Animal models of psychiatric disorders

Microglia contribute to mammary tumor-induced neuroinflammation in a female mouse model

Following diagnosis but before treatment, up to 30% of breast cancer patients report behavioral side effects (e.g., anxiety, depression, memory impairment). Our rodent mammary tumor model recapitulates aspects of these behavioral sequelae, as well as elevated circulating and brain inflammatory mediators. Neuroinflammation is a proposed mechanism underlying the etiology of mood disorders and cognitive deficits, and therefore may be contributing to tumor-associated behavioral side effects. The cellular mechanisms by which tumor-induced neuroinflammation occurs remain unknown, making targeted treatment approaches inaccessible. Here, we tested the hypotheses that microglia are the primary cells driving tumor-induced neuroinflammation and behavioral side effects. Young adult female BALB/c mice were induced with a 67NR mammary tumor; tumor-free controls underwent a sham surgery. Mammary tumors increased IBA1+ and GFAP+ staining in the amygdala and hippocampus relative to tumor-free controls. However, tumors did not alter gene expression of Percoll-enriched microglia isolated from the whole brain. While cognitive, social, and anhedonia-like behaviors were not altered in tumor-bearing mice, tumors increased central tendency in the open-field test; microglia depletion did not reverse this effect. Brain region RT-qPCR data indicated that microglia depletion attenuated tumor-induced elevations of neuroinflammatory gene expression in a region- and mediator-specific manner. These results indicate a causal role of microglia in tumor-induced neuroinflammation. This research advances our understanding of the cellular mechanisms underlying tumor-induced neuroinflammation in order to understand how brain responses (e.g., behavior) may be altered with subsequent cancer-related immune challenges.

Stress-related neuropeptide systems as targets for treatment of alcohol addiction: A clinical perspective

Alcohol use is a major cause of disability and death globally. These negative consequences disproportionately affect people who develop alcohol addiction, a chronic relapsing condition characterized by increased motivation to use alcohol, choice of alcohol over healthy, natural rewards, and continued use despite negative consequences. Available pharmacotherapies for alcohol addiction are few, have effect sizes in need of improvement, and remain infrequently prescribed. Research aimed at developing novel therapeutics has in large part focused on attenuating pleasurable or "rewarding" properties of alcohol, but this targets processes that primarily play a role as initiation factors. As clinical alcohol addiction develops, long-term changes in brain function result in a shift of affective homeostasis, and rewarding alcohol effects become progressively reduced. Instead, increased stress sensitivity and negative affective states emerge in the absence of alcohol and create powerful incentives for relapse and continued use through negative reinforcement, or "relief." Based on research in animal models, several neuropeptide systems have been proposed to play an important role in this shift, suggesting that these systems could be targeted by novel medications. Two mechanisms in this category, antagonism at corticotropin-releasing factor type 1, and neurokinin 1/substance P receptors, have been subject to initial evaluation in humans. A third, kappa-opioid receptor antagonism, has been evaluated in nicotine addiction and could soon be tested for alcohol. This paper discusses findings with these mechanisms to date, and their prospects as future targets for novel medications.

Automated pose estimation in primates

Understanding the behavior of primates is important for primatology, for psychology, and for biology more broadly. It is also important for biomedicine, where primates are an important model organism, and whose behavior is often an important variable of interest. Our ability to rigorously quantify behavior has, however, long been limited. On one hand, we can rigorously quantify low-information measures like preference, looking time, and reaction time; on the other, we can use more gestalt measures like behavioral categories tracked via ethogram, but at high cost and with high variability. Recent technological advances have led to a major revolution in behavioral measurement that offers affordable and scalable rigor. Specifically, digital video cameras and automated pose tracking software can provide measures of full-body position (i.e., pose) of primates over time (i.e., behavior) with high spatial and temporal resolution. Pose-tracking technology in turn can be used to infer behavioral states, such as eating, sleeping, and mating. We call this technological approach behavioral imaging. In this review, we situate the behavioral imaging revolution in the history of the study of behavior, argue for investment in and development of analytical and research techniques that can profit from the advent of the era of big behavior, and propose that primate centers and zoos will take on a more central role in relevant fields of research than they have in the past.

