INTERNEURONS INVOLVED IN THE CONTROL OF MULTIPLE MOTOR CENTERS IN CRAYFISH

A number of studies have suggested that abdominal positioning interneu rons (APIs) in the crayfish Procambarus clarkii can influence activity in multiple motor centers. Previous work on this population of neuron s has demonstrated that they control the activity of tonic abdominal m otor neurons (MNs) which generate postural movements of the abdomen an d, to some extent, the activity of swimmeret MNs. This investigation d emonstrates that many identified APIs also affect the activity of two populations of MNs which open and close the uropods and, in some cases , that of the swimmeret MNs as well. The majority (64%) of APIs examin ed in this study have an excitatory effect on both populations of urop od MNs. A smaller number (23%) increase the level of activity in one p opulation of uropod MNs, and suppress, or have no effect on, the activ ity of the other population of uropod MNs. Approximately 25% of the AP Is which were examined influence the output of swimmeret MNs, in addit ion to affecting the activity of uropod MNs. There are also indication s that previous estimates of the number of APIs may have been too low This is based on the observation that many APIs possess what appear to be similar morphologies but generate different patterns of motor outp ut. Taken together, these findings support the idea that APIs influenc e the output of multiple motor centers which play a role in the contro l of general body posture and balance in crayfish. (C) 1995 Wiley-Liss , Inc.