The striatal region of the mouse’s brain was cryosectioned to 10 m slices and imaged by the dual-wavelength microscope setup (Fig. calcium ([Ca2+]i, marker of neuronal activation) to acute cocaine in striatal D1R-EGFP and D2R-EGFP-expressing neurons between control and chronically treated mice. Chronic cocaine attenuated responses to acute cocaine in D1R (blunting Ca2+ increases by 67 16%) and D2R (blunting Ca2+ decrease by 72 17%) neurons in most D1R and D2R neurons (75%). However, the dynamics Celecoxib of this attenuation during cocaine intoxication was longer lasting for D2R than for D1R. Thus, whereas control mice showed a fast but short-lasting predominance of D1R over D2R signaling (peaking at 8 min) during acute cocaine intoxication, in chronically treated mice D1R predominance was sustained for 30 min (throughout the measurement period). Thus, chronic cocaine use dramatically reduced cocaine-induced DA signaling, shifting the balance between D1R and D2R signaling during intoxication to a predominance of D1R (stimulatory) over D2R (inhibitory) signaling, which might facilitate compulsive intake in addiction. Introduction Dopamine (DA) increases triggered by cocaine and the consequent stimulation of DA receptors (including D1 and D2 receptors) in brain reward regions are associated with its rewarding effects (Koob and Bloom, 1988). However, while facilitation of D1 Celecoxib receptor (D1R) signaling enhances the rewarding effects of cocaine (Graham et al., 2007), facilitation of D2R signaling decreases cocaine reward (Lobo et al., 2010), which indicates that for cocaine to be rewarding it must result in a predominance of D1R over D2R signaling. Thus, an imbalance between the signaling through D1R (enhancing) and D2R (attenuating) resulting in enhanced D1R or attenuated D2R signaling during cocaine intoxication could increase its incentive salience as observed in cocaine addiction (Thompson et al., 2010). Preclinical studies have shown that the enhancement of D2R signaling decreases cocaine reward (Lobo et al., 2010) and interferes with cocaine self-administration (Thanos et al., 2008), whereas interfering with D2R signaling facilitates cocaine sensitization (Luo et al., 2011). This is in contrast with the increased sensitivity to cocaine reward reported with enhancement of D1R signaling (Lobo et al., Celecoxib 2010). In the striatum, D1R and D2R are expressed in medium spiny neurons (MSNs) and exert opposing intracellular effects on cAMP signaling; D1R activates it, whereas D2R inhibits it (Sibley et al., 1993). Repeated cocaine use has been reported to upregulate the cAMP signaling pathway, which would be suggestive of enhanced D1R over D2R signaling (Anderson and Pierce, 2005). However, others have reported no changes or decreases in cAMP with chronic cocaine exposures (Crawford et al., 2004). Thus, the extent to which chronic cocaine use can modify the relative prevalence of D1R over D2R signaling is still unclear. Moreover, the effects of chronic cocaine use on the relative changes in D1R over D2R signaling during cocaine intoxication have not been investigated. In cocaine abusers, D2R signaling during intoxication with stimulant drugs (methylphenidate and amphetamine) is markedly attenuated when compared with controls (for review, see Volkow et al., 2011). Since the loss of control in cocaine-addicted individuals is triggered when they are exposed to cocaine or to cocaine cues, it is important to study the effects of chronic cocaine exposure on DA signaling during cocaine intoxication. Here, we tested the hypothesis that chronic cocaine exposure reduces cocaine-induced increases in DA signaling but enhances the predominance of D1R over D2R signaling during cocaine intoxication. For this purpose, optical imaging was used to measure the effects of acute cocaine intake on the dynamic changes in [Ca2+]i (a marker of cell function) using Rhod2 (a fluorescent [Ca2+]i indicator) in striatal MSNs of transgenic mice that expressed EGFP under the control of either the D1R or the D2R gene (Gong et al., 2003). A custom epifluorescence microscope integrated with a microneedle endoscope [Luo et al., Rabbit polyclonal to PBX3 2011; , 1 25 mm; 0.65 numerical aperture (NA)] allowed us to simultaneously image striatal EGFP in individual D1R- or D2R-expressing neurons and their [Ca2+]i changes in response to acute cocaine use (8 Celecoxib mg/kg, i.p.) in naive mice (referred to as control mice) and in.