AGED FOREBRAIN CHOLINERGIC NEURONS AND NGF DELIVERY

老化的大脑表现为胆碱能神经元的退化

The aging brain manifests a deterioration of cholinergic neurons in the basal forebrain, which has been suggested to be one important factor for age-related decreases in memory and learning functions. Since these neurons are dependent on nerve growth factor (NGF) for maintenance of cholinergic phenotype, it has been suggested, that NGF administration into the brain might aid in the treatment of age-related dementias of the Alzheimer type. However, this molecule is too large to be transferred across the blood-brain barrier in any significant amounts. We have recently documented a novel approach for delivering NGF across the blood- brain barrier (BBB). An antibody (OX-26) directed against transferrin receptors, which are present at high levels on the BBB vessels, is covalently linked to the NGF molecule: Transcytosis with the entire OX-26- NGF conjugate occurs across the endothelial cells of brain capillaries. We have recently demonstrated that intravenous treatment with the OX-26-NGF conjugate significantly enhances both overall growth and cholinergic neuron survival in intraocular medical forebrain transplants, which have been shown to develop an intact BBB. In the present proposal we will utilize intraocular septal grafts to obtain a dose-response curve for OX-26-NGF on 1) survival, 2) growth, and 3) maintenance of cholinergic phenotype in cholinergic neurons during aging. The transplants will be investigated using antibodies directed against choline acetyltransferase, receptors for NGF and synapsin protein at both light and electron microscopic level. Furthermore, we propose to investigate if hippocampal transplants have the ability to produce sufficient amounts of endogenous NGF to support cholinergic neurons in septal co-grafts, if this NGF production is decreased during aging in hippocampal grafts, and whether the addition of OX-26-NGF conjugate can increase the density of cholinergic innervation from septal to hippocampal co-grafts. Finally, it will be investigated whether administration of OX-26-NGF to septal-hippocampal double grafts can increase cholinergic sprouting in such grafts during aging or at least diminish possible age-related declines in this isolated pathway. The long- term groups in experiment 2 and 3 will take 2 years between grafting and evaluation, while the short-term experiments will stretch over 2-3 months. We postulate that these experiments will lead to a greater understanding of NGF functions during development and especially during aging in the septo- hippocampal system. Furthermore, we hope that these findings will aid in planning the strategy for potential use of transferrin receptor antibody- NGF conjugates for treatment of patients with dementias of the Alzheimer type.