Methadone patients exhibit increased startle and cortisol response after intravenous yohimbine

Metabolic profiles associated with opioid use and opioid use disorder: a narrative review of the literature

Purpose of Review

Opioid use disorder (OUD) is a chronic, relapsing condition that is epidemic in the USA. OUD is associated with serious adverse consequences, including higher incarceration rates, impaired medical and mental health, and overdose-related fatalities. Several medications with demonstrated clinical efficacy in reducing opioid use are approved to treat OUD. However, there is evidence that medications for OUD cause metabolic impairments, which raises concerns over the long-term metabolic health of individuals recovering from OUD. Here, we summarize the scientific literature on the metabolic effects of the use of opioids, including medications for treating OUD.

Recent Findings

Our findings showed lower body weight and adiposity, and better lipid profiles in individuals with OUD. In individuals with diabetes mellitus, opioid use was associated with lower blood glucose levels. In contrast, among individuals without underlying metabolic conditions, opioids promoted insulin resistance. Treatment of OUD patients with the agonists methadone or buprenorphine caused weight gain, increased liking and intake of sugar, and impaired lipid profile and glucose metabolism, whereas treatment with the antagonist naltrexone demonstrated evidence for reduced sweet preferences.

Summary

Our findings highlighted a gap in knowledge regarding the safety of medications for OUD. Further research is needed to determine how best to reduce the risk of metabolic disorder in the treatment of OUD with opioid agonists versus antagonists.

Acute prazosin administration does not reduce stressor reactivity in healthy adults

RATIONALE

Norepinephrine plays a critical role in the stress response. Clarifying the psychopharmacological effects of norepinephrine manipulation on stress reactivity in humans has important implications for basic neuroscience and treatment of stress-related psychiatric disorders, such as posttraumatic stress disorder and alcohol use disorders. Preclinical research implicates the norepinephrine alpha-1 receptor in responses to stressors. The No Shock, Predictable Shock, Unpredictable Shock (NPU) task is a human laboratory paradigm that is well positioned to test cross-species neurobiological stress mechanisms and advance experimental therapeutic approaches to clinical trials testing novel treatments for psychiatric disorders.

OBJECTIVES

We hypothesized that acute administration of prazosin, a noradrenergic alpha-1 antagonist, would have a larger effect on reducing stress reactivity during unpredictable, compared to predictable, stressors in the NPU task.

METHODS

We conducted a double-blind, placebo-controlled, crossover randomized controlled trial in which 64 healthy adults (32 female) completed the NPU task at two visits (2 mg prazosin vs. placebo).

RESULTS

A single acute dose of 2 mg prazosin did not reduce stress reactivity in a healthy adult sample. Neither NPU startle potentiation nor self-reported anxiety was reduced by prazosin (vs. placebo) during unpredictable (vs. predictable) stressors.

CONCLUSIONS

Further research is needed to determine whether this failure to translate preclinical neuroscience to human laboratory models is due to methodological factors (e.g., acute vs. chronic drug administration, brain penetration, study population) and/or suggests limited clinical utility of noradrenergic alpha-1 antagonists for treating stress-related psychiatric disorders.

Probing for Neuroadaptations to Unpredictable Stressors in Addiction: Translational Methods and Emerging Evidence

Stressors clearly contribute to addiction etiology and relapse in humans, but our understanding of specific mechanisms remains limited. Rodent models of addiction offer the power, flexibility, and precision necessary to delineate the causal role and specific mechanisms through which stressors influence alcohol and other drug use. This review describes a program of research using startle potentiation to unpredictable stressors that is well positioned to translate between animal models and clinical research with humans on stress neuroadaptations in addiction. This research rests on a solid foundation provided by three separate pillars of evidence from (a) rodent behavioral neuroscience on stress neuroadaptations in addiction, (b) rodent affective neuroscience on startle potentiation, and (c) human addiction and affective science with startle potentiation. Rodent stress neuroadaptation models implicate adaptations in corticotropin-releasing factor and norepinephrine circuits within the central extended amygdala following chronic alcohol and other drug use that mediate anxious behaviors and stress-induced reinstatement among drug-dependent rodents. Basic affective neuroscience indicates that these same neural mechanisms are involved in startle potentiation to unpredictable stressors in particular (vs. predictable stressors). We believe that synthesis of these evidence bases should focus us on the role of unpredictable stressors in addiction etiology and relapse. Startle potentiation in unpredictable stressor tasks is proposed to provide an attractive and flexible test bed to encourage tight translation and reverse translation between animal models and human clinical research on stress neuroadaptations. Experimental therapeutics approaches focused on unpredictable stressors hold high promise to identify, repurpose, or refine pharmacological and psychosocial interventions for addiction.

