Abstract
In order to analyse more precisely the effects of single pulse stimulation of the brain stem upon monosynaptic reflex, effects upon individual motoneurons were investigated by means of the firing index method of LLOYD and MCINTYRE. Effects upon gamma efferents were also examined by picking up afferent discharges of group Ia, II and Ib fibers from dorsal root filaments in comparison with the effects upon monosynaptic reflex to the same muscles.
Experiments were conducted on 42 adult cats decerebrated at precollicularchiasma level.
1. Two kinds of firing index curve, a monophasic positive and a monophasic negative, were obtained from ventral root filaments by stimulation of single points in the brain stem which gave diphasic inhibitory effect on the monosynaptic reflex by single pulse stimulation. These patterns of firing index curve resembled the excitatory and inhibitory post-synaptic potentials of the motoneuron, respectively, in time course.
2. Effects of brain stem stimulation upon afferent discharges of group Ia, II and Ib fibers from extensor muscles were investigated separately. It was observed that afferent discharges of group Ia fibers showed a tendency to respond in the same way as the effect on monosynaptic reflex to the same muscles, whereas the result was almost reversed in the case of group II fibers.
However, it is noteworthy that, in relatively high percentages, no effect resulted upon these afferent discharges from stimulation of the points which gave distinct effects upon monosynaptic reflex.
