The involvement of an opiate mechanism in the sensitized behavioral deficit induced by early chronic variable stress: influence of desipramine

Protective effects of curcumin and sertraline on the behavioral changes in chronic variable stress-induced rats

Behavioral characteristics of the animal models and humans are impaired in chronic stress. The present study aimed to evaluate and compare the protective effects of sertraline and curcumin on stress-induced learning and memory impairment, anxiety and anhedonia in rats. Male rats were divided into seven groups: stress+water, stress+olive oil, stress+curcumin (100 mg/kg/day), stress+sertraline (10 mg/kg/day), curcumin, sertraline, and control groups. The rats were exposed to chronic variable stress for 56 days. At the end of 40 days and while the previous treatments were continued, the rats were tested in the eight radial maze, elevated plus maze, and sucrose consumption for learning and memory, anxiety, and anhedonia, respectively. In comparison to the non-stressed group, stress+water and stress+olive oil groups revealed a significantly lower percent of correct choices and higher reference and working memory errors during learning and retention phases (p<0.001). In addition these stress groups showed a significant lower percent of the open arms time and open arms entries in the elevated plus maze and consuming less sucrose solution. In addition, the stress+curcumin and stress+sertraline groups showed a better performance in the evaluated parameters of the radial arm maze, elevated plus maze, and sucrose consumption tests. It appears that curcumin and sertraline have the similar effectiveness on behavioral changes in chronic variable stress-induced rats.

Quetiapine prevents anhedonia induced by acute or chronic stress

The role of atypical antipsychotics as add-on treatments and as primary mood stabilizers in different phases of bipolar disorder is an important current research area. Although in bipolar patients the main therapeutic indication of quetiapine (QTP) is the management of acute mania, several observations suggest that this agent may exert antidepressant as well as antimanic effects. However, in our knowledge, there are no preclinical studies supporting this hypothesis. Thus, the main goal of the present work was to evaluate the putative antidepressant effect of QTP (0.4, 2.0, or 10 mg/kg/day), in comparison to amitriptyline (AMI) (2 or 5 mg/kg/day), in rats exposed to acute or chronic stress. The administration of QTP, 2 mg/kg/day, prevents the onset of anhedonia in rats exposed to a 6-week chronic mild stress (CMS) protocol. The effect of QTP has a slow onset, beginning at week 5, and causes a complete recovery from anhedonia. In this respect, the effect of QTP is similar to that obtained after chronic administration of AMI 2 or 5 mg/kg/day. Our findings also indicate that a 6-week administration of QTP, 2 or 10 mg/kg/day, has protective effects against the onset of anhedonia caused by the exposure to an acute subthreshold stressful event in rats that have previously experienced the CMS procedure. The results suggest that QTP is able to prevent both the transient mood depression caused by acute stress and the long-lasting anhedonic state induced by exposure, over a period of weeks, to a variety of unpredictable mild stressors.

Cholecystokinin and endogenous opioid peptides: interactive influence on pain, cognition, and emotion

It is well documented that stressful life experiences contribute to the etiology of human mood disorders. Cholecystokinin (CCK) is a neuropeptide found in high concentrations throughout the central nervous system, where it is involved in numerous physiological functions. A role for CCK in the induction and persistence of anxiety and major depression appears to be conspicuous. While increased CCK has been associated with motivational loss, anxiety and panic attacks, an increase in mesocorticolimbic opioid availability has been associated with coping and mood elevation. The close neuroanatomical distribution of CCK with opioid peptides in the limbic system suggests that there may be an opioid-CCK link in the modulation and expression of anxiety or stressor-related behaviors. In effect, while CCK induces relatively protracted behavioral disturbances in both animal and human subjects following stressor applications, opioid receptor activation may change the course of psychopathology. The antagonistic interaction of CCK and opioid peptides is evident in psychological disturbances as well as stress-induced analgesia. There appears to be an intricate balance between the memory-enhancing and anxiety-provoking effects of CCK on one hand, and the amnesic and anxiolytic effects of opioid peptides on the other hand. Potential anxiogenic and mnemonic influences of site-specific mesocorticolimbic CCK and opioid peptide availability, the relative contributions of specific CCK and opioid receptors, as well as the time course underlying neuronal substrates of long-term behavioral disturbances as a result of stressor manipulations, are discussed.

