OX is an excitatory neuropeptide that exists in two forms, OX-A (hypocretin-1) and OX-B (hypocretin-2) (De Lecea et al., 1998; Sakurai et al., 1998b). Both are derived from the proteolytic cleavage of the common precursor prepro-OX (De Lecea et al., 1998; Gatfield et al., 2010; Sakurai et al., 1998a; Tsujino and Sakurai, 2009). Two OX receptors have been identified: OX1R and OX2R. OX-A has stronger affinity for OX1Rs and OX2Rs relative to OX-B (Ammoun et al., 2003; Sakurai et al., 1998a; Scammell and Winrow, 2011). OX is produced only in the HYP, a region that is critically involved in arousal and motivated behavior, comprising the lateral HYP (LH), dorsomedial HYP (DMH), and perifornical area (PFA), and regulates a range of physiological and behavioral functions, including arousal, sleep/wakefulness, feeding, and energy metabolism (Edwards et al., 1999; Haynes et al., 2002; Haynes et al., 2000; Sakurai et al., 1998a; Sutcliffe and De Lecea, 2002; Taheri et al., 2002; Teske et al., 2010; Willie et al., 2001). Although OX neurons originate in the HYP, they project widely throughout the PVT and other brain regions, which contributes to a multitude of physiological functions, including the mediation of motivated behavior and reward processing (De Lecea et al., 1998; Marcus et al., 2001). OX synthesis and projection sites are depicted in Figure 1. In addition to regulating arousal and motivated behavior, OXR signaling is strongly influenced by stress and contributes to stress responsivity across multiple brain regions, including the PVT, suggesting an important role in stress-related alcohol behaviors (Grafe and Bhatnagar, 2018; Heydendael et al., 2011; Kim et al., 2023).

OX neurons project to the whole PVT, with the pPVT receiving the greatest density of OX afferent terminals (Kirouac et al., 2005), and regions that participate in the regulation of drug seeking and stress response, including the NAc shell (NAcSh), ventral pallidum (VP), VTA, CeA, BNST, and mPFC (Baldo et al., 2003; Peyron et al., 1998). OX transmission influences neurobehavioral and motivational effects of drugs of abuse (Bonci and Borgland, 2009; Borgland et al., 2006; Thompson and Borgland, 2011). OX neurons become activated by food-, morphine-, cocaine-, and alcohol-related stimuli in the absence of the substance itself (Dayas et al., 2008; Harris et al., 2005; Jupp et al., 2011a; Martin-Fardon et al., 2010; Martin-Fardon and Weiss, 2017).

Greater LH OX neuron activation was associated with more intense alcohol-seeking behavior in rats during relapse-like responding for alcoholic beer (Hamlin et al., 2007; Millan et al., 2010). Similarly, OX1R blockade decreased alcohol self-administration (Lawrence et al., 2006) and the cue- and stress-induced reinstatement of alcohol seeking in rats (Jupp et al., 2011a; Lawrence et al., 2006; Richards et al., 2008; Smith et al., 2010). This suggests that OX neurons encode conditioned associations between environmental cues and reward availability, positioning them as key drivers of relapse (James et al., 2016; Mahler et al., 2012).

Literature illustrates stress-inducing effects of alcohol exposure in both voluntary (Richardson et al., 2008) and forced (Rivier, 1993; Rivier et al., 1984) alcohol administration paradigms. Willey et al. (2012) reported that intraperitoneal (i.p.) alcohol administration (0.5–1.5 g/kg) dose-dependently increased plasma corticosterone levels in male and female Sprague-Dawley rats of different ages (Willey et al., 2012). This indicates activation of the hypothalamic-pituitary-adrenal (HPA) axis, a central component of the stress response that is consistent with earlier findings (Ellis, 1966; Thiagarajan et al., 1989). Increases in adrenocorticotropic hormone (ACTH) that were positively related to blood alcohol levels were also observed in response to numerous modes of alcohol delivery, including acute i.p. and intragastric administration (Ogilvie et al., 1997). Long-term disruptions of other stress peptides and pathways, particularly OX neurocircuitry that is involved in regulating stress and arousal, may facilitate chronic alcohol use and dependence.

