Place Preference Research Articles

The instrumental value of advance directives: lesson learned from the COVID-19 pandemic for policymaking

Open conversations between patients and healthcare professionals (HCP) are required to evaluate which treatments are reasonable for the individual case, especially towards the end of life. Advance Care Planning (ACP), which often results in drafting an Advance Directive (AD), is a useful tool to help with decisions in these circumstances, but the rate of AD completion remains low. During the COVID-19 pandemic, ACP and AD gained popularity due to the alleged advantage that they could facilitate resource allocation, to the benefit of public health. In this article, which presents a theoretical reflection grounded in scientific evidence, we underline an even stronger ethical argument to support the implementation of AD in end-of-life care (eol-C) i.e. the instrumental value at the individual level. We show, with particular reference to lessons learned from the COVID-19 pandemic, that AD are instrumentally valuable in that they: (1) allow to thematise death; (2) ensure that overtreatment is avoided; (3) enable to better respect the wish of people to die at their preferred place; (4) help revive the “lost skill” of prognostication. We thus conclude that these arguments speak for promoting the territorially uniform implementation and accessibility of high-quality AD in care.

Corticosteroid receptor antagonism in the medial prefrontal cortex reduces morphine-induced place preference and dopamine transporter expression decline in rats.

Corticosteroid signaling plays a critical role in modulating the neural systems underlying reward and addiction, but the specific contributions of glucocorticoid receptors (GRs) and mineralocorticoid receptors (MRs) in the medial prefrontal cortex (mPFC) to opioid reward and dopaminergic plasticity remain unclear. Here, we investigated the effects of intra-mPFC injection of corticosteroid receptor ligand (corticosterone; CORT), glucocorticoid receptor antagonist (RU38486; RU), and mineralocorticoid receptor antagonist (spironolactone; SP) on morphine-induced conditioned place preference (CPP) and dopamine transporter (DAT) expression in the mPFC. Adult male Wistar rats received intra-mPFC injections of CORT, RU, SP, or their respective vehicles prior to morphine CPP conditioning. Blockade of GRs with RU (10 or 100ng) or MRs with a low dose of SP (10ng) attenuated the expression of morphine CPP. Morphine reduced DAT expression in the mPFC, but RU and SP prevented this effect. These findings demonstrate that corticosteroid receptor signaling within the mPFC modulates the rewarding properties of morphine and morphine-induced dopaminergic plasticity. This preclinical study suggests that targeting GRs and MRs in the mPFC could be a possible therapeutic approach for treating opioid addiction. By targeting these receptors, it may be possible to reduce opioid reward and counteract the neuroadaptations in dopamine systems associated with addiction.

Atp1a2 and Kcnj9 Are Candidate Genes Underlying Sensitivity to Oxycodone-Induced Locomotor Activation and Withdrawal-Induced Anxiety-Like Behaviors in C57BL/6 Substrains.

Opioid use disorder is heritable, yet its genetic etiology is largely unknown. C57BL/6J and C57BL/6NJ mouse substrains exhibit phenotypic diversity in the context of limited genetic diversity which together can facilitate genetic discovery. Here, we found C57BL/6NJ mice were less sensitive to oxycodone (OXY)-induced locomotor activation versus C57BL/6J mice in a conditioned place preference paradigm. Narrow-sense heritability of OXY-induced locomotor activity traits ranged from 0.22 to 0.31, implicating suitability for genetic analysis. Quantitative trait locus (QTL) mapping in an F2 cross identified a chromosome 1 QTL explaining 7%-12% of the variance in OXY locomotion and anxiety-like withdrawal in the elevated plus maze. A second QTL for EPM withdrawal behavior on chromosome 5 near Gabra2 (alpha-2 subunit of GABA-A receptor) explained 9% of the variance. To narrow the chromosome 1 locus, we generated recombinant lines spanning 163-181 Mb, captured the QTL for OXY locomotor traits and withdrawal, and fine-mapped a 2.45-Mb region (170.16-172.61 Mb). Transcriptome analysis identified five, localized striatal cis-eQTL transcripts and two were confirmed at the protein level (KCNJ9, ATP1A2). Kcnj9 codes for a potassium channel (GIRK3) that is a major effector of mu opioid receptor signaling. Atp1a2 codes for a subunit of a Na+/K+ ATPase enzyme that regulates neuronal excitability and shows functional adaptations following chronic opioid administration. To summarize, we identified two candidate genes underlying the physiological and behavioral properties of opioids, with direct preclinical relevance to investigators employing these widely used substrains and clinical relevance to human genetic studies of opioid use disorder.

