Probes for INS

We recently developed a rat model of incubation of methamphetamine craving after choice-based voluntary abstinence. Here, we studied the role of dorsolateral and dorsomedial striatum (DLS, DMS) in this incubation.We trained rats to self-administer palatable food pellets (6 days, 6-h/d) and methamphetamine (12 days, 6-h/d). We then assessed relapse to methamphetamine seeking under extinction conditions after 1 and 21 abstinence days. Between tests, the rats underwent voluntary abstinence (using a discrete choice procedure between methamphetamine and food; 20 trials/day) for 19 days. We used in situ hybridization to measure co-labeling of the activity marker Fos with Drd1 and Drd2 in DMS and DLS after the tests. Based on the in situ hybridization co-labeling results, we tested the causal role of DMS D1- and D2-family receptors, and DMS neuronal ensembles in 'incubated' methamphetamine seeking, using selective dopamine receptor antagonists (SCH39166 or raclopride) and the Daun02 chemogenetic inactivation procedure, respectively.Methamphetamine seeking was higher after 21 days of voluntary abstinence than after 1 day (incubation of methamphetamine craving). The 'incubated' response was associated with increased Fos expression in DMS but not DLS; Fos was co-labeled with both Drd1 and Drd2 DMS injections of SCH39166 or raclopride selectively decreased methamphetamine seeking after 21 abstinence days. In Fos-lacZ transgenic rats, selective inactivation of relapse test-activated Fos neurons in DMS on abstinence day 18 decreased incubated methamphetamine seeking on day 21.Results demonstrate a role of DMS dopamine D1 and D2-receptors in incubation of methamphetamine craving after voluntary abstinence and that DMS neuronal ensembles mediate this incubation.

SIGNIFICANCE STATEMENT:

In human addicts, abstinence is often self-imposed and relapse can be triggered by exposure to drug-associated cues that induce drug craving. We recently developed a rat model of incubation of methamphetamine craving after choice-based voluntary abstinence. Here, we used classical pharmacology, in situ hybridization, immunohistochemistry, and the Daun02 inactivation procedure to demonstrate a critical role of dorsomedial striatum neuronal ensembles in this new form of incubation of drug craving.

Background

Mu opioid receptors (MORs) are central to pain control, drug reward and addictive behaviors, but underlying circuit mechanisms have been poorly explored by genetic approaches. Here we investigate the contribution of MORs expressed in GABAergic forebrain neurons to major biological effects of opiates, and also challenge the canonical disinhibition model of opiate reward.

Methods

We used Dlx5/6-mediated recombination to create conditional Oprm1 mice in GABAergic forebrain neurons. We characterized the genetic deletion by histology, electrophysiology and microdialysis, probed neuronal activation by c-Fos immunohistochemistry and resting state-functional magnetic resonance imaging, and investigated main behavioral responses to opiates, including motivation to obtain heroin and palatable food.

Results

Mutant mice showed MOR transcript deletion mainly in the striatum. In the ventral tegmental area (VTA), local MOR activity was intact, and reduced activity was only observed at the level of striatonigral afferents. Heroin-induced neuronal activation was modified at both sites, and whole-brain functional networks were altered in live animals. Morphine analgesia was not altered, neither was physical dependence to chronic morphine. In contrast, locomotor effects of heroin were abolished, and heroin-induced catalepsy was increased. Place preference to heroin was not modified, but remarkably, motivation to obtain heroin and palatable food was enhanced in operant self-administration procedures.

Conclusions

Our study reveals dissociable MOR functions across mesocorticolimbic networks. Thus beyond a well-established role in reward processing, operating at the level of local VTA neurons, MORs also moderate motivation for appetitive stimuli within forebrain circuits that drive motivated behaviors.

Motor tics are sudden, repetitive, involuntary movements representing the hallmark behaviors of the neurodevelopmental disease Tourette's syndrome (TS). The primary cause of TS remains unclear. The initial observation that dopaminergic antagonists alleviate tics led to the development of a dopaminergic theory of TS etiology which is supported by post mortem and in vivo studies indicating that non-physiological activation of the striatum could generate tics. The striatum controls movement execution through the balanced activity of dopamine receptor D1 and D2-expressing medium spiny neurons of the direct and indirect pathway, respectively. Different neurotransmitters can activate or repress striatal activity and among them, dopamine plays a major role. In this study we introduced a chronic dopaminergic alteration in juvenile rats, in order to modify the delicate balance between direct and indirect pathway. This manipulation was done in the dorsal striatum, that had been associated with tic-like movements generation in animal models. The results were movements resembling tics, which were categorized and scored according to a newly developed rating scale and were reduced by clonidine and riluzole treatment. Finally, post mortem analyses revealed altered RNA expression of dopaminergic receptors D1 and D2, suggesting an imbalanced dopaminergic regulation of medium spiny neuron activity as being causally related to the observed phenotype.

Major depressive disorder (MDD) patients display a common but often variable set of symptoms making successful, sustained treatment difficult to achieve. Separate depressive symptoms may be encoded by differential changes in distinct circuits in the brain, yet how discrete circuits underlie behavioral subsets of depression and how they adapt in response to stress has not been addressed. We identify two discrete circuits of parvalbumin-positive (PV) neurons in the ventral pallidum (VP) projecting to either the lateral habenula or ventral tegmental area contributing to depression. We find that these populations undergo different electrophysiological adaptations in response to social defeat stress, which are normalized by antidepressant treatment. Furthermore, manipulation of each population mediates either social withdrawal or behavioral despair, but not both. We propose that distinct components of the VP PV circuit can subserve related, yet separate depressive-like phenotypes in mice, which could ultimately provide a platform for symptom-specific treatments of depression.