Habituation in the crab Chasmagnathus granulatus: effect of morphine and naloxone.

The escape response decrement shown by the crab Chasmagnathus granulatus as a consequence of repeated shadow presentation, meets five of the seven tested parametric criteria of habituation. Results concerning stimulus generalization and dishabituation strongly suggest that neither motor fatigue nor sensory adaptation can account for the response waning. The effects of morphine and naloxone on performance were also studied. Neither 50 nor 5 micrograms morphine/g exerted any modulatory effect on memory retention. A dose of 50 micrograms morphine/g produced an anterograde detrimental effect on responsiveness but no long-term training effects could be detected after the drug's period of action. A dose of naloxone of 1.6 micrograms/g did not antagonize the effect of morphine. The potential value of the response habituation as a model for studying both habituation dynamics and the mechanisms that subserve it, and also for elucidating the effects of opiates on this memory process, is discussed.