The locus coeruleus-noradrenergic system: modulation of behavioral state and state-dependent cognitive processes

Through a widespread efferent projection system, the locus coeruleus-noradrenergic system supplies norepinephrine throughout the central nervous system. Initial studies provided critical insight into the basic organization and properties of this system. More recent work identifies a complicated array of behavioral and electrophysiological actions that have in common the facilitation of processing of relevant, or salient, information. This involves two basic levels of action. First, the system contributes to the initiation and maintenance of behavioral and forebrain neuronal activity states appropriate for the collection of sensory information (e.g. waking). Second, within the waking state, this system modulates the collection and processing of salient sensory information through a diversity of concentration-dependent actions within cortical and subcortical sensory, attention, and memory circuits. Norepinephrine-dependent modulation of long-term alterations in synaptic strength, gene transcription and other processes suggest a potentially critical role of this neurotransmitter system in experience-dependent alterations in neural function and behavior. The ability of a given stimulus to increase locus coeruleus discharge activity appears independent of affective valence (appetitive vs. aversive). Combined, these observations suggest that the locus coeruleus-noradrenergic system is a critical component of the neural architecture supporting interaction with, and navigation through, a complex world. These observations further suggest that dysregulation of locus coeruleus-noradrenergic neurotransmission may contribute to cognitive and/or arousal dysfunction associated with a variety of psychiatric disorders, including attention-deficit hyperactivity disorder, sleep and arousal disorders, as well as certain affective disorders, including post-traumatic stress disorder. Independent of an etiological role in these disorders, the locus coeruleus-noradrenergic system represents an appropriate target for pharmacological treatment of specific attention, memory and/or arousal dysfunction associated with a variety of behavioral/cognitive disorders.

Immune activation during pregnancy in rats leads to a postpubertal emergence of disrupted latent inhibition, dopaminergic hyperfunction, and altered limbic morphology in the offspring: a novel neurodevelopmental model of schizophrenia

Prenatal exposure to infection is associated with increased liability to schizophrenia, and it is believed that such an association is mediated by the maternal immune response, in particular, the proinflammatory cytokines released by the maternal immune system, which may disrupt fetal brain development. Impaired capacity to ignore irrelevant stimuli is one of the central deficits in schizophrenia, and is manifested, among others, in loss of latent inhibition (LI), a phenomenon whereby repeated inconsequential pre-exposure to a stimulus impairs its subsequent capacity to signal significant consequences. We tested the effects of prenatal immune activation induced by peripheral administration of the synthetic cytokine releaser polyriboinosinic-polyribocytidilic acid (poly I : C) to pregnant dams, on LI in juvenile and adult offspring. Consistent with the characteristic maturational delay of schizophrenia, prenatal immune activation did not affect LI in the juvenile offspring, but led to LI disruption in adulthood. Both haloperidol (0.1 mg/kg) and clozapine (5 mg/kg) reinstated LI in the adult offspring. In addition, prenatal immune activation led to a postpubertal emergence of increased sensitivity to the locomotor-stimulating effects of amphetamine and increased in vitro striatal dopamine release, as well as to morphological alterations in the hippocampus and the entorhinal cortex in the adult offspring, consistent with the well-documented mesolimbic dopaminergic and temporolimbic pathology in schizophrenia. These results suggest that prenatal poly I : C administration may provide a neurodevelopmental model of schizophrenia that reproduces a putative inducing factor; mimics the temporal course as well as some central abnormalities of the disorder; and predicts responsiveness to antipsychotic drugs. Neuropsychopharmacology (2003) 28, 1778-1789. advance online publication, 16 July 2003; doi:10.1038/sj.npp.1300248

Marked inhibition of mesolimbic dopamine release: a common feature of ethanol, morphine, cocaine and amphetamine abstinence in rats

Withdrawal of rats from chronic ethanol, morphine, cocaine and amphetamine resulted in a marked reduction in extracellular dopamine (DA) concentration in the ventral striatum as measured by microdialysis. Following ethanol and naloxone-precipitated morphine withdrawal, the time course of DA reduction paralleled that of the withdrawal symptomatology. On the other hand, following discontinuation of chronic cocaine, DA reduction was delayed by over 24 h but persisted for several days. After amphetamine withdrawal the fall in DA occurred more rapidly but the reduction also persisted for several days. The administration of the NMDA receptor antagonist, MK-801, to rats withdrawn from chronic ethanol, morphine or amphetamine, but not from chronic cocaine, readily reversed the fall in DA output. The reduction in extracellular DA during ethanol withdrawal was also reversed by SL 82.0715, another NMDA receptor antagonist.