Neonatal immune challenge influences the microbiota and behaviour in a sexually dimorphic manner

There is comorbidity between anxiety disorders and gastrointestinal disorders, with both linked to adverse early life events. The microbiome gut-brain-axis, a bidirectional communication system, is plastic throughout the neonatal period and is a possible mediator of this relationship. Here, we used a well-established neonatal rodent immune activation model to investigate the long-term effect of neonatal lipopolysaccharide (LPS) exposure on adult behaviour and the relationship to microbiome composition. Wistar rats were injected with LPS (0.05 mg/kg) or saline (equivolume) on postnatal days 3 and 5. In adulthood, behavioural tests were performed to assess anxiety-like behaviour, and microbiota sequencing was performed on stool samples. There were distinctly different behavioural phenotypes for LPS-exposed males and females. LPS-exposed males displayed typical anxiety-like behaviours with significantly decreased social interaction (F_(1,22) = 7.576, p = 0.009) and increased defecation relative to saline controls (F_(1,23) = 8.623, p = 0.005). LPS-exposed females displayed a different behavioural phenotype with significantly increased social interaction (F_(1,22) = 6.094, p = 0.018), and exploration (F_(1,24) = 6.359, p = 0.015), compared to saline controls. With respect to microbiota profiling data, Bacteroidota was significantly increased for LPS-exposed females (F_(1,14) = 4.931p = 0.035) and Proteobacteria was decreased for LPS-exposed rats of both sexes versus controls (F_(1,30) = 4.923p = 0.035). Furthermore, alterations in predicted functional pathways for neurotransmitters in faeces were observed with a decrease in the relative abundance of D-glutamine and D-glutamate metabolism in LPS exposed females compared to control females (p < 0.05). This suggests that neonatal immune activation alters both later life behaviour and adult gut microbiota in sex-specific ways. These findings highlight the importance of sex in determining the impact of neonatal immune activation on social behaviour and the gut microbiota.

Increased negative affect when combining early-life maternal deprivation with adolescent, but not adult, cocaine exposure in male rats: regulation of hippocampal FADD

RATIONALE

Besides early drug initiation during adolescence, another vulnerability factor associated with increased risk for substance abuse later in life is early-life stress. One way of assessing such combined risk is by evaluating the emergence of increased negative affect during withdrawal (i.e., linked to persistence in drug seeking).

OBJECTIVES

To compare the impact of maternal deprivation with cocaine exposure at different ages on affective-like behavior and hippocampal neuroplasticity regulation.

METHODS

Maternal deprivation was performed in whole-litters of Sprague-Dawley rats (24 h, PND 9-10). Cocaine (15 mg/kg, 7 days, i.p.) was administered in adolescence (PND 33-39) or adulthood (PND 64-70). Changes in affective-like behavior were assessed by diverse tests across time (forced-swim, open field, novelty-suppressed feeding, sucrose preference). Hippocampal multifunctional FADD protein (balance between cell death and plasticity) was evaluated by Western blot.

RESULTS

Exposing rats to either maternal deprivation or adolescent cocaine did not modulate affective-like behavior immediately during adolescence, but increased negative affect in adulthood. Maternal deprivation combined with adolescent cocaine advanced the negative impact to adolescence. Adult cocaine exposure alone and/or in combination with maternal deprivation did not induce any behavioral changes at the time-points analyzed. FADD regulation might participate in the neural adaptations taking place in the hippocampus in relation to the observed behavioral changes.

CONCLUSIONS

Adolescence is a more vulnerable period, as compared to adulthood, to the combined impact of cocaine and early maternal deprivation, thus suggesting that the accumulation of stress early in life can anticipate the negative behavioral outcome associated with drug consumption.

Exploring Anhedonia in Kennelled Dogs: Could Coping Styles Affect Hedonic Preferences for Sweet and Umami Flavours?

