CORE Metadata, citation and similar papers at core.ac.uk Provided by Frontiers - Publisher Connector ORIGINAL RESEARCH ARTICLE published: 19 May 2014 BEHAVIORAL NEUROSCIENCE doi: 10.3389/fnbeh.2014.00183 Behavioral and electrophysiological effects of endocannabinoid and dopaminergic systems on salient stimuli Daniela Laricchiuta 1,2*, Alessandra Musella 1,3, Silvia Rossi 1,3 and Diego Centonze 1,3 1 IRCCS Fondazione Santa Lucia, Rome, Italy 2 Dipartimento di Psicologia, Facoltà di Medicina e Psicologia, Università “Sapienza” di Roma, Rome, Italy 3 Dipartimento di Neuroscienze, Università Tor Vergata, Rome, Italy Edited by: Rewarding effects have been related to enhanced dopamine (DA) release in James P.Herman, University of corticolimbic and basal ganglia structures. The DAergic and endocannabinoid interaction Cincinnati, USA in the responses to reward is described. This study investigated the link between Reviewed by: Gregg Stanwood, Vanderbilt endocannabinoid and DAergic transmission in the processes that are related to response University, USA to two types of reward, palatable food and novelty. Mice treated with drugs acting on Steven R. Laviolette, University of endocannabinoid system (ECS) (URB597, AM251) or DAergic system (haloperidol) were Western Ontario, Canada submitted to approach-avoidance conflict tasks with palatable food or novelty. In the same *Correspondence: mice, the cannabinoid type-1 (CB1)-mediated GABAergic transmission in medium spiny Daniela Laricchiuta, Dipartimento di Psicologia, Facoltà di Medicina e neurons of the dorsomedial striatum was analyzed. The endocannabinoid potentiation by Psicologia, Università “Sapienza” di URB597 magnified approach behavior for reward (food and novelty) and in parallel inhibited Roma, via dei Marsi 78, 00185 dorsostriatal GABAergic neurotransmission. The decreased activity of CB1 receptor by Rome, Italy AM251 (alone or with URB597) or of DAergic D receptor by haloperidol had inhibitory e-mail: 2 [email protected] effects toward the reward and did not permit the inhibition of dorsostriatal GABAergic transmission. When haloperidol was coadministered with URB597, a restoration effect on reward and reward-dependent motor activity was observed, only if the reward was the palatable food. In parallel, the coadministration led to restoring inhibition of CB1-mediated GABAergic transmission. Thus, in the presence of simultaneous ECS activation and inhibition of DAergic system the response to reward appears to be a stimulus-dependent manner. Keywords: conflicting tasks, approach/avoidance motivation, haloperidol, URB597, AM251 INTRODUCTION ganglia structures (Bassareo et al., 2002; Ito et al., 2002; Lupica Survival strictly depends on the drive with which subjects seek and Riegel, 2005). Thus, DA is a neurosignal that has been natural reinforcers, such as food, water, sex, and maternal evolutionarily adjusted to boost the organism toward reinforcer care. Converging electrophysiological, biochemical, and behav- (Alcaro and Panksepp, 2011). ioral evidence implicates the endocannabinoid system (ECS) in There is increasing evidence that implicates a dynamic DAergic the neurobiological events that attribute value to various types and endocannabinoid interaction in neuronal, endocrine, and of reinforcers (Maldonado et al., 2006; Marsicano and Lutz, metabolic responses to reward (Di Marzo et al., 2004; Fernández- 2006; Laricchiuta et al., 2012a,b). The ECS mediates the balance Ruiz et al., 2010). The inhibitory effects of the ECS against DAer- between approach and avoidance behaviors toward stimuli in gic neurons in mesolimbic structures have been hypothesized humans (Van Laere et al., 2009) and rodents (Lafenêtre et al., to attribute the salience to reward. Supporting this model, CB1 2009; Laricchiuta et al., 2012a,b), the detailed mechanism of antagonists impair the attribution of salience to a stimulus (De which is unknown. Vries et al., 2001; Fattore et al., 2003). Further, the ECS has been Most central ECS functions are mediated by cannabinoid implicated in several neuropsychiatric conditions, including DA- type-1 (CB1) receptors (Freund et al., 2003; Piomelli, 2003) that related disorders, such as schizophrenia (Emrich et al., 1997), presynaptically inhibit primarily glutamatergic and GABAergic Parkinson disease (Maccarrone et al., 2003), and drug addiction transmission, but also dopaminergic and cholinergic transmis- (Maldonado and Rodríguez de Fonseca, 2002). In these patholog- sion (Matias and Di Marzo, 2007; Kano et al., 2009). Notably, ical conditions, involvement of the ECS likely reflects the activity the reward effects of primary reinforcers or environmental stimuli of reward circuitry, which comprises midbrain DAergic neurons that are associated with food or drug intake have been related and their target structures (Berke and Hyman, 2000; Everitt and to enhanced dopamine (DA) release in corticolimbic and basal Wolf, 2002). Frontiers in Behavioral Neuroscience www.frontiersin.org May 2014 | Volume 8 | Article 183 | 1 Laricchiuta et al. Endocannabinoids, dopamine and reward This study aimed to behaviorally and electrophysiologically BEHAVIORAL TESTING: APPROACH/AVOIDANCE Y-MAZE (A/A Y-MAZE) examine endocannabinoid and DAergic involvement in processes This test was performed as previously described (Laricchiuta et al., that are related to seeking two types of reward: palatable food and 2012a,b). In particular, the apparatus consisted of a Plexiglas Y- novelty. The interaction between the ECS and DAergic system in maze with a starting gray arm from which two arms (8 cm × processing salient information is attracting significant interest. 