Behavioural hyperactivity and risk-taking in young-adult male mice correlate with increased dopamine release in dorsal, but not ventral, striatum

Adolescence is characterized by increased novelty seeking, impulsivity, locomotion and risk-taking, behaviours that facilitate the transition to adulthood but may also increase vulnerability to psychiatric illness. Maturation of dopamine (DA) transmission within the striatum is thought to contribute to these behavioural changes. However, the developmental trajectory of striatal DA release remains unclear, with conflicting evidence regarding age- and sex-dependent changes, particularly across dorsal and ventral striatal regions. Complicating interpretation, many studies classify mice younger than 2 months as 'adults,' potentially obscuring important developmental differences. Here, we examined how age, sex and striatal subregion influence DA release during adolescence and early adulthood. DA release was measured in dorsal and ventral striatal brain slices from male and female C57BL/6J mice at 2 and 4 months of age, corresponding to adolescence and young adulthood. Ultrafast imaging of the genetically encoded DA sensor, dLight, was used to quantify extracellular DA transients evoked by low- and high-frequency electrical stimulation. Glutamatergic and cholinergic transmission was pharmacologically blocked to isolate DA release intrinsic to dopaminergic axons. DA release measures were related to exploratory and locomotor behaviour. We identified a male-specific increase in dorsal striatal DA release between 2 and 4 months of age that coincided with increased locomotion and risk-taking. In contrast, DA release in the ventral striatum did not show comparable age- or sex-dependent changes. These differences were not attributable to altered glutamatergic or cholinergic contributions to DA release. Together, these findings demonstrate that maturation of striatal DA transmission is region- and sex-dependent, with prominent developmental changes occurring in the dorsal striatum during the transition from adolescence to adulthood. These findings help reconcile conflicting reports of developmental DA release and emphasize the importance of considering age, sex and striatal subregion when defining mature dopaminergic function in rodents.