Extinction of opiate reward reduces dendritic arborization and c-Fos expression in the nucleus accumbens core

Transcriptional characterization of cocaine withdrawal versus extinction within nucleus accumbens

Substance use disorder is characterized by a maladaptive imbalance wherein drug seeking persists despite negative consequences or drug unavailability. This imbalance correlates with neurobiological alterations some of which are amplified during forced abstinence, thereby compromising the capacity of extinction-based approaches to prevent relapse. Cocaine use disorder (CUD) exemplifies this phenomenon in which neurobiological modifications hijack brain reward regions such as the nucleus accumbens (NAc) to manifest craving and withdrawal-like symptoms. While increasing evidence links transcriptional changes in the NAc to specific phases of addiction, genome-wide changes in gene expression during withdrawal vs. extinction (WD/Ext) have not been examined in a context- and NAc-subregion-specific manner. Here, we used cocaine self-administration (SA) in rats combined with RNA-sequencing (RNA-seq) of NAc subregions (core and shell) to transcriptionally profile the impact of experiencing withdrawal in the home cage or in the previous drug context or experiencing extinction training. As expected, home-cage withdrawal maintained drug seeking in the previous drug context, whereas extinction training reduced it. By contrast, withdrawal involving repetitive exposure to the previous drug context increased drug-seeking behavior. Bioinformatic analyses of RNA-seq data revealed gene expression patterns, networks, motifs, and biological functions specific to these behavioral conditions and NAc subregions. Comparing transcriptomic analysis of the NAc of patients with CUD highlighted conserved gene signatures, especially with rats that were repetitively exposed to the previous drug context. Collectively, these behavioral and transcriptional correlates of several withdrawal-extinction settings reveal fundamental and translational information about potential molecular mechanisms to attenuate drug-associated memories.

Adaptations in Nucleus Accumbens Neuron Subtypes Mediate Negative Affective Behaviors in Fentanyl Abstinence

BACKGROUND

Opioid discontinuation generates a withdrawal syndrome marked by increased negative affect. Increased symptoms of anxiety and dysphoria during opioid discontinuation are significant barriers to achieving long-term abstinence in opioid-dependent individuals. While adaptations in the nucleus accumbens are implicated in opioid abstinence syndrome, the precise neural mechanisms are poorly understood. Additionally, our current knowledge is limited to changes following natural and semisynthetic opioids, despite recent increases in synthetic opioid use and overdose.

METHODS

We used a combination of cell subtype-specific viral labeling and electrophysiology in male and female mice to investigate structural and functional plasticity in nucleus accumbens medium spiny neuron (MSN) subtypes after fentanyl abstinence. We characterized molecular adaptations after fentanyl abstinence with subtype-specific RNA sequencing and weighted gene co-expression network analysis. We used viral-mediated gene transfer to manipulate the molecular signature of fentanyl abstinence in D1-MSNs.

RESULTS

Here, we show that fentanyl abstinence increases anxiety-like behavior, decreases social interaction, and engenders MSN subtype-specific plasticity in both sexes. D1-MSNs, but not D2-MSNs, exhibit dendritic atrophy and an increase in excitatory drive. We identified a cluster of coexpressed dendritic morphology genes downregulated selectively in D1-MSNs that are transcriptionally coregulated by E2F1. E2f1 expression in D1-MSNs protects against loss of dendritic complexity, altered physiology, and negative affect-like behaviors caused by fentanyl abstinence.

CONCLUSIONS

Our findings indicate that fentanyl abstinence causes unique structural, functional, and molecular changes in nucleus accumbens D1-MSNs that can be targeted to alleviate negative affective symptoms during abstinence.