Simple Summary

Kennelled dogs are susceptible to suffer chronic stress when social interactions with conspecifics and spatial needs are long-term restricted. Chronic stress may affect pleasure perception of food and solutions in dogs as observed in several animals, a phenomenon known as anhedonia. However, little information exists on how different coping styles could prevent the onset of anhedonia. Fourteen kennelled Beagle dogs were used to study the acceptability and preference for different dilute palatable sucrose and monosodium glutamate (MSG) solutions. Coping style of animals was previously evaluated through a modified human-approach test. This test consisted in assessing whether or not dogs approached an unfamiliar human when a feeding opportunity was presented, classifying them as close dogs (CD; proactive) or distant dogs (DD; reactive) respectively. It was observed that DD presented a lower intake of both sucrose and MSG dilute solutions compared with CD. Moreover, DD exhibited a higher consumption of MSG than CD at the highest concentrations, supporting that their intake depends on solution palatability. Finally, DD did not prefer sucrose or MSG solutions over water at any dilute solution offered. Together, these results suggest that dogs that are categorized as reactive animals could diminish their ability to perceive dilute palatable solutions reflecting depressive-like behaviours such as anhedonia.

Abstract

Kennelled dogs are at risk of suffering chronic stress due to long-term spatial, social and feeding restrictions. Chronic stress may decrease the dogs’ capacity to feel pleasure when facing hedonic experiences, modifying their perception for palatable ingredients. However, different abilities to cope with environmental stressors could prevent the onset of anhedonia. Fourteen kennelled Beagle dogs were used to study the acceptability and preference for different dilute sucrose and monosodium glutamate (MSG) solutions. Coping style of animals was previously evaluated through a human approach test (HAT) and classified as close dogs (CD; proactive) or distant dogs (DD; reactive) according to whether or not they approached an unfamiliar human when a feeding opportunity was presented. Consumption results were analysed taking into account the sucrose/MSG concentrations, HAT (CD or DD), age, and weight of the animals. DD presented a lower intake of sucrose (p = 0.041) and MSG (p = 0.069) solutions compared with CD. However, DD exhibited a higher consumption of MSG than CD at its highest concentrations, supporting that their intake depends on solution palatability. Finally, DD did not prefer sucrose or MSG solutions over water at any dilute solution offered. Together, these results suggest that dogs that are categorized as reactive animals could diminish their ability to perceive dilute palatable solutions, reflecting depressive-like behaviours as anhedonia.

Short-term withdrawal from repeated exposure to cocaine during adolescence modulates dynorphin mRNA levels and BDNF signaling in the rat nucleus accumbens

BACKGROUND

Early-life stressful events affect the neurobiological maturation of cerebral circuitries including the endogenous opioid system and the effects elicited by adolescent cocaine exposure on this system have been poorly investigated. Here, we evaluated whether cocaine exposure during adolescence causes short- or long-term alterations in mRNAs codifying for selected elements belonging to the opioid system. Moreover, since brain-derived neurotrophic factor (BDNF) may undergo simultaneous alterations with the opioid peptide dynorphin, we also evaluated its signaling pathway as well.

METHODS

Adolescent male rats were exposed to cocaine (20 mg/kg/day) from post-natal day (PND) 28 to PND42, approximately corresponding to human adolescence. After short- (PND45) or long-term (PND90) abstinence, prodynorphin-κ-opioid receptor (pDYN-KOP) and pronociceptin-nociceptin receptor (pN/OFQ-NOP) gene expression were evaluated in the nucleus accumbens (NAc) and hippocampus (Hip) together with the analysis of BDNF signaling pathways.

RESULTS

In the NAc of PND45 rats, pDYN mRNA levels were up-regulated, an effect paralled by increased BDNF signaling. Differently from NAc, pDYN mRNA levels were down-regulated in the Hip of PND45 rats without significant changes of BDNF pathway. At variance from PND45 rats, we did not find any significant alteration of the investigated parameters either in NAc and Hip of PND90 rats.

CONCLUSIONS

Our results indicate that the short-term withdrawal from adolescent cocaine exposure is characterized by a parallel pDYN mRNA and BDNF signaling increase in the NAc. Given the depressive-like state experienced during short abstinence in humans, we hypothesize that such changes may contribute to promote the risk of cocaine abuse escalation and relapse.

