Muscarinic Acetylcholine M2 Receptors Regulate Lateral Habenula Neuron Activity and Control Cocaine Seeking Behavior.

The lateral habenula (LHb) balances reward and aversion by opposing activation of brain reward nuclei and is involved the inhibition of responding for cocaine in a model of impulsive behavior. Previously, we reported that the suppression of cocaine seeking was prevented by LHb inactivation or nonselective antagonism of LHb mAChRs. Here, we investigate mAChR subtypes mediating the effects of endogenous acetylcholine in this model of impulsive drug seeking and define cellular mechanisms in which mAChRs alter LHb neuron activity. Using in vitro electrophysiology, we find that LHb neurons are depolarized or hyperpolarized by the cholinergic agonists oxotremorine-M (Oxo-M) and carbachol (CCh), and that mAChRs inhibit synaptic GABA and glutamatergic inputs to these cells similarly in male and female rats. Synaptic effects of CCh were blocked by the M2-mAChR (M2R) antagonist AFDX-116 and not by pirenzepine, an M1-mAChR (M1R) antagonist. Oxo-M-mediated depolarizing currents were also blocked by AFDX-116. Although M2R activation inhibited excitatory and inhibitory inputs to LHb neurons, the effect on excitation was greater, suggesting a shift in excitatory-inhibitory balance toward net inhibition. Activation of VTA inhibitory inputs to LHb neurons, via channelrhodopsin-2 expression, evoked IPSCs that were inhibited by M2Rs. Finally, we measured LHb-dependent operant response inhibition for cocaine and found it impaired by antagonism of M2Rs, and not M1Rs. In summary, we show that a cholinergic signal to LHb and activation of M2Rs are critical to enable inhibition of responding for cocaine, and we define cellular mechanisms through which this may occur.Significance Statement:The lateral habenula (LHb) is a brain region receiving information from brain areas involved in decision-making, and its output influences motivation, reward, and movement. This interface between thoughts, emotions, and actions is how the LHb permits adaptive behavior, and LHb dysfunction is implicated in psychiatric and drug use disorders. Silencing the LHb impairs control over cocaine seeking in rats, and mAChRs are also implicated. Here, we measured cocaine seeking while blocking different mAChRs and examined mechanisms of mAChR effects on LHb neurons. M2-mAChRs were necessary for control of cocaine seeking, and these receptors altered LHb neuron activity in several ways. Our study reveals that LHb M2-mAChRs represent a potential target for treating substance use disorders.

Retinoic acid-mediated homeostatic plasticity in the nucleus accumbens core contributes to incubation of cocaine craving.

RATIONALE: Incubation of cocaine craving refers to the progressive intensification of cue-induced craving during abstinence from cocaine self-administration. We showed previously that homomeric GluA1 Ca2+-permeable AMPARs (CP-AMPAR) accumulate in excitatory synapses of nucleus accumbens core (NAcc) medium spiny neurons (MSN) after ∼1 month of abstinence and thereafter their activation is required for expression of incubation. Therefore, it is important to understand mechanisms underlying CP-AMPAR plasticity. OBJECTIVES: We hypothesize that CP-AMPAR upregulation represents a retinoic acid (RA)-dependent form of homeostatic plasticity, previously described in other brain regions, in which a reduction in neuronal activity disinhibits RA synthesis, leading to GluA1 translation and CP-AMPAR synaptic insertion. We tested this using viral vectors to bidirectionally manipulate RA signaling in NAcc during abstinence following extended-access cocaine self-administration. RESULTS: We used shRNA targeted to the RA degradative enzyme Cyp26b1 to increase RA signaling. This treatment accelerated incubation; rats expressed incubation on abstinence day (AD) 15, when it is not yet detected in control rats. It also accelerated CP-AMPAR synaptic insertion measured with slice physiology. CP-AMPARs were detected in Cyp26b1 shRNA-expressing MSN, but not control MSN, on AD15-18. Next, we used shRNA targeted to the major RA synthetic enzyme Aldh1a1 to reduce RA signaling. In MSN expressing Aldh1a1 shRNA, synaptic CP-AMPARs were reduced in late withdrawal (AD42-60) compared to controls. However, we did not detect an effect of this manipulation on incubated cocaine seeking (AD40). CONCLUSIONS: These findings support the hypothesis that increased RA signaling during abstinence contributes to CP-AMPAR accumulation and incubation of cocaine craving.

Persistent Neuroadaptations in the Nucleus Accumbens Core Accompany Incubation of Methamphetamine Craving in Male and Female Rats.

