An arginine-rich nuclear localization signal (ArgiNLS) strategy for streamlined image segmentation of single-cells

High-throughput volumetric fluorescent microscopy pipelines can spatially integrate whole-brain structure and function at the foundational level of single-cells. However, conventional fluorescent protein (FP) modifications used to discriminate single-cells possess limited efficacy or are detrimental to cellular health. Here, we introduce a synthetic and non-deleterious nuclear localization signal (NLS) tag strategy, called 'Arginine-rich NLS' (ArgiNLS), that optimizes genetic labeling and downstream image segmentation of single-cells by restricting FP localization near-exclusively in the nucleus through a poly-arginine mechanism. A single N-terminal ArgiNLS tag provides modular nuclear restriction consistently across spectrally separate FP variants. ArgiNLS performance in vivo displays functional conservation across major cortical cell classes, and in response to both local and systemic brain wide AAV administration. Crucially, the high signal-to-noise ratio afforded by ArgiNLS enhances ML-automated segmentation of single-cells due to rapid classifier training and enrichment of labeled cell detection within 2D brain sections or 3D volumetric whole-brain image datasets, derived from both staining-amplified and native signal. This genetic strategy provides a simple and flexible basis for precise image segmentation of genetically labeled single-cells at scale and paired with behavioral procedures.

Current Status and Future Strategies for Advancing Functional Circuit Mapping In Vivo

The human brain represents one of the most complex biological systems, containing billions of neurons interconnected through trillions of synapses. Inherent to the brain is a biochemical complexity involving ions, signaling molecules, and peptides that regulate neuronal activity and allow for short- and long-term adaptations. Large-scale and noninvasive imaging techniques, such as fMRI and EEG, have highlighted brain regions involved in specific functions and visualized connections between different brain areas. A major shortcoming, however, is the need for more information on specific cell types and neurotransmitters involved, as well as poor spatial and temporal resolution. Recent technologies have been advanced for neuronal circuit mapping and implemented in behaving model organisms to address this. Here, we highlight strategies for targeting specific neuronal subtypes, identifying, and releasing signaling molecules, controlling gene expression, and monitoring neuronal circuits in real-time in vivo Combined, these approaches allow us to establish direct causal links from genes and molecules to the systems level and ultimately to cognitive processes.

Temporal scaling of dopamine neuron firing and dopamine release by distinct ion channels shape behavior

Dopamine is broadly implicated in reinforcement learning, but how patterns of dopamine activity are generated is poorly resolved. Here, we demonstrate that two ion channels, Kv4.3 and BKCa1.1, regulate the pattern of dopamine neuron firing and dopamine release on different time scales to influence separate phases of reinforced behavior in mice. Inactivation of Kv4.3 in VTA dopamine neurons increases ex vivo pacemaker activity and excitability that is associated with increased in vivo firing rate and ramping dynamics before lever press in a learned instrumental paradigm. Loss of Kv4.3 enhances performance of the learned response and facilitates extinction. In contrast, loss of BKCa1.1 increases burst firing and phasic dopamine release that enhances learning of an instrumental response and enhances extinction burst lever pressing in early extinction that is associated with a greater change in activity between reinforced and unreinforced actions. These data demonstrate that disruption of intrinsic regulators of neuronal activity differentially affects dopamine dynamics during reinforcement and extinction learning.

Netrin-1 regulates the balance of synaptic glutamate signaling in the adult ventral tegmental area

The axonal guidance cue netrin-1 serves a critical role in neural circuit development by promoting growth cone motility, axonal branching, and synaptogenesis. Within the adult mouse brain, expression of the gene encoding (Ntn1) is highly enriched in the ventral midbrain where it is expressed in both GABAergic and dopaminergic neurons, but its function in these cell types in the adult system remains largely unknown. To address this, we performed viral-mediated, cell-type specific CRISPR-Cas9 mutagenesis of Ntn1 in the ventral tegmental area (VTA) of adult mice. Ntn1 loss-of-function in either cell type resulted in a significant reduction in excitatory postsynaptic connectivity. In dopamine neurons, the reduced excitatory tone had a minimal phenotypic behavioral outcome; however, reduced glutamatergic tone on VTA GABA neurons induced behaviors associated with a hyperdopaminergic phenotype. Simultaneous loss of Ntn1 function in both cell types largely rescued the phenotype observed in the GABA-only mutagenesis. These findings demonstrate an important role for Ntn1 in maintaining excitatory connectivity in the adult midbrain and that a balance in this connectivity within two of the major cell types of the VTA is critical for the proper functioning of the mesolimbic system.

