Involvement of Sigma receptors in the detrimental effects of chronic alcohol exposure

Alcohol Use Disorder (AUD) is complex psychiatric disease characterized by increased alcohol intake, inability to control consumption, and a negative emotional state during withdrawal. In particular, one often-ignored feature of this negative state is the emergence of alcoholic-induced pain states, manifesting as both allodynia (when a non-noxious stimulus induces a nociceptive response) and hyperalgesia (when a noxious stimulus produces a heightened nociceptive response). Here, we first present evidence identifying standard chow diet as a factor in determining the amount of ethanol consumed as well as the preference for alcohol in an intermittent access to two bottle choice paradigm in mice. Additionally, while all ethanol experienced mice exhibit allodynia during withdrawal compared to the water drinking controls, the type of chow diet does not appear to affect its severity. We then investigated, using the same mouse model, the role of each of the two known subtypes of Sigma receptors, Sig-1R and Sig-2R, in both heavy alcohol drinking and associated pain states. We found that Sig-1R antagonists and Sig-2R modulators are able to decrease ethanol intake and hyperalgesia. Both excessive alcohol drinking and heightened pain states were found to be common outcomes also of another well-established model of alcohol dependence, the chronic intermittent ethanol vapor exposure (CIE), together with an increase of impulsive action. We, therefore, further investigated the role of Sig-1R in this post-dependent phenotype, and found that CIE increases Sig-1R levels in the prefrontal cortex, specifically in the anterior cingulate cortex (ACC) and the prelimbic cortex (PrL). Notably, knockdown of Sig-1Rs in the ACC via viral approach rescues hyperalgesia, but not allodynia nor impulsive action, suggesting that the ACC may be a critical area for alcohol-induced hyperalgesia, but not allodynia or impulsive action. Altogether, the results of this work give important insights into the role of Sig-1Rs in alcohol addiction, and have the potential to lead to novel pharmacological treatments for AUD.2023-03-27T00:00:00

Complex interactions between the subject factors of biological sex and prior histories of binge-drinking and unpredictable stress influence behavioral sensitivity to alcohol and alcohol intake

Alcohol use disorders, affective disorders and their comorbidity are sexually dimorphic in humans. However, it is difficult to disentangle the interactions between subject factors influencing alcohol sensitivity in studies of humans. Herein, we combined murine models of unpredictable, chronic, mild stress (UCMS) and voluntary binge-drinking to examine for sex differences in the interactions between prior histories of excessive ethanol-drinking and stress upon ethanol-induced changes in motor behavior and subsequent drinking. In Experiment 1, female mice were insensitive to the UCMS-induced increase in ethanol-induced locomotion and ethanol intake under continuous alcohol-access. Experiment 2 revealed interactions between ethanol dose and sex (females>males), binge-drinking history (water>ethanol), and UCMS history (UCMS>controls), with no additive effect of a sequential prior history of both binge drinking and UCMS observed. We also observed an interaction between UCMS history and sex for righting recovery. UCMS history potentiated subsequent binge-drinking in water controls of both sexes and in male binge-drinking mice. Conversely, a prior binge-drinking history increased subsequent ethanol intake in females only, irrespective of prior UCMS history. In Experiment 3, a concurrent history of binge-drinking and UCMS did not alter ethanol intake, nor did it influence the ethanol dose-locomotor response function, but it did augment alcohol-induced sedation and reduced subsequent alcohol intake over that produced by binge-drinking alone. Thus, the subject factors of biological sex, prior stressor history and prior binge-drinking history interact in complex ways in mice to impact sensitivity to alcohol's motor-stimulating, -incoordinating and intoxicating effects, as well as to influence subsequent heavy drinking

ERK-Directed Phosphorylation of mGlu5 Gates Methamphetamine Reward and Reinforcement in Mouse.

Methamphetamine (MA) is a highly addictive psychomotor stimulant drug. In recent years, MA use has increased exponentially on a global scale, with the number of MA-involved deaths reaching epidemic proportions. There is no approved pharmacotherapy for treating MA use disorder, and we know relatively little regarding the neurobiological determinants of vulnerability to this disease. Extracellular signal-regulated kinase (ERK) is an important signaling molecule implicated in the long-lasting neuroadaptations purported to underlie the development of substance use disorders, but the role for this kinase in the propensity to develop addiction, particularly MA use disorder, is uncharacterized. In a previous MA-induced place-conditioning study of C57BL/6J mice, we characterized mice as MA-preferring, -neutral, or -avoiding and collected tissue from the medial prefrontal cortex (mPFC). Using immunoblotting, we determined that elevated phosphorylated ERK expression within the medial prefrontal cortex (mPFC) is a biochemical correlate of the affective valence of MA in a population of C57BL/6J mice. We confirmed the functional relevance for mPFC ERK activation for MA-induced place-preference via site-directed infusion of the MEK inhibitor U0126. By contrast, ERK inhibition did not have any effect upon MA-induced locomotion or its sensitization upon repeated MA treatment. Through studies of transgenic mice with alanine point mutations on T1123/S1126 of mGlu5 that disrupt ERK-dependent phosphorylation of the receptor, we discovered that ERK-dependent mGlu5 phosphorylation normally suppresses MA-induced conditioned place-preference (MA-CPP), but is necessary for this drug's reinforcing properties. If relevant to humans, the present results implicate individual differences in the capacity of MA-associated cues/contexts to hyper-activate ERK signaling within mPFC in MA Use Disorder vulnerability and pose mGlu5 as one ERK-directed target contributing to the propensity to seek out and take MA

ERK-Directed Phosphorylation of mGlu5 Gates Methamphetamine Reward and Reinforcement in Mouse.

