Dopamine Overflow in the Nucleus Accumbens during Extinction and Reinstatement of Cocaine Self-Administration Behavior

146

143

The transition from drug use to drug addiction is associated with a process of escalation, whereby drug use becomes excessive and difficult to control. Several mechanisms have been advanced to explain escalating patterns of drug use as opposed to nonescalating patterns. Although current evidence favors hedonic tolerance, there remains some dispute about the contribution of behavioral sensitization to cocaine intake escalation. Here, we concurrently assessed the ability of cocaine to induce psychomotor sensitization and drug-seeking behavior in animals with 1-h (short access or ShA) vs 6-h (long access or LgA) access to intravenous (i.v.) cocaine selfadministration. As expected, cocaine intake by LgA rats escalated over time and became excessive compared to cocaine intake by ShA rats, which remained low and stable. Despite escalated levels of cocaine consumption, however, LgA rats were not more sensitized to cocaine than ShA rats. The dose-effect function for cocaine-induced locomotion (0.125-1 mg, i.v.) was shifted to the left in LgA rats by the same amount as in ShA rats after cocaine self-administration. In contrast, LgA rats were much more responsive than ShA rats to the motivational effects of cocaine, as measured by the ability of i.v. cocaine to reinstate extinguished drug-seeking behavior. This study demonstrates a dissociation of psychomotor sensitization from the change in motivation underlying the transition to compulsive cocaine consumption, and therefore suggests that responsiveness to the motivational effects of the drug, not psychomotor sensitization, would represent a specific behavioral marker of the transition to and maintenance of compulsive cocaine use.

Section: Discussioncontrasting

confidence: 40%

Dissociation of Psychomotor Sensitization from Compulsive Cocaine Consumption

Ahmed¹,

Cador²

2005

146

143

“…of cocaine. It has been reported that in rats undergoing reinstatement testing or extinction from cocaine self-administration, there is significant attenuation of cocaine-induced increases in extracellular DA in the nucleus accumbens (Neisewander et al, 1996;Mateo et al, 2005; but see Hooks et al, 1994). In contrast, electrical BSR per se appears to enhance nucleus accumbens DA (You et al, 2001).…”

Section: Ngb 2904's Inhibition Of Cocaine-triggered Reinstatement Of mentioning

confidence: 99%

The Novel Dopamine D3 Receptor Antagonist NGB 2904 Inhibits Cocaine's Rewarding Effects and Cocaine-Induced Reinstatement of Drug-Seeking Behavior in Rats

Newman

Gilbert

et al. 2005

145

177

Accumulating evidence indicates that dopamine (DA) D 3 receptor antagonists appear highly promising in attenuating cocaine reward and relapse in preclinical models of addiction. In the present study, we investigated the effects of the novel D 3 -selective antagonist NGB 2904 (N-(4-[4-{2,3-dichlorophenyl}-1-piperazinyl]butyl)-3-fluorenylcarboxamide) on cocaine self-administration, cocaine-enhanced brain stimulation reward (BSR), and cocaine-triggered reinstatement of drug-seeking behavior in male Long-Evans rats. We found that: (1) acute intraperitoneal (i.p.) administration of NGB 2904 (0.1-10 mg/kg) failed to alter cocaine self-administration (0.5 mg/kg/infusion) under fixed-ratio 2 (FR2) reinforcement, but 1 or 5 mg/kg NGB 2904 significantly lowered the break-point for cocaine self-administration under progressive-ratio (PR) reinforcement; (2) cocaine (1, 2, and 10 mg/kg) significantly enhanced electrical BSR (decreased brain reward thresholds), while NGB 2904 significantly inhibited the enhancement of BSR elicited by 2 mg/kg, but not 10 mg/kg of cocaine; (3) NGB 2904 alone neither maintained self-administration behavior nor altered brain reward thresholds; and (4) NGB 2904 significantly inhibited cocaine-triggered reinstatement of extinguished drug-seeking behavior, but not sucrose-plus-sucrose-cue-triggered reinstatement of sucrose-seeking behavior. Overall, these data show that the novel D 3 -selective antagonist NGB 2904 attenuates cocaine's rewarding effects as assessed by PR self-administration, BSR, and cocaine-triggered reinstatement of cocaine-seeking behavior. Owing to these properties and to its lack of rewarding effects (as assessed by BSR and by substitution during drug self-administration), NGB 2904 merits further investigation as a potential agent for treatment of cocaine addiction.

“…Thus, as with the behavioral profiles produced by these early environmental insults, a presensitization of mesolimbic dopamine transmission may be a common neurochemical alteration produced by prenatal and early postnatal stress that endures into adulthood. Given the important role for NAC dopamine transmission in drug-seeking behavior (Anderson et al, 2003Bachtell et al, 2005;Di Ciano et al, 2001;Neisewander et al, 1996;Ranaldi et al, 1999;, enhanced NAC dopamine responsiveness may contribute to the enhanced cocaineseeking observed in PNS rats.…”

Section: Influence Of Pns On Neurochemical Responses To Cocainementioning

confidence: 99%

Prenatal Stress Enhances Responsiveness to Cocaine

Kippin

Szumlinski

Kapasova

et al. 2007

Early environmental events have profound influences on a wide range of adult behavior. In the current study, we assessed the influence of maternal stress during gestation on psychostimulant and neurochemical responsiveness to cocaine, cocaine self-administration, and reinstatement of cocaine-seeking in adult offspring. Pregnant, female Sprague-Dawley rats were subjected to either no treatment or to restraint stress three times per day for the last 7 days of gestation and cocaine-related behavior was assessed in offspring at 10 weeks of age. Relative to controls, a noncontingent cocaine injection elevated locomotor activity as well as nucleus accumbens levels of extracellular dopamine and glutamate to a greater extent in both cocaine-naïve and cocaine-experienced prenatal stress (PNS) rats and elevated prefrontal cortex dopamine in cocaine-experienced PNS rats. To assess the impact of PNS on cocaine addiction-related behavior, rats were trained to lever press for intravenous (i.v.) infusions of cocaine (0.25, 0.5, or 1 mg/kg/infusion), with each infusion paired with a light + tone-conditioned stimulus. Lever-pressing was extinguished and cocaine-seeking reinstated by re-exposure to the conditioned cues or by intraperitoneal cocaine-priming injections (5 or 10 mg/kg). PNS elevated active lever responding both during extinction and cocaine-primed reinstatement, but not during self-administration or conditioned-cued reinstatement. PNS also did not alter intake during self-administration. These findings demonstrate that PNS produces enduring nervous system alterations that increase the psychomotor stimulant, motivational, and neurochemical responsiveness to noncontingent cocaine. Thus, early environmental factors contribute to an individual's initial responsiveness to cocaine and propensity to relapse to cocaine-seeking.