Neurobiology of dopamine in schizophrenia

This chapter is an update on the dopamine (DA) imbalance in schizophrenia, including the evidence for subcortical hyperstimulation of D2 receptors underlying positive symptoms and cortical hypodopaminergia-mediating cognitive disturbances and negative symptoms. After a brief review of the anatomical neurocircuitry of this transmitter system as a background, we summarize the evidence for dopaminergic alterations deriving from pharmacological, postmortem, and imaging studies. This evidence supports a prominent role for D2 antagonism in the treatment of positive symptoms of schizophrenia and strongly suggests the need for alternative approaches to address the more challenging problem of negative symptoms and cognitive disturbances.

Long-term stimulant treatment of children with attention-deficit hyperactivity disorder symptoms. A randomized, double-blind, placebo-controlled trial

BACKGROUND

We wanted to study the effects of amphetamine on symptoms of attention-deficit hyperactivity disorder (ADHD) over a longer period than has been reported in previous studies of central stimulants in this condition.

METHODS

Sixty-two children, aged 6 to 11 years, meeting DSM-III-R symptom criteria for ADHD participated in a parallel-group design, randomized, double-blind, placebo-controlled study of amphetamine treatment. Treatment was not restricted to children with "pure" ADHD, ie, some had comorbid diagnoses. In the amphetamine group, children received active treatment for 15 months.

RESULTS

Amphetamine was clearly superior to placebo in reducing inattention, hyperactivity, and other disruptive behavior problems and tended to lead to improved results on the Wechsler Intelligence Scale for Children--Revised. Treatment failure rate was considerably lower and time to treatment failure was longer in the amphetamine group. Adverse effects were few and relatively mild.

CONCLUSION

The results of this long-term, placebo-controlled study of the central stimulant amphetamine in the treatment of ADHD indicate that there are remaining positive effects of the drug 15 months after starting treatment.

Dopaminergic mechanisms in idiopathic and drug-induced psychoses

Stimulant drugs such as cocaine and amphetamine are among the most commonly abused substances by schizophrenic patients. This may be due in part to aspects of the illness and treatment side effects that impel patients to use dopamine agonist drugs. Dopaminergic neural systems have been shown to mediate both stimulant drug effects and schizophrenia. Because of the hypothesized overlap in the pathophysiology of schizophrenia and the neurobiological effects of chronic stimulant use, the potential for serious complication of the primary disease by substance abuse exists. This article reviews the neurobiological mechanisms of behavioral sensitization and neurotoxicity associated with chronic stimulant administration in the context of pathophysiological theories of schizophrenia. Discussion focuses on the potential impact of stimulant use on the disease process as well as the manifest phenomenology and course of schizophrenia.

Potential adverse effects of amphetamine treatment on brain and behavior: a review

Amphetamine stimulants have been used medically since early in the twentieth century, but they have a high abuse potential and can be neurotoxic. Although they have long been used effectively to treat attention deficit hyperactivity disorder (ADHD) in children and adolescents, amphetamines are now being prescribed increasingly as maintenance therapy for ADHD and narcolepsy in adults, considerably extending the period of potential exposure. Effects of prolonged stimulant treatment have not been fully explored, and understanding such effects is a research priority. Because the pharmacokinetics of amphetamines differ between children and adults, reevaluation of the potential for adverse effects of chronic treatment of adults is essential. Despite information on the effects of stimulants in laboratory animals, profound species differences in susceptibility to stimulant-induced neurotoxicity underscore the need for systematic studies of prolonged human exposure. Early amphetamine treatment has been linked to slowing in height and weight growth in some children. Because the number of prescriptions for amphetamines has increased several fold over the past decade, an amphetamine-containing formulation is the most commonly prescribed stimulant in North America, and it is noteworthy that amphetamines are also the most abused prescription medications. Although early treatment does not increase risk for substance abuse, few studies have tracked the compliance and usage profiles of individuals who began amphetamine treatment as adults. Overall, there is concern about risk for slowed growth in young patients who are dosed continuously, and for substance abuse in patients first medicated in late adolescence or adulthood. Although most adult patients also use amphetamines effectively and safely, occasional case reports indicate that prescription use can produce marked psychological adverse events, including stimulant-induced psychosis. Assessments of central toxicity and adverse psychological effects during late adulthood and senescence of adults who receive prolonged courses of amphetamine treatment are warranted. Finally, identification of the biological factors that confer risk and those that offer protection is also needed to better specify the parameters of safe, long-term, therapeutic administration of amphetamines to adults.

