Toward affective circuit-based preclinical models of depression: sensitizing dorsal PAG arousal leads to sustained suppression of positive affect in rats

Drive, instinct, reflex—Applications to treatment of anxiety, depressive and addictive disorders

The neuropsychoanalytic approach solves important aspects of how to use our understanding of the brain to treat patients. We describe the neurobiology underlying motivation for healthy behaviors and psychopathology. We have updated Freud’s original concepts of drive and instinct using neuropsychoanalysis in a way that conserves his insights while adding information that is of use in clinical treatment. Drive (Trieb) is a pressure to act on an internal stimulus. It has a motivational energic source, an aim, an object, and is terminated by the satisfaction of a surge of serotonin. An instinct (Instinkt) is an inherited pattern of behavior that varies little from species to species. Drives are created by internal/ventral brain factors. Instincts require input from the outside that arrive through dorsal brain structures. In our model unpleasure is the experience of unsatisfied drives while pleasure if fueled by a propitious human environment. Motivational concepts can be used guide clinical work. Sometimes what had previously described psychoanalytically as, “Internal conflict,” can be characterized neurobiologically as conflicts between different motivational systems. These motivational systems inform treatment of anxiety and depression, addiction in general and specific problems of opioid use disorder. Our description of motivation in addictive illness shows that the term, “reward system,” is incorrect, eliminating a source of stigmatizing addiction by suggesting that it is hedonistic. Understanding that motivational systems that have both psychological and brain correlates can be a basis for treating various disorders. Over many papers the authors have described the biology of drives, instincts, unpleasure and pleasure. We will start with a summary of our work, then show its clinical application.

Association of plasma tryptophan concentration with periaqueductal gray matter functional connectivity in migraine patients

Altered periaqueductal gray matter (PAG) functional connectivity contributes to brain hyperexcitability in migraine. Although tryptophan modulates neurotransmission in PAG projections through its metabolic pathways, the effect of plasma tryptophan on PAG functional connectivity (PAG-FC) in migraine has not been investigated yet. In this study, using a matched case-control design PAG-FC was measured during a resting-state functional magnetic resonance imaging session in migraine without aura patients (n = 27) and healthy controls (n = 27), and its relationship with plasma tryptophan concentration (TRP) was assessed. In addition, correlations of PAG-FC with age at migraine onset, migraine frequency, trait-anxiety and depressive symptoms were tested and the effect of TRP on these correlations was explored. Our results demonstrated that migraineurs had higher TRP compared to controls. In addition, altered PAG-FC in regions responsible for fear-cascade and pain modulation correlated with TRP only in migraineurs. There was no significant correlation in controls. It suggests increased sensitivity to TRP in migraine patients compared to controls. Trait-anxiety and depressive symptoms correlated with PAG-FC in migraine patients, and these correlations were modulated by TRP in regions responsible for emotional aspects of pain processing, but TRP did not interfere with processes that contribute to migraine attack generation or attack frequency.

BNST specific mGlu5 receptor knockdown regulates sex-dependent expression of negative affect produced by adolescent ethanol exposure and adult stress

Adolescent alcohol use is one of the strongest predictors for the development of an alcohol use disorder (AUD). Notably, this period of risk coincides with the development of affective disorders, which disproportionately impact and drive problematic drinking behavior in women. Stress is a particularly salient factor that drives relapse during periods of abstinence. Previous work in our lab has shown that adolescent intermittent ethanol vapor (AIE) produces sex-dependent changes in glutamatergic activity in the bed nucleus of the stria terminalis (BNST) and behavioral outcomes following acute restraint stress in adulthood. In females, AIE disrupts group 1 metabotropic glutamate (mGlu1/5) receptor activity and enhances anhedonia-like behavior. The current study site-specifically knocked down mGlu5 receptors in the BNST of male and female Grm5loxp mice, exposed them to AIE, and observed the interaction of AIE and stress on negative affect-like behaviors in adulthood. These negative affect-like behaviors included the novelty-induced hypophagia task following acute restraint stress, open field activity, and contextual fear conditioning. Overall, we replicated our previous findings that AIE enhanced anhedonia-like activity in the novelty-induced hypophagia task in females and fear acquisition in males. The primary effect of BNST-mGlu5 receptor knockdown was that it independently enhanced anhedonia-like activity in females. Correlation analyses revealed that behavior in these paradigms showed poor interdependence. These results indicate that preclinical models of negative affective-like states encompass distinct features that may have independent, clinically relevant mechanisms. Further, modulating mGlu5 receptors is a prospective treatment target for females experiencing anhedonic-like states that make them susceptible to alcohol relapse.

