Biology subjects

Fox, L. D.

Publications and source records attributed to Fox, L. D..

3 recordsLinked to original sources

bioRxiv2025

Projection-defined ventral tegmental area neurons exhibit distinct fentanyl-induced molecular and functional adaptations that differentially support drug-context associations

RationaleSynthetic opioids like fentanyl are contributing to unprecedented overdose rates, yet the neural circuitry underlying fentanyl-associated behaviors remains poorly understood. The ventral tegmental area (VTA) projects to both the nucleus accumbens (NAc) and prefrontal cortex (PFC), forming distinct pathways that are implicated in drug-cue associations, though their specific roles in fentanyl-context encoding are not well defined. ObjectivesThis study aimed to determine how VTA-NAc and VTA-PFC circuits contribute to fentanyl-context associations, and to assess the role of downstream dopamine receptor signaling in fentanyl context-seeking. MethodsMale and female mice underwent fentanyl conditioned place preference (CPP; 0.2 mg/kg). We locally inhibited dopamine D1 or D2 receptors in NAc or PFC during CPP expression. We used fiber photometry calcium imaging to measure activity in VTA-NAc and VTA-PFC projection neurons, and chemogenetic inhibition to suppress activity during CPP expression. ResultsFentanyl CPP expression was attenuated by blocking D1 but not D2 receptors in PFC, and D2 but not D1 receptors in NAc. We found both VTA-NAc and VTA-PFC exhibited increased calcium activity during fentanyl exposure and during entries to the fentanyl-paired context. We further identified a functional role for VTA-NAc, as chemogenetic inhibition of VTA-NAc, but not VTA-PFC, reduced fentanyl context-seeking. ConclusionsWhile both VTA-NAc and VTA-PFC pathways are recruited by fentanyl exposure, fentanyl context-seeking relies on different downstream dopamine receptors in NAc vs PFC. Further, activity in VTA-NAc functionally supports the expression of fentanyl CPP. Together, these findings indicate that VTA circuits differentially contribute to fentanyl context-seeking.

neuroscience↗

bioRxiv2025

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-cre120Mxu 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 naive mice, we found Drd1-cre120Mxu mice have elevated D1 receptor expression in NAc, alongside increased expression of MSN marker genes Chrm4 and Penk. We show Drd1-cre120Mxu 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-cre120Mxu mice. Conversely, chemogenetic stimulation of 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.

neuroscience↗

bioRxiv2023

Transcriptional signatures of fentanyl use in the mouse ventral tegmental area

Synthetic opioids such as fentanyl contribute to the vast majority of opioid-related overdose deaths, but fentanyl use remains broadly understudied. Like other substances with misuse potential, opioids cause lasting molecular adaptations to brain reward circuits, including neurons in the ventral tegmental area (VTA). The VTA contains numerous cell types that play diverse roles in opioid use and relapse, however it is unknown how fentanyl experience alters the transcriptional landscape in specific subtypes. Here, we performed single nuclei RNA sequencing to study transcriptional programs in fentanyl experienced mice. Male and female C57/BL6 mice self-administered intravenous fentanyl (1.5 {micro}g/kg/infusion) or saline for 10 days. After 24 hr abstinence, VTA nuclei were isolated and prepared for sequencing on the 10X platform. We identified different patterns of gene expression across cell types. In dopamine neurons, we found enrichment of genes involved in growth hormone signaling. In dopamine-glutamate-GABA combinatorial neurons, and some GABA neurons, we found enrichment of genes involved in Pi3k-Akt signaling. In glutamate neurons, we found enrichment of genes involved in cholinergic signaling. We identified transcriptional regulators for the differentially expressed genes in each neuron cluster, including downregulation of transcriptional repressor Bcl6, and upregulation of Wnt signaling partner Tcf4. We also compared the fentanyl-induced gene expression changes identified in mouse VTA with a published rat dataset in bulk VTA, and found overlap in genes related to GABAergic signaling and extracellular matrix interaction. Together, we provide a comprehensive picture of how fentanyl self-administration alters the transcriptional landscape of the mouse VTA, that serves for the foundation for future mechanistic studies.

neuroscience↗