Withdrawal from chronic amphetamine induces depressive-like behavioral effects in rodents

BACKGROUND

Amphetamine withdrawal and major depression share many behavioral commonalities in humans. Therefore, the examination of the behavioral effects of amphetamine withdrawal in rodents may provide insights into the neurobiological mechanisms underlying both disorders and aid in the development of animal models of depression that are sensitive to antidepressant agents.

METHODS

We examined the behavioral effects of withdrawal from chronic continuous infusion of amphetamine (via minipump) in three behavioral paradigms: the intracranial self-stimulation (ICSS) procedure in rats, the modified forced swim test in rats, and the tail suspension test in mice.

RESULTS

Amphetamine withdrawal resulted in a prolonged (5 day) deficit in brain reward function as assessed by elevations in ICSS thresholds. Using a similar regimen of amphetamine administration, we examined the behavioral effects of withdrawal in a modified rat forced swim test. Animals that were treated with the highest dose of amphetamine (10 mg/kg/day) exhibited increased climbing behavior and decreased immobility 24 hours after withdrawal; by the 48-hour testing time point, this effect had dissipated. In contrast, animals that had been pretreated with 5 mg/kg/day amphetamine exhibited a pronounced increase in immobility indicative of an increase in "depressive-like" behavior, coupled with decreases in swimming and climbing. In the mouse tail suspension test, both regimens of amphetamine pretreatment induced increases in immobility scores, also indicative of "depressive-like" behavior, 24 hours following withdrawal.

CONCLUSIONS

Withdrawal from chronic amphetamine administration results in behavioral changes that may be analogous to some aspects of depression in humans, such as reward deficits (i.e., elevations in brain reward thresholds) and behaviors opposite to those seen after treatment with antidepressant drugs, such as decreased immobility in the forced swim test and the tail suspension test.

The neuropharmacology of ADHD drugs in vivo: insights on efficacy and safety

Results from in vivo techniques, especially intracerebral microdialysis in freely-moving rats, have provided insights into potential mechanisms responsible for the efficacy and safety of catecholaminergic drugs for ADHD treatment. The drugs reviewed come from distinct pharmacological classes: psychostimulant releasing agents, eg d-amphetamine; psychostimulant reuptake inhibitors, eg dl-threo-methylphenidate (dl-MPH), and non-stimulant reuptake inhibitors, eg atomoxetine. Psychostimulants, which currently deliver the best efficacy in treating ADHD, exhibit the following characteristics on extraneuronal catecholamine concentrations in rodent brain in vivo: 1) They enhance the efflux and function of both noradrenaline and dopamine in the central nervous system. 2) The increase of dopamine efflux that they produce is not limited to cortical regions. 3) They have a rapid onset of action with no ceiling on drug effect. d-Amphetamine has a mechanism independent of neuronal firing rate, displacing intraneuronal stores of catecholamines, delaying their reuptake and inhibiting catabolism by monoamine oxidase. dl-MPH has an enigmatic, extraneuronal action that is neuronal firing rate-dependent and reuptake transporter-mediated, yet paradoxically, almost as powerful as that of d-amphetamine. In safety terms, these powerful catecholaminergic effects also make the psychostimulants liable for abuse. Since efficacy and safety derive from the same pharmacological mechanisms, it has not yet been possible to separate these two components. However, the development of once-daily psychostimulant formulations and a prodrug, lisdexamfetamine, has improved patient compliance and markedly reduced scope for their diversion/abuse. This review will discuss the in vivo pharmacological profiles of approved catecholaminergic drugs for treatment of ADHD and implications for their clinical efficacy and abuse liability.

