Colocalization of Choline Acetyltransferase and Nerve Growth Factor Receptor in the Rat Basal Forebrain

Nerve growth factor (NGF) is regarded as an important trophic factor for central cholinergic neurons. It only acts on neurons expressing NGF receptors (NGFR). In this study, the extent of colocalization of NGFR and the cholinergic marker, choline acetyltransferase (ChAT), was examined in the basal forebrain of adult rats. Simultaneous labelling for NGFR and ChAT was accomplished by a specific double-immunofluorescence method. An almost complete colocalization of the two antigens was observed in the regions studied. The extent of double-stained neurons ranged from 89.2% (basal nucleus) and 96.9% (horizontal diagonal band) to 99% (vertical diagonal band) and 100% (medial septum). The remaining single labelled cells were immunopositive for ChAT, and only a negligible fraction of them, 0.2% (basal nucleus) and 0.4% (horizontal diagonal band), displayed NGFR immunoreactivity alone. This result emphasizes the specific relationship between NGF and cholinergic neurons in the basal forebrain. These neurons are projecting to hippocampal and cortical targets and are involved in cognition and memory. Investigations evaluating the applicability of NGF treatment to prevent neuronal degeneration may be encouraged by the finding that NGF obviously plays a very specific role in this system.