Interactions between the dopaminergic and glutamatergic neurotransmission systems were investigated in the adult brain of wild‐type (WT) and transgenic mice lacking the dopamine D₁ or D₂ receptor subtypes. Activity of the glutamine cycle was evaluated by using ¹³C NMR spectroscopy, and striatal activity was assessed by c‐Fos expression and motor coordination. Brain extracts from (1,2‐¹³C₂) acetate‐infused mice were prepared and analyzed by ¹³C NMR to determine the incorporation of the label into the C4 and C5 carbons of glutamate and glutamine. D₁R^−/− mice showed a significantly higher concentration of cerebral (4,5‐¹³C₂) glutamine, consistent with an increased activity of the glutamate‐glutamine cycle and of glutamatergic neurotransmission. Conversely, D₂R^−/− mice did not show any significant changes in (4,5‐¹³C₂) glutamate or (4,5‐¹³C₂) glutamine, suggesting that alterations in glutamine metabolism are mediated through D₁ receptors. This was confirmed with D₁R^−/− and WT mice treated with reserpine, a dopamine‐depleting drug, or with reserpine followed by L‐DOPA, a dopamine precursor. Exposure to reserpine increased (4,5‐¹³C₂) glutamine in WT to levels similar to those found in untreated D₁R^−/− mice. These values were the same as those reached in the reserpine‐treated D₁R^−/− mice. Treatment of WT animals with L‐DOPA returned (4,5‐¹³C₂) glutamine levels to normal, but this was not verified in D₁R^−/− animals. Reserpine impaired motor coordination and decreased c‐Fos expression, whereas L‐DOPA restored both variables to normal values in WT but not in D₁R^−/−. Together, our results reveal novel neurometabolic interactions between glutamatergic and dopaminergic systems that are mediated through the D₁, but not the D₂, dopamine receptor subtype. © 2007 Wiley‐Liss, Inc.