Error-related Alpha Suppression: Scalp Topography and (Lack of) Modulation by Modafinil.

Errors in performance trigger cognitive and neural changes that are implemented to adaptively adjust to fluctuating demands. Error-related alpha suppression (ERAS)-which refers to decreased power in the alpha frequency band after an incorrect response-is thought to reflect cognitive arousal after errors. Much of this work has been correlational, however, and there are no direct investigations into its pharmacological sensitivity. In Study 1 (n = 61), we evaluated the presence and scalp distribution of ERAS in a novel flanker task specifically developed for cross-species assessments. Using this same task in Study 2 (n = 26), which had a placebo-controlled within-subject design, we evaluated the sensitivity of ERAS to placebo (0 mg), low (100 mg), and high (200 mg) doses of modafinil, a wakefulness promoting agent. Consistent with previous work, ERAS was maximal at parieto-occipital recording sites in both studies. In Study 2, modafinil did not have strong effects on ERAS (a significant Accuracy × Dose interaction emerged, but drug-placebo differences did not reach statistical significance after correction for multiple comparisons and was absent after controlling for accuracy rate). ERAS was correlated with accuracy rates in both studies. Thus, modafinil did not impact ERAS as hypothesized, and findings indicate ERAS may reflect an orienting response to infrequent events.

Dopamine and Addiction.

Addiction is commonly identified with habitual nonmedical self-administration of drugs. It is usually defined by characteristics of intoxication or by characteristics of withdrawal symptoms. Such addictions can also be defined in terms of the brain mechanisms they activate; most addictive drugs cause elevations in extracellular levels of the neurotransmitter dopamine. Animals unable to synthesize or use dopamine lack the conditioned reflexes discussed by Pavlov or the appetitive behavior discussed by Craig; they have only unconditioned consummatory reflexes. Burst discharges (phasic firing) of dopamine-containing neurons are necessary to establish long-term memories associating predictive stimuli with rewards and punishers. Independent discharges of dopamine neurons (tonic or pacemaker firing) determine the motivation to respond to such cues. As a result of habitual intake of addictive drugs, dopamine receptors expressed in the brain are decreased, thereby reducing interest in activities not already stamped in by habitual rewards.

Differential Effects of Nicotine and Nicotine Withdrawal on Fear Conditioning in Male Rats.

BACKGROUND: Tobacco use is prevalent in individuals who are routinely exposed to stress. However, little is known about how nicotine affects responses to trauma. We examined in rats how nicotine exposure affects fear conditioning, a procedure often used to study stress-related psychiatric illness. METHODS: We examined 2 methods of nicotine exposure: self-administration, modeling voluntary use, and experimenter-programmed subcutaneous administration, modeling medicinal administration (nicotine patch). For self-administered nicotine, rats trained to self-administer nicotine i.v. were fear conditioned (via light cue preceding foot-shock) either immediately after a 12-hour self-administration session or 12 hours later during a period with somatic signs of nicotine withdrawal. For experimenter-delivered nicotine, rats were conditioned after 1-21 days of nicotine delivered by programmable (12 hours on) subcutaneous mini-pumps. Tests to evaluate acoustic startle responses to the conditioning environment (context-potentiated startle) and in the presence or absence of the light cue (fear-potentiated startle) occurred after a 10-day period. RESULTS: Rats fear conditioned immediately after nicotine self-administration showed reduced responses to the shock-associated context, whereas those trained during nicotine withdrawal showed exaggerated responses. Experimenter-programmed nicotine produced effects qualitatively similar to those seen with self-administered nicotine. CONCLUSIONS: Self-administration or experimenter-programmed delivery of nicotine immediately before exposure to aversive events can reduce conditioned fear responses. In contrast, exposure to aversive events during nicotine withdrawal exacerbates fear responses. These studies raise the possibility of developing safe and effective methods to deliver nicotine or related drugs to mitigate the effects of stress while also highlighting the importance of preventing withdrawal in nicotine-dependent individuals.

Drug predictive cues activate aversion-sensitive striatal neurons that encode drug seeking.

