Involvement of GABAergic neural mechanisms in the nucleus accumbens in delta‐ and mu‐opioid receptor‐mediated increases in accumbal dopamine efflux

Abstract

The nucleus accumbens (NAc) is a terminal area of mesolimbic dopaminergic neurons that originate in the ventral tegmental area. Additionally, the NAc contains GABAergic neurons that interact with dopaminergic neurons. This review describes the GABAergic neural mechanisms in NAc that regulate increases in accumbal dopamine (DA) efflux induced by selective stimulation of delta‐ and mu‐opioid receptor (‐R) subtypes in freely moving rats, focusing on findings from experiments using in vivo microdialysis techniques. First, we consider how endogenous GABA exerts inhibition of accumbal DA efflux through GABA‐R subtypes, namely GABA_A‐ and GABA_B‐Rs. The NAc contains GABAergic neurons that express delta‐ or mu‐opioid‐Rs, hence decreases in GABA input to GABA_A‐ and/or GABA_B‐Rs on dopaminergic nerve endings could mediate delta‐ or mu‐opioid‐R‐mediated increases in accumbal DA efflux. Therefore, we summarize the effects of selective GABA_A‐ and GABA_B‐R ligands on delta‐ and mu‐opioid‐R subtype‐mediated accumbal DA efflux. This is to increase understanding of the mechanisms of interaction between GABAergic neurons that contain delta‐ or mu‐opioid‐Rs and dopaminergic neurons in NAc. Finally, we provide a synaptic network to explain the interactions among delta‐ or mu‐opioid‐R subtypes, GABAergic neurons, GABA‐R subtypes and dopaminergic neurons in NAc.