Rat ultrasonic vocalizations as an index of memory

The emission of 50 kHz frequency-modulated ultrasonic vocalizations (FM USVs) in rats has been associated with positive affective states, while a decrease in FM USVs has been associated with anxiety-like states. We tested the hypothesis in male Sprague-Dawley rats that FM USVs would complement measures of aversive memories (decrease in FM USVs) in a conditioned fear task in which we examined extinction or reconsolidation disruption. In Experiment 1, rats were fear conditioned using low-level footshock followed by extinction while monitoring freezing and FM USVs. In Experiment 2, rats were fear conditioned, the alpha-1 antagonist prazosin was used to disrupt reconsolidation of memory, and freezing and FM USVs were measured. Rats fear conditioned with low-level shock showed minimal freezing that rapidly extinguished, despite a persistent decrease in FM USVs throughout extinction. Prazosin reduced freezing in a memory reactivation-dependent manner as expected, but the reduction in FM USVs after fear conditioning remained decreased, suggesting that an affective component of memory was not impacted by prazosin. These findings indicate that FM USVs may be used as an index of fear- or anxiety-like memory, and their measurement could benefit pre-clinical animal models for assessing reduction of aversive memories.

Adolescent alcohol exposure produces sex differences in negative affect-like behavior and group I mGluR BNST plasticity

Adolescent alcohol exposure increases the risk of developing alcohol use disorders (AUDs), yet the mechanisms responsible for this vulnerability remain largely unknown. One potential target for alcohol-induced changes is the circuitry that modulates negative affect and stress, two sexually dependent drivers of alcohol relapse. The bed nucleus of the stria terminalis (BNST) is a sexually dimorphic region that critically regulates negative affective- and stress-induced relapse. Group I metabotropic glutamate receptors (mGluR) are a target of interest due to their regulation of stress, anxiety behaviors, and BNST plasticity. The current studies investigate sex-dependent sensitivity to the effects of adolescent intermittent ethanol vapor exposure (AIE) on negative affect during acute and protracted alcohol withdrawal and following stress in adulthood. This work also assessed whether BNST group I mGluR-mediated long-term depression (LTD) was disrupted at these timepoints. During acute withdrawal, AIE altered LTD induced by the group I mGluR antagonist DHPG in females, but not males. During adulthood, stress unmasked persistent changes in DHPG-induced LTD and behavior that were not present under basal conditions. Females with an AIE history demonstrated enhanced negative affective-like behavior in the novelty-induced hypophagia test following restraint stress-a phenotype that could be blocked with systemic mGluR5 allosteric antagonism via MTEP. Conversely, males with an AIE history demonstrated elevated freezing in a contextual fear conditioning paradigm. These studies demonstrate long-lasting, sex-dependent phenotypes produced by AIE and suggest pharmaceutical interventions for alcohol use and comorbid disorders may be more effective if designed with sex differences in mind.

Plasticity of the Reward Circuitry After Early-Life Adversity: Mechanisms and Significance

Disrupted operation of the reward circuitry underlies many aspects of affective disorders. Such disruption may manifest as aberrant behavior including risk taking, depression, anhedonia, and addiction. Early-life adversity is a common antecedent of adolescent and adult affective disorders involving the reward circuitry. However, whether early-life adversity influences the maturation and operations of the reward circuitry, and the potential underlying mechanisms, remain unclear. Here, we present novel information using cutting-edge technologies in animal models to dissect out the mechanisms by which early-life adversity provokes dysregulation of the complex interactions of stress and reward circuitries. We propose that certain molecularly defined pathways within the reward circuitry are particularly susceptible to early-life adversity. We examine regions and pathways expressing the stress-sensitive peptide corticotropin-releasing factor (CRF), which has been identified in critical components of the reward circuitry and interacting stress circuits. Notably, CRF is strongly modulated by early-life adversity in several of these brain regions. Focusing on amygdala nuclei and their projections, we provide evidence suggesting that aberrant CRF expression and function may underlie augmented connectivity of the nucleus accumbens with fear/anxiety regions, disrupting the function of this critical locus of pleasure and reward.

