Inhibition of Wnt signalling dose-dependently impairs the acquisition and expression of amphetamine-induced conditioned place preference.

The mechanisms by which dopaminergic neurotransmission in the nucleus accumbens (NAc) is involved in incentive learning produced by rewarding stimuli remain unclear. Recently, Wnt signalling has been implicated in synaptic plasticity and learning and memory. Functional interactions between Wnt and dopamine (DA) signalling has been demonstrated using in vitro and tissue physiology approaches, however there remains a lack of in vivo research into the involvement of Wnt in DA-mediated learning in behaving animals. The present study assessed the role of Wnt signalling in DA-mediated incentive learning using the conditioned place preference (CPP) paradigm. We hypothesized that inhibition of Wnt with intra-NAc microinjections of Wnt palmitoylation inhibitor IWP-2 will dose-dependently block the acquisition and expression of amphetamine (AMPH)-induced CPP in rats. Intra-NAc IWP-2 (0.001, 0.05, 1.0 but not 0.0001µg/0.5µl/side) prior to conditioning with AMPH (20.0µg/0.5µl/side) blocked acquisition of CPP. Intra-NAc IWP-2 (0.05, 0.5, 1.0 but not 0.001µg/0.5µl/side) during test following conditioning with AMPH blocked expression but at a higher dose than was need to block acquisition. Sensitization of locomotor activity to AMPH was observed during conditioning and this effect was blocked in groups given IWP-2 prior to AMPH. However, intra-NAc IWP-2 during conditioning did not block the locomotor stimulant effects of AMPH. These results implicate Wnt in DA-mediated incentive learning and suggest that Wnt signalling may be more important for the acquisition of CPP then for its expression. However, mechanisms by which Wnt and DA signalling pathways interact to influence DA-mediated reward-related learning remain to be elucidated.

Inhibition of glycogen synthase kinase-3 by SB 216763 affects acquisition at lower doses than expression of amphetamine-conditioned place preference in rats.

Dopamine (DA) drives incentive learning, whereby neutral stimuli acquire the ability to elicit responses. DA influences the signaling molecule glycogen synthase kinase-3 (GSK3). Inhibition of GSK3 attenuates the development of behavioral sensitization to stimulant drugs and conditioned place preference (CPP), a measure of incentive learning. We examined the role of GSK3 in the nucleus accumbens (NAc) of rats in CPP produced by amphetamine (1.5 mg/kg, i.p. or 20.0 µg/0.5 µl/side intra-NAc) by administering the inhibitor SB 216763 (1.0, 2.0, and 2.5 mg/kg, i.p. or 0.03, 0.30, 3.00, and 5.00 µg/0.5 µl/side intra-NAc) during acquisition or expression. We hypothesized a dose-dependent effect of SB 216763 and that acquisition would be affected by smaller doses than expression. For the systemic groups, 1.0 mg/kg of SB 216763 did not block CPP; 2.0 mg/kg administered in acquisition but not expression blocked CPP; and 2.5 mg/kg administered in either phase blocked CPP. For the central groups, 0.03 µg/0.5 µl/side of SB 216763 prevented acquisition but not expression, whereas larger doses administered in either phase blocked CPP. Thus, systemic or NAc inhibition of GSK3 by SB 216763 during acquisition or expression blocks amphetamine-produced CPP and acquisition is sensitive to lower doses than expression.

Spiroperidol, but not eticlopride or aripiprazole, produces gradual increases in descent latencies in the bar test in rats.

Rats repeatedly exposed to the bar test following injections with a dopamine D2-like receptor antagonist such as haloperidol show increased descent latencies, suggesting that contextual stimuli may lose their ability to elicit approach and other responses. Here, we showed that rats took progressively longer to initiate descent from a horizontal bar across sessions following daily intraperitoneal treatment (paired group) with the D2-like receptor antagonist, spiroperidol (0.125 and 0.25 mg/kg), but not in the control group that received 0.25 mg/kg in their home cage and testing following saline. When both groups were tested following an injection of spiroperidol or following saline, a sensitized and a conditioned increase in descent latency, respectively, were observed in the paired but not in the unpaired group. No evidence of sensitization or conditioning was found with the substituted benzamide compound, eticlopride (0.15-0.5 mg/kg), or the D2-like receptor partial agonist, aripiprazole (0.25-0.5 mg/kg). The different effects of these agents on learning may be related to different region-specific affinities for dopamine receptors or differences in receptor dissociation profiles. We suggest that the behavioural changes observed in spiroperidol-treated rats may reflect inverse incentive learning.

