Challenges for translational psychopharmacology research--some basic principles

Measuring the replicability of our own research

In the study of transgenic mouse models of neurodevelopmental and neurodegenerative disorders, we use batteries of tests to measure deficits in behaviour and from the results of these tests, we make inferences about the mental states of the mice that we interpret as deficits in "learning", "memory", "anxiety", "depression", etc. This paper discusses the problems of determining whether a particular transgenic mouse is a valid mouse model of disease X, the problem of background strains, and the question of whether our behavioural tests are measuring what we say they are. The problem of the reliability of results is then discussed: are they replicable between labs and can we replicate our results in our own lab? This involves the study of intra- and inter- experimenter reliability. The variables that influence replicability and the importance of conducting a complete behavioural phenotype: sensory, motor, cognitive and social emotional behaviour are discussed. Then the thorny question of failure to replicate is examined: Is it a curse or a blessing? Finally, the role of failure in research and what it tells us about our research paradigms is examined.

Characterization of Amphetamine, Methylphenidate, Nicotine, and Atomoxetine on Measures of Attention, Impulsive Action, and Motivation in the Rat: Implications for Translational Research

Amphetamine (AMP), methylphenidate (MPH), and atomoxetine (ATX) are approved treatments for ADHD, and together with nicotine (NIC), represent pharmacological agents widely studied on cognitive domains including attention and impulsive action in humans. These agents thus represent opportunities for clinical observation to be reinvestigated in the preclinical setting, i.e., reverse translation. The present study investigated each drug in male, Long Evans rats trained to perform either (1) the five-choice serial reaction time task (5-CSRTT), (2) Go/NoGo task, or (3) a progressive ratio (PR) task, for the purpose of studying each drug on attention, impulsive action and motivation. Specific challenges were adopted in the 5-CSRTT designed to tax attention and impulsivity, i.e., high frequency of stimulus presentation (sITI), variable reduction in stimulus duration (sSD), and extended delay to stimulus presentation (10-s ITI). Initially, performance of a large (> 80) cohort of rats in each task variant was conducted to examine performance stability over repeated challenge sessions, and to identify subgroups of "high" and "low" attentive rats (sITI and sSD schedules), and "high" and "low" impulsives (10-s ITI). Using an adaptive sequential study design, the effects of AMP, MPH, ATX, and NIC were examined and contrasting profiles noted across the tests. Both AMP (0.03-0.3 mg/kg) and MPH (1-6 mg/kg) improved attentional performance in the sITI but not sSD or 10-s ITI condition, NIC (0.05-0.2 mg/kg) improved accuracy across all conditions. ATX (0.1-1 mg/kg) detrimentally affected performance in the sITI and sSD condition, notably in "high" performers. In tests of impulsive action, ATX reduced premature responses notably in the 10-s ITI condition, and also reduced false alarms in Go/NoGo. Both AMP and NIC increased premature responses in all task variants, although AMP reduced false alarms highlighting differences between these two measures of impulsive action. The effect of MPH was mixed and appeared baseline dependent. ATX reduced break point for food reinforcement suggesting a detrimental effect on motivation for primary reward. Taken together these studies highlight differences between AMP, MPH, and ATX which may translate to their clinical profiles. NIC had the most reliable effect on attentional accuracy, whereas ATX was reliably effective against all tests of impulsive action.

Influence of the Novelty-Seeking Endophenotype on the Rewarding Effects of Psychostimulant Drugs in Animal Models

Novelty seeking (NS), defined as a tendency to pursue novel and intense emotional sensations and experiences, is one of the most relevant individual factors predicting drug use among humans. High novelty seeking (HNS) individuals present an increased risk of drug use compared to low novelty seekers. The NS endophenotype may explain some of the differences observed among individuals exposed to drugs of abuse in adolescence. However, there is little research about the particular response of adolescents to drugs of abuse in function of this endophenotype, and the data that do exist are inconclusive. The present work reviews the literature regarding the influence of NS on psychostimulant reward, with particular focus on adolescent subjects. First, the different animal models of NS and the importance of this endophenotype in adolescence are discussed. Later, studies that have used the most common animal models of reward (self-administration, conditioned place preference paradigms) to evaluate how the NS trait influences the rewarding effects of psychostimulants are reviewed. Finally, possible explanations for the enhanced risk of developing substance dependence among HNS individuals are discussed. In conclusion, the studies referred to in this review show that the HNS trait is associated with: (1) increased initial sensitivity to the rewarding effects of psychostimulants, (2) a higher level of drug craving when the subject is exposed to the environmental cues associated with the drug, and (3) enhanced long-term vulnerability to relapse to drug consumption after prolonged abstinence.

