Fig. 10. Octopamine reduced the resistance of the preparation in a dose-dependent manner. (A) For resistance measurements, 10 subsequent pulses of negative current were applied. When compared with the averaged voltage response (V) before drug injection (left), an injection of 150nmol of octopamine decreased the response (right). (B) The normalized resistance R_after/R_before was computed. While control injections of haemolymph Ringer (HLR) did not alter the resistance of the preparation, octopamine (OA) reduced it in a dose-dependent manner. Serotonin (5-HT), however, had no effect. Values are means + S.E.M. The asterisk indicates a significant difference from the control (P<0.02, Student's t-test).