Partial extinction of a conditioned context enhances preference for elements previously associated with cocaine but not with chocolate

Genotype-dependent functional role of the anterior and posterior paraventricular thalamus in pavlovian conditioned approach

RATIONALE

The specific location of deviations from normative models of brain function varies considerably across individuals with the same diagnoses. However, as pathological processes are distributed across interconnected systems, this heterogeneity of individual brain deviations may also reveal similarities and differences between disorders. The paraventricular nucleus of the thalamus (PVT) is a potential switcher to various behavioral responses where functionally distinct cell types exist across its antero-posterior axis.

OBJECTIVES

This study aimed to test the hypothesis that genotype-dependent differences in the anterior and posterior PVT subregions (aPVT and pPVT) are involved in the Sign-tracking (ST) behavior expressed by C57BL/6J (C57) and DBA/2J (DBA) inbred mice.

METHODS

Based on previous findings, male mice of the two strains were tested at ten weeks of age. The density of c-Fos immunoreactivity along the antero-posterior axis of PVT was assessed following the expression of ST behavior. Selective excitotoxic lesions of the aPVT or the pPVT by the NMDA infusion were performed prior to development of ST behavior. Finally, the distribution of neuronal populations expressing the Drd2 and Gal genes (D2R + and Gal +) was measured by in situ hybridization (ISH).

RESULTS

The involvement of PVT subregions in ST behavior is strain-specific, as aPVT is crucial for ST acquisition in DBA mice while pPVT is crucial for C57 mice. Despite similar antero-posterior distribution of D2R + and Gal + neurons, density of D2R + neurons differentiate aPVT in C57 and DBA mice.

CONCLUSIONS

These genotype-dependent results offer valuable insights into the nuanced organization of brain networks and individual variability in behavioral responses.

Exploring time-dependent changes in conditioned place preference for food reward and associated changes in the nucleus accumbens

The conditioned place preference (CPP) procedure has been used to study the incubation of craving phenomenon with rewarding drugs such as cocaine and methamphetamine. The present study examined whether rats trained in a CPP behavioral design would display an incubation of craving response for chocolate-flavored pellets or milk chocolate chips at the behavioral and neural levels. Rats were conditioned using an unbiased CPP design then underwent abstinence from food reward for 24 hs, 7, 14, or 28 days at which point they were tested for CPP. Brains underwent immunohistochemical staining for c-Fos and FosB as well as Golgi staining to assess dendritic spine density in the nucleus accumbens (NAc). A time-dependent increase in CPP and entries into the previously paired compartment was observed in the chocolate-flavored pellet group but not the milk chocolate group. Time-dependent neural changes were not directly associated with behavioral outcomes but c-Fos labelling was higher in the chocolate pellet group than controls at the 7-day abstinence period. The behavioral results show that chocolate pellets are rewarding and are associated with long-term behavioral changes but, as evidenced by limited neural changes, these food rewards do not have the same effects on the NAc as drugs of abuse.

Consumption of a highly palatable food induces a lasting place-conditioning memory in marmoset monkeys

Highly palatible foods may induce addiction-related behaviors. However, this has yet to be established in non-human primates. Therefore, we evaluated whether marmoset monkeys (Calllithrix penicillata) acquire a conditioned-place-preference (CPP) for chocolate and if this response is detectable after a 24-h and 15-day period. Subjects were first habituated to a two-compartment CPP box and then randomly assigned to a chocolate or control group. Thereafter, they were given access to only one compartment during daily 15-min conditionings, held on six consecutive days. On each trial, the chocolate group received pieces of chocolate (50g) in this context, whereas controls were not given a food reward. Marmosets were subsequently tested for preferring this (food) paired context after a 24-h and 15-day interval. During conditioning, individual foraging and the amount of chocolate ingested by each pair of the chocolate group remained constant. However, compared to pre-CPP levels, the time spent inside/in contact with the conditioned compartment increased significantly, while the latency to first entry decreased on both post-CPP intervals. For controls, the parameters remained unaltered. Thus, chocolate induced a persistent CPP response-an aspect usually associated with drug-related rewards.