Lane Michael A, White Todd E, Coutts Marcella A, Jones Alex L, Sandhu Milapjit S, Bloom David C, Bolser Donald C, Yates Bill J, Fuller David D, Reier Paul J
Department of Neuroscience, College of Medicine, University of Florida, Gainesville, Florida 32610, USA.
J Comp Neurol. 2008 Dec 10;511(5):692-709. doi: 10.1002/cne.21864.
Although monosynaptic bulbospinal projections to phrenic motoneurons have been extensively described, little is known about the organization of phrenic premotor neurons in the adult rat spinal cord. Because interneurons may play an important role in normal breathing and recovery following spinal cord injury, the present study has used anterograde and transneuronal retrograde tracing to study their distribution and synaptic relations. Exclusive unilateral, first-order labeling of the phrenic motoneuron pool with pseudorabies virus demonstrated a substantial number of second-order, bilaterally distributed cervical interneurons predominantly in the dorsal horn and around the central canal. Combined transneuronal and anterograde tracing revealed ventral respiratory column projections to prephrenic interneurons, suggesting that some propriospinal relays exist between medullary neurons and the phrenic nucleus. Dual-labeling studies with pseudorabies virus recombinants also showed prephrenic interneurons integrated with either contralateral phrenic or intercostal motoneuron pools. The stability of interneuronal pseudorabies virus labeling patterns following lateral cervical hemisection was then addressed. Except for fewer infected contralateral interneurons at the level of the central canal, the number and distribution of phrenic-associated interneurons was not significantly altered 2 weeks posthemisection (i.e., the point at which the earliest postinjury recovery of phrenic activity has been reported). These results demonstrate a heterogeneous population of phrenic-related interneurons. Their connectivity and relative stability after cervical hemisection raise speculation for potentially diverse roles in modulating phrenic function normally and postinjury.
尽管已经对支配膈运动神经元的单突触延髓脊髓投射进行了广泛描述，但对于成年大鼠脊髓中膈前运动神经元的组织情况却知之甚少。由于中间神经元可能在正常呼吸以及脊髓损伤后的恢复过程中发挥重要作用，因此本研究采用顺行和跨神经元逆行示踪技术来研究它们的分布及突触关系。用伪狂犬病病毒对膈运动神经元池进行独家单侧、一级标记，结果显示大量二级、双侧分布的颈段中间神经元主要位于背角和中央管周围。联合跨神经元和顺行示踪显示，腹侧呼吸柱向膈前中间神经元投射，这表明在延髓神经元和膈核之间存在一些脊髓 propriospinal 中继。用伪狂犬病病毒重组体进行的双标记研究还表明，膈前中间神经元与对侧膈或肋间运动神经元池整合。随后研究了颈外侧半横断后中间神经元伪狂犬病病毒标记模式的稳定性。除了中央管水平处对侧受感染的中间神经元较少外，半横断后 2 周（即据报道膈活动最早出现损伤后恢复的时间点），与膈相关的中间神经元的数量和分布没有明显改变。这些结果表明存在一群异质性的膈相关中间神经元。它们在颈半横断后的连接性和相对稳定性引发了人们对其在正常和损伤后调节膈功能中可能具有多种不同作用的推测。
