Not all stress is equal: CREB is not necessary for restraint stress reinstatement of cocaine-conditioned reward

Restraint stress effects on glutamate signaling protein levels in the rats' frontal cortex: Does β1 adrenoceptor activity matter?

Introduction

Stress-evoked dysfunctions of the frontal cortex (FC) are correlated with changes in the functioning of the glutamatergic system, and evidence demonstrates that noradrenergic transmission is an important regulator of this process. In the current study, we adopted a restraint stress (RS) model in male Wistar rats to investigate whether the blockade of β1 adrenergic receptors (β1AR) with betaxolol (BET) in stressed animals influences the body's stress response and the expression of selected signaling proteins in the medial prefrontal cortex (mPFC).

Methods

The study was divided into two parts. In the first part, rats were exposed to RS for 3, 7, or 14 days, and the expression of glutamate signaling proteins (p(S845)/t GluA1, p(Y1472)/t GluN2B, VGLUT1, and VGLUT2) in the FC was analyzed to determine the optimal RS duration for studying the mechanisms of hypofrontality. In the second part, rats were exposed to RS for 14 days, and BET (5 mg/kg, p. o.) was administered during the last 8 days immediately after RS. The body's stress reaction was assessed by analyzing body weight and blood levels of adrenocorticotropic hormone (ACTH) and corticosterone (CORT). Behavioral responses were evaluated using the novel object recognition (NOR) and elevated plus maze (EPM) tests. The impact of RS and BET on the expression of p(Y530)/t Fyn and p (S133)/t CREB in the mPFC was measured via Western blotting.

Results and Discussion

The first part of the study demonstrated a decreased level of glutamate receptors in rats exposed to 14 days of RS, following an initial increase observed after 7 days of RS. Results from the second part revealed that chronic RS reduced body weight, impaired recognition memory in the NOR test, augmented blood levels of ACTH, and increased the expression of p(Y530) Fyn in the mPFC. However, β1AR blockade did not alter the effects of RS on weight gain, cognitive function, or the expression of p(Y530) Fyn. β1AR blockade normalized only the blood concentration of ACTH. These results suggest that decreased Fyn kinase activity, indicated by phosphorylation at Y530, underlies the stress-evoked downregulation of GluN2B in the FC in a manner independent of β1AR activity.

The guanine nucleotide exchange factor RapGEF2 is required for ERK-dependent immediate-early gene (Egr1) activation during fear memory formation

The MAP kinase ERK is important for neuronal plasticity underlying associative learning, yet specific molecular pathways for neuronal ERK activation are undetermined. RapGEF2 is a neuron-specific cAMP sensor that mediates ERK activation. We investigated whether it is required for cAMP-dependent ERK activation leading to other downstream neuronal signaling events occurring during associative learning, and if RapGEF2-dependent signaling impairments affect learned behavior. Camk2α-cre+/-::RapGEF2fl/fl mice with depletion of RapGEF2 in hippocampus and amygdala exhibit impairments in context- and cue-dependent fear conditioning linked to corresponding impairment in Egr1 induction in these two brain regions. Camk2α-cre+/-::RapGEF2fl/fl mice show decreased RapGEF2 expression in CA1 and dentate gyrus associated with abolition of pERK and Egr1, but not of c-Fos induction, following fear conditioning, impaired freezing to context after fear conditioning, and impaired cAMP-dependent long-term potentiation at perforant pathway and Schaffer collateral synapses in hippocampal slices ex vivo. RapGEF2 expression is largely eliminated in basolateral amygdala, also involved in fear memory, in Camk2α-cre+/-::RapGEF2fl/fl mice. Neither Egr1 nor c-fos induction in BLA after fear conditioning, nor cue-dependent fear learning, are affected by ablation of RapGEF2 in BLA. However, Egr1 induction (but not that of c-fos) in BLA is reduced after restraint stress-augmented fear conditioning, as is freezing to cue after restraint stress-augmented fear conditioning, in Camk2α-cre+/-::RapGEF2fl/fl mice. Cyclic AMP-dependent GEFs have been genetically associated as risk factors for schizophrenia, a disorder associated with cognitive deficits. Here we show a functional link between one of them, RapGEF2, and cognitive processes involved in associative learning in amygdala and hippocampus.

