Prior morphine experience induces long-term increases in social interest and in appetitive behavior for natural reward

Differential effects of acute and prolonged morphine withdrawal on motivational and goal-directed control over reward-seeking behavior

Opioid addiction is a relapsing disorder marked by uncontrolled drug use and reduced interest in normally rewarding activities. The current study investigated the impact of spontaneous withdrawal from chronic morphine exposure on emotional, motivational, and cognitive processes involved in regulating the pursuit and consumption of natural food rewards in male rats. In Experiment 1, rats experiencing acute morphine withdrawal lost weight and displayed somatic signs of drug dependence. However, hedonically-driven sucrose consumption was significantly elevated, suggesting intact and potentially heightened emotional reward processing. In Experiment 2, rats undergoing acute morphine withdrawal displayed reduced motivation when performing an effortful response for palatable food reward. Subsequent reward devaluation testing revealed that acute withdrawal also disrupted their ability to exert flexible goal-directed control over their reward-seeking behavior. Specifically, morphine-withdrawn rats displayed insensitivity to reward devaluation both when relying on prior action-outcome learning and when given direct feedback about the consequences of their actions. In Experiment 3, rats tested after prolonged morphine withdrawal displayed heightened rather than diminished motivation for food rewards and retained their ability to engage in flexible goal-directed action selection. However, brief re-exposure to morphine was sufficient to impair motivation and disrupt goal-directed action selection, though in this case insensitivity to reward devaluation was only observed in the presence of morphine-paired context cues and in the absence of response-contingent feedback. We suggest that these opioid-withdrawal induced deficits in motivation and goal-directed control may contribute to addiction by interfering with the pursuit of adaptive alternatives to drug use.

The Neurobiology of Behavior and Its Applicability for Animal Welfare: A Review

Simple Summary

Animal welfare is the result of physical and psychological well-being and is expected to occur if animals are free: (1) from hunger, thirst and malnutrition, (2) from discomfort, (3) from pain, (4) to express normal behavior, and (5) from fear and distress. Nevertheless, well-being is not a constant state but rather the result of certain brain dynamics underlying innate motivated behaviors and learned responses. Thus, by understanding the foundations of the neurobiology of behavior we fathom how emotions and well-being occur in the brain. Herein, we discuss the potential applicability of this approach for animal welfare. First, we provide a general view of the basic responses coordinated by the central nervous system from the processing of internal and external stimuli. Then, we discuss how those stimuli mediate activity in seven neurobiological systems that evoke innate emotional and behavioral responses that directly influence well-being and biological fitness. Finally, we discuss the basic mechanisms of learning and how it affects motivated responses and welfare.

Abstract

Understanding the foundations of the neurobiology of behavior and well-being can help us better achieve animal welfare. Behavior is the expression of several physiological, endocrine, motor and emotional responses that are coordinated by the central nervous system from the processing of internal and external stimuli. In mammals, seven basic emotional systems have been described that when activated by the right stimuli evoke positive or negative innate responses that evolved to facilitate biological fitness. This review describes the process of how those neurobiological systems can directly influence animal welfare. We also describe examples of the interaction between primary (innate) and secondary (learned) processes that influence behavior.

Understanding Addiction Using Animal Models

Drug addiction is a neuropsychiatric disorder with grave personal consequences that has an extraordinary global economic impact. Despite decades of research, the options available to treat addiction are often ineffective because our rudimentary understanding of drug-induced pathology in brain circuits and synaptic physiology inhibits the rational design of successful therapies. This understanding will arise first from animal models of addiction where experimentation at the level of circuits and molecular biology is possible. We will review the most common preclinical models of addictive behavior and discuss the advantages and disadvantages of each. This includes non-contingent models in which animals are passively exposed to rewarding substances, as well as widely used contingent models such as drug self-administration and relapse. For the latter, we elaborate on the different ways of mimicking craving and relapse, which include using acute stress, drug administration or exposure to cues and contexts previously paired with drug self-administration. We further describe paradigms where drug-taking is challenged by alternative rewards, such as appetitive foods or social interaction. In an attempt to better model the individual vulnerability to drug abuse that characterizes human addiction, the field has also established preclinical paradigms in which drug-induced behaviors are ranked by various criteria of drug use in the presence of negative consequences. Separation of more vulnerable animals according to these criteria, along with other innate predispositions including goal- or sign-tracking, sensation-seeking behavior or impulsivity, has established individual genetic susceptibilities to developing drug addiction and relapse vulnerability. We further examine current models of behavioral addictions such as gambling, a disorder included in the DSM-5, and exercise, mentioned in the DSM-5 but not included yet due to insufficient peer-reviewed evidence. Finally, after reviewing the face validity of the aforementioned models, we consider the most common standardized tests used by pharmaceutical companies to assess the addictive potential of a drug during clinical trials.