Obsessive-compulsive disorder: Insights from animal models.

Research with animal models of obsessive-compulsive disorder (OCD) shows the following: (1) Optogenetic studies in mice provide evidence for a plausible cause-effect relation between increased activity in cortico-basal ganglia-thalamo-cortical (CBGTC) circuits and OCD by demonstrating the induction of compulsive behavior with the experimental manipulation of the CBGTC circuit. (2) Parallel use of several animal models is a fruitful paradigm to examine the mechanisms of treatment effects of deep brain stimulation in distinct OCD endophenotypes. (3) Features of spontaneous behavior in deer mice constitute a rich platform to investigate the neurobiology of OCD, social ramifications of a compulsive phenotype, and test novel drugs. (4) Studies in animal models for psychiatric disorders comorbid with OCD suggest comorbidity may involve shared neural circuits controlling expression of compulsive behavior. (5) Analysis of compulsive behavior into its constitutive components provides evidence from an animal model for a motivational perspective on OCD. (6) Methods of behavioral analysis in an animal model translate to dissection of compulsive rituals in OCD patients, leading to diagnostic tests.

Contextual response time adaptation in the countermanding performance of rats.

Humans and non-human primates are known to lengthen their response time (RT) to a go signal when they occasionally must cancel their responses following a stop signal in a countermanding task as well as to adjust their RT adaptively on a trial-by-trial basis. Less is clear regarding the adaptive RT adjustments in the countermanding performance of rodents. To investigate this question, male Wistar rats (N=12) were trained with food reward to press a lever directly below an illuminated light (go signal), but to countermand the lever press subsequent to a tone (stop signal) presented infrequently (25% of trials) at variable delays. Rats were then tested in a standard responding task (0% stop trials) or a countermanding task with a 10-s or 1-s TO interval following errors. Rats exhibited significant RT lengthening in the countermanding task, compared with the standard responding task, and RT shortening following consecutive correct go trials. They also show RT lengthening following both error trials in the standard responding task and unrewarded, non-canceled stop trials in the countermanding task. RT lengthening following erroneous stop trials was observed in sessions with a 10-s TO interval, but not with a 1-s TO interval. Analyses of RT distributions suggest that RT lengthening results largely from reduced sensitivity to the go signal, but also from reduced readiness. These findings indicate that rats exert control in the countermanding task by lengthening RT in anticipation of stop trials to avoid long, unrewarded TO intervals.

Lifespan Changes in the Countermanding Performance of Young and Middle Aged Adult Rats.

Inhibitory control can be investigated with the countermanding task, which requires subjects to make a response to a go signal and cancel that response when a stop signal is presented occasionally. Adult humans performing the countermanding task typically exhibit impaired response time (RT), stop signal response time (SSRT) and response accuracy as they get older, but little change in post-error slowing. Rodent models of the countermanding paradigm have been developed recently, yet none have directly examined age-related changes in performance throughout the lifespan. Male Wistar rats (N = 16) were trained to respond to a visual stimulus (go signal) by pressing a lever directly below an illuminated light for food reward, but to countermand the lever press subsequent to a tone (stop signal) that was presented occasionally (25% of trials) at a variable delay. Subjects were tested in 1 h sessions at approximately 7 and 12 months of age with intermittent training in between. Rats demonstrated longer go trial RT, a higher proportion of go trial errors and performed less total trials at 12, compared to 7 months of age. Consistent SSRT and post-error slowing were observed for rats at both ages. These results suggest that the countermanding performance of rats does vary throughout the lifespan, in a manner similar to humans, suggesting that rodents may provide a suitable model for behavioral impairment related to normal aging. These findings also highlight the importance of indicating the age at which rodents are tested in countermanding investigations.

Ventromedial prefrontal theta activity during rapid eye movement sleep is associated with improved decision-making on the Iowa Gambling Task.