Characteristics of Stress Sensitivity in Heroin Use Disorder Patients during Their Opioid Agonist Treatment

In the present study, performed on a sample of Heroin Use Disorder (HUD) patients undergoing Opioid Agonist Treatment (OAT), we attempted to explore the relationships between stress sensitivity and heroin addiction-related clinical aspects. HUD patients' stress sensitivity was evaluated with the Heroin/PTSD-Spectrum questionnaire (H/PSTD-S). The Drug Addiction History Questionnaire (DAH-Q), the Symptomatological Check List-90 (SCL-90), and The Behavioural Covariate of Heroin Craving inventory (CRAV-HERO) were all used, as were the Deltito Subjective Wellness Scale (D-SWS), a self-report scale evaluating subjective well-being; the Cocaine Problem Severity Index (CPSI), a questionnaire determining the extent of a cocaine problem; and the Marijuana Craving Questionnaire (MC-Q), an instrument assessing craving for cannabinoids. We checked correlations between stress sensitivity and the extent of HUD clinical features and compared patients with and without problematic stress sensitivity. H/PTSD-S was positively correlated with patients' income, altered mental status, legal problems, the lifetime different treatments index, the current treatment load index, and all SCL-90 indexes and factors. Regarding subjective well-being, stress sensitivity negatively correlated with the contrast best week (last five years) index. Patients with high-stress sensitivity were females with a low income. They exhibited a more severe mental status at treatment entry, greater difficulty in working adaptation, and legal problems during treatment. Additionally, these patients showed a higher level of psychopathology, more impairment in well-being, and more risky behaviours during treatment. Stress sensitivity, as H/PTSD-S, must be considered an outcome of HUD. HUD's addiction history and clinical features are significant risk factors for H/PTSD-S. Therefore, social and behavioural impairment in HUD patients could be considered the clinical expression of the H/PTSD spectrum. In summary, the long-term outcome of HUD is not represented by drug-taking behaviours. Rather, the inability to cope with the contingent environmental conditions is the key feature of such a disorder. H/PTSD-S, therefore, should be seen as a syndrome caused by an acquired inability (increased salience) concerning regular (daily) life events.

Cocaine-Dependent Acquisition of Locomotor Sensitization and Conditioned Place Preference Requires D1 Dopaminergic Signaling through a Cyclic AMP, NCS-Rapgef2, ERK, and Egr-1/Zif268 Pathway

Elucidation of the mechanism of dopamine signaling to ERK that underlies plasticity in dopamine D1 receptor-expressing neurons leading to acquired cocaine preference is incomplete. NCS-Rapgef2 is a novel cAMP effector, expressed in neuronal and endocrine cells in adult mammals, that is required for D1 dopamine receptor-dependent ERK phosphorylation in mouse brain. In this report, we studied the effects of abrogating NCS-Rapgef2 expression on cAMP-dependent ERK→Egr-1/Zif268 signaling in cultured neuroendocrine cells; in D1 medium spiny neurons of NAc slices; and in either male or female mouse brain in a region-specific manner. NCS-Rapgef2 gene deletion in the NAc in adult mice, using adeno-associated virus-mediated expression of cre recombinase, eliminated cocaine-induced ERK phosphorylation and Egr-1/Zif268 upregulation in D1-medium spiny neurons and cocaine-induced behaviors, including locomotor sensitization and conditioned place preference. Abrogation of NCS-Rapgef2 gene expression in mPFC and BLA, by crossing mice bearing a floxed Rapgef2 allele with a cre mouse line driven by calcium/calmodulin-dependent kinase IIα promoter also eliminated cocaine-induced phospho-ERK activation and Egr-1/Zif268 induction, but without effect on the cocaine-induced behaviors. Our results indicate that NCS-Rapgef2 signaling to ERK in dopamine D1 receptor-expressing neurons in the NAc, but not in corticolimbic areas, contributes to cocaine-induced locomotor sensitization and conditioned place preference. Ablation of cocaine-dependent ERK activation by elimination of NCS-Rapgef2 occurred with no effect on phosphorylation of CREB in D1 dopaminoceptive neurons of NAc. This study reveals a new cAMP-dependent signaling pathway for cocaine-induced behavioral adaptations, mediated through NCS-Rapgef2/phospho-ERK activation, independently of PKA/CREB signaling.SIGNIFICANCE STATEMENT ERK phosphorylation in dopamine D1 receptor-expressing neurons exerts a pivotal role in psychostimulant-induced neuronal gene regulation and behavioral adaptation, including locomotor sensitization and drug preference in rodents. In this study, we examined the role of dopamine signaling through the D1 receptor via a novel pathway initiated through the cAMP-activated guanine nucleotide exchange factor NCS-Rapgef2 in mice. NCS-Rapgef2 in the NAc is required for activation of ERK and Egr-1/Zif268 in D1 dopaminoceptive neurons after acute cocaine administration, and subsequent enhanced locomotor response and drug seeking behavior after repeated cocaine administration. This novel component in dopamine signaling provides a potential new target for intervention in psychostimulant-shaped behaviors, and new understanding of how D1-medium spiny neurons encode the experience of psychomotor stimulant exposure.