Drug-associated cues have profound effects on an addict's emotional state and drug-seeking behavior. Although this influence must involve the motivational neural system that initiates and encodes the drug-seeking act, surprisingly little is known about the nature of such physiological events and their motivational consequences. Three experiments investigated the effect of a cocaine-predictive stimulus on dopamine signaling, neuronal activity, and reinstatement of cocaine seeking. In all experiments, rats were divided into two groups (paired and unpaired), and trained to self-administer cocaine in the presence of a tone that signaled the immediate availability of the drug. For rats in the paired group, self-administration sessions were preceded by a taste cue that signaled delayed drug availability. Assessments of hedonic responses indicated that this delay cue became aversive during training. Both the self-administration behavior and the immediate cue were subsequently extinguished in the absence of cocaine. After extinction of self-administration behavior, the presentation of the aversive delay cue reinstated drug seeking. In vivo electrophysiology and voltammetry recordings in the nucleus accumbens measured the neural responses to both the delay and immediate drug cues after extinction. Interestingly, the presentation of the delay cue simultaneously decreased dopamine signaling and increased excitatory encoding of the immediate cue. Most importantly, the delay cue selectively enhanced the baseline activity of neurons that would later encode drug seeking. Together these observations reveal how cocaine cues can modulate not only affective state, but also the neurochemical and downstream neurophysiological environment of striatal circuits in a manner that promotes drug seeking.

Corticosterone acts in the nucleus accumbens to enhance dopamine signaling and potentiate reinstatement of cocaine seeking.

Stressful life events are important contributors to relapse in recovering cocaine addicts, but the mechanisms by which they influence motivational systems are poorly understood. Studies suggest that stress may "set the stage" for relapse by increasing the sensitivity of brain reward circuits to drug-associated stimuli. We examined the effects of stress and corticosterone on behavioral and neurochemical responses of rats to a cocaine prime after cocaine self-administration and extinction. Exposure of rats to acute electric footshock stress did not by itself reinstate drug-seeking behavior but potentiated reinstatement in response to a subthreshold dose of cocaine. This effect of stress was not observed in adrenalectomized animals, and was reproduced in nonstressed animals by administration of corticosterone at a dose that reproduced stress-induced plasma levels. Pretreatment with the glucocorticoid receptor antagonist RU38486 did not block the corticosterone effect. Corticosterone potentiated cocaine-induced increases in extracellular dopamine in the nucleus accumbens (NAc), and pharmacological blockade of NAc dopamine receptors blocked corticosterone-induced potentiation of reinstatement. Intra-accumbens administration of corticosterone reproduced the behavioral effects of stress and systemic corticosterone. Corticosterone treatment acutely decreased NAc dopamine clearance measured by fast-scan cyclic voltammetry, suggesting that inhibition of uptake2-mediated dopamine clearance may underlie corticosterone effects. Consistent with this hypothesis, intra-accumbens administration of the uptake2 inhibitor normetanephrine potentiated cocaine-induced reinstatement. Expression of organic cation transporter 3, a corticosterone-sensitive uptake2 transporter, was detected on NAc neurons. These findings reveal a novel mechanism by which stress hormones can rapidly regulate dopamine signaling and contribute to the impact of stress on drug intake.

Concurrent electrophysiological recording and cognitive testing in a rodent touchscreen environment.

Challenges in therapeutics development for neuropsychiatric disorders can be attributed, in part, to a paucity of translational models capable of capturing relevant phenotypes across clinical populations and laboratory animals. Touch-sensitive procedures are increasingly used to develop innovative animal models that better align with testing conditions used in human participants. In addition, advances in electrophysiological techniques have identified neurophysiological signatures associated with characteristics of neuropsychiatric illness. The present studies integrated these methodologies by developing a rat flanker task with electrophysiological recordings based on reverse-translated protocols used in human electroencephalogram (EEG) studies of cognitive control. Various touchscreen-based stimuli were evaluated for their ability to efficiently gain stimulus control and advance to flanker test sessions. Optimized stimuli were then examined for their elicitation of prototypical visual evoked potentials (VEPs) across local field potential (LFP) wires and EEG skull screws. Of the stimuli evaluated, purple and green photographic stimuli were associated with efficient training and expected flanker interference effects. Orderly stimulus-locked outcomes were also observed in VEPs across LFP and EEG recordings. These studies along with others verify the feasibility of concurrent electrophysiological recordings and rodent touchscreen-based cognitive testing and encourage future use of this integrated approach in therapeutics development.

Nucleus Accumbens Medium Spiny Neuron Subtypes Differentially Regulate Stress-Associated Alterations in Sleep Architecture.