The effect of intracerebroventricular injection of melatonin on the period of acquisition, expression, extinction, and reinstatement of morphine conditioned place preference in the male rat: A behavioral and biochemical study.

Behavior in both humans and animals is significantly influenced by the brain's reward system. Many studies have shown that this dopaminergic system is the root of drug addiction and abuse. Melatonin, an indoleamine neurohormone, has been studied for its potential negative effects on addictive drugs such as morphine. This study evaluates the effect of intraventricular melatonin injection during different phases of morphine conditioning. Rats were conditioned with morphine [5 mg/kg; subcutaneously (SC)] for three days. The changes in conditioned place preference (CPP) scores following the injection of different doses of melatonin [25, 50, and 100 μg/kg; intracerebroventricular (ICV)] were investigated during the acquisition, expression, extinction, and reinstatement phases of morphine conditioning. After completing these steps, the c-Fos level in the nucleus accumbens (NAc) was measured using the ELISA technique. The results indicated that daily injections of 50 and 100 μg/kg melatonin during the acquisition and expression phases caused a dose-dependent decrease in the conditioning score. During the extinction phase, melatonin administration reduced its duration incrementally. Notably, only the 100 μg/kg dose significantly decreased morphine reinstatement. In terms of c-Fos levels, which were elevated after morphine consumption, melatonin administration led to a significant reduction across all phases. This study demonstrates the neural interaction between melatonin and the opioid system. The evidence suggests that melatonin may be effective at decreasing drug-related rewards and has potential utility in preventing addiction.

Brain CYPD2 Inhibitor Pretreatment Blunts Oral Oxycodone Induced Conditioned Place Preference in Rats

Brain CYPD2 Inhibitor Pretreatment Blunts Oral Oxycodone Induced Conditioned Place Preference in Rats

Perspectives on the infringement of criminal laws by adolescents following the use of drugs or hallucinogenic substances in Puerto Maldonado, Peru

The purpose of the research is to determine and describe the influence of drug use in adolescents to infringe and commit criminal offenses in the province of Tambopata. The design used in this research is quantitative, descriptive and analytical to perform a critical analysis and a non-experimental design was used. The methodology used are direct interviews with the officials who handle these cases of infractions such a judges and lawyers, a multiple choice survey interview was used for the dimension of drug use and a dichotomous option survey was used for the dimension of criminal infractions. The surveys were conducted directly with an interview in which the answers on drug use and criminal offenses were filled in. As main result it was found that there are significant effects before and after drug use in adolescents, and as preferred places for consumption are squares or parks, and the main instigators are friends or classmates, family abandonment and others who promote drug use. It was concluded that there should be more control in educational institutions as student tutoring centers. One of the limitations was not having direct access to interviews with those involved.

Vagal nerve stimulation dynamically alters anxiety-like behavior in rats.

