Repeated cocaine administration upregulates CB2 receptor expression in striatal medium-spiny neurons that express dopamine D1 receptors in mice

Hai-Ying Zhang1,2, Lindsay De Biase3, Ramesh Ch, ra4, Hui Shen1, Qing-Rong Liu5, Eliot Gardner1, Mary Kay Lobo4, Zheng-Xiong Xi1
1 Intramural Research Program, National Institute on Drug Abuse, Baltimore, MD, USA
2 Section on Molecular Neuroscience, National Institute of Mental Health, Bethesda, MD, USA
3 Department of Physiology, David Geffen School of Medicine at University of California, Los Angeles, Los Angeles, CA, USA
4 Department of Anatomy and Neurobiology, University of Maryland School of Medicine, Baltimore, MD, USA
5 Laboratory of Clinical Investigation, Intramural Research Program, National Institute on Aging, Baltimore, MD, USA
Correspondence to: Hai-Ying Zhang:, Zheng-Xiong Xi:,
DOI: 10.1038/s41401-021-00712-6
Received: 31 January 2021
Accepted: 2 June 2021
Advance online: 27 July 2021


Cannabinoid CB2 receptors (CB2R) are importantly involved in drug reward and addiction. However, the cellular mechanisms underlying CB2R action remain unclear. We have previously reported that cocaine self-administration upregulates CB2R expression in midbrain dopamine (DA) neurons. In the present study, we investigated whether cocaine or heroin also alters CB2R expression in striatal medium-spiny neurons that express dopamine D1 or D2 receptors (D1-MSNs, D2-MSNs) and microglia. Due to the concern of CB2R antibody specificity, we developed three mouse CB2-specific probes to detect CB2R mRNA using quantitative RT-PCR and RNAscope in situ hybridization (ISH) assays. We found that a single injection of cocaine failed to alter, while repeated cocaine injections or self-administration dose-dependently upregulated CB2R gene expression in both brain (cortex and striatum) and periphery (spleen). In contrast, repeated administration of heroin produced a dose-dependent reduction in striatal CB2 mRNA expression. RNAscope ISH assays detected CB2R mRNA in striatal D1- and D2-MSNs, not in microglia. We then used transgenic CX3CR1eGFP/+ microglia reporter mice and D1- or D2-Cre-RiboTag mice to purify striatal microglia or ribosome-associated mRNAs from CX3CR1eGFP/+, D1-MSNs, or D2-MSNs, respectively. We found that CB2R upregulation occurred mainly in D1-MSNs, not in D2-MSNs or microglia, in the nucleus accumbens rather than the dorsal striatum. These findings indicate that repeated cocaine exposure may upregulate CB2R expression in both brain and spleen, with regional and cell type-specific profiles. In the striatum, CB2R upregulation occurs mainly in D1-MSNs in the nucleus accumbens. Given the important role of D1-MSNs in brain reward function, the present findings provide new insight into mechanisms by which brain CB2Rs modulate cocaine action.
Keywords: cocaine; cannabinoid; CB2 receptor; microglia; self-administration; D1-MSNs

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