Recent research is beginning to reveal an intricate relationship between sleep and decision-making. The Iowa Gambling Task (IGT) is a unique decision-making task that relies on the ventromedial prefrontal cortex (vmPFC), an area that integrates and weighs previous experiences with reward and loss to select choices with the highest overall value. Recently, it has been demonstrated that a period of sleep can enhance decision-making on this task. Our study investigated the sleep mechanisms (sleep stages and cortical activity) that underlie this improvement. We recorded electrophysiology for 3 consecutive nights: a habituation, baseline, and acquisition night. On acquisition night participants were administered either a 200-trial IGT (IGT group; n = 13) or a 200-trial control (IGT-control group; n = 8) version of the task prior to sleep. Compared with baseline, the IGT group had a significant increase in theta frequency (4 Hz-8 Hz) on cites located above vmPFC and left prefrontal cortex during REM sleep. This increase correlated with subsequent performance improvement from deck B, a high reward deck with negative long-term outcomes. Furthermore, presleep emotional arousal (measured via skin conductance response) toward deck B correlated to increased theta activity above the right vmPFC during REM sleep. Overall, these results suggests that insight into deck B may be enhanced via vmPFC theta activity during REM sleep and REM sleep may have distinct mechanisms for processing decision-making information. (PsycINFO Database Record

Brain regions associated with inverse incentive learning: c-Fos immunohistochemistry after haloperidol sensitization on the bar test in rats.

Inverse incentive learning is the loss by stimuli of their ability to elicit approach and other responses. We used c-Fos immunohistochemistry to identify brain regions associated with inverse incentive learning. Rats that had daily treatments with haloperidol (0.25mg/kg) paired with placing their forepaws on a horizontal bar elevated 10cm above the floor initially descended almost immediately but over days descent latencies grew longer, revealing inverse incentive learning. Control rats that were tested daily and received haloperidol (Unpaired group) or saline later in their home cage showed no evidence of increased descent latencies. On the final test day, all groups were tested after haloperidol and only the Paired group showed increased descent latencies. c-Fos levels in the nucleus accumbens core and ventral pallidum were lower in the Paired group than in the Unpaired and Saline groups even though all groups received haloperidol on the test day. Compared to the Saline group both the Paired and Unpaired groups showed evidence of lower c-Fos levels in the dorsal striatum and nucleus accumbens shell, possibly a result of daily haloperidol injections. No group differences in c-Fos were found in the piriform cortex, ventral hippocampus, ventral tegmental area or lateral habenula. Results reveal, by means of different patterns of c-Fos expression, brain region-specific changes in neuronal activity associated with inverse incentive learning. Results support possible underlying neuroplastic changes for learned decreases in responsivity to environmental stimuli.

A response strategy predicts acquisition of schedule-induced polydipsia in rats.

Schedule-induced polydipsia (SIP) is excessive, non-regulatory drinking. We aimed to identify phenotypic learning traits representative of neural circuitry that underlies SIP and hypothesized that rats that are response-learners will be more susceptible in developing compulsive water drinking. Using the Y-maze, the rats were characterized as either place- or response-learners. They were exposed to the SIP protocol for a period of 21days. Subsequent histological staining for FosB/ΔFosB examined neuronal activation associated with SIP in several brain regions. The rats with a preference for a response-learning strategy were more likely to develop SIP than the rats using a place-learning strategy. Furthermore amphetamine sensitization, observed to increase SIP, also shifted learning strategy to a response-learning strategy. No differences were observed in FosB/ΔFosB expression between SIP and non-SIP rats in the dorsolateral striatum (DLS) and CA1 region of the hippocampus. However, SIP rats had greater FosB/ΔFosB expression in prefrontal cortex regions. The rats that develop SIP have a preference for response-learning strategies and increased neuronal activation in frontal cortical regions associated with habit formation and compulsion.

Differential effects of clozapine, metoclopramide, haloperidol and risperidone on acquisition and performance of operant responding in rats.

