Repeated use of opioids can lead to the development of analgesic tolerance and dependence. Additionally, chronic opioid exposure can cause a paradoxical emergence of heightened pain sensitivity to noxious stimuli, termed hyperalgesia, which may drive continued or escalated use of opioids to manage worsening pain symptoms. Opioid-induced hyperalgesia has traditionally been measured in rodents via reflex-based assays, including the von Frey method. To better model the cognitive/motivational dimension of pain in a state of opioid dependence and withdrawal, we employed a recently developed non-reflex-based method for measuring pain avoidance-like behavior in animals (mechanical conflict avoidance test). Adult male Wistar rats were administered an escalating dose regimen of morphine (opioid-dependent group) or repeated saline (control group). Morphine-dependent rats exhibited significantly greater avoidance of noxious stimuli during withdrawal. We next investigated individual relationships between pain avoidance-like behavior and alterations in protein phosphorylation in central motivation-related brain areas. We discovered that pain avoidance-like behavior was significantly correlated with alterations in phosphorylation status of protein kinases (ERK, CaMKII), transcription factors (CREB), presynaptic markers of neurotransmitter release (Synapsin), and the rate-limiting enzyme for dopamine synthesis (TH) across specific brain regions. Our findings suggest that alterations in phosphorylation events in specific brain centers may support cognitive/motivational responses to avoid pain.

The prefrontal cortex (PFC) represents and executes the highest forms of goal-directed behavior, and has thereby attained a central neuroanatomical position in most pathophysiological conceptualizations of motivational disorders, including alcohol use disorder (AUD). Excessive, intermittent exposure to alcohol produces an allostatic dysregulation of the hypothalamic-pituitary-adrenal (HPA) axis along with heightened forebrain glucocorticoid signaling that can damage PFC architecture and function. Negative affective states intimately associated with the transition to alcohol dependence result not only from a dysregulated HPA axis, but also from the inability of a damaged PFC to regulate subcortical stress and reinforcement centers, including the ventral striatum and amygdala. Several cognitive symptoms commonly associated with severe AUD, ranging from poor risk management to the cognitive/affective dimension of pain, are likely mediated by altered function of key anatomical elements that modulate PFC executive function, including contributions from the cingulate cortex and insula. Future therapeutic strategies for severe AUD should focus on attenuating the deleterious effects of excessive stress hormone activity on cognitive/affective and motivational behaviors gated by the PFC.

Background Nicotine use increases alcohol drinking, suggesting that the combination of these drugs may produce synergistic effects in activating reward circuitry. Alternatively, use of either of these drugs may facilitate the development of cross-tolerance to the other to promote intake escalation. Methods In the current study, adult male Wistar rats were chronically exposed to room air or chronic, intermittent nicotine vapor, which has been shown to produce symptoms of nicotine dependence as evidenced by elevated nicotine self-administration and a host of somatic and motivational withdrawal symptoms during withdrawal. We examined regional neuroadaptations in nicotine-experienced vs. non-experienced animals, focusing on changes in phosphorylation of the AMPA glutamate channel subunit GluA1 in reward-related brain regions since excitatory neuroadaptations are heavily implicated in both alcohol and nicotine addiction. Results During withdrawal, nicotine exposure and alcohol challenge (1g/kg) interactively produced neuroadaptations in GluA1 phosphorylation in a brain region-dependent manner. Alcohol robustly increased protein kinase A (PKA)-mediated phosphorylation of GluA1 at serine 845 in multiple regions. However, this neuroadaptation was largely absent in three areas (dorsomedial prefrontal cortex, dorsal striatum, and central amygdala) in nicotine-experienced animals. This interactive effect suggests a molecular tolerance to alcohol-stimulated phosphorylation of GluA1 in the context of nicotine dependence. Conclusions Nicotine may modify the rewarding or reinforcing effects of alcohol by altering glutamate signaling in a region-specific manner, thereby leading to increased drinking in heavy smokers.