Several reports indicate that alcohol consumption promotes OX transmission through increases in Hcrtr mRNA expression (Barson et al., 2015) and Hcrt mRNA expression (Lawrence et al., 2006; Morganstern et al., 2010) in rats and increases in OX peptides in zebrafish (Sterling et al., 2015). Following chronic voluntary alcohol consumption in male inbred alcohol-preferring (iP) rats, Hcrt mRNA expression was upregulated in the LH, suggesting the enhancement of OX transmission in this key arousal and motivation region (Lawrence et al., 2006). Similarly, in male Long-Evans rats, alcohol use increased Hcrt and Hcrtr mRNA expression in the HYP and anterior PVT (aPVT), respectively, indicating upregulation of the OX system during alcohol intake (Barson et al., 2015). This effect was corroborated in Wistar rats (males and females), such that intermittent alcohol vapor-induced dependence increased hypothalamic Hcrt mRNA expression and Hcrtr1/2 mRNA expression at acute (i.e., 8 h) abstinence (Matzeu and Martin-Fardon, 2020a). Conversely, alcohol dependence that was induced by forced intragastric alcohol administration in male Sprague-Dawley rats (Braconi et al., 2010; Majchrowicz, 1975) decreased Hcrt mRNA expression at 12 h of abstinence (Sharma et al., 2020), indicating a model- and time-dependent effect on OX regulation and transcription.

In rats, the link between OX Fos activation and alcohol seeking has been observed in models of reinstatement or renewal that is triggered by alcohol-associated discriminative stimuli (Dayas et al., 2008; Moorman et al., 2016), alcohol-related environmental contexts (Hamlin et al., 2007; Millan et al., 2010; Moorman et al., 2016), yohimbine-induced stress (Kastman et al., 2016), and, to a lesser extent, discrete alcohol-paired cues (Moorman et al., 2016). Dayas et al. (2008) reported a significant increase of Fos expression in HYP OX neurons in male Wistar rats following the presentation of alcohol-associated contextual stimuli and an increase in Fos expression in the PVT (Dayas et al., 2008). In mice, Fos activation in OX neurons is also seen following alcohol sensitization (Macedo et al., 2013), suggesting that OX becomes more engaged after repeated exposure to alcohol itself. This parallels other findings that the magnitude of OX neuron activation positively correlates with motivational drive, such as the renewal of alcohol-seeking behavior following extinction (Hamlin et al., 2007; Millan et al., 2010; Moorman et al., 2016), highlighting the role of OX transmission in alcohol-motivated behaviors. Notably, direct causal evidence indicates that the inhibition of OX transmission blocks the reinstatement of drug- and alcohol-seeking behavior (Illenberger et al., 2023; Martin-Fardon and Weiss, 2014a; Martin-Fardon and Weiss, 2014b; Matzeu and Martin-Fardon, 2020b; Richards et al., 2008; Smith et al., 2009).

Human studies show higher plasma OX levels in early alcohol withdrawal compared with OX levels later in abstinence (Bayerlein et al., 2011; Ziółkowski et al., 2016), and these elevated levels correlate with psychological distress, particularly depression-like symptoms, during withdrawal (Von Der Goltz et al., 2011). Interestingly, Bayerlein et al. (2011) reported that higher peripheral blood lymphocyte HCRT mRNA levels were associated with less severe physical withdrawal symptoms in male and female patients, suggesting that OX transmission may be inversely related to withdrawal intensity in AUD (Bayerlein et al., 2011). Collectively, alcohol exposure and stress-related alcohol behaviors induce neuroplastic changes in the OX system that may contribute to the development of pathological compulsive alcohol-seeking behavior (Aston-Jones and Harris, 2004; Kalivas and O'Brien, 2008; Kelley and Berridge, 2002; Wanat et al., 2009).

The OX system plays a pivotal role in regulating alcohol-motivated behavior. Several reviews have delineated its unique roles in alcohol consumption and withdrawal following dependence (Barson and Leibowitz, 2016; Brown and Lawrence, 2013; Capó et al., 2025; Lawrence, 2010; Mahler et al., 2012; Moorman, 2018; Walker and Lawrence, 2016). OX1R antagonism significantly decreased the motivation to consume alcohol in models of high vs. low alcohol-preferring rats and mice (Alcaraz-Iborra et al., 2017; Moorman et al., 2017), in rats and mice that were genetically modified to prefer alcohol or trained to binge drink (Anderson et al., 2014; Dhaher et al., 2010; Olney et al., 2015), and in alcohol-dependent mice that underwent alcohol vapor exposure (Lopez et al., 2016).

