Non-Contingent Exposure to Amphetamine in Adolescence Recruits miR-218 to Regulate Dcc Expression in the VTA.

The development of the dopamine input to the medial prefrontal cortex occurs during adolescence and is a process that is vulnerable to disruption by stimulant drugs such as amphetamine. We have previously linked the amphetamine-induced disruption of dopamine connectivity and prefrontal cortex maturation during adolescence to the downregulation of the Netrin-1 receptor, DCC, in dopamine neurons. However, how DCC expression in dopamine neurons is itself regulated is completely unknown. MicroRNA (miRNA) regulation of mRNA translation and stability is a prominent mechanism linking environmental events to changes in protein expression. Here, using male mice, we show that miR-218 is expressed in dopamine neurons and is a repressor of DCC. Whereas Dcc mRNA levels increase from early adolescence to adulthood, miR-218 exhibits the exact opposite switch, most likely maintaining postnatal Dcc expression. This dynamic regulation appears to be selective to Dcc since the expression of Robo 1, the other guidance cue receptor target of miR-218, does not vary with age. Amphetamine in adolescence, but not in adulthood, increases miR-218 in the VTA and this event is required for drug-induced downregulation of Dcc mRNA and protein expression. This effect seems to be specific to Dcc because amphetamine does not alter Robo1. Furthermore, the upregulation of miR-218 by amphetamine requires dopamine D2 receptor activation. These findings identify miR-218 as regulator of DCC in the VTA both in normal development and after drug exposure in adolescence.