Effect of combined opioid receptor and α2-adrenoceptor blockade on anxiety and electrically evoked startle responses

The R3 component of the electrically evoked blink reflex may form part of a startle reaction. Acoustic startle responses are augmented by yohimbine, an α₂-adrenoceptor antagonist that blocks α₂-autoreceptors, and are potentiated by opioid receptor blockade. To investigate these influences on electrically evoked startle responses, 16 mg yohimbine, with (16 participants) or without 50 mg naltrexone (23 participants), was administered in separate double-blind placebo-controlled cross-over experiments. In each experiment, R3 (a probable component of the startle response) was examined before and after high-frequency electrical stimulation of the forearm, a procedure that initiates inhibitory pain controls. Anxiety and somatic symptoms were greater after yohimbine than placebo, and were potentiated by naltrexone. Pain ratings for the electrically evoked startle stimuli decreased after high-frequency electrical stimulation in the placebo session but remained stable after drug administration. Yohimbine with naltrexone, but not yohimbine alone, also blocked an inhibitory effect of high-frequency electrical stimulation on electrically evoked sharp sensations and R3. Together, the findings suggest that adding naltrexone to yohimbine potentiated anxiety and blocked inhibitory influences of high-frequency electrical stimulation on electrically evoked sensations and startle responses. Thus, opioid peptides could reduce activity in nociceptive and startle-reflex pathways, or inhibit crosstalk between these pathways. Failure of this inhibitory opioid influence might be important in chronically painful conditions that are aggravated by startle stimuli.

Elevated Hair Cortisol Levels among Heroin Addicts on Current Methadone Maintenance Compared to Controls

Whether methadone maintenance treatment (MMT) can improve the basal function of the hypothalamic–pituitary–adrenal (HPA) axis, which is suppressed by long-term heroin consumption, is a matter of debate. The stress state and depression and anxiety symptoms may affect the basal activity of the HPA axis in MMT patients. However, the effect of psychological factors on HPA activity was not simultaneously controlled in previous studies. This study investigated differences in HPA basal activity between MMT patients and controls using psychological variables as covariates. The participants included 52 MMT patients and 41 age-matched, non-heroin-dependent controls. Psychological states were self-reported with the Perceived Stress Scale, Self-Rating Depression Scale and Self-Rating Anxiety Scale. The hair cortisol level was adopted as a biomarker of HPA basal activity and was determined with liquid chromatography tandem mass spectrometry. The results revealed that MMT patients had significantly higher hair cortisol levels than the controls (p<0.05), but the difference was not significant (p>0.05) when the perceived stress, depression and anxiety scores were used as covariates. We concluded that patients with long-term MMT showed higher basal activity of the HPA axis. The high chronic stress state and increase in depression and anxiety symptoms may mask the suppression effect of methadone on the HPA activity.

Substance use modulates stress reactivity: Behavioral and physiological outcomes

Drug addiction is a major public health concern in the United States costing taxpayers billions in health care costs, lost productivity and law enforcement. However, the availability of effective treatment options remains limited. The development of novel therapeutics will not be possible without a better understanding of the addicted brain. Studies in both clinical and preclinical models indicate that chronic drug use leads to alterations in the body and brain's response to stress. Dysregulation of the hypothalamic-pituitary-adrenal (HPA) axis may shed light on the ability of stress to increase vulnerability to relapse. Further, within both the HPA axis and limbic brain regions, corticotropin-releasing factor (CRF) is critically involved in the brain's response to stress. Alterations in both central and peripheral CRF activity seen following chronic drug use provide a mechanism by which substance use can alter stress reactivity, thus mediating addictive phenotypes. While many reviews have focused on how stress alters drug-mediated changes in physiology and behavior, the goal of this review is to focus on how substance use alters responses to stress.

New mechanisms and perspectives in nicotine withdrawal

Diseases associated with tobacco use constitute a major health problem worldwide. Upon cessation of tobacco use, an unpleasant withdrawal syndrome occurs in dependent individuals. Avoidance of the negative state produced by nicotine withdrawal represents a motivational component that promotes continued tobacco use and relapse after smoking cessation. With the modest success rate of currently available smoking cessation therapies, understanding mechanisms involved in the nicotine withdrawal syndrome are crucial for developing successful treatments. Animal models provide a useful tool for examining neuroadaptative mechanisms and factors influencing nicotine withdrawal, including sex, age, and genetic factors. Such research has also identified an important role for nicotinic receptor subtypes in different aspects of the nicotine withdrawal syndrome (e.g., physical vs. affective signs). In addition to nicotinic receptors, the opioid and endocannabinoid systems, various signal transduction pathways, neurotransmitters, and neuropeptides have been implicated in the nicotine withdrawal syndrome. Animal studies have informed human studies of genetic variants and potential targets for smoking cessation therapies. Overall, the available literature indicates that the nicotine withdrawal syndrome is complex, and involves a range of neurobiological mechanisms. As research in nicotine withdrawal progresses, new pharmacological options for smokers attempting to quit can be identified, and treatments with fewer side effects that are better tailored to the unique characteristics of patients may become available. This article is part of the Special Issue entitled 'The Nicotinic Acetylcholine Receptor: From Molecular Biology to Cognition'.