OX1R antagonists powerfully attenuate alcohol seeking and reinstatement across multiple paradigms, particularly under conditions of high motivational demand, including cue-induced responding, pharmacological stress, discriminative stimuli, and alcohol-conditioned reward (Jupp et al., 2011a; Lawrence et al., 2006; Macedo et al., 2013; Richards et al., 2008). Consistent with a state-dependent profile, these effects are most evident in operant models requiring increased effort or following alcohol dependence, whereas effects on low-level, non-pathological drinking are less consistent (Alcaraz-Iborra et al., 2017; Anderson et al., 2014; Capó et al., 2025; Dhaher et al., 2010; Lei et al., 2016; Lopez et al., 2016; Moorman et al., 2017).

Functional differences between OX1Rs vs. OX2Rs were suggested (Aston-Jones et al., 2010), although attributing specific alcohol-related behaviors to individual receptor subtypes remains challenging. OX1Rs are primarily implicated in alcohol-motivated behavior, particularly under conditions of high effort, stress, or reinstatement vulnerability, whereas OX2R signaling appears to contribute to alcohol consumption and conditioned reward in a region- and paradigm-specific manner (Alcaraz-Iborra et al., 2017; Anderson et al., 2014; Moorman, 2018; Olney et al., 2017; Srinivasan et al., 2012).

Selective OX2R antagonists have been shown to reduce alcohol consumption and self-administration in rodents, but effects are region- and model-specific. For example, intracerebroventricular (i.c.v.) and intra-NAc core administration of the OX2R antagonist TCSOX229 reduced alcohol self-administration in male iP rats (Brown et al., 2013), and microinjections of TCSOX229 in the aPVT decreased intermittent-access alcohol drinking in male Long-Evans rats (Barson et al., 2015). Similarly, OX2R antagonism attenuated the stress-induced reinstatement of alcohol seeking when targeted to the nucleus incertus and reduced alcohol-induced conditioned place preference and its reinstatement following systemic administration, supporting a role for OX2Rs in alcohol consumption and select conditioned reward processes in a circuit-dependent manner (Kastman et al., 2016; Shoblock et al., 2011).

Olney et al. (2017) directly compared OX1R and OX2R antagonism in the VTA and CeA of male C57BL/6J mice and found site-specific effects. The blockade of OX1Rs in the VTA reduced binge-like alcohol drinking, whereas OX2R blockade had no significant effect (Olney et al., 2017). In contrast, OX2R blockade in the aPVT reduced OX-A- and OX-B-induced increases in alcohol intake, whereas OX1R antagonism did not (Barson et al., 2015). These data illustrate the region- and paradigm-specific roles of OX1Rs and OX2Rs in targeting rewarding and motivational effects of alcohol consumption and reinstatement (Anderson et al., 2014; Brown et al., 2013; Kastman et al., 2016; Olney et al., 2017; Shoblock et al., 2011). Taken together, these findings suggest that OX1R antagonism preferentially reduces pathological or dependence-related alcohol seeking, whereas OX2R antagonism more broadly attenuates alcohol-related behaviors in a region- and task-dependent manner.

The DYN/KOP system is widely distributed in the central nervous system (Watson et al., 1982) and plays a key role in the development of behavioral alterations that are consistent with the “dark side” of addiction or the aversive emotional state that accompanies dependence (Bruchas et al., 2010; Carroll and Carlezon, 2013; Chavkin and Koob, 2016; Koob, 2015; Land et al., 2008). DYN, derived from the Pdyn gene, is processed into DYN-A and DYN-B peptides, with variants like DYN-A (1–17), DYN-A (1–8), and DYN-B (1–29). These DYN variants preferentially bind to KOPs (Chavkin et al., 1982) but also show affinity for μ-opioid (MOP) and δ-opioid (DOP) receptors (Fallon and Leslie, 1986; Schwarzer, 2009).

