Conditioned Place Aversion Model Research Articles

A Series Circuit from CA1 of Dorsal Hippocampus to Basolateral Amygdala via Postrhinal Cortex Participates in Conditioned Context-Induced Retrieval of Morphine Withdrawal Memory

Background: Conditioned context-induced retrieval of drug withdrawal memory contributes to drug relapse. The basolateral amygdala (BLA) plays an important role in conditioned context-induced retrieval of morphine withdrawal memory. However, the upstream pathways of the activation of the BLA by conditioned context remains to be studied. Methods: Using the conditioned place aversion model, chemical-genetic method, trans-neuronal virus tracing technique and immunohistochemical method, we studied the upstream neural circuits of the activation of the BLA during conditioned context-induced retrieval of morphine withdrawal memory. Findings: The present results show that the dorsal CA1 of the hippocampus is an upstream brain region of the activation of the BLA during conditioned context-induced withdrawal memory retrieval; the indirect connection from dorsal CA1 of the hippocampus to the BLA is enhanced in mice with conditioned place aversion; the postrhinal cortex (POR) is a brain region that connects the dorsal CA1 of the hippocampus and the activation of the BLA in conditioned context-induced retrieval of morphine withdrawal memory. Interpretation: These results suggest that a series circuit from CA1 of dorsal hippocampus to basolateral amygdala via postrhinal cortex participates in conditioned context-induced retrieval of morphine withdrawal memory. Funding Statement: This study was supported by the National Program of Basic Research sponsored by the Ministry of Science and Technology of China (2009CB52201 and 2013CB835100) and Project of Foundation of National Natural Science of China (31121061, 91332204, 81371466 and 31070932). Declaration of Interests: All authors declare no conflicts of interest. Ethics Approval Statement: All experimental procedures conformed to Fudan University as well as international guidelines on the ethical use of animals. All efforts were made to minimize animal suffering and reduce the number of animals used.

Expression of protein kinase A and the kappa opioid receptor in selected brain regions and conditioned place aversion in morphine-dependent rats.

This study examined adaptive changes in protein kinase A (PKA) and kappa opioid receptor (KOR) in selected addiction-related brain regions before and after conditioned place aversion (CPA). Seventy-two male SD rats were randomly assigned to an experimental group (morphine + naloxone, “MN”) and 2 control groups: MS (morphine + saline) and SN (saline + naloxone). MN rats were intraperitoneally injected with morphine twice per day for 6.5 days and naloxone once and trained to establish CPA model. MS and SN rats were injected with equivalent volumes of morphine plus saline and saline plus naloxone, respectively. PKA and KOR in AcbSH, CeA and VTA were measured by immunohistochemistry. Before CPA, there were no significant differences in PKA and KOR expression levels in the AcbSH, CeA and VTA between MN and 2 control groups. After CPA, significant differences in PKA expression were detected in the AcbSH (P<0.001) and VTA (P=0.018) between MN and 2 control groups. The average gray intensity of MN group (109.50±4.66) in AcbSH was significantly higher than that of MS (126.50±3.70, P<0.001) and MN (133.50±6.364, P<0.001) groups. Significant differences in KOR expression were also detected between MN and 2 control groups in CeA (P<0.001). In MN group, PKA and KOR expression levels showed adaptive changes at different points of CPA. These findings demonstrated that neuroadaptation mediated by PKA and KOR may be an important molecular neurobiology basis for CPA. The upregulation of AC-cAMP-PKA-CREB signaling pathway in AcbSH and VTA has some role in the neurobiological mechanism of CPA.

The anxiolytic- and antidepressant-like effects of ATPM-ET, a novel κ agonist and μ partial agonist, in mice.

Opioid receptors are implicated in the regulation of motivation and emotion. However, animal studies show that activation of κ opioid receptor produces contrasting mood-altering effects in models of anxiety-like and depressive-like behaviors, and consequently, the role of κ receptor in mood control remains unsettled. The effect of κ/μ opioid combination in emotion regulation was unexplored. The aim of the study was to investigate the effects of (-)-3-N-ethylaminothiazolo [5,4-b]-N-cyclopropylmethylmorphinan hydrochloride (ATPM-ET), a novel κ agonist and μ partial agonist, in regulating emotional responses. The emotional responses of ATPM-ET were detected in the elevated plus maze (EPM), open field test (OFT), forced swim test (FST), and tail suspension test (TST). Selective κ antagonist nor-binaltorphimine (nor-BNI) and μ antagonist β-funaltrexamine (β-FNA) were applied to determine the type of receptor involved. The conditioned place aversion model was used to evaluate the effects on aversive emotion. In the EPM and OFT, ATPM-ET (1 and 2mg/kg, s.c.) significantly increased the time spent in the open arm and in the central area, respectively. In the FST and TST, ATPM-ET (0.5 and 1mg/kg, s.c.) significantly reduced the duration of immobility. These effects were prevented by nor-BNI (10mg/kg, i.p., -24h), but not by β-FNA (10 and20mg/kg, i.p., -24h) pretreatment. At the dose of 2mg/kg, ATPM-ET did not induce conditioned place aversion. ATPM-ET, at doses from 0.5 to 2mg/kg, produced anxiolytic- and antidepressant-like effects without inducing aversive emotion. These effects were more closely mediated by activation of κ receptor than μ receptor.

