study examined neural activation associated with this protective effect of EE using Fos protein expression as a marker. Rats were trained to press a lever reinforced by cocaine (0.75 mg/kg/0.1 mL infusion) and light and tone cues across 15 consecutive days during which they were all housed in isolated conditions (IC). Rats were then assigned to either remain in IC, or to live in pair-housed conditions (PC) or EE for 30 days of forced abstinence from cocaine. Subsequently, cocaine-seeking behavior (lever presses without cocaine reinforcement) elicited by response-contingent cue presentations was assessed for 90 min, after which the rats' brains were immediately harvested for Fos protein immunohistochemistry. EE attenuated, whereas IC enhanced, cue-elicited cocaine-seeking behavior relative to PC. Also, within the prelimbic and orbitofrontal cortices and basolateral amygdala, IC enhanced, whereas EE reduced, Fos expression relative to PC. Furthermore, EE attenuated Fos expression in the infralimbic and anterior cingulate cortices, the nucleus accumbens (core and shell), bed nucleus of the stria terminalis, and ventral tegmental area, evident as a reduction relative to both PC and IC. In contrast, IC enhanced Fos expression in the dorsal caudate putamen, substantia nigra, and central amygdala, evident as an increase relative to both PC and EE. These results suggest that EE blunts neural activation throughout the mesocorticolimbic circuitry involved in cue-elicited incentive motivation for cocaine, whereas IC enhances activation primarily within the nigrostriatal dopamine pathway. These findings have important implications for understanding and treating drug-conditioned craving in humans.

Working memory circuitry in schizophrenia shows widespread cortical inefficiency and compensation

BACKGROUND

Working memory studies in schizophrenia (SZ), using functional magnetic resonance imaging (fMRI) and univariate analyses, have led to observations of hypo- or hyperactivation of discrete cortical regions and subsequent interpretations (e.g. neural inefficiencies). We employed a data-driven, multivariate analysis to identify the patterns of brain-behavior relationships in SZ during working memory.

METHODS

fMRI scans were collected from 13 SZ and 18 healthy control (HC) participants performing a modified Sternberg item recognition paradigm with three memory loads. We applied partial least squares analysis (PLS) to assess brain activation during the task both alone and with behavioral measures (accuracy and response time, RT) as covariates.

RESULTS

While the HC primary pattern was not affected by increasing load demands, SZ participants showed an exaggerated change in the Blood Oxygenation Level Dependent (BOLD) signal from the low to moderate memory load conditions and subsequent decrease in the greatest memory load, in frontal, motor, parietal and subcortical areas. With behavioral covariates, the separate groups identified distinct brain-behavior relationships and circuits. Increased activation of the middle temporal gyrus was associated with greater accuracy and faster RT only in SZ.

CONCLUSIONS

The inverted U-shaped curves in the SZ BOLD signal in the same areas that show flat activation in the HC data indicate widespread neural inefficiency in working memory in SZ. While both groups performed the task with similar levels of accuracy, participants with schizophrenia show a compensatory network of different sub-regions of the prefrontal cortex, parietal lobule, and the temporal gyri in this working memory task.

Functional neurosurgery in the treatment of severe obsessive compulsive disorder and major depression: overview of disease circuits and therapeutic targeting for the clinician

Over the past 20 years, there has been a concerted effort to expand our understanding of the neural circuitry involved in the pathogenesis of psychiatric disorders. Distinct neuronal circuits and networks have been implicated in obsessive compulsive disorder (OCD) and major depressive disorder (MDD) involving feedback loops between the cortex, striatum, and thalamus. When neurosurgery is used as a therapeutic tool in severe OCD and MDD, the goal is to modulate specific targets or nodes within these networks in an effort to produce symptom relief.Currently, four lesioning neurosurgical procedures are utilized for treatment refractory OCD and MDD: cingulotomy, capsulotomy, subcaudate tractotomy, and limbic leucotomy. Deep brain stimulation (DBS) is a novel neurosurgical approach that has some distinct advantages over lesioning procedures. With DBS, the desired clinical effect can be achieved by reversible, high frequency stimulation in a nucleus or at a node in the circuit without the need to produce an irreversible lesion. Recent trials of deep brain stimulation in both OCD and MDD at several neuroanatomical targets have reported promising early results in highly refractory patients and with a good safety profile. Future definitive trials in MDD and OCD are envisaged.