Midbrain projection to the basolateral amygdala encodes anxiety-like but not depression-like behaviors

Anxiety disorders are complex diseases, and often co-occur with depression. It is as yet unclear if a common neural circuit controls anxiety-related behaviors in both anxiety-alone and comorbid conditions. Here, utilizing the chronic social defeat stress (CSDS) paradigm that induces singular or combined anxiety- and depressive-like phenotypes in mice, we show that a ventral tegmental area (VTA) dopamine circuit projecting to the basolateral amygdala (BLA) selectively controls anxiety- but not depression-like behaviors. Using circuit-dissecting ex vivo electrophysiology and in vivo fiber photometry approaches, we establish that expression of anxiety-like, but not depressive-like, phenotypes are negatively correlated with VTA → BLA dopamine neuron activity. Further, our optogenetic studies demonstrate a causal link between such neuronal activity and anxiety-like behaviors. Overall, these data establish a functional role for VTA → BLA dopamine neurons in bi-directionally controlling anxiety-related behaviors not only in anxiety-alone, but also in anxiety-depressive comorbid conditions in mice.

The Resilient Phenotype Induced by Prophylactic Ketamine Exposure During Adolescence Is Mediated by the Ventral Tegmental Area-Nucleus Accumbens Pathway

BACKGROUND

Major depressive disorder is prevalent in children and adolescents and is associated with a high degree of morbidity throughout life, with potentially devastating personal consequences and public health impact. The efficacy of ketamine (KET) as an antidepressant has been demonstrated in adolescent rodents; however, the neurobiological mechanisms underlying these effects are unknown. Recent evidence showed that KET reverses stress-induced (i.e., depressive-like) deficits within major mesocorticolimbic regions, such as the prefrontal cortex, nucleus accumbens (NAc), and hippocampus, in adult rodents. However, little is known about KET's effect in the ventral tegmental area (VTA), which provides the majority of dopaminergic input to these brain regions.

METHODS

We characterized behavioral, biochemical, and electrophysiological effects produced by KET treatment in C57BL/6J male mice during adolescence (n = 7-10 per condition) within the VTA and its major projection regions, namely, the NAc and prefrontal cortex. Subsequently, molecular targets within the VTA-NAc projection were identified for viral gene transfer manipulations to recapitulate the effects of stress or KET treatment.

RESULTS

Repeated KET treatment produced a robust proresilient response to chronic social defeat stress. This effect was largely driven by Akt signaling activity within the VTA and NAc, and it could be blocked or recapitulated through direct Akt-viral-mediated manipulation. Additionally, we found that the KET-induced resilient phenotype is dependent on VTA-NAc, but not VTA-prefrontal cortex, pathway activity.

CONCLUSIONS

These findings indicate that KET exposure during adolescence produces a proresilient phenotype mediated by changes in Akt intracellular signaling and altered neuronal activity within the VTA-NAc pathway.

CRISPR knockdown of Kcnq3 attenuates the M-current and increases excitability of NPY/AgRP neurons to alter energy balance

OBJECTIVE

Arcuate nucleus neuropeptide Y/agouti-related peptide (NPY/AgRP) neurons drive ingestive behavior. The M-current, a subthreshold non-inactivating potassium current, plays a critical role in regulating NPY/AgRP neuronal excitability. Fasting decreases while 17β-estradiol increases the M-current by regulating the mRNA expression of Kcnq2, 3, and 5 (Kv7.2, 3, and 5) channel subunits. Incorporating KCNQ3 into heteromeric channels has been considered essential to generate a robust M-current. Therefore, we investigated the behavioral and physiological effects of selective Kcnq3 deletion from NPY/AgRP neurons.

METHODS

We used a single adeno-associated viral vector containing a recombinase-dependent Staphylococcus aureus Cas9 with a single-guide RNA to selectively delete Kcnq3 in NPY/AgRP neurons. Single-cell quantitative measurements of mRNA expression and whole-cell patch clamp experiments were conducted to validate the selective knockdown. Body weight, food intake, and locomotor activity were measured in male mice to assess disruptions in energy balance.

