Glucocorticoid receptors in the basolateral amygdala mediated the restraint stress-induced reinstatement of methamphetamine-seeking behaviors in rats

Cross-talk between the HPA axis and addiction-related regions in stressful situations

Addiction is a worldwide problem that has a negative impact on society by imposing significant costs on health care, public security, and the deactivation of the community economic cycle. Stress is an important risk factor in the development of addiction and relapse vulnerability. Here we review studies that have demonstrated the diverse roles of stress in addiction. Term searches were conducted manually in important reference journals as well as in the Google Scholar and PubMed databases, between 2010 and 2022. In each section of this narrative review, an effort has been made to use pertinent sources. First, we will provide an overview of changes in the Hypothalamus-Pituitary-Adrenal (HPA) axis component following stress, which impact reward-related regions including the ventral tegmental area (VTA) and nucleus accumbens (NAc). Then we will focus on internal factors altered by stress and their effects on drug addiction vulnerability. We conclude that alterations in neuro-inflammatory, neurotrophic, and neurotransmitter factors following stress pathways can impact related mechanisms on craving and relapse susceptibility.

The Antagonism of Corticotropin-Releasing Factor Receptor-1 in Brain Suppress Stress-Induced Propofol Self-Administration in Rats

Propofol addiction has been detected in humans and rats, which may be facilitated by stress. Corticotropin-releasing factor acts through the corticotropin-releasing factor (CRF) receptor-1 (CRF1R) and CRF2 receptor-2 (CRF2R) and is a crucial candidate target for the interaction between stress and drug abuse, but its role on propofol addiction remains unknown. Tail clip stressful stimulation was performed in rats to test the stress on the establishment of the propofol self-administration behavioral model. Thereafter, the rats were pretreated before the testing session at the bilateral lateral ventricle with one of the doses of antalarmin (CRF1R antagonist, 100–500 ng/site), antisauvagine 30 (CRF2R antagonist, 100–500 ng/site), and RU486 (glucocorticoid receptor antagonist, 100–500 ng/site) or vehicle. The dopamine D1 receptor (D1R) in the nucleus accumbens (NAc) was detected to explore the underlying molecular mechanism. The sucrose self-administration establishment and maintenance, and locomotor activities were also examined to determine the specificity. We found that the establishment of propofol self-administration was promoted in the tail clip treated group (the stress group), which was inhibited by antalarmin at the dose of 100–500 ng/site but was not by antisauvagine 30 or RU486. Accordingly, the expression of D1R in the NAc was attenuated by antalarmin, dose-dependently. Moreover, pretreatments fail to change sucrose self-administration behavior or locomotor activities. This study supports the role of CRF1R in the brain in mediating the central reward processing through D1R in the NAc and provided a possibility that CRF1R antagonist may be a new therapeutic approach for the treatment of propofol addiction.

Repeated oxytocin treatment during abstinence inhibited context- or restraint stress-induced reinstatement of methamphetamine-conditioned place preference and promoted adult hippocampal neurogenesis in mice

Propensity to relapse, even after long-term abstinence, is a crucial feature of methamphetamine (METH) abuse. We and other laboratories have reported that acute treatment of oxytocin (OXT), a hormone and neuropeptide, could inhibit reinstatement of METH seeking in animal studies. However, the effects of repeated OXT treatment on METH reinstatement as well as underlying mechanisms are still unclear. In the present study, the effects of repeated OXT treatment during abstinence on context- or restraint stress-induced reinstatement were investigated using the mice conditioned place preference (CPP) paradigm. After three intermittent injections of METH (2 mg/kg, i.p.) to induce CPP, mice received a daily bilateral intra-hippocampus injection of OXT (0.625, 1.25 or 2.5 μg) for 8 consecutive days before the context- or restraint stress-induced reinstatement test. Meanwhile, adult hippocampal neurogenesis (AHN) level was detected using immunostaining. To further clarify the role of AHN underlying OXT's effects on METH-CPP reinstatement, temozolomide (TMZ, 25 mg/kg, i.p.) was employed to deplete AHN prior to OXT treatment. The data showed that repeated OXT treatment (1.25 and 2.5 μg, intra-hippocampus) significantly inhibited both context- and restraint stress-induced METH-CPP reinstatement and concomitantly promoted AHN in a dose-dependent manner. Notably, TMZ pre-treatment markedly abolished all the above-mentioned effects of OXT, suggesting that AHN was closely involved in OXT's inhibition on reinstatement induced by both triggers. Taken together, the present study indicated that repeated OXT treatment during abstinence could inhibit both context- and restraint stress-induced METH-CPP reinstatement possibly by promoting AHN in mice, which provided a better understanding for OXT's beneficial effects on METH addiction.