Metabotropic Glutamate Receptor Subtype 5 in Alcohol-Induced Negative Affect

Allosteric modulators of metabotropic glutamate 5 receptors (mGlu5 receptors) have been identified as a promising treatment to independently alleviate both negative affective states and ethanol-seeking and intake. However, these conditions are often comorbid and might precipitate one another. Acute and protracted ethanol withdrawal can lead to negative affective states. In turn, these states are primary drivers of alcohol relapse, particularly among women. The current review synthesizes preclinical studies that have observed the role of mGlu5 receptor modulation in negative affective states following ethanol exposure. The primary behavioral assays discussed are ethanol-seeking and intake, development and extinction of ethanol-associated cues and contexts, behavioral despair, and anxiety-like activity. The work done to-date supports mGlu5 receptor modulation as a promising target for mediating negative affective states to reduce ethanol intake or prevent relapse. Limitations in interpreting these data include the lack of models that use alcohol-dependent animals, limited use of adolescent and female subjects, and a lack of comprehensive evaluations of negative affective-like behavior.

Why Do Birds Flock? A Role for Opioids in the Reinforcement of Gregarious Social Interactions

The formation of social groups provides safety and opportunities for individuals to develop and practice important social skills. However, joining a social group does not result in any form of obvious, immediate reinforcement (e.g., it does not result in immediate copulation or a food reward), and individuals often remain in social groups despite agonistic responses from conspecifics. Much is known about neural and endocrine mechanisms underlying the motivation to perform mate- or offspring-directed behaviors. In contrast, relatively little is known about mechanisms underlying affiliative behaviors outside of these primary reproductive contexts. Studies on flocking behavior in songbirds are beginning to fill this knowledge gap. Here we review behavioral evidence that supports the hypothesis that non-sexual affiliative, flocking behaviors are both (1) rewarded by positive social interactions with conspecifics, and (2) reinforced because affiliative contact reduces a negative affective state caused by social isolation. We provide evidence from studies in European starlings, Sturnus vulgaris, that mu opioid receptors in the medial preoptic nucleus (mPOA) play a central role in both reward and the reduction of a negative affective state induced by social interactions in flocks, and discuss potential roles for nonapeptide/opioid interactions and steroid hormones. Finally, we develop the case that non-sexual affiliative social behaviors may be modified by two complementary output pathways from mPOA, with a projection from mPOA to the periaqueductal gray integrating information during social interactions that reduces negative affect and a projection from mPOA to the ventral tegmental area integrating information leading to social approach and reward.

Periaqueductal Gray Sheds Light on Dark Areas of Psychopathology

Neurons in the periaqueductal gray (PAG) integrate negative emotions with the autonomic, neuroendocrine, and immune systems to facilitate responses to threat. Modern functional track tracing in animals and optogenetic and chemogenetic techniques show that the PAG is a rich substrate for the integration of active and passive responses to threat. In humans, the same regions of the PAG that give rise to adaptive anger/fight, fear/panic, depression/shutdown, pain, and predatory behaviors in response to challenging situations or overwhelming threats can become activated pathologically, resulting in symptoms that resemble those of psychiatric disorders. This review coalesces human and animal studies to link PAG neuropathways to specific elements of psychiatric diagnoses. The insights gained from this overview may eventually lead to new therapeutic interventions.

Positive Emotional Learning Induces Resilience to Depression: A Role for NMDA Receptor-mediated Synaptic Plasticity

BACKGROUND

Positive emotions have been shown to induce resilience to depression and anxiety in humans, as well as increase cognitive abilities (learning, memory and problem solving) and improve overall health. In rats, frequency modulated 50-kHz ultrasonic vocalizations (Hedonic 50-kHz USVs) reflect a positive affective state and are best elicited by rough-and-tumble play.

METHODS

The effect of positive affect induced by rough-and tumble play was examined on models of depression and learning and memory. The molecular and pharmacological basis of play induced positive affect was also examined.

RESULTS

Rough-and-tumble play induced Hedonic 50-kHz USVs, lead to resilience to depression and anxiety, and facilitation of learning and memory. These effects are mediated, in part, by increased NMDAR expression and activation in the medial prefrontal cortex.