30 cm × 15 cm) stemmed, arranged 90◦ to each other. A T- In this study, mice that were treated with drugs that act on guillotine door was placed at the end of the starting arm to prevent the ECS or DAergic system were subjected to approach-avoidance the animal from returning to the start. An arm entry was defined conflict tasks with two rewards (food or novelty). In addition, as four legs entering one of the arms. The two arms of choice CB1-mediated GABAergic transmission in medium spiny neu- differed in color and brightness—one of the two arms had a rons of the dorsomedial striatum was analyzed. This area is the black and opaque floor and walls and no light inside, whereas ideal structure to study the interplay between the ECS or DAergic the other had a white floor and walls and was lit by a 16-W neon systems, because it has a high density of CB1 and DAergic recep- lamp. Notably, the colored “furniture” and the neon lamp were tors (Piomelli, 2003) and is critical in goal-directed behaviors exchangeable between arms to alternate the position of the white (Koob and Volkow, 2010). and black arms. The apparatus was placed in a dim room that was lit by a MATERIALS AND METHODS red light (40 W) and was cleaned thoroughly with 70% ethanol SUBJECTS and dried after each trial to remove scent cues. At the end of Young (32 ± 2 days) male C57BL/6JOlaHsd mice (Harlan, Italy) each arm of choice, there was a blue chemically inert tube cap were used. All animals were housed, 4 per cage, with food (3 cm in diameter, 1 cm deep) that was used as a food tray. (Mucedola 4RF21, Italy) and water ad libitum. The mice were kept The depth of the tray prevented mice from seeing the reward at under a 12-h light/dark cycle with the lights coming on at 07:00 h, a distance but permitted easy reward—i.e., eating. Because the controlled temperature (22–23◦C), and constant humidity (60 ± appetites for palatable foods must be learned (Lafenêtre et al., 5%). All efforts were made to minimize animal suffering and 2009), 1 week before the behavioral testing, the animals were reduce the number of animals that were used, per the European exposed to a novel palatable food (Fonzies, KP Snack Foods, Directive (2010/63/EU). Munchen, Germany) in their home cages for three consecutive All animals (n = 10/group) included in the present study were days (Bassareo et al., 2002). Fonzies (8% protein, 33% fat, and behaviorally tested in the Approach/Avoidance Y-Maze (A/A Y- 53% carbohydrate, for a caloric value of 541 kcal/100 gm) consist Maze) and the Open-Field test with novel object. Both tasks of corn flour, hydrogenate vegetable fat, cheese powder, and permit to detect crucial components of animal behavior linked salt. to approach-avoidance motivation, as the tendency to explore, At the start of behavioral testing, the mice were subjected to a respond to an environmental change or seek for reward and 1-day habituation phase in which all Y-Maze arms were opened to novelty. In fact, the explorative drive represents the prerequisite of encourage exploration of the maze without the presence of food. the recognition and seeking for novel stimuli, crucial components The white and lit arm was placed on the right side of the apparatus of approach and avoidance motivation. for the first 5 min and then on the left side for the subsequent Experimental procedures are shown in Figure 1. 5 min. To increase the motivation to search for the reward, the animals were slightly food-deprived by limiting access to food in the 10 h before the test; this procedure did not result in any body weight loss. The testing phase (24 h after the habituation phase) comprised two 10-trial sessions. In Session 1 (S1), the animal was placed in the starting arm and could choose to enter one of the two arms, both containing the same standard food reward. After eating, the animal was allowed to stand in its cage for a 1-min intertrial interval. At the end of each trial, the reward was replaced. The spatial position of each arm (black and dark or white and lit) was sequentially exchanged and side-balanced during the entire test to exclude any preference with regard to side. During Session 2 (S2), starting 24 h after S1, the white arm was rewarded with the highly palatable food (Fonzies), and the black arm was rewarded with the standard food pellet. Forty-eighty hours after S2, the animals were retested (S3) in FIGURE 1 | Procedures and global timing of experimental design.