Methamphetamine (MA) is a highly addictive psychomotor stimulant drug. In recent years, MA use has increased exponentially on a global scale, with the number of MA-involved deaths reaching epidemic proportions. There is no approved pharmacotherapy for treating MA use disorder, and we know relatively little regarding the neurobiological determinants of vulnerability to this disease. Extracellular signal-regulated kinase (ERK) is an important signaling molecule implicated in the long-lasting neuroadaptations purported to underlie the development of substance use disorders, but the role for this kinase in the propensity to develop addiction, particularly MA use disorder, is uncharacterized. In a previous MA-induced place-conditioning study of C57BL/6J mice, we characterized mice as MA-preferring, -neutral, or -avoiding and collected tissue from the medial prefrontal cortex (mPFC). Using immunoblotting, we determined that elevated phosphorylated ERK expression within the medial prefrontal cortex (mPFC) is a biochemical correlate of the affective valence of MA in a population of C57BL/6J mice. We confirmed the functional relevance for mPFC ERK activation for MA-induced place-preference via site-directed infusion of the MEK inhibitor U0126. By contrast, ERK inhibition did not have any effect upon MA-induced locomotion or its sensitization upon repeated MA treatment. Through studies of transgenic mice with alanine point mutations on T1123/S1126 of mGlu5 that disrupt ERK-dependent phosphorylation of the receptor, we discovered that ERK-dependent mGlu5 phosphorylation normally suppresses MA-induced conditioned place-preference (MA-CPP), but is necessary for this drug's reinforcing properties. If relevant to humans, the present results implicate individual differences in the capacity of MA-associated cues/contexts to hyper-activate ERK signaling within mPFC in MA Use Disorder vulnerability and pose mGlu5 as one ERK-directed target contributing to the propensity to seek out and take MA

Homer2 regulates alcohol and stress cross-sensitization

An interaction exists between stress and alcohol in the etiology and chronicity of alcohol use disorders; yet a knowledge gap exists regarding the neurobiological underpinnings of this interaction. In this regard, we employed an 11-day unpredictable, chronic, mild stress (UCMS) procedure to examine for stress-alcohol cross-sensitization of motor activity, as well as alcohol consumption/preference and intoxication. We also employed immunoblotting to relate the expression of glutamate receptor-related proteins within subregions of the nucleus accumbens (NAC) to the manifestation of behavioral cross-sensitization. UCMS mice exhibited a greater locomotor response to an acute injection of 2 g/kg alcohol than unstressed controls and this cross-sensitization extended to alcohol intake (0–20%), as well as to the intoxicating and sedative properties of 3 and 5 g/kg alcohol, respectively. Regardless of prior alcohol injection (2 g/kg), UCMS mice exhibited elevated NAC shell levels of mGlu1α, GluN2b and Homer2, as well as lower PLCβ within this subregion. GluN2b levels were also lower within the NAC core of UCMS mice. The expression of stress-alcohol locomotor cross-sensitization was associated with lower mGlu1α within the NAC core and lower ERK activity within both NAC subregions. As Homer2 regulates alcohol sensitization, we assayed also for locomotor cross-sensitization in Homer2 wild-type (WT) and knock-out (KO) mice. WT mice exhibited a very robust cross-sensitization, that was absent in KO animals. These results indicate that a history of mild stress renders an animal more sensitive to the psychomotor and rewarding properties of alcohol, which may depend upon neuroplasticity within NAC glutamate transmission

UCMS and alcohol

An interaction exists between stress and alcohol in the etiology and chronicity of alcohol use disorders, yet a knowledge gap exists regarding the neurobiological underpinnings of this interaction. In this regard, we employed an 11-day unpredictable, chronic, mild stress (UCMS) procedure to examine for stress-alcohol cross-sensitization of motor activity as well as alcohol consumption/preference and intoxication. We also employed immunoblotting to relate the expression of glutamate receptor-related proteins within subregions of the nucleus accumbens (NAC) to the manifestation of behavioral cross-sensitization. UCMS mice exhibited a greater locomotor response to an acute injection of 2 g/kg alcohol than unstressed controls and this cross-sensitization extended to alcohol intake (0-20 percent), as well as to the intoxicating and sedative properties of 3 and 5 g/kg alcohol, respectively. Regardless of prior alcohol injection (2 g/kg), UCMS mice exhibited elevated NAC shell levels of mGlu1α, GluN2b and Homer2, as well as lower phospholipase Cβ within this subregion. GluN2b levels were also lower within the NAC core of UCMS mice. The expression of stress-alcohol locomotor cross-sensitization was associated with lower mGlu1α within the NAC core and lower extracellular signal-regulated kinase activity within both NAC subregions. As Homer2 regulates alcohol sensitization, we assayed also for locomotor cross-sensitization in Homer2 wild-type (WT) and knock-out (KO) mice. WT mice exhibited a very robust cross-sensitization that was absent in KO animals. These results indicate that a history of mild stress renders an animal more sensitive to the psychomotor and rewarding properties of alcohol, which may depend on neuroplasticity within NAC glutamate transmission