The variable number of tandem repeats polymorphism of the dopamine transporter gene is not associated with significant change in dopamine transporter phenotype in humans

A 40 base polymorphism of a variable number of tandem repeats (VNTR) has been described in the 3' untranslated region of the gene (SLC6A3) coding for the dopamine transporter (DAT). Despite being located in the untranslated region of the gene, this polymorphism has been associated with clinical phenotypes associated with dysregulation of dopamine transmission, such as attention deficit hyperactivity disorder and cocaine-induced paranoia. To examine the neurochemical phenotype associated with this polymorphism, we compared amphetamine-induced dopamine release (measured as displacement of the radiotracer [123I]IBZM) and DAT expression (measured with [123I]beta-CIT) in the striatum with Single Photon Computerized Emission Tomography (SPECT). Our sample included 59 subjects, 31 healthy controls and 29 patients with schizophrenia. No significant association was found between VNTR polymorphism and amphetamine-induced dopamine release or DAT density in the total sample, nor when each diagnostic group was considered separately. Thus, we did not replicate the findings of two previous studies, which had suggested that the 9 repeat allele was associated with either an increased or decreased DAT expression, albeit in different patient populations.

Emergence of recreational drug abuse as a major risk factor for stroke in young adults

OBJECTIVE

To investigate the clinical and epidemiologic relations between recreational drug abuse and stroke in young persons.

DESIGN

A case-control study based on medical records.

SETTING

San Francisco General Hospital, a 400-bed municipal hospital.

PATIENTS

Consecutive sample of 214 patients aged 15 to 44 years, admitted between 1979 and 1988 with a diagnosis of ischemic or hemorrhagic stroke. An equal number of control patients admitted with diagnoses of status asthmaticus, acute appendicitis, or acute cholecystitis were matched to stroke patients by age, sex, and year of hospitalization.

MEASUREMENTS AND MAIN RESULTS

Seventy-three patients with stroke (34%) were drug abusers compared with 18 (8%) of the controls. In 47 patients with stroke, temporal proximity of drug administration (n = 34) or infectious endocarditis (n = 13) suggested a direct association between drug abuse and stroke. After controlling for other identifiable stroke risk factors, the estimated relative risk for stroke among drug abusers compared with that among non-drug abusers was 6.5 (95% CI, 3.1 to 13.6), and this increased to 49.4 (CI, 6.4 to 379.0) for those patients whose symptoms began within 6 hours of drug administration. Among patients less than 35 years of age, drug abuse was the most commonly identified potential predisposing condition (47%), and it was the only condition with a significantly elevated relative risk for stroke (11.7; CI, 3.2 to 42.5). Further, a substantial rise in the proportion of drug-related strokes was observed in the last 3 years of the study (31% in 1986 to 1988, compared with 15% in 1979 to 1985, P = 0.008). Cocaine, especially recently, was the drug used most frequently in drug-related strokes.

CONCLUSION

In an urban population such as ours, recreational drug abuse appears to be a prominent and growing risk factor for strokes in young adults.

Evaluation of Amphetamine-Related Hospitalizations and Associated Clinical Outcomes and Costs in the United States

IMPORTANCE

Despite indications of increasing amphetamine availability and psychostimulant deaths in the United States, evidence across data sources is mixed, and data on amphetamine-related hospitalizations are lacking.

OBJECTIVE

To clarify trends in amphetamine-related hospitalizations and their clinical outcomes and costs in the United States.

DESIGN, SETTING, AND PARTICIPANTS

This repeated, cross-sectional study used hospital discharge data from the Healthcare Cost and Utilization Project National Inpatient Sample. The nationally representative sample included US adults (n = 1 292 300) who had amphetamine-related hospitalizations between January 1, 2003, and December 31, 2015. Multivariable logistic and Poisson regression models were used to examine in-hospital mortality and length of stay. Analysis of these data was conducted from November 2017 to August 2018.

EXPOSURE

Amphetamine dependence or abuse or amphetamine poisoning.

MAIN OUTCOMES AND MEASURES

Annual hospitalizations, in-hospital mortality, length of stay, transfer to another facility, and costs.

