Quantifying conditioned place preference: a review of current analyses and a proposal for a novel approach

Therapeutic effects of metformin on cocaine conditioned place preference and locomotion

Lack of Food and Drug Administration-approved treatments for cocaine use disorder contributes to high rates of treatment attrition, relapse, and overdose. Metformin is a Type 2 diabetes drug being investigated for multiple new therapeutic indications. This study set out to determine whether metformin would impact the conditioned rewarding effects of cocaine in an abbreviated or standard two-chamber conditioned place preference (CPP) assay. Adult male (n = 73) and female (n = 82) Sprague Dawley rats were conditioned in a 7-day (abbreviated: 2 × 30 min sessions daily) or a 12-day timeline (standard: 1 × 30 min sessions daily) alternating control and treatment sessions using an unbiased design. Metformin (175 mg/kg) or saline pretreatment occurred 30 min before conditioning with cocaine (20 mg/kg) or vehicle (saline). Data showed sex differences in physiological responses to cocaine and metformin, as well as variant behavioral patterns with different conditioning paradigms. Metformin pretreatment impaired acquisition of cocaine CPP in abbreviated, but not standard conditioning among male rats only. Cocaine-induced locomotor effects are moderated with metformin pretreatment in both female and male rats in different phases of conditioning, suggesting the potential therapeutic value of symptom alleviation when tapering patients off cocaine use with the goal of abstinence. Sex differences observed highlight the importance in better understanding the unique pharmacological profiles of female and male patients. This study provides evidence supporting the potential repurposing of metformin for disrupting rewarding and psychomotor effects of cocaine, paving the way for safe, low-cost, and accessible treatment. (PsycInfo Database Record (c) 2025 APA, all rights reserved).

Nursing is rewarding for lactating rabbit does

Investigating affective experiences in animals is inherently challenging. However, the conditioned place preference (CPP) paradigm offers a valuable method for inferring internal states. Understanding the neural and hormonal mechanisms underlying emotions in animals is crucial for elucidating the biological basis of human emotions. CPP assesses an animal's preference for an environment associated with a rewarding or aversive stimulus. While extensively used to study drug effects, the CPP paradigm has been less frequently applied to investigate the effects of natural stimuli. Furthermore, most studies using this paradigm have been conducted with rodents. This study utilizes the CPP paradigm to investigate the rewarding properties of nursing in lactating rabbits, a unique mammalian behavior that occurs once daily. We found that nursing induced CPP in the lactating doe, which we interpret as a positive affective state-an event fulfilling a motivational drive that occurs only every 24hours. The results of this study provide valuable insights into the affective state of this species and the neurobiological basis of motivation and reward in a natural context.

Sexual Motivation (Desire): Problems with Current Preclinical and Clinical Evaluations of Treatment Effects and a Solution

There has been an extensive search for efficient pharmacological treatment of female sexual interest/arousal disorder and other sexual dysfunctions. However, available treatments have met limited success, except for the drugs used for treating erectile deficiency. A possible reason for this may be that both the preclinical and clinical evaluation of treatment effects have been inadequate. The present literature review shows that the intensity of sexual approach behaviors in non-human animals appears to be predictive of clinical effect whereas the traditional studies of copulatory behaviors and associated motor patterns have questionable predictive power regarding effects on human sexual desire. In clinical studies, it is essential to include the unconscious components of sexual motivation in any approach to its quantification. This basic fact is incompatible with the use of self-reports for evaluating treatment effects on motivation. Genital responses to sexual incentives are automatic and therefore outside of volitional control and can, therefore, provide unbiased estimates of the intensity of sexual motivation. These responses may be objectively quantified. Tests for implicit sexual motivation must also be used for capturing unconscious mental components. Including the unconscious components of sexual motivation as well as of objective measures of genital responses in clinical studies may improve evaluations of the effectiveness of drug treatment of low sexual interest/arousal disorder. In preclinical studies, predictive validity can be improved by quantifying sexual approach behaviors rather than copulatory behavior. The paradigm shift suggested here may finally allow for the discovery of efficient treatments for some sexual dysfunctions.

Beneficial effects of Esketamine on Morphine preference reacquisition in male rats

Addiction is a chronic condition that poses a serious public health challenge, particularly highlighted by the global opioid crisis involving drugs such as morphine (MORPH). One of the major obstacles in effective detoxification is the high relapse rate, with many individuals resuming drug use after withdrawal. Pharmacological treatments developed so far have generally shown limited efficacy in addressing substance use disorder. In this context, esketamine (ESK), the S-ketamine isomer, has been used in cases of treatment-resistant recurrent depression and depression with suicide risk. In our study, rats were treated with two doses of ESK every five days (acute - A-ESK) or daily (sub-chronic - SC-ESK) during MORPH-conditioned place preference (CPP) extinction. After 10 days, the animals were re-exposed to MORPH to assess preference reacquisition in the CPP paradigm. Our findings showed that both acute and sub-chronic ESK (A-ESK and SC-ESK) effectively prevented MORPH-CPP reestablishment. To our knowledge, this is the first experimental study to demonstrate the potential of ESK as a promising treatment for opioid abuse disorder. Clinical studies are needed to confirm its efficacy in human rehabilitation centers.