Dexamethasone attenuates the modulatory effect of the insular cortex on the baroreflex in anesthetized rat

The arterial baroreflex (BR) is an important neural mechanism for the stabilization of arterial pressure (AP). It is known that the insular cortex (IC) and other parts of the central autonomic network (CAN) are able to modulate the BR arc, altering baroreflex sensitivity (BRS). In addition, the sensitivity of the BR changes under the influence of hormones, in particular glucocorticoids (GC). It has been suggested that GC may influence BRS by altering the ability of the IC to modulate the BR. This hypothesis has been tested in experiments on rats anesthetized with urethane. It was found that microelectrostimulation of the visceral area in the left IC causes a short-term drop in AP, which is accompanied by bradycardia, and impairs BRS. The synthetic GC dexamethasone (DEX) did not significantly affect the magnitude of depressor responses but increased BRS and impaired the effect of IC stimulation on the BR. The results obtained confirm the hypothesis put forward and suggest that GC can attenuate the inhibitory effects of the IC on the BR arc, thereby enhancing the sensitivity of the BR.

Spectral power and theta-gamma coupling in the basolateral amygdala related with methamphetamine conditioned place preference in mice

The basolateral amygdala (BLA) plays a crucial role in conditioned place preference (CPP) for addictive drugs. However, neural signaling associated with methamphetamine (METH) craving and seeking remained to be investigated. This study characterized local field potential (LFP) oscillatory patterns in the BLA and conditioned place preference induced by METH-related context. Male Swiss albino ICR mice were deeply anesthetized for LFP intracranial electrode implantation in the BLA. Control and METH groups received sessions to learn to associate saline-paired and METH-paired compartments of the CPP apparatus with saline and METH injections, respectively, for 10 days. LFP signals and exploring behavior were recorded simultaneously during pre- and post-conditioning phases. Time spent in METH-paired compartment was normalized and expressed as CPP scores. Fast Fourier Transform (FFT) algorithm was used to analyze LFP powers of 8 discrete frequency ranges (delta, theta, alpha, beta, gamma I-IV). During post-conditioning phase of METH CPP with METH cues, statistical analysis revealed that METH group significantly increased time spent in METH-paired compartment. Significant suppressions of theta and alpha powers were observed. Phase-amplitude cross frequency coupling analyses confirmed significant increases in maximal modulation index (MI), frequency for phase of slow wave and MI of theta-gamma II coupling. Taken together, LFP oscillation in the BLA was sensitive in association with METH CPP. These research findings might suggest the underlying mechanisms of drug reward learning and adaptive changes in the BLA in acquisition of METH CPP and dependence.

The neural, behavioral, and epidemiological underpinnings of comorbid alcohol use disorder and post-traumatic stress disorder

Alcohol use disorder (AUD) and (PTSD) frequently co-occur and individuals suffering from this dual diagnosis often exhibit increased symptom severity and poorer treatment outcomes than those with only one of these diseases. Although there have been significant advances in our understanding of the neurobiological mechanisms underlying each of these disorders, the neural underpinnings of the comorbid condition remain poorly understood. This chapter summarizes recent epidemiological findings on comorbid AUD and PTSD, with a focus on vulnerable populations, the temporal relationship between these disorders, and the clinical consequences associated with the dual diagnosis. We then review animal models of the comorbid condition and emerging human and non-human animal research that is beginning to identify maladaptive neural changes common to both disorders, primarily involving functional changes in brain reward and stress networks. We end by proposing a neural framework, based on the emerging field of affective valence encoding, that may better explain the epidemiological and neural findings on AUD and PTSD.

Smaller left hippocampal subfield CA1 volume is associated with reported childhood physical and/or sexual abuse in major depression: A pilot study

BACKGROUND

Smaller hippocampal volumes are reported in adults with major depressive disorder (MDD) and in reported childhood abuse. The hippocampus is a complex structure with distinct functional subfields. We sought to examine the effect of MDD diagnosis and childhood abuse on hippocampal subfields.