Electrical vagal nerve stimulation (VNS), at currents designed to target sensory, interoceptive neurons, decreases anxiety-like behavior. We hypothesized that different VNS current intensities would differentially alter anxiety-like behavior through the activation of distinct brainstem circuits. Electrodes were implanted to stimulate the left vagus nerve and to record diaphragm muscle and electrocardiogram activity. The VNS current required to elicit the A-fiber-mediated Hering-Breuer Reflex (HBR) was determined for each animal. Based on this threshold, animals received either sham stimulation or VNS at 1.5 (mid-intensity VNS) or 3 (higher-intensity VNS) times the threshold for HBR activation. Anxiety-like behavior was assessed using the elevated plus maze, open field test, and novelty-suppressed feeding test. Additionally, a place preference assay determined whether VNS is rewarding or aversive. Finally, a c-Fos assay was performed to evaluate VNS-driven neuronal activation within the brainstem. Mid-intensity VNS reduced anxiety-like behavior in the elevated plus maze and open field test. Higher-intensity VNS was aversive during the place preference assay, confounding anxiety measures. Both intensities increased overall c-Fos expression in neurons within the nucleus of the solitary tract, but mid-intensity VNS specifically increased c-Fos expression in noradrenergic neurons within the nucleus of the solitary tract while decreasing it in the locus coeruleus. In contrast, higher-intensity VNS had no effect on c-Fos expression in noradrenergic neurons of either the nucleus of the solitary tract or locus coeruleus. Delivery of VNS induced reproducible, current intensity-dependent, effects on anxiety-like and aversive behavior in rats.

Nitrous oxide exerts rewarding effect via regulating D1 receptor and BDNF pathway in ventral tegmental area-nucleus accumbens dopamine circuit

Recreational use of nitrous oxide (N2O) has risen dramatically over the past decades. This study aimed to examine its rewarding effect and the underlying mechanisms. The exposure of mice to a subanesthetic concentration (20%) of N2O for 30 min for 4 consecutive days paired with N2O in the morning and paired with the air in the afternoon produced apparent rewarding behavior in the conditioned place preference (CPP) paradigm. This was abrogated by microinjection into the nucleus accumbens (NAc) of the dopamine (DA) D1 receptor antagonist SCH23390, but not the D2 antagonist haloperidol. N2O robustly enhanced DAergic neuronal activity of the ventral tegmental area (VTA) and the concentration of DA in the NAc. The repeated N2O exposure also upregulated the expression of brain-derived neurotrophic factor (BDNF) in the VTA and its multiple downstream mediators in the NAc. Conversely, VTA focal knockdown of BDNF and the inhibition of the downstream mediators suppressed the N2O-induced rewarding effect and the DAergic neuronal activity of the VTA. Further, the combined intervention of BDNF knockdown and D1 antagonist significantly inhibited the N2O-induced rewarding effect in mice, which was greater than that of BDNF knockdown alone, but was not significantly different from that of D1 antagonist alone. These results indicate that the rewarding properties of N2O at subanesthetic concentration are associated with its upregulation of the VTA-NAc DA reward pathway probably via mediation of D1 receptor and BDNF/TrkB signaling. Among them, the modulation of BDNF may be the upstream of D1 receptor involved in N2O rewarding effect.

Decision-making regarding place of end-of-life care for children with life-limiting and life-threatening conditions: a systematic integrative review

BackgroundDue to medical advancements the number of children living with life-limiting and life-threatening conditions is rising, meaning more children and their families will require palliative and end-of-life care in the future. While ‘home’ is often the preferred place of end-of-life care, the evidence around best practice for decision-making about place of end-of-life care remains inadequate.AimTo synthesise evidence on the factors influencing decision-making regarding place of end-of-life care for children with life-limiting and life-threatening conditions.DesignA systematic integrative literature review. The review protocol was registered in Prospero: CRD42023406800.Data sourcesCINAHL, MEDLINE, EMBASE, PsycINFO, and Maternal and Infant Health were searched for studies published between 2013 and 2024. Any empirical, peer-reviewed journal articles published in English that included data pertaining to decision-making about place of end-of-life care for children (≤ 18 years) with life-limiting or life-threatening conditions were considered. Quality appraisal was conducted using the Mixed Methods Appraisal Tool.ResultsEleven eligible studies were included. Using an iterative process of constant data comparison, four themes were identified, highlighting that (i) consideration of the child, (ii) availability and suitability of end-of-life care services, (iii) parents’ capacity and control in providing care, and (iv) family and sibling well-being were factors influencing decision-making about place of end-of-life care.ConclusionThere are a complex range of factors surrounding decision-making regarding place of end-of-life care for children with life-limiting and life-threatening conditions. Studies focused primarily on parents’ perspectives. Further research is needed to identify how to best support decisions about place of end-of-life care for families of children with life-limiting and life-threatening conditions.

