Original article 589 Selective effects of low-dose dopamine D 1 and D 2 receptor antagonists on rat information processing A. Courtie `re a , J. Hardouin a , A. Goujon a , F. Vidal a,b and T. Hasbroucq a,b It is well established that the dopaminergic system influences simple reaction time (RT) performance. However, the role of this system in more complex information processing remains to be clarified. The present study was aimed at addressing this issue. To this end, we used an inferential method that relies on choice RT procedures and allows one to identify information processing stages in both humans and rats. Long–Evans rats responded to lateral visual cues (left or right). Two task factors, signal intensity and foreperiod duration, were manipulated. Low doses of two pharmacological agents, SCH 23390 (a D 1 receptor antagonist; 0.015 and 0.025 lmol/kg) and eticlopride (a D 2 receptor antagonist; 0.01 and 0.02 lmol/kg), were administrated systemically. Both drugs increased choice RT: eticlopride interacted with signal intensity on RT, showing that D 2 receptors mediate at least the sensory stage of stimulus preprocessing. In addition, eticlopride interacted with signal intensity on omission rate, thereby suggesting an involvement of D 2 receptors in attentional processes; and SCH 23390 interacted with foreperiod duration on RT, indicating that D 1 receptors specifically mediate the response adjustment stage. The effect of this drug on RT rests entirely in its interaction with foreperiod duration, allowing us to conclude that this D 1 antagonist affects the response adjustment stage while sparing all other processing stages. Behavioural Pharmacology 14:589–598  c 2003 Lippincott Williams & Wilkins. Behavioural Pharmacology 2003, 14:589–598 Keywords: information processing, dopamine receptor antagonists, reaction time, additive factor method, rat, Parkinson’s disease a Institut de Me ´ decine Navale du Service de Sante ´ des Arme ´es, Toulon and b Centre National de la Recherche Scientifique et Universite ´ de Provence, Laboratoire de Neurobiologie de la Cognition, Marseille, France. Sponsorship: The present work was supported in part by the Direction Ge ´ ne ´ rale pour l’Armement (grant no. 99 08 01). Correspondence and requests for reprints to Alain Courtie ` re, Institut de Me ´ decine Navale du Service de Sante ´ des Arme ´es, 83800 Toulon Naval, France. E-mail: a.courtiere@imnssa.net Received 21 July 2003 Accepted as revised 26 September 2003 Introduction Parkinson’s disease is associated with the loss of dopaminergic neurons in the substantia nigra. Patients suffering from this disease typically display longer reaction times (RTs) than matched controls (Phillips et al., 1989), which indicates that dopamine plays an important role in sensorimotor performance. Numerous studies performed in patients with Parkinson’s disease (Hallett, 1990; Jahanshahi et al., 1992; Brown et al., 1993; for a review see Gauntlett-Gilbert and Brown, 1998) and in lesioned rats (Brown and Robbins, 1991; Amalric et al., 1995; Baunez et al., 1995; Baunez and Robbins, 1999) allow us to refine this conclusion by showing that the dopaminergic system is involved in the control of motor processes specifically implemented during the RT interval. In addition, dopamine is a major neurotransmit- ter in the retina (for reviews see Witkovsky and Dearry, 1992; Djamgoz et al., 1997; Nguyen-Legros et al., 1999), suggesting that it may likewise mediate visual non-motor processing. D 1 and D 2 receptors are both found in retina cells, but their respective contribution to visual informa- tion processing has not been evaluated a priori. Previous RT studies evaluating the effects of dopamine antagonists have mostly been conducted in animals performing simple RT tasks (Amalric et al., 1993; Marrow et al., 1993; Smith et al., 2000) or more rarely choice RT task (Blokland and Honig, 1999). Different deficits have been elicited by D 1 and D 2 receptor antagonists. In the experiment of Amalric et al. (1993), for instance, D 2 receptor antagonists increased both simple RT and the frequency of incorrect responses, while D 1 receptor antagonists were ineffective in the same task. D 2 receptors seem therefore more involved in sensorimotor processing than D 1 receptors. However, owing to the use of a simple RT task, this conclusion may require further refinement. In simple RT tasks, there is no uncertainty regarding the stimulus to be presented and the response to be emitted, because these events are always the same. The subject can prepare responses in advance and simply release the prepared response when the go-signal occurs (Durup and Requin, 1970; Requin et al., 1991). As a consequence, the processing necessary to perform a simple RT task efficiently consists in synchronizing the prepared response with the occurrence of the response signal (for a recent thoughtful description of the processes involved in simple RT, see Risterucci et al., 2003). Therefore, it seems premature to ascribe simple RT variations unambiguously to differences in the processing of the information conveyed by the go-signal. 0955-8810  c 2003 Lippincott Williams & Wilkins DOI: 10.1097/01.fbp.0000104030.08123.de Copyright © Lippincott Williams & Wilkins. Unauthorized reproduction of this article is prohibited. Copyright © Lippincott Williams & Wilkins. Unauthorized reproduction of this article is prohibited.