Nerve growth factor and the basal forebrain cholinergic system: a link in the etiopathology of neurodegenerative dementias?

The discovery of a specific association between nerve growth factor (NGF) and basal forebrain cholinergic neurons (BFCNs) marks the beginning of a new era of research into neurodegenerative diseases such as Alzheimer disease (AD). Degeneration of BFCNs appears to be one of the earliest and most prominent neuropathological features of a broad range of diseases of the human brain that give rise to loss of memory and dementia (including, in addition to Alzheimer disease, Parkinson disease, Lewy body dementia, progressive supranuclear palsy, dementia pugilistica, olivopontocerebellar atrophy, and Wernicke-Korsakoff syndrome). Selective localization of NGF receptors on BFCN, the relatively high levels of NGF mRNA in BFCN target areas, and numerous effects of exogenous NGF in vivo and in vitro provide overwhelming evidence that the structure and function of BFCNs in the adult brain are dependent on this molecule. The question then arises as to how this special relationship is disturbed in the diseased human brain? Initial investigations in AD have already indicated a normality of NGF mRNA and retention of receptors in the basal forebrain region. Interpretation of these results and the therapeutic relevance of NGF obviously depend upon future developments in understanding the role of NGF in the normal and pathological brain.