Beta-adrenoreceptor blockade abolishes atomoxetine-induced risk taking

Sex differences in noradrenergic modulation of attention and impulsivity in rats

RATIONALE

Noradrenaline (NE) is closely related to attentive performance and impulsive control. However, the potential sex differences regarding attention and impulsivity under the noradrenergic modulation have been largely neglected. Therefore, our study aimed to investigate whether male and female rats exhibit differential responses to NE-related drugs during the five-choice serial reaction time task (5CSRT).

METHODS

Male and female rats were trained in 5CSRT and administered with different NE drugs after obtaining stable baseline performance: atipamezole, a highly selective α2 receptor antagonist; prazosin, an α1 receptor antagonist; and atomoxetine, a selective NE reuptake inhibitor. Later, prazosin was selected to co-administration with atomoxetine.

RESULTS

Male and female rats exhibited equal learning speed, and no significant baseline differences were found as measured by the 5CSRT. Atomoxetine decreased premature responses in both sexes, but the extent of this reduction was different, with the reduction greater in males. Besides, atomoxetine (1.8 mg/kg) increased the error of omissions in females. The high dose of prazosin (0.5 mg/kg) decreased the accuracy only in male rats, but this was ameliorated by the co-administration with atomoxetine.

CONCLUSIONS

Atomoxetine showed significant improvement in impulsivity, but atomoxetine had less beneficial effects on impulsive control in females than in males, and it even impaired attentional performance in female rats. The α1 receptors were mainly responsible for NE drug-related sex differences in attention rather than impulsivity. The results obtained in this study indicate that the sex differences exist in both attention and impulsivity by the modulation of noradrenaline and raise the concern to improve sex-specific treatments.

Involvement of noradrenergic and serotonergic systems in risk-based decisions between options of equivalent expected value in rats

Risk perception is an important factor that may mediate risk-based decision-making processes regulated by noradrenergic (NA) and serotonergic (5-HT) systems. Most risk-based decision-making models involve complex factors, such as risk perception or reward value, such that the final decision is the result of the interactions among these factors. However, the contribution of risk perception per se in risk decisions has remained unclear. Therefore, in the present study, we made some modifications to the classical probabilistic discounting task (PDT) to focus on the impact of risk perception and noradrenergic/serotonergic systems on decision-making behavior. Meanwhile, we conducted an elevated plus-maze (EPM) test to detect the correlation between anxiety and choice behavior. In the current study, rats had to choose between a "certain" lever that delivered a certain number of pellets and a "risky" lever that delivered eight pellets in a probabilistic manner (descending: 50%, 25%, 12.5% or ascending 12.5%, 25%, 50% of the time). The long-term rewarding values of the two levers were always identical in each block within each session. According to their baseline performances in choosing the risky lever, rats were divided into the risk-prefer group and risk-averse group. The results showed that there was a significant correlation between open arm time in EPM and risky choice for both descending order and ascending order, indicating that highly anxious rats more often preferred the safe option under risk. Pharmacological stimulation of α2-adrenergic receptors via dexmedetomidine (0.01 mg/kg) decreased the preference of probabilistic rewards in the risk-prefer group, while blocking α2 receptors by atipamezole (0.3 mg/kg) also reduced risky choices. The NA reuptake inhibitor, atomoxetine, increased the preference for risky choices in the risk-prefer group, the effect of which was attained via multiple superimposed doses. Administration of the 5-HT_2A receptor agonist, DOI (0.1 mg/kg), increased risk-taking behavior in the risk-prefer group. Taken together, these results suggest that NA may be more inclined to process negative information such as loss or uncertainty in the regulation of risk-related decision making, whereas 5-HT may function primarily to increase risk-taking behavior. Our findings may help to further elucidate how noradrenergic and serotonergic systems differentially affect individuals with different risk preferences in terms of regulating risk perception in risk-related decision making.