RESULTS

The virus reduced the expression of Kcnq3 mRNA without affecting Kcnq2 or Kcnq5. The M-current was attenuated, causing NPY/AgRP neurons to be more depolarized, exhibit a higher input resistance, and require less depolarizing current to fire action potentials, indicative of increased excitability. Although the resulting decrease in the M-current did not overtly alter ingestive behavior, it significantly reduced the locomotor activity as measured by open-field testing. Control mice on a high-fat diet exhibited an enhanced M-current and increased Kcnq2 and Kcnq3 expression, but the M-current remained significantly attenuated in KCNQ3 knockdown animals.

CONCLUSIONS

The M-current plays a critical role in modulating the intrinsic excitability of NPY/AgRP neurons that is essential for maintaining energy homeostasis.

Repetitive blast mild traumatic brain injury increases ethanol sensitivity in male mice and risky drinking behavior in male combat veterans

BACKGROUND

Mild traumatic brain injury (mTBI) is common in civilians and highly prevalent among military service members. mTBI can increase health risk behaviors (e.g., sensation seeking, impulsivity) and addiction risk (e.g., for alcohol use disorder (AUD)), but how mTBI and substance use might interact to promote addiction risk remains poorly understood. Likewise, potential differences in single vs. repetitive mTBI in relation to alcohol use/abuse have not been previously examined.

METHODS

Here, we examined how a history of single (1×) or repetitive (3×) blast exposure (blast-mTBI) affects ethanol (EtOH)-induced behavioral and physiological outcomes using an established mouse model of blast-mTBI. To investigate potential translational relevance, we also examined self-report responses to the Alcohol Use Disorders Identification Test-Consumption questions (AUDIT-C), a widely used measure to identify potential hazardous drinking and AUD, and used a novel unsupervised machine learning approach to investigate whether a history of blast-mTBI affected drinking behaviors in Iraq/Afghanistan Veterans.

RESULTS

Both single and repetitive blast-mTBI in mice increased the sedative properties of EtOH (with no change in tolerance or metabolism), but only repetitive blast potentiated EtOH-induced locomotor stimulation and shifted EtOH intake patterns. Specifically, mice exposed to repetitive blasts showed increased consumption "front-loading" (e.g., a higher rate of consumption during an initial 2-h acute phase of a 24-h alcohol access period and decreased total daily intake) during an intermittent 2-bottle choice condition. Examination of AUDIT-C scores in Iraq/Afghanistan Veterans revealed an optimal 3-cluster solution: "low" (low intake and low frequency), "frequent" (low intake and high frequency), and "risky" (high intake and high frequency), where Veterans with a history of blast-mTBI displayed a shift in cluster assignment from "frequent" to "risky," as compared to Veterans who were deployed to Iraq/Afghanistan but had no lifetime history of TBI.

CONCLUSIONS

Together, these results offer new insight into how blast-mTBI may give increase AUD risk and highlight the increased potential for adverse health risk behaviors following repetitive blast-mTBI.

Different adaptations of dopamine release in Nucleus Accumbens shell and core of individual alcohol drinking groups of mice

Alcohol use disorder (AUD) places a tremendous burden on society, with approximately two billion alcohol users in the world. While most people drink alcohol recreationally, a subpopulation (3-5%) engages in reckless and compulsive drinking, leading to the development of AUD and alcohol dependence. The Ventral Tegmental Area (VTA)-Nucleus Accumbens (NAc) circuit has been shown to encode rewarding stimuli and drive individual alcohol drinking behavior. Our previous work successfully separated C57BL/6J isogenic mice into high or low alcohol drinking subgroups after a 12-day, two-bottle choice voluntary alcohol access paradigm. Electrophysiological studies revealed that low alcohol drinking mice exhibited elevated spontaneous and burst firing properties of their VTA dopamine (DA) neurons and specifically mimicking this pattern of activity in VTA-NAc neurons in high alcohol drinking mice using optogenetics decreased their alcohol preference. It is also known that VTA DA neurons encode the salience and rewarding properties of external stimuli while also regulating downstream dopamine concentrations. Here, as a follow-up to this study, we utilized Fast Scan Cyclic Voltammetry (FSCV) to examine dopamine release in the NAc shell and core between alcohol drinking groups. We observed dynamic changes of dopamine release in the core of high drinking mice, but failed to see widely significant differences of dopamine release in the shell of both groups, when compared with ethanol-naive controls. Overall, the present data suggest subregion-specific differences of evoked dopamine release in the NAc of low and high alcohol drinking mice, and may provide an anatomical substrate for individual alcohol drinking behavior. This article is part of the special issue on Stress, Addiction and Plasticity.

