Abstract
Effects of the chlorpromazine, pentobarbital and atropine on gamma-motor activity was studied, recording the single unit activity of the primary ending muscle spindle of the ankle flexor and extensor muscle in pentobarbitalized cats. Changes of the frequency of the spontaneous discharge and change of activation threshold during high cycle stimulation of the central nervous structures, such as globus pallidum, caudate nucleus, posterior hypothalamus, internal capsule and mesencephalic reticula formation were studied. With 5 mg/kg or more of pentobarbital, the threshold of diffuse facilitation any point above mentioned structures became similarly higher, 2 to 3 times than the control. As for the amount of the threshold increase nosignificant differences were found among any of these points.
In case of the chlor promazine, the rate of the discharge decreased or disappeared even at dose of 0.2 mg/kg. The threshold of the diffuse facilitation from post hypothalamus was specifically increased even when the threshold from the mesencephalic reticular formation did not show the increase. The threshold for the reciprocal pattern response from the internal capsule etc. was uninfluenced. It was summarized that the chlorpromazine selectively blocked the facilitatory action from the posterior hypothalamus to gamma-motor neuron activity.
Atropine produced dissociation of the EEG and gamma activity. EEG pattern of neocortex become spindle burst pattern after administration of 0.3 mg/kg of atropine, whereas muscle spindle discharge is enhanced in some case. This dissociation can also be seen when stimulation is applied to central nervous structures. Atropine extinguishes the activation of EEG pattern during stimulation of globus pallidum, mesencephalic reticular formation or posterior hypothalamus, but leaves increased discharge of GIα during central stimulation unchanged.
