A common SNP in Chrna5 enhances morphine reward in female mice

The single nucleotide polymorphism (SNP) D398N (rs16969968) in CHRNA5, the gene encoding the α5 subunit of the nicotinic acetylcholine receptors (nAChR), has been associated with both nicotine and opiate dependence in human populations. Expression of this SNP on presynaptic VTA dopaminergic (DA) neurons is known to cause a reduction in calcium signaling, leading to alterations in transmitter signaling and altered responses to drugs of abuse. To examine the impact of the Chrna5 SNP on opiate reward and underlying dopaminergic mechanisms, mice harboring two copies of the risk-associated allele (Chrna5 A/A) at a location equivalent to human rs16969968 were generated via CRISPR/cas9 genome editing. We sought to determine whether Chrna5 A/A mice show differences in sensitivity to rewarding properties of morphine using the conditioned place preference paradigm. When mice were tested two weeks after conditioning, female Chrna5 A/A mice showed significantly enhanced preference for the morphine-paired chamber relative to WT females, suggesting that this genotype may enhance opioid reward specifically in females. In contrast, Chrna5 genotype had no effect on locomotor sensitization in male or female mice. Relative to WT females, peak amplitude of ACh-gated currents recorded from VTA DA neurons in Chrna5 A/A females was potentiated 1 day after conditioning with morphine. Increased FOS expression was also observed in Chrna5 A/A mice relative to WT mice following exposure to the morphine CPP chamber. We propose that impaired α5 nAChR subunit function alters DA neuron response following repeated morphine exposures, and that this early cellular response could contribute to enhanced opiate reward two weeks after conditioning.