Fig. 4. Effect of ovotestis (OT) mechanical stimulation on the frequency of afferent spikes in the intestinal nerve. (A) Representative traces from three electrodes placed on the intact nerve (see Fig. 1). A wooden applicator stick mounted on a micro manipulator was used to gently stroke the surface of the OT for 3 s; arrow indicates the onset of stimulation. (B) A representative portion of the record from A is amplified to illustrate the discrimination of efferent spikes (open arrowheads) and afferent spikes (filled arrowheads) based on inter-spike intervals recorded at distal and proximal electrodes positioned along the seminal vesicle; signals recorded at the central electrode were not used for this purpose. (C) Raster plot showing the timing of afferent spike activity for 30 s periods before and after the stimulus. The arrow at time 0 indicates the onset of mechanical stimulation.