Early exposure to chronic variable stress facilitates the occurrence of anhedonia and enhanced emotional reactions to novel stressors: reversal by naltrexone pretreatment

The present research studied the influence of an early chronic variable stress (CVS) paradigm - an animal model of depression - on behavioral responses to subsequent environmental challenges suggested to model anhedonia and emotional reactions such as anxiety and fear. In order to explore a potential involvement of an endogenous opiate mechanism - presumably activated during CVS exposure - in the development of such behavioral reactions, in all experiments rats were administered naltrexone (NAL, 2 mg/kg, i.p.) or vehicle (VH) prior to each daily stressor of the CVS procedure. Animals were exposed to CVS and 1 week later tested for sucrose preference (1%) in a free choice paradigm after the presentation or not of a 90-min restraint period. Only CVS treated animals that were later exposed to restraint showed a reduction of sucrose preference, this reduction was absent when CVS rats were pretreated previously with NAL. Moreover, CVS rats were one week later tested on the elevated plus maze (EPM) and in their conditioned and unconditioned freezing response to a single shock session. Early chronic stress resulted in an anxiogenic behavior in the EPM and in an enhanced conditioned and unconditioned freezing which were all abolished by NAL pretreatment. These behavioral findings suggest that the potential activation of an endogenous opiate mechanism during CVS participates in the development of anhedonia and exaggerated emotional reactions in response to subsequent stressful experiences.

Endogenous opiates: 1999

This paper is the twenty-second installment of the annual review of research concerning the opiate system. It summarizes papers published during 1999 that studied the behavioral effects of the opiate peptides and antagonists, excluding the purely analgesic effects, although stress-induced analgesia is included. The specific topics covered this year include stress; tolerance and dependence; learning, memory, and reward; eating and drinking; alcohol and other drugs of abuse; sexual activity, pregnancy, and development; mental illness and mood; seizures and other neurologic disorders; electrical-related activity; general activity and locomotion; gastrointestinal, renal, and hepatic function; cardiovascular responses; respiration and thermoregulation; and immunologic responses.

Benzodiazepine withdrawal facilitates the subsequent onset of escape failures and anhedonia: influence of different antidepressant drugs

The effect of benzodiazepine (BDZ) withdrawal on escape acquisition and on the behavioral response to two different reinforcing stimuli was investigated. In addition, the influence of antidepressant drugs (AD) differing in their mechanism of action on these behavioral outputs was also evaluated. Rats subjected to withdrawal from a chronic treatment with diazepam (DZM; 2 mg/kg per day, i.p.) during 21 days were subsequently exposed to a brief inescapable shock session (IS) and 48 h later to an active avoidance test. Only withdrawn animals exposed to the IS exhibited enhanced escape failures. In an additional experiment, withdrawn rats were repeatedly administered with vehicle (VEH), desipramine (DMI; 5 mg/kg, i.p.), fluoxetine (FLU; 5 mg/kg, i.p.) or phenelzine (PHEN; 5 mg/kg, i.p.) and subsequently exposed to IS and to active avoidance task. A significant reversal of escape deficit was only observed following DMI and PHEN but not after FLU. Furthermore, withdrawn rats showed a reduced preference for a sexually relevant olfactory cue, this reduced sensitivity was only normalized following DMI but not after the administration of FLU or PHEN. Finally, rats exposed to abrupt cessation of chronic BDZ administration did not exhibit preference for a context previously associated with amphetamine (AMP) under the conditioned place preference (CPP) procedure. All these findings are indicative that BDZ withdrawal facilitates the subsequent occurrence of behavioral changes-escape failures and reduced behavioral response to rewarding stimuli-suggested to parallel important symptoms of human depression. In addition, DMI seems to be much more effective in restoring such behavioral abnormalities as compared to a MAO inhibitor and to a inhibitor of 5-HT uptake.

Chronic stress sensitizes frontal cortex dopamine release in response to a subsequent novel stressor: reversal by naloxone

The present study examined the influence of an early chronic variable stress procedure with or without concurrent naloxone administration at different doses (1, 2 or 3 mg/kg, i.p.) on stress (restraint)-induced dopamine release in the frontal cortex in vivo. A higher increase in cortical dopamine release in response to a subsequent restraint event was observed in chronically stressed rats as compared with those without chronic stress exposure. Naloxone pretreatment normalized this sensitized response only at the higher dose (3 mg/kg, i.p.). The present results indicate that cortical dopamine response to a novel and uncontrollable stressor sensitizes after exposure to a chronic variable stress procedure and that an endogenous opiate mechanism, presumably activated during chronic stress, may be involved in the development of such a sensitization process.