•Early life stress has sex- and model-dependent effects on adult ethanol intake.•Females show more overall and punishment-resistant ethanol intake than males.•Sex- and stress-specific effects on ...self-administration intake and responding.
Alcohol use disorder (AUD) is a debilitating psychiatric disorder characterized by drinking despite negative social and biological consequences. AUDs make up 71% of substance use disorders, with relapse rates as high as 80%. Current treatments stem from data conducted largely in males and fail to target the psychological distress motivating drinking in stress-vulnerable and at-risk populations. Here we employed a rat model and hypothesized that early life stress would reveal sex differences in ethanol intake and drinking despite negative consequences in adulthood. Rats were group housed or isolated postweaning to evaluate sex and stress effects on ethanol consumption in homecage drinking, self-administration (SA), and punished SA (drinking despite negative consequences) in adulthood. Stressed rats showed elevated homecage ethanol intake, an effect more pronounced in females. During SA, males were more sensitive to stress-induced elevations of drinking over time, but females drank more overall. Stressed rats, regardless of sex, responded more for ethanol than their non-stressed counterparts. Stressed females showed greater resistance to punishment-suppressed SA than stressed males, indicating a more stress-resistant drinking phenotype. Results support our hypothesis that adolescent social isolation stress enhances adult ethanol intake in a sex- and model-dependent manner with females being especially sensitive to early life stress-induced elevations in ethanol intake and punished SA in adulthood. Our findings echo the clinical literature which indicates that stress-vulnerable populations are more likely to ‘self-medicate’ with substances. Elucidating a potential mechanism that underlies why vulnerable populations ‘self-medicate’ with alcohol can lead towards developing catered pharmacotherapeutics that could reduce punishment-resistant drinking and relapse.
Previous studies have identified potential antidepressant effects of buprenorphine (BPN), a drug with high affinity for mu opioid receptor (MORs) and kappa opioid receptors (KORs) and some affinity ...at delta opioid receptor (DOR) and opioid receptor-like 1 (ORL-1) receptors. Therefore, these studies examined which opioid receptors were involved in BPN's effects on animal behavior tests sensitive to antidepressant drugs. The acute effects of BPN were tested in the forced swim test (FST) using mice with genetic deletion of individual opioid receptors or after pharmacological blockade of receptors. For evaluating the effects of BPN on chronic stress, separate groups of mice were exposed to unpredictable chronic mild stress (UCMS) for 3 weeks and treated with BPN for at least 7 days before behavioral assessment and subsequent measurement of Oprk1, Oprm1, and Pdyn mRNA expression in multiple brain regions. BPN did not reduce immobility in mice with KOR deletion or after pretreatment with norbinaltorphimine, even though desipramine remained effective. In contrast, BPN reduced immobility in MOR and DOR knockout mice and in mice pretreated with the ORL-1 antagonist JTC-801. UCMS reduced sucrose preference, decreased time in the light side of the light/dark box, increased immobility in the FST and induced region-specific alterations in Oprk1, Oprm1, and PDYN mRNA expression in the frontal cortex and striatum. All of these changes were normalized following BPN treatment. The KOR was identified as a key player mediating the effects of BPN in tests sensitive to antidepressant drugs in mice. These studies support further development of BPN as a novel antidepressant.
Rationale
The serotonin (5-hydroxytryptamine, 5-HT) system plays an important role in stress-related psychiatric disorders and substance abuse. Our previous data show that stressors can inhibit 5-HT ...neuronal activity and release by stimulating the release of the stress neurohormone corticotropin-releasing factor (CRF) within the serotonergic dorsal raphe nucleus (DRN). The inhibitory effects of CRF on 5-HT DRN neurons are indirect, mediated by CRF-R1 receptors located on GABAergic afferents.
Objectives
We tested the hypothesis that DRN CRF-R1 receptors contribute to stress-induced reinstatement of morphine-conditioned place preference (CPP). We also examined the role of this circuitry in stress-induced negative affective state with 22-kHz distress ultrasonic vocalizations (USVs), which are naturally emitted by rats in response to environmental challenges such as pain, stress, and drug withdrawal.
Methods
First, we tested if activation of CRF-R1 receptors in the DRN with the CRF-R1-preferring agonist ovine CRF (oCRF) would reinstate morphine CPP and then if blockade of CRF-R1 receptors in the DRN with the CRF-R1 antagonist NBI 35965 would attenuate swim stress–induced reinstatement of morphine CPP. Second, we tested if intra-DRN pretreatment with NBI 35965 would attenuate foot shock stress–induced 22-kHz USVs.
Results
Intra-DRN injection of oCRF reinstated morphine CPP, while intra-DRN injection of NBI 35965 attenuated swim stress–induced reinstatement. Moreover, intra-DRN pretreatment with NBI 35965 significantly reduced 22-kHz distress calls induced by foot shock.