The effects of acute stress on consummatory and motivational responses for sucrose in rats after long-term withdrawal from morphine

BACKGROUND

Negative affective states, e.g., anhedonia, may be linked to the long-lasting motivational processes associated with relapse. Here, this study investigated whether, and how, anhedonic states are influenced by stressful events that contribute to craving and relapse.

METHODS

All male rats were pretreated with a binge-like morphine paradigm for five days. After 12 to 16 days of withdrawal, rats were subjected to a one-hour free consumption test or three operant tasks with increasing cost/benefit ratio, i.e., fixed ratio 1 (FR1), progressive ratio (PR), and PR-punishment procedure of reinforcement, with sucrose solutions of three concentrations (4%, 15%, and 60%) as rewards. The consumption and operant responses under FR1 and PR procedures were measured following exposure to acute foot-shock stress (intermittent foot shock, 0.5 mA × 0.5 s × 10 min; mean intershock interval, 40 s), and the operant responses for 60% sucrose solution under PR-punishment procedure was measured following a forced-swim stress (5 minutes).

RESULT

Foot-shock stress increased water consumption in a subpopulation of rats and decreased consumption of sucrose solutions, while it did not influence the operant responses for sucrose solutions under either FR1 or PR procedure. The forced-swim stress reduced operant responses for 60% sucrose solution under PR-punishment procedure, but did not influence responding for 60% sucrose solution under PR procedure. In addition, the forced-swim stress also elevated anxiety level of rats in an open area test.

CONCLUSIONS

Acute stress induced hedonic but not motivational deficit for sucrose reward in protracted drug-abstinent animals. Additional negative emotional states besides anhedonia were evoked by acute stress.

Sustained opioid antagonism modulates striatal sensitivity to baby schema in opioid use disorder

BACKGROUND

Chronic opioid misuse is associated with reduced sensitivity to natural rewards and social motivation deficits that include impaired caregiving. The neurobiological mechanisms underlying these deficits and their response to treatment are not well understood. Baby schema (Kindchenschema) is a set of juvenile physical features, which is perceived as "cute" and triggers motivation for caregiving. Recent studies suggest that the "baby schema effect" is mediated by the brain "reward" network. We studied the impact of opioid antagonist treatment on the baby schema response in patients with opioid use disorder.

METHODS

Forty-seven (24 F) recently detoxified patients with opioid use disorder underwent functional magnetic resonance imaging (fMRI) while viewing infant portraits that were parametrically manipulated for baby schema content and rating them for cuteness, at baseline and during treatment with the injectable extended release opioid antagonist naltrexone (XRNTX). The study was not placebo-controlled.

RESULTS

The behavioral effect of baby schema, indexed by "cuteness" ratings, was present and unaffected by XRNTX. The brain response to baby schema was absent at baseline, but present in the bilateral ventral striatum after two weeks of XRNTX treatment. The decline in self-reported craving for opioids was positively correlated with the brain fMRI response to baby schema in the bilateral ventral striatum.

CONCLUSIONS

Opioid antagonist treatment modulated the brain reward system response to a marker of caregiving motivation in patients with opioid use disorder. Neural response to baby schema may offer a novel probe of social motivation and affiliative behaviors in this population.

Acute stress worsens the deficits in appetitive behaviors for social and sexual stimuli displayed by rats after long-term withdrawal from morphine

RATIONALE

Negative affective states, e.g., anhedonia, are suggested to be involved in the long-lasting motivational processes associated with relapse. Here, we investigated whether anhedonic behaviors could be elicited by an acute stress after protracted abstinence from morphine.

OBJECTIVES

The behavioral responses to natural stimuli following exposure to an acute stress were examined after 14 days of withdrawal from morphine. Male rats were pretreated with either a binge-like morphine regimen or daily saline injections for 5 days. The motivation for two natural stimuli, i.e., a social stimulus (male rat) and a sexual stimulus (estrous female rat), was measured, following exposure to an acute stress (intermittent foot shock, 0.5 mA * 0.5 s * 10 min; mean inter-shock interval 40 s), under three conditions: free approach and effort- and conflict-based approaches.

RESULTS

Foot-shock-induced stress did not influence free-approach behavior (sniffing time) towards the social or sexual stimulus. However, in the effort-based approach task, the stressed morphine-withdrawn rats demonstrated an attenuated motivation to climb over a partition to approach the social stimulus while the stressed saline-pretreated rats showed an increased motivation to approach the social stimulus. When an aversive stimulus (pins) was introduced in order to induce an approach-avoidance conflict, both drug-withdrawn and drug-naïve groups exhibited a bimodal distribution of approach behavior towards the sexual stimulus after the stress was introduced, i.e., the majority of rats had low risky appetitive behaviors but a minority of them showed rather highly "risky" approach behavior.

