Identification of Serotonergic Neuronal Modules that Affect Aggressive Behavior.

Escalated aggression can have devastating societal consequences, yet underlying neurobiological mechanisms are poorly understood. Here, we show significantly increased inter-male mouse aggression when neurotransmission is constitutively blocked from either of two subsets of serotonergic, Pet1 neurons: one identified by dopamine receptor D1(Drd1a)::cre-driven activity perinatally, and the other by Drd2::cre from pre-adolescence onward. Blocking neurotransmission from other Pet1 neuron subsets of similar size and/or overlapping anatomical domains had no effect on aggression compared with controls, suggesting subtype-specific serotonergic neuron influences on aggression.

Pet-1 Switches Transcriptional Targets Postnatally to Regulate Maturation of Serotonin Neuron Excitability.

Unlabelled: Newborn neurons enter an extended maturation stage, during which they acquire excitability characteristics crucial for development of presynaptic and postsynaptic connectivity. In contrast to earlier specification programs, little is known about the regulatory mechanisms that control neuronal maturation. The Pet-1 ETS (E26 transformation-specific) factor is continuously expressed in serotonin (5-HT) neurons and initially acts in postmitotic precursors to control acquisition of 5-HT transmitter identity.

Deep sequencing reveals cell-type-specific patterns of single-cell transcriptome variation.

Background: Differentiation of metazoan cells requires execution of different gene expression programs but recent single-cell transcriptome profiling has revealed considerable variation within cells of seeming identical phenotype. This brings into question the relationship between transcriptome states and cell phenotypes. Additionally, single-cell transcriptomics presents unique analysis challenges that need to be addressed to answer this question.

α2-Adrenergic stimulation of the ventrolateral preoptic nucleus destabilizes the anesthetic state.

The sleep-promoting ventrolateral preoptic nucleus (VLPO) shares reciprocal inhibitory inputs with wake-active neuronal nuclei, including the locus ceruleus. Electrophysiologically, sleep-promoting neurons in the VLPO are directly depolarized by the general anesthetic isoflurane and hyperpolarized by norepinephrine, a wake-promoting neurotransmitter. However, the integration of these competing influences on the VLPO, a sleep- and anesthetic-active structure, has yet to be evaluated in either brain slices in vitro or the intact organism.

Dorsal raphe serotonin neurons in mice: immature hyperexcitability transitions to adult state during first three postnatal weeks suggesting sensitive period for environmental perturbation.

Trauma during early life is a major risk factor for the development of anxiety disorders and suggests that the developing brain may be particularly sensitive to perturbation. Increased vulnerability most likely involves altering neural circuits involved in emotional regulation. The role of serotonin in emotional regulation is well established, but little is known about the postnatal development of the raphe where serotonin is made.

Optogenetic modulation of descending prefrontocortical inputs to the dorsal raphe bidirectionally bias socioaffective choices after social defeat.

It has been well established that modulating serotonin (5-HT) levels in humans and animals affects perception and response to social threats, however the circuit mechanisms that control 5-HT output during social interaction are not well understood. A better understanding of these systems could provide groundwork for more precise and efficient therapeutic interventions. Here we examined the organization and plasticity of microcircuits implicated in top-down control of 5-HT neurons in the dorsal raphe nucleus (DRN) by excitatory inputs from the ventromedial prefrontal cortex (vmPFC) and their role in social approach-avoidance decisions.

Antidepressant-like effects of cortical deep brain stimulation coincide with pro-neuroplastic adaptations of serotonin systems.

Background: Cortical deep brain stimulation (DBS) is a promising therapeutic option for treatment-refractory depression, but its mode of action remains enigmatic. Serotonin (5-HT) systems are engaged indirectly by ventromedial prefrontal cortex (vmPFC) DBS. Resulting neuroplastic changes in 5-HT systems could thus coincide with the long-term therapeutic activity of vmPFC DBS.

Effects of chronic sleep fragmentation on wake-active neurons and the hypercapnic arousal response.

Study Objectives: Delayed hypercapnic arousals may occur in obstructive sleep apnea. The impaired arousal response is expected to promote more pronounced oxyhemoglobin desaturations. We hypothesized that long-term sleep fragmentation (SF) results in injury to or dysfunction of wake-active neurons that manifests, in part, as a delayed hypercapnic arousal response.

