On the relationship between the autonomic nervous system and the inner ear, a considerable amount of researches with electrophysiological and histological techniques have been reported. But, there has been found no definite correlation between the sympaticomimetic and parasympaticomimetic drugs and those effects. The author presumed that the autonomic reactivity might be different in each experimented animal. As for the inner ear itself, the effects of autonomic nervous system acts on it so irregularily that the further investigations on this problem seemed to be necessary.
Taking into consideration the well known fact that the stimulation of the hypothalamus anterior and hypothalamus posterior increases temporarily the excitability of the parasympathetic and sympathetic centers, the author tried to cause some autonomic unbalance in the inner ear. In this study, the influences of electrostimulation of the hypothalamus and the reticular formation upon the cerebral and cochlear micro blood circulation were observed and the changes in the cochlear microphonics from the bilateral ears by the stimulation were also observed. Cats were immobilized with decamethonium bromide (C-10), and no anesthesia was used.
Blood pressure of femoral artery was recorded by means of a straingauge and penwriting-osci llograph.
The microcirculations in the temporal and frontal lobes and in the inner ear were recorded continuously by impedance plethysmographies, each of which had a pair of electrodes (0.1mm insulated steel wires, 1.5mm apart from each other). This method is based on the principle that the changes of blood volume in a given part cause the changes of electrical impedance in the same portion (Literature 84, 118).
To cause electrical stimulation, bipolar stainless steel electrodes, 0.7mm in diameter were implanted stereotaxically in the anterior hypothalamus, the posterior hypothalamus, and the reticular formation.
As the indicator of excitability in the hypothalamus, the pupille reflex, the nictitate membrane reflex and the changes of blood pressure were tested, and in view of those results the adequate parameter of stimulation on the animal was decided to be approximately of 3-5 voltage, 0.3 msec pulse duration, 60-80 pulses/sec during 5-10 secs at the hypothalamus, and approximately of 3-5 volts, 0.03 msec pulse duration, 300 pulses/sec during 5-10 secs at the reticular formation (Table 1).
1) The changes of contraction rate in the nictitate membrane, of heart contraction rate and of femoral blood pressure resulting from various parameters of electric stimulation are shown in Fig. 2a, 2b and 2c. The electrostimulation of hypothalamus posterior caused an irregular and fluctuating excitability of the sympathetic center repeatedly.
2) The changes of temporal blood flow resulting from hypothalamic stimulation were compared with the results from 10% CO2 inhalation. The changes of the latter were more conspicuous than the former (Fig. 1).
3) The effects of electrostimulation of the reticular formation, the hypothalamus anterior, and the hypothalamus posterior on the blood flow in the temporal and the frontal lobes are shown in Fig. 3, 4 and 5. The stimulation of the hypothalamus anterior (parasympathetic area) was followed by no demonstrable change in the frontal and temporal blood circulation nor in the blood pressure (Fig. 3). After the stimulation of the hypothalamus posterior (sympathetic area), the blood pressure rose several times 50-80 mmHg higher than usual during about 10 minutes before it became normalized. The blood flow in the frontal lobe was more stable than in the temporal lobe, but both of them corresponded to the change of blood pressure (Fig. 3, 4, 5).
4) The changes of cerebral blood flow in the frontal and the temporal lobes after a 10 γ noradrenaline intravenous injection were similar in the pattern of blood pressure to those of the hypothalamic stimulation (Fig. 4, 7).
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