CONCLUSIONS

The acute stress induces differential motivational deficits for social and sexual rewards in protracted drug-abstinent rats.

The consummatory and motivational behaviors for natural rewards following long-term withdrawal from morphine: no anhedonia but persistent maladaptive behaviors for high-value rewards

RATIONALE

The negative affective state, e.g., anhedonia, emerges after abstinence from abused drugs may be linked to the motivational processes of drug craving and relapse. Although anhedonia diminishes over time with drug abstinence, it is not yet rather explicit whether anhedonia exists or not following protracted withdrawal.

OBJECTIVES

The behavioral responses to natural rewards were examined after 2 to 3 weeks withdrawal from morphine. Male rats were pretreated with either a binge-like morphine paradigm or daily saline injection for 5 days. The consummatory and motivational behaviors for three natural rewards (sucrose solutions 4, 15, and 60%, social stimulus: male rat, and sexual stimulus: estrous female rat) were examined under varied testing conditions.

RESULTS

The morphine-withdrawn rats significantly increased their intake of 15% sucrose solution during the 1-h consumption test and their operant responding for 15% sucrose solution under a progressive ratio (PR) schedule of reinforcement. When obtaining a reinforcer was associated with a 0.5 mA foot shock under a PR-punishment schedule, the morphine-withdrawn rats showed a higher performance for 60% sucrose solution. Meanwhile, the morphine-withdrawn rats displayed a higher motivation to sexual stimulus during the free-approach test and more approaching behaviors towards sexual stimulus in a conflict-based approach test (concurrent presence of reward and aversive stimulus).

CONCLUSIONS

No anhedonia-like behavior but sensitized behaviors for natural rewards were found after long-term morphine withdrawal. Notably, the morphine-withdrawn rats displayed persistent motivated behaviors for high-value rewards (60% sucrose and sexual stimulus) in the conflict tests suggesting impairments in inhibitory control in morphine-treated rats.

Sex differences in morphine-induced behavioral sensitization and social behaviors in ICR mice

Gender and genetic strain are two prominent variants that influence drug abuse. Although certain sex-related behavioral responses have been previously characterized in ICR mice, little is known about the effects of sex on morphine-induced behavioral responses in this outbred strain. Therefore, in this study, we investigated the sex differences of morphine-induced locomotion, anxiety-like and social behaviors in ICR mice. After morphine or saline exposure for four consecutive days (twice daily), increased locomotion, more time spent in the central area, as well as attenuated rearing and self-grooming behaviors were found in morphine-treated females in an open field; no differences were found in locomotion and the time spent in the central area between male and female controls. When interacting with the same-sex individuals, female controls were engaged in more social investigation, following, body contacting and self-grooming behaviors than controls; morphine exposure reduced contacting and self-grooming behaviors in females; in contrast, these effects were not found in males. These results indicate that female ICR mice are more prosocial and are more susceptible to morphine exposure than males.

The effects of nicotine dependence and acute abstinence on the processing of drug and non-drug rewards

RATIONALE

Drug addiction may be characterised by a hypersensitivity to drug rewards and a hyposensitivity to non-drug rewards. This imbalance may become further polarised during acute abstinence.

OBJECTIVES

(i) Examine the differences between dependent and occasional smokers in choices for, motivation for and self-reported wanting and liking of cigarette and non-drug rewards. (ii) Examine the effects of 12-h nicotine abstinence on these metrics.

METHODS

Dependent (n = 20) and occasional, non-dependent smokers (n = 20) were tested after ad libitum smoking and ≥12-h of nicotine abstinence. A novel task was developed (Drug, Reward and Motivation-Choice (DReaM-Choice)) in which different rewards (cigarettes, music and chocolate) could be won. In each trial, participants chose between two rewards and then could earn the chosen reward via repeated button-pressing. Participants subsequently 'consumed' and rated subjective liking of the rewards they had won.

RESULTS

Compared with occasional smokers, dependent smokers made more choices for (p < 0.001), pressed more for (p = 0.046) and reported more wanting (p = 0.007) and liking (p < 0.001) of cigarettes, and also made fewer choices for chocolate (p = 0.005). There were no differences between the groups on button-pressing for chocolate or music. However, the balance between drug and non-drug reward processing was different between the groups across all metrics. Twelve-hour nicotine abstinence led to more cigarette choices (p < 0.001) and fewer music choices (p = 0.042) in both groups.

CONCLUSIONS

Nicotine dependence was associated with a hypersensitivity to cigarette rewards, but we found little evidence indicating a hyposensitivity to non-drug rewards. Our findings question the moderating influence of dependence on how acute nicotine abstinence affects reward processing.