Conclusions
These data provide evidence that stress-induced negative affective state is mediated by DRN CRF-R1 receptors and may contribute to reinstatement of morphine CPP.
Emerging evidence indicates the involvement of GPR55 and its proposed endogenous ligand, lysophosphatidylinositol (LPI), in nociception, yet their role in central pain processing has not been ...explored. Using Ca(2+) imaging, we show here that LPI elicits concentration-dependent and GPR55-mediated increases in intracellular Ca(2+) levels in dissociated rat periaqueductal gray (PAG) neurons, which express GPR55 mRNA. This effect is mediated by Ca(2+) release from the endoplasmic reticulum via inositol 1,4,5-trisphosphate receptors and by Ca(2+) entry via P/Q-type of voltage-gated Ca(2+) channels. Moreover, LPI depolarizes PAG neurons and upon intra-PAG microinjection, reduces nociceptive threshold in the hot-plate test. Both these effects are dependent on GPR55 activation, because they are abolished by pretreatment with ML-193 N-(4-(N-(3,4-dimethylisoxazol-5-yl)sulfamoyl)-phenyl)-6,8-dimethyl-2-(pyridin-2-yl)quinoline-4-carboxamide, a selective GPR55 antagonist. Thus, we provide the first pharmacological evidence that GPR55 activation at central levels is pronociceptive, suggesting that interfering with GPR55 signaling in the PAG may promote analgesia.
Abstract The serotonin (5-hydroxytryptamine, 5-HT) system plays an important role in stress-related psychiatric disorders and substance abuse. Stressors and stress hormones can inhibit the dorsal ...raphe nucleus (DRN)-5-HT system, which composes the majority of forebrain-projecting 5-HT. This inhibition is mediated via stimulation of GABA synaptic activity at DRN-5-HT neurons. Using swim stress-induced reinstatement of morphine conditioned place-preference, recent data from our laboratory indicate that morphine history sensitizes DRN-5-HT neurons to GABAergic inhibitory effects of stress. Moreover, GABAA receptor-mediated inhibition of the serotonergic DRN is required for this reinstatement. In our current experiment, we tested the hypothesis that GABAergic sensitization of DRN-5-HT neurons is a neuroadaptation elicited by multiple classes of abused drugs across multiple models of stress-induced relapse by applying a chemical stressor (yohimbine) to induce reinstatement of previously extinguished cocaine self-administration in Sprague-Dawley rats. Whole-cell patch-clamp recordings of GABA synaptic activity in DRN-5-HT neurons were conducted after the reinstatement. Behavioral data indicate that yohimbine triggered reinstatement of cocaine self-administration. Electrophysiology data indicate that 5-HT neurons in the cocaine group exposed to yohimbine had increased amplitude of inhibitory postsynaptic currents compared to yoked-saline controls exposed to yohimbine or unstressed animals in both drug groups. These data, together with previous findings, indicate that interaction between psychostimulant or opioid history and chemical or physical stressors may increase postsynaptic GABA receptor density and/or sensitivity in DRN-5-HT neurons. Such mechanisms may result in serotonergic hypofunction and consequent dysphoric mood states which confer vulnerability to stress-induced drug reinstatement.
Background:
The serotonin (5-hydroxytryptamine (5-HT))-mediated system plays an important role in stress-related psychiatric disorders and substance abuse. Our previous studies showed that stress and ...drug exposure can modulate the dorsal raphe nucleus (DRN)-5-HT system via γ-aminobutyric acid (GABA)A receptors. Moreover, GABAA receptor-mediated inhibition of serotonergic DRN neurons is required for stress-induced reinstatement of opioid seeking.
Aim/methods:
To further test the role of GABAA receptors in the 5-HT system in stress and opioid-sensitive behaviors, our current study generated mice with conditional genetic deletions of the GABAA α1 subunit to manipulate GABAA receptors in either the DRN or the entire population of 5-HT neurons. The GABAA α1 subunit is a constituent of the most abundant GABAA subtype in the brain and the most highly expressed subunit in 5-HT DRN neurons.
Results:
Our results showed that mice with DRN-specific knockout of α1-GABAA receptors exhibited a normal phenotype in tests of anxiety- and depression-like behaviors as well as swim stress-induced reinstatement of morphine-conditioned place preference. By contrast, mice with 5-HT neuron-specific knockout of α1-GABAA receptors exhibited an anxiolytic phenotype at baseline and increased sensitivity to post-morphine withdrawal-induced anxiety.
Conclusions:
Our data suggest that GABAA receptors on 5-HT neurons contribute to anxiety-like behaviors and sensitivity of those behaviors to opioid withdrawal.