Hippocampal and amygdalar increased BDNF expression in the extinction of opioid-induced place preference

The opioid crisis was exacerbated during the COVID-19 pandemic in the United States with alarming statistics about overdose-related deaths. Current treatment options, such as medication assisted treatments, have been unable to prevent relapse in many patients, whereas cue-based exposure therapy have had mixed results in human trials. To improve patient outcomes, it is imperative to develop animal models of addiction to understand molecular mechanisms and identify potential therapeutic targets. We previously found increased brain derived neurotrophic factor (bdnf) transcript in the ventral striatum/nucleus accumbens (VS/NAc) of rats that extinguished morphine-induced place preference. Here, we expand our study to determine whether BDNF protein expression was modulated in mesolimbic brain regions of the reward system in animals exposed to extinction training. Drug conditioning and extinction sessions were followed by Western blots for BDNF in the hippocampus (HPC), amygdala (AMY) and VS/NAc. Rears, as a measure of withdrawal-induced anxiety were also measured to determine their impact on extinction. Results showed that animals who received extinction training and successfully extinguished morphine CPP significantly increased BDNF in the HPC when compared to animals deprived of extinction training (sham-extinction). This increase was not significant in animals who failed to extinguish (extinction-resistant). In AMY, all extinction-trained animals showed increased BDNF, regardless of behavior phenotype. No BDNF modulation was observed in the VS/NAc. Finally, extinction-trained animals showed no difference in rears regardless of extinction outcome, suggesting that anxiety elicited by drug withdrawal did not significantly impact extinction of morphine CPP. Our results suggest that BDNF expression in brain regions of the mesolimbic reward system could play a key role in extinction of opioid-induced maladaptive behaviors and represents a potential therapeutic target for future combined pharmacological and extinction-based therapies.

Behavioral sex differences in cocaine and opioid use disorders: The role of gonadal hormones

Females are more vulnerable than males to many aspects of cocaine use disorder. This vulnerability also translates to opioid use disorder, with females exhibiting stronger behavioral responses than males to drugs such as heroin and morphine. While there is evidence for many overlapping neural mechanisms underlying cocaine and opioid abuse, there is also a breadth of evidence indicating divergent effects of the drugs on synaptic plasticity. This makes it unclear whether the behavioral sex differences seen in substance use disorder across different drugs of abuse rely on the same mechanisms. Ovarian hormones have consistently been implicated as drivers of the behavioral sex differences in cocaine taking and seeking. While there are far fewer studies on the role of ovarian hormones in opioid use disorder, the existing data suggest that ovarian hormones may not drive these behavioral effects in the same manner as in cocaine use disorder. This review highlights evidence that behavioral sex differences in substance use disorder might be driven by different mechanisms depending on drug class.

Bidirectional role of acupuncture in the treatment of drug addiction

Drug addiction is a chronically relapsing disorder, affecting people from all walks of life. Studies of acupuncture effects on drug addiction are intriguing in light of the fact that acupuncture can be used as a convenient therapeutic intervention for treating drug addiction by direct activation of brain pathway. The current review aims to discuss the neurobiological mechanisms underlying acupuncture's effectiveness in the treatment of drug addiction, on the basis of two different theories (the incentive sensitization theory and the opponent process theory) that have seemingly opposite view on the role of the mesolimbic reward pathways in mediating compulsive drug-seeking behavior. This review provides evidence that acupuncture may reduce relapse to drug-seeking behavior by regulating neurotransmitters involved in drug craving modulation via somatosensory afferent mechanisms. Also, acupuncture normalizes hyper-reactivity or hypoactivity of the mesolimbic dopamine system in these opposed processes in drug addiction, suggesting bidirectional role of acupuncture in regulation of drug addiction. This proposes that acupuncture may reduce drug craving by correcting both dysfunctions of the mesolimbic dopamine pathway.

Effects of processed Aconiti tuber on the extinction and reinstatement of morphine-induced conditioned place preference in rats

AIM OF THE STUDY

To investigate the effect of processed Aconiti tuber (PAT) administered during or after the time of conditioned place preference (CPP) training on the extinction and reinstatement of morphine-priming CPP in rats. The dynorphin level in rats' nucleus accumbens (NAc) is detected as a target of the Dynorphin/Kappa Opioid Receptor (KOR) system for the possible mechanism.

