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Figure 4: Electron microscopy of masticatory muscles. Shown are the ultrastructures of the masticatory muscles observed by transmission electron microscopy at a magnification of 8000X (panel 1, 2, 4, 5, 7, and 8) and 25000X (panel 3, 6, and 9). Panels 1, 2, and 3 refer to the control group (CON). Panels 4, 5, and 6 refer to the psychological group (PS) after three weeks of stimulation. Panels 7, 8, and 9 refer to PS after five weeks of stimulation. Swollen mitochondria with cristae loss and reduction of matrix density were found in the masticatory muscles of PS rats after three weeks or five weeks of stimulation, as marked by black arrows in Panel 5 and 8. Dramatic vacuolar changes in mitochondria appeared in PS rats after five weeks of stimulation, as marked by white arrows in Panel 8. The ultrastructure of capillaries in both control (Panel 3) and 3-w PS specimens (Panel 6) were generally normal, except a few signs of electron density decrease in the capillary cells, as marked by black arrow in Panel 6. Cytoplasm of some capillary cells of 5-w PS rats appeared to be more electron-lucent than those in control specimens, as marked by black arrows in Panel 9. Some places of the capillary basal laminae became accidented, with significantly increased exudation around, as marked by white arrows in Panel 9.