Relapse is a major problem in treating methamphetamine use disorder. "Incubation of craving" during abstinence is a rat model for persistence of vulnerability to craving and relapse. While methamphetamine incubation has previously been demonstrated in male and female rats, it has not been demonstrated after withdrawal periods greater than 51 d and most mechanistic work used males. Here, we address both gaps. First, although methamphetamine intake was higher in males during self-administration training (6 h/d × 10 d), incubation was similar in males and females, with "incubated" craving persisting through withdrawal day (WD)100. Second, using whole-cell patch-clamp recordings in medium spiny neurons (MSNs) of the nucleus accumbens (NAc) core, we assessed synaptic levels of calcium-permeable AMPA receptors (CP-AMPARs), as their elevation is required for expression of incubation in males. In both sexes, compared with saline-self-administering controls, CP-AMPAR levels were significantly higher in methamphetamine rats across withdrawal, although this was less pronounced in WD100-135 rats than WD15-35 or WD40-75 methamphetamine rats. We also examined membrane properties and NMDA receptor (NMDAR) transmission. In saline controls, MSNs from males exhibited lower excitability than females. This difference was eliminated after incubation because of increased excitability of MSNs from males. NMDAR transmission did not differ between sexes and was not altered after incubation. In conclusion, incubation persists for longer than previously described and equally persistent CP-AMPAR plasticity in NAc core occurs in both sexes. Thus, abstinence-related synaptic plasticity in NAc is similar in males and females although other methamphetamine-related behaviors and neuroadaptations show differences.

Positive Allosteric Modulation of mGlu1 Reverses Cocaine-Induced Behavioral and Synaptic Plasticity Through the Integrated Stress Response and Oligophrenin-1.

BACKGROUND: Cue-induced cocaine craving progressively intensifies (incubates) during abstinence from cocaine self-administration. Expression of incubated cocaine craving depends on elevated calcium-permeable AMPA receptors (CP-AMPARs) on medium spiny neurons in the nucleus accumbens (NAc) core. After incubation has occurred, stimulation of NAc metabotropic glutamate 1 (mGlu1) receptors or systemic administration of mGlu1 positive allosteric modulators removes CP-AMPARs from NAc synapses via dynamin-dependent internalization (mGlu1 long-term depression [LTD]) and thereby reduces incubated cocaine craving. Because mGlu1 positive allosteric modulators are potential therapeutics for cocaine craving, it is important to further define the mechanism triggering this mGlu1-LTD. METHODS: Male and female rats self-administered saline or cocaine (10 days) using a long access regimen (6 h/day). Following ≥40 days of abstinence, we assessed the ability of an mGlu1 positive allosteric modulator to inhibit expression of incubated craving and remove CP-AMPARs from NAc synapses under control conditions, after blocking the integrated stress response (ISR), or after knocking down oligophrenin-1, a mediator of the ISR that can promote AMPAR endocytosis. AMPAR transmission in NAc medium spiny neurons was assessed with ex vivo slice recordings. RESULTS: mGlu1 stimulation reduced cue-induced craving and removed synaptic CP-AMPARs. When the ISR was blocked prior to mGlu1 stimulation, there was no reduction in cue-induced craving, nor were CP-AMPARs removed from the synapse. Further, selective knockdown of oligophrenin-1 blocked mGlu1-LTD. CONCLUSIONS: Our results indicate that mGlu1-LTD in the NAc and consequently the reduction of cue-induced seeking occur through activation of the ISR, which induces translation of oligophrenin-1. We also demonstrate CP-AMPAR accumulation and mGlu1 reversal in female rats, as previously shown in male rats.

Does the Association Between Fatigue and Fatigue Self-management Preference Vary by Breast Cancer Stage?

BACKGROUND: Cancer-related fatigue (CRF) is a major issue facing breast cancer survivors (BCS) that can negatively impact their symptoms and quality of life. OBJECTIVES: The aims of this study were to examine levels of fatigue, identify preferred types of fatigue self-management, and explore the relationship between fatigue levels and management choices by cancer stage. METHODS: This cross-sectional descriptive study included 229 BCS recruited from 5 hospitals in Korea. The study inclusion criteria were limited to BCS between 20 and 69 years old in stages 1, 2, or 3 who were undergoing or had completed active therapy. The Revised Piper Fatigue Scale and a questionnaire developed for fatigue management were used for data collection. RESULTS: The stage 2 group experienced more fatigue (mean, 5.31) than the other cancer stage groups, and significant differences in fatigue were found between stages 1 and 2 (P < .001). Fatigue self-management choices showed different correlations with fatigue levels in each stage. Physical activity control was most frequently used in stage 1, whereas exercise was most frequently used in stages 2 and 3. Multivariate regression analysis showed that exercise consistently and effectively decreased all fatigue dimensions. CONCLUSION: Stage 2 BCS experienced the greatest level of CRF, and fatigue levels and management choices differed in BCS by cancer stage. IMPLICATIONS FOR PRACTICE: Recognizing how CRF and patients' preferences for fatigue self-management may differ by cancer stage can alert clinicians in assessing CRF and tailoring effective fatigue management for BCS.