Stress modulates illness-course of substance use disorders: a translational review

Childhood trauma and post-childhood chronic/repeated stress could increase the risk of a substance use disorder by affecting five stages of addiction illness-course: (a) initial experimentation with substances; (b) shifting from experimental to regular use; (c) escalation from regular use to abuse or dependence; (d) motivation to quit; and (e) risk of (re-)lapse. We reviewed the human literature on relationships between stress and addiction illness-course. We explored per illness-course stage: (i) whether childhood trauma and post-childhood chronic/repeated stress have comparable effects and (ii) whether effects cut across classes of substances of abuse. We further discuss potential underlying mechanisms by which stressors may affect illness-course stages for which we relied on evidence from studies in animals and humans. Stress and substances of abuse both activate stress and dopaminergic motivation systems, and childhood trauma and post-childhood stressful events are more chronic and occur more frequently in people who use substances. Stressors increase risk to initiate early use potentially by affecting trait-like factors of risk-taking, decision making, and behavioral control. Stressors also accelerate transition to regular use potentially due to prior effects of stress on sensitization of dopaminergic motivation systems, cross-sensitizing with substances of abuse, especially in people with high trait impulsivity who are more prone to sensitization. Finally, stressors increase risk for abuse and dependence, attenuate motivation to quit, and increase relapse risk potentially by intensified sensitization of motivational systems, by a shift from positive to negative reinforcement due to sensitization of the amygdala by corticotropin releasing factor, and by increased sensitization of noradrenergic systems. Stress generally affects addiction illness-course across stressor types and across classes of substances of abuse.

Yohimbine-induced amygdala activation in pathological gamblers: a pilot study

Rationale and Objectives

There is evidence that drug addiction is associated with increased physiological and psychological responses to stress. In this pilot functional magnetic resonance imaging (fMRI) study we assessed whether a prototype behavioral addiction, pathological gambling (PG), is likewise associated with an enhanced response to stress.

Methods

We induced stress by injecting yohimbine (0.2–0.3 mg/kg, IV), an alpha-2 adrenoceptor antagonist that elicits stress-like physiological and psychological effects in humans and in laboratory animals, to four subjects with PG and to five non-gamblers mentally healthy control subjects. Their fMRI brain responses were assessed along with subjective stress and gambling urges ratings.

Results

Voxelwise analyses of data sets from individual subjects, utilizing generalized linear model approach, revealed significant left amygdala activation in response to yohimbine across all PG subjects. This amygdala effect was not observed in the five control individuals. Yohimbine elicited subjective stress ratings in both groups with greater (albeit not statically significantly) average response in the PG subjects. On the other hand, yohimbine did not induce urges to gamble.

Conclusions

The present data support the hypothesis of brain sensitization to pharmacologically-induced stress in PG.

Protracted manifestations of acute dependence after a single morphine exposure

RATIONALE

Acute opiate exposure produces a state of dependence in humans and animals, which is revealed by signs and symptoms of withdrawal precipitated by opioid receptor antagonists. The physiological changes that underlie this state of acute dependence develop rapidly and can persist long after the end of chronic opiate exposure.

OBJECTIVES

The purpose of this investigation was to determine the persistence of acute dependence after a single morphine exposure in rodents, focusing on changes in behavior thought to reflect the negative emotional consequences of withdrawal.

METHODS

The acoustic startle reflex and conditioned place aversion were measured following naloxone administration at different time points after a single morphine exposure.

RESULTS

Naloxone administration produced significant potentiation of acoustic startle-a form of anxiety-like behavior-for at least 80 days after one exposure to morphine. In contrast, naloxone produced a conditioned place aversion 24 h but not 20 days after one morphine exposure.

CONCLUSIONS

Together with existing literature, these results suggest acute as well as chronic opiate exposure leave rodents persistently vulnerable to express anxiety-like behavior in response to opioid receptor antagonists or stressful experience. The adaptations in brain function that underlie this protracted state of dependence may provide a foundation for the escalation of withdrawal severity that develops over repeated opiate exposure, and increase the likelihood of progression from casual drug use to compulsive drug abuse.