Protocol for alleviating alcohol-induced conditioned place preference in mice using alternating bilateral sensory stimulation.

Alternating bilateral sensory stimulation (ABS) is a clinical physical therapy technique effective in treating post-traumatic stress disorder (PTSD). However, its utilization in treating conditions beyond PTSD remains limited. Here, we present a protocol to reduce ethanol-induced conditioned place preference (CPP) using 4Hz ABS. We describe steps for the assembly of ABS apparatus, CPP training, and ABS treatment. This protocol has been validated in male mice and can be used to explore the mechanism behind the therapeutic effect of ABS. For complete details on the use and execution of this protocol, please refer to Lei etal.1.

Evidence-based preventive care guidelines in pediatric primary care

Evidence-based preventive care guidelines offer a systematic approach to early detection, prompt intervention, and the promotion of health, encompassing various aspects of physical, mental, and developmental well-being. Recently, more focus has been placed on improving guidelines for preventive interventions for pediatric populations. Primary care is considered a great venue for implementing these preventive interventions. In addition, primary care is the preferable place for parents to do such preventive interventions. Multiple authorized organizations have developed new guidelines and recommendations in order to improve the delivery of preventive measures in pediatric primary care in recent years. Unlike adults’ guidelines, pediatric preventive guidelines are confusing and of low quality, leading to more challenges faced by primary care providers. This review aimed to evaluate the quality of recent studies on this topic, with a focus on the accuracy and efficacy of current evidence-based guidelines. Despite advancements, challenges such as childhood obesity, speech disorders, and depression require further refinement of evidence-based guidelines, supported by high-quality research. Additionally, the integration of technology has demonstrated potential for enhancing the delivery and outcomes of pediatric primary care.

Telehealth-facilitated palliative care enables more people to die at home: An analysis of clinical outcomes and service activity data

BackgroundTelehealth-facilitated models of palliative care are a patient-focused way to deliver specialist care in or closer to home for people with a life-limiting illness. Telehealth can increase access to palliative care and support people experiencing symptoms of advanced disease in their own home, reducing the discomfort of travel. This retrospective cohort study examines the activity and outcomes of a regional telehealth-facilitated palliative care service to (i) describe which patients are most likely to use telehealth; and (ii) explore possible impacts of telehealth on patient outcomes including place of death, timely access to care, responsiveness to urgent needs and pain management.MethodsAnalysis of service activity data (patient demographics, care modality, consultation frequency) and Palliative Care Outcomes Collaborative data registry (place of death, timely access to palliative care, responsiveness to urgent needs as measured by time in unstable phase, pain management) were undertaken. Outcomes were compared between patients who had no videoconsultations (n = 683) and those who had one or more videoconsultations (n = 524).ResultsCompared to people who had no videoconsultations, those who had at least one appointment via video were: more than twice as likely to die at home and spent a shorter amount of time in the unstable phase of palliation. Mixed results were found regarding timely access to palliative care. There was no significant difference in pain management between consultation modes.ConclusionTelehealth-facilitated palliative care has multiple benefits, including the increased likelihood of fulfilling someone’s wish to die at home, often their preferred place of death.

What are family caregivers' experiences of coordinating end-of-life care at home? A narrative review.