Impairment of Synaptic Plasticity by Cannabis, Δ9-THC, and Synthetic Cannabinoids.

The ability of neurons to dynamically and flexibly encode synaptic inputs via short- and long-term plasticity is critical to an organism's ability to learn and adapt to the environment. Whereas synaptic plasticity may be encoded by pre- or postsynaptic mechanisms, current evidence suggests that optimization of learning requires both forms of plasticity. Endogenous cannabinoids (eCBs) play critical roles in modulating synaptic transmission via activation of cannabinoid CB1 receptors (CB1Rs) in many central nervous system (CNS) regions, and the eCB system has been implicated, either directly or indirectly, in several forms of synaptic plasticity. Because of this, perturbations within the eCB signaling system can lead to impairments in a variety of learned behaviors. One agent of altered eCB signaling is exposure to "exogenous cannabinoids" such as the primary psychoactive constituent of cannabis, Δ9-THC, or illicit synthetic cannabinoids that in many cases have higher potency and efficacy than Δ9-THC. Thus, by targeting the eCB system, these agonists can produce widespread impairment of synaptic plasticity by disrupting ongoing eCB function. Here, we review studies in which Δ9-THC and synthetic cannabinoids impair synaptic plasticity in a variety of neuronal circuits and examine evidence that this contributes to their well-documented ability to disrupt cognition and behavior.

mGlu5 function in the nucleus accumbens core during the incubation of methamphetamine craving.

Many studies have demonstrated that negative allosteric modulators (NAM) of metabotropic glutamate receptor 5 (mGlu5) reduce cocaine and methamphetamine seeking in extinction-reinstatement animal models of addiction. Less is known about effects of mGlu5 NAMs in abstinence models, particularly for methamphetamine. We used the incubation of drug craving model, in which cue-induced craving progressively intensifies after withdrawal from drug self-administration, to conduct the first studies of the following aspects of mGlu5 function in the rat nucleus accumbens (NAc) core during abstinence from methamphetamine self-administration: 1) functionality of the major form of synaptic depression in NAc medium spiny neurons, which is induced postsynaptically via mGlu5 and expressed presynaptically via cannabinoid type 1 receptors (CB1Rs), 2) mGlu5 surface expression and physical associations between mGlu5, Homer proteins, and diacylglycerol lipase-α, and 3) the effect of systemic and intra-NAc core administration of the mGlu5 NAM 3-((2-methyl-4-)ethynyl)pyridine (MTEP) on expression of incubated methamphetamine craving. We found that mGlu5/CB1R-dependent synaptic depression was lost during the rising phase of methamphetamine incubation but then recovered, in contrast to its persistent impairment during the plateau phase of incubation of cocaine craving. Furthermore, whereas the cocaine-induced impairment was accompanied by reduced mGlu5 levels and mGlu5-Homer associations, this was not the case for methamphetamine. Systemic MTEP reduced incubated methamphetamine seeking, but also reduced inactive hole nose-pokes and locomotion, while intra-NAc core MTEP had no significant effects. These findings provide the first insight into the role of mGlu5 in the incubation of methamphetamine craving and reveal differences from incubation of cocaine craving.

Altered Corticolimbic Control of the Nucleus Accumbens by Long-term Δ9-Tetrahydrocannabinol Exposure.

BACKGROUND: The decriminalization and legalization of cannabis and the expansion of availability of medical cannabis in North America have led to an increase in cannabis use and the availability of high-potency strains. Cannabis potency is determined by the concentration of Δ9-tetrahydrocannabinol (Δ9-THC), a psychoactive constituent that activates cannabinoid CB1 and CB2 receptors. The use of high-potency cannabis is associated with cannabis use disorder and increased susceptibility to psychiatric illness. The nucleus accumbens (NAc) is part of a brain reward circuit affected by Δ9-THC through modulation of glutamate afferents arising from corticolimbic brain areas implicated in drug addiction and psychiatric disorders. Moreover, brain imaging studies show alterations in corticolimbic and NAc properties in human cannabis users. METHODS: Using in vitro electrophysiology and optogenetics, we examined how Δ9-THC alters corticolimbic input to the NAc in rats. RESULTS: We found that long-term exposure to Δ9-THC weakens prefrontal cortex glutamate input to the NAc shell and strengthens input from basolateral amygdala and ventral hippocampus. Further, whereas long-term exposure to Δ9-THC had no effect on net strength of glutamatergic input to NAc shell arising from midbrain dopamine neurons, it alters fundamental properties of these synapses. CONCLUSIONS: Long-term exposure to Δ9-THC shifts control of the NAc shell from cortical to limbic input, likely contributing to cognitive and psychiatric dysfunction that is associated with cannabis use.