Organic cation transporter 3 and the dopamine transporter differentially regulate catecholamine uptake in the basolateral amygdala and nucleus accumbens

Regional alterations in kinetics of catecholamine uptake are due in part to variations in clearance mechanisms. The rate of clearance is a critical determinant of the strength of catecholamine signaling. Catecholamine transmission in the nucleus accumbens core (NAcc) and basolateral amygdala (BLA) is of particular interest due to involvement of these regions in cognition and motivation. Previous work has shown that catecholamine clearance in the NAcc is largely mediated by the dopamine transporter (DAT), but clearance in the BLA is less DAT-dependent. A growing body of literature suggests that organic cation transporter 3 (OCT3) also contributes to catecholamine clearance in both regions. Consistent with different clearance mechanisms between regions, catecholamine clearance is more rapid in the NAcc than in the BLA, though mechanisms underlying this have not been resolved. We compared the expression of DAT and OCT3 and their contributions to catecholamine clearance in the NAcc and BLA. We found DAT protein levels were ~ 4-fold higher in the NAcc than in the BLA, while OCT3 protein expression was similar between the two regions. Immunofluorescent labeling of the two transporters in brain sections confirmed these findings. Ex vivo voltammetry demonstrated that the magnitude of catecholamine release was greater, and the clearance rate was faster in the NAcc than in the BLA. Additionally, catecholamine clearance in the BLA was more sensitive to the OCT3 inhibitor corticosterone, while clearance in the NAcc was more cocaine sensitive. These distinctions in catecholamine clearance may underlie differential effects of catecholamines on behavioral outputs mediated by these regions.

Stress-induced neural activation is altered during early withdrawal from chronic methamphetamine

Chronic methamphetamine (MA) use can lead to increased symptoms of depression and anxiety during abstinence. Less is known about the specific brain regions that are altered following repeated MA that may be associated with these behavioral perturbations. Furthermore, MA has been reported to recruit and activate microglia in the brain, which may exacerbate stress-associated behavioral changes. In the present study, male and female mice were injected with MA (5 mg/kg) or saline once daily for 10 days, and during early withdrawal were assessed for alterations in immediate early gene (c-Fos) responses to a forced swim stressor. Chronic MA exposure increased floating and decreased swim time in the forced swim test in male and female mice tested 48 h after the final dose, indicating elevated depressive-like behavior. Furthermore, assessment of nest building, a measure of distress or despair-like behavior, revealed a sex-specific effect with only MA-treated females showing impairments. The c-Fos response to forced swim was attenuated by prior MA exposure in the central amygdala, CA3 hippocampal region, prefrontal cortex, and bed nucleus of the stria terminalis (BST). In the BST this attenuation occurred only in males. Neither the total number of microglia or activated microglia were altered by chronic MA exposure in regions examined. The primary findings indicate that chronic MA exposure attenuates activation of select stress-associated brain regions, a dysregulation that might contribute to alterations in mood-related behaviors.

Effects of head-only or whole-body exposure to very low doses of 4He (1000 MeV/n) particles on neuronal function and cognitive performance

On exploratory class missions, astronauts will be exposed to a range of heavy particles which vary in linear energy transfer (LET). Previous research has shown a direct relationship between particle LET and cognitive performance such that, as particle LET decreases the dose needed to affect cognitive performance also decreases. Because a significant portion of the total dose experienced by astronauts may be expected to come from exposure to low LET ⁴He particles, it would be important to establish the threshold dose of ⁴He particles that can produce changes in cognitive performance. The results indicated that changes in neuronal function and cognitive performance could be observed following both head-only and whole-body exposures to ⁴He particles at doses as low as 0.01-0.025 cGy. These results, therefore, suggest the possibility that astronauts on exploratory class missions may be at a greater risk for HZE-induced deficits than previously anticipated.

