Regulation of nerve growth factor mRNA in the hippocampal formation effects of N-methyl-D-aspartate receptor activation.

In the hippocampal formation, nerve growth factor (NGF) is produced in granule cells of the dentate gyrus and a few pyramidal cells of Ammon's horn. Both neuronal populations express N-methyl-D-aspartate (NMDA) receptors and receive putative glutamatergic afferents originating in the entorhinal cortex and projecting via the perforant path. We report in this study that intra-hippocampal or intraventricular injections of NMDA increase NGF mRNA levels in dentate gyrus granule cells as determined using in situ hybridization histochemistry and a solution hybridization assay. NGF mRNA induction is detected within 2 h following NMDA treatment and returns to control levels within 24 h. This NMDA effect is dose-dependent and blocked by pretreatment with 2-amino-5-phosphonopentanoic acid, a competitive NMDA antagonist. Finally, the induction of NGF mRNA is observed in the absence of detectable neurotoxicity or seizure activity. We postulate that normal physiological events associated with the activation of hippocampal NMDA receptors may regulate mRNA expression of this neurotrophic factor.