The primary goal of this research is to characterize the effects of administration of exogenous nerve growth factor (NGF) on cholinergic neurotransmission and synaptic function within the projection systems of basal forebrain cholinergic neurons (BFCN) in both normal adult and aged mammalian brain. This understanding is being sought to determine whether treatment with NGF might prove effective in maintaining and/or restoring the functional integrity of forebrain cholinergic projections in individuals suffering from age-related neurodegenerative disorders, particularly Alzheimer's disease (AD). The work is predicated on prior knowledge that NGF stimulates the expression of a host of cholinergic neuronal traits in forebrain areas in rodents -- a major objective is to determine the functional significance that such effects might have on neurotransmission between BFCN and their postsynaptic target cells. To accomplish this, current-clamp and single electrode voltage-clamp techniques will be used to intracellularly record cholinergic effects produced by stimulation of forebrain inputs from nucleus basalis magnocellularis (NBM) to pyrmaidal neurons in basolateral amygdala (BLA) in rat brain slice preparations. NGF-related changes in forebrain cholinergic neurotransmission will be assessed by comparing the ability of NBM stimulation to elicit a cholinergic slow depolarization and its underlying synaptic current and to inhibit several intrinsic membrane potassium conductances in BLA neurons in slices from control and NGF-treated rats. The responses of control and NGF-treated neurons to bath application of cholinergic agonists will be compared to address the possibility that treatment with the neurotrophic factor might induce changes in postsynaptic cholinergic sensitivity. In addition, we will measure the activity of choline acetyltransferase (ChAT) and high affinity choline uptake in tissue samples taken from many of the same preparations in which recordings will be obtained to determine whether any NGF-related changes in NBM-mediated synaptic action within the BLA can be linked to alterations in presynaptic mechanisms that regulate acetylcholine (ACh) synthesis and/or release. Additional comparisons will be made of the release of 3H-ACh evoked by electrical field stimulation in slices of amygdala prepared from control and NGF-treated rats to directly ascertain whether treatment with NGF results in a facilitated release of transmitter from terminals of NBM cholinergic neurons. These investigations will be carried out in brain slices taken from young adult animals and in preparations obtained from aged rats at different stages of senescence. Overall, the proposed research is designed to provide a comprehensive picture of the ability of exogenous NGF to maintain central cholinergic transmission under conditions of cholinergic neurodegeneration that are associated with the aging process and which approximate the neuropathological profile found in patients with AD.
