Comparison of Defolliculated Oocytes and Intact Follicles of the Cockroach Using the Vibrating Probe to Record Steady Currents

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Follicle cells were removed by dissection from early vitellogenic oocytes of the cockroach Blattella germanica. The vibrating probe was used to record steady currents from 19 defolliculated oocytes and 19 intact follicles of the same developmental stage. Defolliculated oocytes generated currents that were stable and distinguishable (by intensity or selective direction) from background reference values. Distributions of the intensities of reference values and experimental values were, in general, similar in both intact and defolliculated preparations. The patterns of currents generated by preparations recorded in the mid-sagittal plane were analyzed for both defolliculated oocytes (n = 8) and intact follicles (n = 10). The larger, generally more mature preparations in both groups generated patterns of current similar to the pattern seen in mid-vitellogenic follicles (focused inward near the germinal vesicle (GV), the presumptive ventral side, and broadly outward on the apo-GV side, the presumptive dorsal side). Smaller sized preparations in both groups showed inward or outward current on the apo-GV aspect and, typically, inward current at the GV. Only two defolliculated oocytes, and no intact follicles, appeared to generate outward current at the GV, and we believe this observation resulted from recording slightly outside the mid-sagittal plane. We conclude that preparations during early-vitellogenesis initially generate currents without an asymmetric pattern and that the inward flux at the GV is the first step in developing patterns of currents. The results suggest that the oocyte (and not the follicle cell epithelium) is responsible for generating the various patterns of currents observed in early-vitellogenic stages. At the end of early-vitellogenesis, the follicle cell epithelium begins to adhere tightly to the oocyte. The possibility is considered that the follicle cells may influence the currents generated during mid-vitellogenesis.