D2 dopamine modulation of corticoaccumbens synaptic responses changes during adolescence

Dopaminergic afferents from the ventral tegmental area (VTA) modulate information processing in the nucleus accumbens (NA), a brain region critical for motivation and reward mechanisms. In NA medium spiny neurons (MSNs) from young rats, D-2 agonists have been shown to decrease the amplitude of corticoaccumbens synaptic responses. As several dopamine-related functions change during adolescence, we assessed the D-2 modulation of cortical inputs with whole-cell recordings in slices obtained from adult and preadolescent rats. The D-2 agonist quinpirole (5 mu M) decreased synaptic response of NA MSNs to electrical cortical stimulation in slices from preadolescent rats. In slices from adult rats, however, quinpirole increased both the amplitude of evoked synaptic responses and the frequency of spontaneous synaptic events. These effects were blocked by the GABA-A antagonist picrotoxin (50 mu M), revealing a D-2-mediated decrease These results suggest that D-2 receptors modulate NA neurons differently in young and adult rats, due to the emergence of a D-2-facilitated GABA component in corticoaccumbens responses during adolescence.