Adolescent cocaine exposure enhanced negative affect following drug re-exposure in adult rats: Attenuation of c-Fos activation

BACKGROUND

The goal of the present study was to utilize the adolescent drug experience as an emerging vulnerability factor for developing psychiatric comorbidities in adulthood that could, in turn, help to elucidate and/or hypothesize possible mechanisms contributing to higher relapse rates.

OUTCOMES

The current results showed that adolescent cocaine exposure (15 mg/kg, intraperitoneally, seven days) during early-mid adolescence (postnatal days 33-39) enhanced negative affect in adulthood, by increasing behavioral despair following drug re-exposure and by increasing anhedonia. Thus, these behavioral data provided a good model to further ascertain the long-term cellular and molecular adaptations that might take place in the brain in response to adolescent cocaine exposure as well as the impact of drug re-exposure in adulthood. In this regard, the results showed that adolescent cocaine exposure did not modulate cell proliferation (Ki-67+ cells) or c-Fos protein activation in the dentate gyrus region of the hippocampus, but attenuated c-Fos activation in the dorsal striatum.

CONCLUSIONS

These results proved that a history of cocaine exposure during adolescence increased the vulnerability to induce negative affect (i.e. emergence of psychiatric comorbidity) in adulthood while it decreased neuronal activation in the dorsal striatum. Interestingly, these effects were only observed following cocaine re-exposure in adulthood, suggesting that avoiding drug contact in adulthood could prevent the long-term negative effects induced by adolescent cocaine.

Social stress during adolescence activates long-term microglia inflammation insult in reward processing nuclei

The experience of social stress during adolescence is associated with higher vulnerability to drug use. Increases in the acquisition of cocaine self-administration, in the escalation of cocaine-seeking behavior, and in the conditioned rewarding effects of cocaine have been observed in rodents exposed to repeated social defeat (RSD). In addition, prolonged or severe stress induces a proinflammatory state with microglial activation and increased cytokine production. The aim of the present work was to describe the long-term effects induced by RSD during adolescence on the neuroinflammatory response and synaptic structure by evaluating different glial and neuronal markers. In addition to an increase in the conditioned rewarding effects of cocaine, our results showed that RSD in adolescence produced inflammatory reactivity in microglia that is prolonged into adulthood, affecting astrocytes and neurons of two reward-processing areas of the brain (the prelimbic cortex, and the nucleus accumbens core). Considered as a whole these results suggest that social stress experience modulates vulnerability to suffer a loss of glia-supporting functions and neuronal functional synaptic density due to drug consumption in later life.

Advancing Pharmacotherapy Development from Preclinical Animal Studies

Animal models provide rapid, inexpensive assessments of an investigational drug's therapeutic potential. Ideally, they support the plausibility of therapeutic efficacy and provide a rationale for further investigation. Here, I discuss how the absence of clear effective-ineffective categories for alcohol use disorder (AUD) medications and biases in the clinical and preclinical literature affect the development of predictive preclinical alcohol dependence (AD) models. Invoking the analogical argument concept from the philosophy of science field, I discuss how models of excessive alcohol drinking support the plausibility of clinical pharmacotherapy effects. Even though these models are not likely be completely discriminative, they are sensitive to clinically effective medications and have revealed dozens of novel medication targets. In that context, I discuss recent preclinical work on GLP-1 receptor agonists, phosphodiesterase inhibitors, glucocorticoid receptor antagonists, nociception agonists and antagonists, and CRF1 antagonists. Clinically approved medications are available for each of these drug classes. I conclude by advocating a translational approach in which drugs are evaluated highly congruent preclinical models and human laboratory studies. Once translation is established, I suggest the burden is to develop hypothesis-based therapeutic interventions maximizing the impact of the confirmed pharmacotherapeutic effects in the context of additional variables falling outside the model.

Abstinence from cocaine-self-administration activates the nELAV/GAP -43 pathway in the hippocampus: A stress-related effect?