Effect of acute and chronic restraint stress on electrical activity of prefrontal cortex neurons in the reinstatement of extinguished methamphetamine-induced conditioned place preference: An electrophysiological study

Increased vulnerability to drug abuse has been observed after exposure to stress and the prefrontal cortex (PFC) plays a major role in the control of the stress response and reward pathway. The current study was conducted to clarify the effects of acute and chronic restraint stress on PFC neural activity during the reinstatement of methamphetamine (METH)-induced conditioned place preference (CPP) in rats. Following the establishment of CPP (METH 0.5 mg/kg; s.c. for 3 days) and the extinction phase, male Wistar rats were divided into threshold (0.25 mg/kg; s.c.) and sub-threshold (0.125 mg/kg; s.c.) METH-treated super groups to induce reinstatement. Each super group contained control (non-stressed), acute restraint stress (ARS) and chronic restraint stress (CRS) groups. in vivo single unit recordings were performed on the urethane-anesthetized rats in these groups. After baseline recordings (10-min period) of the neurons in the PFC, their firing activity was recorded for 50 min during the reinstatement phase after injection of METH. The results showed that the threshold dose, but not the sub-threshold dose, of METH significantly increased PFC neural activity in the non-stressed animals. The sub-threshold dose of METH notably changed this activity in both the ARS and CRS groups. These changes in the excited neurons after the sub-threshold dose in the ARS and CRS groups were significantly higher than those in the non-stressed group. It appears that the PFC is implicated in the associated reward pathway and stress functions. METH affected the firing rate of PFC neurons and stress amplified the effect of METH on changes in the neuronal firing rate in the PFC.

Effects of Acute and Chronic Restraint Stress on Reinstatement of Extinguished Methamphetamine-induced Conditioned Place Preference in Rats

Introduction:

Methamphetamine (METH) is a neurotoxic psychostimulant with highly addictive potential that leads to compulsive drug use and vulnerability to relapse. Environmental cues, such as drug exposure, peer influence, and social stress, are the powerful triggers of drug relapse. In this study, we tried to find out the effect of acute and chronic restraint stress on reinstatement of extinguished METH-induced Conditioned Place Preference (CPP) in rats.

Methods:

Subcutaneous (SC) administration of METH (0.125, 0.25, 0.5, 1, 2 and 4 mg/kg) could induce CPP and it was found that METH with the dose of 0.5 mg/kg was more potent than other doses. In extinction phase, rats were put in the CPP box for 30 min per day for 8 consecutive days. After extinction, animals were exposed to restraint stress (3-h period, as an acute stress) 60 min before subcutaneous administration of ineffective dose of METH (0.125 mg/kg) in order to reinstate the extinguished METH-induced CPP. For induction of the chronic stress during extinction phase, the animals were exposed to the restraint stress for one hour per day.

Results:

The results showed that the effective dose of METH to induce CPP was 0.5 mg/kg. Based on the results, physical stress (restraint stress) whether acute and chronic, can significantly induce reinstatement of METH-induced CPP (P˂0.001) in extinguished animals.

Conclusion:

Additionally, the chronic restraint stress could reduce duration of extinction (maintenance) of METH-induced CPP. It seems that exposure to the stress induces the relapse in abstinent amphetamine, but acute and chronic situation have a different reaction.

NMDA antagonist MK 801 in nucleus accumbens core but not shell disrupts the restraint stress-induced reinstatement of extinguished cocaine-conditioned place preference in rats

Relapse is a common feature of cocaine addiction. In rodents, it can be elicited by cues, stress or the drug. Restraint stress-induced reinstatement of cocaine-conditioned place preference (CPP) is a useful model to study the mechanisms involved in stress-induced relapse of drug-seeking behavior. There is evidence that the glutamate NMDA receptors are critically involved in drug- and cue-induced reinstatement of seeking behavior and drug-CPP responses. The aim of this study was to investigate the contribution of NMDA receptors within core vs. shell nucleus accumbens (NAc) subregions to restraint stress-induced reinstatement of extinguished cocaine-CPP. After extinction of cocaine-conditioned preference, animals were administered MK 801 systemically or directly into intra-core or intra-shell, and restrained for 30min or left undisturbed in their home-cages. First, we demonstrated that restraint stress-induced reinstatement of extinguished cocaine-CPP depends on the duration of restraint as well as on the context in which it is applied. Second, this effect was blocked by systemic MK 801 administration either before or after restraint. Third, intra-core but not intra-shell administration abrogated the restraint stress-induced reinstatement. These findings show that NMDA receptors within NAc core, but not shell, play a critical role in restraint stress-induced reinstatement of cocaine-CPP.