CONCLUSIONS

We hypothesize that positive affect induces resilience to depression by facilitating NMDAR-dependent synaptic plasticity in the medial prefrontal cortex. Targeting MPFC synaptic plasticity may lead to novel treatments for depression.

The Psycho-Neurology of Cross-Species Affective/Social Neuroscience: Understanding Animal Affective States as a Guide to Development of Novel Psychiatric Treatments

During the past half century of research with preclinical animal models, affective neuroscience has helped identify and illuminate the functional neuroanatomies and neurochemistries of seven primary process, i.e., genetically provided emotional systems of mammalian brains. All are subcortically localized, allowing animal models to guide the needed behavioral and neuroscientific analyses at levels of detail that cannot be achieved through human research, including modern brain imaging. They consist of the following neuronal processes: SEEKING/Enthusiasm, RAGE/Anger, FEAR/Anxiety, sexual LUST/Passion, maternal CARE/Nurturance, separation-distress PANIC/Grief and PLAY/Social Joy. Several of these systems figure heavily in social bonding. I will focus here especially on the genesis of depression. Its genesis is significantly influenced by (i) sustained overactivity of the separation-distress PANIC system reflecting severed social bonds and the excessive "psychological pain" of loneliness that can, if sustained, lead to a downward cascade known as psychological despair, and (ii) the despair phase that follows the acute PANIC response, which is characterized by abnormally low activity of the SEEKING, the so-called brain reward networks, leading to amotivational states that characterize depression. Depressive affect is promoted by such brain affective mechanisms of social attachments and social loss as well as diminished arousability of the SEEKING system, leading to chronic dysphoria. To understand why depression feels so bad, we must understand the neural mechanisms that mediate such social feelings.

The cross-mammalian neurophenomenology of primal emotional affects: From animal feelings to human therapeutics

The neural correlates of human emotions are easy to harvest. In contrast, the neural constitution of emotional feelings in humans has resisted systematic scientific analysis. This review summarizes how preclinical affective neuroscience initiatives are making progress in decoding the neural nature of such feelings in animal brains. This has been achieved by studying the rewarding and punishing effects of deep brain stimulation (DBS) of subcortical emotional networks (labeled SEEING, RAGE, FEAR, LUST, CARE, PANIC, and PLAY systems) that evoke distinct emotion action patterns, as well as rewarding and punishing effects in animals. The implications of this knowledge for development of new psychiatric interventions, especially depression, are discussed. Three new antidepressive therapeutics arising from this work are briefly noted: 1) DBS of the medial forebrain bundle (MFB) in humans, 2) reduction of psychological pain that may arise from excessive PANIC arousal, and 3) facilitation of social joy through the study of social play in rats The overall argument is that we may more readily develop new psychiatric interventions through preclinical models if we take animal emotional feelings seriously, as opposed to just behavioral changes, as targets for development of new treatments.

Affective preclinical modeling of psychiatric disorders: taking imbalanced primal emotional feelings of animals seriously in our search for novel antidepressants

Preclinical animal models of psychiatric disorders are of critical importance for advances in development of new psychiatric medicine. Regrettably, behavior-only models have yielded no novel targeted treatments during the past half-century of vigorous deployment. This may reflect the general neglect of experiential aspects of animal emotions, since affective mental states of animals supposedly cannot be empirically monitored. This supposition is wrong—to the extent that the rewarding and punishing aspects of emotion circuit arousals reflect positive and negative affective states. During the past decade, the use of such affective neuroscience-based animal modeling has yielded three novel antidepressants (i) via the alleviation of psychic pain with low doses of buprenorphine; (ii) via the amplification of enthusiasm by direct stimulation of the medial forebrain bundle); and (iii) via the facilitation of the capacity for social joy with play facilitators such as rapastinel (GLYX13). All have progressed to successful human testing. For optimal progress, it may be useful for preclinical investigators to focus on the evolved affective foundations of psychiatrically relevant brain emotional disorders for optimal animal modeling.