Prenatal exposure to methadone and buprenorphine: a review of the potential effects on cognitive development

The amount of opioid users receiving opioid maintenance therapy has increased significantly over the last few years. As a result, an increasing number of children are prenatally exposed to long-lasting opioids such as methadone and buprenorphine. This article reviews the literature on the cognitive development of children born to mothers in opioid maintenance therapy. Topics discussed are the effects of prenatal exposure on prematurity, somatic growth, brain volume, myelination, and the endocrine and neurotransmitter system. Social-environmental factors, including parental functioning, as well as genetic factors are also described. Areas requiring further research are identified.

Acoustic startle reduction in cocaine dependence persists for 1 year of abstinence

RATIONALE

Chronic cocaine use results in long-lasting neurochemical changes that persist beyond the acute withdrawal period. Previous work from our group reported a profound reduction in the acoustic startle response (ASR) in chronic cocaine-dependent subjects in early abstinence compared to healthy controls that may be related to long-lasting neuroadaptations following withdrawal from chronic cocaine use.

OBJECTIVES

This study aims to investigate the persistence and time course of the decrements in the ASR of cocaine-dependent subjects during prolonged abstinence.

METHODS

Seventy-six cocaine-dependent (COC) subjects and 30 controls (CONT) were tested, the former after a period of heavy cocaine dependence. COC subjects were retested sequentially for 1 year of abstinence or until relapse. ASR testing was conducted at 3-dB levels and the eye-blink component of the startle response was quantified with electromyographic recording of the orbicularis oculi muscle.

RESULTS

While there was no difference in startle magnitude between CONT and COC in early abstinence, by day 40 of abstinence COC subjects exhibited a statistically significant decline (p = 0.0057) in ASR magnitude as compared with CONT and this decrement persisted for up to 1 year of abstinence (p = 0.0165). In addition, startle latency was slower in COC subjects as compared with CONT at all stages of abstinence.

CONCLUSIONS

These results replicate and expand upon the earlier finding that chronic cocaine use impairs the ASR in a manner that persists beyond the acute withdrawal period. This phenomenon may represent a biological measure of long-term neural changes accompanying cocaine dependence and subsequent withdrawal.

The World Federation of Societies of Biological Psychiatry (WFSBP) guidelines for the biological treatment of substance use and related disorders. Part 2: Opioid dependence

OBJECTIVES

To develop evidence-based practice guidelines for the pharmacological treatment of opioid abuse and dependence.

METHODS

An international task force of the World Federation of Societies of Biological Psychiatry (WFSBP) developed these practice guidelines after a systematic review of the available evidence pertaining to the treatment of opioid dependence. On the basis of the evidence, the Task Force reached a consensus on practice recommendations, which are intended to be clinically and scientifically meaningful for physicians who treat adults with opioid dependence. The data used to develop these guidelines were extracted primarily from national treatment guidelines for opioid use disorders, as well as from meta-analyses, reviews, and publications of randomized clinical trials on the efficacy of pharmacological and other biological treatments for these disorders. Publications were identified by searching the MEDLINE database and the Cochrane Library. The literature was evaluated with respect to the strength of evidence for efficacy, which was categorized into one of six levels (A-F).

RESULTS

There is an excellent evidence base supporting the efficacy of methadone and buprenorphine or the combination of buprenorphine and naloxone for the treatment of opioid withdrawal, with clonidine and lofexidine as secondary or adjunctive medications. Opioid maintenance with methadone and buprenorphine is the best-studied and most effective treatment for opioid dependence, with heroin and naltrexone as second-line medications.

CONCLUSIONS

There is enough high quality data to formulate evidence-based guidelines for the treatment of opioid abuse and dependence. This task force report provides evidence for the efficacy of a number of medications to treat opioid abuse and dependence, particularly the opioid agonists methadone or buprenorphine. These medications have great relevance for clinical practice.

Translational research in addiction: toward a framework for the development of novel therapeutics

The development of novel substance use disorder (SUD) therapeutics is insufficient to meet the medical needs of a growing SUD patient population. The identification of translatable SUD models and tests is a crucial step in establishing a framework for SUD therapeutic development programs. The present review begins by identifying the clinical features of SUDs and highlights the narrow regulatory end-point required for approval of a novel SUD therapeutic. A conceptual overview of dependence is provided, followed by identification of potential intervention targets in the addiction cycle. The main components of the addiction cycle provide the framework for a discussion of preclinical models and their clinical analogs, all of which are focused on isolated behavioral end-points thought to be relevant to the persistence of compulsive drug use. Thus, the greatest obstacle to successful development is the gap between the multiplicity of preclinical and early clinical end-points and the regulatory end-point of sustained abstinence. This review proposes two pathways to bridging this gap: further development and validation of the preclinical extended access self-administration model; inclusion of secondary end-points comprising all of the measures highlighted in the present discussion in Phase 3 trials. Further, completion of the postdictive validation of analogous preclinical and clinical assays is of high priority. Ultimately, demonstration of the relevance and validity of a variety of end-points to the ultimate goal of abstinence will allow researchers to identify truly relevant therapeutic mechanisms and intervention targets, and establish a framework for SUD therapeutic development that allows optimal decision-making and resource allocation.

