Fig. 2. Effects of sodium nitroprusside (SNP) on the swim motor program. (A) Control recording showing typical fictive swimming. Fifteen minutes after the addition of 1 mmol l^–1 SNP, the period of the swim rhythm increased and became more erratic. This effect was reversible, as indicated by a return to a normal swimming pattern after a 23-min wash in seawater. (B) Reduced oxyhemoglobin blocked the effects of 1 mmol l^–1 SNP. This confirms that the effects from SNP were in fact due to NO and not to some other chemical property of the NO donor. All recordings were from the same cell.