Dissociating Motivational From Physiological Withdrawal in Alcohol Dependence: Role of Central Amygdala κ-Opioid Receptors

Chronic intermittent alcohol vapor exposure leads to increased dynorphin (DYN) A-like peptide expression and heightened kappa-opioid receptor (KOR) signaling in the central nucleus of the amygdala (CeA) and these neuroadaptive responses differentiate alcohol-dependent from non-dependent phenotypes. Important for therapeutic development efforts is understanding the nature of the stimulus that drives dependence-like phenotypes such as escalated alcohol self-administration. Accordingly, the present study examined the impact of intra-CeA KOR antagonism on escalated operant alcohol self-administration and physiological withdrawal symptoms during acute withdrawal and protracted abstinence in rats previously exposed to chronic intermittent alcohol vapor. Following operant training, rats were implanted with intra-CeA guide cannula and exposed to long-term intermittent alcohol vapor exposure that resulted in escalated alcohol self-administration and elevated physiological withdrawal signs during acute withdrawal. Animals received intra-CeA infusions of the KOR antagonist nor-binaltorphimine (nor-BNI; 0, 2, 4, or 6 μg) prior to operant alcohol self-administration sessions and physiological withdrawal assessment during acute withdrawal and protracted abstinence. The results indicated that site-specific KOR antagonism in the CeA ameliorated escalated alcohol self-administration during both acute withdrawal and protracted abstinence test sessions, whereas KOR antagonism had no effect on physiological withdrawal scores at either time point. These results dissociate escalated alcohol self-administration from physiological withdrawal symptoms in relation to KOR signaling in the CeA and help clarify the nature of the stimulus that drives escalated alcohol self-administration during acute withdrawal and protracted abstinence.

The neuroscience of placebo effects: connecting context, learning and health

Placebo effects are beneficial effects that are attributable to the brain-mind responses to the context in which a treatment is delivered rather than to the specific actions of the drug. They are mediated by diverse processes--including learning, expectations and social cognition--and can influence various clinical and physiological outcomes related to health. Emerging neuroscience evidence implicates multiple brain systems and neurochemical mediators, including opioids and dopamine. We present an empirical review of the brain systems that are involved in placebo effects, focusing on placebo analgesia, and a conceptual framework linking these findings to the mind-brain processes that mediate them. This framework suggests that the neuropsychological processes that mediate placebo effects may be crucial for a wide array of therapeutic approaches, including many drugs.

The one-two punch of alcoholism: role of central amygdala dynorphins/kappa-opioid receptors

BACKGROUND

The dynorphin (DYN)/kappa-opioid receptor (KOR) system undergoes neuroadaptations following chronic alcohol exposure that promote excessive operant self-administration and negative affective-like states; however, the exact mechanisms are unknown. The present studies tested the hypothesis that an upregulated DYN/KOR system mediates excessive alcohol self-administration that occurs during withdrawal in alcohol-dependent rats by assessing DYN A peptide expression and KOR function, in combination with site-specific pharmacologic manipulations.

METHODS

Male Wistar rats were trained to self-administer alcohol using operant behavioral strategies and subjected to intermittent alcohol vapor or air exposure. Changes in self-administration were assessed by pharmacologic challenges during acute withdrawal. In addition, 22-kHz ultrasonic vocalizations were utilized to measure negative affective-like states. Immunohistochemical techniques assessed DYN A peptide expression and [(35)S]GTPγS coupling assays were performed to assess KOR function.

RESULTS

Alcohol-dependent rats displayed increased alcohol self-administration, negative affective-like behavior, DYN A-like immunoreactivity, and KOR signaling in the amygdala compared with nondependent control rats. Site-specific infusions of a KOR antagonist selectively attenuated self-administration in dependent rats, whereas a mu-opioid receptor/delta-opioid receptor antagonist cocktail selectively reduced self-administration in nondependent rats. A mu-opioid receptor antagonist/partial KOR agonist attenuated self-administration in both cohorts.

CONCLUSIONS

Increased DYN A and increased KOR signaling could set the stage for a one-two punch during withdrawal that drives excessive alcohol consumption in alcohol dependence. Importantly, intracentral nucleus of the amygdala pharmacologic challenges functionally confirmed a DYN/KOR system involvement in the escalated alcohol self-administration. Together, the DYN/KOR system is heavily dysregulated in alcohol dependence and contributes to the excessive alcohol consumption during withdrawal.

