Effects of D3-preferring agonist PD 128907 on compulsive behaviour and decision making as assessed by the 5C-CPT

BackgroundRepetitive rituals in OCD patients result from pathological doubt, which has been linked to dysfunction in decision-making. First-line drug treatments for OCD are selective serotonin reuptake inhibitors; however, 40% of OCD patients do not respond to these. As brain activity patterns in OCD resemble those in schizophrenic patients, this suggests a dopaminergic component, supported by data showing that the D2/D3 receptor agonist Quinpirole induces compulsive checking in male rats. OCD has proved difficult to model in rodents and the contribution of decision making to compulsive behaviour in such models has not been studied. The five-choice continuous performance task (5C-CPT) measures both decision making and compulsive behaviour, making it possible to evaluate whether OCD models show correlated changes in these two behaviours. Establishing this would provide a new model approach to help develop therapeutic agents for OCD. AimsThe role of dopaminergic D3 receptors in decision making and compulsive behaviour was determined by testing the effect of the preferential D3 agonist PD 128907 on 5C-CPT performance measures. Oldhams method was used to determine the presence of any rate-dependent effect. MethodsFemale Lister hooded rats were trained to criterion in the 5C-CPT (>70% accuracy, < 30% omission and < 40% false alarms). The effects of PD128907 (0.25-1 mg/kg) were then investigated under challenging task conditions. ResultsOldham method revealed: a moderate positive association between baseline perseverative correct responses and the change at 0.05 mg/kg PD 128907; a strong positive association between baseline perseverative false alarm and the change at 0.2 mg/kg; a positive association between baseline total number of perseverative responses and the change at 0.05 mg/kg or 0.2 mg/kg PD 128907; a positive relationship between baseline accuracy and the change at 0.05 mg/kg PD 128907; and a moderate positive association between baseline correct response latency and the change at 0.05 mg/kg or 0.2 mg/kg PD 128907. The angle measurements and the direction of movement (clockwise or counterclockwise) showed how effective is one dose at increasing compulsive behaviour compared with other doses. ConclusionsPD 128907 effects on compulsive like behaviour and decision making in poor performing female lister hooded rats with long correct response latency and high perseveration at baseline (vulnerable population) in the 5C-CPT task matches two key features of OCD compulsions in humans (perseveration and indecision), this suggests that PD 128907 is more effective than Quinpirole in simulating the brain network conditions that underpin OCD. This model could help to develop more successful pharmacological interventions and to generate data translatable to clinical studies.