A prefrontal cortex-brainstem neuronal projection that controls response to behavioural challenge

Valence processing in the PFC: Reconciling circuit-level and systems-level views

An essential component in animal behavior is the ability to process emotion and dissociate among positive and negative valence in response to a rewarding or aversive stimulus. The medial prefrontal cortex (mPFC)-responsible for higher order executive functions that include cognition, learning, and working memory; and is also involved in sociability-plays a major role in emotional processing and control. Although the amygdala is widely regarded as the "emotional hub," the mPFC encodes for context-specific salience and elicits top-down control over limbic circuitry. The mPFC can then conduct behavioral responses, via cortico-striatal and cortico-brainstem pathways, that correspond to emotional stimuli. Evidence shows that abnormalities within the mPFC lead to sociability deficits, working memory impairments, and drug-seeking behavior that include addiction and compulsive disorders; as well as conditions such as anhedonia. Recent studies investigate the effects of aberrant salience processing on cortical circuitry and neuronal populations associated with these behaviors. In this chapter, we discuss mPFC valence processing, neuroanatomical connections, and physiological substrates involved in mPFC-associated behavior. We review neurocomputational and theoretical models such as "mixed selectivity," that describe cognitive control, attentiveness, and motivational drives. Using this knowledge, we describe the effects of valence imbalances and its influence on mPFC neural pathways that contribute to deficits in social cognition, while understanding the effects in addiction/compulsive behaviors and anhedonia.

Serotonergic neurons in the treatment of mood disorders: The dialogue with astrocytes

Astrocytes were traditionally regarded as cells important to neuronal activity, providing both metabolic and structural supports. Recent evidence suggests that they may also play a crucial role in the control of higher brain functions. In keeping with this hypothesis, it is now well accepted that astrocytes contribute to stress but also react to antidepressant drugs as they express serotonergic transporters and receptors. However, the downstream mechanisms leading to the fine-tuned regulation of mood are still unknown. This chapter pays attention to the role of astrocytes in the regulation of emotional behavior and related serotonergic neurotransmission. In particular, it gives a current state of the clinical and preclinical evidence showing that astrocytes respond to environmental conditions and antidepressant drugs through the release of gliotransmitters and neurotrophic factors which in turn, influence serotonergic tone in discrete brain areas. This state-of-the-art review aims at demonstrating the remarkable potential for novel therapeutic antidepressant strategies targeting these glial cells.

Mediodorsal and Ventromedial Thalamus Engage Distinct L1 Circuits in the Prefrontal Cortex

Interactions between the thalamus and prefrontal cortex (PFC) play a critical role in cognitive function and arousal. Here, we use anatomical tracing, electrophysiology, optogenetics, and 2-photon Ca2+ imaging to determine how ventromedial (VM) and mediodorsal (MD) thalamus target specific cell types and subcellular compartments in layer 1 (L1) of mouse PFC. We find thalamic inputs make distinct connections in L1, where VM engages neuron-derived neurotrophic factor (NDNF+) cells in L1a and MD drives vasoactive intestinal peptide (VIP+) cells in L1b. These separate populations of L1 interneurons participate in different inhibitory networks in superficial layers by targeting either parvalbumin (PV+) or somatostatin (SOM+) interneurons. NDNF+ cells also inhibit the apical dendrites of L5 pyramidal tract (PT) cells to suppress action potential (AP)-evoked Ca2+ signals. Lastly, NDNF+ cells mediate a unique form of thalamus-evoked inhibition at PT cells, selectively blocking VM-evoked dendritic Ca2+ spikes. Together, our findings reveal how two thalamic nuclei differentially communicate with the PFC through distinct L1 micro-circuits.

The anterior cingulate cortex and event-based modulation of autonomic states

In spite of being an intensive area of research focus, the anterior cingulate cortex (ACC) remains somewhat of an enigma. Many theories have focused on its role in various aspects of cognition yet surgically precise lesions of the ACC, used to treat severe emotional disorders in human patients, typically have no lasting effects on cognition. An alternative view is that the ACC has a prominent role in regulating autonomic states. This view is consistent with anatomical data showing that a main target of the ACC are regions involved in autonomic control and with the observation that stimulation of the ACC evokes changes in autonomic states in both animals and humans. From an electrophysiological perspective, ACC neurons appear able to represent virtually any event or internal state, even though there is not always a strong link between these representations and behavior. Ensembles of neurons form robust contextual representations that strongly influence how specific events are encoded. The activity patterns associated with these contextually-based event representations presumably impact activity in downstream regions that control autonomic state. As a result, the ACC may regulate the autonomic and perhaps emotional reactions to events it is representing. This event-based control of autonomic tone by the ACC would likely arise during all types of cognitive and affective processes, without necessarily being critical for any of them.

A Multichannel Flexible Optoelectronic Fiber Device for Distributed Implantable Neurological Stimulation and Monitoring

Optical fibers made of polymeric materials possess high flexibility that can potentially integrate with flexible electronic devices to realize complex functions in biology and neurology. Here, a multichannel flexible device based on four individually addressable optical fibers transfer-printed with flexible electronic components and controlled by a wireless circuit is developed. The resulting device offers excellent mechanics that is compatible with soft and curvilinear tissues, and excellent diversity through switching different light sources. The combined configuration of optical fibers and flexible electronics allows optical stimulation in selective wavelengths guided by the optical fibers, while conducting distributed, high-throughput biopotential sensing using the flexible microelectrode arrays. The device has been demonstrated in vivo with rats through optical stimulation and simultaneously monitoring of spontaneous/evoked spike signals and local field potentials using 32 microelectrodes in four brain regions. Biocompatibility of the device has been characterized by behavior and immunohistochemistry studies, demonstrating potential applications of the device in long-term animal studies. The techniques to integrate flexible electronics with optical fibers may inspire the development of more flexible optoelectronic devices for sophisticated applications in biomedicine and biology.

Integration of value and action in medial prefrontal neural systems

The rodent medial prefrontal cortex (mPFC) plays a key role in regulating cognition, emotion, and behavior. mPFC neurons are activated in diverse experimental paradigms, raising the questions of whether there are specific task elements or dimensions encoded by mPFC neurons, and whether these encoded parameters are selective to neurons in particular mPFC subregions or networks. Here, we consider the role of mPFC neurons in processing appetitive and aversive cues, outcomes, and related behaviors. mPFC neurons are strongly activated in tasks probing value and outcome-associated actions, but these responses vary across experimental paradigms. Can we identify specific categories of responses (e.g., positive or negative value), or do mPFC neurons exhibit response properties that are too heterogeneous/complex to cluster into distinct conceptual groups? Based on a review of relevant studies, we consider what has been done and what needs to be further explored in order to address these questions.