α1- and β3-Adrenergic Receptor-Mediated Mesolimbic Homeostatic Plasticity Confers Resilience to Social Stress in Susceptible Mice

BACKGROUND

Homeostatic plasticity in mesolimbic dopamine (DA) neurons plays an essential role in mediating resilience to social stress. Recent evidence implicates an association between stress resilience and projections from the locus coeruleus (LC) to the ventral tegmental area (VTA) (LC→VTA) DA system. However, the precise circuitry and molecular mechanisms of the homeostatic plasticity in mesolimbic DA neurons mediated by the LC→VTA circuitry, and its role in conferring resilience to social defeat stress, have not been described.

METHODS

In a well-established chronic social defeat stress model of depression, using projection-specific electrophysiological recordings and optogenetic, pharmacological, and molecular profiling techniques, we investigated the functional role and molecular basis of an LC→VTA circuit in conferring resilience to social defeat stress.

RESULTS

We found that LC neurons projecting to the VTA exhibit enhanced firing activity in resilient, but not susceptible, mice. Optogenetically mimicking this firing adaptation in susceptible mice reverses their depression-related behaviors, and induces reversal of cellular hyperactivity and homeostatic plasticity in VTA DA neurons projecting to the nucleus accumbens. Circuit-specific molecular profiling studies reveal that α₁- and β₃-adrenergic receptors are highly expressed in VTA→nucleus accumbens DA neurons. Pharmacologically activating these receptors induces similar proresilient effects at the ion channel and cellular and behavioral levels, whereas antagonizing these receptors blocks the proresilient effect of optogenetic activation of LC→VTA circuit neurons in susceptible mice.

CONCLUSIONS

These findings reveal a key role of the LC→VTA circuit in mediating homeostatic plasticity in stress resilience and reveal α₁- and β₃-adrenergic receptors as new molecular targets for therapeutically promoting resilience.

Optogenetic investigation of neural mechanisms for alcohol-use disorder

Optogenetic techniques have been widely used in the study of neuropsychiatric diseases such as anxiety, depression, and drug addiction. Cell-type specific targeting of optogenetic tools to neurons has contributed to a tremendous understanding of the function of neural circuits for future treatment of neuropsychiatric disorders. Though optogenetics has been widely used in many research areas, the use of optogenetic tools to uncover and elucidate neural circuit mechanisms of alcohol's actions in the brain are still developing. Here in this review article, we will provide a basic introduction to optogenetics and discuss how these optogenetic experimental approaches can be used in alcohol studies to reveal neural circuit mechanisms of alcohol's actions in regions implicated in the development of alcohol addiction.

Sex Differences in the Neuroadaptations of Reward-related Circuits in Response to Subchronic Variable Stress

Women are twice as likely to be diagnosed with major depressive disorder. However, fewer studies in rodent models of depression have used female animals, leading to a relative lack of understanding of the female brain's response to stress, especially at a neural circuit level. In this study, we utilized a 6-day subchronic variable stress (SCVS) mouse model and measured novelty suppressed feeding as behavioral criteria to evaluate susceptibility to SCVS in male and female mice. First, we showed that SCVS induced a decrease in latency to eat (susceptible phenotype) in female mice, but not in males (resilient phenotype). After determining behavioral phenotypes, we investigated the firing activities of dopamine (DA) neurons in the ventral tegmental area (VTA), as well as the neurons that project from lateral habenula (LHb) to the VTA and from locus coeruleus (LC) to the VTA. Utilizing retrograding lumafluor fluorescent tracers and electrophysiology techniques, we performed cell type- and circuit-specific measures of neuronal firing rates. Our data show that SCVS significantly increased the firing rate of LHb-VTA circuit neurons in female mice when compared to that of their female controls, an effect that was absent in SCVS-exposed males. Interestingly, SCVS did not induce significant firing alterations in VTA DA neurons and LC-VTA circuit neurons in either female mice or male mice when compared to their stress-naïve controls. Overall, our data show sex differences in the LHb-VTA circuit responses to SCVS, and implicates a potential role of this projection in mediating vulnerability of female mice to stress-induced depression.

