Autogenetic excitation of extensor gamma-motoneurones by group II muscle afferents in the cat.

Triceps surae gamma-efferents have been isolated in intact ventral root filaments in order to study the autogenetic Group II effects evoked by stimulation of the nerve to the triceps surae in decerebrate cats. Half of the 22 cells tested were facilitated by repetitive stimulation of this nerve in the Group II range. Six cells showed a mixture response pattern with an initial facilitation followed by declining activity during the ongoing stimulation. Eight cells were not influenced within the Group II range. The results suggest that autogenetic Group II facilitation of gamma-motoneurones plays a functional role in the gain control of muscle spindle endings.