Activation of the vestibular system produces reflex modulation of expiratory muscle activity. The purpose of the present study was to investigate the possible role of bulbospinal expiratory (E) neurons located in the caudal ventral respiratory group (VRG) in mediating vestibulo-respiratory reflexes. Experiments were carried out in decerebrated, paralyzed, and artificially ventilated cats. 2. Electrical stimulation of the vestibular nerve (VN), using short trains of current pulses, elicited bilateral reflex responses on abdominal muscle nerves (ABDNs). This response was not affected by lesions of the cochlear nuclei made by kainic acid injections. The ABDN response typically consisted of a combination of short-latency excitation and long-latency inhibition on the ipsilateral side and, in contrast, a combination of short-latency inhibition and long-latency excitation on the contralateral side. 3. Extracellular recordings were made from 43 caudal VRG bulbospinal E neurons that were activated antidromically from the contralateral upper lumbar spinal cord. More than 80% of these neurons responded to either ipsi- and/or contralateral VN stimulation. The neuronal response consisted of either a combination of excitation and inhibition or only inhibition. The majority of neurons had response patterns appropriate to contribute to the response observed on the contralateral ABDN; however, the latency of the VRG E neuron response was too long to initiate the ABDN response. 4. To further evaluate the contribution of caudal VRG E neurons to the vestibulo-abdominal reflex, ABDN responses were compared before and after sectioning the axons of caudal VRG bulbospinal E neurons where they cross the midline between the obex and first cervical spinal segment. These midsagittal lesions abolished expiratory modulation of ABDN discharge. The lesions also decreased the amplitude of the vestibular-evoked ABDN response but could not abolish the response. The postlesion amplitude was decreased on average to approximately 70% of prelesion values. 5. In conclusion, although the present results indicate that the majority of caudal VRG bulbospinal E neurons respond appropriately to contribute to the vestibulo-abdominal reflex, the reflex largely is unaffected by the removal of caudal VRG E input. The additional descending inputs that are important for mediating the reflex remain to be investigated and may include vestibulospinal and/or reticulospinal tracts.
摘要
前庭系统的激活会引起呼气肌活动的反射性调节。本研究的目的是调查位于延髓尾端腹侧呼吸组（VRG）的延髓脊髓呼气（E）神经元在介导前庭 - 呼吸反射中可能发挥的作用。实验在去大脑、麻痹并进行人工通气的猫身上进行。2. 使用短串电流脉冲对前庭神经（VN）进行电刺激，可在双侧腹肌神经（ABDNs）上引发反射性反应。这种反应不受 kainic 酸注射造成的耳蜗核损伤的影响。ABDN 反应通常包括同侧短潜伏期兴奋和长潜伏期抑制的组合，相反，对侧则是短潜伏期抑制和长潜伏期兴奋的组合。3. 从 43 个延髓尾端 VRG 延髓脊髓 E 神经元进行细胞外记录，这些神经元通过对侧上腰脊髓的逆向激活。其中超过 80%的神经元对同侧和/或对侧 VN 刺激有反应。神经元反应包括兴奋和抑制的组合或仅为抑制。大多数神经元的反应模式有助于对侧 ABDN 上观察到的反应；然而，VRG E 神经元反应的潜伏期太长，无法引发 ABDN 反应。4. 为了进一步评估延髓尾端 VRG E 神经元对前庭 - 腹肌反射的贡献，在切断延髓尾端 VRG 延髓脊髓 E 神经元轴突在闩和第一颈髓节段之间穿过中线的部位前后，比较了 ABDN 反应。这些矢状面中部损伤消除了 ABDN 放电的呼气调节。损伤还降低了前庭诱发的 ABDN 反应的幅度，但不能消除该反应。损伤后幅度平均降低到损伤前值的约 70%。5. 总之，尽管目前的结果表明大多数延髓尾端 VRG 延髓脊髓 E 神经元的反应有助于前庭 - 腹肌反射，但去除延髓尾端 VRG E 输入后，该反射在很大程度上不受影响。介导该反射的其他下行输入仍有待研究，可能包括前庭脊髓束和/或网状脊髓束。
