Profiling prefrontal cortex protein expression in rats exhibiting an incubation of cocaine craving following short-access self-administration procedures

AMPA receptor activation within the prelimbic cortex is necessary for incubated cocaine-craving

The incubation of craving is a behavioral phenomenon in which cue-elicited craving increases during a period of drug abstinence. Incubated cocaine-craving is associated with increased extracellular glutamate within the medial prefrontal cortex (mPFC) and this release, particularly within the prelimbic (PL) subregion, is necessary for incubated cocaine-craving. A potential candidate mediating these incubation-driving effects of glutamate release within the PL are alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid receptors (AMPARs). To investigate the role of mPFC AMPARs in incubated craving, male and female Sprague-Dawley rats were trained to self-administer cocaine for 6 h/day for 10 consecutive days. Either during early or later withdrawal, rats were infused intra-PL with the AMPAR antagonist NBQX (0 or 1 μg/0.5 μl per side), followed by 30-min tests for cue-reinforced responding. Immunoblotting was also conducted to relate the expression of incubated cocaine- and sucrose-craving to AMPAR subunit expression within mPFC subregions. Intra-PL NBQX blocked incubated craving expressed in late, but not early, withdrawal. No incubation-related changes in AMPAR subunit expression were detected within the PL or IL of rats of either sex and no estrus-associated changes in subunit expression were detected in female rats exhibiting incubated cocaine-craving. In contrast, elevated GluA1 expression was observed within the IL of male rats exhibiting an incubation of sucrose-craving. Together, these findings indicate a necessary role for AMPARs within the PL in driving incubated cocaine-craving and suggest that AMPARs located within the IL may be involved also in sucrose-craving selectively in males.

Cross-Sensitization between Binge Eating and Binge Drinking in a Novel C57BL/6NJ Murine Model of Disease Comorbidity Requires PDE4B Activation

There is a high rate of comorbidity between binge eating (BE) and binge drinking (BD) behaviors, suggesting a common neuropathology. Recently, phosphodiesterase 4B (PDE4B) was identified as a pleiotropic gene associated with comorbid alcohol use disorder (AUD) and anorexia nervosa with BE in a genome-wide association study, implicating PDE4B as a potential contributor to shared genetic risk between these disorders. Here, we developed a novel mouse model of comorbid BE and BD in C57BL/6NJ mice in which mice underwent 10 d of BE, followed by 10 d of BD. Females exhibited cross-sensitization from BE to BD, which was apparent on the first day of ethanol access, whereas cross-sensitization emerged in males over multiple trials of BD. Accordingly immunoblotting of the nucleus accumbens tissue indicated a female-selective increase in PDE4B protein expression that was apparent on both the first and last day of BD in mice with a prior BE history. Acute pretreatment with the selective PDE4B inhibitor A33 (1.0 mg/kg) reduced the expression of cross-sensitization to BD in females on Day 1, and this effect was maintained during a 5 d A33 treatment regimen. The 5 d A33 treatment regimen also reduced expression of cross-sensitization to BD that had emerged in males over repeated sessions. These results provide preclinical, functional validation of PDE4B as a driver of food-ethanol cross-sensitization in a novel model for BE and BD comorbidity and support PDE4B in the shared genetic risk for these behavioral pathologies and as a target for pharmacotherapeutic intervention in comorbid AUD and BE behaviors.

Replication and extension of the subregion selectivity of glutamate-related changes within the nucleus accumbens associated with the incubation of cocaine-craving

Cue-elicited drug-seeking behavior intensifies with the passage of time during withdrawal from drug taking and this "incubation of cocaine-craving" involves alterations in nucleus accumbens (NA) glutamate transmission. Here, we employed a combination of in vivo microdialysis and immunoblotting approaches to further examine changes in biochemical indices of glutamate transmission within NA subregions that accompany the incubation of cocaine-craving exhibited by male rats with a 10-day history of 6-h access to intravenous cocaine (0.25 mg/infusion). Immunoblotting on whole cell lysates from the core subregion (NAc core) revealed interactions between cocaine self-administration history, withdrawal and drug cue re-exposure for Homer2a/b, mGlu1, and GluN2b expression, as well as indices of Akt and ERK activity. With the exception of PKCε phosphorylation, most protein changes within the shell subregion (NAc shell) depended on drug cue re-exposure and cocaine history rather than varying in a consistent time-dependent manner. Reduced basal extracellular glutamate content was apparent only in the NAc core of cocaine-experienced rats during protracted (30 days) withdrawal and this was accompanied by a markedly blunted capacity of the mGlu1/5 agonist DHPG to elevate glutamate levels within this subregion. Finally, over-expressing neither Homer1c nor Homer2b within the NAc core during protracted cocaine withdrawal altered the magnitude of cue-elicited responding, its extinction or cocaine-primed reinstatement of drug-seeking behavior. The present findings are consistent with the extant literature implicating changes in Group 1 mGlu receptor function within the NAc core subregion as central to incubated cocaine-craving and provide further evidence against a major role for Homer proteins in gating incubated cocaine-craving. Further, our results provide novel correlational evidence implicating elevated Akt and blunted ERK activity within the NAc core as potential contributors to the expression of incubated cocaine-craving, worthy of future investigation.