MATERIALS AND METHODS

Eight groups of rats were subcutaneously (s.c.) injected with morphine (10mg/kg) (on days 2,4,6,8) or saline (1ml/kg) (on days 3,5,7,9) alternately for 8 days. Five groups, including groups (Mor + Water, Mor + PAT (1.0/3.0g/kg) (S) and Sal + PAT(1.0/3.0g/kg)), were orally given distilled water or PAT 1.0 or 3.0 g/kg daily on days 1-8 during CPP training while other three groups, including groups (Sal + Water and Mor + PAT (1.0/3.0g/kg)(P), were given distilled water or PAT daily from day 10 until CPP was extinct. Morphine 1mg/kg (s.c.) was used to reinstate the extinct CPP and the CPP scores were recorded. The dynorphin concentration in nucleus accumbens (NAc) was assayed by radioimmunoassay after the last CPP measurement.

RESULTS

1) The CPP extinction shortened in Mor + PAT (1.0/3.0 g/kg) (S) groups but extended in Mor + PAT (1.0/3.0 g/kg)(P) groups. 2) Morphine-priming CPP did not change either in Mor + PAT (1.0/3.0 g/kg) (S) or Mor + PAT (1.0/3.0 g/kg)(P) groups. 3) The dynorphin concentration in NAc increased either in Mor + PAT (1.0/3.0 g/kg)(S) or Mor + PAT (1.0/3.0 g/kg)(P) groups.

CONCLUSIONS

1) PAT shortened the extinction from morphine induced CPP when administrated before CPP acquisition, whereas it extended the extinction when administrated after CPP formation. 2) PAT administrated during or after CPP training did not affect morphine-priming reinstatement of morphine induced CPP. 3) Dynorphin/KOR system might be a target to regulate morphine-induced CPP extinction but not reinstatement.

Dynamic Changes of Cytoskeleton-Related Proteins Within Reward-Related Brain Regions in Morphine-Associated Memory

Drug-induced memory engages complex and dynamic processes and is coordinated at multiple reward-related brain regions. The spatiotemporal molecular mechanisms underlying different addiction phases remain unknown. We investigated the role of β-actin, as well as its potential modulatory protein activity-regulated cytoskeletal-associated protein (Arc/Arg3.1) and extracellular signal-regulated kinase (ERK), in reward-related associative learning and memory using morphine-induced conditioned place preference (CPP) in mice. CPP was established by alternate morphine (10 mg/kg) injections and extinguished after a 10-day extinction training, while the withdrawal group failed to extinguish without training. In the nucleus accumbens (NAc), morphine enhanced the level of β-actin and Arc only during extinction, while p-ERK1/2 was increased during both CPP acquisition and extinction phases. In the dorsal hippocampus, morphine induced an upregulation of p-ERK only during extinction, while p-β-actin was elevated during both CPP establishment and extinction. In the dorsal hippocampus, Arc was elevated during CPP formation and suppressed during extinction. Compared with the NAc and dorsal hippocampus, dynamic changes in the medial prefrontal cortex (mPFC) and caudate putamen (CPu) were not very significant. These results suggested region-specific changes of p-β-actin, Arc/Arg3.1, and p-ERK1/2 protein during establishment and extinction phases of morphine-induced CPP. These findings unveiled a spatiotemporal molecular regulation in opiate-induced plasticity.

Microinjection of the BDNF receptor antagonist ANA-12 into the nucleus accumbens and medial-prefrontal cortex attenuates morphine-induced reward memory, and alterations of BDNF levels and apoptotic cells in rats

This study was designed to examine the effects of intra- nucleus accumbens (NAc) of BDNF receptor antagonist ANA-12 on the acquisition and expression and intra- medial-prefrontal cortex (mPFC) of ANA-12 on the extinction and reinstatement of morphine-induced conditioned place preference (CPP) and also BDNF levels and apoptotic neurons in the NAc and mPFC of rats. In this study, adult male Wistar rats (200-250 g) were used. Two separate cannulas were inserted bilaterally into the NAc and/or mPFC. ANA-12 (3 μg/0.5 μl/side) was injected into the NAc and/or mPFC to evaluate the rewarding effects of morphine using a CPP paradigm. Then, the levels of BDNF and apoptotic in the NAc and mPFC were assessed at the end of each treatment phase using ELISA and TUNEL methods, respectively. All of vehicle-treated rats following morphine CPP showed the increase of BDNF levels and apoptotic neurons in the NAc and mPFC. ANA-12 significantly attenuated the acquisition and expression of morphine-induced CPP, BDNF levels and apoptotic neurons in the NAc during the acquisition, but not the expression phase. Also, ANA-12 significantly facilitated the extinction, but no effect on reinstatement of morphine CPP, and decreased BDNF levels and apoptotic neurons in the mPFC during the extinction, but not the reinstatement. We conclude that blocking TrkB with ANA-12 showed therapeutic effects on morphine-associated reward memory and neuronal death in the NAc and mPFC induced by morphine CPP. Thus, the BDNF-TrkB signaling may be important in the acquisition, expression, extinction, but not the reinstatement of morphine CPP.

