Infusions of NMDA into the vSub increase DA neuron population activity. A, Activation of the vSub led to a dose-dependent increase in spontaneously active DA neurons. The mean number of spontaneously active DA neurons (+SEM) recorded per electrode track from rats receiving vehicle infusions (n = 6 rats; white bar), 0.25 or 0.75 μg of NMDA (n = 6 rats, 7 rats, respectively;black bars), or TTX (n = 6 rats;gray bar) into the vSub is shown. B, Blockade of glutamate transmission in the NAc prevented the activation of VTA DA neuron firing by vSub stimulation in a manner that was independent of the vSub–mPFC pathway. The mean number of spontaneously active DA neurons (+SEM) recorded per electrode track from rats receiving vehicle infusions (same as A; white bar), infusions of kynurenic acid (Kyn) into the NAc in combination with vehicle infusions into the vSub (n = 6 rats; hatched bar), infusions of kynurenic acid into the NAc in combination with 0.75 μg of NMDA into the vSub (n = 6 rats; cross-hatched bar), or infusions of TTX into the mPFC in combination with 0.75 μg of NMDA into the vSub (n = 5 rats;gray bar) is shown. *p < 0.05 and **p < 0.01 versus control; †p< 0.05 versus the group receiving 0.75 μg of NMDA.