RESULTS

Over the 2003 to 2015 study period, there were 1 292 300 weighted amphetamine-related hospitalizations. Of this population, 541 199 (41.9%) were female and 749 392 (58.1%) were male, with a mean age of 37.5 years (95% CI, 37.4-37.7 years). Amphetamine-related hospitalizations, compared with other hospitalizations, were associated with age younger than 65 years (98.0% vs 58.0%; P < .001), male sex (60.3% [95% CI, 59.7%-60.8%] vs 41.1% [95% CI, 40.9%-41.3%]), Medicaid coverage (51.2% [95% CI, 49.8%-52.7%] vs 17.8% [95% CI, 17.5%-18.1%]), and residence in the western United States (58.5% [95% CI, 55.9%-61.0%] vs 18.9% [95% CI, 18.0%-19.8%]). Amphetamine-related hospitalizations declined between 2005 and 2008, and then increased from 55 447 hospitalizations (95% CI, 44 936-65 959) in 2008 to 206 180 hospitalizations (95% CI, 95% CI, 189 188-223 172) in 2015. Amphetamine-related hospitalizations increased to a greater degree than hospitalizations associated with other substances. Adjusted mean length of stay (5.9 [95% CI, 5.8-6.0] vs 4.7 [95% CI, 4.7-4.8] days; P < .001), transfer to another facility (26.0% [95% CI, 25.3%-26.8%] vs 18.5% [95% CI, 18.3%-18.6%]; P < .001), and mean in-hospital mortality (28.3 [95% CI, 26.2-30.4] vs 21.9 [95% CI, 21.6-22.1] deaths per 1000 hospitalizations; P < .001) were higher for amphetamine-related than other hospitalizations. Annual hospital costs related to amphetamines increased from $436 million (95% CI, $312 million-$559 million) in 2003 to $2.17 billion (95% CI, $1.95 billion-$2.39 billion) by 2015.

CONCLUSIONS AND RELEVANCE

Given that amphetamine-related hospitalizations and costs substantially increased between 2003 and 2015, pharmacologic and nonpharmacologic therapies for amphetamine use disorders and a coordinated public health response are needed to curb these rising rates.

Stimulant abuse: pharmacology, cocaine, methamphetamine, treatment, attempts at pharmacotherapy

The high prevalence of stimulant abuse and its harmful consequences make the screening, diagnosis, and referral for treatment of persons with stimulant abuse a top concern for primary care providers. Having a working knowledge of use patterns, clinical symptomatology, end-organ effects, and advances in treatment of stimulant abuse is essential. Although cocaine and amphetamine have different use patterns, duration of action, and so forth, the consequences of use are remarkably similar. Primary care is at the forefront of screening, brief risk reduction interventions, and diagnosis of medical sequelae, with referral to addiction specialist treatment when necessary.

Pharmacological Treatment of Methamphetamine/Amphetamine Dependence: A Systematic Review

BACKGROUND

Stimulant drugs are second only to cannabis as the most widely used class of illicit drug globally, accounting for 68 million past-year consumers. Dependence on amphetamines (AMPH) or methamphetamine (MA) is a growing global concern. Yet, there is no established pharmacotherapy for AMPH/MA dependence. A comprehensive assessment of the research literature on pharmacotherapy for AMPH/MA dependence may inform treatment guidelines and future research directions.

METHODS

We systematically reviewed the peer-reviewed literature via the electronic databases PubMed, EMBASE, CINAHL and SCOPUS for randomised controlled trials reported in the English language examining a pharmacological treatment for AMPH/MA dependence or use disorder. We included all studies published to 19 June 2019. The selected studies were evaluated for design; methodology; inclusion and exclusion criteria; sample size; pharmacological and (if included) psychosocial interventions; length of follow-up and follow-up schedules; outcome variables and measures; results; overall conclusions and risk of bias. Outcome measures were any reported impact of treatment related to AMPH/MA use.

RESULTS

Our search returned 43 studies that met our criteria, collectively enrolling 4065 participants and reporting on 23 individual pharmacotherapies, alone or in combination. Disparate outcomes and measures (n = 55 for the primary outcomes) across studies did not allow for meta-analyses. Some studies demonstrated mixed or weak positive signals (often in defined populations, e.g. men who have sex with men), with some variation in efficacy signals dependent on baseline frequency of AMPH/MA use. The most consistent positive findings have been demonstrated with stimulant agonist treatment (dexamphetamine and methylphenidate), naltrexone and topiramate. Less consistent benefits have been shown with the antidepressants bupropion and mirtazapine, the glutamatergic agent riluzole and the corticotropin releasing factor (CRF-1) antagonist pexacerfont; whilst in general, antidepressant medications (e.g. selective serotonin reuptake inhibitors [SSRIs], tricyclic antidepressants [TCAs]) have not been effective in reducing AMPH/MA use.