People with life-limiting diseases, who are no longer receiving active or curable treatment, often state their preferred place of care and death as the home. This requires coordinating a multidisciplinary approach, using available health and social care services to synchronize care. Family caregivers are key to enabling home-based end-of-life support; however, the 2 elements that facilitate success - coordination and family caregiver - are not necessarily associated as being intertwined or one and the same. This narrative review explores family caregiver experiences of coordinating end-of-life care in the home setting. Studies were identified systematically following the Preferred Reporting Items for Systematic reviews and Meta-Analyses (PRISMA) guidelines. A search of 5 databases (CINAHL, AMED, MEDLINE, Joanna Briggs Institute for Systematic Reviews, and the Cochrane Database) was conducted using Medical Subject Headings search terms and Boolean operators. Seven hundred and eighty papers were screened. Quality assessment was conducted using the JBI Critical Appraisal Checklist for Qualitative Research. Characteristics of included studies were extracted using the Joanna Briggs Institute Qualitative Assessment and Review Instrument (JBI-QARI) extraction tool. Ten qualitative studies were included. A meta-aggregative approach was used to assemble findings and categories extracted from the included papers, which led to identification of 3 overall themes: (1) family caregiver identity, (2) strategies for care, and (3) practicalities of care. Research suggests there should be a designated care coordinator to support people nearing the end of life at home. However, this review shows that family caregivers intrinsically take on this role. Their experiences, frequently share commonalities across different cultures and regions, highlighting the universal nature of their challenges. Difficulties associated with providing home-based care are evident, but the undertaking of care coordination by relatives highlights a need for a change in approach. Future studies could explore the impact of having a designated "facilitator" or single point of contact for families, as well as the development of tailored communication strategies.

Nicotinic α7 receptors on cholinergic neurons in the striatum mediate cocaine-reinforcement, but not food reward.

The neurotransmitter acetylcholine has since long been implicated in reward learning and drug addiction. However, the role of specific cholinergic receptor subtypes on different neuronal populations remain elusive. Here, we studied the function of nicotinic acetylcholinergic alpha 7 receptors (α7 nAChRs) in cocaine and food-enforced behaviors. We found that global deletion of α7 nAChRs in mice attenuates cocaine seeking in a Pavlovian conditioned place preference paradigm and decreases operant responding to cocaine in a runway task and in self-administration, without influencing responding to palatable food. This effect can be attributed to alpha 7 receptor signaling in the striatum, as selective deletion of striatal α7 nAChRs using a viral vector approach resulted in a similar decrease in cocaine-preference as that of global deletion. To investigate which type of striatal neurons are responsible for this effect, we selectively targeted Cholinergic (ChAT-expressing) neurons and dopamine D1-receptor (D1R) expressing neurons. Mice with conditional deletion of α7 nAChRs in ChAT-neurons (α7 nAChR-ChATCre) exhibited decreased cocaine place preference and intact place preference for food, while α7 nAChR-D1RCre mice had no changes in reward learning to neither food nor cocaine. Cocaine induction of striatal immediate early gene expression of cFos, FosB, Arc and EGR2 was blocked in α7 nAChR-ChATCre mice, demonstrating the importance of α7 nAChRs on cholinergic neurons for striatal neuronal activity changes. Collectively, our findings show that α7 nAChRs on cholinergic interneurons in the striatum are pivotal for learning processes related to cocaine, but not food reward.

The Histone Lysine Demethylase KDM7A Contributes to Reward Memory via Fscn1-Induced Synaptic Plasticity in the Medial Prefrontal Cortex.

Lysine demethylase 7A (KDM7A) catalyzes the removal of dimethylation from histone H3 lysine 9 and lysine 27, both of which are associated with transcription repression. Previous study indicates that Kdm7a mRNA in the medial prefrontal cortex (mPFC) increases after drug exposure, yet its role in drug-related behaviors is largely unknown. In a morphine-conditioned place preference (CPP) paradigm, these findings reveal a specific increase of Kdm7a expression in the mPFC 7 days after drug withdrawal. Subsequently, these results demonstrate that knockdown of Kdm7a in the mPFC do not affect the acquisition of morphine-induced CPP, but it attenuate memory consolidation. To further explore Kdm7a-mediated transcriptomic changes, this work employs Nanopore direct RNA sequencing. Transcriptome profiling unveils several gene expression alterations impacted by KDM7A, which are enriched in relevant neural function categories. Notably, this work identifies and validates fascin actin-bundling protein 1 (Fscn1) as a downstream molecular target. Knockdown of Fscn1 has a similar impact on CPP to Kdm7a, along with corresponding decrease of dendritic spine density and neuronal activity in the mPFC. Additionally, silencing Kdm7a decreases enrichment of H3K9me2 and H3K27me2 at the Fscn1 promoter region, suggesting that KDM7A may act as a crucial regulator of transcriptional responses to morphine-related reward memory via Fscn1.