Opioid-induced structural and functional plasticity of medium-spiny neurons in the nucleus accumbens

Opioid Use Disorder (OUD) is a chronic relapsing clinical condition with tremendous morbidity and mortality that frequently persists, despite treatment, due to an individual's underlying psychological, neurobiological, and genetic vulnerabilities. Evidence suggests that these vulnerabilities may have neurochemical, cellular, and molecular bases. Key neuroplastic events within the mesocorticolimbic system that emerge through chronic exposure to opioids may have a determinative influence on behavioral symptoms associated with OUD. In particular, structural and functional alterations in the dendritic spines of medium spiny neurons (MSNs) within the nucleus accumbens (NAc) and its dopaminergic projections from the ventral tegmental area (VTA) are believed to facilitate these behavioral sequelae. Additionally, glutamatergic neurons from the prefrontal cortex, the basolateral amygdala, the hippocampus, and the thalamus project to these same MSNs, providing an enriched target for synaptic plasticity. Here, we review literature related to neuroadaptations in NAc MSNs from dopaminergic and glutamatergic pathways in OUD. We also describe new findings related to transcriptional, epigenetic, and molecular mechanisms in MSN plasticity in the different stages of OUD.

Different roles of Rac1 in the acquisition and extinction of methamphetamine-associated contextual memory in the nucleus accumbens

Rationale: Repeated methamphetamine (METH) exposure induces long-term cognitive deficits and pathological drug-associated memory that can be disrupted by manipulating memory reconsolidation and extinction. The nucleus accumbens (NAc) is the key region of the brain reward system and predominantly consists of two subtypes of medium spiny neurons (MSNs) based on the expression of D1 or D2 dopamine receptors (D1-MSNs or D2-MSNs). Spine structural plasticity in the NAc is critical for the acquisition, reconsolidation and extinction of drug-associated memory. However, the molecular mechanisms underlying METH-associated memory and spine remodelling in each type of MSNs in the NAc remain unknown. Here, we explored whether Rac1 in the NAc mediates METH-associated contextual memory and spine remodelling.

Methods: Pharmacological and genetic manipulations of Rac1 were used to investigate its role during the acquisition, reconsolidation and extinction of METH-associated contextual memory. Recombinant adeno-associated viruses expressing mCherry under the control of the dopamine D1 receptor gene promoter (Drd1-mCherry) or dopamine D2 receptor gene promoter (Drd2-mCherry) were used to specifically label D1-MSNs or D2-MSNs.

Results: Using viral-mediated gene transfer, we demonstrated that decreased Rac1 activity was required for the acquisition of METH-associated contextual memory and the METH-induced increase in thin spine density, whereas increased Rac1 signalling was important for the extinction of METH-associated contextual memory and the related elimination of thin spines. Moreover, the increase of dendritic spines was both found in D1-MSNs and D2-MSNs during the acquisition process, but extinction training selectively decreased the spine density in D1-MSNs. Interestingly, Rac1 was responsible for METH-induced spine plasticity in D1-MSNs but not in D2-MSNs. Additionally, we found that microinjection of a Rac1 inhibitor or activator into the NAc was not sufficient to disrupt reconsolidation, and the pharmacological activation of Rac1 in the NAc facilitated the extinction of METH-associated contextual memory. Regarding cognitive memory, decreased Rac1 activity improved the METH-induced impairment in object recognition memory.