Relative prevalence of 10 types of pharmacodynamic interactions in psychiatric treatment

OBJECTIVE

To assess the relative prevalence and factors affecting the prescription of medication combinations with a theoretical efficacy limiting pharmacodynamic interaction, defined as two medications with opposing indications and side effects or antagonistic action at the primary receptor of mechanism of action.

METHOD

One hundred sixteen combinations were identified for 10 types of pharmacodynamic interactions. PubMed was searched for each combination to assess the quality of evidence either supporting clinical use or verifying reduced efficacy. Micromedex was searched to determine the presence of warnings to prescribers of reduced efficacy. The prevalence in clinical practice was determined by computer review of the Genoa Healthcare database for all prescribers at 10 participating community mental health centers. The expected prevalence was calculated as the product of the probability of each medication prescribed alone and was compared with the actual prevalence of the combination using the test of proportions.

RESULTS

The frequency of prescription of eight combinations met the Bonferroni corrected level of significance of p < 0.001. Four were combinations of amphetamine and D2 antagonists and each were prescribed less often than chance, p = 0.0001 consistent with epidemiological studies and multiple animal studies verifying an efficacy limiting interaction. Despite epidemiological studies indicating increased risk of accidents, alprazolam and amphetamine were prescribed more often than chance, p = 0.0001. Micromedex generated warnings for efficacy limiting interactions for five other combinations, but with no subsequent change in prescription frequency.

CONCLUSIONS

Neither presence of medical evidence nor warnings from Micromedex consistently affect the prescription of combinations with pharmacodynamic efficacy limiting interactions.

Differential effects of d-amphetamine and atomoxetine on risk-based decision making of Lewis and Fischer 344 rats

Individuals with attention-deficit/hyperactivity disorder tend to make risker choices during probabilistic-discounting procedures. Thus, how common attention-deficit/hyperactivity disorder medications affect probabilistic discounting is of interest. In general, d-amphetamine increases risk-taking while atomoxetine has produced mixed effects in rats. Results from previous studies may result from genetic factors. Lewis and F344 rats have neurochemical differences that may be relevant to probabilistic discounting and how drugs affect such behavior. In this study, we evaluated dose-dependent effects of d-amphetamine and atomoxetine on probabilistic discounting of Lewis and F344. Male Lewis and F344 chose between one food pellet delivered 100% of the time and three food pellets delivered following decreasing probabilities of delivery (i.e. 100%, 66.7%, 33.3%, 16.5%, and 8.25%). Saline, d-amphetamine (0.1-1.8 mg/kg), and atomoxetine (0.1-7.8 mg/kg) were tested acutely. Lewis and F344 did not differ in choice at baseline. d-Amphetamine increased risky choice for both rat strains at low-to-moderate doses, although it did so at a lower dose (0.1 and 0.3 mg/kg) for F344 as compared to Lewis (0.3 mg/kg only). At high doses (1.0 and 1.8 mg/kg), d-amphetamine disrupted choice, increased frequencies of omitted trials, and reduced reinforcer sensitivity. Although atomoxetine increased frequencies of omitted trials at high doses (5.6 and 7.8 mg/kg), it had no effect on probabilistic discounting for either rat strain. Although Lewis and F344 differ in various types of impulsivity (i.e. motor, choice), with Lewis being the more impulsive of the two, the present results suggest that Lewis and F344 do not differ in risk-based decision-making. Effects of d-amphetamine on probabilistic discounting may be biology-dependent and differ from effects of atomoxetine.

Monoaminergic modulation of decision-making under risk of punishment in a rat model

The ability to decide advantageously among options that vary in both their risks and rewards is critical for survival and well-being. Previous work shows that some forms of risky decision-making are robustly modulated by monoamine signaling, but it is less clear how monoamine signaling modulates decision-making under risk of explicit punishment. The goal of these experiments was to determine how this form of decision-making is modulated by dopamine, serotonin, and norepinephrine signaling, using a task in which rats choose between a small, 'safe' food reward and a large food reward associated with variable risks of punishment. Preference for the large, risky reward (risk-taking) was reduced by administration of a D2/3 dopamine receptor agonist (bromocriptine) and a selective D2 agonist (sumanirole). The selective D3 agonist PD128907 appeared to attenuate reward discrimination abilities but did not affect risk-taking per se. In contrast, drugs targeting serotonergic and noradrenergic signaling had few if any effects on choice behavior. These data suggest that in contrast to other forms of risky decision-making, decision-making under risk of punishment is selectively modulated by dopamine signaling, predominantly through D2 receptors.