Stress-related psychiatric disorders such as anxiety and depression involve dysfunction of the serotonin 5-hydroxytryptamine (5-HT) system. Previous studies have found that the stress neurohormone ...corticotropin-releasing factor (CRF) inhibits 5-HT neurons in the dorsal raphe nucleus (DRN) in vivo. The goals of the present study were to characterize the CRF receptor subtypes (CRF-R1 and -R2) and cellular mechanisms underlying CRF-5-HT interactions. Visualized whole-cell patch-clamp recording techniques in brain slices were used to measure spontaneous or evoked GABA synaptic activity in DRN neurons of rats and CRF effects on these measures. CRF-R1 and -R2-selective agonists were bath applied alone or in combination with receptor-selective antagonists. CRF increased presynaptic GABA release selectively onto 5-HT neurons, an effect mediated by the CRF-R1 receptor. CRF increased postsynaptic GABA receptor sensitivity selectively in 5-HT neurons, an effect to which both receptor subtypes contributed. CRF also had direct effects on DRN neurons, eliciting an inward current in 5-HT neurons mediated by the CRF-R2 receptor and in non-5-HT neurons mediated by the CRF-R1 receptor. These results indicate that CRF has direct membrane effects on 5-HT DRN neurons as well as indirect effects on GABAergic synaptic transmission that are mediated by distinct receptor subtypes. The inhibition of 5-HT DRN neurons by CRF in vivo may therefore be primarily an indirect effect via stimulation of inhibitory GABA synaptic transmission. These results regarding the cellular mechanisms underlying the complex interaction between CRF, 5-HT, and GABA systems could contribute to the development of novel treatments for stress-related psychiatric disorders.
Abstract Background 5-Lipoxygenase (5-LO) is a protein widely distributed in the central nervous system where it modulates amyloidosis and memory impairments in transgenic mouse models of Alzheimer’s ...disease. However, no data are available as to whether 5-LO is elevated in human tauopathy or if it directly influences tau pathology in a relevant model of the disease. Methods We assayed 5-LO levels in brain samples from patients with tauopathy and transgenic tau mice, and we evaluated the effect of 5-LO pharmacologic inhibition on the phenotype of these mice. Results The 5-LO protein is upregulated in human tauopathy and transgenic tau mice brains. Pharmacologic blockade of 5-LO in tau mice resulted in significant memory improvement, rescue of synaptic integrity and dysfunction, and reduction of tau pathology via a cdk5-dependent mechanism. Conclusions These results establish a key role of 5-LO in the development of the tau pathology phenotype and demonstrate it to be a novel viable therapeutic target for the pharmacologic treatment of human tauopathy.
Research highlights ► Chemokine receptors (CXCR4 and CX3CR1) colocalize with the mu-opioid receptor in the rat brain. ► Chemokine–opioid receptor interactions are studied by electrophysiology in ...periaqueductal grey. ► The activation of chemokine receptors blocks morphine-mediated electrophysiological responses. ► Heterologous desensitization between these receptors occurs at the single-cell level in the brain. ► Interactions between these receptor classes may contribute to the immunomodulation of opioids.
•We propose planarians to study defensive responding and anxiety-like effects.•The invertebrate model is designated as the PLDT (planarian light/dark test).•Clorazepate, fluoxetine, ethanol and a ...synthetic cathinone decreased defensive responding.•An inverse benzodiazepine agonist and predator odor increased defensive responding.•PLDT may be as a predictive, cost-effective screen to study anxiety-like effects.
Planarians, like rodents, instinctively spend more time in dark versus light environments when given a choice. This behavioral phenomenon is called negative phototaxis, which may reflect defensive responding related to an anxiety-like phenotype.
We propose a planarian light/dark test, designated PLDT, to predict anxiogenic- or anxiolytic-like effects. Experimentally, we placed a planarian at the midline of a Petri dish, containing test compound or water, that was split evenly into light and dark compartments and determined time spent in the light over 10min.
A clinically-approved benzodiazepine agonist (clorazepate; 10μM) increased time spent in the light whereas an inverse benzodiazepine agonist (FG-7142; 1, 10μM) produced the opposite response. Fluoxetine (1μM) or ethanol (1%), as well as the ‘bath salt’ cathinone S-mephedrone (300μM), enhanced time spent in the light. Planarians exposed to predator (frog) odor spent more time in the dark.
The light/dark box (LDB) test in rodents is used to screen putative medications for possible anxiolytic and anxiogenic effects. Our results showing that time spent in the light by planarians is enhanced by common anxiety-relieving drugs (e.g. benzodiazepine agonist, ethanol, fluoxetine) and decreased by anxiogenic substances (e.g. predator odor, benzodiazepine inverse agonist) reveal directionally similar effects in the established (LDB) and new (PLDT) assays.
Our data identify the PLDT as a cost-effective, invertebrate assay for quantifying the effects of practically any water-soluble substance on defensive responding and for studying and teaching anxiety-like responses in a living organism.
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