METHODS

Forty-one MDD participants (17 reported abuse and 24 did not) and 46 healthy volunteers (HV) (2 reported abuse) underwent T1- weighted structural magnetic resonance imaging (MRI) and clinical characterization in a retrospective design. A subfield segmentation program was used to measure the whole and subfield hippocampal volumes. Linear mixed-effects models were fitted for group comparisons.

RESULTS

No main effect of diagnosis interaction effect between diagnosis and subfield region was observed. However, a comparison of abused MDD vs. HVs showed a group by region interaction. A significant interaction between childhood abuse and region was observed. Effects were confined to the left side of the brain, and post hoc, exploratory region-specific tests indicated smaller left CA1 volume in abused MDD compared with non-abused MDD. In addition, smaller amygdala volume was found in all MDD compared with HVs.

LIMITATIONS

We did not have a sample of healthy volunteers with reported childhood abuse.

CONCLUSIONS

The diagnosis of pure MDD may not be sufficient to exert effects on hippocampal volumes, indicating the importance of taking into account childhood trauma in studies on psychopathological mechanisms. Left CA1 might be the hippocampal subfield most relevant to reported childhood abuse. Smaller amygdala volume may be related to MDD diagnosis independent of childhood abuse.

Retrieval-Extinction and Relapse Prevention: Rewriting Maladaptive Drug Memories?

Addicted individuals are highly susceptible to relapse when exposed to drug-associated conditioned stimuli (CSs; "drug cues") even after extensive periods of abstinence. Until recently, these maladaptive emotional drug memories were believed to be permanent and resistant to change. The rediscovery of the phenomenon of memory reconsolidation-by which retrieval of the memory can, under certain conditions, destabilize the previously stable memory before it restabilizes in its new, updated form-has led to the hypothesis that it may be possible to disrupt the strong maladaptive drug-memories that trigger a relapse. Furthermore, recent work has suggested that extinction training "within the reconsolidation window" may lead to a long-term reduction in relapse without the requirement for pharmacological amnestic agents. However, this so-called "retrieval-extinction" effect has been inconsistently observed in the literature, leading some to speculate that rather than reflecting memory updating, it may be the product of facilitation of extinction. In this mini review article, we will focus on factors that might be responsible for the retrieval-extinction effects on preventing drug-seeking relapse and how inter-individual differences may influence this therapeutically promising effect. A better understanding of the psychological and neurobiological mechanisms underpinning the "retrieval-extinction" paradigm, and individual differences in boundary conditions, should provide insights with the potential to optimize the translation of "retrieval-extinction" to clinical populations.

Differences of physical vs. psychological stress: evidences from glucocorticoid receptor expression, hippocampal subfields injury, and behavioral abnormalities

The glucocorticoid receptor (GR) is the main effector of the activation of the hypothalamus-pituitary-adrenal (HPA) axis, which is caused by different types of stress that can be divided into two major categories: physical stress and psychological stress. Given the marked presence of GR in the hippocampus, GR-mediated hippocampal injury might be the core event under stress. The aim of this study was to investigate GR expression, hippocampal injury, and behaviors in rats to explore the differences between these types of stressors. Adult male rats were stressed using a classical model (electrical foot shock and a yoked psychologically stressful situation) to induce physical or psychological stress. The GR expression, injury of hippocampal subfields and behavioral abnormalities were dynamic, as demonstrated using immunofluorescence, 3D magnetic resonance imaging (MRI) and open field exploration (OFE), respectively. In addition, housing in a normal environment for 6 weeks was used to verify the recovery ability of rats. First, GR-mediated hippocampal atrophy and behavioral abnormalities were found in the second week under physical stress, but those changes did not appear until the fourth week under psychological stress. Second, the effects of stress were more pronounced after physical stressors than after psychological stressors in the fourth week, but this trend had reversed by the sixth week, especially in the DG (Dentate Gyrus) subfield. Except for the rats that had experienced 6 weeks of psychological stress, all rats showed significant recovery after 6 weeks of housing in a normal environment. The effects of physical stress appeared early but were relatively moderate, whereas the effects of psychological stress appeared late but were more severe. In addition, GR-mediated serious injury in the DG might be the cause of the DG volume loss and behaviors that could not be reversed.

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.