BACKGROUND: Stress is implicated in the pathophysiology of major depression and posttraumatic stress disorder. These conditions share core features, including motivational deficits, heighted anxiety, and sleep dysregulation. Chronic stress produces these same features in rodents, with some individuals being susceptible or resilient, as seen in humans. While stress-induced neuroadaptations within the nucleus accumbens are implicated in susceptibility-related dysregulation of motivational and emotional behaviors, their effects on sleep are unclear. METHODS: We used chemogenetics (DREADDs [designer receptors exclusively activated by designer drugs]) to examine the effects of selective alterations in activity of nucleus accumbens medium spiny neurons expressing dopamine D1 receptors (D1-MSNs) or dopamine D2 receptors (D2-MSNs) on sleep-related end points. Mice were implanted with wireless transmitters enabling continuous collection of data to quantify vigilance states over a 20-day test period. Parallel cohorts were examined in behavioral tests assessing stress susceptibility. RESULTS: D1- and D2-MSNs play dissociable roles in sleep regulation. Stimulation of inhibitory or excitatory DREADDs expressed in D1-MSNs exclusively affects rapid eye movement sleep, whereas targeting D2-MSNs affects slow wave sleep. The combined effects of D1-MSN inhibition and D2-MSN activation on sleep resemble those of chronic social defeat stress. Alterations in D1-MSN function also affect stress susceptibility in social behavior tests. Elevation of CREB (cAMP response element-binding protein) within D1-MSNs is sufficient to produce stress-like effects on rapid eye movement sleep. CONCLUSIONS: In addition to regulation of motivational and emotional behaviors, the nucleus accumbens also influences sleep, an end point with high translational relevance. These findings provide a neural basis for comorbidity in key features of stress-related illness.

Concordant neurophysiological signatures of cognitive control in humans and rats.

Progress towards understanding neural mechanisms in humans relevant to psychiatric conditions has been hindered by a lack of translationally-relevant cognitive tasks for laboratory animals. Accordingly, there is a critical need to develop parallel neurophysiological assessments of domains of cognition, such as cognitive control, in humans and laboratory animals. To address this, we developed a touchscreen-based cognitive (Eriksen Flanker) task in rats and used its key characteristics to construct a novel human version, with similar testing parameters and endpoints across species. We obtained continuous electroencephalogram (EEG) recordings, including local field potentials in rats, and compared electrophysiological signatures locked to stimulus onset and responses across species. We also assessed whether behavioral or physiological task effects were modulated by modafinil, which enhances aspects of cognitive function in humans. In both species, the task elicited expected flanker interference effects (reduced accuracy) during high-conflict trials. Across homologous neuroanatomical loci, stimulus-locked increases in theta power during high-conflict trials as well as error-related negative potentials were observed. These endpoints were not affected by modafinil in either species. Despite some species-specific patterns, our findings demonstrate the feasibility of a rat Flanker task as well as cross-species behavioral and neurophysiological similarities, which may enable novel insights into the neural correlates of healthy and aberrant behavior and provide mechanistic insights relevant to treatment.

Learned avoidance requires VTA KOR-mediated reductions in dopamine.

Proper learning from an aversive experience is essential for survival, yet it is an aberrant process in a wide range of mental disorders, as well as dopaminergic neurodegenerative disease. While the mesolimbic dopamine system is known to be essential for reward learning, the characterization of a potential pattern of dopamine signaling that guides avoidance remains unknown. Aversive stimuli may directly modulate dopamine signaling through the dynorphin/kappa opioid receptor (KOR) system, as kappa opioid receptors are expressed in this neural circuit and their activation is aversive in both rodents and humans. Ventral tegmental area (VTA) KORs are ideally positioned to directly shape aversion-induced reductions in dopamine signaling, but their role in this process has received little consideration. To determine the necessity of VTA KOR activity in the regulation of dopamine signaling and avoidance, we tested the effects of VTA KOR blockade on real time dopaminergic responses to aversive stimuli and learned avoidance in male Sprague-Dawley rats. We found that blockade of VTA KORs attenuated aversion-induced reductions in dopamine, and this treatment also prevented avoidance following the aversive experience. To determine whether aversion-induced reductions in striatal dopamine are necessary for avoidance, we tested avoidance following treatment with an intra nucleus accumbens D2 receptor agonist. This treatment also prevented avoidance and is consistent with the view that aversion-induced reductions in dopamine reduce dopamine signaling at high affinity D2 receptors and disinhibit an aversion-sensitive striatal output circuit to promote avoidance.

Aversive stimuli drive drug seeking in a state of low dopamine tone.