Conclusion: Our findings indicate that Rac1 plays opposing roles in the acquisition and extinction of METH-associated contextual memory and reveal the cell-specific role of Rac1 in METH-associated spine remodelling, suggesting that Rac1 is a potential therapeutic target for reducing relapse in METH addiction and remediating METH-induced recognition memory impairment.

Neuroplasticity transcript profile of the ventral striatum in the extinction of opioid-induced conditioned place preference

Persistent drug-seeking behavior has been associated with deficits in neural circuits that regulate the extinction of addictive behaviors. Although there is extensive data that associates addiction phases with neuroplasticity changes in the reward circuit, little is known about the underlying mechanisms of extinction learning of opioid associated cues. Here, we combined morphine-conditioned place preference (CPP) with real-time polymerase chain reaction (RT-PCR) to identify the effects of extinction training on the expression of genes (mRNAs) associated with synaptic plasticity and opioid receptors in the ventral striatum/nucleus accumbens (VS/NAc). Following morphine extinction training, we identified two animal subgroups showing either extinction (low CPP) or extinction-resistance (high CPP). A third group were conditioned to morphine but did not receive extinction training (sham-extinction; high CPP). RT-PCR results showed that brain derived neurotrophic factor (Bdnf) was upregulated in rats showing successful extinction. Conversely, the lack of extinction training (sham-extinction) upregulated genes associated with kinases (Camk2g), neurotrophins (Ngfr), synaptic connectivity factors (Ephb2), glutamate neurotransmission (Grm8) and opioid receptors (μ1, Δ1). To further identify genes modulated by morphine itself, comparisons with their saline-counterparts were performed. Results revealed that Bdnf was consistently upregulated in the extinction group. Alternatively, widespread gene modulation was observed in the group with lack of extinction training (i.e. Drd2, Cnr1, Creb, μ1, Δ1) and the group showing extinction resistance (i.e. Crem, Rheb, Tnfa). Together, our study builds on the identification of putative genetic markers for the extinction learning of drug-associated cues.

New Features for Neuron Classification

This paper addresses the problem of obtaining new neuron features capable of improving results of neuron classification. Most studies on neuron classification using morphological features have been based on Euclidean geometry. Here three one-dimensional (1D) time series are derived from the three-dimensional (3D) structure of neuron instead, and afterwards a spatial time series is finally constructed from which the features are calculated. Digitally reconstructed neurons were separated into control and pathological sets, which are related to three categories of alterations caused by epilepsy, Alzheimer's disease (long and local projections), and ischemia. These neuron sets were then subjected to supervised classification and the results were compared considering three sets of features: morphological, features obtained from the time series and a combination of both. The best results were obtained using features from the time series, which outperformed the classification using only morphological features, showing higher correct classification rates with differences of 5.15, 3.75, 5.33% for epilepsy and Alzheimer's disease (long and local projections) respectively. The morphological features were better for the ischemia set with a difference of 3.05%. Features like variance, Spearman auto-correlation, partial auto-correlation, mutual information, local minima and maxima, all related to the time series, exhibited the best performance. Also we compared different evaluators, among which ReliefF was the best ranked.

Differential effects of aprepitant, a clinically used neurokinin-1 receptor antagonist on the expression of conditioned psychostimulant versus opioid reward

RATIONALE

Neurokinin-1 receptor (NK1R) signaling modulates behaviors associated with psychostimulants and opioids. Psychostimulants, such as amphetamine (AMPH) and cocaine, bind to monoamine transporters and alter their functions. Both dopamine and norepinephrine transporters are regulated by NK1R activation suggesting a role for NK1R mediated catecholamine transporter regulation in psychostimulant-mediated behaviors.

OBJECTIVES

The effect of in vivo administration of aprepitant (10 mg/kg) on the expression of AMPH (0.5 and 2 mg/kg) and cocaine (5 and 20 mg/kg)-induced conditioned place preference (CPP) as well as locomotor activation was examined in C57BL/6J mice. The effect of aprepitant on morphine (1 and 5 mg/kg)-induced CPP was also examined to identify the specific actions of aprepitant on psychostimulant versus opioid-induced behaviors.

