ウサギ海馬と眼球運動

A series of experiments using rabbits were made on the functional correlation between the limbic system, particularly the hippocampus, and the oculomotor system to obtain a better understanding of the neural mechanism of neurotic vertigo in humans. Through a series of experiments, the following facts were noted:<br>(1) When a certain amount of electric stimulation (1msec, 200Hz, pulse waves at 3 volts for 30 seconds per day) was given repeatedly to the hippocampus of rabbits, the animals tended to show a nystagmus-like eye movement. This eye movement appeared with a fairly long latency (about 25 minutes) and was directed to the right and left. The EEG's (the hippocampus, midbrain reticular formation and neocortex) related to the period of latency showed decreased activity of the brain, whereas those related to that of the nystagmus-like eye movement showed increased brain activity. Furthermore, autonomic responses suggestive of parasympathetic nerve irritation were seen in the period of latency, whereas those suggestive of sympathetic nerve irritation were seen in the period of nystagmus-like eye movement. These indicate that after repeated electric stimulation of the hippocampus of rabbits, over-excitement of the adrenergic component involved in this brain is brought about and such ensues over-excitement of the oculomotor system. The over-excitement of the oculomotor system leads to the appearance of the nystagmus-like eye movement mentioned above.<br>(2) Rabbits which had shown eye movements as a result of either repeated electric stimulation of the unilateral lumbar erector muscles or lesions of the unilateral labyrinth developed eye movements more easily than normal after stimulation of the hippocampus. Furthermore, the eye movements thus induced were similar to those which the animals had developed previously due to the treatments mentioned above. These eye movements tended to appear with a fairly long latency as described in (1).<br>(3) A nystagmus-like eye movement appeared when repeated electric stimulation was given to the medial nucleus of the mamillary body and/or the septal area of rabbits. The eye movement thus induced was similar to that elicited from the hippocampus. However, reinforcement was found more markedly in the eye movement elicited from the mammillary body than in that elicited from the septal area after intravenous injection of adrenaline and, moreover, a similarity was found between the hippocampus and the medial nucleus of the mammillary body with regard to the reinfrocement of the above-mentioned eye movements. Thus, the importance of the role of the medial nucleus of the mammillary body was noted with regard to the development of the eye movement of hippocampal origin.<br>(4) A small amount of adrenaline was injected into the hippocampus of rabbits before and after repeated electric stimulation of the cerebellum, particularly the Folium vermis and the resulting changes in the ENG and the EEG's (the hippocampus, midbrain reticular formation, cerebellum and neocortex) were observed. After repeated electric stimulation of the cerebellum, animals tended to develop and/or increase nystagmus-like eye movements when adrenaline was injected into the hippocampus and, moreover, the appearance and/or increase of these eye movements paralleled the arousal state in the EEG's. This finding indicates that the cerebellum plays a certain role in the reinforcement of the ocular ataxia of hippocampal origin, increasing the activity of the adrenergic component involved in the latter brain.<br>(5) A small amount of cholinergic stimulant (carbachol) and/or adrenergic stimulant (adrenaline) were injected into the hippocampus of rabbits before and after repeated electric stimulation of this brain and the resulting changes in the ENG and EEG's (the hippocampus, midbrain reticular formation and neocortex) were observed. The following facts were noted:<br>Before repeated electric stimulation of the hippocampus, animals hype