More Than Mortar: Glia as Architects of Nervous System Development and Disease

Glial cells are an essential component of the nervous system of vertebrates and invertebrates. In the human brain, glia are as numerous as neurons, yet the importance of glia to nearly every aspect of nervous system development has only been expounded over the last several decades. Glia are now known to regulate neural specification, synaptogenesis, synapse function, and even broad circuit function. Given their ubiquity, it is not surprising that the contribution of glia to neuronal disease pathogenesis is a growing area of research. In this review, we will summarize the accumulated evidence of glial participation in several distinct phases of nervous system development and organization-neural specification, circuit wiring, and circuit function. Finally, we will highlight how these early developmental roles of glia contribute to nervous system dysfunction in neurodevelopmental and neurodegenerative disorders.

Implication of 5-HT7 receptor in prefrontal circuit assembly and detrimental emotional effects of SSRIs during development

Altered development of prefrontal cortex (PFC) circuits can have long-term consequences on adult emotional behavior. Changes in serotonin homeostasis during critical periods produced by genetic or pharmacological inactivation of the serotonin transporter (SERT, or Slc6a4), have been involved in such developmental effects. In mice, selective serotonin reuptake inhibitors (SSRIs), administered during postnatal development cause exuberant synaptic connectivity of the PFC to brainstem dorsal raphe nucleus (DRN) circuits, and increase adult risk for developing anxiety and depressive symptoms. SERT is transiently expressed in the glutamate neurons of the mouse PFC, that project to the DRN. Here, we find that 5-HTR7 is transiently co-expressed with SERT by PFC neurons, and it plays a key role in the maturation of PFC-to-DRN synaptic circuits during early postnatal life. 5-HTR7-KO mice show reduced PFC-to-DRN synaptic density (as measured by array-tomography and VGLUT1/synapsin immunocytochemistry). Conversely, 5-HTR7 over-expression in the developing PFC increased PFC-to-DRN synaptic density. Long-term consequences on depressive-like and anxiogenic behaviors were observed in adults. 5-HTR7 over-expression in the developing PFC, results in depressive-like symptoms in adulthood. Importantly, the long-term depressive-like and anxiogenic effects of SSRIs (postnatal administration of fluoxetine from P2 to P14) were not observed in 5-HTR7-KO mice, and were prevented by co-administration of the selective inhibitor of 5-HTR7, SB269970. This study identifies a new role 5-HTR7 in the postnatal maturation of prefrontal descending circuits. Furthermore, it shows that 5-HTR7 in the PFC is crucially required for the detrimental emotional effects caused by SSRI exposure during early postnatal life.

Depression and substance use disorders: Clinical comorbidity and shared neurobiology

Mood disorders, including major depressive disorder (MDD), are the most prevalent psychiatric illnesses, and pose an incredible burden to society, both in terms of disability and in terms of costs associated with medical care and lost work time. MDD has extremely high rates of comorbidity with substance use disorders (SUD) as many of the same neurobiological circuits and molecular mechanisms regulate the reward pathways disrupted in both conditions. MDD may induce SUDs, SUD may contribute to MDD development, or underlying vulnerabilities and common life experience may confer risk to developing both conditions. In this chapter we explore theories of MDD and SUD comorbidity, the neurobiological underpinnings of depression, overlapping cellular and molecular pathways for both conditions, and current treatment approaches for these comorbid conditions.

Interplay of Prenatal and Postnatal Risk Factors in the Behavioral and Histological Features of a "Two-Hit" Non-Genetic Mouse Model of Schizophrenia

Schizophrenia is a multifactorial developmental neuropsychiatric disorder. This study examined the interplay of maternal infection and postweaning social isolation, which are prenatal and postnatal risk factors, respectively. Pregnant mice received poly I:C or saline injection on gestation day 9 and the pups were weaned at postnatal day 28. After weaning, male offspring were randomly assigned into group-rearing and isolation-rearing groups. In their adulthood, we performed behavioral tests and characterized the histochemical features of their mesocorticolimbic structures. The sociability and anxiety levels were not affected by either manipulation, but synergistic effects of the two hits on stress-coping behavior was observed. Either of the single manipulations caused defects in sensorimotor gating, novel object recognition and spatial memory tests, but the combination of the two hits did not further exacerbate the disabilities. Prenatal infection increased the number of dopaminergic neurons in midbrain, whereas postweaning isolation decreased the GABAergic neurons in cortex. Single manipulation reduced the dendritic complexity and spine densities of neurons in the medial prefrontal cortex (mPFC) and dentate gyrus. Our results support the current perspective that disturbances in brain development during the prenatal or postnatal period influence the structure and function of the brain and together augment the susceptibility to mental disorders, such as schizophrenia.

Infralimbic cortical glutamate output is necessary for the neural and behavioral consequences of chronic stress

Exposure to prolonged stress is a major risk-factor for psychiatric disorders such as generalized anxiety and major depressive disorder. Human imaging studies have identified structural and functional abnormalities in the prefrontal cortex of subjects with depression and anxiety disorders, particularly Brodmann's area 25 (BA25). Further, deep brain stimulation of BA25 reduces symptoms of treatment-resistant depression. The rat homolog of BA25 is the infralimbic cortex (IL), which is critical for cognitive appraisal, executive function, and physiological stress reactivity. Previous studies indicate that the IL undergoes stress-induced changes in excitatory/inhibitory balance culminating in reduced activity of glutamate output neurons. However, the regulatory role of IL glutamate output in mood-related behaviors after chronic variable stress (CVS) is unknown. Here, we utilized a lentiviral-packaged small-interfering RNA to reduce translation of vesicular glutamate transporter 1 (vGluT1 siRNA), thereby constraining IL glutamate output. This viral-mediated gene transfer was used in conjunction with a quantitative anatomical analysis of cells expressing the stable immediate-early gene product FosB/ΔFosB, which accumulates in response to repeated neural activation. Through assessment of FosB/ΔFosB-expressing neurons across the frontal lobe in adult male rats, we mapped regions altered by chronic stress and determined the coordinating role of the IL in frontal cortical plasticity. Specifically, CVS-exposed rats had increased density of FosB/ΔFosB-expressing cells in the IL and decreased density in the insula. The latter effect was dependent on IL glutamate output. Next, we examined the interaction of CVS and reduced IL glutamate output in behavioral assays examining coping, anxiety-like behavior, associative learning, and nociception. IL glutamate knockdown decreased immobility during the forced swim test compared to GFP controls, both in rats exposed to CVS as well as rats without previous stress exposure. Further, vGluT1 siRNA prevented CVS-induced avoidance behaviors, while also reducing risk aversion and passive coping. Ultimately, this study identifies the necessity of IL glutamatergic output for regulating frontal cortical neural activity and behavior following chronic stress. These findings also highlight how disruption of excitatory/inhibitory balance within specific frontal cortical cell populations may impact neurobehavioral adaptation and lead to stress-related disorders.