Ultrasonic vocalizations: evidence for an affective opponent process during cocaine self-administration

RATIONALE

Preclinical models of cocaine addiction in the rodent have shown that cocaine induces both positive and negative affective states. These observations have led to the notion that the initial positive/euphoric state induced by cocaine administration may be followed by an opposing, negative process. In the rodent, one method for inferring positive and negative affective states involves measuring their ultrasonic vocalizations (USVs). Previous USV recordings from our laboratory suggested that the transition between positive and negative affect might involve decaying or sub-satiety levels of self-administered cocaine.

OBJECTIVES

In order to explicitly test the role of cocaine levels on these affective states, the present study examined USVs when calculated body levels of cocaine were clamped (i.e., held at a constant level via experimenter-controlled infusions) at, below, or above subjects' self-determined drug satiety thresholds.

RESULTS

USVs indicated that (1) positive affect was predominantly observed during the drug loading period, but declined quickly to near zero during maintenance and exhibited little relation to calculated drug level, and (2) in contrast, negative affect was observed at sub-satiety cocaine levels, but was relatively absent when body levels of cocaine were clamped at or above subjects' satiety thresholds.

CONCLUSIONS

The results reinforce the opponent-process hypothesis of addiction and suggest that an understanding of the mechanisms underlying negative affect might serve to inform behavioral and pharmacological therapies.

The kappa opioid receptor: from addiction to depression, and back

Comorbidity is a major issue in psychiatry that notably associates with more severe symptoms, longer illness duration, and higher service utilization. Therefore, identifying key clusters of comorbidity and exploring the underlying pathophysiological mechanisms represent important steps toward improving mental health care. In the present review, we focus on the frequent association between addiction and depression. In particular, we summarize the large body of evidence from preclinical models indicating that the kappa opioid receptor (KOR), a member of the opioid neuromodulatory system, represents a central player in the regulation of both reward and mood processes. Current data suggest that the KOR modulates overlapping neuronal networks linking brainstem monoaminergic nuclei with forebrain limbic structures. Rewarding properties of both drugs of abuse and natural stimuli, as well as the neurobiological effects of stressful experiences, strongly interact at the level of KOR signaling. In addiction models, activity of the KOR is potentiated by stressors and critically controls drug-seeking and relapse. In depression paradigms, KOR signaling is responsive to a variety of stressors, and mediates despair-like responses. Altogether, the KOR represents a prototypical substrate of comorbidity, whereby life experiences converge upon common brain mechanisms to trigger behavioral dysregulation and increased risk for distinct but interacting psychopathologies.

Preclinical modeling of primal emotional affects (Seeking, Panic and Play): gateways to the development of new treatments for depression

Mammalian brains contain at least 7 primal emotional systems--Seeking, Rage, Fear, Lust, Care, Panic and Play (capitalization reflects a proposed primary-process terminology, to minimize semantic confusions and mereological fallacies). These systems help organisms feel affectively balanced (e.g. euthymic) and unbalanced (e.g. depressive, irritable, manic), providing novel insights for understanding human psychopathologies. Three systems are especially important for understanding depression: The separation distress (Panic) system mediates the psychic pain of separation distress (i.e. excessive sadness and grief), which can be counteracted by minimizing Panic arousals (as with low-dose opioids). Depressive dysphoria also arises from reduced brain reward-seeking and related play urges (namely diminished enthusiasm (Seeking) and joyful exuberance (Play) which promote sustained amotivational states). We describe how an understanding of these fundamental emotional circuits can promote the development of novel antidepressive therapeutics--(i) low-dose buprenorphine to counteract depression and suicidal ideation emanating from too much psychic pain (Panic overarousal), (ii) direct stimulation of the Seeking system to counteract amotivational dysphoria, and (iii) the discovery and initial clinical testing of social-joy-promoting molecules derived from the analysis of the Play system.