The role of various nicotinic receptor subunits and factors influencing nicotine conditioned place aversion

Affective nicotine withdrawal symptoms are of major motivational significance in contributing to relapse and continued tobacco use; thus, it is important to understand the molecular and receptor-mediated mechanisms that mediate affective withdrawal behaviors. Previous work using the conditioned place aversion (CPA) model has shown that nicotine withdrawal is associated with a negative affective state, and place aversion to previously neutral environmental stimuli represents a motivational component in the maintenance of drug use. Thus, the purpose of this study was to evaluate the role of genotype, sex, and age and to extend previous studies examining the role of various nicotinic receptor subtypes in the development of nicotine withdrawal aversion using the CPA model. Mice were chronically treated with nicotine and conditioned for two days with various nicotinic receptor antagonists. The major findings showed that mecamylamine and dihydro-β-erythroidine (DHβE), but not hexamethonium or methyllycaconitine citrate (MLA), precipitated significant aversion in the CPA model. This pharmacological data support our previous knockout mouse data suggesting that nicotine CPA is mediated by central β2-containing nicotinic receptors, but not α7 nicotinic receptors. Further, we show that sex and age are contributing factors to the development of nicotine CPA. Overall, the results of our study provide some insight into pharmacological and behavioral factors involved in the development of an aversive motivational component associated with nicotine withdrawal.

Differential Role of Nicotinic Acetylcholine Receptor Subunits in Physical and Affective Nicotine Withdrawal Signs

It has been suggested that the negative effects associated with nicotine withdrawal promote continued tobacco use and contribute to the high relapse rate of smoking behaviors. Thus, it is important to understand the receptor-mediated mechanisms underlying nicotine withdrawal to aid in the development of more successful smoking cessation therapies. The effects of nicotine withdrawal are mediated through nicotinic acetylcholine receptors (nAChRs); however, the role of nAChRs in nicotine withdrawal remains unclear. Therefore, we used mecamylamine-precipitated, spontaneous, and conditioned place aversion (CPA) withdrawal models to measure physical and affective signs of nicotine withdrawal in various nAChR knockout (KO) mice. beta2, alpha7, and alpha5 nAChR KO mice were chronically exposed to nicotine through surgically implanted osmotic minipumps. Our results show a loss of anxiety-related behavior and a loss of aversion in the CPA model in beta2 KO mice, whereas alpha7 and alpha5 KO mice displayed a loss of nicotine withdrawal-induced hyperalgesia and a reduction in somatic signs, respectively. These results suggest that beta2-containing nAChRs are involved in the affective signs of nicotine withdrawal, whereas non-beta2-containing nAChRs are more closely associated with physical signs of nicotine withdrawal; thus, the nAChR subtype composition may play an important role in the involvement of specific subtypes in nicotine withdrawal.

ORIGINAL INVESTIGATIONS ON CPP: Development, extinction and reinstatement of morphine withdrawal‐induced conditioned place aversion in rats

The motivational component of drug withdrawal may contribute to drug seeking and relapse through the negative reinforcement-based process. Here, we used conditioned place aversion (CPA) induced by naloxone-precipitated morphine withdrawal to measure the aversive effects. Using an unbiased conditioning paradigm, we treated rats with morphine hydrochloride [(10 mg/kg intraperitoneally (i.p.)] twice per day (at 08:00 and 20:00) for 6.5 days (from day 1 to day 7 morning), while gave them naloxone (0.3 mg/kg i.p.) on day 6, a precipitated withdrawal paired with a compartment that caused CPA to the side. Then, the rats exhibited CPA were received 12 extinction trials from days 7 to 13, by daily exposed to the two compartments for free exploration. On day 13, the rats with extinguished CPA were treated with a priming injection of morphine (10 mg/kg i.p.) followed by naloxone (0.3 mg/kg i.p.) that reliably reinstated CPA. These results demonstrated that repeatedly morphine-treated rats showed the formation, extinction and reinstatement of CPA. The present CPA model induced by these procedures may be useful for studying the biological mechanisms underlying the aversive motivational component of opiate withdrawal.