Sex differences in corticotropin-releasing factor receptor-1 action within the dorsal raphe nucleus in stress responsivity.

Background: Women are twice as likely as men to suffer from stress-related affective disorders. Corticotropin-releasing factor (CRF) is an important link between stress and mood, in part through its signaling in the serotonergic dorsal raphe (DR). Development of CRF receptor-1 (CRFr1) antagonists has been a focus of numerous clinical trials but has not yet been proven efficacious.

Serotonergic neuron regulation informed by in vivo single-cell transcriptomics.

Despite the recognized importance of the dorsal raphe (DR) serotonergic (5-HT) nuclei in the pathophysiology of depression and anxiety, the molecular components/putative drug targets expressed by these neurons are poorly characterized. Utilizing the promoter of an ETS domain transcription factor that is a stable marker of 5-HT neurons (Pet-1) to drive 5-HT neuronal expression of YFP, we identified 5-HT neurons in live acute slices. We isolated RNA from single 5-HT neurons in the ventromedial and lateral wings of the DR and performed single-cell RNA-Seq analysis identifying >500 G-protein coupled receptors (GPCRs) including receptors for classical transmitters, lipid signals, and peptides as well as dozens of orphan-GPCRs.

Raphe GABAergic neurons mediate the acquisition of avoidance after social defeat.

Serotonin (5-HT) modulates neural responses to socioaffective cues and can bias approach or avoidance behavioral decisions, yet the cellular mechanisms underlying its contribution to the regulation of social experiences remain poorly understood. We hypothesized that GABAergic neurons in the dorsal raphe nucleus (DRN) may participate in socioaffective regulation by controlling serotonergic tone during social interaction. We tested this hypothesis using whole-cell recording techniques in genetically identified DRN GABA and 5-HT neurons in mice exposed to social defeat, a model that induces long-lasting avoidance behaviors in a subset of mice responsive to serotonergic antidepressants.

Developmental effects of serotonin 1A autoreceptors on anxiety and social behavior.

The serotonin 1A receptor (5-HT1A) has a major role in modulating the effects of serotonin on mood and behavior. Previous studies have shown that knockout of 5-HT1A selectively in the raphe leads to higher levels of anxiety during adulthood. However, it remains unclear whether this phenotype is due to variation in receptor levels specifically during development or throughout life.

Social stress alters inhibitory synaptic input to distinct subpopulations of raphe serotonin neurons.

Anxiety disorders are among the most prevalent psychiatric disorders, yet much is unknown about the underlying mechanisms. The dorsal raphe (DR) is at the crux of the anxiety-inducing effects of uncontrollable stress, a key component of models of anxiety. Though DR serotonin (5-HT) neurons play a prominent role, anxiety-associated changes in the physiology of 5-HT neurons remain poorly understood.

Direct activation of sleep-promoting VLPO neurons by volatile anesthetics contributes to anesthetic hypnosis.

Background: Despite seventeen decades of continuous clinical use, the neuronal mechanisms through which volatile anesthetics act to produce unconsciousness remain obscure. One emerging possibility is that anesthetics exert their hypnotic effects by hijacking endogenous arousal circuits. A key sleep-promoting component of this circuitry is the ventrolateral preoptic nucleus (VLPO), a hypothalamic region containing both state-independent neurons and neurons that preferentially fire during natural sleep.

HDAC6 regulates glucocorticoid receptor signaling in serotonin pathways with critical impact on stress resilience.

Genetic variations in certain components of the glucocorticoid receptor (GR) chaperone complex have been associated with the development of stress-related affective disorders and individual variability in therapeutic responses to antidepressants. Mechanisms that link GR chaperoning and stress susceptibility are not well understood. Here, we show that the effects of glucocorticoid hormones on socioaffective behaviors are critically regulated via reversible acetylation of Hsp90, a key component of the GR chaperone complex.

Glutamatergic input is selectively increased in dorsal raphe subfield 5-HT neurons: role of morphology, topography and selective innervation.

Characterization of glutamatergic input to dorsal raphe (DR) serotonin (5-HT) neurons is crucial for understanding how the glutamate and 5-HT systems interact in psychiatric disorders. Markers of glutamatergic terminals, vGlut1, 2 and 3, reflect inputs from specific forebrain and midbrain regions. Punctate staining of vGlut2 was homogeneous throughout the mouse DR whereas vGlut1 and vGlut3 puncta were less dense in the lateral wing (lwDR) compared with the ventromedial (vmDR) subregion.

