Zuzana Babinská

Sex Differences in the Reinstatement of Methamphetamine Seeking after Forced Abstinence in Sprague-Dawley Rats

Preventing relapse to drug abuse is one of the struggles faced by clinicians in order to treat patients with substance use disorders (DSM-5). There is a large body of clinical evidence suggesting differential characteristics of the disorder in men and women, which is in line with preclinical findings as well. The aim of this study was to assess differences in relapse-like behavior in methamphetamine (METH) seeking after a period of forced abstinence, which simulates the real clinical situation very well. Findings from such study might add new insights in gender differences in relapse mechanisms to previous studies, which employ a classical drug or cue-induced reinstatement procedure following the extinction training. Adult male and female Sprague-Dawley rats were used in IV self-administration procedure conducted in operant boxes using nose-poke operandi (Coulborn Instruments, USA). Active nose-poke resulted in activation of the infusion pump to deliver one intravenous infusion of METH (0.08 mg/kg). After baseline drug intake was established (maintenance phase), a period of forced abstinence was initiated and rats were kept singly in their home cages for 14 days. Finally, one reinstatement session in operant boxes was conducted. Females were found to self-administer significantly lower dose of METH. The relapse rate was assessed as a number of active nose-pokes during the reinstatement session, expressed as a percentage of active nose-poking during the maintenance phase. Females displayed approximately 300% of active nose-pokes compared to 50% in males. This indicates higher vulnerability to relapse of METH seeking behavior in female rats. This effect was detected in all females, independently of current phase of their estrous cycle. Therefore, this paradigm using operant drug self-administration and reinstatement of drug-seeking after forced abstinence model can be used for preclinical screening for potential new anti-relapse medications specific for women.

Enhanced self-administration of the CB1 receptor agonist WIN55,212-2 in olfactory bulbectomized rats: evaluation of possible serotonergic and dopaminergic underlying mechanisms

Depression has been associated with drug consumption, including heavy or problematic cannabis use. According to an animal model of depression and substance use disorder comorbidity, we combined the olfactory bulbectomy (OBX) model of depression with intravenous drug self-administration procedure to verify whether depressive-like rats displayed altered voluntary intake of the CB1 receptor agonist WIN55,212-2 (WIN, 12.5 μg/kg/infusion). To this aim, olfactory-bulbectomized (OBX) and sham-operated (SHAM) Lister Hooded rats were allowed to self-administer WIN by lever-pressing under a continuous [fixed ratio 1 (FR-1)] schedule of reinforcement in 2 h daily sessions. Data showed that both OBX and SHAM rats developed stable WIN intake; yet, responses in OBX were constantly higher than in SHAM rats soon after the first week of training. In addition, OBX rats took significantly longer to extinguish the drug-seeking behavior after vehicle substitution. Acute pre-treatment with serotonin 5HT1B receptor agonist, CGS-12066B (2.5–10 mg/kg), did not significantly modify WIN intake in OBX and SHAM Lister Hooded rats. Furthermore, acute pre-treatment with CGS-12066B (10 and 15 mg/kg) did not alter responses in parallel groups of OBX and SHAM Sprague Dawley rats self-administering methamphetamine under higher (FR-2) reinforcement schedule with nose-poking as operandum. Finally, dopamine levels in the nucleus accumbens (NAc) of OBX rats did not increase in response to a WIN challenge, as in SHAM rats, indicating a dopaminergic dysfunction in bulbectomized rats. Altogether, our findings suggest that a depressive-like state may alter cannabinoid CB1 receptor agonist-induced brain reward function and that a dopaminergic rather than a 5-HT1B mechanism is likely to underlie enhanced WIN self-administration in OBX rats.

A preliminary study of endocannabinoid system regulation in psychosis: Distinct alterations of CNR1 promoter DNA methylation in patients with schizophrenia

Compelling evidence supports the involvement of the endocannabinoid system (ECS) in psychosis vulnerability. We here evaluated the transcriptional regulation of ECS components in human peripheral blood mononuclear cells (PBMCs) obtained from subjects suffering from bipolar disorder, major depressive disorder and schizophrenia, focusing in particular on the effects of DNA methylation. We observed selective alterations of DNA methylation at the promoter of CNR1, the gene coding for the type-1 cannabinoid receptor, in schizophrenic patients (N=25) with no changes in any other disorder. We confirmed the regulation of CNR1 in a well-validated animal model of schizophrenia, induced by prenatal methylazoxymethanol (MAM) acetate exposure (N=7 per group) where we found, in the prefrontal cortex, a significant increase in CNR1 expression and a consistent reduction in DNA methylation at specific CpG sites of gene promoter. Overall, our findings suggest a selective dysregulation of ECS in psychosis, and highlight the evaluation of CNR1 DNA methylation levels in PBMCs as a potential biomarker for schizophrenia.