Heroin reduces startle and cortisol response in opioid-maintained heroin-dependent patients

Heroin dependence (HD) is a chronic relapsing brain disorder characterized by a compulsion to seek and use heroin. Stress is seen as a key factor for heroin use. Methadone maintenance and the prescription of pharmaceutical heroin [diacetylmorphine (DAM)] are established treatments for HD in several countries. The present study examined whether DAM-maintained patients and methadone-maintained patients differ from healthy controls in startle reflex and cortisol levels. Fifty-seven participants, 19 of each group matched for age, sex and smoking status, completed a startle session which included the presentation of 24 bursts of white noise while eye-blink responses to startling noises were recorded. Salivary cortisol was collected three times after awakening, before, during and after the startle session. DAM was administered before the experiment, while methadone was administered afterwards. Both heroin-dependent patient groups exhibited significantly smaller startle responses than healthy controls (P < 0.05). Whereas the cortisol levels after awakening did not differ across the three groups, the experimental cortisol levels were significantly lower in DAM-maintained patients, who received their opioid before the experiment, than in methadone-maintained patients and healthy controls (P < 0.0001). Opioid maintenance treatment for HD is associated with reduced startle responses. Acute DAM administration may suppress cortisol levels, and DAM maintenance treatment may represent an effective alternative to methadone in stress-sensitive, heroin-dependent patients.

Effects of sleep deprivation on sleep homeostasis and restoration during methadone-maintenance: a [31]P MRS brain imaging study

Insomnia afflicts many individuals, but particularly those in chronic methadone treatment. Studies examining sleep deprivation (SD) have begun to identify sleep restoration processes involving brain bioenergetics. The technique ([31])P magnetic resonance spectroscopy (MRS) can measure brain changes in the high-energy phosphates: alpha-, beta-, and gamma-nucleoside triphosphate (NTP). In the present study, 21 methadone-maintained (MM) and 16 control participants underwent baseline (BL), SD (40 wakeful hours), recovery1 (RE1), and recovery2 (RE2) study nights. Polysomnographic sleep was recorded each night and ([31])P MRS brain scanning conducted each morning using a 4T MR scanner (dual-tuned proton/phosphorus head-coil). Interestingly, increases in total sleep time (TST) and sleep efficiency index (SEI) commonly associated with RE sleep were not apparent in MM participants. Analysis of methadone treatment duration revealed that the lack of RE sleep increases in TST and SEI was primarily exhibited by short-term MM participants (methadone <12 months), while RE sleep in long-term MM (methadone >12 months) participants was more comparable to control participants. Slow wave sleep increased during RE1, but there was no difference between MM and control participants. Spectral power analysis revealed that compared to control participants; MM participants had greater delta, theta, and alpha spectral power during BL and RE sleep. ([31])P MRS revealed that elevations in brain beta-NTP (a direct measure of ATP) following RE sleep were greater in MM compared to control participants. Results suggest that differences in sleep and brain chemistry during RE in MM participants may be reflective of a disruption in homeostatic sleep function.

Potentiated startle as a measure of the negative affective consequences of repeated exposure to nicotine in rats

RATIONALE

Elevated acoustic startle amplitude has been used to measure anxiety-like effects of drug withdrawal in humans and animals. Withdrawal from a single opiate administration has been shown to produce robust elevations in startle amplitude ("withdrawal-potentiated startle") that escalate in severity with repeated exposure. Although anxiety is a clinical symptom of nicotine dependence, it is currently unknown whether anxiety-like behavior is elicited during the early stages of nicotine dependence in rodents.

OBJECTIVE

The objective of this study is to examine whether, as is the case with opiates, single or repeated exposure to nicotine can produce withdrawal-potentiated startle.

METHODS

Rats received daily nicotine injections for 14 days, and startle amplitude was tested during spontaneous withdrawal on injection days 1, 7, and 14.

RESULTS

Elevated startle responding was observed during nicotine withdrawal on days 7 and 14 but not on day 1, was greater at higher nicotine doses, and was reduced by a nicotine replacement injection given during an additional test session on day 15. Additional experiments demonstrated that nicotine withdrawal-potentiated startle was reduced by the alpha(2)-adrenergic agonist clonidine and that precipitated withdrawal-potentiated startle could not be induced by injection of the nicotinic acetylcholine receptor antagonist mecamylamine.

CONCLUSIONS

These results suggest that nicotine withdrawal escalates in severity across days, similar to the previously reported escalation of opiate withdrawal-potentiated startle. Potentiated startle may be a reliable measure of withdrawal from different classes of abused drugs and may be useful in the study of the early stages of drug dependence.