Increased prefrontal oxygenation prior to and at the onset of over-ground locomotion in humans

We found using wireless near-infrared spectroscopy that prefrontal oxygenation increased before the onset of arbitrary over-ground walking, whereas the preexercise increase was absent when walking was suddenly started by cue. The difference in prefrontal oxygenation between start modes (considered related to central command) preceded heart rate response variances and demonstrated a positive relationship with the difference in heart rate. The central command-related prefrontal activity may contribute to cardiac adjustment, synchronized with the beginning of over-ground walking.

Circuit-Based Biomarkers for Mood and Anxiety Disorders

Mood and anxiety disorders are complex heterogeneous syndromes that manifest in dysfunctions across multiple brain regions, cell types, and circuits. Biomarkers using brain-wide activity patterns in humans have proven useful in distinguishing between disorder subtypes and identifying effective treatments. In order to improve biomarker identification, it is crucial to understand the basic circuitry underpinning brain-wide activity patterns. Leveraging a large repertoire of techniques, animal studies have examined roles of specific cell types and circuits in driving maladaptive behavior. Recent advances in multiregion recording techniques, data-driven analysis approaches, and machine-learning-based behavioral analysis tools can further push the boundary of animal studies and bridge the gap with human studies, to assess how brain-wide activity patterns encode and drive emotional behavior. Together, these efforts will allow identifying more precise biomarkers to enhance diagnosis and treatment.

Prefrontal cortex circuits in depression and anxiety: contribution of discrete neuronal populations and target regions

Our understanding of depression and its treatment has advanced with the advent of ketamine as a rapid-acting antidepressant and the development and refinement of tools capable of selectively altering the activity of populations of neuronal subtypes. This work has resulted in a paradigm shift away from dysregulation of single neurotransmitter systems in depression towards circuit level abnormalities impacting function across multiple brain regions and neurotransmitter systems. Studies on the features of circuit level abnormalities demonstrate structural changes within the prefrontal cortex (PFC) and functional changes in its communication with distal brain structures. Treatments that impact the activity of brain regions, such as transcranial magnetic stimulation or rapid-acting antidepressants like ketamine, appear to reverse depression associated circuit abnormalities though the mechanisms underlying the reversal, as well as development of these abnormalities remains unclear. Recently developed optogenetic and chemogenetic tools that allow high-fidelity control of neuronal activity in preclinical models have begun to elucidate the contributions of the PFC and its circuitry to depression- and anxiety-like behavior. These tools offer unprecedented access to specific circuits and neuronal subpopulations that promise to offer a refined view of the circuit mechanisms surrounding depression and potential mechanistic targets for development and reversal of depression associated circuit abnormalities.

Decreased dendritic spine density in posterodorsal medial amygdala neurons of proactive coping rats

There are large individual differences in the way animals, including humans, behaviorally and physiologically cope with environmental challenges and opportunities. Rodents with either a proactive or reactive coping style not only differ in their capacity to adapt successfully to environmental conditions, but also have a differential susceptibility to develop stress-related (psycho)pathologies when coping fails. In this study, we explored if there are structural neuronal differences in spine density in brain regions important for the regulation of stress coping styles. For this, the individual coping styles of wild-type Groningen (WTG) rats were determined using their level of offensive aggressiveness assessed in the resident-intruder paradigm. Subsequently, brains from proactive (high-aggressive) and reactive (low-aggressive) rats were Golgi-cox stained for spine quantification. The results reveal that dendritic spine densities in the dorsal hippocampal CA1 region and basolateral amygdala are similar in rats with proactive and reactive coping styles. Interestingly, however, dendritic spine density in the medial amygdala (MeA) is strikingly reduced in the proactive coping rats. This brain region is reported to be strongly involved in rivalry aggression which is the criterion by which the coping styles in our study are dissociated. The possibility that structural differences in spine density in the MeA are involved in other behavioral traits of distinct coping styles needs further investigation.

Brain-wide, scale-wide physiology underlying behavioral flexibility in zebrafish

The brain is tasked with choosing actions that maximize an animal's chances of survival and reproduction. These choices must be flexible and informed by the current state of the environment, the needs of the body, and the outcomes of past actions. This information is physiologically encoded and processed across different brain regions on a wide range of spatial scales, from molecules in single synapses to networks of brain areas. Uncovering these spatially distributed neural interactions underlying behavior requires investigations that span a similar range of spatial scales. Larval zebrafish, given their small size, transparency, and ease of genetic access, are a good model organism for such investigations, allowing the use of modern microscopy, molecular biology, and computational techniques. These approaches are yielding new insights into the mechanistic basis of behavioral states, which we review here and compare to related studies in mammalian species.

Activity of a vmPFC-DRN Pathway Corresponds With Resistance to Acute Social Defeat Stress

The ventromedial prefrontal cortex (vmPFC) plays a critical role in stress resilience through top-down inhibition of key stress-sensitive limbic and hindbrain structures, including the dorsal raphe nucleus (DRN). In a model of experience-dependent stress resistance, socially dominant Syrian hamsters display fewer signs of anxiety following acute social defeat when compared to subordinate or control counterparts. Further, dominants activate vmPFC neurons to a greater degree during stress than do subordinates and become stress-vulnerable following pharmacological inhibition of the vmPFC. Dominants also display fewer stress-activated DRN neurons than subordinates do, suggesting that dominance experience gates activation of vmPFC neurons that inhibit the DRN during social defeat stress. To test whether social dominance alters stress-induced activity of a vmPFC-DRN pathway, we injected a retrograde tracer, cholera toxin B (CTB), into the DRN of dominant, subordinate, and control hamsters and used a dual-label immunohistochemical approach to identify vmPFC neurons co-labeled with CTB and the defeat-induced expression of an immediate early gene, cFos. Results indicate that dominant hamsters display more cFos+ and dual-labeled cells in layers V/VI of infralimbic and prelimbic subregions of the vmPFC compared to other animals. Furthermore, vmPFC-DRN activation corresponded directly with proactive behavioral strategies during defeat, which is indicative of stress resilience. Together, results suggest that recruiting the vmPFC-DRN pathway during acute stress corresponds with resistance to the effects of social defeat in dominant hamsters. Overall, these findings indicate that a monosynaptic vmPFC-DRN pathway can be engaged in an experience-dependent manner, which has implications for behavioral interventions aimed at alleviating stress-related psychopathologies.