In vivo Calcium Extrusion from Accumbal Astrocytes Reduces Anxiety-like Behaviors but Increases Compulsive-like Responses and Compulsive ethanol drinking in Mice.

The ventral striatum is crucially involved in reward processing. The present study investigates the behavioral effects of astrocyte-specific calcium extrusion virus "CalEx" on perseverative responses in the operant five-choice serial reaction time task and ethanol-conditioned place preference. Mice were injected with CalEx via the GfaABC1D promoter to extrude cytosolic calcium from astrocytes within the ventral striatum. We found that CalEx transfection in the ventral striatum reduced evoked response duration, the maximum amplitude, and the response frequency to 500 μM ATP as measured by ΔF/F fluorescence intensity of the genetically encoded calcium indicator targeting astrocytes GCaMP6f. During the five-choice serial reaction time task, CalEx mice persisted in perseverative responses compared to their counterparts. Additionally, during ethanol-conditioned place preference, CalEx mice showed increased place preference for a low ethanol concentration compared to control group. Furthermore, we found that accumbal astrocytic calcium extrusion increased quinine adulterated ethanol drinking. Our findings suggest that diminishing ventral striatum astrocyte calcium activity contributes to compulsive behaviors, ethanol drinking, and enhanced ethanol drug reward.

D1 dopamine / mu opioid receptor interactions in operant conditioning assays of pain-depressed responding and drug-induced rate suppression, and a conditioned place preference procedure: assessment of therapeutic index in male Sprague Dawley rats.

In vivo receptor interactions vary as a function of behavioral endpoint, with key differences between reflexive and non-reflexive measures that assess the motivational aspects of pain and pain relief. There have been no assessments of D1 dopamine agonist / mu opioid receptor (MOR) agonist interactions in non-reflexive behavioral measures of pain. We examined the hypothesis that D1/MOR mixtures show enhanced effectiveness in blocking pain depressed behaviors while showing decreased side effects such as sedation and drug reward. SKF82958 and methadone were used as selective/high efficacy D1 and mu agonists, respectively. An FR10 operant schedule was utilized in the presence and absence of a lactic acid inflammatory pain-like manipulation, to measure antinociceptive and operant-rate-suppressing effects, respectively. Rewarding properties of the drug combinations were determined using a conditioned place preference procedure. Methadone alone, but not SKF82958 alone, produced dose-dependent restoration of pain-depressed responding. Both SKF82958 and methadone produced dose-dependent response rate suppression. Three fixed proportion mixtures, based on the relative potencies of the drugs in the rate suppression assay, produced dose-dependent antinociception and sedation. Isobolographic analysis indicated that the 0.17:1 mixture produced supra-additive antinociception and additive sedation. The 0.055:1 mixture produced additive antinociception with sub-additive sedation, and the 0.018:1 mixture had the highest therapeutic index (TI) relative to other mixtures and drugs alone. The antinociceptive doses and component doses for the 0.018:1 mixture did not produce conditioned place preference. These results suggest that D1-selective dopamine agonists may have utility as candidate opioid-sparing analgesics.

Mu opioid receptors expressed in striatal D2 medium spiny neurons have divergent contributions to cocaine and morphine reward.