Alcohol use disorder (AUD) is a chronic, relapsing psychiatric disease characterized by the emergence of negative emotional states and the development of motivational deficits that manifest during alcohol withdrawal. Accordingly, alcohol may be sought after and taken in excessive amounts to alleviate withdrawal-related symptoms. To develop more effective treatments for AUD, it is necessary to identify potential molecular targets that underlie the transition from initial alcohol use to alcohol dependence, and our previous work has implicated a role for potentiated glucocorticoid receptor (GR) signaling in this regard. As a key negative regulator of GR-mediated signaling, the current study first measured c-Jun N-terminal kinase (JNK) phosphorylation in animals following an acute alcohol challenge. We found that JNK phosphorylation (pJNK) was significantly increased in the hippocampus, frontal cortical regions, and striatum of adult male Wistar rats following alcohol challenge, indicating that initial alcohol exposure increases JNK activity across several brain regions. A separate group of adult male Wistar rats were made dependent via chronic, intermittent ethanol vapor exposure and were trained to self-administer alcohol. We found that alcohol-dependent animals consumed significantly more alcohol and escalated their drinking over time compared to non-dependent animals. We then measured alterations in JNK phosphorylation in this alcohol-dependent group during acute withdrawal and found that pJNK was selectively decreased in the dorsal hippocampus, dorsomedial prefrontal cortex, and cingulate cortex. These findings demonstrate that withdrawal from chronic alcohol exposure leads to region-specific deficits in JNK phosphorylation. JNK signaling dysregulation *

In contrast to their analgesic properties, excessive use of either alcohol or opioids produces a paradoxical emergence of heightened pain sensitivity to noxious stimuli, termed hyperalgesia, which may promote further drinking or use of opioids to manage worsening pain symptoms. Hyperalgesia has traditionally been measured in rodents via reflex‐based assays, including the von Frey method. To better model the cognitive/motivational dimension of pain in a state of alcohol/opioid dependence and withdrawal, we employed a recently developed non‐reflex‐based method for measuring pain avoidance‐like behavior in animals (Mechanical Conflict Avoidance test). Adult male Wistar rats were administered an escalating dose regimen of morphine (opioid‐dependent group) or repeated saline (control group). Morphine‐dependent rats exhibited significantly greater avoidance of noxious stimuli during withdrawal. Such pain avoidance‐like behavior exhibited a modest correlation with mechanical paw withdrawal thresholds as measured via the von Frey method (r=−0.4413, p=0.0452), indicating that the two behavioral assays measure overlapping but not entirely similar pain‐like conditions. We next investigated individual relationships between pain avoidance‐like behavior and alterations in protein phosphorylation in central motivation‐related brain areas. We discovered that pain avoidance‐like behavior was significantly correlated with alterations in phosphorylation status of protein kinases (ERK, CaMKII), transcription factors (CREB), presynaptic markers of neurotransmitter release (Synapsin), and the rate‐limiting enzyme for dopamine synthesis (TH) across specific brain regions. Separate groups of male Wistar rats were made dependent on alcohol via exposure to chronic, intermittent ethanol vapor and compared to air‐exposed (non‐dependent) controls. Here, alcohol‐dependent animals exhibited enhanced pain avoidance‐like behavior of shorter probe heights that were innocuous (i.e., not avoided) in non‐dependent animals, indicative of a state of allodynia. We are currently examining the neural correlates of pain avoidance in these groups to compare to our results in opioid‐dependent animals. Our findings suggest that alterations in phosphorylation events in specific brain centers may support cognitive/motivational responses to avoid pain, and that qualitatively distinct dimensions of pain avoidance‐like behavior (hyperalgesia vs. allodynia) may exist in opioid‐ vs. alcohol‐dependent animals.Support or Funding InformationNational Institute on Alcohol Abuse and Alcoholism (T32AA007577, ARP; R00AA020839, SE), LSUHSC School of Medicine start‐up funds.This abstract is from the Experimental Biology 2018 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.

No abstract