Dopamine transporter (DAT) homozygous knockout (DAT(-/-)) mice have a 10-fold higher extracellular (DA) concentration in the caudate-putamen and nucleus accumbens than do wildtype (DAT(+/+)) mice, but show reduced presynaptic DA synthesis and fewer postsynaptic D(2) receptors. One aspect of neurotransmission involves DA binding to postsynaptic D(2)-like receptors coupled to cytosolic phospholipase A(2) (cPLA(2)), which releases the second messenger, arachidonic acid (AA), from synaptic membrane phospholipid. We hypothesized that tonic overactivation of D(2)-like receptors in DAT(-/-) mice due to the excess DA would not increase brain AA signaling, because of compensatory downregulation of postsynaptic DA signaling mechanisms.[1-(14)C]AA was infused intravenously for 3 min in unanesthetized DAT(+/+), heterozygous (DAT(+/-)), and DAT(-/-) mice. AA incorporation coefficients k* and rates J(in), markers of AA metabolism and signaling, were imaged in 83 brain regions using quantitative autoradiography; brain cPLA(2)-IV activity also was measured.Neither k* nor J(in) for AA in any brain region, or brain cPLA(2)-IV activity, differed significantly among DAT(-/-), DAT(+/-), and DAT(+/+) mice.These results differ from reported increases in k* and J(in) for AA, and in brain cPLA(2) expression, in serotonin reuptake transporter (5-HTT) knockout mice, and suggest that postsynaptic dopaminergic neurotransmission mechanisms involving AA are downregulated despite elevated DA in DAT(-/-) mice.