Nitric oxide synthase inhibition blocks octopus touch learning without producing sensory or motor dysfunction

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Abstract
We trained a set of eight octopuses to discriminate by touch between smooth and rough plastic balls. A food reward was given for taking the positive ball and a 5-6 V AC electric shock for taking the negative ball. The animals were trained until they regularly accepted positive balls and rejected negative balls. We then injected four with L-NAME, blocking nitric oxide synthase, and four with D-NAME for control. We continued the training and found no alterations in behaviour during six successive training sessions. We looked, in particular, for signs of sensory or motor dysfunction and observed none. We then reversed the paradigm, making the formerly positive ball negative. All controls readily learned the reversal; soon taking all the positive balls and rejecting the negative ones entirely. The L-NAME injected animals did not learn the reversal. However, they gradually stopped taking the newly negative smooth ball and increased their positive responses to the formerly negative rough ball, eventually taking approximately equal numbers of each. This experiment provided evidence that L-NAME impaired learning without affecting sensory or motor functions or central retrieval and/or retention mechanisms.