Increased reactivity of the paraventricular nucleus of the hypothalamus and decreased threat responding in male rats following psilocin administration

Abstract Psychedelics have experienced renewed interest following positive clinical effects, however the neurobiological mechanisms underlying effects remain unclear. The paraventricular nucleus of the hypothalamus (PVN) plays an integral role in stress response, autonomic function, social behavior, and other affective processes. We investigated the effect of psilocin, the psychoactive metabolite of psilocybin, on PVN reactivity in Sprague Dawley rats. Psilocin increased stimulus-independent PVN activity as measured by c-Fos expression in male and female rats. Psilocin increased PVN reactivity to an aversive air-puff stimulus in males but not females. Reactivity was restored at 2- and 7-days post-injection with no group differences. Additionally, prior psilocin injection did not affect PVN reactivity following acute restraint stress. Experimental groups sub-classified by baseline threat responding indicate that increased male PVN reactivity is driven by active threat responders. These findings identify the PVN as a significant site of psychedelic drug action with implications for threat responding behavior

Methamphetamine Addiction Vulnerability: The Glutamate, the Bad, and the Ugly

BackgroundThe high prevalence and severity of methamphetamine (MA) abuse demands greater neurobiological understanding of its etiology.MethodsWe conducted immunoblotting and in vivo microdialysis procedures in MA high/low drinking mice, as well as in isogenic C57BL/6J mice that varied in their MA preference/taking, to examine the glutamate underpinnings of MA abuse vulnerability. Neuropharmacological and Homer2 knockdown approaches were also used in C57BL/6J mice to confirm the role for nucleus accumbens (NAC) glutamate/Homer2 expression in MA preference/aversion.ResultsWe identified a hyperglutamatergic state within the NAC as a biochemical trait corresponding with both genetic and idiopathic vulnerability for high MA preference and taking. We also confirmed that subchronic subtoxic MA experience elicits a hyperglutamatergic state within the NAC during protracted withdrawal, characterized by elevated metabotropic glutamate 1/5 receptor function and Homer2 receptor-scaffolding protein expression. A high MA-preferring phenotype was recapitulated by elevating endogenous glutamate within the NAC shell of mice and we reversed MA preference/taking by lowering endogenous glutamate and/or Homer2 expression within this subregion.ConclusionsOur data point to an idiopathic, genetic, or drug-induced hyperglutamatergic state within the NAC as a mediator of MA addiction vulnerability

Prefrontal glutamate correlates of methamphetamine sensitization and preference.

Methamphetamine (MA) is a widely misused, highly addictive psychostimulant that elicits pronounced deficits in neurocognitive function related to hypo-functioning of the prefrontal cortex (PFC). Our understanding of how repeated MA impacts excitatory glutamatergic transmission within the PFC is limited, as is information about the relationship between PFC glutamate and addiction vulnerability/resiliency. In vivo microdialysis and immunoblotting studies characterized the effects of MA (ten injections of 2 mg/kg, i.p.) upon extracellular glutamate in C57BL/6J mice and upon glutamate receptor and transporter expression, within the medial PFC. Glutamatergic correlates of both genetic and idiopathic variance in MA preference/intake were determined through studies of high vs. low MA-drinking selectively bred mouse lines (MAHDR vs. MALDR, respectively) and inbred C57BL/6J mice exhibiting spontaneously divergent place-conditioning phenotypes. Repeated MA sensitized drug-induced glutamate release and lowered indices of N-methyl-d-aspartate receptor expression in C57BL/6J mice, but did not alter basal extracellular glutamate content or total protein expression of Homer proteins, or metabotropic or α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid glutamate receptors. Elevated basal glutamate, blunted MA-induced glutamate release and ERK activation, as well as reduced protein expression of mGlu2/3 and Homer2a/b were all correlated biochemical traits of selection for high vs. low MA drinking, and Homer2a/b levels were inversely correlated with the motivational valence of MA in C57BL/6J mice. These data provide novel evidence that repeated, low-dose MA is sufficient to perturb pre- and post-synaptic aspects of glutamate transmission within the medial PFC and that glutamate anomalies within this region may contribute to both genetic and idiopathic variance in MA addiction vulnerability/resiliency