Social status-dependent modulation of LG-flip habituation in the crayfish.

Strong stimuli applied to the tailfan of the crayfish Procambarus clarkii evoked lateral giant interneurone (LG)-mediated tailflips. When the sensory stimulus was applied repeatedly, the response of the LG habituated until it failed to give rise to a spike. We found that this LG-flip habituation was dependent on social status. With a short interstimulus interval of 5 s, the rate of habituation of the LG in both socially dominant and subordinate crayfish was lower than that in socially isolated animals. By contrast, with a long interstimulus interval of 60 s, the rate of habituation of subordinate animals was lower than that of both socially isolated and dominant animals. The excitability of the LGs following habituation was also dependent on social status. Following habituation, the spike response of LGs recovered within several minutes; however, they showed significant depression with a decrease in excitability. With a 5 or 60 s interstimulus interval, subordinate animals showed longer delays of depression compared with dominant animals. A decrease in the rate of habituation and a delay of depression in subordinate crayfish would be advantageous for maintaining an active escape response to evade repeated attacks of dominant animals and a reduced learning ability to adapt to social status.