CONCLUSIONS

No pharmacotherapy yielded convincing results for the treatment of AMPH/MA dependence; mostly studies were underpowered and had low treatment completion rates. However, there were positive signals from several agents that warrant further investigation in larger scale studies; agonist therapies show promise. Common outcome measures should include change in use days. Future research must address the heterogeneity of AMPH/MA dependence (e.g. coexisting conditions, severity of disorder, differences between MA and AMPH dependence) and the role of psychosocial intervention.

Dysbindin-1 modulates prefrontal cortical activity and schizophrenia-like behaviors via dopamine/D2 pathways

Dysbindin-1 regulates D2-receptor trafficking and is implicated in schizophrenia and related cognitive abnormalities, but whether this molecular effect mediates the clinical manifestations of the disorder is unknown. We explored in dysbindin-1-deficient mice (dys-/-) (1) schizophrenia-related behaviors, (2) molecular and electrophysiological changes in medial prefrontal cortex (mPFC) and (3) the dependence of these on D2-receptor stimulation. Dysbindin-1 disruption altered dopamine-related behaviors and impaired working memory under challenging/stressful conditions. Dys-/- pyramidal neurons in mPFC layers II/III were hyperexcitable at baseline but hypoexcitable following D2 stimulation. Dys-/- were also respectively more and less sensitive to D2 agonist- and antagonist-induced behavioral effects. Dys-/- had reduced expression of Ca(2+)/calmodulin-dependent protein kinase II (CaMKII) and CaMKKβ in mPFC. Chronic D2 agonist treatment reproduced these changes in protein expression, and some of the dys-/- behavioral effects. These results elucidate dysbindin's modulation of D2-related behavior, cortical activity and mPFC CaMK components, implicating cellular and molecular mechanisms of the association of dysbindin with psychosis.

Amphetamine psychosis and psychotic symptoms

Amphetamine psychosis has been considered to be a pharmacologic model of schizophrenia. Fifteen previously reported cases were reviewed in which experimental induction of amphetamine psychosis occurred in nonschizophrenic drug abusers. Seven (possibly ten) cases manifested Schneider's first rank symptoms and all had World Health Organization Present-State Exam symptoms which discriminated schizophrenia. This observation draws further parallels between the phenomenology of amphetamine psychosis and schizophrenic symptoms.

Amphetamine primes motivation to gamble and gambling-related semantic networks in problem gamblers

Previous research suggests that gambling can induce effects that closely resemble a psychostimulant drug effect. Modest doses of addictive drugs can prime motivation for drugs with similar properties. Together, these findings imply that a dose of a psychostimulant drug could prime motivation to gamble in problem gamblers. This study assessed priming effects of oral D-amphetamine (AMPH) (30 mg) in a within-subject, counter-balanced, placebo-controlled design in problem gamblers (n=10), comorbid gamblerdrinkers (n=6), problem drinkers (n=8), and healthy controls (n=12). Modified visual analog scales assessed addictive motivation and subjective effects. A modified rapid reading task assessed pharmacological activation of words from motivationally relevant and irrelevant semantic domains (Gambling, Alcohol, Positive Affect, Negative Affect, Neutral). AMPH increased self-reported motivation for gambling in problem gamblers. Severity of problem gambling predicted positive subjective effects of AMPH and motivation to gamble under the drug. There was little evidence that AMPH directly primed motivation for alcohol in problem drinkers. On the reading task, AMPH produced undifferentiated improvement in reading speed to all word classes in Nongamblers. By contrast, in the two problem gambler groups, AMPH improved reading speed to Gambling words while profoundly slowing reading speed to motivationally irrelevant Neutral words. The latter finding was interpreted as directly congruent with models, which contend that priming of addictive motivation involves a linked suppression of motivationally irrelevant stimuli. This study provides experimental evidence that psychostimulant-like neurochemical activation is an important component of gambling addiction.

