延腦吻端腹側核區神經元對於不同頻段0~1 Hz交感神經律動之貢獻

Abstract

交感神經活性對於心血管的調控相當重要。目前已知血壓律動與交感神經訊號律動在低頻(約0.45 Hz)有極高的相關性，反應出交感神經對於血管管徑的調控行為。但直至目前，0~1 Hz交感神經律動的頻譜組成與來源仍不清楚。因此本研究分兩部份實驗來解決問題。第一部分為直接紀錄清醒老鼠的腎交感神經活性與血壓，以頻譜分析方法探討0~1 Hz的交感神經律動頻譜組成究竟為何？並分析該頻段的交感神經律動與同頻段血壓律動之量化關係。第二部份則是選擇交感神經活性的主要輸入來源－延腦腹側核區（rostral ventrolateral medulla; RVLM）作為研究對象，探討RVLM中是否有參予0~1 Hz內特別頻段的交感神經律動之神經元。第一部份實驗在平均7隻老鼠0~1 Hz的交感神經頻譜後，發現0~1 Hz的交感神經頻譜組成具有兩個高峰(peak)，peak frequency分別是0.16 Hz (極低頻區)與0.45 Hz(低頻區)。另發現0.016~0.85 Hz交感神經的頻譜與血壓的頻譜功率比值之對數值，對應頻率的關係為線性負相關。第二部份的實驗則採用7隻雄性老鼠，於麻醉、人工控制呼吸的狀況下進行細胞外紀錄，並同時量測血壓與交感神經活性。將所記錄到的85個RVLM神經元，利用其對應血壓變化的關係分成三群：(1)與血壓變化負相關者（negatively response with blood pressure），簡稱BP(-)。(2) 與血壓變化正相關者（positively response with blood pressure），簡稱BP(+)。(3)與血壓變化無關係者，簡稱control。透過coherence analysis，發現BP(-)可能是主要貢獻極低頻區(0~0.3 Hz)、低頻(0.3~0.6 Hz)與高頻(0.6~1 Hz)交感神經律動的來源。其中，貢獻低頻與高頻的BP(-)神經元放電後，會興奮交感神經活性。因此，推測RVLM內包含功能性不同的神經元類群，但其中還是以受到感壓反射調節的BP(-)神經元對於0~1 Hz交感神經頻譜的極低頻區和低頻區的貢獻程度最高。

Sympathetic nerve activity (SNA) is important in regulation of cardiovascular functions. Slow oscillations in blood pressure fluctuation is highly correlated with SNA fluctuation of the same frequency, and some studies suggest that this slow rhythms reflect the sympathetic modulation of resistance vessels. However, the frequency components and the origin of sympathetic rhythms at 0~1 Hz is still not clear. Therefore, two objectives of this study is to figure out the frequency components of sympathetic oscillations at 0~1 Hz and to determine whether different RVLM neurons, which are critically important in the generation of the sympathetic rhythms, contributed to specific frequencies in SNA. Blood pressure and renal SNA were recorded simultaneously in awaked rats. Group- average spectra of SNA in 7 rats showed that spectral power both in the very low frequency(VLF) range and low frequency(LF) range were prominent in sympathetic rhythms at 0~1 Hz. In addition, the second experiment was performed. Blood pressure, renal SNA and neuronal activity in RVLM were recorded simultaneously in anesthetized, paralyzed and artificially ventilated rats. We found 85 RVLM neurons recorded. Neuronal activity changed in response to increased blood pressure were used to classify RVLM neurons into three groups, including negatively response with blood pressure (BP(-) neurons), positively response with blood pressure (BP(+) neurons) and no response with blood pressure (control). According to coherence analysis, BP(-) may provide the major contribution to all three frequency bands in the sympathetic rhythms. Among them, neurons which contributed to LF range and HF range excited SNA while these neurons were firing. These results show that there may be separate functional group in the RVLM, but only one group of neurons that were modulated by baroreflex contribute to both VLF and LF rhythms in SNA.