Raphe serotonin neurons are not homogenous: electrophysiological, morphological and neurochemical evidence.

The median (MR) and dorsal raphe (DR) nuclei contain the majority of the 5-hydroxytryptamine (5-HT, serotonin) neurons that project to limbic forebrain regions, are important in regulating homeostatic functions and are implicated in the etiology and treatment of mood disorders and schizophrenia. The primary synaptic inputs within and to the raphe are glutamatergic and GABAergic. The DR is divided into three subfields, i.

Serotonin-1A autoreceptors are necessary and sufficient for the normal formation of circuits underlying innate anxiety.

Identifying the factors contributing to the etiology of anxiety and depression is critical for the development of more efficacious therapies. Serotonin (5-HT) is intimately linked to both disorders. The inhibitory serotonin-1A (5-HT(1A)) receptor exists in two separate populations with distinct effects on serotonergic signaling: (1) an autoreceptor that limits 5-HT release throughout the brain and (2) a heteroreceptor that mediates inhibitory responses to released 5-HT.

Stress-hyperresponsive WKY rats demonstrate depressed dorsal raphe neuronal excitability and dysregulated CRF-mediated responses.

Major depression is a debilitating psychiatric disease that may be precipitated by a dysregulation of stress neurocircuitry caused by chronic or severe stress exposure. Moreover, hyperresponsivity to stressors correlates with depressed mood and may contribute to the etiology of major depression. The serotonergic dorsal raphe nucleus (DRN) is an important site in the neurocircuitry underlying behavioral responses to stressors, and is tightly regulated, in part, by a combination of intrinsic cell properties, autoinhibition, and GABAergic synaptic transmission.

The presynaptic component of the serotonergic system is required for clozapine's efficacy.

Clozapine, by virtue of its absence of extrapyramidal side effects and greater efficacy, revolutionized the treatment of schizophrenia, although the mechanisms underlying this exceptional activity remain controversial. Combining an unbiased cheminformatics and physical screening approach, we evaluated clozapine's activity at >2350 distinct molecular targets. Clozapine, and the closely related atypical antipsychotic drug olanzapine, interacted potently with a unique spectrum of molecular targets.

Cellular correlates of anxiety in CA1 hippocampal pyramidal cells of 5-HT1A receptor knockout mice.

Rationale: 5-HT(1A) receptor knockout (1AKO) mice have a robust anxiety phenotype. Tissue-specific "rescue" strategies and electrophysiology have implicated a critical role for postsynaptic 5-HT(1A) receptors, particularly in the CA1 region of the hippocampus.

Objectives: In this study, we evaluated differences in membrane properties and synaptic activity in CA1 hippocampal pyramidal cells between 1AKOs and wild-type (WT) controls to better understand the cellular correlates of anxiety in this mouse model.

Swim stress differentially blocks CRF receptor mediated responses in dorsal raphe nucleus.

Modulation of the serotonergic (5-HT) neurotransmitter system arising from the dorsal raphe nucleus (DR) is thought to support the behavioral effects of swim stress, i.e., immobility.

Increased intrinsic excitability of lateral wing serotonin neurons of the dorsal raphe: a mechanism for selective activation in stress circuits.

The primary center of serotonin (5-HT) projections to the forebrain is the dorsal raphe nucleus (DR), a region known for its role in the limbic stress response. The ventromedial subregion of the DR (vmDR) has the highest density of 5-HT neurons and is the major target in experiments that involve the DR. However, studies have demonstrated that a variety of stressors induce activation of neurons that is highest in the lateral wing subregion (lwDR) and includes activation of lwDR 5-HT neurons.

5-HT1A autoreceptor levels determine vulnerability to stress and response to antidepressants.

Most depressed patients don't respond to their first drug treatment, and the reasons for this treatment resistance remain enigmatic. Human studies implicate a polymorphism in the promoter of the serotonin-1A (5-HT(1A)) receptor gene in increased susceptibility to depression and decreased treatment response. Here we develop a new strategy to manipulate 5-HT(1A) autoreceptors in raphe nuclei without affecting 5-HT(1A) heteroreceptors, generating mice with higher (1A-High) or lower (1A-Low) autoreceptor levels.