The goals of this proposal will focus on the involvement of specific neurotransmitter systems in regulating nerve growth factor (NGF) gene expression in the central nervous system (CNS). The studies described are designed to test the hypothesis that the neurotransmitters glutamate, via N-methyl-d-aspartate (NMDA) receptor activation, and norepinephrine (NE) are involved in the regulation of NGF gene expression. These neurotransmitter systems were chosen for a number of reasons. Both of these neurotransmitter systems are known to play a role in synaptic plasticity. In addition, there is electrophysiological, neuroanatomical, and pharmacological data supporting the interaction of these two neurotransmitter systems. We will focus on each system separately and then formulate the hypothesis that these two neurotransmitter systems interact in the hippocampal formation and cortex to regulate levels of NGF mRNA. It could be postulated that the activation of these two neurotransmitter systems may ultimately influence the function (survival and plasticity) of NGF responsive cholinergic basal forebrain neurons through activation of NGF expression. However, at this time we will focus our efforts on NGF gene expression, with the understanding that future goals will be to test the consequence of NE and glutamate (NMDA)-induced changes in NGF on cholinergic function. The studies in this proposal are relevant for further understanding of the actions of NGF in the CNS, as well as potential processes involved in neurodegeneration associated with Alzheimer's disease. There is evidence for altered function in the cholinergic, noradrenergic, and glutamate neurotransmitter systems in patients suffering from Alzheimer's disease. Because the basal forebrain cholinergic neurons are thought to be sensitive to the neurotrophic properties of NGF, studying the regulation of this neurotrophic factor by NE and glutamate may be critical in understanding some of the neurodegenerative processes associated with Alzheimer's disease. We will use in situ hybridization histochemistry and a ribonuclease protection assay to study neurotransmitter-induced changes in NGF mRNA levels in vitro (tissue slices) and in vivo. These two techniques will be utilized for quantification and localization of changes in NGF gene expression in the hippocampal formation and cortex. In the early phases of the proposal, we will use tissue slices of hippocampal and cortical tissue to investigate the specific conditions (neurotransmitter dose, time course, receptor pharmacology, secondary messengers, etc.) necessary for understanding neurotransmitter regulation of NGF gene expression. Once these conditions are established, we will then move to in vivo studies in order to localize NGF mRNA expressing cells that are responding to neurotransmitter challenge. Finally, we propose to study the physiological actions (and interactions) of these two neurotransmitters in vivo using well-studied paradigms designed to stimulate the endogenous actions of each neurotransmitter separately and in parallel.