Stereotypy in monkeys and humans

Stereotyped movements are described in monkeys and humans and are classified as arising from constraint, sensory deprivation in infancy, amphetamine treatment or psychotic states. It is argued that, with the exception of cage stereotypies, stereotyped behaviour is evidence of abnormality in the nervous system consequent upon distorted maturational processes, organic defect or biochemical disturbance. Stereotypy is associated with a state of cognitive inflexibility and social and sensory isolation in humans and monkeys. It is suggested that, while no simple biochemical disturbance in the brain can describe these various occurrences of stereotypy, the cross-species occurrence of a syndrome of isolation, cognitive inflexibility and stereotypy implies a related mechanism mediating these divergent effects. If stereotypy is regarded as a consequence of failure to use sensory input to direct behaviour, therapeutic regimes designed to stimulate responsive behaviours and social interactions are more likely to be effective in the long run than direct attempts to suppress stereotypy.

Sensitization to amphetamine, but not PCP, impairs attentional set shifting: reversal by a D1 receptor agonist injected into the medial prefrontal cortex

RATIONALE

Repeated exposure to psychomotor stimulants can lead to sensitization to their effects, and sensitization has been implicated in the pathophysiology of schizophrenia and drug abuse. These disorders are characterized by cognitive deficits, particularly in prefrontally mediated executive function.

OBJECTIVE

The present experiments were conducted to investigate the effects of sensitizing regimens of amphetamine and phencyclidine (PCP) on attentional set shifting.

METHODS

Rats received injections of amphetamine, PCP or saline three times per week for 5 weeks. Four weeks later, rats were trained to dig for food in one of two bowls, each bowl having an odour and a texture. Only one dimension (odour or texture) correctly predicted which bowl was baited. Rats were then tested on a series of discriminations including those requiring an intra-dimensional shift (IDS), an extra-dimensional shift (EDS) or a reversal of previously relevant and irrelevant stimuli.

RESULTS

Rats sensitized to amphetamine performed normally on the IDS, but were impaired on the EDS, as well as on reversal discriminations. PCP-sensitized rats were unaffected on any of the discriminations. In amphetamine-sensitized rats the deficit at the EDS stage was reversed by infusion of the D(1) receptor agonist SKF38393 into the medial prefrontal cortex (mPFC).

CONCLUSIONS

Results show that the amphetamine-sensitized state impairs prefrontally mediated attentional set shifting. This is consistent with cognitive deficits in schizophrenia and addiction, and with the evidence that amphetamine sensitization is accompanied by functional changes in the mPFC. These results further add to a growing literature showing that activating D(1) receptors in the mPFC improves aspects of cognition.

Effect of stimulants on 24-h ambulatory blood pressure in children with ADHD: a double-blind, randomized, cross-over trial

Millions of children with attention deficit hyperactivity disorder (ADHD) are treated with stimulant medications. To evaluate cardiovascular risk, 24-h ambulatory blood pressure monitoring (ABPM) was performed on and off medication. Thirteen subjects underwent APBM both on stimulant therapy and placebo using a placebo-controlled, double-blind, randomized, cross-over design. After a 3-day run-in followed by a 24-h monitoring period, subjects crossed over to the alternate therapy for repeated ABPM. Subjects demonstrated elevations in most hemodynamic parameters derived from ABPM during the active treatment period. Total diastolic blood pressure (69.7 mmHg vs 65.8 mmHg, p =0.02) and waking diastolic blood pressure (75.5 mmHg vs 72.3 mmHg, p =0.03) were significantly higher during active treatment. Total heart rate was also significantly higher during active treatment (85.5 beats/min vs 79.9 beats/min, p =0.004). The rate-pressure product (the product of systolic blood pressure x heart rate), an index of myocardial oxygen demand, was higher during active treatment (9,958 vs 9,076, p =0.008). This study provides evidence for a possible negative cardiovascular effect of stimulant medications in children with ADHD. This potential cardiovascular risk should be balanced against the beneficial behavioral effects of this class of medication.

