BACKGROUND: The supernatant of interferon-gamma (IFN γ ) co-cultured with neonatal rat cortical glia can promote the cells in embryonic basal forebrain/septal nuclei to differentiate into cholinergic neurons, but the mechanism is still unclear.OBJECTIVE: To analyze the pathways for IFN γ to promote the differentiation of primarily cultured cholinergic neurons in rat embryonic basal forebrain/septal nuclei through culture in different conditioned medium.DESIGN: A controlled experiment taking cells as the observational target.SETTINGS: Department of Biochemistry and Molecular Biology, Youjiang Medical College for Nationalities; Department of Cell Biology, Beijing University Health Science Center.MATERIALS: Sixty-four pregnant Wistar rats for 16 days (250 - 350 g) and 84 Wistar rats (either male or female, 5 - 7 g) of 0 - 1 day after birth were provided by the experimental animal department of Beijing University Health Science Center. Rat IFN γ were provided by Gibco Company; Glial fibrillary acidic protein by Huamei Company.METHODS: The experiments were carried out in the Department of Cell Biology, Beijing University Health Science Center and Daheng Image Company of Chinese Academy of Science from July 1995 to December 2002. ① Interventions: The nerve cells in the basal forebrain/septal nuclei of the pregnant Wistar rats for 16 days were primarily cultured, and then divided into four groups: Blank control group (not any supernatant and medium was added); Control group (added by mixed glial cell or astrocyte conditioned medium); IFN γ group (added by mixed glial cell or astrocyte conditioned medium+IFN γ ). Antibody group (added by mixed glial cell or astrocyte conditioned medium+IFN γ +Ab-IFN γ ). Mixed glial cell or astrocyte conditioned medium was prepared using cerebral cortex of Wistar rats of 0 - 1 day after birth. ② Evaluation: The immunohistochemical method was used to perform the choline acetyltransferase (ChAT) staining of cholinergic neurons. The ChAT positive cells were counted.MAIN OUTCOME MEASURES: Comparison of ChAT positive cells in rat basal forebrain and septal nuclei in different conditioned medium.RESULTS: ① ChAT positive cells in mixed glial cell conditioned medium: The ChAT positive cells in the IFN γ group and antibody group were significantly more than those in the control group (P ＜ 0.01). ② ChAT positive cells in astrocyte conditioned medium: The ChAT positive cells in the IFN γ group were significantly more than those in the control group, but there was no significant difference between the antibody group and control group (P ＞ 0.05).CONCLUSION: IFN γ cannot directly promote the differentiation of cholinergic neurons, but plays a role through activating glial cells (except astrocytes) to produce IFN γ like molecules.