RESULTS

Aprepitant administration significantly attenuated the CPP expression and locomotor activation produced by AMPH and cocaine. In contrast, aprepitant significantly enhanced the expression of CPP produced by morphine while significantly suppressing the locomotor activity of the mice conditioned with morphine. Aprepitant by itself did not induce significant CPP or conditioned place aversion or locomotor activation or suppression.

CONCLUSIONS

Attenuation of AMPH or cocaine-induced CPP and locomotor activation by aprepitant suggests a role for NK1R signaling in psychostimulant-mediated behaviors. Stimulation of morphine-induced CPP expression and suppression of locomotor activity of morphine-conditioned mice suggest differential effects of NK1R antagonism on conditioned psychostimulant versus opioid reward. Collectively, these findings indicate that clinically used NK1R antagonist, aprepitant may serve as a potential therapeutic agent in the treatment of psychostimulant abuse.

Endogenous Opiates and Behavior: 2015

This paper is the thirty-eighth consecutive installment of the annual review of research concerning the endogenous opioid system. It summarizes papers published during 2015 that studied the behavioral effects of molecular, pharmacological and genetic manipulation of opioid peptides, opioid receptors, opioid agonists and opioid antagonists. The particular topics that continue to be covered include the molecular-biochemical effects and neurochemical localization studies of endogenous opioids and their receptors related to behavior, and the roles of these opioid peptides and receptors in pain and analgesia, stress and social status, tolerance and dependence, learning and memory, eating and drinking, drug abuse and alcohol, sexual activity and hormones, pregnancy, development and endocrinology, mental illness and mood, seizures and neurologic disorders, electrical-related activity and neurophysiology, general activity and locomotion, gastrointestinal, renal and hepatic functions, cardiovascular responses, respiration and thermoregulation, and immunological responses.

Dopamine D1 receptor agonist treatment attenuates extinction of morphine conditioned place preference while increasing dendritic complexity in the nucleus accumbens core

The dopamine D1 receptor (D1R) has a role in opioid reward and conditioned place preference (CPP), but its role in CPP extinction is undetermined. We examined the effect of D1R agonist SKF81297 on the extinction of opioid CPP and associated dendritic morphology in the nucleus accumbens (NAc), a region involved with reward integration and its extinction. During the acquisition of morphine CPP, mice received morphine and saline on alternate days; injections were given immediately before each of eight daily conditioning sessions. Mice subsequently underwent six days of extinction training designed to diminish the previously learned association. Mice were treated with either 0.5mg/kg SKF81297, 0.8mg/kg SKF81297, or saline immediately after each extinction session. There was a dose-dependent effect, with the highest dose of SKF81297 attenuating extinction, as mice treated with this dose had significantly higher CPP scores than controls. Analysis of medium spiny neuron morphology revealed that in the NAc core, but not in the shell, dendritic arbors were significantly more complex in the morphine conditioned, SKF81297-treated mice compared to controls. In separate experiments using mice conditioned with only saline, SKF81297 administration after extinction sessions had no effect on CPP and produced differing effects on dendritic morphology. At the doses used in our experiments, SKF81297 appears to maintain previously learned opioid conditioned behavior, even in the face of new information. The D1R agonist's differential, rather than unidirectional, effects on dendritic morphology in the NAc core suggests that it may be involved in encoding reward information depending on previously learned behavior.

Acquisition of morphine conditioned place preference increases the dendritic complexity of nucleus accumbens core neurons