Lateral Habenula Involvement in Impulsive Cocaine Seeking.

The lateral habenula (LHb) is a brain structure receiving inputs from limbic forebrain areas and innervating major midbrain monoaminergic nuclei. Evidence indicates LHb involvement in sleep control, reward-based decision making, avoidance of punishment, and responses to stress. Additional work has established that the LHb mediates negative feedback in response to aversive events. As a hallmark of drug addiction is the inability to limit drug use despite negative consequences, we hypothesize that LHb dysfunction may have a role in the lack of control over drug seeking. Here we examine the effects of LHb inactivation in control over drug seeking in several cocaine self-administration (SA) paradigms in rats. We find that inhibition of the LHb with GABAergic agonists did not alter cocaine SA under progressive ratio or seeking/taking chained reinforcement schedules, or during punishment-induced suppression of cocaine-reinforced responding. In contrast, LHb inhibition increased cocaine seeking when the drug was not available in rats trained to discriminate its presence using an environmental cue. This effect of LHb inhibition was selective for cocaine, as it did not impair responding for sucrose reinforcement. The effect of LHb injection of GABA agonists was mimicked by intra-LHb muscarinic cholinergic (mACh) antagonist injection, and activation of mACh receptors excited a majority of LHb neurons in in vitro electrophysiology experiments. These results indicate that the LHb participates in the suppression of impulsive responding for cocaine through the activation of a cholinergic circuit, and they suggest that LHb dysfunction may contribute to impaired impulse control associated with drug addiction.

5HT(1B) receptor-mediated pre-synaptic depression of excitatory inputs to the rat lateral habenula.

Accumulating lines of evidence indicate that the lateral habenula (LHb), which reciprocally interacts with raphe nuclei (RN), displays hyperactivity including synaptic potentiation of excitatory inputs to the LHb during a depressed state. Despite the potential importance of glutamatergic excitatory synapses in depression-like behavior, modulation of these LHb synapses by monoamines such as serotonin (5HT) is not fully understood at the cellular and molecular level. Therefore, we used whole cell voltage-clamp recording to examine the molecular mechanisms by which 5HT modulates glutamatergic transmission in the LHb. The present study provides the first evidence that glutamatergic transmission of LHb synapses is inhibited by activation of the 5HT(1B) receptor at the pre-synapse in both acute depression (5HT-AD) and long-term depression (5HT-LTD). We further show that 5HT-AD results from the activation of Shaker-type K(+) channels whereas 5HT-LTD depends on inhibition of the adenylyl cyclase-cAMP (AC-cAMP) pathway with an increase in pre-synaptic Ca(2+) release from ryanodine-sensitive internal stores in an NO-dependent manner.

Details of Lymphedema, Upper Limb Morbidity, and Self Management in Women after Breast Cancer Treatment.

PURPOSE: To examine the details of lymphedema, upper limb morbidity, and its self management in women after breast cancer treatment. METHODS: Using a cross-sectional survey design, 81 women were recruited from a university hospital. Lymphedema was detected by a nurse as a 2-cm difference between arm circumferences at 6 different points on the arm. Degrees of pain, stiffness, and numbness were scored using a drawing of upper limb on a 0~10 point scale. Aggravating conditions and self-management for lymphedema were also recorded. RESULTS: The mean age of the participants was 52.5 years; the average time since breast surgery was 29.7 months. Histories of modified radical mastectomy (55%) and lymph node dissection (81%) were noted. Lymphedema was found in 59% of women, then pain and stiffness were prevalent most at upper arm while numbness was apparentat fingers, and the symptom distress scores ranged 3.9~6.7. Women experienced aggravated arm swelling after routine housework with greatly varied duration. Self-management was conservative with a wide range of times for the relief of symptoms. CONCLUSION: Lymphedema education for women with breast cancer should be incorporated into the oncologic nursing care system to prevent its occurrence and arm morbidity. Risk reduction guidelines, individually tailored self-care strategies, and self-awareness for early detection need to be refined in clinical nursing practices.