We previously demonstrated that nELAV/GAP-43 pathway is pivotal for learning and its hippocampal expression is up-regulated by acute stress following repeated cocaine administration. We therefore hypothesized that abstinence-induced stress may sustain nELAV/GAP-43 pathway during early abstinence following 2 weeks of cocaine self-administration. We found that contingent, but not non-contingent, cocaine exposure selectively increases hippocampal nELAV, but not GAP-43, expression immediately after the last self-administration session, an effect that wanes after 24 h and that comes back 7 days later when nELAV activation becomes associated with increased expression of GAP-43, an effect again observed only in animals self-administering the psychostimulant. Such effect is specific for nELAV since the ubiquitous ELAV/HuR is unchanged. This nELAV profile suggests that its initial transient alteration is perhaps related to the daily administration of cocaine, while the increase in the nELAV/GAP-43 pathway following a week of abstinence may reflect the activation of this cascade as a target of stressful conditions associated with drug-related memories. © 2016 Wiley Periodicals, Inc.

Crazy like a fox. Validity and ethics of animal models of human psychiatric disease

Animal models of human disease play a central role in modern biomedical science. Developing animal models for human mental illness presents unique practical and philosophical challenges. In this article we argue that (1) existing animal models of psychiatric disease are not valid, (2) attempts to model syndromes are undermined by current nosology, (3) models of symptoms are rife with circular logic and anthropomorphism, (4) any model must make unjustified assumptions about subjective experience, and (5) any model deemed valid would be inherently unethical, for if an animal adequately models human subjective experience, then there is no morally relevant difference between that animal and a human.

Consensus paper of the WFSBP task force on biological markers: biological markers for alcoholism

OBJECTIVES

This article presents an overview of the current literature on biological markers for alcoholism, including markers associated with the pharmacological effects of alcohol and markers related to the clinical course and treatment of alcohol-related problems. Many of these studies are well known, while other studies cited are new and still being evaluated.

METHODS

In this paper we first describe known biomarkers of alcohol-related disorders, review their features and the problems involved in their use. We then consider future developments on biomarkers and their possible impact on the field.

RESULTS

More recent findings cited include the work on type 7 adenylcyclase (AC) polymorphism and its lower expression levels in female alcoholics. Neuroimaging studies involving biomarkers have also reported brain volume reductions of gray and white matter, including amygdala and subcortical regions in alcoholic patients, while a high association between the copy number variations (CNVs) in 6q14.1/5q13.2 and alcohol dependence has more recently been identified in genetic studies.

CONCLUSIONS

In addition to their possible importance for diagnosis, biomarkers may have utility for predicting prognosis, progression of the disorder, the development of new treatments, and monitoring treatment effects. Although such findings should be verified in independent studies, the search for new biomarkers is continuing. Several potential candidate biomarkers have been found recently in blood, imaging, and genetic studies with encouraging results.

Intranasal infusion of melanocortin receptor four (MC4R) antagonist to rats ameliorates development of depression and anxiety related symptoms induced by single prolonged stress

Brain melanocortinergic systems and specifically melanocortin receptor four (MC4R) are implicated in modulation of anxiety- and depressive-like behavior induced by mild or moderate stress. Here we examine whether blockage of central MC4Rs with HS014 before severe traumatic stress may protect against development of anxiety and depression co-morbid with post-traumatic stress disorder (PTSD). Male rats were treated intranasally (IN) with vehicle or varied doses of HS014, 30min prior to single prolonged stress (SPS) animal model of PTSD. IN administration of 100μg HS014 pre-SPS improved despair behavior in forced swim (FS) immediately after immobilization stress part of SPS protocol. During all 4 intervals of 20min FS these rats spent less time immobile than rats given vehicle or 3.5ng HS014. This dose of HS014 also had a long-term beneficial effect manifested as reduction of immobility time in forced swim test performed after SPS. However, both HS014 doses were effective in ameliorating development of anxiety-like behavior after traumatic stress. Thus, rats given IN HS014 prior to SPS exhibited less open arms (OA) visits in elevated plus maze (EPM), spent longer time in OA and less in closed arms, had lower anxiety index, higher risk assessment and more head dips over borders in OA. They also spent longer time in the center of the open field and defecated less. Reduced grooming behavior in EPM was observed with 100μg HS014. This is the first study revealing pronounced resilience effects of HS014 on development of behavioral symptoms co-morbid with PTSD.