Glutamate concentration in the medial prefrontal cortex predicts resting-state cortical-subcortical functional connectivity in humans

Communication between cortical and subcortical regions is integral to a wide range of psychological processes and has been implicated in a number of psychiatric conditions. Studies in animals have provided insight into the biochemical and connectivity processes underlying such communication. However, to date no experiments that link these factors in humans in vivo have been carried out. To investigate the role of glutamate in individual differences in communication between the cortex--specifically the medial prefrontal cortex (mPFC)--and subcortical regions in humans, a combination of resting-state fMRI, DTI and MRS was performed. The subcortical target regions were the nucleus accumbens (NAc), dorsomedial thalamus (DMT), and periaqueductal grey (PAG). It was found that functional connectivity between the mPFC and each of the NAc and DMT was positively correlated with mPFC glutamate concentrations, whilst functional connectivity between the mPFC and PAG was negatively correlated with glutamate concentration. The correlations involving mPFC glutamate and FC between the mPFC and each of the DMT and PAG were mirrored by correlations with structural connectivity, providing evidence that the glutamatergic relationship may, in part, be due to direct connectivity. These results are in agreement with existing results from animal studies and may have relevance for MDD and schizophrenia.

The effect of intermittent alcohol vapor or pulsatile heroin on somatic and negative affective indices during spontaneous withdrawal in Wistar rats

RATIONALE

Once dependent on alcohol or opioids, negative affect may accompany withdrawal. Dependent individuals are hypothesized to "self-medicate" in order to cope with withdrawal, which promotes escalated alcohol and drug use.

OBJECTIVES

The current study aimed to develop a reliable animal model to assess symptoms that occur during spontaneous alcohol and opioid withdrawal.

METHODS

Dependence was induced using intermittent alcohol exposure or pulsatile heroin delivery and assessed for the presence of withdrawal symptoms during acute withdrawal by measuring somatic signs, behavior in the forced swim test (FST), and air-puff-induced 22-kHz ultrasonic vocalizations (USVs). Additional animals subjected to 8 weeks of alcohol vapor exposure were evaluated for altered somatic signs, operant alcohol self-administration, and 22-kHz USV production, as well as performance in the elevated plus maze (EPM).

RESULTS

During spontaneous withdrawal from pulsatile heroin or intermittent alcohol vapor, animals displayed increased somatic withdrawal signs, FST immobility, and 22-kHz USV production but did not show any behavioral change in the EPM unless the duration of alcohol exposure was extended to 4 weeks. Following 8 weeks of alcohol vapor exposure, animals displayed somatic withdrawal signs, escalated alcohol self-administration, and increased 22-kHz USVs.

CONCLUSIONS

These paradigms provide consistent methods to evaluate the behavioral ramifications, and neurobiological substrates, of alcohol and opioid dependence during spontaneous withdrawal. As immobility in the FST and percent open-arm time in the EPM were dissociable, with 22-kHz USVs paralleling immobility in the FST, assessment of air-puff-induced 22-kHz USVs could provide an ethologically valid alternative to the FST.

Differential changes of metabolic brain activity and interregional functional coupling in prefronto-limbic pathways during different stress conditions: functional imaging in freely behaving rodent pups

The trumpet-tailed rat or degu (Octodon degus) is an established model to investigate the consequences of early stress on the development of emotional brain circuits and behavior. The aim of this study was to identify brain circuits, that respond to different stress conditions and to test if acute stress alters functional coupling of brain activity among prefrontal and limbic regions. Using functional imaging (2-Fluoro-deoxyglucose method) in 8-day-old male degu pups the following stress conditions were compared: (A) pups together with parents and siblings (control), (B) separation of the litter from the parents, (C) individual separation from parents and siblings, and (D) individual separation and presentation of maternal calls. Condition (B) significantly downregulated brain activity in the prefrontal cortex, hippocampus, nucleus accumbens (NAcc), and sensory areas compared to controls. Activity decrease was even more pronounced during condition (C), where, in contrast to all other regions, activity in the PAG was increased. Interestingly, brain activity in stress-associated brain regions such as the amygdala and habenula was not affected. In condition (D) maternal vocalizations "reactivated" brain activity in the cingulate and precentral medial cortex, NAcc, and striatum and in sensory areas. In contrast, reduced activity was measured in the prelimbic and infralimbic cortex (IL) and in the hippocampus and amygdala. Correlation analysis revealed complex, region- and situation-specific changes of interregional functional coupling among prefrontal and limbic brain regions during stress exposure. We show here for the first time that early life stress results in a widespread reduction of brain activity in the infant brain and changes interregional functional coupling. Moreover, maternal vocalizations can partly buffer stress-induced decrease in brain activity in some regions and evoked very different functional coupling patterns compared to the three other conditions.