Substance use modulates stress reactivity: Behavioral and physiological outcomes

Drug addiction is a major public health concern in the United States costing taxpayers billions in health care costs, lost productivity and law enforcement. However, the availability of effective treatment options remains limited. The development of novel therapeutics will not be possible without a better understanding of the addicted brain. Studies in both clinical and preclinical models indicate that chronic drug use leads to alterations in the body and brain's response to stress. Dysregulation of the hypothalamic-pituitary-adrenal (HPA) axis may shed light on the ability of stress to increase vulnerability to relapse. Further, within both the HPA axis and limbic brain regions, corticotropin-releasing factor (CRF) is critically involved in the brain's response to stress. Alterations in both central and peripheral CRF activity seen following chronic drug use provide a mechanism by which substance use can alter stress reactivity, thus mediating addictive phenotypes. While many reviews have focused on how stress alters drug-mediated changes in physiology and behavior, the goal of this review is to focus on how substance use alters responses to stress.

Assessment of Cocaine-induced Behavioral Sensitization and Conditioned Place Preference in Mice

It is thought that rewarding experiences with drugs create strong contextual associations and encourage repeated intake. In turn, repeated exposures to drugs of abuse make lasting alterations in the brain function of vulnerable individuals, and these persistent alterations likely serve to maintain the maladaptive drug seeking and taking behaviors characteristic of addiction/dependence(2). In rodents, reward experience and contextual associations are frequently measured using the conditioned place preference assay, or CPP, wherein preference for a previously drug-paired context is measured. Behavioral sensitization, on the other hand, is an increase in a drug-induced behavior that develops progressively over repeated exposures. Since sensitized behaviors can often be measured after several months of drug abstinence, depending on the dose and length of initial exposure, they are considered observable correlates of lasting drug-induced plasticity. Researchers have found these assays useful in determining the neurobiological substrates mediating aspects of addiction as well as assessing the potential of different interventions in disrupting these behaviors. This manuscript describes basic, effective protocols for mouse CPP and locomotor behavioral sensitization to cocaine.

Inducible forebrain-specific ablation of the transcription factor Creb during adulthood induces anxiety but no spatial/contextual learning deficits

The cyclic AMP (cAMP)-response element binding protein (CREB) is an activity-dependent transcription factor playing a role in synaptic plasticity, learning and memory, and emotional behavior. However, the impact of Creb ablation on rodent behavior is vague as e.g., memory performance of different Creb mutant mice depends on the specific type of mutation per se but additionally on the background and learning protocol differences. Here we present the first targeted ablation of CREB induced during adulthood selectively in principal forebrain neurons in a pure background strain of C57BL/6 mice. All hippocampal principal neurons exhibited lack of CREB expression. Mutant mice showed a severe anxiety phenotype in the openfield and novel object exploration test as well as in the Dark-Light Box Test, but unaltered hippocampus-dependent long-term memory in the Morris water maze and in context dependent fear conditioning. On the molecular level, CREB ablation led to CREM up regulation in the hippocampus and frontal cortex which may at least in part compensate for the loss of CREB. BDNF, a postulated CREB target gene, was down regulated in the frontal lobe but not in the hippocampus; neurogenesis remained unaltered. Our data indicate that in the adult mouse forebrain the late onset of CREB ablation can, in case of memory functionality, be compensated for and is not essential for memory consolidation and retrieval during adulthood. In contrast, the presence of CREB protein during adulthood seems to be pivotal for the regulation of emotional behavior.

The transcription factor Zif268/Egr1, brain plasticity, and memory

The capacity to remember our past experiences and organize our future draws on a number of cognitive processes that allow our brain to form and store neural representations that can be recalled and updated at will. In the brain, these processes require mechanisms of neural plasticity in the activated circuits, brought about by cellular and molecular changes within the neurons activated during learning. At the cellular level, a wealth of experimental data accumulated in recent years provides evidence that signaling from synapses to nucleus and the rapid regulation of the expression of immediate early genes encoding inducible, regulatory transcription factors is a key step in the mechanisms underlying synaptic plasticity and the modification of neural networks required for the laying down of memories. In the activated neurons, these transcriptional events are thought to mediate the activation of selective gene programs and subsequent synthesis of proteins, leading to stable functional and structural remodeling of the activated networks, so that the memory can later be reactivated upon recall. Over the past few decades, novel insights have been gained in identifying key transcriptional regulators that can control the genomic response of synaptically activated neurons. Here, as an example of this approach, we focus on one such activity-dependent transcription factor, Zif268, known to be implicated in neuronal plasticity and memory formation. We summarize current knowledge about the regulation and function of Zif268 in different types of brain plasticity and memory processes.