Preclinical animal anxiety research - flaws and prejudices

The current tests of anxiety in mice and rats used in preclinical research include the elevated plus-maze (EPM) or zero-maze (EZM), the light/dark box (LDB), and the open-field (OF). They are currently very popular, and despite their poor achievements, they continue to exert considerable constraints on the development of novel approaches. Hence, a novel anxiety test needs to be compared with these traditional tests, and assessed against various factors that were identified as a source of their inconsistent and contradictory results. These constraints are very costly, and they are in most cases useless as they originate from flawed methodologies. In the present report, we argue that the EPM or EZM, LDB, and OF do not provide unequivocal measures of anxiety; that there is no evidence of motivation conflict involved in these tests. They can be considered at best, tests of natural preference for unlit and/or enclosed spaces. We also argued that pharmacological validation of a behavioral test is an inappropriate approach; it stems from the confusion of animal models of human behavior with animal models of pathophysiology. A behavioral test is developed to detect not to produce symptoms, and a drug is used to validate an identified physiological target. In order to overcome the major methodological flaws in animal anxiety studies, we proposed an open space anxiety test, a 3D maze, which is described here with highlights of its various advantages over to the traditional tests.

Effects of chronic fluoxetine treatment on anxious behaviour of BALB/c mice in a 3-dimensional maze

Here we used a 3-dimensional (3D) maze, a modification of the radial maze, to assess the effects of treatment for two weeks with a single daily dose of fluoxetine (20 mg/kg, i.p.) on anxiety in male BALB/c mice. We examined whether anxiolytic effects of fluoxetine can be detected over three daily test sessions. We examined also whether repeated handling associated with chronic treatment interferes with effects of fluoxetine on anxiety responses. The 3D maze comprises nine arms, each connected to an upward inclined bridge radiating from a central platform. In this maze, BALB/c mice cross frequently into the bridges but avoid the arms. This avoidance is used as an index of anxiety. Two separate groups received once a day either saline (SALCH, n = 8) or fluoxetine (FLUCH, n = 8) for 14 days, and up to 30 min before the test during the subsequent 3 days. A third group received saline (SALAC, n = 8) 30 min before the test, once a day for 3 days. SALAC mice did not cross into the arms, and continued this avoidance over 3 sessions. SALCH mice avoided the arms in session 1 whereas FLUCH mice did cross into the arms, and like SALCH mice, increased number of crossings into and time on the arms in subsequent sessions. Fluoxetine evidently had an anxiolytic effect but only in the first session. These results indicate that handling experience decreased fear and anxiety in the mice, which may have masked the anxiolytic effect of fluoxetine in the second and third test sessions.

An efficient early phase 2 procedure to screen medications for efficacy in smoking cessation

RATIONALE

Initial screening of new medications for potential efficacy (i.e., Food and Drug Administration (FDA) early phase 2), such as in aiding smoking cessation, should be efficient in identifying which drugs do, or do not, warrant more extensive (and expensive) clinical testing.

OBJECTIVES

This focused review outlines our research on development, evaluation, and validation of an efficient crossover procedure for sensitivity in detecting medication efficacy for smoking cessation. First-line FDA-approved medications of nicotine patch, varenicline, and bupropion were tested as model drugs, in three separate placebo-controlled studies. We also tested specificity of our procedure in identifying a drug that lacks efficacy, using modafinil.

RESULTS

This crossover procedure showed sensitivity (increased days of abstinence) during week-long "practice" quit attempts with each of the active cessation medications (positive controls) versus placebo, but not with modafinil (negative control) versus placebo, as hypothesized. Sensitivity to medication efficacy signal was observed only in smokers high in intrinsic quit motivation (i.e., already preparing to quit soon) and not smokers low in intrinsic quit motivation, even if monetarily reinforced for abstinence (i.e., given extrinsic motivation).

CONCLUSIONS

A crossover procedure requiring less time and fewer subjects than formal trials may provide an efficient strategy for a go/no-go decision whether to advance to subsequent phase 2 randomized clinical trials with a novel drug. Future research is needed to replicate our results and evaluate this procedure with novel compounds, identify factors that may limit its utility, and evaluate its applicability to testing efficacy of compounds for treating other forms of addiction.

Social stress alters inhibitory synaptic input to distinct subpopulations of raphe serotonin neurons