Unlike OX, which is synthesized primarily in the HYP, DYN is produced in a range of brain areas beyond the HYP, including mesolimbic structures that are implicated in addiction (Bali et al., 2014; Watson et al., 1982). In the human brain, PDYN mRNA is strongly expressed in reward-related regions, such as the dorsal and ventral striatum, NAc, amygdala, and mPFC (Hurd, 1996). DYN projections (e.g., NAc to VTA), can modulate dopamine signaling relevant to drug-motivated behavior (Shippenberg et al., 2001). Oprk1 mRNA, which encodes the KOP, is prominent in the midline thalamic nuclei, including the PVT, and is associated with robust KOP binding (Mansour et al., 1994). This anatomical mapping positions the PVT as a critical node where KOP signaling can regulate motivational and stress-related states, supporting its therapeutic relevance (Butelman et al., 2012; Tejeda et al., 2012).

While HYP-OX neurons represent one source of DYN input to the PVT, anatomical evidence suggests that DYN-expressing neurons from additional regions, including the mPFC, insular cortex, extended amygdala, and brainstem nuclei such as the nucleus of the solitary tract, also project to the PVT, positioning this region as a convergence point for multiple DYN inputs (Hsu et al., 2014; Kirouac, 2015; Penzo and Gao, 2021). The relative contribution of these distinct DYN sources to stress-related alcohol behaviors, particularly within PVT subregions, remains largely unexplored and an important direction for future investigation.

DYN/KOP expression increases in response to stress across several brain regions, including the HPA axis that modulates glucocorticoid release in animal models (Bali et al., 2015; Van’T Veer and Carlezon, 2013), humans (Ur et al., 1997), and nonhuman primates (Pascoe et al., 2008). In restraint/immobilization stress and learned helplessness paradigms, Pdyn mRNA expression is upregulated in the NAc, hippocampus, and HYP, which exclusively synthesizes OX (Bali et al., 2014; De Lecea et al., 1998; Lucas et al., 2011; Palkovits, 2000; Shirayama et al., 2004). In preclinical studies, KOP agonists trigger taste aversion and conditioned place aversion (Mucha and Herz, 1985), and KOP activation mediates depressive-like behavior in male Sprague-Dawley rats via increased forced swim test immobility and elevated ICSS thresholds (Carlezon et al., 2006), suggesting that KOP activation contributes to dysphoria and aversive states. Models that use KOP antagonists support this finding, showing that KOP blockade reduces anxiety- and depressive-like behavior in stressed rodents and exerts analgesic effects in models of forced swim and restraint stress (Knoll et al., 2007; McLaughlin et al., 2003; Shirayama et al., 2004; Suh et al., 2000).

KOP agonists produce aversive and dysphoric effects in humans (Leconte et al., 2022; Pfeiffer et al., 1986; Walsh et al., 2001). Patients who were given butorphanol, a mixed KOP/partial-MOP agonist, reported markedly heightened negative affect on a subjective measure of dysphoric symptoms (Schlaepfer et al., 1998), while other KOP agonists, including enadoline and ketocyclazocine, induced visual distortions, dissociation, and dysphoric states (Kumor et al., 1986; Walsh et al., 2001), further indicating a pivotal role of the DYN/KOP system in mediating dysphoria and negative affect across species, contributing to vulnerability to alcohol use and relapse.

DYN/KOP expression and signaling are highly responsive to alcohol exposure and play a complex role in modulating alcohol-seeking behavior (Bloodgood et al., 2021; Butelman et al., 2012; Haun et al., 2022; Karkhanis and Al-Hasani, 2020; Karpyak et al., 2013; Wee and Koob, 2010). In paradigms of chronic alcohol consumption and withdrawal in rodents, Pdyn mRNA increased across several brain regions that are implicated in stress and reward, including the CeA (Zhou et al., 2013), HYP (Barson and Leibowitz, 2016; Gustafsson et al., 2007), and NAc (Przewłocka et al., 1997). During acute withdrawal following alcohol self-administration and 4 months of chronic alcohol vapor exposure, Oprk1 mRNA expression was upregulated in the BNST in male Wistar rats (Erikson et al., 2018). Furthermore, in dependent animals, these molecular changes were accompanied by enhanced KOP signaling and functional impairments, including deficits in working memory that are reversed by KOP antagonism (Wei et al., 2022).