Contexts associated with opioid reward trigger craving and relapse in opioid addiction. Effects of reward-context associative learning on nucleus accumbens (NAc) dendritic morphology were studied using morphine conditioned place preference (CPP). Morphine-conditioned mice received saline and morphine 10 mg/kg subcutaneous (s.c.) on alternate days. Saline-conditioned mice received saline s.c. each day. Morphine-conditioned and saline-conditioned groups received injections immediately before each of eight daily conditioning sessions. Morphine homecage controls had no CPP training, but received saline and morphine in the homecage concomitantly with the morphine-conditioned group. Morphine conditioning produced greater place preference than saline conditioning. Mice were sacrificed 1 day after CPP expression. Dendritic changes were studied using Golgi-Cox staining and digital tracing of NAc core and shell neurons. In the NAc core, morphine homecage administration increased spine density, while morphine conditioning increased dendritic complexity, as defined by increased dendritic count, length and intersections. Place preference positively correlated with dendritic length and intersections in the NAc core. The core may mediate reward consolidation and determine how context-related signals from the shell lead to motor behavior. The combination of drug and conditioning in the morphine-conditioned group produced unique morphological effects different from the effects of drug or conditioning procedures by themselves. An additional study found no differences in neuron morphology between saline-conditioned mice, trained as described earlier, and mice that were not conditioned, but received saline in the homecage. The unique effect of morphine reward learning on NAc core dendrites reflects a brain substrate that could be targeted for therapeutic intervention in addiction.

Role of the ventral tegmental area in methamphetamine extinction: AMPA receptor-mediated neuroplasticity

The molecular mechanisms underlying drug extinction remain largely unknown, although a role for medial prefrontal cortex (mPFC) glutamate neurons has been suggested. Considering that the mPFC sends glutamate efferents to the ventral tegmental area (VTA), we tested whether the VTA is involved in methamphetamine (METH) extinction via conditioned place preference (CPP). Among various METH-CPP stages, we found that the amount of phospho-GluR1/Ser845 increased in the VTA at behavioral extinction, but not the acquisition or withdrawal stage. Via surface biotinylation, we found that levels of membrane GluR1 were significantly increased during METH-CPP extinction, while no change was observed at the acquisition stage. Specifically, the number of dendritic spines in the VTA was increased at behavioral extinction, but not during acquisition. To validate the role of the mPFC in METH-CPP extinction, we lesioned the mPFC. Ibotenic acid lesioning of the mPFC did not affect METH-CPP acquisition, however, it abolished the extinction stage and reversed the enhanced phospho-GluR1/Ser845 levels as well as increases in VTA dendritic spines during METH-CPP extinction. Overall, this study demonstrates that the mPFC plays a critical role in METH-CPP extinction and identifies the VTA as an alternative target in mediating the extinction of drug conditioning.

Effects of auditory stimulation with music of different intensities on heart period

Various studies have indicated that music therapy with relaxant music improves cardiac function of patients treated with cardiotoxic medication and heavy-metal music acutely reduces heart rate variability (HRV). There is also evidence that white noise auditory stimulation above 50 dB causes cardiac autonomic responses. In this study, we aimed to evaluate the acute effects of musical auditory stimulation with different intensities on cardiac autonomic regulation. This study was performed on 24 healthy women between 18 and 25 years of age. We analyzed HRV in the time [standard deviation of normal-to-normal RR intervals (SDNN), percentage of adjacent RR intervals with a difference of duration >50 ms (pNN50), and root-mean square of differences between adjacent normal RR intervals in a time interval (RMSSD)] and frequency [low frequency (LF), high frequency (HF), and LF/HF ratio] domains. HRV was recorded at rest for 10 minutes. Subsequently, the volunteers were exposed to baroque or heavy-metal music for 5 minutes through an earphone. The volunteers were exposed to three equivalent sound levels (60–70, 70–80, and 80–90 dB). After the first baroque or heavy-metal music, they remained at rest for 5 minutes and then they were exposed to the other music. The sequence of songs was randomized for each individual. Heavy-metal musical auditory stimulation at 80–90 dB reduced the SDNN index compared with control (44.39 ± 14.40 ms vs. 34.88 ± 8.69 ms), and stimulation at 60–70 dB decreased the LF (ms²) index compared with control (668.83 ± 648.74 ms² vs. 392.5 ± 179.94 ms²). Baroque music at 60–70 dB reduced the LF (ms²) index (587.75 ± 318.44 ms² vs. 376.21 ± 178.85 ms²). In conclusion, heavy-metal and baroque musical auditory stimulation at lower intensities acutely reduced global modulation of the heart and only heavy-metal music reduced HRV at higher intensities.