Three-Week Treadmill Exercise Enhances Persistent Inward Currents, Facilitates Dendritic Plasticity, and Upregulates the Excitability of Dorsal Raphe Serotonin Neurons in ePet-EYFP Mice

Exercise plays a key role in preventing or treating mental or motor disorders caused by dysfunction of the serotonergic system. However, the electrophysiological and ionic channel mechanisms underlying these effects remain unclear. In this study, we investigated the effects of 3-week treadmill exercise on the electrophysiological and channel properties of dorsal raphe nucleus (DRN). Serotonin (5-HT) neurons in ePet-EYFP mice, using whole-cell patch clamp recording. Treadmill exercise was induced in ePet-EYFP mice of P21–24 for 3 weeks, and whole-cell patch clamp recording was performed on EYFP-positive 5-HT neurons from DRN slices of P42–45 mice. Experiment data showed that 5-HT neurons in the DRN were a heterogeneous population with multiple firing patterns (single firing, phasic firing, and tonic firing). Persistent inward currents (PICs) with multiple patterns were expressed in 5-HT neurons and composed of Cav1.3 (Ca-PIC) and sodium (Na-PIC) components. Exercise hyperpolarized the voltage threshold for action potential (AP) by 3.1 ± 1.0 mV (control: n = 14, exercise: n = 18, p = 0.005) and increased the AP amplitude by 6.7 ± 3.0 mV (p = 0.031) and firing frequency by more than 22% especially within a range of current stimulation stronger than 70 pA. A 3-week treadmill exercise was sufficient to hyperpolarize PIC onset by 2.6 ± 1.3 mV (control: −53.4 ± 4.7 mV, n = 28; exercise: −56.0 ± 4.7 mV, n = 25, p = 0.050) and increase the PIC amplitude by 28% (control: 193.6 ± 81.8 pA; exercise: 248.5 ± 105.4 pA, p = 0.038). Furthermore, exercise hyperpolarized Na-PIC onset by 3.8 ± 1.8 mV (control: n = 8, exercise: n = 9, p = 0.049) and increased the Ca-PIC amplitude by 23% (p = 0.013). The exercise-induced enhancement of the PIC amplitude was mainly mediated by Ca-PIC and hyperpolarization of PIC onset by Na-PIC. Moreover, exercise facilitated dendritic plasticity, which was shown as the increased number of branch points by 1.5 ± 0.5 (p = 0.009) and dendritic branches by 2.1 ± 0.6 (n = 20, p = 0.001) and length by 732.0 ± 100.1 μm (p < 0.001) especially within the range of 50–200 μm from the soma. Functional analysis suggested that treadmill exercise enhanced Na-PIC for facilitation of spike initiation and Ca-PIC for regulation of repetitive firing. We concluded that PICs broadly existed in DRN 5-HT neurons and could influence serotonergic neurotransmission in juvenile mice and that 3-week treadmill exercise induced synaptic adaptations, enhanced PICs, and thus upregulated the excitability of the 5-HT neurons.

Cumulative Effects of Social Stress on Reward-Guided Actions and Prefrontal Cortical Activity

BACKGROUND

When exposed to chronic social stress, animals display behavioral changes that are relevant to depressive-like phenotypes. However, the cascading relationship between incremental stress exposure and neural dysfunctions over time remains incompletely understood.

METHODS

We characterized the longitudinal effect of social defeat on goal-directed actions and prefrontal cortical activity in mice using a novel head-fixed sucrose preference task and two-photon calcium imaging.

RESULTS

Behaviorally, stress-induced loss of reward sensitivity intensifies over days. Motivational anhedonia, the failure to translate positive reinforcements into future actions, requires multiple sessions of stress exposure to become fully established. For neural activity, individual layer 2/3 pyramidal neurons in the cingulate and medial secondary motor subregions of the medial prefrontal cortex have heterogeneous responses to stress. Changes in ensemble activity differ significantly between susceptible and resilient mice after the first defeat session and continue to diverge following successive stress episodes before reaching persistent abnormal levels.

CONCLUSIONS

Collectively, these results demonstrate that the cumulative impact of an ethologically relevant stress can be observed at the level of cellular activity of individual prefrontal neurons. The distinct neural responses associated with resilience versus susceptibility suggests the hypothesis that the negative impact of social stress is neutralized in resilient animals, in part through an adaptive reorganization of prefrontal cortical activity.

Involvement of P2X2 receptor in the medial prefrontal cortex in ATP modulation of the passive coping response to behavioral challenge

P2X2 and P2X3 receptors are widely expressed in both the peripheral nervous system and the central nervous system and have been proven to participate in different peripheral sensory functions, but there are few studies on the involvement of P2X2 and P2X3 receptors in animal behaviors. Here we used P2X2 and P2X3 knockout mice to address this issue. P2X2 knockout mice showed normal motor function, exploratory behavior, anxiety-like behaviors, learning and memory behaviors and passive coping response to behavioral challenge. Nevertheless, the effect of ATP infusion in the medial prefrontal cortex (mPFC) on the passive coping response was blocked by P2X2 but not P2X3 receptor deletion. Additionally, no deficits in a wide variety of behavioral tests were observed in P2X3 knockout mice. These findings demonstrate a role of P2X2 receptor in the mPFC in adenosine-5'-triphosphate modulation of the passive coping response to behavioral challenge and show that the P2X2/P2X3 receptor is dispensable for behaviors.

Psychological mechanisms and functions of 5-HT and SSRIs in potential therapeutic change: Lessons from the serotonergic modulation of action selection, learning, affect, and social cognition

Uncertainty regarding which psychological mechanisms are fundamental in mediating SSRI treatment outcomes and wide-ranging variability in their efficacy has raised more questions than it has solved. Since subjective mood states are an abstract scientific construct, only available through self-report in humans, and likely involving input from multiple top-down and bottom-up signals, it has been difficult to model at what level SSRIs interact with this process. Converging translational evidence indicates a role for serotonin in modulating context-dependent parameters of action selection, affect, and social cognition; and concurrently supporting learning mechanisms, which promote adaptability and behavioural flexibility. We examine the theoretical basis, ecological validity, and interaction of these constructs and how they may or may not exert a clinical benefit. Specifically, we bridge crucial gaps between disparate lines of research, particularly findings from animal models and human clinical trials, which often seem to present irreconcilable differences. In determining how SSRIs exert their effects, our approach examines the endogenous functions of 5-HT neurons, how 5-HT manipulations affect behaviour in different contexts, and how their therapeutic effects may be exerted in humans - which may illuminate issues of translational models, hierarchical mechanisms, idiographic variables, and social cognition.

