In lampreys, respiration consists of a fast and a slow rhythm. This study was aimed at characterizing both anatomically and physiologically the brainstem regions involved in generating the two rhythms. The fast rhythm generator has been located by us and others in the rostral hindbrain, rostro-lateral to the trigeminal motor nucleus. More recently, this was challenged by researchers reporting that the fast rhythm generator was located more rostrally and dorsomedially, in a region corresponding to the mesencephalic locomotor region. These contradictory observations made us re-examine the location of the fast rhythm generator using anatomical lesions and physiological recordings. We now confirm that the fast respiratory rhythm generator is in the rostro-lateral hindbrain as originally described. The slow rhythm generator has received less attention. Previous studies suggested that it was composed of bilateral, interconnected rhythm generating regions located in the caudal hindbrain, with ascending projections to the fast rhythm generator. We used anatomical and physiological approaches to locate neurons that could be part of this slow rhythm generator. Combinations of unilateral injections of anatomical tracers, one in the fast rhythm generator area and another in the lateral tegmentum of the caudal hindbrain, were performed to label candidate neurons on the non-injected side of the lateral tegmentum. We found a population of neurons extending from the facial to the caudal vagal motor nuclei, with no clear clustering in the cell distribution. We examined the effects of stimulating different portions of the labeled population on the respiratory activity. The rostro-caudal extent of the population was arbitrarily divided in three portions that were each stimulated electrically or chemically. Stimulation of either of the three sites triggered bursts of discharge characteristic of the slow rhythm, whereas inactivating any of them stopped the slow rhythm. Substance P injected locally in the lateral tegmentum accelerated the slow respiratory rhythm in a caudal hindbrain preparation. Our results show that the fast respiratory rhythm generator consists mostly of a population of neurons rostro-lateral to the trigeminal motor nucleus, whereas the slow rhythm generator is distributed in the lateral tegmentum of the caudal hindbrain.

中文翻译：

---

重新审视七鳃鳗呼吸的两个节律发生器

七鳃鳗的呼吸由快节奏和慢节奏组成。这项研究的目的是从解剖学和生理学上描述参与产生两种节律的脑干区域。我们和其他人已经将快节奏发生器定位在后脑的喙侧，三叉神经运动核的喙外侧。最近，这一点受到了研究人员的挑战，他们报告称快节奏发生器位于更靠近头侧和背侧的位置，位于与中脑运动区域相对应的区域。这些矛盾的观察结果使我们利用解剖损伤和生理记录重新检查快节奏发生器的位置。我们现在确认，快速呼吸节律发生器位于头外侧后脑，正如最初所描述的那样。慢节奏发生器受到的关注较少。先前的研究表明，它由位于尾侧后脑的双边、相互连接的节律生成区域组成，并具有向上的投射到快节律发生器。我们使用解剖学和生理学方法来定位可能成为这个慢节奏发生器一部分的神经元。结合单侧注射解剖示踪剂，一个注射在快节律发生器区域，另一个注射在尾侧后脑的外侧被盖，以标记外侧被盖非注射侧的候选神经元。我们发现一群神经元从面部延伸到尾部迷走神经运动核，细胞分布没有明显的聚集。我们研究了刺激标记群体的不同部分对呼吸活动的影响。群体的头尾范围被任意分为三个部分，每个部分都受到电或化学刺激。刺激这三个部位中的任何一个都会引发慢节奏特征的放电爆发，而失活其中任何一个都会停止慢节奏。在尾部后脑准备中，在外侧被盖局部注射P物质加速了缓慢的呼吸节律。我们的结果表明，快速呼吸节律发生器主要由三叉神经运动核的嘴侧神经元群组成，而慢速呼吸节律发生器则分布在尾侧后脑的外侧被盖中。