BACKGROUND: Stressors negatively impact emotional state and drive drug seeking, in part, by modulating the activity of the mesolimbic dopamine system. Unfortunately, the rapid regulation of dopamine signaling by the aversive stimuli that cause drug seeking is not well characterized. In a series of experiments, we scrutinized the subsecond regulation of dopamine signaling by the aversive stimulus, quinine, and tested its ability to cause cocaine seeking. Additionally, we examined the midbrain regulation of both dopamine signaling and cocaine seeking by the stress-sensitive peptide, corticotropin releasing factor (CRF). METHODS: Combining fast-scan cyclic voltammetry with behavioral pharmacology, we examined the effect of intraoral quinine administration on nucleus accumbens dopamine signaling and hedonic expression in 21 male Sprague-Dawley rats. We tested the role of CRF in modulating aversion-induced changes in dopamine concentration and cocaine seeking by bilaterally infusing the CRF antagonist, CP-376395, into the ventral tegmental area (VTA). RESULTS: We found that quinine rapidly reduced dopamine signaling on two distinct time scales. We determined that CRF acted in the VTA to mediate this reduction on only one of these time scales. Further, we found that the reduction of dopamine tone and quinine-induced cocaine seeking were eliminated by blocking the actions of CRF in the VTA during the experience of the aversive stimulus. CONCLUSIONS: These data demonstrate that stress-induced drug seeking can occur in a terminal environment of low dopamine tone that is dependent on a CRF-induced decrease in midbrain dopamine activity.

Sensory reinforcement as a predictor of cocaine and water self-administration in rats.

RATIONALE: The ability of locomotor activity in a novel environment (Loco) and visual stimulus reinforcement (VSR) to predict acquisition of responding for cocaine and water reinforcers in the absence of explicit audiovisual signals was evaluated. METHODS: In Experiment 1 (Exp 1), rats (n = 60) were tested for VSR, followed by Loco, and finally acquisition of responding for cocaine (0.3 mg/kg/inf). In Experiment 2 (Exp 2), rats (n = 32) were tested for VSR, followed by Loco, and finally acquisition of responding for water (0.01 mL/reinforcer). RESULTS: There were three main findings. First, Loco and VSR were significantly associated (Exp 1: r = 0.49, p < 0.00; Exp 2: r = 0.35, p < 0.05). Second, neither Loco (r = .00, p = 0.998) nor VSR (r = -0.12, p = 0.352) predicted acquisition of cocaine SA. Third, in the subgroup of animals that acquired cocaine SA, VSR (r = 0.41, p < 0.01) but not Loco (r = 0.28, p = 0.10) was positively associated with operant responding for cocaine. Both Loco and VSR (Loco: r = 0.37, p < 0.04; VSR: r = 0.51, p < 0.00) were positively associated with operant responding for water reinforcers. CONCLUSIONS: The results indicate that VSR is at least as good a predictor of cocaine reinforced responding as Loco. VSR was predictive of operant responding for both drug and water reinforcers, while Loco was found to be predictive of responding only for water reinforcers. In studies that present visual stimuli in association with drug delivery, Loco may be predicting acquisition of responding for VSR rather than drug.

Association between locomotor response to novelty and light reinforcement: sensory reinforcement as a rodent model of sensation seeking.

BACKGROUND: The human personality trait of sensation seeking (SS) indicates an attraction to novel sensations and experiences, and is associated with greater likelihood of drug abuse. In rodents, locomotor activity in a novel environment (Loco) has been found to predict drug self-administration (SA), and has been hypothesized to be a translational model of human SS. Previously, we reported (Gancarz et al., 2011) that high responder (HR) animals responded more than low responder (LR) animals to produce a response contingent light onset. The primary goal of this paper was a detailed analysis of the association between Loco and light contingent responding in a large sample of rats (n = 93). METHODS: Male rats were pre-exposed to dark operant test chambers for ten 30 min sessions and baseline levels of responding (snout poking) were determined. The pre-exposure phase was followed by 6 sessions during which active responding produced a visual sensory reinforcer (VSR; 5 s light onset) according to a variable interval 1 min schedule of reinforcement. After completion of the VSR phase, Loco was tested. RESULTS: The activating effects (total responding) of light were associated with Loco, but the response guiding effects (proportion of active responding) of the light were not. In addition, HR rats habituated more slowly in both the VSR and Loco tests than LR rats. CONCLUSIONS: These data indicate that VSR measures aspects of the rodent's response to novel sensations and experiences that are not detected by Loco. These data provide some evidence for the use of light reinforcement as an animal model of SS.