While our understanding of the neurobiological mechanisms underlying cocaine and opiate reward has historically been dopamine-focused, evidence from genetic and pharmacological approaches indicates that µ-opioid receptors (MORs) in the striatum are important contributors. Within the striatum, MORs are expressed in both dopamine D1-receptor and D2-receptor expressing GABAergic medium spiny neurons (MSNs), as well as in interneurons and various afferents. Thus, it remains unclear how these distinct MOR populations regulate drug reward. To address this, we generated mice with a targeted deletion of MORs from dopamine D2 receptor-expressing MSNs (D2-MORKO) and tested the locomotor and conditioned rewarding effects of cocaine and morphine. D2-MORKO mice showed blunted acquisition of cocaine place preference and suppressed expression of preference when tested in the presence of cocaine. Conversely, the acute and sensitized locomotor responses to cocaine and morphine, as well as morphine conditioned place preference, were normal in D2-MORKOs. This indicates MORs expressed in D2-MSNs facilitate cocaine reward. Further, these data suggest these MORs play divergent roles in cocaine and morphine reward.

Impact of Exercise on Tramadol-Conditioned Place Preference.

Tramadol (TRA) is an opioid that is used to manage moderate to severe pain. Long-term use of TRA can lead to the development of opioid use disorder. This study investigates the role of forced exercise in reducing TRA-seeking behavior. Adult male rats (240-260 g) were divided into five groups; the control group received vehicle injections, the TRA group received TRA (75 mg/kg, i.p) every other day for 8 days, and three TRA-exercise groups were forced to run on a treadmill (60 min/day, 5 days/week) for 2, 4, or 6 weeks prior to conditioning with TRA. A tramadol-conditioned place preference (CPP) procedure assessed TRA reinforcement, after which all rats were euthanized, tissue extracted, and mRNA expression for brain-derived neurotrophic factor (Bdnf) and interleukin 1 beta (Il-1β) determined in hippocampus (Hipp), prefrontal cortex (PFC), and nucleus accumbens (NAc). TRA-seeking behavior was seen in the TRA group and the 6 weeks forced exercise group. By contrast, forced exercise for 2 or 4 weeks attenuated TRA-seeking behavior. This attenuation was associated with a significant increase in Bdnf mRNA expression in the Hipp and NAc, but not the PFC. Additionally, the TRA-induced elevations in Il-1β mRNA expression were reversed by all durations of exercise in Hipp. However, only 2 and 4 weeks, but not 6 weeks, of exercise reduced elevations in PFC and NAc Il-1β expression. Forced exercise for 2 and 4 weeks attenuates TRA-seeking behavior partially through the regulation of Bdnf and Il-1β mRNA expression.

The Role of Endogenous Beta-Endorphin and Enkephalins in the Crosstalk Between Ethanol and Morphine.

Background: There is clinical concern about the combined use of alcohol and opiates. Several lines of evidence support an interaction between alcohol and the endogenous opioid system. Thus, we hypothesized that ethanol, by causing the release of opioid peptides, may sensitize the system to the action of exogenous opioids such as morphine. Objectives: In this study, using the place conditioning paradigm, a model of reward, we determined whether a morphine challenge would alter the pre-established preference induced by ethanol conditioning in mice, and whether this response was mediated by the mu opioid receptor (MOP). Given that ethanol exposure stimulates the release of opioid peptides, we also assessed the role of beta-endorphin (β-END) and enkephalins (ENKs) in this response. Methods: Mice lacking MOPs, β-END, and/or ENKs, and their respective wild-type controls were tested for preconditioning place preference on day 1. Mice were then conditioned with ethanol (2 g/kg) versus saline on days 2 to 4 and then tested under a drug-free state for postconditioning place preference on day 5. On day 8, mice received a single injection of morphine (5 mg/kg) and were tested for place preference. On the test days, mice were placed in the central chamber and allowed to explore the chambers. The amount of time that mice spent in the drug-paired chamber was recorded. Results: We found that a challenge dose of morphine given on day 8 enhanced the conditioned place preference (CPP) response in mice previously conditioned with ethanol. This response was abolished in MOP-null mice, confirming the role of MOPs in this response. Although this enhanced response was not altered in mice lacking either β-END or ENKs compared to their wild-type littermates/controls, it was completely blunted in mice lacking both β-END and enkephalins. Conclusions: Together, these results suggest that these opioid peptides jointly mediate the crosstalk between the rewarding actions of morphine and ethanol.