FREQUENCY-DEPENDENT INTERFERENCE BY MAGNETIC-FIELDS OF NERVE GROWTH FACTOR-INDUCED NEURITE OUTGROWTH IN PC-12 CELLS

We have shown that 50 Hz sinusoidal magnetic fields within the 5-10 mi croTesla (mu T) rms range cause an intensity-dependent reduction in ne rve growth factor (NGF) stimulation of neurite outgrowth (NO) in PC-12 cells. Here we report on the frequency dependence of this response ov er the 15-70 Hz range at 5 Hz intervals. Primed PC-12 cells were plate d in collagen-coated, 60 mm plastic petri dishes with or without 5 ng/ ml NGF and were exposed to sinusoidal magnetic fields for 22 h in a CO 2 incubator at 37 degrees C. One 1,000-turn coil, 20 cm in diameter, g enerated vertically oriented magnetic fields. The dishes were stacked on the center axis of the coil to provide a range of intensities betwe en 3.5 and 9.0 mu T rms. The flux density of the ambient DC magnetic f ield was 37 mu T vertical and 19 mu T horizontal. The assay consisted of counting over 100 cells in the central portion (radius less than or equal to 0.3 cm) of each dish and scoring cells positive for NO. Sham exposure of cells treated identically with NGF demonstrated no differ ence in the percentage of cells with NO between exposed and magnetical ly shielded locations within the incubator. Analysis of variance demon strated flux density-dependent reductions in NGF-stimulated NO over th e 35-70 Hz frequency range, whereas frequencies between 15 Hz and 30 H z produced no obvious reduction. The results also demonstrated a relat ive maximal sensitivity of cells at 40 Hz with a possible additional s ensitivity region at or above 70 Hz. These findings suggest a biologic al influence of perpendicular AC/DC magnetic fields different from tho se identified by the ion parametric resonance model, which uses strict ly parallel AC/DC fields. (C) 1995 Wiley-Liss, Inc.