AKT kinase activity is required for lithium to modulate mood-related behaviors in mice

Bipolar disorder (BP) is a debilitating psychiatric disorder, affecting ∼2% of the worldwide population, for which the etiological basis, pathogenesis, and neurocircuitry remain poorly understood. Individuals with BP suffer from recurrent episodes of mania and depression, which are commonly treated with the mood stabilizer lithium. However, nearly half of BP patients do not respond adequately to lithium therapy and the clinically relevant mechanisms of lithium for mood stabilization remain elusive. Here, we modeled lithium responsiveness using cellular assays of glycogen synthase kinase 3 (GSK-3) signaling and mood-related behavioral assays in inbred strains of mice that differ in their response to lithium. We found that activating AKT through phosphosrylation of a key regulatory site (Thr308) was associated with lithium response-activation of signaling pathways downstream of GSK-3 in cells and attenuation of mood-related behaviors in mice-and this response was attenuated by selective and direct inhibition of AKT kinase activity. Conversely, the expression of constitutively active AKT1 in both the cellular and behavioral assays conferred lithium sensitivity. In contrast, selective and direct GSK-3 inhibition by the ATP-competitive inhibitor CHIR99021 bypassed the requirement for AKT activation and modulated behavior in both lithium-responsive and non-responsive mouse strains. These results distinguish the mechanism of action of lithium from direct GSK-3 inhibition both in vivo and in vitro, and highlight the therapeutic potential for selective GSK-3 inhibitors in BP treatment.

Withdrawal from chronic amphetamine elevates baseline intracranial self-stimulation thresholds

Intracranial self-stimulation was assessed before, within, and after a chronic amphetamine treatment regimen. Amphetamine was given twice daily 5 days per week for 6 weeks at dosages escalating from 1 to 10 mg/kg per injection. Lateral hypothalamic self-stimulation rate-frequency functions were taken 36 h after the last injection in each weekly series and weekly for 3 weeks following the last injection. Frequency thresholds increased and maximal response rates decreased progressively as a function of amphetamine withdrawal during treatment; each returned to near normal levels within 2 weeks of the last injection. When subsequently tested under amphetamine, animals previously receiving the 6-week amphetamine treatment regimen had self-stimulation thresholds and maximal response rates that did not differ significantly from those of saline-treated control animals. These data confirm that chronic amphetamine treatment results in a dependence syndrome characterized in part by a phasic depression in the brain mechanism mediating the reinforcing effects of lateral hypothalamic electrical stimulation.

Psychosis with Methylphenidate or Amphetamine in Patients with ADHD

BACKGROUND

The prescription use of the stimulants methylphenidate and amphetamine for the treatment of attention deficit-hyperactivity disorder (ADHD) has been increasing. In 2007, the Food and Drug Administration mandated changes to drug labels for stimulants on the basis of findings of new-onset psychosis. Whether the risk of psychosis in adolescents and young adults with ADHD differs among various stimulants has not been extensively studied.

METHODS

We used data from two commercial insurance claims databases to assess patients 13 to 25 years of age who had received a diagnosis of ADHD and who started taking methylphenidate or amphetamine between January 1, 2004, and September 30, 2015. The outcome was a new diagnosis of psychosis for which an antipsychotic medication was prescribed during the first 60 days after the date of the onset of psychosis. To estimate hazard ratios for psychosis, we used propensity scores to match patients who received methylphenidate with patients who received amphetamine in each database, compared the incidence of psychosis between the two stimulant groups, and then pooled the results across the two databases.

RESULTS

We assessed 337,919 adolescents and young adults who received a prescription for a stimulant for ADHD. The study population consisted of 221,846 patients with 143,286 person-years of follow up; 110,923 patients taking methylphenidate were matched with 110,923 patients taking amphetamines. There were 343 episodes of psychosis (with an episode defined as a new diagnosis code for psychosis and a prescription for an antipsychotic medication) in the matched populations (2.4 per 1000 person-years): 106 episodes (0.10%) in the methylphenidate group and 237 episodes (0.21%) in the amphetamine group (hazard ratio with amphetamine use, 1.65; 95% confidence interval, 1.31 to 2.09).

CONCLUSIONS

Among adolescents and young adults with ADHD who were receiving prescription stimulants, new-onset psychosis occurred in approximately 1 in 660 patients. Amphetamine use was associated with a greater risk of psychosis than methylphenidate. (Funded by the National Institute of Mental Health and others.).