Anti-relapse medications: preclinical models for drug addiction treatment

Addiction is a chronic relapsing brain disease and treatment of relapse to drug-seeking is considered the most challenging part of treating addictive disorders. Relapse can be modeled in laboratory animals using reinstatement paradigms, whereby behavioral responding for a drug is extinguished and then reinstated by different trigger factors, such as environmental cues or stress. In this review, we first describe currently used animal models of relapse, different relapse triggering factors, and the validity of this model to assess relapse in humans. We further summarize the growing body of pharmacological interventions that have shown some promise in treating relapse to psychostimulant addiction. Moreover, we present an overview on the drugs tested in cocaine or methamphetamine addicts and examine the overlap of existing preclinical and clinical data. Finally, based on recent advances in our understanding of the neurobiology of relapse and published preclinical data, we highlight the most promising areas for future anti-relapse medication development.

Neonatal programming of rat behavior by downregulation of alpha2A-adrenoreceptor gene expression in the brain

Short-term knockdown of alpha2A-adrenergic receptor gene expression in the rat brain by siRNA or antisense oligodeoxynucleotide during the first days of life induced acute and long-lasting neurochemical and behavioral alterations. The acute effects in the neonatal rats were consistent with the known functions of the alpha2A-adrenergic receptors in the mature animals. The long-lasting alterations suggested involvement of receptor-specific gene expression during the critical period of brain development in early-life programming of anxiety-related behavior.

The anxiogenic drug yohimbine activates central viscerosensory circuits in rats

Systemic administration of the alpha(2)-adrenoceptor antagonist yohimbine (YO) activates the HPA stress axis and promotes anxiety in humans and experimental animals. We propose that visceral malaise contributes to the stressful and anxiogenic effects of systemic YO and that YO recruits brainstem noradrenergic (NA) and peptidergic neurons that relay viscerosensory signals to the hypothalamus and limbic forebrain. To begin testing these hypotheses, the present study explored dose-related effects of YO on food intake, conditioned flavor avoidance (CFA), and Fos immunolabeling in rats. Systemic YO (5.0 mg/kg BW, i.p.) inhibited food intake, supported CFA, and increased Fos immunolabeling in identified NA neurons in the ventrolateral medulla, nucleus of the solitary tract, and locus coeruleus. YO also increased Fos in the majority of corticotropin releasing hormone-positive neurons in the paraventricular nucleus of the hypothalamus. YO administered at 1.0 mg/kg BW did not inhibit food intake, did not support CFA, and did not increase Fos immunolabeling. Retrograde neural tracing demonstrated that neurons activated by YO at 5.0 mg/kg BW included medullary and pontine neurons that project to the central nucleus of the amygdala and to the lateral bed nucleus of the stria terminalis, the latter region receiving comparatively greater input by Fos-positive neurons. We conclude that YO produces anorexigenic and aversive effects that correlate with activation of brainstem viscerosensory inputs to the limbic forebrain. These findings invite continued investigation of how central viscerosensory signaling pathways interact with hypothalamic and limbic regions to influence interrelated physiological and behavioral components of anxiety, stress, and visceral malaise.

Punishment induces risky decision-making in methadone-maintained opiate users but not in heroin users or healthy volunteers

Reinforcing properties of psychoactive substances are considered to be critically involved in the development and maintenance of substance dependence. While accumulating evidence suggests that the sensitivity to reinforcement values may generally be altered in chronic substance users, relatively little is known about the influence reinforcing feedback exerts on ongoing decision-making in these individuals. Decision-making was investigated using the Cambridge Risk Task, in which there is a conflict between an unlikely large reward option and a likely small reward option. Responses on a given trial were analyzed with respect to the outcome on the previous trial, providing a measure of the impact of prior feedback in modulating behavior. Five different groups were compared: (i) chronic amphetamine users, (ii) chronic opiate users in methadone maintenance treatment (MMT), (iii) chronic users of illicit heroin, (iv) ex-drug users who had been long-term amphetamine / opiate users but were abstinent from all drugs of abuse for at least 1 year and (v) matched controls without a history of illicit substance use. Contrary to our predictions, choice preference was modified in response to feedback only in opiate users enrolled in MMT. Following a loss, the MMT opiate group chose the likely small reward option significantly less frequently than controls and heroin users. Our results suggest that different opiates are associated with distinctive behavioral responses to feedback. These findings are discussed with respect to the different mechanisms of action of heroin and methadone. Neuropsychopharmacology (2005) 30, 2115-2124. doi:10.1038/sj.npp.1300812; published online 6 July 2005.