Essential Role of Mesolimbic Brain-Derived Neurotrophic Factor in Chronic Social Stress-Induced Depressive Behaviors

BACKGROUND

Previous work has shown that chronic social defeat stress (CSDS) induces increased phasic firing of ventral tegmental area (VTA) dopamine (DA) neurons that project to the nucleus accumbens (NAc) selectively in mice that are susceptible to the deleterious effects of the stress. In addition, acute optogenetic phasic stimulation of these neurons promotes susceptibility in animals exposed to acute defeat stress. These findings are paradoxical, as increased DA signaling in NAc normally promotes motivation and reward, and the influence of chronic phasic VTA firing in the face of chronic stress is unknown.

METHODS

We used CSDS with repeated optogenetic activation and pharmacologic manipulations of the mesolimbic VTA-NAc pathway to examine the role of brain-derived neurotrophic factor (BDNF) and DA signaling in depressive-like behaviors. We measured BDNF protein expression and DA release in this model.

RESULTS

Pharmacologic blockade of BDNF-tyrosine receptor kinase B (TrkB) signaling, but not DA signaling, in NAc prevented CSDS-induced behavioral abnormalities. Chronic optogenetic phasic stimulation of the VTA-NAc circuit during CSDS exacerbated the defeat-induced behavioral symptoms, and these aggravated symptoms were also normalized by BDNF-TrkB blockade in NAc. The aggravated behavioral deficits induced by phasic stimulation of the VTA-NAc pathway were blocked as well by local knockdown of BDNF in VTA.

CONCLUSIONS

These findings show that BDNF-TrkB signaling, rather than DA signaling, in the VTA-NAc circuit is crucial for facilitating depressive-like outcomes after CSDS and they establish BDNF-TrkB signaling as a pathologic mechanism during periods of chronic stress.

KCNQ channel openers reverse depressive symptoms via an active resilience mechanism

Less than half of patients suffering from major depressive disorder, a leading cause of disability worldwide, achieve remission with current antidepressants, making it imperative to develop more effective treatment. A new therapeutic direction is emerging from the increased understanding of natural resilience as an active stress-coping process. It is known that potassium (K(+)) channels in the ventral tegmental area (VTA) are an active mediator of resilience. However, no druggable targets have been identified to potentiate active resilience mechanisms. In the chronic social defeat stress model of depression, we report that KCNQ-type K(+) channel openers, including FDA-approved drug retigabine (ezogabine), show antidepressant efficacy. We demonstrate that overexpression of KCNQ channels in the VTA dopaminergic neurons and either local infusion or systemic administration of retigabine normalized neuronal hyperactivity and depressive behaviours. These findings identify KCNQ as a target for conceptually novel antidepressants that function through the potentiation of active resilience mechanisms.

Surgical Facilitated Orthodontics for the Correction of an Over Erupted Upper First Molar

The loss of one or several teeth is a common finding in adult patients. Over-erupted molars due to the loss of the antagonist, the lack of space, or the unwanted inclination of the adjacent teeth are real complications specific to dental implant prosthetic rehabilitation A patient with an over erupted upper left first molar was treated with surgical-facilitated orthodontics.

Enhancing depression mechanisms in midbrain dopamine neurons achieves homeostatic resilience

Typical therapies try to reverse pathogenic mechanisms. Here, we describe treatment effects achieved by enhancing depression-causing mechanisms in ventral tegmental area (VTA) dopamine (DA) neurons. In a social defeat stress model of depression, depressed (susceptible) mice display hyperactivity of VTA DA neurons, caused by an up-regulated hyperpolarization-activated current (I(h)). Mice resilient to social defeat stress, however, exhibit stable normal firing of these neurons. Unexpectedly, resilient mice had an even larger I(h), which was observed in parallel with increased potassium (K(+)) channel currents. Experimentally further enhancing Ih or optogenetically increasing the hyperactivity of VTA DA neurons in susceptible mice completely reversed depression-related behaviors, an antidepressant effect achieved through resilience-like, projection-specific homeostatic plasticity. These results indicate a potential therapeutic path of promoting natural resilience for depression treatment.