Reward related neurotransmitter changes in a model of depression: An in vivo microdialysis study.

Abstract Objectives: The self-medication hypothesis assumes that symptoms related to potential monoaminergic deficits in depression may be relieved by drug abuse. The aim of this study was to elucidate the neurotransmitter changes in a rat model of depression by measuring their levels in the nucleus accumbens shell, which is typically involved in the drug of abuse acquisition mechanism. Methods: Depression was modelled by the olfactory bulbectomy (OBX) in Wistar male rats. In vivo microdialysis was performed, starting from the baseline and following after a single methamphetamine injection and behaviour was monitored. The determination of neurotransmitters and their metabolites was performed by high-performance liquid chromatography combined with mass spectrometry. Results: OBX animals had lower basal levels of dopamine and serotonin and their metabolites. However, γ-aminobutyric acid (GABA) and glutamate levels were increased. The methamphetamine injection induced stronger dopamine and serotonin release in the OBX rats and lower release of glutamate in comparison with sham-operated rats; GABA levels did not differ significantly. Conclusions: This study provides an evidence of mesolimbic neurotransmitter changes in the rat model of depression which may elucidate mechanisms underlying intravenous self-administration studies in which OBX rats were demonstrated to have higher drug intake in comparison to intact controls.

Reactivity to addictive drugs in the methylazoxymethanol (MAM) model of schizophrenia in male and female rats.

Abstract Objectives: Patients with schizophrenia often suffer comorbid substance abuse regardless of gender. However, the vast majority of studies are only conducted in male subjects. Therefore, the aim of these experiments is to assess addictive behaviors of both sexes in a neurodevelopmental model of schizophrenia induced by prenatal methylazoxymethanol (MAM) acetate exposure. Methods: MAM (22 mg/kg) was administered intraperitoneally on gestational day 17. Two studies were performed in the offspring: (1) an alcohol-drinking procedure to assess daily intake of 20% alcohol and relapse-like behavior after a period of forced abstinence; (2) Methamphetamine (METH) intravenous self administration (IVSA) followed by forced abstinence and reinstatement phases. Results: MAM exposure during the prenatal period did not change alcohol drinking regardless of sex. However, MAM females showed higher alcohol consumption in comparison to MAM males. The METH IVSA study revealed only a modest increase of drug consumption in MAM males, while there was no difference between the female groups. Reinstatement data showed no effect of the MAM model in either sex, but suggested increased responding in female rats. Conclusions: This study suggests that female sex and schizophrenia-like phenotype may work synergistically to enhance alcohol consumption. However, future research is needed to establish paradigms in which these findings would be readily assessed to test anti-addiction treatments.

Differential characteristics of ketamine self-administration in the olfactory bulbectomy model of depression in male rats

Ketamine has been extensively studied for its antidepressant potential, with promising results in both preclinical and clinical studies. However, concerns regarding its abuse liabilities greatly limit its potential to become an approved treatment for depression. Therefore, a better understanding the risks and benefits of ketamine use in depression is needed. This study aimed to assess the characteristics of operant intravenous (IV) ketamine self-administration and relapse-like behavior in the olfactory bulbectomy (OBX) model of depression in male rats. Twenty-five male Wistar rats were divided randomly into 2 groups; in 1 group the bilateral olfactory bulbectomy was performed, whereas the other group was sham-operated. Intravenous self-administration of ketamine (.5 mg/kg/infusion) was conducted under a fixed ratio 1 schedule of reinforcement. After reaching stable drug intakes, rats then underwent a 14-day period of forced abstinence followed by a drug-free relapse-like session. The forced swim test was conducted before the commencement of the self-administration protocol and on the 1st day of abstinence. Consistent with findings in previous studies on other substances, OBX animals showed increased operant IV ketamine self-administration. In contrast, ketamine-seeking behavior in the OBX group did not differ from sham-operated animals during the relapse-like session, whereas previous studies on other psychostimulants like methamphetamine and cocaine reported increases. Our findings suggest substantially different underlying neuroadaptations between chronic ketamine and psychostimulant exposure.

Olanzapine-depot administration induces time-dependent changes in adipose tissue endocrine function in rats.