Repeated psychological stress testing in stimulant-dependent patients

Decreasing response to stress has been one goal of interventions aimed at reducing relapse to substances of abuse. A laboratory stress test that can be repeated would be helpful in testing the efficacy of interventions in decreasing the response to stress before more extensive trials are begun. The effects of two types of psychological stress tests, the Trier Social Stress Test (TSST) and a stress imagery test, on psychological, physiological, and hormonal responses (salivary cortisol and DHEA) were examined when each test was given twice to cocaine- or methamphetamine-dependent human subjects, 24 of whom completed at least one session. The stress imagery test produced significant changes in several of the subjective response measures in both first and second sessions, including several measures of negative affect and a craving measure. The TSST produced significant changes only in the second session. The stress imagery protocol showed better replicability across two sessions. Cocaine users and methamphetamine users did not respond similarly in their craving responses. Reported craving for methamphetamine after stress testing showed decreases or much smaller increases compared to that for cocaine. Neither stress test significantly increased salivary cortisol or DHEA, and changes in hormone concentrations were not related to subjective responses. These results suggest that stress imagery testing procedures may be useful as provocative tests of stress-induced affect and stimulant drug craving. Although less convincing because of the heterogeneity of the subjects, they also suggest that HPA axis responsivity is not clearly linked to acute stress-induced stimulant craving or affective response.

Influence of neonatal short-term reduction in brainstem alpha2A-adrenergic receptors on receptor ontogenesis, acoustic startle reflex, and prepulse inhibition in rats

Neonatal treatments can disrupt prepulse inhibition (PPI) of startle response later in life. Alpha2A-adrenergic receptors (alpha2A-ARs) regulate the release of brain neurotransmitters that may influence PPI. The authors examined the effects of short-term reduction in the neonatal brainstem alpha2A-ARs on subsequent development of this receptor system and acoustic startle reflex in rats. Administration of antisense oligodeoxynucleotide complementary to the alpha2A-ARs on Days 2-4 of life reduced receptor expression in the brainstem by Day 5. The treatment increased alpha2-AR numbers in the cortex, hippocampus, and amygdala at 40 days of age, and in cortex and hypothalamus at 90 days of age. Transient increases in hippocampal and amygdalar alpha2-ARs were accompanied by attenuation of acoustic startle response and impairment of PPI.

HPA axis dysregulation following prenatal opiate exposure and postnatal withdrawal

We examined the effects of prenatal exposure to the long acting opiate l-alpha-acetylmethadol (LAAM) followed by postnatal withdrawal on hypothalamic-pituitary-adrenal (HPA) axis reactivity in neonatal and adult rats and anxiety-like behavior in adult rats. Female rats were treated with LAAM (0, 0.2, or 1.0 mg/kg/day) via oral gavage for 28 days prior to and continuing throughout pregnancy. Pups were fostered at birth to nontreated, lactating dams and underwent opiate withdrawal. On postnatal day (PND) 18, prenatal opiate-exposed male and female rat pups displayed a decreased corticosterone response 2 h after the application of an immunological stressor and 15 min following a social stressor compared to controls. In contrast, in adulthood, prenatal opiate-treated rats showed a heightened corticosterone response compared to prenatal water-treated controls at 3 h, but not 8 h, following an immunological stressor. Males prenatally treated with 1.0 mg/kg LAAM displayed elevated startle responding compared to the other prenatally treated male groups, but there was no effect of prenatal treatment in females. There were no effects of prenatal treatment in the open field test in either sex. These results suggest that prenatal opiate exposure followed by postnatal withdrawal dysregulated the HPA axis response to stressors in the neonate and adult and differentially affected adult anxiety-like behavior in males and females.

The anxiogenic drug yohimbine reinstates methamphetamine seeking in a rat model of drug relapse

BACKGROUND

Brain noradrenaline is involved in footshock stress-induced reinstatement of drug seeking in a rat relapse model. We studied whether yohimbine, an alpha-2 adrenoceptor antagonist that increases noradrenaline release and induces anxiety-like responses in human and nonhuman subjects, would reinstate methamphetamine seeking in rats.

METHODS

In experiment 1, the effect of yohimbine (1.25-2.5 mg/kg) on reinstatement was compared with that of intermittent footshock (5 min;.2-.6 mA) in rats that were trained to lever press for intravenous methamphetamine (9-11 days) and subsequently underwent 7 days of extinction training. In experiment 2, the effect of yohimbine on reinstatement of drug seeking was determined during early (1 day) and late (21 or 51 days) withdrawal periods. On the test days, rats were first given 3-hour extinction sessions and were then tested for reinstatement induced by yohimbine.

RESULTS

In experiment 1, both yohimbine and footshock stress reinstated methamphetamine seeking after extinction. In experiment 2, extinction responding was higher after 21 or 51 withdrawal days than after 1 withdrawal day. In contrast, no significant time-dependent changes in yohimbine-induced reinstatement were observed.