Biochemical changes precede affective and cognitive anomalies in aging adult C57BL/6J mice with a prior history of adolescent alcohol binge-drinking

The early initiation of binge-drinking and biological sex are critical risk factors for the development of affective disturbances and cognitive decline, as well as neurodegenerative diseases including Alzheimer's disease. Further, a history of excessive alcohol consumption alters normal age-related changes in the pattern of protein expression in the brain, which may relate to an acceleration of cognitive decline. Here, we aimed to disentangle the interrelation between a history of binge-drinking during adolescence, biological sex and normal aging on the manifestation of negative affect, cognitive decline and associated biochemical pathology. To this end, adolescent male and female C57BL/6J mice (PND 28-29) underwent 30 days of alcohol binge-drinking using a modified drinking-in-the-dark (DID) paradigm. Then, mice were assayed for negative affect, sensorimotor gating and cognition at three developmental stages during adulthood-mature adulthood (6 months), pre-middle age (9 months) and middle age (12 months). Behavioural testing was then followed by immunoblotting to index the protein expression of glutamate receptors, neuropathological markers [Tau, p (Thr217)-Tau, p (Ser396)-Tau, BACE, APP, Aβ], as well as ERK activation within the entorhinal cortex, prefrontal cortex and amygdala. Across this age span, we detected only a few age-related changes in our measures of negative affect or spatial learning/memory in the Morris water maze and all of these changes were sex-specific. Prior adolescent binge-drinking impaired behaviour only during reversal learning in 9-month-old females and during radial arm maze testing in 12-month-old females. In contrast to behaviour, we detected a large number of protein changes related to prior binge-drinking history, several of which manifested as early as 6 months of age, with the prefrontal cortex particularly affected at this earlier age. While 6-month-old mice exhibited relatively few alcohol-related protein changes within the entorhinal cortex and amygdala, the number of alcohol-related protein changes within the entorhinal cortex increased with age, while the 12-month-old mice exhibited the largest number of protein changes within the amygdala. Approximately a third of the alcohol-related protein changes were sex-selective. Taken together, the results of our longitudinal study using a murine model of binge-drinking indicate that a prior history of heavy alcohol consumption, beginning in adolescence, is sufficient to induce what we presume to be latent changes in protein indices of cellular activity, glutamate transmission and neuropathology within key brain regions governing cognition, executive function and emotion that appear to precede the onset of robust behavioural signs of dysregulated affect and cognitive impairment.

Neuropharmacological Evidence Implicating Drug-Induced Glutamate Receptor Dysfunction in Affective and Cognitive Sequelae of Subchronic Methamphetamine Self-Administration in Mice

Methamphetamine (MA) is a highly addictive drug, and MA use disorder is often comorbid with anxiety and cognitive impairment. These comorbid conditions are theorized to reflect glutamate-related neurotoxicity within the frontal cortical regions. However, our prior studies of MA-sensitized mice indicate that subchronic, behaviorally non-contingent MA treatment is sufficient to dysregulate glutamate transmission in mouse brain. Here, we extend this prior work to a mouse model of high-dose oral MA self-administration (0.8, 1.6, or 3.2 g/L; 1 h sessions × 7 days) and show that while female C57BL/6J mice consumed more MA than males, MA-experienced mice of both sexes exhibited some signs of anxiety-like behavior in a behavioral test battery, although not all effects were concentration-dependent. No MA effects were detected for our measures of visually cued spatial navigation, spatial learning, or memory in the Morris water maze; however, females with a history of 3.2 g/L MA exhibited reversal-learning deficits in this task, and mice with a history of 1.6 g/L MA committed more working-memory incorrect errors and relied upon a non-spatial navigation strategy during the radial-arm maze testing. Relative to naïve controls, MA-experienced mice exhibited several changes in the expression of certain glutamate receptor-related proteins and their downstream effectors within the ventral and dorsal areas of the prefrontal cortex, the hippocampus, and the amygdala, many of which were sex-selective. Systemic pretreatment with the mGlu1-negative allosteric modulator JNJ 162596858 reversed the anxiety-like behavior expressed by MA-experienced mice in the marble-burying test, while systemic pretreatment with NMDA or the NMDA antagonist MK-801 bi-directionally affected the MA-induced reversal-learning deficit. Taken together, these data indicate that a relatively brief history of oral MA is sufficient to induce some signs of anxiety-like behavior and cognitive dysfunction during early withdrawal that reflect, at least in part, MA-induced changes in the corticolimbic expression of certain glutamate receptor subtypes of potential relevance to treating symptoms of MA use disorder.

Alcohol-drinking during later life by C57BL/6J mice induces sex- and age-dependent changes in hippocampal and prefrontal cortex expression of glutamate receptors and neuropathology markers

Heavy drinking can induce early-onset dementia and increase the likelihood of the progression and severity of Alzheimer's Disease and related dementias (ADRD). Recently, we showed that alcohol-drinking by mature adult C57BL/6J mice induces more signs of cognitive impairment in females versus males without worsening age-related cognitive decline in aged mice. Here, we immunoblotted for glutamate receptors and protein markers of ADRD-related neuropathology within the hippocampus and prefrontal cortex (PFC) of these mice after three weeks of alcohol withdrawal to determine protein correlates of alcohol-induced cognitive decline. Irrespective of alcohol history, age-related changes in protein expression included a male-specific decline in hippocampal glutamate receptors and an increase in the expression of a beta-site amyloid precursor protein cleaving enzyme (BACE) isoform in the PFC as well as a sex-independent increase in hippocampal amyloid precursor protein. Alcohol-drinking was associated with altered expression of glutamate receptors in the hippocampus in a sex-dependent manner, while all glutamate receptor proteins exhibited significant alcohol-related increases in the PFC of both sexes. Expression of BACE isoforms and phosphorylated tau varied in the PFC and hippocampus based on age, sex, and drinking history. The results of this study indicate that withdrawal from a history of alcohol-drinking during later life induces sex- and age-selective effects on glutamate receptor expression and protein markers of ADRD-related neuropathology within the hippocampus and PFC of potential relevance to the etiology, treatment and prevention of alcohol-induced dementia and Alzheimer's Disease.