Anxiety disorders are among the most prevalent psychiatric disorders, yet much is unknown about the underlying mechanisms. The dorsal raphe (DR) is at the crux of the anxiety-inducing effects of uncontrollable stress, a key component of models of anxiety. Though DR serotonin (5-HT) neurons play a prominent role, anxiety-associated changes in the physiology of 5-HT neurons remain poorly understood. A 5-day social defeat model of anxiety produced a multifaceted, anxious phenotype in intruder mice that included increased avoidance behavior in the open field test, increased stress-evoked grooming, and increased bladder and heart weights when compared to control mice. Intruders were further compared to controls using electrophysiology recordings conducted in midbrain slices wherein recordings targeted 5-HT neurons of the ventromedial (vmDR) and lateral wing (lwDR) subfields of the DR. Though defining membrane characteristics of 5-HT neurons were unchanged, γ-aminobutyric-acid-mediated (GABAergic) synaptic regulation of 5-HT neurons was altered in a topographically specific way. In the vmDR of intruders, there was a decrease in the frequency and amplitude of GABAergic spontaneous inhibitory postsynaptic currents (sIPSCs). However, in the lwDR, there was an increase in the strength of inhibitory signals due to slower sIPSC kinetics. Synaptic changes were selective for GABAergic input, as glutamatergic synaptic input was unchanged in intruders. The distinct inhibitory regulation of DR subfields provides a mechanism for increased 5-HT output in vmDR target regions and decreased 5-HT output in lwDR target regions, divergent responses to uncontrollable stress that have been reported in the literature but were previously poorly understood.

Nonhuman primate models of social behavior and cocaine abuse

RATIONALE

Although cocaine is often abused in social situations, very few animal studies examine the effects of cocaine in the context of social behavior.

OBJECTIVES

This review highlights studies investigating the behavioral effects of cocaine in the context of social housing conditions using nonhuman primates. In addition, this review presents recent findings examining the effects of self-administering cocaine on social behavior and the effects of manipulations hypothesized to be stressful or enriching on the interactions between cocaine reinforcement and social rank. The following dependent variables are examined: (1) cocaine-induced changes in social behavior and (2) cocaine self-administration in cynomolgus monkeys of varying social ranks. The independent variables examined include several environmental and pharmacological manipulations.

CONCLUSIONS

The studies reviewed here indicate that several variables can differentially affect cocaine self-administration when studied in a social context, rather than in individually housed animals. These variables include the social rank and sex of the individual, drug history, the nature of the "fear"-inducing manipulation, and the reliability of cortisol as an appropriate measure of "stress." While the inclusion of socially housed animals necessitates larger sample sizes, animal models incorporating social behavior are more homologous to the human condition and should be implemented when possible.

Cognitive bias in the chick anxiety-depression model

Cognitive bias is a phenomenon that presents in clinical populations where anxious individuals tend to adopt a more pessimistic-like interpretation of ambiguous aversive stimuli whereas depressed individuals tend to adopt a less optimistic-like interpretation of ambiguous appetitive stimuli. To further validate the chick anxiety-depression model as a neuropsychiatric simulation we sought to quantify this cognitive endophenotype. Chicks exposed to an isolation stressor of 5m to induce an anxiety-like or 60 m to induce a depressive-like state were then tested in a straight alley maze to a series of morphed ambiguous appetitive (chick silhouette) to aversive (owl silhouette) cues. In non-isolated controls, runway start and goal latencies generally increased as a function of greater amounts of aversive characteristics in the cues. In chicks in the anxiety-like state, runway latencies were increased to aversive ambiguous cues, reflecting more pessimistic-like behavior. In chicks in the depression-like state, runway latencies were increased to both aversive and appetitive ambiguous cues, reflecting more pessimistic-like and less optimistic-like behavior, respectively.

Big ideas for small brains: what can psychiatry learn from worms, flies, bees and fish?

While the research community has accepted the value of rodent models as informative research platforms, there is less awareness of the utility of other small vertebrate and invertebrate animal models. Neuroscience is increasingly turning to smaller, non-rodent models to understand mechanisms related to neuropsychiatric disorders. Although they can never replace clinical research, there is much to be learnt from 'small brains'. In particular, these species can offer flexible genetic 'tool kits' that can be used to explore the expression and function of candidate genes in different brain regions. Very small animals also offer efficiencies with respect to high-throughput screening programs. This review provides a concise overview of the utility of models based on worm, fruit fly, honeybee and zebrafish. Although these species may have small brains, they offer the neuropsychiatric research community opportunities to explore some of the most important research questions in our field.

Neuroendocrine and neurochemical impact of aggressive social interactions in submissive and dominant mice: implications for stress-related disorders

Social conflicts may engender stress-related behavioural and physiological disturbances in the victims of aggression. In addition, stress-like neurochemical changes and ensuing depressive and anxiety symptoms might also be evident in the perpetrators of aggressive acts. The present investigation assessed basal levels of circulating corticosterone and of brain serotonin (5-HT) and norepinephrine (NE) in pre-identified submissive and dominant mice. In addition, brain neurochemical changes were determined following a single or three 15-min aggressive episodes both in submissive mice and in those that dominated the aggressive interplay. Three minutes after single and repeated confrontations, plasma corticosterone levels and 5-HT utilization within the prefrontal cortex (PFC) and hippocampus were increased to a comparable extent in submissive and dominant animals. Interestingly, however, NE utilization within the PFC and hippocampus was augmented to a greater level in submissive mice. These results suggest that 5-HT neuronal functioning was generally responsive to aggressive events, irrespective of social rank, whereas NE neuronal activity within the PFC and hippocampus was more sensitive to the submissive/dominance attributes of the social situation. It is possible that NE and 5-HT variations associated with an aggressive experience contribute to depressive- and anxiety-like manifestations typically observed after such psychosocial stressors, particularly in submissive mice. However, given that 5-HT changes occur irrespective of social rank, these data suggest that a toll is taken on both submissive and dominant mice, leaving them vulnerable to stress-related pathology.

