Cue-induced conditioned activity does not incubate but is mediated by the basolateral amygdala

Cannabinoid Type 1 Receptors in the Basolateral Amygdala Regulate ACPA-Induced Place Preference and Anxiolytic-Like Behaviors

The number of cannabis users is increasing in the world. However, the mechanisms involved in the psychiatric effects and addiction formation remain unclear. Medical treatments against cannabis addiction have not yet been established. Δ9-Tetrahydrocannabinol (THC), the main active substance in cannabis, binds and affects cannabinoid type 1 receptors (CB1R) in the brain. The mice were intraperitoneally (i.p.) administered arachidonylcyclopropylamide (ACPA), a CB1R-selective agonist, and then two behavioral experiments on anxiety and addiction were performed. Administration of ACPA caused anxiolytic-like behavior in the elevated plus maze test. In addition, ACPA increased place preference in a conditioned place preference (CPP) test. The basolateral amygdala (BLA), which is the focus of this study, is involved in anxiety-like behavior and reward and is reported to express high levels of CB1R. We aimed to reveal the role of CB1R in BLA for ACPA-induced behavior. AM251, a CB1R selective antagonist, was administered intra-BLA before i.p. administration of ACPA. Intra-BLA administration of AM251 inhibited ACPA-induced anxiolytic-like behavior and place preference. These results suggest that CB1R in the BLA contributes to behavior disorders caused by the acute or chronic use of cannabis.

Comparison of the Time-Dependent Changes in Immediate Early Gene Labeling and Spine Density Following Abstinence From Contingent or Non-contingent Chocolate Pellet Delivery

Rationale: Incubation of craving is a phenomenon whereby responding for cues associated with a reward increases over extended periods of abstinence. Both contingent and non-contingent behavioral designs have been used to study the incubation of craving phenomenon with differing results. The present study directly compares behavioral and neural changes following contingent or non-contingent administration of chocolate flavored pellets.

Objective: The current study examined whether an incubation of craving response would be observed at the behavioral and neural levels following delays of abstinence from chocolate pellets in a contingent or non-contingent reinforcement design.

Methods: Rats were trained for 10 days to bar press for chocolate pellets (contingent) or received chocolate pellets in a non-contingent design (classical conditioning). Groups were then subjected to abstinence from the reward for 24 h, 7, 14 or 28 days at which point they were tested for responding for reward associated cues. Following the test, brains from all rats were processed and assessed for c-Fos and FosB labeling as well as dendritic spine density in the nucleus accumbens (NAc).

Results: Behavioral measures during the test (lever presses, food hopper entries and locomotor activity) revealed similar behavioral outcomes across all delays indicating the lack of an incubation of craving response on both the contingent and non-contingent designs. Overall, labeling of c-Fos in the NAc was lower for the non-contingent group compared to the operant-trained and food restricted control. Compared to the operant-trained and non-trained control groups, a significantly reduced FosB labeling was noted in the NAc of the classically conditioned groups across all abstinence periods. Spine density in the NAc was elevated in both the classically and operant conditioned compared to the food-restricted, non-trained controls.

Conclusions: Chocolate pellet reward did not result in incubation of craving but did produce behavioral learning that was associated with increased spine density. This suggests that chocolate pellet administration results in long-term structural and functional changes that are present for at least 28 days following abstinence. Contingent and non-contingent administration resulted in differential immediate early gene labeling in the NAc, but the functional significance of this has yet to be elucidated.

Age-dependent differences in the strength and persistence of psychostimulant-induced conditioned activity in rats: effects of a single environment-cocaine pairing

The aim of the present study was to determine the strength and persistence of cocaine-induced conditioned activity in young and adult rats. A one-trial protocol has proven useful for studying the ontogeny of psychostimulant-induced behavioral sensitization; therefore, a similar procedure was used to examine conditioned activity. On postnatal day (PD) 19 or PD 80, rats were injected with saline or cocaine in either a novel test chamber or the home cage. After various drug abstinence intervals (1-21 days), rats were injected with saline and returned to the test chamber, where conditioned activity was assessed. In a separate experiment, we examined whether cocaine-induced conditioned activity was a consequence of Pavlovian conditioning or a failure to habituate to the test environment. The results indicated that adult rats showed strong one-trial conditioned activity that persisted for at least 21 days, whereas young rats did not show a conditioned locomotor response. The conditioned activity shown by adult rats did not result from a failure to habituate to the cocaine-paired environment. These results indicate that cocaine-paired contextual stimuli differentially affect behavior depending on the age of the animal. The data obtained from adult rats have potential translational relevance for humans because a single environment-drug pairing caused long-term alterations in behavior.

Activation of physiological stress responses by a natural reward: Novel vs. repeated sucrose intake

Pharmacological rewards, such as drugs of abuse, evoke physiological stress responses, including increased heart rate and blood pressure, and activation of the hypothalamic-pituitary-adrenal (HPA) axis. It is not clear to what extent the natural reward of palatable foods elicits similar physiological responses. In order to address this question, HPA axis hormones, heart rate, blood pressure and brain pCREB immunolabeling were assessed following novel and repeated sucrose exposure. Briefly, adult, male rats with ad libitum food and water were given either a single (day 1) or repeated (twice-daily for 14 days) brief (up to 30 min) exposure to a second drink bottle containing 4 ml of 30% sucrose drink vs. water (as a control for bottle presentation). Sucrose-fed rats drank more than water-fed on all days of exposure, as expected. On day 1 of exposure, heart rate, blood pressure, plasma corticosterone, and locomotion were markedly increased by presentation of the second drink bottle regardless of drink type. After repeated exposure (day 14), these responses habituated to similar extents regardless of drink type and pCREB immunolabeling in the hypothalamic paraventricular nucleus (PVN) also did not vary with drink type, whereas basolateral amygdala pCREB was increased by sucrose intake. Taken together, these data suggest that while sucrose is highly palatable, physiological stress responses were evoked principally by the drink presentation itself (e.g., an unfamiliar intervention by the investigators), as opposed to the palatability of the offered drink.