Neuroimaging Risk Markers for Substance Abuse: Recent Findings on Inhibitory Control and Reward System Functioning

Rates of alcohol and other drug use rise sharply throughout adolescence and peak in the early 20s. Likewise, prevalence of first-time substance use disorder (SUD) and past-year SUD both peak between ages 18-23. SUD is associated with a host of negative outcomes and is a serious health concern. Understanding the mechanisms that precede the onset and escalation of substance use is crucial in order to develop more effective prevention and intervention strategies for children and adolescents at risk for SUD. In this review, we discuss recent findings from functional neuroimaging studies in children, adolescents, and emerging adults that focus on uncovering the neural underpinnings of SUD risk. The focus is on inhibitory control and reward circuitry due to their involvement in risk-taking behaviors, which are heightened in adolescence and may facilitate substance use. We discuss convergences in the literature and highlight findings suggesting that the association between SUD risk and neurofunctioning may be moderated by age, gender, and history of substance use. Recommendations for future directions are also discussed.

Effects of ethanol on social approach and 50 kHz ultrasonic vocalization production in adolescent male Sprague-Dawley rats

Low doses of ethanol have been shown to facilitate social behavior in adolescent rats. The present study sought to investigate whether this ethanol effect is associated with increases in the incentive salience of social stimuli when assessed via approach behavior toward a peer (separated from the experimental animal by a mesh barrier) and 50 kHz ultrasonic vocalization (USV) production in that context. A 0.5 g/kg ethanol dose was found to increase social approach/investigation of adolescent male Sprague-Dawley rats during the first 5 min of the 10 min test whereas 50 kHz USV production was elevated by 0.25 g/kg during the last 5 min of testing. 50 kHz USV production and social approach were generally not correlated, indicating a clear dissociation between these measures. This is the first study to demonstrate that ethanol-induced social facilitation in adolescents is associated with an ethanol-induced increase in the incentive salience of social stimuli.

Differential effects on natural reward processing in rats after repeated heroin

RATIONALE

Heroin users report reward deficits as well as reward enhancements (to drug stimuli). To better understand the causal relation between chronic heroin and alterations in natural reward processing, we used experimental techniques in animal models.

METHODS

Separate groups of rats were trained in several food reward paradigms: conditioned place preference (CPP), food-reinforced lever pressing under a progressive ratio schedule of reinforcement, free feeding, and lever pressing with conditioned reinforcement. After training, the rats were subjected to 10 daily heroin (2 mg/kg) or saline vehicle injections and tested at 3, 15, and 30 days post-treatment.

RESULTS

Repeated heroin treatment abolished the CPP and significantly reduced break points for food reward at 3, 15, and 30 days post-treatment. Repeated heroin did not affect free feeding. Finally, repeated heroin significantly enhanced responding for a food-based conditioned reinforcer.

CONCLUSIONS

Repeated heroin decreases the attractiveness of food-associated cues and reduces motivation to work for natural reward. However, it appears to enhance natural conditioned reward processes that involve the acquisition of novel responding. Thus, repeated heroin appears to produce differential effects on natural reward processing depending on the nature of the reward-directed behavior.

Mutuality and the social regulation of neural threat responding

Recent studies have shown that the presence of a caring relational partner can attenuate neural responses to threat. Here we report reanalyzed data from Coan, Schaefer, and Davidson ( 2006 ), investigating the role of relational mutuality in the neural response to threat. Mutuality reflects the degree to which couple members show mutual interest in the sharing of internal feelings, thoughts, aspirations, and joys - a vital form of responsiveness in attachment relationships. We predicted that wives who were high (versus low) in perceived mutuality, and who attended the study session with their husbands, would show reduced neural threat reactivity in response to mild electric shocks. We also explored whether this effect would depend on physical contact (hand-holding). As predicted, we observed that higher mutuality scores corresponded with decreased neural threat responding in the right dorsolateral prefrontal cortex and supplementary motor cortex. These effects were independent of hand-holding condition. These findings suggest that higher perceived mutuality corresponds with decreased self-regulatory effort and attenuated preparatory motor activity in response to threat cues, even in the absence of direct physical contact with social resources.

The effects of pre-test social deprivation on a natural reward incentive test and concomitant 50 kHz ultrasonic vocalization production in adolescent and adult male Sprague-Dawley rats

In rats, ultrasonic vocalizations (USVs) are often used as a measure of affect, with 22 kHz USVs reflecting negative affect and 50 kHz USVs reflecting positive affect. This study used a modified reward approach task to assess behavioral approach and concomitant USV production toward either a food or social stimulus following varied amounts of pre-test social deprivation in both adolescent and adult rats. Adolescents spent significantly more time investigating the social stimulus than adults, although in the presence of the social stimulus isolate housed adults emitted more 50 kHz USVs than isolate housed adolescents. Isolate housed adults emitted more USVs to a social stimulus than adults that received less pre-test social isolation, a social deprivation effect not evident in the social approach data or any measure when animals were tested with a food stimulus. When tested with a food stimulus, adults emitted more 50 kHz USVs than adolescents, although they spent the same (or even less) time investigating that stimulus than did adolescents. Together, these data demonstrate that 50 kHz USV production and time spent investigating a rewarding stimulus are clearly dissociable and hence seemingly measure different states.