RATIONALE: Prior research has not systematically investigated the effects of systemic antipsychotic drugs on operant response acquisition, specifically their behavioural microstructure, reinforcement blunting and relative potency in acquisition compared to performance once operant responding has stabilized. OBJECTIVES: This study aims to systematically investigate the effects of systemically administered clozapine, metoclopramide, haloperidol and risperidone during free operant response acquisition and performance. METHODS: Following magazine training, food-restricted male Wistar rats lever pressed for food reward in 15 min daily operant conditioning sessions. RESULTS: All drugs suppressed operant response acquisition and performance. Risperidone and metoclopramide, but not clozapine or haloperidol, suppressed operant responding more potently during acquisition than performance. The dopamine D2-like receptor antagonists haloperidol and metoclopramide that affect the ventral and dorsal striatum blunted reinforcement and decreased inactive lever presses in acquisition. In contrast, the atypical antipsychotics clozapine and risperidone that affect the ventral striatum and prefrontal cortex failed to decrease inactive lever presses during acquisition, suggesting a possible decision-making deficit. Haloperidol decreased active lever pressing over performance days. The drugs did not appear to affect rats' sensitivity to active lever press outcome, even though they suppressed active lever pressing. CONCLUSIONS: Results suggest that reinforcement impact during operant acquisition is dependent on dopamine D2 receptors while drugs affecting, among other areas, the prefrontal cortex produce a deficit in ability to suppress inactive lever press responses.

Post learning sleep improves cognitive-emotional decision-making: evidence for a 'deck B sleep effect' in the Iowa Gambling Task.

The Iowa Gambling Task (IGT) is widely used to assess real life decision-making impairment in a wide variety of clinical populations. Our study evaluated how IGT learning occurs across two sessions, and whether a period of intervening sleep between sessions can enhance learning. Furthermore, we investigate whether pre-sleep learning is necessary for this improvement. A 200-trial version of the IGT was administered at two sessions separated by wake, sleep or sleep and wake (time-of-day control). Participants were categorized as learners and non-learners based on initial performance in session one. In session one, participants initially preferred the high-frequency reward decks B and D, however, a subset of learners decreased choice from negative expected value 'bad' deck B and increased choices towards with a positive expected value 'good' decks (decks C and D). The learners who had a period of sleep (sleep and sleep/wake control conditions) between sessions showed significantly larger reduction in choices from deck B and increase in choices from good decks compared to learners that had intervening wake. Our results are the first to show that post-learning sleep can improve performance on a complex decision-making task such as the IGT. These results provide new insights into IGT learning and have important implications for understanding the neural mechanisms of "sleeping on" a decision.

8-pCPT, an Epac activator, impairs conditioned place preference based on nucleus accumbens amphetamine in rats.

OBJECTIVES: Dopamine receptor-mediated 3',5'-cyclic adenosine monophosphate (cAMP)-dependent intracellular signalling is important for reward-related learning. cAMP activates cAMP-dependent protein kinase (PKA) and exchange protein directly activated by cAMP (Epac). We tested the hypothesis that reward-related learning may be mediated by Epac. METHODS: We evaluated conditioned place preference (CPP) on the basis of nucleus accumbens (NAc) injections of amphetamine (20 µg/0.5 µl/side) plus Sp-adenosine 3',5'-cyclic monophosphorothioate triethylamanine (Sp-cAMPS) (0.1, 1.0, 10, 15, 20 µg/0.5 µl/side), an activator of both PKA and Epac, or amphetamine (20 µg) plus 8-(4-chlorophenylthio)-2'-O-methyladenosine-3',5'-cyclic monophosphate (8-pCPT) (0.73, 1.27, 1.45, 2.89, 5.78, 11.56 µg/0.5 µl/side), an activator of Epac. RESULTS: In agreement with previous results, Sp-cAMPS dose-dependently impaired CPP. 8-pCPT impaired CPP at one dose (1.45 µg/0.5 µl/side) and we replicated this effect three times. CONCLUSION: The results implicate Epac in the acquisition of reward-related learning.

The effect of quetiapine (Seroquel™) on conditioned place preference and elevated plus maze tests in rats when administered alone and in combination with (+)-amphetamine.