Relapse induced by cues predicting cocaine depends on rapid, transient synaptic potentiation

Cocaine addiction is characterized by long-lasting vulnerability to relapse arising because neutral environmental stimuli become associated with drug use and then act as cues that induce relapse. It is not known how cues elicit cocaine seeking, and why cocaine seeking is more difficult to regulate than seeking a natural reward. We found that cocaine-associated cues initiate cocaine seeking by inducing a rapid, transient increase in dendritic spine size and synaptic strength in the nucleus accumbens. These changes required neural activity in the prefrontal cortex. This is not the case when identical cues were associated with obtaining sucrose, which did not elicit changes in spine size or synaptic strength. The marked cue-induced synaptic changes in the accumbens were correlated with the intensity of cocaine, but not sucrose seeking, and may explain the difficulty addicts experience in managing relapse to cocaine use.

N-acetylcysteine possesses antidepressant-like activity through reduction of oxidative stress: behavioral and biochemical analyses in rats

The growing body of evidence implicates the significance of oxidative stress in the pathophysiology of depression. The aim of this paper was to examine N-acetylcysteine (NAC) - a putative precursor of the most important tissue antioxidant glutathione - in an animal model of depression and in ex vivo assays to detect oxidative stress parameters. Imipramine (IMI), a classical and clinically-approved antidepressant drug was also under investigation. Male Wistar rats which underwent either bulbectomy (BULB; removal of the olfactory bulbs) or sham surgery (SHAM; olfactory bulbs were left undestroyed) were treated acutely or repeatedly with NAC (50-100mg/kg, ip) or IMI (10mg/kg, ip). Following 10-daily injections with NAC or IMI or their solvents, or 9-daily injections with a corresponding solvent plus acute NAC or acute IMI forced swimming test on day 10, and locomotor activity were performed; immediately after behavioral tests animals were decapitated. Biochemical tests (the total antioxidant capacity - TAC and the superoxide dismutase activity - SOD) were performed on homogenates in several brain structures. In behavioral studies, chronic (but not acute) administration of NAC resulted in a dose-dependent reduction in the immobility time seen only in BULB rats while chronic IMI produced a significant decrease in this parameter in both SHAM and BULB animals. On the other hand, chronic administration of NAC and IMI resulted in a significant increase in cellular antioxidant mechanisms (SOD activity) that reversed the effects of BULB in the frontal cortex, hippocampus and striatum. Our study further supports the antidepressant-like activity of NAC and links its effect as well as IMI actions with the enhancement of brain SOD activity.

GABAergic control of critical developmental periods for anxiety- and depression-related behavior in mice

Vulnerability for anxiety and depressive disorders is thought to have origins in early life and is increasingly recognized to involve deficits in GABAergic neurotransmission. Mice that were rendered heterozygous for the γ2 subunit gene of GABA(A) receptors (GABA(A)Rs) show behavioral, cognitive, neuroendocrine and pharmacologic features expected of a mouse model of melancholic anxious depression, including reduced survival of adult-born hippocampal neurons. Here we embarked on elucidating the developmental substrate underlying this phenotype, focusing on the Elevated Plus Maze and Forced Swim Test as relevant behavioral paradigms. In a first series of experiments using hemizygous tamoxifen-induced genetic inactivation of a floxed γ2 genomic locus we show that reducing the gene dosage at postnatal days (P)13/14 but not P27/28 results in altered behavior in both of these tests in adulthood, reminiscent of the anxious-depressive phenotype previously described for global heterozygous mice. However, in contrast to global heterozygous mice, the behavioral changes induced by γ2 subunit knockdown at P13/14 occurred without changes in adult hippocampal neurogenesis, indicating that altered neurogenesis is not an absolute prerequisite for anxiety- and depression-related behavior in this model. In a separate series of experiments using a pharmacological approach, acute but transient potentiation of GABA(A)Rs with diazepam uncovered distinct developmental vulnerabilities for altered behavior in the Elevated Plus Maze and Forced Swim Test, respectively. Specifically, diazepam given during P10-16 but not during later weeks resulted in increased anxiety-like behavior in adulthood, while diazepam administered during P29-35 but not earlier nor later resulted in increased immobility behavior in adulthood. We conclude that anxiety-like behavior in the Elevated Plus Maze and behavioral despair-like immobility in the Forced Swim Test are controlled by separate postnatal critical periods characterized by distinct developmental sensitivity to manipulation of GABAergic transmission via γ2 subunit-containing GABA(A)Rs.