Functional properties of habenular neurons are determined by developmental stage and sequential neurogenesis

The developing brain undergoes drastic alterations. Here, we investigated developmental changes in the habenula, a brain region that mediates behavioral flexibility during learning, social interactions, and aversive experiences. We showed that developing habenular circuits exhibit multiple alterations that lead to an increase in the structural and functional diversity of cell types, inputs, and functional modules. As the habenula develops, it sequentially transforms into a multisensory brain region that can process visual, olfactory, mechanosensory, and aversive stimuli. Moreover, we observed that the habenular neurons display spatiotemporally structured spontaneous activity that shows prominent alterations and refinement with age. These alterations in habenular activity are accompanied by sequential neurogenesis and the integration of distinct neural clusters across development. Last, we revealed that habenular neurons with distinct functional properties are born sequentially at distinct developmental time windows. Our results highlight a strong link between the functional properties of habenular neurons and their precise birthdate.

A discrete serotonergic circuit regulates vulnerability to social stress

Exposure to social stress and dysregulated serotonergic neurotransmission have both been implicated in the etiology of psychiatric disorders. However, the serotonergic circuit involved in stress vulnerability is still unknown. Here, we explored whether a serotonergic input from the dorsal raphe (DR) to ventral tegmental area (VTA) influences vulnerability to social stress. We identified a distinct, anatomically and functionally defined serotonergic subpopulation in the DR that projects to the VTA (5-HTDR→VTA neurons). Moreover, we found that susceptibility to social stress decreased the firing activity of 5-HTDR→VTA neurons. Importantly, the bidirectional manipulation of 5-HTDR→VTA neurons could modulate susceptibility to social stress. Our findings reveal that the activity of 5-HTDR→VTA neurons may be an essential factor in determining individual levels of susceptibility to social stress and suggest that targeting specific serotonergic circuits may aid the development of therapies for the treatment of stress-related disorders.

Astrocyte-Derived Lactate Modulates the Passive Coping Response to Behavioral Challenge in Male Mice

Every organism inevitably experiences stress. In the face of acute, intense stress, for example, periods of passivity occur when an organism's actions fail to overcome the challenge. The occurrence of inactive behavior may indicate that struggling would most likely be fruitless. Repeated serious stress has been associated with mood disorders such as depression. The modulation of passive coping response patterns has been explored with a focus on the circuit level. However, the cellular and molecular mechanisms are largely uncharacterized. Here, we report that lactate is a key factor in the astrocytic modulation of the passive coping response to behavioral challenge in adult mice. We found increased extracellular lactate in the medial prefrontal cortex (mPFC) when mice experienced the forced swimming test (FST). Furthermore, we discovered that disturbing astrocytic glycogenolysis, which is a key step for lactate production in the mPFC, decreased the duration of immobility in the FST. Knocking down monocarboxylate transporter 4 (MCT4), which is expressed exclusively in astrocytes and transports lactate from astrocytes to the extracellular space, caused similar results in the FST. The behavioral effect of both the pharmacological disturbance of astrocytic glycogenolysis and viral disruption of MCT4 expression was rescued via the administration of L-lactate. Moreover, we found that both pharmacological and viral modulation of astrocyte-derived lactate in mPFC slices increased the excitability of layer V pyramidal neurons, and this enhancement was reversed by exogenous L-lactate administration. These results highlight astrocyte-derived lactate as a biological mechanism underlying the passive coping response to behavioral challenge and may provide new strategies to prevent mood disorders.

Rostromedial tegmental nucleus-substantia nigra pars compacta circuit mediates aversive and despair behavior in mice

GABAergic neurons in the rostromedial tegmental nucleus (RMTg) receive major input from the lateral habenula (LHb), which conveys negative reward and motivation related information, and project intensively to midbrain dopamine neurons, including those in the ventral tegmental area (VTA) and substantia nigra pars compacta (SNc). The RMTg-VTA circuit has been shown to be linked to the affective behavior, but the role of the RMTg-SNc circuit in aversion and depression has not been well understood. This study demonstrated that exciting or inhibiting Vgat^RMTg-SNc neurons was sufficient to increase or decrease immobility time in the forced swim test (FST), respectively. Furthermore, exciting the Vgat^RMTg-SNc pathway caused aversive behavior. Ninety percent of the SNc putative dopamine neurons were inhibited in extracellular recordings. Furthermore, inhibiting the Vgat^RMTg-SNc pathway reversed behavioral despair in chronic restraint stress (CRS) depression model mice. Manipulations of the pathway did not affect the hedonic value of the reward in the sucrose-preference test (SPT) or general motor function. In conclusion, these results indicate that the Vgat^RMTg-SNc pathway regulates aversive and despair behavior, which suggests that the RMTg may mediate the role of LHb in negative behaviors through regulating the activity of SNc neurons.

The innate immune toll-like-receptor-2 modulates the depressogenic and anorexiolytic neuroinflammatory response in obstructive sleep apnoea

The increased awareness of obstructive sleep apnoea’s (OSA) links to Alzheimer’s disease and major psychiatric disorders has recently directed an intensified search for their potential shared mechanisms. We hypothesised that neuroinflammation and the microglial TLR2-system may act as a core process at the intersection of their pathophysiology. Moreover, we postulated that inflammatory-response might underlie development of key behavioural and neurostructural changes in OSA. Henceforth, we set out to investigate effects of 3 weeks’ exposure to chronic intermittent hypoxia in mice with or without functional TRL2 (TLR2^+/+, C57BL/6-Tyrc-Brd-Tg(Tlr2-luc/gfp)Kri/Gaj;TLR2^−/−,C57BL/6-Tlr2tm1Kir). By utilising multimodal imaging in this established model of OSA, a discernible neuroinflammatory response was demonstrated for the first time. The septal nuclei and forebrain were shown as the initial key seed-sites of the inflammatory cascade that led to wider structural changes in the associated neurocircuitry. Finally, the modulatory role for the functional TLR2-system was suggested in aetiology of depressive, anxious and anorexiolytic symptoms in OSA.

Prefrontal - subthalamic pathway supports action selection in a spatial working memory task

Subthalamic nucleus (STN) is the main source of feed-forward excitation in the basal ganglia and a main target of therapeutic deep brain stimulation in movement disorders. Alleviation of motor symptoms during STN stimulation can be accompanied by deterioration of abilities to quickly choose between conflicting alternatives. Cortical afferents to the subthalamic region (ST), comprising STN and zona incerta (ZI), include projections from the medial prefrontal cortex (mPFC), yet little is known about prefrontal-subthalamic coordination and its relevance for decision-making. Here we combined electrophysiological recordings with optogenetic manipulations of projections from mPFC to ST in mice as they performed a spatial working memory task (T-maze) or explored an elevated plus maze (anxiety test). We found that gamma oscillations (30–70 Hz) are coordinated between mPFC and ST at theta (5–10 Hz) and, less efficiently, at sub-theta (2–5 Hz) frequencies. An optogenetic detuning of the theta/gamma cross-frequency coupling between the regions into sub-theta range impaired performance in the T-maze, yet did not affect anxiety-related behaviors in the elevated plus maze. Both detuning and inhibition of the mPFC-ST pathway led to repeated incorrect choices in the T-maze. These effects were not associated with changes of anxiety and motor activity measures. Our findings suggest that action selection in a cognitively demanding task crucially involves theta rhythmic coordination of gamma oscillatory signaling in the prefrontal-subthalamic pathway.