Stress and CRF gate neural activation of BDNF in the mesolimbic reward pathway

Mechanisms controlling release of brain-derived neurotrophic factor (BDNF) in the mesolimbic dopamine reward pathway remain unknown. We report that phasic optogenetic activation of this pathway increases BDNF amounts in the nucleus accumbens (NAc) of socially stressed mice but not of stress-naive mice. This stress gating of BDNF signaling is mediated by corticotrophin-releasing factor (CRF) acting in the NAc. These results unravel a stress context-detecting function of the brain's mesolimbic circuit.

BDNF is a negative modulator of morphine action

Brain-derived neurotrophic factor (BDNF) is a key positive regulator of neural plasticity, promoting, for example, the actions of stimulant drugs of abuse such as cocaine. We discovered a surprising opposite role for BDNF in countering responses to chronic morphine exposure. The suppression of BDNF in the ventral tegmental area (VTA) enhanced the ability of morphine to increase dopamine (DA) neuron excitability and promote reward. In contrast, optical stimulation of VTA DA terminals in nucleus accumbens (NAc) completely reversed the suppressive effect of BDNF on morphine reward. Furthermore, we identified numerous genes in the NAc, a major target region of VTA DA neurons, whose regulation by BDNF in the context of chronic morphine exposure mediated this counteractive function. These findings provide insight into the molecular basis of morphine-induced neuroadaptations in the brain's reward circuitry.

Lithium enhances cortical mRNA expression in ovariectomized C57BL/6J mice

The hippocampus and cortex of the mammalian brain are regions involved in learning and long-term memory. Estrogen and lithium affect similar learning and memory molecular processes. We hypothesized that in ovariectomized mice lithium treatment will enhance genetic factors in the brain that are involved in neuroprotection, learning and memory. Our study used bilaterally ovariectomized (bOVX) C57BL÷6J mice treated for one month with 14.2 mM LiCl in their drinking water. Results indicate that LiCl-treated bOVX mice show enhanced cortical increases in mRNA expression of ER-alpha, NR1, Bcl-2, BDNF, and CaMkII-alpha; hippocampal mRNA showed no changes. Our results indicate that in bOVX C57BL÷6J mice, lithium enhances the expression of specific cortical genes coded for proteins involved in learning, memory and neuroprotection.

Growth of Azotobacter chroococcum in chemically defined media containing p-hydroxybenzoic acid and protocatechuic acid

Growth and utilization of different phenolic acids present in olive mill wastewater (OMW) by Azotobacter chroococcum were studied in chemically defined media. Growth and utilization of phenolic acids were only detected when the microorganism was cultured on p-hydroxybenzoic acid at concentration from 0.01% to 0.5% (w/v) and protocatechuic acid at concentration from 0.01% to 0.3% (w/v) as sole carbon sources suggesting that only these phenolic compounds could be utilized as a carbon source by A. chroococcum. Moreover when culture media were added with a mixture of 0.3% of protocatechuic acid and 0.3% p-hydroxybenzoic acid, the microorganism degradated in first place protocatechuic acid and once the culture medium was depleted of this compound, the degradation of p-hydroxybenzoic acid commenced very fast.

Parent-adolescent communication and support for diabetes management as reported by adolescents with type 1 diabetes

This study examined parental involvement in terms of communication and support and these variables in relationship to diabetes management responsibility and metabolic control from the perspective of adolescents. The sample consisted of 27 adolescents who were 12 to 19 years of age (M=15.0 years, SD=1.9) and had type 1 diabetes. Participants completed Independent Functioning, Independent Decision Making, Parent-Adolescent Communication, and Parental Support Checklists. Adolescents reported relatively high level of communication with parents and relatively low level of parental support. These adolescents reported more agreement than amount of communication with parents and reported more parental support received than sought. Although not significantly different, the means for amount of communication and agreement decreased from early to middle to late adolescence and the means for seeking and receiving support increased from early to middle and then decreased from middle to late adolescence. When working with parents and adolescents with type 1 diabetes, health care professionals need to be cognizant of adolescents' view of specific ways that parents are involved and the developmental influences on parent-adolescent relationships.