OBJECTIVE Metabolic adverse effects of atypical antipsychotics (AAP) contribute significantly to increased risk of cardiovascular morbidity and mortality in patients suffering from schizophrenia. Extensive preclinical research has addressed this issue over the past years, though mechanisms underlying these adverse effects of AAP are still not understood completely. Recently, attention is drawn towards the role of adipose tissue metabolism and neurohormonal regulations. METHODS The aim of this study was to evaluate the time-dependent effects of olanzapine depot administration at clinically relevant dosing on the regulation of energy homeostasis, glucose and lipid metabolism, gastrointestinal and adipose tissue-derived hormones involved in energy balance regulations in female Sprague-Dawley rats. The study lasted 8 weeks and the markers were assayed at day 8, 15, 29, 43 and 57. RESULTS The results indicate that in the absence of hyperphagia, olanzapine chronic exposure induced weight gain from the beginning of the study. In the later time-point, increased adiposity was also observed. In the initial phase of the study, lipid profile was altered by an early increase in triglyceride level and highly elevated leptin level was observed. Clear bi-phasic time-dependent effect of olanzapine on leptin serum concentration was demonstrated. Olanzapine treatment did not lead to changes in serum levels of ghrelin, FGF-21 and pro-inflammatory markers IL-1a, IL-6 and TNF-α at any time-point of the study. CONCLUSION This study provides data suggesting early alteration in adipose tissue endocrine function as a factor involved in mechanisms underlying metabolic adverse effects of antipsychotics.

Both ketamine and NBQX attenuate alcohol drinking in male Wistar rats

The devastating consequences of alcohol-use disorder (AUD) on the individual and the society are well established. Current treatments of AUD encompass various strategies, all of which have only modest effectiveness. Hence, there is a critical need to develop more efficacious therapies. Recently, specific glutamatergic receptors have been identified as potential novel targets for intervention in AUD. Thus, the current study was designed to evaluate the effects of acute administration of sub-anesthetic doses of ketamine, an NMDA receptor antagonist, as well as NBQX, an AMPA/kainate receptor antagonist on alcohol intake and its possible behavioural consequences. Adult male Wistar rats were trained in drinking in dark paradigm (3 weeks), and following stable alcohol intake, ketamine, NBQX as well as their combination were injected prior to a 90 min drinking session. In addition to alcohol intake, sucrose preference (overnight), and locomotor activity and forced swim test (FST) were also evaluated before and following alcohol intake. Both doses of ketamine (5 and 10 mg/kg) and NBQX (5 and 10 mg/kg) significantly attenuated percent alcohol intake. The combination of the higher dose of ketamine and NBQX, however, did not significantly affect percent alcohol intake. Moreover, animals exposed to alcohol showed decreased sucrose intake (reflective of anhedonia), decreased locomotor activity and swimming in the FST (reflective of helplessness), that were not affected by ketamine and/or NBQX. These results suggest that selective antagonism of the NMDA or AMPA/kainate receptors may be of therapeutic potential in AUD.

Olfactory bulbectomy increases reinstatement of methamphetamine seeking after a forced abstinence in rats

Drug addiction is commonly associated with depression and comorbid patients also suffer from higher cravings and increased relapse rate. To address this issue preclinically we combined the olfactory bulbectomy (OBX) model of depression and intravenous methamphetamine self-administration procedure in rats to assess differences in relapse-like behavior. Male Sprague-Dawley rats were divided randomly into two groups; in one group the bilateral olfactory bulbectomy (OBX) was performed while the other group was sham operated. After recovery, intracardiac catheter was implanted. Intravenous self-administration procedure was conducted in operant boxes using nose-poke operandi (Coulbourn Instruments, Inc., USA) under fixed ratio 1 schedule of reinforcement. Methamphetamine was available at dose 0.08 mg/kg/infusion. After stable methamphetamine intake was maintained, a period of forced abstinence was initiated and rats were kept in their home-cages for 14 days. Finally, one reinstatement session was conducted in operant boxes with no drug delivery. In the reinstatement session the mean of 138.4 active nose-pokes was performed by the OBX group, while the sham group displayed 41 responses, i.e. 140 % and 48 % of basal nose-poking during maintenance phase in OBX and sham operated group respectively. OBX group also showed significantly more passive nose-pokes indicating hyperactive behavioral traits in bulbectomized rats. However, the % of active operandum preference was equal in both groups. Olfactory bulbectomy model significantly increased reinstatement of methamphetamine seeking behavior. This paradigm can be used to evaluate potential drugs that are able to suppress the drug-seeking behavior.