ウサギの中枢電気現象に及ぼす乳頭体刺激の影響について検討した.脳幹網様体(RF)および大脳皮質刺激による覚醒反応の刺激閾値は,乳頭体に3Hzの電気刺激を与えることにより下降したが,100Hz刺激では上昇した.RF及び大脳皮質刺激による誘発筋放電の刺激閾値は,乳頭体100Hz刺激により上昇したが,海馬刺激による筋放電の刺激閾値は,乳頭体100Hz刺激により下降した.あらかじめ視床のnucl.ventralis anterior(VA)を電気的に破壊したウサギでは,RF刺激による覚醒反応の刺激閾値の乳頭体刺激(3・100Hz)による変化は認められなかった.以上の成績より,乳頭体の低頻度刺激は意識に対して促進的に作用するが,乳頭体の高頻度刺激は意識ならびに錐体路系の運動機能に対しては抑制的に作用し,錐体外路系運動機能に対しては促進的に作用することが考えられ,これらの促進・抑制効果にはVAを含む汎性視床投射系の関与が推定された.

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As a part of the study to elucidate the influence of exteroceptive stimulation on the excitability of the brain stem reticular formation (RF) in presence of flash stimuli, the effect of hippocampal stimulation on the threshold of the RF was investigated in the rabbit and th e following observed.
1) The threshold of the arousal reaction appearing in the cerebral cortex EEG and the hippocampus (HPC) EEG and the evoked muscular discharge in the fore- and hind limbs, due to stimulation of the RF with 100 Hz was decreased by stimultaneous 100 Hz (0.2-1.0V)stimulation of the HPC.
2) The threshold of the arousal reaction and the evoked muscular discharge was increased by simultaneous 3 Hz (0.5-2.0V) stimulation of the HPC.
3) The decrease or increase in the threshold of the arousal reaction and the evoked muscular discharge following stimulation (100 Hz or 3 Hz) of the HPC, was abolished by destruction of the nucleus ventralis anterior or nucleus reticularis, which belong to the diffuse thalamocortical projection system. From these results, it w as concluded that the increase in excitability of the RF by HPC stimulation with 100 Hz, and the decline by stimulation with 3 Hz, can be attributed to a decrease in indirect inhibition and rise in indirect inhibition of the RF, respectively, via the diffuse thalamocortical projection system. The findings suggest that the previously reported increase in excitability of the RF by attachment of the contact lens in the presence of the flash stimuli (I), corresponds to the effect of 100 Hz HPC stimulation while the decrease in excitability of the RF by the contact lens in the absence of the flash stimuli corresponds to the effect of 3 Hz HPC stimulation.

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The changes in consciousness and motor activity due to exteroceptive stimulation in the presence and the absence of flash stimuli were studied in the kindled rabbits. The exteroceptive stimulation consisted of the attachment of a har d contact lens (CL) to the eye of the rabbits.
1) In control group, the threshold of the arousal-like reaction and the evoked muscular discharge due to 100 Hz stimulation of the cerebral cortex increased on attachment of CL in the absence of flash stimuli, but decreased in the presence of flash stimuli.
2) In amygdaloid kindled group and hippocampal kindled one, the threshold of the arousallike reaction and the evoked muscular discharge due to 100 Hz stimulation of the cerebral cortex decreased on attachment of CL both in the presence and the absence of flash stimuli.
These findings in kindled rabbits suggest that exteroceptive stimulation facilitates farther excitability of the brainstem reticular formation and the level of consciousness and motor activity.

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The effects of YM-14673 on central nervous system activity in rabbits were investigated electrophysiologically.
1. The threshold of arousal reaction of the cerebral cortex and hippocampus and those of evoked muscular discharges in the fore and hind limbs due to stimulation of the brain stem reticular formation decreased after administration of YM-14673.
2. The threshold of the evoked muscular discha rges in the fore and hind limbs due to stimulation of the cerebral cortex decreased after administration of YM-14673.
3. The threshold of the evoked muscular discharges in the fore and hi nd limbs due to stimulation of the hippocampus increased after administration of YM-14673.
4. The threshold of arousal reaction and evoked muscular dis charges in the fore and hind limbs due to stimulation of the cerebral cortex, which had been elevated by destruction of the internal capsule, was lowered after daily administration of YM-14673 0.05mg/kg.
The findings suggest that YM-14673 has a consciousness-arousing effect, a facil itatory effect on the pyramidal system and an inhibitory effect on the extrapyramidal system.