Effects of acute ethanol administration and chronic stress exposure on social investigation and 50kHz ultrasonic vocalizations in adolescent and adult male Sprague-Dawley rats

Adolescents drink largely in social situations, likely in an attempt to facilitate social interactions. This study sought to examine alterations in the incentive salience of a social stimulus following repeated stress exposure and acute ethanol administration in adolescent and adult male Sprague-Dawley rats. Subjects were either exposed to 5days of restraint stress, chronic variable stress (CVS), which consisted of a different stressor every day, or non-stressed. On test day, the animals were injected with 0, 0.25, 0.5, or 0.75g/kg ethanol and placed in a social approach test in which they could see, hear, and smell a social conspecific, but could not physically interact with it. All the animals showed an interest in the social stimulus, with adolescents engaging in more social investigation than adults. Restraint stressed adults showed ethanol-induced increases in social investigation, while ethanol effects were not seen in any other group. An ethanol-associated increase in 50kHz ultrasonic vocalization (USV) production was only evident in restraint stressed adolescents following 0.75g/kg ethanol. 50kHz USVs were not correlated with time spent investigating the social stimulus in any test condition. These results show that age differences in the facilitatory effects of ethanol on incentive salience of social stimuli are moderated by stress, with the facilitation of social approach by ethanol only evident in restraint stressed adults.

Volume transmission of beta-endorphin via the cerebrospinal fluid; a review

There is increasing evidence that non-synaptic communication by volume transmission in the flowing CSF plays an important role in neural mechanisms, especially for extending the duration of behavioral effects. In the present review, we explore the mechanisms involved in the behavioral and physiological effects of β-endorphin (β-END), especially those involving the cerebrospinal fluid (CSF), as a message transport system to reach distant brain areas. The major source of β-END are the pro-opio-melano-cortin (POMC) neurons, located in the arcuate hypothalamic nucleus (ARH), bordering the 3^rd ventricle. In addition, numerous varicose β-END-immunoreactive fibers are situated close to the ventricular surfaces. In the present paper we surveyed the evidence that volume transmission via the CSF can be considered as an option for messages to reach remote brain areas. Some of the points discussed in the present review are: release mechanisms of β-END, independence of peripheral versus central levels, central β-END migration over considerable distances, behavioral effects of β-END depend on location of ventricular administration, and abundance of mu and delta opioid receptors in the periventricular regions of the brain.

Long-term changes in reward-seeking following morphine withdrawal are associated with altered N-methyl-D-aspartate receptor 1 splice variants in the amygdala

The NR1 subunit of the NMDA receptor can be alternatively spliced by the insertion or removal of the N1, C1, C2, or C2' regions. Morphine dependence and withdrawal were previously demonstrated to lower N1 and C2' in the accumbens and lower N1, C1, and C2' in the amygdala (AMY). Withdrawal has also been demonstrated to increase motivational and anxiety/stress behaviors in rats. We tested the hypothesis that NR1 splicing would be associated with these behaviors during an extended withdrawal period of 2 months. Motivation was measured using an operant orofacial assay at non-aversive temperatures (37°C) while anxiety and stress were measured by examining this behavior at aversive temperatures (46°C). Lower C1 and C2 expression levels were observed in the AMY in a subset of the population of withdrawn rats even after 2 months of morphine withdrawal. These subsets were associated with a hypersensitivity to adverse conditions which may reflect long-term alterations in the withdrawn population.

Reinforcing properties of pups versus cocaine for fathers and associated central expression of Fos and tyrosine hydroxylase in mandarin voles (Microtus mandarinus)