Cocaine withdrawal causes delayed dysregulation of stress genes in the hippocampus

Relapse, even following an extended period of withdrawal, is a major challenge in substance abuse management. Delayed neurobiological effects of the drug during prolonged withdrawal likely contribute to sustained vulnerability to relapse. Stress is a major trigger of relapse, and the hippocampus regulates the magnitude and duration of stress responses. Recent work has implicated hippocampal plasticity in various aspects of substance abuse. We asked whether changes in stress regulatory mechanisms in the hippocampus may participate in the neuroadaptations that occur during prolonged withdrawal. We therefore examined changes in the rat stress system during the course of withdrawal from extended daily access (5-hours) of cocaine self-administration, an animal model of addiction. Tissue was collected at 1, 14 and 28 days of withdrawal. Plasma corticosterone levels were determined and corticosteroid receptors (GR, MR, MR/GR mRNA ratios) and expression of other stress-related molecules (HSP90AA1 and HSP90AB1 mRNA) were measured in hippocampal subfields using in situ hybridization. Results showed a delayed emergence of dysregulation of stress genes in the posterior hippocampus following 28 days of cocaine withdrawal. This included increased GR mRNA in DG and CA3, increased MR and HSP90AA1 mRNA in DG, and decreased MR/GR mRNA ratio in DG and CA1. Corticosterone levels progressively decreased during the course of withdrawal, were normalized following 28 days of withdrawal, and were correlated negatively with GR and positively with MR/GR mRNA ratio in DG. These results suggest a role for the posterior hippocampus in the neuroadaptations that occur during prolonged withdrawal, and point to a signaling partner of GR, HSP90AA1, as a novel dysregulated target during cocaine withdrawal. These delayed neurobiological effects of extended cocaine exposure likely contribute to sustained vulnerability to relapse.

Effects of exogenous cholecystokinin octapeptide on acquisition of naloxone precipitated withdrawal induced conditioned place aversion in rats

Cholecystokinin octapeptide (CCK-8), a gut-brain peptide, regulates a variety of physiological behavioral processes. Previously, we reported that exogenous CCK-8 attenuated morphine-induced conditioned place preference, but the possible effects of CCK-8 on aversively motivated drug seeking remained unclear. To investigate the effects of endogenous and exogenous CCK on negative components of morphine withdrawal, we evaluated the effects of CCK receptor antagonists and CCK-8 on the naloxone-precipitated withdrawal-induced conditioned place aversion (CPA). The results showed that CCK2 receptor antagonist (LY-288,513, 10 µg, i.c.v.), but not CCK1 receptor antagonist (L-364,718, 10 µg, i.c.v.), inhibited the acquisition of CPA when given prior to naloxone (0.3 mg/kg) administration in morphine-dependent rats. Similarly, CCK-8 (0.1–1 µg, i.c.v.) significantly attenuated naloxone-precipitated withdrawal-induced CPA, and this inhibitory function was blocked by co-injection with L-364,718. Microinjection of L-364,718, LY-288,513 or CCK-8 to saline pretreated rats produced neither a conditioned preference nor aversion, and the induction of CPA by CCK-8 itself after morphine pretreatments was not significant. Our study identifies a different role of CCK1 and CCK2 receptors in negative affective components of morphine abstinence and an inhibitory effect of exogenous CCK-8 on naloxone-precipitated withdrawal-induced CPA via CCK1 receptor.