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Effects of TRH on the central nervous system activity were investigated electrophysiologically. TRH (0.05-1.0mg/kg) was injected intravenously in the rabbit and the following were observed.
1. The threshold of arousal reaction of the cerebral cortex EEG and hippocampus EEG and those of evoked muscular discharges in the fore and hind limbs due to 100Hz stimulation of the brain stem reticular formation decreased after administration of TRH.
2. These decreases persisted a considerably long time (at least on e hour).
3. The threshold of the evoked muscular discharges in the fore and hind limbs due to stimulation of the cerebral cortex decreased after administration of TRH.
4. The threshold of the evoked muscular discharges in the for e and hind limbs due to stimulation of the hippocampus increased after administration of TRH. It was suggested that the TRH has consciousness-arousing act ivity, a facilitatory effect on the pyramidal system and an inhibitory effect on the extrapyramidal system.

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The mechanism of photo-evoked eyelid microvibration (MV) was studied in unanesthetized rabbits by giving a series of electrical stimulation on the subcortical structures (such as caudate nucleus, globus pallidus, putamen, amygdaloid nucleus, hippocampus and ventrolateral nucleus of thalamus) or by destroying them electrically.
1. Five components were observed in the MV in response to the photic stimulation. They were named MV₁, MV₂, MV₃, MV₄ and MV₅and their peak latencies were 33.1,44.1,57.3,70.0 and 83.0 msec respectively.
2. The influence on the amplitude of MV by electrical stimulation of subcortical structures was studied with frequencies of 3Hz and 100 Hz. Stimulation of the caudate nucleus with 100 Hz suppressed MV to a greater degree than with 3 Hz.
3. Stimulation of the putamen with 3 Hz suppressed MV to a greater degree than with 100 Hz.
4. Stimulation of the globus pallidus with 3 Hz and 100 ', Hz potentiated MV, and the Potentiation was stronger with 100 Hz.
5. Stimulation of amygdaloid nucleus had either facilitatory or inhibitory effect on MV, depending on the site of stimulation. Inhibitory effect was often observed with stimula t i on of the ventral part of the amygdaloid nucleus.
6. MV was depressed by stimulation of the hippocampus with both frequencies, especially with 100 Hz.
7. Stimulation of the ventrolateral nucleus of the thalamus suppressed MV. Its effect was not dependent on the difference in freqency.
8. MV either increased or decreased in amplitude with stimulation of the internal capsule. In the same animal, the effect on MV was the same with the two diffenent frequencies o f stimulation. In the potentiated case, stimulation of the internal capsule with 100 H z increased to a greater extent than with 3 Hz.
9. MV was recorded 10,60 and 120 minutes after generating a electrical lesion in the caudate nuclei. MV slowly increased step by step after destruction of the bilateral cauda t e nuclei, while MV gradually decreased after destruction of the globus pallidus.
10. MV increased after destruction of the putamen and the maximal response was usually obtained at 60 minutes. In some cases, MV either increased or decreased at 10 min u tes.
11. Destruction of the amygdaloid nucleus markedly potentiated MV, especially, at a later time.
12. Potentiation of MV was observed at both 60 and 120 minutes after widespread destruction of the hippocampus, while some cases, MV decreased at 10 minutes.
13. MV decreased at 10 minutes after damage of the ventrolateral nucleus of the thalamus, whereas it increased at both 60 and 120 minutes after destruction.
14. Destruction of the internal capsule resulted in different effects on MV at 10 minutes, though MV tended to decrease at both 60 and 120 minutes.
15. Intravenous injection of barbiturate (5mg/kg) markedly suppressed MV.
16. The effect of electrical stimulation of the subcortical structures was frequently reversed by the prior application of barbiturate.

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