RATIONALE: Recent case reports describe recreational use of quetiapine and drug-seeking behaviour to obtain quetiapine, an atypical antipsychotic. OBJECTIVE: We examined the hypothesis that quetiapine (10, 20 or 40 mg/kg) alone or co-administered with (+)-amphetamine (0.25, 0.5, 0.75 or 2.0 mg/kg) will affect reward and/or decrease anxiety in rats, as measured by conditioned place preference (CPP) and elevated plus maze (EPM) test, respectively. RESULTS: Quetiapine (20 mg/kg) produced greater open arm time and entries in the EPM test compared to 10 and 40 mg/kg, and quetiapine (10 mg/kg) significantly increased open arm entries and time when co-administered with (+)-amphetamine (0.5 mg/kg) compared to (+)-amphetamine (0.5 mg/kg) alone, suggesting decreased anxiety. Quetiapine (10, 20 or 40 mg/kg) produced no CPP when administered alone; the lowest dose of quetiapine (10 mg/kg) reduced CPP produced by a low dose of (+)-amphetamine (0.25 mg/kg), but had no significant effect on CPP produced by a higher dose (0.5 mg/kg). DISCUSSION: The quetiapine-induced anxiolytic effect in the EPM might explain why humans are misusing quetiapine and combining it with (+)-amphetamine. It is possible that humans experience an anxiolytic effect of the combined drugs and relatively unaltered rewarding effects of (+)-amphetamine. The results shed some light on the question of why humans are abusing and misusing quetiapine, despite its dopamine (DA) D2 receptor antagonism; it will be the task of future studies to identify the pharmacological mechanism mediating this behaviour.

The amphetamine sensitization model of schizophrenia symptoms and its effect on schedule-induced polydipsia in the rat.

RATIONALE: Amphetamine enhances dopamine (DA) transmission and induces psychotic states or exacerbates psychosis in at-risk individuals. Amphetamine sensitization of the DA system has been proposed as a rodent model of schizophrenia-like symptoms. In humans, excessive nonphysiologic drinking or primary polydipsia is significantly associated with a diagnosis of schizophrenia. In rodents, nonphysiologic drinking can be induced by intermittent presentation of food in the presence of a drinking spout to a hungry animal; this phenomenon is termed, "schedule-induced polydipsia" (SIP). OBJECTIVE: This study aims to determine the effects of amphetamine sensitization on SIP. METHODS: We injected rats with amphetamine (1.5 mg/kg) daily for 5 days. Following 4 weeks of withdrawal, animals were food restricted and exposed to the SIP protocol (noncontingent fixed-time 1-min food schedule) for daily 2-h sessions for 24 days. RESULTS: Results showed that previously amphetamine-injected animals drank more in the SIP protocol and drank more than controls when the intermittent food presentation schedule was removed. CONCLUSIONS: These findings suggest that hyperdopaminergia associated with schizophrenia may contribute to the development of polydipsia in this population. Whether animals that develop SIP have DA dysfunction or aberrant activity of other circuits that modulate DA activity has yet to be clearly defined.

Increased drinking following social isolation rearing: implications for polydipsia associated with schizophrenia.

Primary polydipsia, excessive drinking without known medical cause, is especially associated with a diagnosis of schizophrenia. We used animal models of schizophrenia-like symptoms to examine the effects on schedule-induced polydipsia: post-weaning social isolation rearing, subchronic MK-801 treatment (an NMDA-receptor antagonist) or the two combined. Male, Sprague-Dawley rats reared in groups or in isolation beginning at postnatal day 21 were further divided to receive subchronic MK-801 (0.5 mg/kg twice daily) or saline for 7 days beginning on postnatal day 62. Following a 4-day withdrawal period, all groups were trained on a schedule-induced polydipsia paradigm. Under food-restriction, animals reared in isolation and receiving food pellets at 1-min intervals developed significantly more drinking behavior than those reared with others. The addition of subchronic MK-801 treatment did not significantly augment the amount of water consumed. These findings suggest a predisposition to polydipsia is a schizophrenia-like behavioral effect of post-weaning social isolation.

Amphetamine stimulates Wnt3 increases in rat nucleus accumbens.

