Study on the difference in the circulatory response elicited with trigeminal stimulation

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Adult white rabbits were used. The mental nerve and the infraorbital nerve were stimulated by 10s of square pulses, 0.1-0.75ms in duration, 1-50Hz in frequency and 1-20V in strength. At the stimulus frequency of 5Hz, strength of 5-10V and duration of 0.25ms, blood pressure decreased most markedly and the response to the stimulation of the infraorbital nerve was larger than that of the mental nerve. At the stimulus of higher frequency and greater strength, blood pressure fell at first and then rose. This discrepancy suggested that pathways of suppressor response and depressor response were different.Subsequently, the aortic nerve was stimulated. The stimulus mode was 10s of the square wave, 10-50Hz in frequency, 1-10V in strength, 0.1-0.75ms in duration. Falling in blood pressure elicited with the stimulation of the aortic nerve became obvious at higher frequency over 25Hz and decrease in heart rate was more remarkable than that elicited with the trigeminal nerve stimulation. It took more time from the beginning of the stimulation to the peak of low blood pressure compared with the trigeminal nerve stimulation. Response of the aortic nerve and that of the trigeminal nerve were different because there were differences in the medullary pathway of the stimulus conduction and in the vagal nerve activity.Furthermore, the electric stimulation of the infraorbital nerve and the aortic nerve was carried out simultaneously. Decreases of blood pressure and heart rate elicited with simultaneous stimulation were greater than that elicited with single nerve stimulation. However, the unique reaction by simultaneous stimulus could not be checked and the relation of the trigeminal depressor response and baroreflex did not become clear.