Forced swim stress dynamically alters neural activity and bi-directionally modulates NMDA receptors in the prefrontal cortex

Repeated exposure to stress results in progressively divergent effects on cognitive behaviors that are dependent on the integrity of networks in the medial prefrontal cortex (mPFC). To investigate molecular mechanisms responsive to variable repetition of mild stress, we measured persistent neural activity, in vitro, from mPFC slices in mice that had been repetitively exposed to 10 minutes of forced swim stress for 3-10 days. 3-day short-term stress facilitated persistent neural activity by increasing event duration while 10 days suppressed event duration and amplitude. These dynamic changes were accompanied by a similar bi-directional modulation of the NMDA/AMPA receptor current ratio, an important synaptic mechanism for sustaining the persistency of neural activity. Specifically, short-term stress led to potentiated NMDA currents with slower decay kinetics, and extended stress produced smaller currents with faster decay. The inhibitory action of ifenprodil, a specific blocker of NR2B-containing NMDA receptors, was more effective in NMDA current suppression following light stress and less effective after longer stress compared to naive controls. Persistent activity and glutamate receptor balance in the neocortex have been linked to working memory and impulse control. Therefore, these results could provide insight for generating therapeutic strategies to prevent or reverse stress-induced cognitive deficits.

Amphetamine Modulation of Long-Term Object Recognition Memory in Rats: Influence of Stress

Amphetamine is a potent psychostimulant that increases brain monoamine levels. Extensive evidence demonstrated that norepinephrine is crucially involved in the regulation of memory consolidation for stressful experiences. Here, we investigated amphetamine effects on the consolidation of long-term recognition memory in rats exposed to different intensities of forced swim stress immediately after training. Furthermore, we evaluated whether such effects are dependent on the activation of the peripheral adrenergic system. To this aim, male adult Sprague Dawley rats were subjected to an object recognition task and intraperitoneally administered soon after training with amphetamine (0.5 or 1 mg/kg), or its corresponding vehicle. Rats were thereafter exposed to a mild (1 min, 25 ± 1°C) or strong (5 min, 19 ± 1°C) forced swim stress procedure. Recognition memory retention was assessed 24-h after training. Our findings showed that amphetamine enhances the consolidation of memory in rats subjected to mild stress condition, while it impairs long-term memory performance in rats exposed to strong stress. These dichotomic effects is dependent on stress-induced activation of the peripheral adrenergic response.

Changes in c-fos and p-CREB signaling following exposure to forced swim stress or exogenous corticosterone during morphine-induced place preference are dependent on glucocorticoid receptor in the basolateral amygdala

Neural circuitry comprising the nucleus accumbens (NAc), prefrontal cortex (PFC), amygdala (AMY), and hippocampus (HIP) are the main components of the reward circuit. Our previous behavioral data showed that forced swim stress (FSS) and corticosterone administration could inhibit the acquisition of morphine-induced conditioned place preference (CPP), and this effect was blocked by intra-basolateral amygdala (BLA) administration of RU38486, glucocorticoid receptor (GR) antagonist. Therefore, we tried to evaluate the effect of intra-BLA administration of the GR antagonist during the conditioning phase on the c-fos and p-CREB/CREB ratio expression in the AMY, NAc, PFC, and HIP of rats that underwent FSS or received exogenous corticosterone (10 mg/kg; i.p.) before morphine injection (5 mg/kg; s.c.) during 3 conditioning days. Our results showed that morphine-induced CPP could increase c-fos level and p-CREB/CREB ratio in all regions (except in the HIP). In addition, c-fos expression was elevated by FSS in all regions and blockade of GR decreased this effect. In the PFC, in addition to FSS, corticosterone could raise c-fos expression, which was blocked by RU38486. In conclusion, it seems that the intra-BLA administration of RU38486 differently modulates the effect of morphine-induced CPP on the expression of c-fos and p-CREB/CREB ratio in animals that underwent FSS or corticosterone administration.

Activation of the kappa opioid receptor / dynorphin system alters stress and threat responding during acute withdrawal from intermittent alcohol drinking in male mice

The dynorphin/kappa opioid receptor (KOR) system in the brain regulates both stressful experiences and negative, aversive states during withdrawal from drugs of abuse. We explored the role of this system during acute withdrawal from long-term alcohol drinking, focusing on the bed nucleus of the stria terminalis (BNST), a region strongly implicated in alcohol-withdrawal induced alterations of behavior. Male C57BL/6J mice were subjected to repeated forced swim tests, home cage exposure to a predator odor, and a visual threat after eight weeks intermittent access to alcohol or water. Systemic injection of KOR antagonist norBNI reversed alcohol-related differences in immobility time during the second swim test and reduced burying behavior in response to predator odor, but did not affect behavioral response to visual threat. In dynorphin-GFP reporter mice, c-Fos immunoreactivity was increased in dynorphin-containing neurons after repeated swim stress and alcohol drinking. Using dynorphin-GFP mice, there was enhanced spontaneous excitatory synaptic drive onto dynorphin neurons in the BNST after alcohol-drinking mice underwent forced swim stress. Finally, knockdown of dynorphin in the BNST using a viral shRNA affected swim stress behavior and responses to TMT in alcohol drinkers and controls, but did not affect alcohol drinking. These studies confirm BNST dynorphin recruitment during acute withdrawal as playing a key role in altered behavioral responses to stressful stimuli.HighlightsIntermittent alcohol drinking changed stress reactions in mice.KOR antagonist norBNI altered stress responses in alcohol drinkers.Alcohol and swim stress increased c-Fos immunoreactivity in BNST dynorphin neurons.Swim stress enhanced excitatory drive onto BNST dynorphin cells in alcohol mice.BNST dynorphin knockdown affected some stress behavior, but not alcohol drinking.

Transcriptome Analysis of Alcohol Drinking in Non-Dependent and Dependent Mice Following Repeated Cycles of Forced Swim Stress Exposure

Chronic stress is a known contributing factor to the development of drug and alcohol addiction. Animal models have previously shown that repeated forced swim stress promotes escalated alcohol consumption in dependent animals. To investigate the underlying molecular adaptations associated with stress and chronic alcohol exposure, RNA-sequencing and bioinformatics analyses were conducted on the prefrontal cortex (CTX) of male C57BL/6J mice that were behaviorally tested for either non-dependent alcohol consumption (CTL), chronic intermittent ethanol (CIE) vapor dependent alcohol consumption, repeated bouts of forced swim stress alone (FSS), and chronic intermittent ethanol with forced swim stress (CIE + FSS). Brain tissue from each group was collected at 0-h, 72-h, and 168-h following the final test to determine long-lasting molecular changes associated with maladaptive behavior. Our results demonstrate unique temporal patterns and persistent changes in coordinately regulated gene expression systems with respect to the tested behavioral group. For example, increased expression of genes involved in “transmitter-gated ion channel activity” was only determined for CIE + FSS. Overall, our results provide a summary of transcriptomic adaptations across time within the CTX that are relevant to understanding the neurobiology of chronic alcohol exposure and stress.