Dopaminergic neurotransmission is thought to be involved in reward-related incentive learning and addictive behaviour. Amphetamine will alter glycogen synthase kinase-3ß (GSK-3ß) activity by increasing dopamine transporter efflux rates. We investigated the hypothesis that Wnt signalling will be altered in rat nucleus accumbens within 15 min of injection of amphetamine compared with saline. We isolated RNA from the nucleus accumbens and used reverse transcriptase-PCR to screen for altered Wnt expression. We found that amphetamine had no effect on Wnt5a or Wnt7a expression but increased Wnt3. We then measured protein expression of Wnt3, phosphorylated lipoprotein-related peptide 6, GSK-3ß phosphorylated at serine-9 and tyrosine-216 and total ß-catenin. We found that amphetamine increased Wnt3 protein expression, increased pLRP6 (threonine-1572) levels, increased ß-catenin levels, increased GSK-3ß phosphorylation at serine-9, consistent with inhibition of GSK-3ß activity, and diminished GSK-3ß phosphorylation at tyrosine-216. Our data support the hypothesis that proximate Wnt signalling is rapidly activated by amphetamine in the adult rat nucleus accumbens.

People newly in love are more responsive to positive feedback.

Passionate love is associated with increased activity in dopamine-rich regions of the brain. Increased dopamine in these regions is associated with a greater tendency to learn from reward in trial-and-error learning tasks. This study examined the prediction that individuals who were newly in love would be better at responding to reward (positive feedback). In test trials, people who were newly in love selected positive outcomes significantly more often than their single (not in love) counterparts but were no better at the task overall. This suggests that people who are newly in love show a bias toward responding to positive feedback, which may reflect a general bias towards reward-seeking.

Reinforcer devaluation by extinction depends on the food restriction protocol.

A common feature of reinforcer devaluation studies is that new learning induces the devaluation. The present study used extinction to induce new learning about the conditioned reinforcer in a heterogeneous chain schedule. Rats pressed a lever in a heterogeneous chain schedule to produce a conditioned reinforcer (light) associated with the opportunity to obtain an unconditioned reinforcer (food) by pulling a chain. The density of food reinforcement correlated with the conditioned reinforcer was varied in a comparison of continuous and variable-ratio reinforcement schedules of chain pulling; this had no noticeable effect on conditioned reinforcer devaluation produced by extinction of chain pulling. In contrast, how rats were deprived appeared to matter very much. Restricting meal duration to 1h daily produced more lever pressing during baseline training and a greater reductive effect of devaluation on lever pressing than restricting body weight to 80% of a control rat's weight, which eliminated the devaluation effect. Further analysis suggested that meal-duration restriction may have produced devaluation effects because it was more effective than weight restriction in reducing rats' body weights. Our results exposed an important limitation on the devaluation of conditioned reinforcers: slight differences in food restriction, using two commonly employed food-restriction procedures, can produce completely different interpretations of reinforcer devaluation while leaving reinforcer-based learning intact.

The antidepressant phenelzine enhances memory in the double Y-maze and increases GABA levels in the hippocampus and frontal cortex of rats.

Subchronic treatment with a non-competitive glutamate NMDA-receptor antagonist (e.g., MK-801, phencyclidine) or social isolation (SI) from weaning (age 21 days) to adulthood (age 56 days) produces deficits similar to some positive and negative symptoms of schizophrenia. Down-regulation of GABA-ergic neurons has been demonstrated in people with schizophrenia and treatment with GABA-ergic compounds (including benzodiazepines, valproate) has shown some favorable outcomes. We hypothesized that subchronic MK-801 (0.5 mg/kg 2 times daily for 7 days), post-weaning SI or the two in combination will alter activity in a novel environment and memory in the double Y-maze (a test with a spatial discrimination and spatial alternation component) and that treatment with phenelzine (PLZ), a monoamine oxidase (MAO)-inhibiting antidepressant that also produces a rapid increase in brain levels of GABA, will improve memory. SI rats (n=18) showed increased locomotor activity when exposed to a novel environment but no deficits in the double Y-maze and the combination of SI plus subchronic MK-801 did not alter these effects. Delays did not affect performance in the spatial discrimination component of the Y-maze and decreased performance in the alternation component for saline rats but not MK-801 rats. Treatment with PLZ improved performance in both components of the Y-maze in a dose-dependent manner. Neurochemical analyses confirmed that PLZ increased GABA levels in the brain and changes in levels of dopamine, serotonin and their metabolites were consistent with inhibition of MAO. It was concluded that PLZ does not specifically augment memory in SI or subchronic MK-801-treated rats.