Recurrent Inhibition To And From Motoneurons Innervating The Flexor Digitorum And Flexor Hallacis Longus Muscles Of The Cat


T. H. Hamm



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1. Recurrent inhibitory postsynaptic potentials (IPSPs) to and from motoneurons innervating the flexor digitorum longus (FDL) and flexor hallucis longus (FHL) muscles of the cat were investigated to determine whether recurrent inhibitory projections involving these motoneurons are similar - as would be consistent with the Ia and anatomic synergism of FDL and FHL - or are dissimilar, as are the activities of these muscles during locomotion (O'Donovan et al. 1982). 2. Composite recurrent IPSPs were recorded in several species of motoneurons innervating hindlimb muscles in response to stimulation of a number of muscle nerves in cats allowed to become unanesthetized after ischemic decapitation. 3. No recurrent IPSPs from stimulation of the FDL nerve were observed in motoneurons innervating FDL, FHL, lateral gastrocnemius-soleus (LG-S), medial gastrocnemius (MG), plantaris (Pl), tibialis anterior (TA), or extensor digitorum longus (EDL). 4. The recurrent IPSPs produced by stimulation of FHL were larger and found more frequently in LG-S than in FDL motoneurons. Recurrent inhibition from FHL was also greater in Pl than in FDL motoneurons. 5. The recurrent IPSPs produced by stimulation of LG-S, PL, and MG were larger in FHL than in FDL motoneurons, and those from LG-S and MG were found more frequently in FHL than in FDL motoneurons. 6. Stimulation of the TA nerve produces recurrent IPSPs in FDL but not in FHL motoneurons. A few FDL and FHL cells (6 of 23 and 9 of 34, respectively) received small (<0.5 mV) recurrent IPSPs from stimulation of the EDL nerve. 7. Recurrent facilitation produced by stimulation of either the LG-S or MG nerve was observed in 19 of 25 FDL motoneurons. 8. From these results, the conclusion is drawn that the distribution of recurrent inhibition to and from FDL and FHL motoneurons corresponds more closely to patterns of locomotor activity than the organization of monosynaptic Ia connections. The implications of this finding are discussed.

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Journal of Neurophysiology







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