The reciprocal interaction of pups and cocaine on reward effects in rodent mothers is known. However,it remains unclear whether such effects are apparent in father-offspring bonding. The mandarin vole (Microtus mandarinus) is a monogamous rodent with a high level of paternal care. We investigated the reinforcing properties of pups on vole fathers using a conditioned place preference paradigm across the postpartum period and looked for interactions and differences between the reinforcing effects of pups and cocaine. We also measured neuronal Fos and tyrosine hydroxylase (TH) expression underlying the preferences of fathers for pups or cocaine. Our data showed that fathers developed strong preferences for pups at various times (postnatal day 5–9, 13–17 and 19–23) without cocaine conditioning. Fathers showed a reduced preference for pups following simultaneous conditioning with cocaine. Although they preferred cocaine over postnatal day (PND) 5–9 pups, this preference was not detected for PND 13–17 pups. Fathers preferring cocaine exhibited an increase in Fos-immunoreactive neurons in the accumbens,medial nucleus of the amygdala, cingulate cortex, medial preoptic area and ventral tegmental area and had more TH-IR neurons in the ventral tegmental area compared to fathers preferring PND 5–9 pups. These results showed that similar to cocaine, mandarin vole pups elicit significant reward value to their fathers, but that paternal motivation is impaired by cocaine. A preference for cocaine over pups arose from the release of more dopamine and activation of a greater number of neurons within specific reward-associated neuronal subsets.

Nucleus accumbens response to incentive stimuli anticipation in children of alcoholics: relationships with precursive behavioral risk and lifetime alcohol use

Children of alcoholics (COAs) are at elevated risk to develop alcohol and other substance use disorders. The neurobiological underpinnings of this heightened vulnerability are presently not well understood. This study investigated whether, in humans, COAs have different functioning of the mesolimbic reward circuitry beyond previous substance use confounds and examined potential group differences in neural response in relation to alcohol use and behavioral risk. We studied 20 18- to 22-year-old COAs and 20 controls, developmentally well characterized for substance use and selected to match on sex, age, IQ, lifetime substance use and associated problems, and precursive (ages 12-14 years) externalizing behavioral risk. None met criteria for Diagnostic and Statistical Manual of Mental Disorders IV diagnosis. Neural responses to anticipation of reward and loss were assessed using functional magnetic resonance imaging during a monetary incentive delay task. Overall, COAs showed reduced ventral striatum activation during anticipation of monetary reward and loss compared with controls. However, additional analysis revealed that blunted nucleus accumbens (NAcc) response was only observed in COAs who have not demonstrated any problem drinking behavior. In addition, uniquely in COAs, NAcc activation was positively correlated with precursive externalizing risk, as well as current and lifetime alcohol consumption. These findings suggest a multilevel developmental process whereby lower precursive behavioral risk appears protective of later problem alcohol use in COAs, which is further associated with a blunted NAcc response to incentive anticipation, potentially reflecting a resilience mechanism. Moreover, the results suggest that a close association between motivational responses, alcohol consumption, and behavioral risk may underlie addiction vulnerability in COAs.

No change of sleep after 6 and 12 months of methadone maintenance treatment

OBJECTIVE

To determine whether the methadone maintenance treatment (MMT) affects sleep.

METHODS

We prospectively followed up the sleep pattern of 23 opiate addicts when admitted to MMT and after 6 and 12 months of treatment. Pittsburgh Sleep Quality Index, pain self-report questionnaires, urine for drug abuse, and one-night sleep polysomnography were assessed.

RESULTS

The baseline sleep indices (sleep time [5.5 ± 1.1 hours], sleep efficiency [80.6% ± 10.5%], rapid eye movement [REM] stage percent of sleep [14.3% ± 8.4%], percent of non-REM stage 3-4 [6.7% ± 8.6%], and Pittsburgh Sleep Quality Index Scores [11.4 ± 4.8]) did not change at 6 and 12 months. Proportion of patients with absent non-REM stage 3-4 reduced (47.8%, 34.8%, 13%, P = 0.03), and mean REM density increased (P = 0.04). Body mass index increased (24 ± 4.2 kg/m, 25.7 ± 4 kg/m, 27.1 ± 4.8 kg/m, P < 0.0005) with no change in the rate of benzodiazepine abuse or chronic pain. No patient had central sleep apnea. The Respiratory Disturbance Index (apnea or hypopnea numbers/sleep hr) increased among 5 patients who increased ≥25% of their entry weight (3.4 ± 4.1, 11.8 ± 10.1, 29.6 ± 30.4 Respiratory Disturbance Index's) but not with the other 18 (3.9 ± 4.8, 6.2 ± 6.2, 7.8 ± 7.4).

CONCLUSIONS

We conclude that MMT did not negatively affect the opiate addicts' baseline poor perceived and objective sleep. Only extensive weight gain (evident in a minority of patients) was associated with obstructive sleep apnea.

Pleasure seeking and birdsong

Songbirds sing at high rates within multiple contexts, suggesting that they are highly motivated to communicate and that the act of singing itself may be rewarding. Little is known about the neural regulation of the motivation to communicate. Dopamine and opioid neuropeptides play a primary role in reward seeking and sensory pleasure. In songbirds, these neurochemicals are found within brain regions implicated in both motivation and reward, including the medial preoptic nucleus (mPOA) and ventral tegmental area (VTA). Several lines of research indicate that dopamine and opioids in these regions play a role in birdsong that differs depending upon whether song is used to attract females (female-directed song) or is not directed towards other individuals (undirected song). Evidence is reviewed supporting the hypotheses: (1) that distinct patterns of dopamine activity influence the motivation to produce undirected and female-directed song, (2) that undirected communication is intrinsically reinforced by immediate release of opioids induced by the act of singing, and (3) that directed communication is socially reinforced by opioids released as part of social interactions.

