Effects of diet and insulin on dopamine transporter activity and expression in rat caudate-putamen, nucleus accumbens, and midbrain

Food restriction (FR) and obesogenic (OB) diets are known to alter brain dopamine transmission and exert opposite modulatory effects on behavioral responsiveness to psychostimulant drugs of abuse. Mechanisms underlying these diet effects are not fully understood. In this study, we examined diet effects on expression and function of the dopamine transporter (DAT) in caudate-putamen (CPu), nucleus accumbens (NAc), and midbrain regions. Dopamine (DA) uptake by CPu, NAc or midbrain synapto(neuro)somes was measured invitro with rotating disk electrode voltammetry or with [H-3]DA uptake and was found to correlate with DAT surface expression, assessed by maximal [H-3](-)-2--carbomethoxy-3--(4-fluorophenyl)tropane binding and surface biotinylation assays. FR and OB diets were both found to decrease DAT activity in CPu with a corresponding decrease in surface expression but had no effects in the NAc and midbrain. Diet treatments also affected sensitivity to insulin-induced enhancement of DA uptake, with FR producing an increase in CPu and NAc, likely mediated by an observed increase in insulin receptor expression, and OB producing a decrease in NAc. The increased expression of insulin receptor in NAc of FR rats was accompanied by increased DA D-2 receptor expression, and the decreased DAT expression and function in CPu of OB rats was accompanied by decreased DA D-2 receptor expression. These results are discussed as partial mechanistic underpinnings of diet-induced adaptations that contribute to altered behavioral sensitivity to psychostimulants that target the DAT.