Food deprivation facilitates reinstatement of morphine-induced conditioned place preference: Role of intra-accumbal dopamine D2-like receptors in associating reinstatement of morphine CPP with stress

Natural rewards are essential for animal survival. On the other hand, drug-seeking behaviours can be maladaptive and endanger survival. The present study was conducted to enhance our understanding of how animals respond to food and morphine as natural and drug rewards, respectively, in a conditioned place preference (CPP) paradigm. We designed a protocol to induce food-CPP and compare it as a natural reward with morphine-CPP in rats. The protocol for reward induction in all groups (foods and morphine) consisted of three phases: pre-test, conditioning, and post-test. In morphine groups, we injected morphine as a reward (5 mg/kg, s.c.), and for inducing natural-reward, we used two different protocols, by one of the rats were deprived of food for 24h. In the other method, rats were restricted for food for 14 days. During the conditioning period, animals received daily chow, biscuit, or popcorn as a reward inducer. Results revealed that CPP did not induce in food-deprived rats. A combination of food restriction (as a facilitator) and a biscuit or popcorn induced reward using CPP. In contrast, food deprivation did not facilitate food-CPP in response to regular food. Interestingly the CPP score of the group which received biscuit during a 7-day conditioning period was more than that of the morphine group. In conclusion, food restriction could be a better protocol than food deprivation to facilitate food reward.

Download Full-text

The Effect of the mGlu8 Receptor Agonist, S-3,4-DCPG on Acquisition and Expression of Morphine-induced Conditioned Place Preference in Male rats

10.21203/rs.3.rs-114995/v2 ◽

2021 ◽

Author(s):

Nazanin Kahvandi ◽

Zahra Ebrahimi ◽

Seyed Asaad Karimi ◽

Siamak Shahidi ◽

Iraj Salehi ◽

...

Keyword(s):

Conditioned Place Preference ◽

Metabotropic Glutamate Receptors ◽

Preference Test ◽

Place Preference ◽

Male Rats ◽

Dependent Manner ◽

Metabotropic Glutamate ◽

Male Wistar Rats ◽

Dose Dependent

Abstract Background: The nucleus accumbens (NAc) plays a principal role in drug reward. It has been reported that metabotropic glutamate receptors (mGlu receptors) play a key role in the rewarding pathway(s). Previous studies have shown the vast allocation of the different types of mGlu receptors, including mGlu8 receptors, in regions that are associated with opioid rewards, such as the NAc. The aim of the present study was to evaluate the role of mGlu8 receptors within the NAc in the acquisition and expression phases of morphine induced conditioned place preference (CPP). Adult male Wistar rats were bilaterally implanted by two cannulas' in the NAc and were evaluated in a CPP paradigm. Selective mGlu8 receptor allosteric agonist (S-3,4-DCPG) was administered at doses of 0.03, 0.3, and 3 μg/0.5 μL saline per side into the NAc on both sides during the 3 days of morphine (5 mg/kg) conditioning (acquisition) phase, or before place preference test, or post-conditioning (expression) phase of morphine-induced CPP. Results: The results revealed that intra-accumbal administration of S-3,4-DCPG (0.3 and 3 μg) markedly decreased the acquisition in a dose-dependent manner but had no effect on expression of morphine-induced CPP. Conclusions: The findings suggest that activation of mGlu8 receptors in the NAc dose-dependently blocks the establishment of morphine-induced CPP and reduces the rewarding properties of morphine which may be related to the glutamate activity into the NAc and in reward pathway(s). These data suggest that mGlu8 receptor may be involved in conditioned morphine reward.

Download Full-text