Entorhinal lesions result in increased nerve growth factor-like growth-promoting activity in medium conditioned by hippocampal slices.

Nerve growth factor (NGF) is present in high concentrations in the rat hippocampal formation where it may be involved in sympathetic sprouting following septohippocampal denervation. In addition, recent evidence suggests that some forebrain cholinergic neurons, including septohippocampal neurons, are responsive to exogenous NGF. Since septohippocampal neurons have been shown to sprout in response to entorhinal lesions both in rats and, recently, in humans, we sought to determine whether endogenous NGF-like activity increases in the rat hippocampal formation following injury to the entorhinal cortex. We found that entorhinal lesions which result in extensive denervation of the dentate granule cells, and subsequent sprouting of septohippocampal axons, do result in greater NGF-like growth-promoting activity in medium conditioned by slices of the denervated tissue when compared to medium conditioned by control tissue. These results suggest that brain NGF may be involved in injury-induced sprouting of forebrain cholinergic neurons.