Brain NMDA Receptors in Schizophrenia and Depression

N-methyl-D-aspartate (NMDA) receptor antagonists such as phencyclidine (PCP), dizocilpine (MK-801) and ketamine have long been considered a model of schizophrenia, both in animals and humans. However, ketamine has been recently approved for treatment-resistant depression, although with severe restrictions. Interestingly, the dosage in both conditions is similar, and positive symptoms of schizophrenia appear before antidepressant effects emerge. Here, we describe the temporal mechanisms implicated in schizophrenia-like and antidepressant-like effects of NMDA blockade in rats, and postulate that such effects may indicate that NMDA receptor antagonists induce similar mechanistic effects, and only the basal pre-drug state of the organism delimitates the overall outcome. Hence, blockade of NMDA receptors in depressive-like status can lead to amelioration or remission of symptoms, whereas healthy individuals develop psychotic symptoms and schizophrenia patients show an exacerbation of these symptoms after the administration of NMDA receptor antagonists.

Neonatal sevoflurane exposure induces impulsive behavioral deficit through disrupting excitatory neurons in the medial prefrontal cortex in mice

Sevoflurane, in particular multiple exposures, has been reported to cause the abnormal neurological development including attention-deficit/hyperactivity disorder (ADHD). This study is to investigate ADHD-like impulsivity in adult mice after repeated sevoflurane exposures at the neonatal stage. Six-day-old pups were exposed to 60% oxygen in the presence or absence of 3% sevoflurane for 2 h and the treatment was administrated once daily for three consecutive days. To assess the impulsivity, the cliff avoidance reaction (CAR) was carried out at the 8th week. Our results showed that repeated sevoflurane treatment increased the number of jumps and shortened the jumping latency in the CAR test. The cortices were harvested for immunostaining to detect c-Fos and calmodulin-dependent protein kinase IIα (CaMKIIα) expression in the medial prefrontal cortex (mPFC). We found that mPFC neurons, especially excitatory neurons, were highly activated and related to impulsive behavior. The activation viruses (AAV-CaMKIIα-hM3Dq) were injected to evaluate the effects of specific activation of mPFC excitatory neurons on impulsive behavior in the presence of clozapine-N-oxide (CNO). Likewise, the inhibitory viruses (AAV-CaMKIIα-hM4Di) were injected in the sevoflurane group to explore whether the mPFC excitatory neuronal inhibition reduced the impulsivity. Our results revealed that chemogenetic activation of mPFC excitatory neurons induced impulsive behavior whereas inhibition of mPFC excitatory neurons partially rescued the deficit. These results indicate that repeated sevoflurane exposures at the critical time induce impulsive behavior accompanied with overactivation of mPFC excitatory neurons in adult stages. This work may further extend to understand the ADHD-like impulsive behavior of the anesthetic neurotoxicity.

Unanticipated Stressful and Rewarding Experiences Engage the Same Prefrontal Cortex and Ventral Tegmental Area Neuronal Populations

Brain networks that mediate motivated behavior in the context of aversive and rewarding experiences involve the prefrontal cortex (PFC) and ventral tegmental area (VTA). Neurons in both regions are activated by stress and reward, and by learned cues that predict aversive or appetitive outcomes. Recent studies have proposed that separate neuronal populations and circuits in these regions encode learned aversive versus appetitive contexts. But how about the actual experience? Do the same or different PFC and VTA neurons encode unanticipated aversive and appetitive experiences? To address this, we recorded unit activity and local field potentials (LFPs) in the dorsomedial PFC (dmPFC) and VTA of male rats as they were exposed, in the same recording session, to reward (sucrose) or stress (tail pinch) spaced 1 h apart. As expected, experience-specific neuronal responses were observed. Approximately 15–25% of single units in each region responded by excitation or inhibition to either stress or reward, and only stress increased LFP theta oscillation power in both regions and coherence between regions. But the largest number of responses (29% dmPFC and 30% VTA units) involved dual-valence neurons that responded to both stress and reward exposure. Moreover, the temporal profile of neuronal population activity in dmPFC and VTA as assessed by principal component analysis (PCA) were similar during both types of experiences. These results reveal that aversive and rewarding experiences engage overlapping neuronal populations in the dmPFC and the VTA. These populations may provide a locus of vulnerability for stress-related disorders, which are often associated with anhedonia.

Toward Circuit Mechanisms of Pathophysiology in Depression

The search for more effective treatments for depression is a long-standing primary objective in both psychiatry and translational neuroscience. From initial models centered on neurochemical deficits, such as the monoamine hypothesis, research toward this goal has shifted toward a focus on network and circuit models to explain how key nodes in the limbic system and beyond interact to produce persistent shifts in affective states. To build these models, researchers have turned to two complementary approaches: neuroimaging studies in human patients (and their healthy counterparts) and neurophysiology studies in animal models, facilitated in large part by optogenetic and chemogenetic techniques. As the authors discuss, functional neuroimaging studies in humans have included largely task-oriented experiments, which have identified brain regions differentially activated during processing of affective stimuli, and resting-state functional MRI experiments, which have identified brain-wide networks altered in depressive states. Future work in this area will build on a multisite approach, assembling large data sets across diverse populations, and will also leverage the statistical power afforded by longitudinal imaging studies in patient samples. Translational studies in rodents have used optogenetic and chemogenetic tools to identify not just nodes but also connections within the networks of the limbic system that are both critical and permissive for the expression of motivated behavior and affective phenotypes. Future studies in this area will exploit mesoscale imaging and multisite electrophysiology recordings to construct network models with cell-type specificity and high statistical power, identifying candidate circuit and molecular pathways for therapeutic intervention.

Light Up the Brain: The Application of Optogenetics in Cell-Type Specific Dissection of Mouse Brain Circuits

The exquisite intricacies of neural circuits are fundamental to an animal’s diverse and complex repertoire of sensory and motor functions. The ability to precisely map neural circuits and to selectively manipulate neural activity is critical to understanding brain function and has, therefore been a long-standing goal for neuroscientists. The recent development of optogenetic tools, combined with transgenic mouse lines, has endowed us with unprecedented spatiotemporal precision in circuit analysis. These advances greatly expand the scope of tractable experimental investigations. Here, in the first half of the review, we will present applications of optogenetics in identifying connectivity between different local neuronal cell types and of long-range projections with both in vitro and in vivo methods. We will then discuss how these tools can be used to reveal the functional roles of these cell-type specific connections in governing sensory information processing, and learning and memory in the visual cortex, somatosensory cortex, and motor cortex. Finally, we will discuss the prospect of new optogenetic tools and how their application can further advance modern neuroscience. In summary, this review serves as a primer to exemplify how optogenetics can be used in sophisticated modern circuit analyses at the levels of synapses, cells, network connectivity and behaviors.

