A subset of dopamine receptor-expressing neurons in the nucleus accumbens controls feeding and energy homeostasis

A Drd1-cre mouse line with nucleus accumbens gene dysregulation exhibits blunted fentanyl seeking

The synthetic opioid fentanyl remains abundant in the illicit drug supply, contributing to tens of thousands of overdose deaths every year. Despite this, the neurobiological effects of fentanyl use remain largely understudied. The nucleus accumbens (NAc) is a central locus promoting persistent drug use and relapse, largely dependent on activity of dopamine D1 receptors. NAc D1 receptor-expressing medium spiny neurons (D1-MSNs) undergo molecular and physiological neuroadaptations in response to chronic fentanyl that may promote relapse. Here, we obtained Drd1-cre120Mxu mice to investigate D1-dependent mechanisms of fentanyl relapse. We serendipitously discovered this mouse line has reduced fentanyl seeking, despite similar intravenous fentanyl self-administration, similar sucrose self-administration and seeking, and greater fentanyl-induced locomotion compared to wildtype counterparts. We found drug-naïve Drd1-cre120Mxu mice have elevated D1 receptor expression in NAc and increased sensitivity to the D1 receptor agonist SKF-38393. After fentanyl self-administration, Drd1-cre120Mxu mice exhibit divergent expression of MSN markers, opioid receptors, glutamate receptor subunits, and TrkB which may underly their blunted fentanyl seeking. Finally, we show fentanyl-related behavior is unaltered by chemogenetic manipulation of NAc core D1-MSNs in Drd1-cre120Mxu mice. Conversely, chemogenetic stimulation of ventral mesencephalon-projecting NAc core MSNs (putative D1-MSNs) in wildtype mice recapitulated the blunted fentanyl seeking of Drd1-cre120Mxu mice, supporting a role for aberrant D1-MSN signaling in this behavior. Together, our data uncover alterations in NAc gene expression and function with implications for susceptibility and resistance to developing fentanyl use disorder.

A molecularly defined mPFC-BLA circuit specifically regulates social novelty preference

Social novelty preference is an important aspect of social interaction for evaluating new threats and opportunities for survival, but the underlying neuronal mechanism remains unclear. Here, we identify a molecularly defined medial prefrontal cortex (mPFC) excitatory neuron subtype, located in layer 5 expressing Il1rapl2, which is highly associated with social deficit disorders in genome-wide association studies and might be responsible for regulating social novelty preference. Using an Il1rapl2-Cre mouse line, we show that chemogenetic activation of the mPFC Il1rapl2-expressing neurons impairs social novelty preference but with little effect on sociability. In addition, fiber photometry recording indicates that this neuron subtype is inhibited when mice interact with novel but not with familiar mice. Furthermore, viral tracing and terminal manipulation reveal that basolateral amygdala (BLA)-projecting Il1rapl2+ neurons mediate the social novelty preference. Thus, our study uncovers a molecularly defined mPFC-BLA circuit that specifically regulates social novelty preference, highlighting that specific neuron subtypes and circuits could modulate distinct aspects of social behaviors.

Opponent control of reinforcement by striatal dopamine and serotonin

The neuromodulators dopamine (DA) and serotonin (5-hydroxytryptamine; 5HT) powerfully regulate associative learning1-8. Similarities in the activity and connectivity of these neuromodulatory systems have inspired competing models of how DA and 5HT interact to drive the formation of new associations9-14. However, these hypotheses have not been tested directly because it has not been possible to interrogate and manipulate multiple neuromodulatory systems in a single subject. Here we establish a mouse model that enables simultaneous genetic access to the brain's DA and 5HT neurons. Anterograde tracing revealed the nucleus accumbens (NAc) to be a putative hotspot for the integration of convergent DA and 5HT signals. Simultaneous recording of DA and 5HT axon activity, together with genetically encoded DA and 5HT sensor recordings, revealed that rewards increase DA signalling and decrease 5HT signalling in the NAc. Optogenetically dampening DA or 5HT reward responses individually produced modest behavioural deficits in an appetitive conditioning task, while blunting both signals together profoundly disrupted learning and reinforcement. Optogenetically reproducing DA and 5HT reward responses together was sufficient to drive the acquisition of new associations and supported reinforcement more potently than either manipulation did alone. Together, these results demonstrate that striatal DA and 5HT signals shape learning by exerting opponent control of reinforcement.

A Drd1-cre mouse line with nucleus accumbens gene dysregulation exhibits blunted fentanyl seeking

The synthetic opioid fentanyl remains abundant in the illicit drug supply, contributing to tens of thousands of overdose deaths every year. Despite this, the neurobiological effects of fentanyl use remain largely understudied. The nucleus accumbens (NAc) is a central locus promoting persistent drug use and relapse, largely dependent on activity of dopamine D1 receptors. NAc D1 receptor-expressing medium spiny neurons (D1-MSNs) undergo molecular and physiological adaptations that contribute to negative affect during fentanyl abstinence, but whether these neuroadaptations also promote fentanyl relapse is unclear. Here, we obtained Drd1-cre 120Mxu mice to investigate D1-dependent mechanisms of fentanyl relapse. We serendipitously discovered this mouse line is resistant to fentanyl seeking, despite similar intravenous fentanyl self-administration, and greater fentanyl-induced locomotion, compared to wildtype counterparts. In drug naïve mice, we found Drd1-cre 120Mxu mice have elevated D1 receptor expression in NAc, alongside increased expression of MSN marker genes Chrm4 and Penk . We show Drd1-cre 120Mxu mice have increased sensitivity to the D1 receptor agonist SKF-38393, and exhibit divergent expression of MSN markers, opioid receptors, glutamate receptor subunits, and TrkB after fentanyl self-administration that may underly blunted fentanyl seeking. Finally, we show fentanyl-related behavior is unaltered by chemogenetic manipulation of D1-MSNs in Drd1-cre 120Mxu mice. Conversely, chemogenetic stimulation of putative D1-MSNs in wildtype mice recapitulated the blunted fentanyl seeking of Drd1-cre 120Mxu mice, supporting a role for aberrant D1-MSN signaling in this behavior. Together, our data uncover alterations in NAc gene expression and function with implications for susceptibility and resistance to developing fentanyl use disorder.

Corrigendum: The nucleus accumbens shell: a neural hub at the interface of homeostatic and hedonic feeding

[This corrects the article DOI: 10.3389/fnins.2024.1437210.].