Psychiatric disorders in smokers seeking treatment for tobacco dependence: relations with tobacco dependence and cessation

OBJECTIVE

The present research examined the relation of psychiatric disorders to tobacco dependence and cessation outcomes.

METHOD

Data were collected from 1,504 smokers (58.2% women; 83.9% White; mean age = 44.67 years, SD = 11.08) making an aided smoking cessation attempt as part of a clinical trial. Psychiatric diagnoses were determined with the Composite International Diagnostic Interview structured clinical interview. Tobacco dependence was assessed with the Fagerström Test of Nicotine Dependence (FTND) and the Wisconsin Inventory of Smoking Dependence Motives (WISDM).

RESULTS

Diagnostic groups included those who were never diagnosed, those who had ever been diagnosed (at any time, including in the past year), and those with past-year diagnoses (with or without prior diagnosis). Some diagnostic groups had lower follow-up abstinence rates than did the never diagnosed group (ps < .05). At 8 weeks after quitting, strong associations were found between cessation outcome and both past-year mood disorder and ever diagnosed anxiety disorder. At 6 months after quitting, those ever diagnosed with an anxiety disorder (OR = .72, p = .02) and those ever diagnosed with more than one psychiatric diagnosis (OR = .74, p = .03) had lower abstinence rates. The diagnostic categories did not differ in smoking heaviness or the FTND, but they did differ in dependence motives assessed with the WISDM.

CONCLUSION

Information on recent or lifetime psychiatric disorders may help clinicians gauge relapse risk and may suggest dependence motives that are particularly relevant to affected patients. These findings also illustrate the importance of using multidimensional tobacco dependence assessments.

Sensitization processes in drug addiction

In 1993, Robinson and Berridge published their first review that laid out the incentive sensitization theory of addiction (Robinson and Berridge 1993 Brain Res Rev 18:247). Its basic point is that repeated exposure to drugs of abuse causes hypersensitivity to drugs and drug-associated stimuli of the neural circuits mediating incentive salience, an important way in which motivational stimuli influence behavior. In laymen's terms, it states that this drug-induced hypersensitivity of motivational circuitry would mediate an increase in drug "wanting," thus being responsible for the dramatically exaggerated motivation for drugs displayed by addicts. This theory has been exceptionally influential, as evidenced by the fact that the original review paper about this theory (Robinson and Berridge 1993 Brain Res Rev 18:247) has been cited 2,277 times so far, and subsequent updates of this view (Robinson and Berridge 2000 Addiction 95(Suppl 2):S91; Robinson and Berridge 2001 Addiction 96:103; Robinson and Berridge 2003 Ann Rev Psychol 54:25) have been cited 274, 297, and 365 times, respectively, adding up to more than 3,200 citations within 15 years. The present chapter aims to delineate the merits and limitations of the incentive sensitization view of addiction, and whether incentive sensitization occurs in humans. We conclude that since incentive sensitization most prominently occurs after the first few drug exposures, it may represent an important initial step in the addiction process. During the expression of full-blown addiction, characterized by loss of control over drug intake and use of large quantities of drugs, the expression of incentive sensitization may be transiently suppressed. However, detoxification and the gradual disappearance of tolerance and withdrawal symptoms may unmask sensitization, which could then play an important role in the high risk of relapse.

Evidence for opioid involvement in the motivation to sing

Songbirds produce high rates of song within multiple social contexts, suggesting that they are highly motivated to sing and that song production itself may be rewarding. Progress has been made in understanding the neural basis of song learning and sensorimotor processing, however little is known about neurobiological mechanisms regulating the motivation to sing. Neural systems involved in motivation and reward have been conserved across species and in songbirds are neuroanatomically well-positioned to influence the song control system. Opioid neuropeptides within these systems play a primary role in hedonic reward, at least in mammals. In songbirds, opioid neuropeptides and receptors are found throughout the song control system and within several brain regions implicated in both motivation and reward, including the medial preoptic nucleus (POM) and ventral tegmental area (VTA). Growing research shows these regions to play a role in birdsong that differs depending upon whether song is sexually motivated in response to a female, used for territorial defense or sung as part of a flock but not directed towards an individual (undirected song). Opioid pharmacological manipulations and immunocytochemical data demonstrate a role for opioid activity possibly within VTA and POM in the regulation of song production. Although future research is needed, data suggest that opioids may be most critically involved in reinforcing song that does not result in any obvious form of immediate externally mediated reinforcement, such as undirected song produced in large flocks or during song learning. Data are reviewed supporting the idea that dopamine activity underlies the motivation or drive to sing, but that opioid release is what makes song production rewarding.