Female Syrian hamster analyses of bremelanotide, a US FDA approved drug for the treatment of female hypoactive sexual desire disorder

Hypoactive sexual desire disorder (HSDD) is the most reported sexual dysfunction among premenopausal women worldwide. Bremelanotide, trade name Vyleesi, has been approved by the United States Food and Drug Administration to treat HSDD. However, despite approval, very little is known about its neurobiological mechanism of action. In this study, we utilized a female Syrian hamster model to investigate the effects of bremelanotide on melanocortin receptor expression in the mesolimbic dopamine system and sexual reward. We found that the majority of melanocortin 3 and 4 (MC4R) receptor mRNA is expressed in dopamine neurons in the ventral tegmental area (VTA). Fewer neurons express MC4R in the nucleus accumbens (NAc) or dorsal striatum, where they rarely colocalize with neurons expressing dopamine D1 or D2 receptors. Instead, MC4R mRNA is expressed in nucleus accumbens interneurons. Neither the low nor the high dose of bremelanotide had an effect on the expression of melanocortin receptor mRNA in the mesolimbic dopamine system. Finally, sexual experience resulted in a conditioned place preference (CPP) in female Syrian hamsters, though bremelanotide treatment failed to enhance sexual reward in this test. The results of this study are discussed in conjunction with similar studies in rats, with the conclusion that bremelanotide does not act on the VTA-NAc reward circuit and does not enhance the rewarding effects of sexual interactions.

Deep brain stimulation of the anterior cingulate cortex reduces opioid addiction in preclinical studies

Substance Use Disorder (SUD) is a medical condition where an individual compulsively misuses drugs or alcohol despite knowing the negative consequences. The anterior cingulate cortex (ACC) has been implicated in various types of SUDs, including nicotine, heroin, and alcohol use disorders. Our research aimed to investigate the effects of deep brain stimulation (DBS) in the ACC as a potential therapeutic approach for morphine use disorder. Additionally, we measured c-Fos protein expression as an indicator of neural activity in the nucleus accumbens (NAc) and prefrontal cortex (PFC). Our findings indicate that high-frequency (130 Hz) DBS at different amperages, 150 µA and 200 µA in the ACC during the acquisition phase of morphine conditioned place preference (CPP) inhibited the rewarding properties of morphine. Furthermore, DBS at these intensities during the extinction phase facilitated the extinction and mitigated the reinstatement of morphine CPP triggered by drug priming. Morphine conditioning was associated with impaired novel object conditioning (NOR) and locomotor activity. While DBS in the acquisition and extinction phases at both intensities restored NOR memory, only DBS at 200 µA recovered locomotor activity in the open field test. Treatment with DBS at 200 µA decreased c-Fos protein expression in the NAc and PFC (compared to morphine-only group). In conclusion, our data indicate an intensity-dependent effect of ACC DBS on the acquisition, extinction, and reinstatement of morphine-induced CPP in rats. These findings suggest that ACC DBS could be a potential intervention for the treatment of morphine use disorder.

Animal models for studying therapeutic targets and treatments for alcohol use disorder

Over the decades, preclinical models have been developed and refined to investigate the rewarding effects of addictive substances and the neurobiological underpinnings of alcohol and other drug use disorders. This chapter delves into the methodological foundations, advantages, and limitations of leading animal models used to study alcohol use disorders (AUDs). Some models focus on the early stages of alcohol use and abuse. For instance, conditioned place preference assesses associative learning between a specific context and the effects of the drug, while locomotor sensitization measures increased locomotor activity following repeated drug exposure. In contrast, contingent models such as operant and non-operant alcohol self-administration protocols gauge voluntary intake, preference, motivation, and seeking behavior for alcohol solutions among experimental subjects. Additionally, we discuss the chronic intermittent alcohol vapor model, extensively utilized to induce a phenotype resembling dependence through non-contingent inhalation of alcohol vapor, resulting in elevated blood alcohol concentrations. Given the focus on pharmacological treatments for AUDs, we explore how different animal models can be employed to evaluate potential therapies and extrapolate findings to alcohol-related behaviors in humans. This chapter aims to provide readers with a comprehensive understanding of various animal models for AUDs, aiding in the interpretation of preclinical studies and the selection of suitable models for future research endeavors.