Fig. 3. Effect of NOS inhibitors on the embryonic rotation behavior. (A) Application of 10 mmol l^-1 L-NAME resulted in a significant decrease in the rate of embryonic rotation (P<0.01, N=100 embryos), whereas 10 mmol l^-1 D-NAME had no effect. (B) Application of 100 µmol l^-1 7-NI also produced a significant inhibition of rotation rate (P<0.001, N=63 embryos). In A+B, 100 µmol l^-1 serotonin (5-HT) produced the expected three- to fivefold increase in rotation rate. (C) NO donors bypass the inhibitory effect of NOS inhibitors. Coapplication of 10 mmol l^-1 L-NAME with either 1 µmol l^-1 (1) or 10 µmol l^-1 (10) SNAP resulted in a significant increase in embryonic rotation rate, rather than the decrease produced by L-NAME alone (P<0.001, N=137 embryos). Asterisks represent statistically significant differences compared to the control (artificial pondwater, APW) treatment.