Circuits and functions of the lateral habenula in health and in disease

The past decade has witnessed exponentially growing interest in the lateral habenula (LHb) owing to new discoveries relating to its critical role in regulating negatively motivated behaviour and its implication in major depression. The LHb, sometimes referred to as the brain's 'antireward centre', receives inputs from diverse limbic forebrain and basal ganglia structures, and targets essentially all midbrain neuromodulatory systems, including the noradrenergic, serotonergic and dopaminergic systems. Its unique anatomical position enables the LHb to act as a hub that integrates value-based, sensory and experience-dependent information to regulate various motivational, cognitive and motor processes. Dysfunction of the LHb may contribute to the pathophysiology of several psychiatric disorders, especially major depression. Recently, exciting progress has been made in identifying the molecular and cellular mechanisms in the LHb that underlie negative emotional state in animal models of drug withdrawal and major depression. A future challenge is to translate these advances into effective clinical treatments.

Rapid anti-depressant-like effects of ketamine and other candidates: Molecular and cellular mechanisms

Major depressive disorder takes at least 3 weeks for clinical anti‐depressants, such as serotonin selective reuptake inhibitors, to take effect, and only one‐third of patients remit. Ketamine, a kind of anaesthetic, can alleviate symptoms of major depressive disorder patients in a short time and is reported to be effective to treatment‐resistant depression patients. The rapid and strong anti‐depressant‐like effects of ketamine cause wide concern. In addition to ketamine, caloric restriction and sleep deprivation also elicit similar rapid anti‐depressant‐like effects. However, mechanisms about the rapid anti‐depressant‐like effects remain unclear. Elucidating the mechanisms of rapid anti‐depressant effects is the key to finding new therapeutic targets and developing therapeutic patterns. Therefore, in this review we summarize potential molecular and cellular mechanisms of rapid anti‐depressant‐like effects based on the pre‐clinical and clinical evidence, trying to provide new insight into future therapy.

Rapid Anxiolytic Effects of RS67333, a Serotonin Type 4 Receptor Agonist, and Diazepam, a Benzodiazepine, Are Mediated by Projections From the Prefrontal Cortex to the Dorsal Raphe Nucleus

BACKGROUND

Activation of serotonin (5-HT) type 4 receptors (5-HT₄Rs) has been shown to have anxiolytic effects in a variety of animal models. Characterizing the circuits responsible for these effects should offer insights into new approaches to treat anxiety.

METHODS

We evaluated whether acute 5-HT₄R activation in glutamatergic axon terminals arising from the medial prefrontal cortex (mPFC) to the dorsal raphe nucleus (DRN) induced fast anxiolytic effects. Anxiolytic effects of an acute systemic administration (1.5 mg/kg, intraperitoneally) or intra-mPFC infusion with the 5-HT₄R agonist, RS67333 (0.5 μg/side), were examined in mice. To provide evidence that anxiolytic effects of RS67333 recruited an mPFC-DRN neural circuit, in vivo recordings of firing rate of DRN 5-HT neurons, cerebral 5-HT depletion, and optogenetic activation and silencing were performed.

RESULTS

Acute systemic administration and intra-mPFC infusion of RS67333 produced fast anxiolytic effects and increased DRN 5-HT cell firing. Serotonin depletion prevented anxiolytic effects induced by mPFC infusion of RS67333. Surprisingly the anxiolytic effects of mPFC infusion diazepam (1.5 μg/side) were also blocked by 5-HT depletion. Optogenetically activating mPFC terminals targeting the DRN reduced anxiety, whereas silencing this circuit blocked RS67333 and diazepam mPFC infusion-induced anxiolytic effects. Finally, anxiolytic effects induced by an acute systemic RS67333 or diazepam administration were partially blocked after optogenetically inhibiting cortical glutamatergic terminals in the DRN.

CONCLUSIONS

Our findings suggest that activating 5-HT₄R acutely in the mPFC or targeting mPFC pyramidal cell terminals in the DRN might constitute a strategy to produce a fast anxiolytic response.

Astrocytic GABAB Receptors in Mouse Hippocampus Control Responses to Behavioral Challenges through Astrocytic BDNF

Major depressive disorder (MDD) is a common mood disorder that affects almost 20% of the global population. In addition, much evidence has implicated altered function of the gamma-aminobutyric acid (GABAergic) system in the pathophysiology of depression. Recent research has indicated that GABA_B receptors (GABA_BRs) are an emerging therapeutic target in the treatment of stress-related disorders such as MDD. However, which cell types with GABA_BRs are involved in this process is unknown. As hippocampal dysfunction is implicated in MDD, we knocked down GABA_BRs in the hippocampus and found that knocking down these receptors in astrocytes, but not in GABAergic or pyramidal neurons, caused a decrease in immobility in the forced swimming test (FST) without affecting other anxiety- and depression-related behaviors. We also generated astrocyte-specific GABA_BR-knockout mice and found decreased immobility in the FST in these mice. Furthermore, the conditional knockout of GABA_BRs in astrocytes selectively increased the levels of brain-derived neurotrophic factor protein in hippocampal astrocytes, which controlled the decrease in immobility in the FST. Taken together, our findings contribute to the current understanding of which cell types expressing GABA_BRs modulate antidepressant activity in the FST, and they may provide new insights into the pathological mechanisms and potential targets for the treatment of depression.

Functional and Dysfunctional Neuroplasticity in Learning to Cope with Stress

In this brief review, we present evidence of the primary role of learning-associated plasticity in the development of either adaptive or maladaptive coping strategies. Successful interactions with novel stressors foster plasticity within the neural circuits supporting acquisition, consolidation, retrieval, and extinction of instrumental learning leading to development of a rich repertoire of flexible and context-specific adaptive coping responses, whereas prolonged or repeated exposure to inescapable/uncontrollable stressors fosters dysfunctional plasticity within the learning circuits leading to perseverant and inflexible maladaptive coping strategies. Finally, the results collected using an animal model of genotype-specific coping styles indicate the engagement of different molecular networks and the opposite direction of stress effects (reduced vs. enhanced gene expression) in stressed animals, as well as different behavioral alterations, in line with differences in the symptoms profile associated with post-traumatic stress disorder.

