A study on regional difference of reaction to trigeminal stimulation

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Nociceptive stimulation to trigeminal nerve of rabbit causes fluctuations in blood pressure. We examined what stimulation raised or lowered blood pressure and observed change of autonomic nervous activity during stimulation. Stimulation of infraorbital nerve with 5 Hz caused depressor response, stimulation with 25 Hz caused pressor response. When blood pressure fell, a decrease in renal sympathetic nerve activity (RSNA) was observed. On the other hand, when blood pressure fell, a decrease in renal sympathetic nerve activity (RSNA) was observed. On the other hand, when blood pressure rose, an increase in RSNA was observed. These results suggested that the circulatory response elicited by trigeminal stimulation was a somato-sympathetic nerve reflex whose efferent pathway was sympathetic nerve. Next, we examined the factors that influenced these responses. Arterial baroreflex enhanced the depressor response and inhibited the pressor response and inhibited the pressor response. Propofol in … More hibited the pressor response and fentanyl inhibited the depressor response. Isoflurane and phentolamine inhibited the pressor and depressor responses. These results suggested there were different pathways in medulla causing the depressor and pressor responses elicited by trigeminal stimulation. In addition, we examined the change in blood flow volume of arteria carotis communis (CA), arteria renalis (RA), and arteria femoralis (FA) when the depressor response occurred, and the influence of fentanyl on the blood flow volume of each artery was observed. We observed the change in the blood flow volume when trigeminal nerve was stimulated and mean arterial pressure was lowered. The change was large in order of RA, FA, and CA, and there was no significant difference in the change of CA and FA. These results suggested that there were regional differences in level of a decrease in sympathetic nerve activity and self-adjustment ability of the blood flow. Though a decrease in blood pressure by trigeminal stimulation became small by administering fentanyl, the regional differences of arterial flow volume did not be affected with fentanyl. Less