Two different molecules, NGF and free-HCNP, stimulate cholinergic activity in septal nuclei in vitro in a different manner.

Hippocampal cholinergic neurostimulating peptide (HCNP), a novel peptide purified from 10- to 12-day-old rat hippocampus, specifically enhances acetylcholine (AcCho) synthesis in medial septal nuclei in vitro, synthetic de-acetylated HCNP (free-HCNP) elicits more potent enhancement than HCNP. Nerve growth factor (NGF), a neurotrophic substance found in the hippocampus, enhances the cholinergic activity of medial septal nuclei both in vivo and in vitro. The effects of free-HCNP on the development of various cholinergic phenotypes and the interaction of NGF and free-HCNP on cholinergic neurons in vitro were studied. In medial septal nuclei, free-HCNP enhanced AcCho synthesis and choline acetyltransferase (ChoATase) activity and increased Vmax. It did not modulate culture morphology, choline (Cho) uptake, or acetylcholinesterase (AcChoEase) activity. NGF stimulated AcCho synthesis and both ChoATase and AcChoEase activity in the medial septal nuclei and also enhanced AcCho synthesis in a corpus striatum culture. Compared with the effect of either agent alone, the simultaneous application of 3.8 x 10(-11) M NGF and 3 x 10(-11) M free-HCNP (maximal stimulation) to medial septal nucleus culture resulted in a more than additive enhancement of AcCho synthesis, an additive increase in ChoATase activity, and a significant increase in Cho uptake. In corpus striatum and spinal cord cultures, there was no cooperative increase in AcCho synthesis with NGF and free-HCNP nor any enhancement of AcCho synthesis by free-HCNP. These findings suggest that NGF and free-HCNP play a cooperative role during the biochemical differentiation of cholinergic neurons in medial septal nuclei.