New era of optogenetics: from the central to peripheral nervous system

Optogenetics has recently gained recognition as a biological technique to control the activity of cells using light stimulation. Many studies have applied optogenetics to cell lines in the central nervous system because it has the potential to elucidate neural circuits, treat neurological diseases and promote nerve regeneration. There have been fewer studies on the application of optogenetics in the peripheral nervous system. This review introduces the basic principles and approaches of optogenetics and summarizes the physiology and mechanism of opsins and how the technology enables bidirectional control of unique cell lines with superior spatial and temporal accuracy. Further, this review explores and discusses the therapeutic potential for the development of optogenetics and its capacity to revolutionize treatment for refractory epilepsy, depression, pain, and other nervous system disorders, with a focus on neural regeneration, especially in the peripheral nervous system. Additionally, this review synthesizes the latest preclinical research on optogenetic stimulation, including studies on non-human primates, summarizes the challenges, and highlights future perspectives. The potential of optogenetic stimulation to optimize therapy for peripheral nerve injuries (PNIs) is also highlighted. Optogenetic technology has already generated exciting, preliminary evidence, supporting its role in applications to several neurological diseases, including PNIs.

Opioid system is necessary but not sufficient for antidepressive actions of ketamine in rodents

Slow response to the standard treatment for depression increases suffering and risk of suicide. Ketamine, an N-methyl-d-aspartate (NMDA) receptor antagonist, can rapidly alleviate depressive symptoms and reduce suicidality, possibly by decreasing hyperactivity in the lateral habenula (LHb) brain nucleus. Here we find that in a rat model of human depression, opioid antagonists abolish the ability of ketamine to reduce the depression-like behavioral and LHb hyperactive cellular phenotypes. However, activation of opiate receptors alone is not sufficient to produce ketamine-like effects, nor does ketamine mimic the hedonic effects of an opiate, indicating that the opioid system does not mediate the actions of ketamine but rather is permissive. Thus, ketamine does not act as an opiate but its effects require both NMDA and opiate receptor signaling, suggesting that interactions between these two neurotransmitter systems are necessary to achieve an antidepressant effect.

Transient and sustained effects of dopamine and serotonin signaling in motivation-related behavior

Pharmacological studies of antidepressants and atypical antipsychotics have suggested a role of dopamine and serotonin signaling in depression. However, depressive symptoms and treatment effects are difficult to explain based simply on brain-wide decrease or increase in the concentrations of these molecules. Recent animal studies using advanced neuronal manipulation and observation techniques have revealed detailed dopamine and serotonin dynamics that regulate diverse aspects of motivation-related behavior. Dopamine and serotonin transiently modulate moment-to-moment behavior at timescales ranging from sub-second to minutes and also produce persistent effects, such as reward-related learning and stress responses that last longer than several days. Transient and sustained effects often exhibit specific roles depending on the projection sites, where distinct synaptic and cellular mechanisms are required to process the neurotransmitters for each transient and sustained timescale. Therefore, it appears that specific aspects of motivation-related behavior are regulated by distinct synaptic and cellular mechanisms in specific brain regions that underlie the transient and sustained effects of dopamine and serotonin signaling. Recent clinical studies have implied that subjects with depressive symptoms show impaired transient and sustained signaling functions; moreover, they exhibit heterogeneity in depressive symptoms and neuronal dysfunction. Depressive symptoms may be explained by the dysfunction of each transient and sustained signaling mechanism, and distinct patterns of impairment in the relevant mechanisms may explain the heterogeneity of symptoms. Thus, detailed understanding of dopamine and serotonin signaling may provide new insight into depressive symptoms.

Cortical lesions causing loss of consciousness are anticorrelated with the dorsal brainstem

Brain lesions can provide unique insight into the neuroanatomical substrate of human consciousness. For example, brainstem lesions causing coma map to a specific region of the tegmentum. Whether specific lesion locations outside the brainstem are associated with loss of consciousness (LOC) remains unclear. Here, we investigate the topography of cortical lesions causing prolonged LOC (N = 16), transient LOC (N = 91), or no LOC (N = 64). Using standard voxel lesion symptom mapping, no focus of brain damage was associated with LOC. Next, we computed the network of brain regions functionally connected to each lesion location using a large normative connectome dataset (N = 1,000). This technique, termed lesion network mapping, can test whether lesions causing LOC map to a connected brain circuit rather than one brain region. Connectivity between cortical lesion locations and an a priori coma-specific region of brainstem tegmentum was an independent predictor of LOC (B = 1.2, p = .004). Connectivity to the dorsal brainstem was the only predictor of LOC in a whole-brain voxel-wise analysis. This relationship was driven by anticorrelation (negative correlation) between lesion locations and the dorsal brainstem. The map of regions anticorrelated to the dorsal brainstem thus defines a distributed brain circuit that, when damaged, is most likely to cause LOC. This circuit showed a slight posterior predominance and had peaks in the bilateral claustrum. Our results suggest that cortical lesions causing LOC map to a connected brain circuit, linking cortical lesions that disrupt consciousness to brainstem sites that maintain arousal.

Targeting the Neuronal Activity of Prefrontal Cortex: New Directions for the Therapy of Depression

Depression is one of the prevalent psychiatric illnesses with a comprehensive performance such as low self-esteem, lack of motivation, anhedonia, poor appetite, low energy, and uncomfortableness without a specific cause. So far, the cause of depression is not very clear, but it is certain that many aspects of biological psychological and social environment are involved in the pathogenesis of depression. Recently, the prefrontal cortex (PFC) has been indicated to be a pivotal brain region in the pathogenesis of depression. And increasing evidence showed that the abnormal activity of the PFC neurons is linked with depressive symptoms. Unveiling the molecular and cellular, as well as the circuit properties of the PFC neurons will help to find out how abnormalities in PFC neuronal activity are associated with depressive disorders. In addition, concerning many antidepressant drugs, in this review, we concluded the effect of several antidepressants on PFC neuronal activity to better understand its association with depression.

Optogenetic Inhibition of Medial Prefrontal Cortex-Pontine Nuclei Projections During the Stimulus-free Trace Interval Impairs Temporal Associative Motor Learning

The medial prefrontal cortex (mPFC) is closely involved in many higher-order cognitive functions, including learning to associate temporally discontiguous events (called temporal associative learning). However, direct evidence for the role of mPFC and the neural pathway underlying modulation of temporal associative motor learning is sparse. Here, we show that optogenetic inhibition of the mPFC or its axon terminals at the pontine nuclei (PN) during trace intervals or whole trial period significantly impaired the trace eyeblink conditioning (TEC), but had no significant effects on TEC during the conditioned stimulus or intertrial interval period. Our results suggest that activities associated with the mPFC-PN projection during trace intervals is crucial for trace associative motor learning. This finding is of great importance in understanding the mechanisms and the relevant neural pathways underlying mPFC modulation of temporal associative motor learning.