Extraction and microencapsulation of khat: effects on sexual motivation and estradiol level in female rats

INTRODUCTION

Khat (Catha edulis) is an evergreen tree/shrub that is thought to affect sexual motivation or libido. Its positive effect on sexual desire is more frequently observed in females than in males and occurs when khat is chewed. Thus, khat's effects on sexual behavior may depend on the release mode of its active constituent.

AIM

This study aimed to investigate the effect of dried khat alkaloids on the sexual motivation and estradiol levels of female rats, with special emphasis on the importance of the sustained release effect.

METHODS

Dried khat leaves were extracted and isolated. The alkaloids in khat extract were identified and calculated using thin layer chromatography and high-performance liquid chromatography. The isolated khat extract was microencapsulated using a phase separation coacervation method. The morphology, particle size, yield, drug loading, and entrapment efficiency were evaluated. The in vitro release and stability of alkaloids in khat extract and in khat extract microcapsules were determined. The effect of khat extract microcapsules and varying doses of khat extract on sexual motivation in female rats were investigated. Additionally, estradiol levels, vaginal secretions and vaginal pH were determined.

MAIN OUTCOME MEASURES

The differences in the effect of khat extract and khat extract microcapsules on sexual motivation, vaginal secretion and estradiol levels in female rats were compared. Results. Cathine and norephedrine were identified in the isolated khat extract at composition of 81.3% and 17.2%, respectively. Among the formulations studied, khat extract microcapsules of formulation 2:3:5 (containing a ratio of khat extract to ovalbumin to gelatin of 2:3:5) were found to exhibit higher yield, loading, and entrapment efficiency. Khat extract microcapsules showed sustained in vitro release and were more stable than khat extract. In addition, khat extract microcapsules enhanced sexual motivation, increased vaginal secretions, and upregulated estradiol level in female rats.

CONCLUSION

The sustained release of alkaloids from dried khat has significantly enhanced the sexual motivation and increased the estradiol level of female rats. Thus the release of dried khat alkaloids from microcapsules might be an effective means of enhancing the libido in females.

Endogenous opiates and behavior: 2007

This paper is the thirtieth consecutive installment of the annual review of research concerning the endogenous opioid system. It summarizes papers published during 2007 that studied the behavioral effects of molecular, pharmacological and genetic manipulation of opioid peptides, opioid receptors, opioid agonists and opioid antagonists. The particular topics that continue to be covered include the molecular-biochemical effects and neurochemical localization studies of endogenous opioids and their receptors related to behavior, and the roles of these opioid peptides and receptors in pain and analgesia; stress and social status; tolerance and dependence; learning and memory; eating and drinking; alcohol and drugs of abuse; sexual activity and hormones, pregnancy, development and endocrinology; mental illness and mood; seizures and neurologic disorders; electrical-related activity and neurophysiology; general activity and locomotion; gastrointestinal, renal and hepatic functions; cardiovascular responses; respiration and thermoregulation; and immunological responses.

Behavioral functions of the mesolimbic dopaminergic system: an affective neuroethological perspective

The mesolimbic dopaminergic (ML-DA) system has been recognized for its central role in motivated behaviors, various types of reward, and, more recently, in cognitive processes. Functional theories have emphasized DA's involvement in the orchestration of goal-directed behaviors and in the promotion and reinforcement of learning. The affective neuroethological perspective presented here views the ML-DA system in terms of its ability to activate an instinctual emotional appetitive state (SEEKING) evolved to induce organisms to search for all varieties of life-supporting stimuli and to avoid harms. A description of the anatomical framework in which the ML system is embedded is followed by the argument that the SEEKING disposition emerges through functional integration of ventral basal ganglia (BG) into thalamocortical activities. Filtering cortical and limbic input that spreads into BG, DA transmission promotes the "release" of neural activity patterns that induce active SEEKING behaviors when expressed at the motor level. Reverberation of these patterns constitutes a neurodynamic process for the inclusion of cognitive and perceptual representations within the extended networks of the SEEKING urge. In this way, the SEEKING disposition influences attention, incentive salience, associative learning, and anticipatory predictions. In our view, the rewarding properties of drugs of abuse are, in part, caused by the activation of the SEEKING disposition, ranging from appetitive drive to persistent craving depending on the intensity of the affect. The implications of such a view for understanding addiction are considered, with particular emphasis on factors predisposing individuals to develop compulsive drug seeking behaviors.