At the neurochemical level, alcohol exposure increases KOP sensitivity within mesolimbic reward circuits. Acute and repeated alcohol administration elevated DYN release and tissue content in the NAc, producing long-lasting adaptations that persisted into abstinence (Lindholm et al., 2000; Marinelli et al., 2006). In male macaques, chronic voluntary alcohol drinking enhanced KOP-mediated inhibition of dopamine release in the striatum, indicating increased sensitivity of KOP control over reward signaling (Siciliano et al., 2015).

Functionally, KOP agonists U50,488H and bremazocine reduced alcohol intake in male Lewis and Wistar rats (Lindholm et al., 2001; Nestby et al., 1999), and KOP antagonism increased alcohol consumption in male high alcohol-preferring Lewis rats, further underscoring the reward-dampening effects of DYN/KOP signaling. Lasting neuroadaptations of the DYN/KOP system may persist long after the termination of alcohol exposure, increasing its sensitivity to respond to future stress and in turn enhancing vulnerability to the reinstatement of alcohol-seeking behavior (Bruchas et al., 2010; Wee and Koob, 2010). Alcohol also directly altered KOP interactions with the plasma membrane lipid environment, while naltrexone counteracted these effects through both receptor- and membrane-dependent mechanisms, providing a mechanistic explanation for KOP involvement in AUD (Oasa et al., 2024).

Consistent with its role in alcohol reward, KOP activation broadly suppresses reward-related dopamine signaling across drugs of abuse. For example, the systemic administration of the KOP agonist salvinorin A elevated intracranial self-stimulation thresholds (Carlezon et al., 2006), and attenuated drug-induced dopamine release, indicating reduced reward sensitivity across substances through the suppression of dopamine transmission in the NAc and mesocortical projections to the PFC (Maisonneuve et al., 1994; Margolis et al., 2006; Shippenberg et al., 2001; Xi et al., 1998). Similarly, acute KOP activation by systemic salvinorin A and CI-977 (enadoline) administration lowered rewarding effects of intracranial self-stimulation of the medial forebrain bundle in male Wistar and Sprague-Dawley rats (Potter et al., 2011).

Consistent with evidence linking stress circuitry to alcohol dependence, the role of KOP signaling in reinforcing effects of alcohol varies as a function of stress and dependence (Koob, 2008). Models of stress-induced reinstatement show that heightened DYN/KOP activity can worsen stress and dysphoria, thereby increasing vulnerability to the reinstatement of alcohol-seeking behavior (Wee and Koob, 2010). Gillett et al. (2013) showed that systemic administration of norBNI reduced stress-induced anxiety-like behavior in male Wistar rats following chronic alcohol exposure (Gillett et al., 2013), supporting the idea that high DYN/KOP activity during withdrawal may facilitate the stress-induced reinstatement of alcohol-seeking behavior. Importantly, reviews indicate that DYN/KOP signaling exerts state-dependent effects on alcohol-related behavior by suppressing intake acutely while promoting negative affect and reinstatement vulnerability following dependence or stress (Anderson and Becker, 2017; Karkhanis and Al-Hasani, 2020; Pirino et al., 2023; Walker et al., 2012).

Acute treatment with KOP agonists generally suppresses alcohol intake, although the sustained, continuous infusion of a KOP agonist, enadoline, facilitated relapse-like drinking after abstinence in alcohol-experienced male Wistar rats (Hölter et al., 2000). Conversely, KOP antagonism preferentially attenuated withdrawal- and relapse-related drinking without suppressing baseline intake in dependent animals (Uhari-Väänänen et al., 2019; Walker and Koob, 2008), though it can increase unlimited-access alcohol intake in high-drinking male Long-Evans rats (Mitchell et al., 2005). More recently, KOP antagonism selectively reduced alcohol drinking in male and female Wistar rats with a history of alcohol dependence (Flores-Ramirez et al., 2024), highlighting the dependence-sensitive modulation of the DYN/KOP system.

