BDNF mRNA is transneuronally upregulated in the cortex by striatal cell death and not by synaptic activity per se.A–D, Nissl-stained sections in which unilateral lesions were performed. Note the areas of reduced staining (area insidedotted lines) in striata injected with the following:A, 3-NPA (500 nmol); B, 3-NPA (500 nmol) and kynurenic acid (Kyn; 60 nmol); C, 3-NPA (500 nmol) and an NMDA receptor antagonist (MK801; 30 nmol); andD, 3-NPA (500 nmol) and a non-NMDA receptor antagonist (CNQX; 1 nmol). E, Histogram represents BDNF mRNA levels from cerebral cortex 6 hr after intrastriatal injection of PBS, KCl, or 3-NPA alone or in combination with different glutamate receptor antagonists [kynurenic acid (Kyn), MK801, and CNQX]. Values, from three to four animals per condition, were normalized to those obtained in PBS-injected animals and are represented as mean ± SEM (*p < 0.05).