Metabotropic glutamate group II receptor activation in the ventrolateral dorsal striatum suppresses incentive motivation for cocaine in rats

RATIONALE

After a history of intermittent cocaine intake, rats develop patterns of drug use characteristic of substance use disorder. The dorsal striatum is involved in the increased pursuit of cocaine after intermittent drug self-administration experience. Within the dorsal striatum, chronic cocaine use changes metabotropic glutamate type II receptor (mGlu_2/3) density and function.

OBJECTIVES

We examined the extent to which activity at Glu_2/3 receptors mediates responding for cocaine after intermittent cocaine use.

METHODS

Male (n = 11) and female (n = 10) Wistar rats self-administered 0.25 mg/kg/infusion cocaine during 10 daily intermittent access (IntA) sessions (5 min ON/25 min OFF, for 5 h/session). We then examined the effects of microinjections of the mGlu_2/3 receptor agonist LY379268 (0, 1, and 3 µg/hemisphere) into the ventrolateral part of the dorsal striatum on cocaine self-administration under a progressive ratio schedule of reinforcement.

RESULTS

Across 10 IntA sessions, the sexes showed similar levels of cocaine intake. In females only, locomotion significantly increased over sessions, suggesting that female rats developed psychomotor sensitization to self-administered cocaine. After 10 IntA sessions, intra-dorsal striatum LY379268 significantly reduced breakpoints achieved for cocaine, active lever presses, and cocaine infusions earned under progressive ratio. LY379268 had no effects on locomotion or inactive lever presses, indicating no motor effects.

CONCLUSIONS

These results suggest that mGlu_2/3 receptor activation in the ventrolateral dorsal striatum suppresses incentive motivation for cocaine, and this holds promise for new treatments to manage substance use disorder.

Neural correlates of alcohol use disorder severity among nontreatment-seeking heavy drinkers: An examination of the incentive salience and negative emotionality domains of the alcohol and addiction research domain criteria

BACKGROUND

The Alcohol and Addiction Research Domain Criteria (AARDoC) propose that alcohol use disorder is associated with neural dysfunction in three primary domains: incentive salience, negative emotionality, and executive function. Prior studies in heavy drinking samples have examined brain activation changes associated with alcohol and negative affect cues, representing the incentive salience and negative emotionality domains, respectively. Yet studies examining such cue-induced changes in functional connectivity (FC) are relatively sparse.

METHODS

Nontreatment-seeking heavy drinking adults (N = 149, 56.0% male, 48.6% non-white, mean age 34.8 years (SD = 10.0)) underwent functional magnetic resonance imaging during presentation of alcohol, negative, and neutral pictures. We focused on FC changes involving the nucleus accumbens and amygdala in addition to activation and FC correlations with self-reported AUD severity.

RESULTS

For alcohol cues versus neutral cues, we observed accumbens FC changes in the cerebellum and prefrontal cortex (PFC), and amygdala FC changes with occipital, parietal, and hippocampal regions. AUD severity correlated positively with activation in the cerebellum (p < 0.05), accumbens FC in the cingulate gyri, somatosensory gyri, and cerebellum (p < 0.05), and with amygdala FC in the PFC and inferior parietal lobule (p < 0.05) for alcohol cues versus neutral cues. For negative cues versus neutral cues, we observed accumbens FC changes in the lateral temporal, occipital, and parietal regions, and amygdala FC changes in the fusiform and lingual gyri (p < 0.05).

CONCLUSIONS

The present findings provide empirical support for the AARDoC domains of incentive salience and negative emotionality and indicate that AUD severity is associated with salience and response control for reward cues. When covarying for differences in nonalcohol substance use and mood disorder diagnoses, AUD severity was also associated with emotional reactivity for negative cues.

Interactive Effects of Naturalistic Drinking Context and Alcohol Sensitivity on Neural Alcohol Cue-Reactivity Responses

BACKGROUND

Considerable evidence indicates that a low level of subjective response to alcohol's acute effects (i.e., low sensitivity) is associated with enhanced risk for alcohol use disorder (AUD). Recent work suggests that the highest risk response profile consists of blunted sensitivity to alcohol's sedation-like effects, coupled with enhanced sensitivity to alcohol's stimulation-like effects (i.e., differential sensitivity). A largely separate body of work indicates that enhanced reactivity to alcohol-related cues is associated with increased AUD risk.

AIMS

The current research examined the extent to which variability in alcohol response phenotypes is associated with enhanced P3 event-related potential (ERP) responses to alcohol-related pictures (ACR-P3), and whether this reactivity varies according to depicted drinking contexts.

METHODS

Eighty young adults (aged 18 to 33 years) completed a self-report measure of alcohol sensitivity (the Alcohol Sensitivity Questionnaire) and viewed images depicting drinking in naturalistic contexts, alcohol and nonalcohol beverages in isolation (devoid of naturalistic drinking context), and neutral nonbeverage control images while ERPs were recorded.

RESULTS

Results indicated that blunted sensitivity to alcohol's sedative-like effects was differentially associated with enhanced ACR-P3 but reduced P3 reactivity to nonalcohol cues. Variation in sensitivity to alcohol's stimulant-like effects was not associated with differential ACR-P3. Contrary to predictions, these effects were not potentiated by drinking contexts.

CONCLUSIONS

The current results replicate and extend previous work linking low alcohol sensitivity with enhanced incentive salience for alcohol-related cues and suggest that cues depicting drinking contexts are less likely to differentiate high-risk from low-risk drinkers.