Across species, KOP activation consistently dampens alcohol reward. In rodents (Logrip et al., 2009; Matsuzawa et al., 1999) and nonhuman primates (Cosgrove and Carroll, 2002), KOP agonists reduced alcohol self-administration and conditioned reward, whereas KOP antagonism can enhance reward under some conditions. Together, these findings indicate that the DYN/KOP system regulates alcohol reward and is recruited by stress to potentiate alcohol’s motivational value. Importantly, these effects vary across dependence states, stress contexts, and acute vs. sustained KOP activation, reconciling reports of both intake-suppressing and relapse-promoting outcomes.

Notably, emerging evidence indicates that KOP signaling and stress responsivity exhibit important sex-dependent differences that may influence alcohol-related behaviors. Preclinical work reports sex differences in KOP-mediated stress responses, affective behavior, and relapse vulnerability, with female rodents often showing heightened stress sensitivity and distinct behavioral responses to KOP modulation compared to males (Chartoff and Mavrikaki, 2015; Robles et al., 2014; Russell et al., 2014). These findings highlight sex as a critical biological variable in DYN/KOP function and underscore the need to delineate sex-dependent effects across dependence states and stress-related alcohol use.

The OX and DYN/KOP systems are widely distributed in the central nervous system (Watson et al., 1982) and implicated in the regulation of mood, motivation, and stress-related behaviors (Bruijnzeel, 2009; Tejeda et al., 2012), suggesting a viable therapeutic target to treat various neuropsychiatric disorders (Butelman et al., 2012; Knoll and Carlezon, 2010; Tejeda et al., 2012; Walker and Koob, 2008; Wee and Koob, 2010). Nearly all hypothalamic cells (94%) that express Hcrt mRNA also co-express Pdyn mRNA (Chou et al., 2001; Li & Van Den Pol, 2006), and the co-release and opposing effects of both peptides have been observed with electrical stimulation of the HYP (Li & Van Den Pol, 2006; Muschamp et al., 2014). However, they play opposing roles in cocaine self-administration, brain stimulation reward, impulsivity, and VTA neuron firing rate (Muschamp et al., 2014; Reeves et al., 2022; Shippenberg et al., 2001), suggesting that OX and DYN may interact in brain regions to which OX neurons project (Figure 1) and exert opposing, push-pull influences on downstream targets under specific circuit and behavioral conditions. In general, OX promotes arousal, reward seeking, and drug motivation (Lawrence et al., 2006), whereas DYN is linked to reduced reward sensitivity and enhanced stress-related aversion (Land et al., 2008; Bruchas et al., 2010).

At a cellular level, it was shown that OX depolarized target HYP neurons and increased firing, whereas DYN hyperpolarized and inhibited neuronal activity, with both opposing effects observed within the same neurons (Li & Van Den Pol, 2006). Electrophysiological and optogenetic studies also demonstrated that co-activation of OX and DYN signaling produced net-neutral effects on dopamine neuron firing, while selective blockade of OX1Rs or KOPs shifted this “balance” toward excitation or inhibition, respectively (Mohammadkhani et al., 2024; Muschamp et al., 2014). A similar effect was found in Pitx3-GFP mice, in which OXR and KOP signaling from the LH exerted opposing effects on VTA dopamine neuron firing, producing a functional counterbalance that regulates dopaminergic output (Baimel et al., 2017).

Here, the term “balance” is used conceptually to describe the relative influence of OXR- and KOP-sensitive signaling within a given circuit or physiological context. Importantly, some apparent oppositional effects attributed to DYN on OX transmission may also arise from indirect modulation via stress-related neuromodulators, including CRF (Li et al., 2010; Van’T Veer and Carlezon, 2013; Winsky-Sommerer et al., 2004), underscoring the need to distinguish other peptide interactions within the PVT. Together, the co-expression and opposing actions of OX and DYN have been central to the hypothesis that these systems are functionally antagonistic yet complementary in contributing to alcohol relapse, with effects that depend on stress, dependence, and circuit engagement (Farahbakhsh and Siciliano, 2026).