Examining the neurochemical underpinnings of animal models of risky choice: Methodological and analytic considerations

Because risky choice is associated with several psychiatric conditions, recent research has focused on examining the underlying neurochemical processes that control risk-based decision-making. Not surprisingly, several tasks have been developed to study the neural mechanisms involved in risky choice. The current review will briefly discuss the major tasks used to measure risky choice and will summarize the contribution of several major neurotransmitter systems to this behavior. To date, the most common measures of risky choice are the probability discounting task, the risky decision task, and the rat gambling task. Across these three tasks, the contribution of the dopaminergic system has been most studied, although the effects of serotonergic, adrenergic, cholinergic, and glutamatergic ligands will be discussed. Drug effects across these tasks have been inconsistent, which makes determining the precise role of neurotransmitter systems in risky choice somewhat difficult. Furthermore, procedural differences can modulate drug effects in these procedures, and the way data are analyzed can alter the interpretations one makes concerning pharmacological manipulations. By taking these methodological/analytic considerations into account, we may better elucidate the neurochemistry of risky decision-making. (PsycINFO Database Record (c) 2019 APA, all rights reserved).

Differential Contributions of Nucleus Accumbens Subregions to Cue-Guided Risk/Reward Decision Making and Implementation of Conditional Rules

The nucleus accumbens (NAc) is a key node within corticolimbic circuitry for guiding action selection and cost/benefit decision making in situations involving reward uncertainty. Preclinical studies have typically assessed risk/reward decision making using assays where decisions are guided by internally generated representations of choice-outcome contingencies. Yet, real-life decisions are often influenced by external stimuli that inform about likelihoods of obtaining rewards. How different subregions of the NAc mediate decision making in such situations is unclear. Here, we used a novel assay colloquially termed the "Blackjack" task that models these types of situations. Male Long-Evans rats were trained to choose between one lever that always delivered a one-pellet reward and another that delivered four pellets with different probabilities [either 50% (good-odds) or 12.5% (poor-odds)], which were signaled by one of two auditory cues. Under control conditions, rats selected the large/risky option more often on good-odds versus poor-odds trials. Inactivation of the NAc core caused indiscriminate choice patterns. In contrast, NAc shell inactivation increased risky choice, more prominently on poor-odds trials. Additional experiments revealed that both subregions contribute to auditory conditional discrimination. NAc core or shell inactivation reduced Pavlovian approach elicited by an auditory CS+, yet shell inactivation also increased responding during presentation of a CS-. These data highlight distinct contributions for NAc subregions in decision making and reward seeking guided by discriminative stimuli. The core is crucial for implementation of conditional rules, whereas the shell refines reward seeking by mitigating the allure of larger, unlikely rewards and reducing expression of inappropriate or non-rewarded actions.SIGNIFICANCE STATEMENT Using external cues to guide decision making is crucial for adaptive behavior. Deficits in cue-guided behavior have been associated with neuropsychiatric disorders, such as attention deficit hyperactivity disorder and schizophrenia, which in turn has been linked to aberrant processing in the nucleus accumbens. However, many preclinical studies have often assessed risk/reward decision making in the absence of explicit cues. The current study fills that gap by using a novel task that allows for the assessment of cue-guided risk/reward decision making in rodents. Our findings identified distinct yet complementary roles for the medial versus lateral portions of this nucleus that provide a broader understanding of the differential contributions it makes to decision making and reward seeking guided by discriminative stimuli.