An Electrophysiological Study on the Inhibitory Mechanism of Recruiting Response in the Central Nervous System

Abstract

The functional significance of recruiting response was studied in rabbits in relation to the mechanism of cardiazol which prolongs barbiturate anesthesia. The results obtained were as follows.
Following an 8 c/s stimulation on the thalamus, intravenous administration of a small dose of barbiturate to rabbits resulted in the development of recruiting response in EEG and arrest in behavior, which failed to developed in the pre-administration stage.
A similar findings was obtained concerning spike and wave, and behavior following a 3 c/s stimulation. The above results were due to a free development of function of the diffuse thalamocortical projection system which are responsible for the development of recruiting response, and spike and wave. Because a small dose of barbiturate inhibited the function of the brain stem reticular formation which works antagonistically to the diffuse thalamocortical projection system.
When barbiturate was administere d followed by cardiazol at 10 mg/kg each, further increase than with barbiturate only was obserbed in the thresholds of arousal reaction in the cerebral cortex and hippocampus and of evoked muscular discharge in the fore and hind limbs due to stimulation of the brain stem reticular formation. Following a destruction of n. centrum medianum (CM) or n. ventralis anterior (VA), which are among the diffusely projecting nuclei, no further increase of the thresholds was observed. Thus it was demonstrated a prolongation of barbiturate anesthesia by cardiazol was related with the diffusely projecting nuclei such as CM or VA.
In experiments in terms of righting reflex the sub sequent administration of cardiazol prolonged a duration of barbiturate anesthesia in animals whose n. ventralis lateral part (VL) were bilaterally destroyed but not in animals whose diffusely projecting nuclei were bilaterally destroyed. The present data confirmed that the diffusely projecting nuclei played a part in prolonging a duration of barbiturate anesthesia by cardiazol on the basis of behavior. It was also clarified that VL worked antagonistically to the diffuse projection system in the central nervous system.