When exploring the consequence of chronic alcohol on OX/DYN functional outcomes, embryonic alcohol exposure in zebrafish increased OX neurons that lacked DYN co-expression relative to controls in the anterior HYP (Yasmin et al., 2023), creating an imbalance of OX that outweighed inhibitory effects of DYN on alcohol-seeking behavior. This imbalance, marked by a weakened DYN system, may promote heightened vulnerability to circuits that underlie alcohol use and relapse.

In agreement with this developmental finding, studies in adult Wistar rats demonstrated that OX-DYN interactions within the pPVT directly regulate drug-seeking behavior at both the cellular and behavioral levels (Matzeu and Martin-Fardon, 2018). The systemic administration of the OXR1 antagonist SB334867 in adult male Wistar rats increased intracranial self-stimulation thresholds that were driven by LH stimulation in male C57BL/6J mice, indicating lower reward sensitivity. KOP blockade with norBNI alone did not alter intracranial self-stimulation thresholds, but pretreatment with norBNI blocked the SB334867-induced elevation (Muschamp et al., 2014). These findings support our push-pull model in which OXR blockade unmasks DYN-mediated reward inhibition, while KOP blockade removes this inhibitory constraint and restores reward sensitivity, a mechanism that may extend to excessive alcohol motivation and reinstatement.

The pPVT exhibits heightened responsiveness to both chronic and acute stressors (Barson et al., 2020; Beck and Fibiger, 1995; Choi et al., 2019; Zhu et al., 2022). Barson et al. (2020) demonstrated preferential recruitment of the pPVT vs. the aPVT during stress-related states, with dense hypothalamic OX input (Barson et al., 2020). In male Sprague-Dawley rats, acute restraint stress following chronic intermittent cold stress selectively increased Fos expression in the pPVT relative to the aPVT (Bhatnagar and Dallman, 1998), while pPVT lesions enhanced anxiety-like behaviors, including defensive burying, after chronic restraint stress (Bhatnagar et al., 2003). Consistent with these findings, noxious mechanical stimulation (Bullitt, 1990) and food deprivation-induced stress (Timofeeva and Richard, 2001) elicited greater and earlier Fos activation in the pPVT compared with the aPVT, supporting a specialized role for the pPVT in stress-related processing.

The pPVT is increasingly seen as a hub that links signals from the HYP with stress-related brain circuits, highlighting its direct role in shaping stress responses (Hsu et al., 2014). Following chronic repeated restraint stress, the pPVT moderates plasma corticosterone responses, while leaving responses to acute stress unaffected (Jaferi et al., 2003). In parallel, glucocorticoid signaling in the pPVT was essential for HPA axis habituation to repeated or chronic stress, in which blocking glucocorticoid and mineralocorticoid receptors prevented habituation, whereas corticosterone implants enhanced it, without affecting acute stress responses (Jaferi and Bhatnagar, 2006). These data suggest that the pPVT robustly mediates stress responses after chronic or repeated stress exposure, and through its projections to the amygdala and stress-regulatory circuits (Zhao et al., 2024), may contribute to stress-driven alcohol-seeking behavior during dependence and abstinence (Barson et al., 2015; Barson et al., 2020; Hartmann and Pleil, 2021).

OX inputs to the pPVT arise primarily from neurons in the HYP (Kirouac et al., 2005; Li and Kirouac, 2008), serving as a bridge between hypothalamic homeostatic systems and subsequent thalamic and forebrain nodes that modulate stress responsivity and reward processing. Using a repeated swim stress paradigm in male Sprague-Dawley rats, Heydendael et al. (2011) demonstrated that OXR signaling in the pPVT is required for stress sensitization. OX1R blockade in the pPVT during repeated swim stress, but not immediately prior to a novel restraint stressor, prevented subsequent HPA axis activation and attenuated swim stress-induced increases in HYP Crh mRNA expression (Heydendael et al., 2011). This indicates that OXR signaling in the pPVT during repeated stress is necessary for the brain to respond to future stressors. Blocking OXR signaling prevents this stress-sensitization process. Overall, the literature underscores a significant role of pPVT-OX transmission that influences downstream stress circuits associated with stress sensitization and stress-biased motivational states, such as the amygdala and HYP (Barson et al., 2020; Bhatnagar et al., 2002; Flores-Ramirez et al., 2025; Hartmann and Pleil, 2021; Hsu et al., 2014).