Chronic administration of atypical antipsychotics improves behavioral and synaptic defects of STOP null mice

INTRODUCTION

Recent studies have suggested that schizophrenia is associated with alterations in the synaptic connectivity involving cytoskeletal proteins. The microtubule-associated protein stable tubule only polypeptide (STOP) plays a key role in neuronal architecture and synaptic plasticity, and it has been demonstrated that STOP gene deletion in mice leads to a phenotype mimicking aspects of positive and negative symptoms and cognitive deficits classically observed in schizophrenic patients. In STOP null mice, behavioral defects are associated with synaptic plasticity abnormalities including defects in long-term potentiation. In these mice, long-term administration of typical antipsychotics has been shown to partially alleviate behavioral defects but, as in humans, such a treatment was poorly active on deficits related to negative symptoms and cognitive impairments. Here, we assessed the effects of risperidone and clozapine, two atypical antipsychotics, on STOP null mice behavior and synaptic plasticity.

RESULTS

Long-term administration of either drug results in alleviation of behavioral alterations mimicking some negative symptoms and partial amelioration of some cognitive defects in STOP null mice. Interestingly, clozapine treatment also improves synaptic plasticity of the STOP null animals by restoring long-term potentiation in the hippocampus.

DISCUSSION

All together, the pharmacological reactivity of STOP null mice to antipsychotics evokes the pharmacological response of humans to such drugs. Totally, our study suggests that STOP null mice may provide a useful preclinical model to evaluate pharmacological properties of antipsychotic drugs.

Cocaine craving and use during daily life

RATIONALE

Craving is often assumed to cause ongoing drug use and relapse and is a major focus of addiction research. However, its relationship to drug use has not been adequately documented.

OBJECTIVES

The aim of this study was to investigate the relationship between craving and drug use in real time and in the daily living environments of drug users.

METHODS

In a prospective, longitudinal, cohort design (ecological momentary assessment), 112 cocaine-abusing individuals in methadone maintenance treatment rated their craving and mood at random times (two to five times daily, prompted by electronic diaries) as they went about their everyday activities. They also initiated an electronic diary entry each time they used cocaine. Drug use was monitored by thrice-weekly urine testing.

RESULTS

During periods of urine-verified cocaine use, ratings of cocaine craving increased across the day and were higher than during periods of urine-verified abstinence. During the 5 h prior to cocaine use, ratings of craving significantly increased. These patterns were not seen in ratings of heroin craving or mood (e.g., feeling happy or bored).

CONCLUSIONS

Cocaine craving is tightly coupled to cocaine use in users' normal environments. Our findings provide previously unavailable support for a relationship that has been seriously questioned in some theoretical accounts. We discuss what steps will be needed to determine whether craving causes use.

Social stress, therapeutics and drug abuse: preclinical models of escalated and depressed intake

The impact of ostensibly aversive social stresses on triggering, amplifying and prolonging intensely rewarding drug taking is an apparent contradiction in need of resolution. Social stress encompasses various types of significant life events ranging from maternal separation stress, brief episodes of social confrontations in adolescence and adulthood, to continuous subordination stress, each with its own behavioral and physiological profile. The neural circuit comprising the VTA-accumbens-PFC-amygdala is activated by brief episodes of social stress, which is critical for the DA-mediated behavioral sensitization and increased stimulant consumption. A second neural circuit comprising the raphe-PFC-hippocampus is activated by continuous subordination stress and other types of uncontrollable stress. In terms of the development of therapeutics, brief maternal separation stress has proven useful in characterizing compounds acting on subtypes of GABA, glutamate, serotonin and opioid receptors with anxiolytic potential. While large increases in alcohol and cocaine intake during adulthood have been seen after prolonged maternal separation experiences during the first two weeks of rodent life, these effects may be modulated by additional yet to be identified factors. Brief episodes of defeat stress can engender behavioral sensitization that is relevant to escalated and prolonged self-administration of stimulants and possibly opioids, whereas continuous subordination stress leads to anhedonia-like effects. Understanding the intracellular cascade of events for the transition from episodic to continuous social stress in infancy and adulthood may provide insight into the modulation of basic reward processes that are critical for addictive and affective disorders.