Effect of nitric oxide synthase inhibition on the manipulative behaviour of Sepia officinalis

Nitric oxide (NO), produced by nitric oxide synthase (NOS) in brain tissue, is essential for a variety of kinds of learning in vertebrates. In invertebrates, there are clear examples of an association between NO signalling and olfaction, feeding behaviour and learning. The role of NO as a neurotransmitter in the manipulative behaviour of Sepia officinalis was tested. Manipulative behaviour requires extensive chemotactile sensory processing, fine motor control and probably motor learning processes. NADPH-diaphorase activity (a reliable histochemical marker for nitric oxide synthase) was found in sensory epithelia and in the axial nerve cord of the arms. NOS inhibitor injections (L-NAME) produced an increase in the latency of prey paralysis. By placing mechanical constraints on the base of the fifth periopods of the crab, we prevented the cuttlefish from injecting cephalotoxin and, thus, forced it to change injection sites. We showed that L-NAME pretreatment did not affect the flexibility of the manipulative behaviour. The implications of the involvement of NO in the acquisition of chemo-tactile information and in the programming of the motor skills of the manipulative behaviour is discussed.