CONCLUSIONS

Results indicate that yohimbine is a potent stimulus for reinstatement of methamphetamine seeking in a rat relapse model.

Elevated startle during withdrawal from acute morphine: a model of opiate withdrawal and anxiety

RATIONALE

An elevated startle response has been observed in humans and animals during withdrawal from multiple substances of abuse, a phenomenon thought to reflect the anxiogenic effects of withdrawal. Although anxiety is a common symptom of opiate withdrawal, few studies have examined the effects of morphine withdrawal on acoustic startle.

OBJECTIVE

To develop a procedure for assessing opiate dependence through measurement of the startle reflex in rats.

METHODS

The effects of opiate withdrawal on startle were evaluated using both spontaneous and naloxone-precipitated withdrawal from an acute dose of morphine. The ability of the treatment drugs clonidine and chlordiazepoxide to block withdrawal-induced increases in startle was also tested.

RESULTS

Spontaneous withdrawal from an injection of morphine sulfate produced a significant increase in acoustic startle 2 h (3.2 mg/kg) or 4 h (10 mg/kg) after drug administration. Morphine withdrawal (10 mg/kg morphine sulfate) precipitated by the opiate antagonist naloxone (2.5 mg/kg) also produced a significant increase in startle magnitude. This elevation of startle was blocked by both clonidine (35 microg/kg) and chlordiazepoxide (10 mg/kg).

CONCLUSIONS

These data demonstrate that both spontaneous and precipitated withdrawal from an acutely administered opiate produce anxiety-like effects on acoustic startle. This paradigm may be useful in the study of anxiety and the early mechanisms of drug dependence.

Stress hormone responses to corticotropin-releasing hormone in substance abusers without severe comorbid psychiatric disease

BACKGROUND

Preclinical data indicate a crucial role of stress in the acute effects of drugs of abuse, maintenance of self-administration, and susceptibility to relapse. Stress system activation may serve as a marker for a neurochemical dysfunction with prognostic significance in patients with addiction.

METHODS

We tested pituitary adrenocorticotrophin (ACTH) and adrenal cortisol response to ovine corticotropin-releasing hormone (oCRH) to assess the reactivity of the hypothalamic-pituitary-adrenal (HPA) axis in seven nonsubstance-abusing subjects, 31 polysubstance-abusing subjects without depressive symptoms, and seven subjects with substance abuse and depressive symptoms. No subject met diagnostic criteria for depression or other severe psychiatric disease.

RESULTS

Compared with normal control subjects, substance abusers showed significantly lower ACTH and cortisol responses over the course of oCRH stimulation (p <.0001). Substance abusers with depressive symptoms showed similarly blunted responses.

CONCLUSIONS

Polysubstance abusers with no past or current diagnosis of other Axis I disorders show blunted ACTH and cortisol responses to oCRH administration. The finding of an activated HPA axis in this population suggests an overlapping role of central CRH and HPA axis activation in affective disorders and substance abuse, which is likely to constitute an endocrine milieu necessary for the maintenance of addictive behavior. These data support the role of future therapeutic trials with nonpeptide CRH receptor 1 antagonists in these patients.

A review of the modulation of the startle reflex by affective states and its application in psychiatry

OBJECTIVE

To provide an overview of startle reflex methodologies applied to the examination of emotional and motivational states in humans and to review the findings in different forms of psychopathology.

METHODS

Pertinent articles were searched mostly via MEDLINE and PsycINFO.

RESULTS

The startle reflex is a non-invasive translational tool of research that bridges the gap between animal and human investigations. Startle is used to study fear and anxiety, affective disturbances, sensitization, motivational states, and homeostasis.

CONCLUSIONS

The startle reflex is highly sensitive to various factors that are of interest in the studies of emotional disorders and has promoted new areas of investigations in psychiatry. However, research in psychiatry is still in its infancy and most findings await replication. Future progress will benefit from the development of innovative and powerful designs tailored to investigate specific disorders.

SIGNIFICANCE

The startle reflex has utility as a research tool to examine trauma-related disorders, fear learning, drug addiction, and to contrast affective states and emotional processing across diagnostic groups, but its usefulness as a diagnostic tool is limited.

Acoustic startle in maltreated children

We investigated the eyeblink component of acoustic startle reactions in maltreated children. Previous research indicates that acoustic startle is enhanced in adult males with posttraumatic stress disorders (PTSD) whereas findings on women with PTSD have been inconsistent. In accord with the only previous report for children with PTSD, we found that maltreated boys, particularly those who had been physically abused, responded to increases in startle probe loudness with smaller increments in amplitude of startle eyeblink and smaller reductions in blink latency than did comparison boys. Results for girls were inconsistent: younger maltreated girls had smaller startle amplitude and slower onset latency than controls, whereas older maltreated girls exhibited the opposite pattern.