BACKGROUND: Interferon-gamma (IFN-γ) can make neurons in basal forebrain and septal nuclei differentiate into cholinergic neurons by treating the cells in cerebral cortex of newborn rats, without the inhibition from IFN-γ antibody. The important effect of IFN-γ on the development and differentiation of neurons has been found by some scholars. OBJECTIVE:To investigate whether IFN-γ has differentiational effect on cholinergic neurons in basal forebrain and septal nuclei, and make clear that the increased number of cholinergic neurons is resulted by cell differentiation or cell proliferation. DESIGN:Controlled observation trial. SETTING: Department of Cell Biology, Medical School, Beijing University. MATERIALS: Sixty-eight female Wistar rats at embryonic 16 days, weighing 250 to 350 g, were enrolled in this study, and they were provided by the Experimental Animal Center, Medical School, Beijing University. IFN-γ was the product of Gibco Company. METHODS: This study was carried out in the Department of Cell Biology, Medical School, Beijing University and Daheng Image Company of Chinese Academy of Sciences during September 1995 to December 2002.The female Wistar rats at embryonic 16 days were sacrificed, and their fetuses were taken out. Primary culture of the isolated basal forebrain and septal nuclei was performed. The cultured nerve cells were assigned into 3 groups: control group (nothing added), IFN-γ group(1×105 U/L interferon), IFN-γ+ IFN-γ antibody group (1×105 U/L IFN-γ + IFN-γ antibody). The specific marker enzyme (choline acetyl transferase) of cholinergic neuron was stained with immunohistochemical method. Choline acetyl transferase positive cells were counted, and 14C-acetyl CoA was used as substrate to detect the activity of choline acetyl transferase, so as to reflect the differentiational effect of IFN-γ on cholinergic neuron in basal forebrain and septal nuclei. Flow cytometry was used to analyze cell circle and detect the proliferation of nerve cells. Nerve cells were marked with MAP2 and counted to evaluate the neuronal proliferation in basal forebrain and septal nuclei. MAIN OUTCOME MEASURES: Effect of interferon-γ on the number and activity of choline acetyl transferase-positive cells in basal forebrain and septal nuclei as well as the effect on neuronal proliferation. RESULTS:① Nerve cells in the basal forebrain and septal nuclei of IFN-γ group grew well compared with control group. ② The differentiation of cholinergic neurons: The number and activity of choline acetyl transferase positive cells in IFN-γ group were significantly higher than those in the control group [(49.30 ±4.92) /100 cells vs (7.50±1.58) /100 cells; (2 049.00±12.30) min-1 vs (1 227.30±12.59) min-1, P < 0.01], while there was no significant difference in the number and activity of choline acetyl transferase positive cells between IFN-γ + IFN-γ antibody group and control group(P > 0.05). ③ The proliferation of cholinergic neurons: Cell percentage was 17.2% and 19.8% at S-stage, 6.2% and 6.1% at G2+M stage in the control group and IFN-γ group respectively, without significant difference (P > 0.05). CONCLUSION: IFN-γ does not promote the neuronal proliferation in basal forebrain and septal nuclei, and the increased expression of cholinergic neurons is not resulted by the increase in the number of neurons, but its differentiation. BACKGROUND: Interferon-gamma (IFN-γ) can make neurons in basal forebrain and septal nuclei differentiate into cholinergic neurons by treating the cells in cerebral cortex of newborn rats, without the inhibition from IFN-γ antibody. The important effect of IFN-γ on the development and differentiation of neurons has been found by some scholars. OBJECTIVE: To investigate whether IFN-γ has differentiational effect on cholinergic neurons in basal forebrain and septal nuclei, and make clear that the increased number of cholinergic neurons is resulted by cell differentiation DESIGN: Controlled observation trial. SETTING: Department of Cell Biology, Medical School, Beijing University. MATERIALS: Sixty-eight female Wistar rats at embryonic 16 days, weighing 250 to 350 g, were enrolled in this study, and they were provided by the Experimental Animal Center, Medical School, Beijing University. METHODS: This study was carried out in the Department of Cell Biology, Medical School, Beijing University and Daheng Image Company of Chinese Academy of Sciences during September 1995 to December 2002. The female Wistar rats at embryonic 16 days were sacrificed, and their fetuses were taken out. Primary culture of the isolated The cultured nerve cells were assigned into 3 groups: control group (nothing added), IFN-γ group (1 × 105 U / L interferon), IFN-γ + IFN-γ antibody group × 105 U / L IFN-γ + IFN-γ antibody). The specific marker enzyme (choline acetyl transferase) of cholinergic neuron was stained with immunohistochemical method. Choline acetyl transferase positive cells were counted, and 14C-acetyl CoA was used as substrate to detect the activity of choline acetyl transferase, so as to reflect the differentiational effect of IFN-γ on cholinergic neuron in basal forebrain and septal nuclei. Flow cytometry was used to analyze cell circle and detect the proliferation of n erve cells. Nerve cells were marked with MAP2 and counted to evaluate the neuronal proliferation in basal forebrain and septal nuclei. MAIN OUTCOME MEASURES: Effect of interferon-γ on the number and activity of choline acetyl transferase-positive cells in basal forebrain and septal nuclei as well as the effect on neuronal proliferation. RESULTS: ① The differentiation of cholinergic neurons: The number and activity of choline acetyl transferase positive cells in IFN- γ group were significantly higher than those in the control group [(49.30 ± 4.92) / 100 cells vs (7.50 ± 1.58) / 100 cells; (2 049.00 ± 12.30) min-1 vs (227.30 ± 12.59) min- P <0.01], while there was no significant difference in the number and activity of choline acetyl transferase positive cells between IFN-γ + IFN-γ antibody group and control group (P> 0.05). ③ The proliferation of cholinergic neurons: Cell percentagewas 17.2% and 19.8% at S-stage, 6.2% and 6.1% at G2 + M stage in the control group and IFN-γ group respectively, without significant difference (P> 0.05) neuronal proliferation in basal forebrain and septal nuclei, and the increased expression of cholinergic neurons is not resulted by the increase in the number of neurons, but its differentiation.