Transcriptome profiling of the ventral pallidum reveals a role for pallido-thalamic neurons in cocaine reward

Abstract

Psychostimulant exposure alters the activity of ventral pallidum (VP) projection-neurons.However, the molecular underpinnings of these circuit dysfunctions are unclear. We used RNAsequencing to reveal alterations in the transcriptional landscape of the VP that are induced by cocaine self-administration in mice. We then probed gene expression in select VP neuronal subpopulations to isolate a circuit associated with cocaine intake. Finally, we used both overexpression and CRISPR-mediated knockdown to test the role of a gene target on cocainemediated behaviors as well as dendritic spine density. Our results showed that a large proportion (55%) of genes associated with structural plasticity were changed 24 hours following cocaine intake. Among them, the transcription factor Nr4a1 (Nuclear receptor subfamily 4, group A, member 1, or Nur77) showed high expression levels. We found that the VP to mediodorsal thalamus (VPàMDT) projection neurons specifically were recapitulating this increase in Nr4a1 expression. Overexpressing Nr4a1 in VPàMDT neurons enhanced drug-seeking and druginduced reinstatement, while Nr4a1 knock down prevented self-administration acquisition and subsequent cocaine-mediated behaviors. Moreover, we showed that Nr4a1 negatively regulated spine dynamics in this specific cell subpopulation. Together, our study identifies for the first time the transcriptional mechanisms occurring in VP in drug exposure. Our study provides further understanding on the role of Nr4a1 in cocaine-related behaviors and identifies the crucial role of the VPàMDT circuit in drug intake and relapse-like behaviors.. CC-BY-NC-ND 4.0 International license available under a was not certified by peer review) is the author/funder, who has granted bioRxiv a license to display the preprint in perpetuity. It is made

Ventral pallidal regulation of motivated behaviors and reinforcement

“…The majority (~74%) of VP neurons are GABAergic (VP GABA ) and this cell group can be further partitioned into multiple subpopulations (Faget et al, 2018 ; Heinsbroek et al, 2020 ). One subpopulation of VP GABA neurons expresses the opioid neuropeptide precursor pro-enkephalin (Penk; VP Penk ) and projects to the VTA, MD and the striatum (Kalivas et al, 1993 ; Churchill and Kalivas, 1994 ; Engeln et al, 2022 ). In the GP, neurons expressing Penk represent a functionally distinct subpopulation of GABAergic cells (Mallet et al, 2012 ), that co-express the transcription factor Neuronal Per-Arnt-Sim domain 1 (Npas1) and are preferentially innervated by striatal D1-MSNs (Abdi et al, 2015 ; Cui et al, 2021a ).…”

“…This may explain some discrepancies in the literature between single cell axonal reconstruction studies that show dense collateralization of VP neurons and retrograde tracing studies that overall show low levels of overlap in the innervation of multiple structures by VP neurons (Tripathi et al, 2013 ; Leung and Balleine, 2015 ; Prasad and McNally, 2016 ; Bernat et al, 2021 ). Nonetheless, major differences have been reported in the electrophysiological properties, afferent innervation, and gene expression of VP neurons based on their innervation of downstream structures (Knowland et al, 2017 ; Bernat et al, 2021 ; Pribiag et al, 2021 ; Engeln et al, 2022 ). Thus, although VP neurons heavily collateralize, they can be functionally distinguished by their main projection target.…”

“…Interfering with the functioning of a NAshell-vmVP-MD circuit blocks the capacity of incentive conditioned stimuli to drive reward-seeking during Pavlovian-instrumental transfer (Leung and Balleine, 2013 , 2015 ). Furthermore, genetic knockout of the Nuclear receptor family 4a1 transcription factor (Nr4a1) in VP-MD projections disrupts the acquisition of cocaine self-administration (Engeln et al, 2022 ). However, while the VP-MD projection is critical for new reward learning, established reward-seeking behaviors may not require activity in the VP-MD circuit, since pharmacological inhibition of the MD does not impact relapse to cocaine-seeking (McFarland and Kalivas, 2001 ).…”

“…In addition to synaptic changes, drug exposure also produces cell- and pathway-specific changes in the intrinsic excitability and transcriptome of VP neurons (Pribiag et al, 2021 ; Engeln et al, 2022 ). Cocaine self-administration alters the expression of a number of genes implicated in neuronal excitability, neurotransmission, and functional and structural plasticity that share regulation by Nr4a1.…”

“…Interestingly, pathway-specific VP-MD knock-out of Nr4a1 blocked the acquisition of cocaine self-administration, which supports the notion that VP-MD projections are crucial for reward learning. Cocaine also increased spine density on VP-MD neurons, an effect that was blocked by Nr4a1 overexpression (Engeln et al, 2022 ). These data provide the first exciting indication that drug exposure alters structural glutamatergic synaptic plasticity in the VP and match earlier reports that cocaine increases glutamatergic vs. GABAergic neurotransmission in the VP (McDaid et al, 2006 ; Pribiag et al, 2021 ).…”