Effect of chronic alcohol vapor exposure on reinstatement of alcohol seeking induced by U50,488

Abstract

Alcohol dependence and stress are associated with relapse to alcohol during abstinence, but the underlying mechanisms are poorly understood. Kappa opioid receptors (KOR) are involved in alcohol reward and in the effects of stress. Previously, in non-dependent rats, we showed that KOR in the bed nucleus of the stria terminalis (BNST) mediate reinstatement of alcohol seeking induced by the selective KOR agonist U50,488. Here, we determine the effects of chronic, intermittent exposure to alcohol vapor on U50,488-induced reinstatement of alcohol seeking. We also study brain mechanisms involved using the neuronal activity marker Fos and phosphorylated p38 MAPK (p-p38), an intracellular messenger implicated in the effects of KOR stimulation. We trained male Long-Evans rats to self-administer alcohol (12% w/v) and exposed them to alcohol vapor (14 h vapor/10 h air) daily for 24 d or to the control condition, extinguished alcohol-reinforced responding and determined the dose response for U50,488-induced reinstatement. We then determined the effects of vapor exposure on U50,488-induced Fos and p-p38 expression. Vaporexposed rats were more sensitive to U50,488-induced reinstatement. U50,488 increased Fos expression in brain areas involved in stress-induced relapse, and Fos activation in the ventral BNST was greater in vapor exposed rats. Vapor exposed rats had increased basal p-p38 expression in the dorsal BNST, LC and NTS. Our findings suggest that changes in the neuronal responses to KOR stimulation in the ventral BNST may be involved in the increased sensitivity to U50,488 accompanying dependence.

Effects of the alpha-1 antagonist prazosin on KOR agonist-induced reinstatement of alcohol seeking

“…Studies using local inactivation with baclofen/muscimol support the role of a number of these sites in reinstatement induced by footshock, including the OFC, NAC core, ventral BNST, CeA, and VTA (Capriles et al, 2003; McFarland et al, 2004). This earlier work using local inactivation and our present and previous data using Fos mapping are consistent with the importance of the extended amygdala in stress-induced reinstatement (Kalivas and McFarland, 2003; Funk et al, 2016, 2019; Koob and Volkow, 2016; Lê et al, 2018).…”

“…See Figure 1A for experimental timeline. As in our previous publication using similar training conditions (Lê et al, 2018; Funk et al, 2019), rats demonstrated reliable alcohol self-administration (approximately 0.7 g/kg at the end of training) and comparable extinction of the alcohol-reinforced responding (Figure 1B–C).…”

“…Prazosin (Sigma Aldrich, Oakville, ON) and U50,488 hydrochloride (Vibrant Pharma, Brantford, ON) were dissolved in distilled water. We selected prazosin and U50,488 doses (free base) and pretreatment times based on our previously published data on the effects of U50,488 on reinstatement and Fos expression and the effects of prazosin on yohimbine-induced reinstatement and Fos expression (Lê et al, 2011; Funk et al, 2014, 2016, 2019; Grella et al, 2014; Lê et al, 2018).…”

“…Brain sections were collected from dorsal and ventral medial prefrontal cortex (mPFC), orbitofrontal cortex (OFC), nucleus accumbens (NAC) core and shell, dorsal and ventral bed nucleus of the stria terminalis (BNST), central and basolateral amygdala (CeA, BLA), lateral hypothalamus (LH), dorsal and median raphe nuclei (DRN, MRN), ventral tegmental area (VTA), locus coeruleus (LC), and nucleus of the solitary tract (NTS) based on a brain atlas (Paxinos and Watson, 2005). These regions were selected based on previous work from our laboratory and elsewhere indicating their role in footshock-, yohimbine-, or U50,488-induced reinstatement and the inhibitory effects of prazosin on yohimbine-induced brain activation (McFarland et al, 2004; Funk et al, 2006, 2016, 2019; Koob and Volkow, 2016; Lê et al, 2018).…”

Moderate adolescent chronic intermittent ethanol exposure sex-dependently disrupts synaptic transmission and kappa opioid receptor function in the basolateral amygdala of adult rats

“…In the central amygdala, increased levels of dynorphin release and receptor coupling have been linked to elevated alcohol consumption and negative affect following chronic alcohol exposure (Kissler et al, 2014;Kissler & Walker, 2016). Finally, blockade of KORs in the BNST reduced alcohol consumption, negative affect, and physiological withdrawal symptoms following chronic alcohol exposure (Erikson, Wei, & Walker, 2018), while activation of KORs in this region enhanced alcohol seeking following chronic alcohol exposure (Funk, Coen, Tamadon, & Le, 2019). Together, these studies clearly demonstrate that parts of the extended amygdala which regulate negative affective states and modulation of reward have disrupted KOR function following chronic alcohol exposure; however, whether similar adaptations occur in the BLA, particularly in response to exposure in adolescence, is unknown.…”