Cervical prephrenic interneurons in the normal and lesioned spinal cord of the adult rat

Abstract

While 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. As 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 pre-phrenic interneurons suggesting some propriospinal relays exist between medullary neurons and the phrenic nucleus. Dual-labeling studies with pseudorabies virus recombinants also showed pre-phrenic 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 phrenicassociated interneurons was not significantly altered two weeks post-hemisection (i.e. when the earliest post-injury 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 raises speculation for potentially diverse roles in modulating phrenic function normally and post-injury.

Noxious Colorectal Distention in Spinalized Rats Reduces Pseudorabies Virus Labeling of Sympathetic Neurons

“…The present findings could influence interpretation of previous studies using PRV to assess neural pathways in intact and spinal cord-injured animals (Bareyre et al, 2004;Kim et al, 2002;Lane et al, 2008;Pan et al, 2005;Yu et al, 2003), including analysis of changes in c-Fos staining after SCI (Im et al, 2008). For example, decreased numbers of neurons observed in autonomic centers after SCI may be attributed to diminished viral uptake, in addition to decreased integrity of motor neuron pathways (Kim et al, 2002).…”

“…For example, decreased numbers of neurons observed in autonomic centers after SCI may be attributed to diminished viral uptake, in addition to decreased integrity of motor neuron pathways (Kim et al, 2002). Alternatively, complete SCI has little effect on PRV transport below a lesion (Yu et al, 2003), whereas studies with incomplete lesion models do not provide insight about whether reported injuryinduced alterations of neural circuitry are accompanied by attenuated PRV uptake and expression (Bareyre et al, 2004;Lane et al, 2008;Pan et al, 2005). Notably, increases in PRVlabeled spinal neurons are seen weeks to months after complete SCI following bladder inoculation, suggesting a reorganization of the spinal cord circuitry controlling the bladder after injury (Yu et al, 2003).…”

“…With the development of neurotropic viruses as an alternative to traditional tract tracing tools, our understanding of complex neuronal circuitry, particularly the innervation of thoracic and abdominal viscera, has greatly advanced (Buijs et al, 2003;Cano et al, 2000Cano et al, , 2004Card et al, 1990;Glatzer et al, 2003;Hadziefendic and Haxhiu, 1999;Jansen et al, 1997;Nadelhaft et al, 1992;Schramm et al, 1993;Standish et al, 1995). Notwithstanding this progress, there is a paucity of knowledge concerning how neurotrauma, particularly spinal cord injury (SCI), affects neuronal circuitry and/or plasticity as demarcated with the use of neurotropic viruses (Bareyre et al, 2004;Duale et al, 2009;Kim et al, 2002;Lane et al, 2008;Pan et al, 2005;Yu et al, 2003).…”

The Therapeutic Effectiveness of Delayed Fetal Spinal Cord Tissue Transplantation on Respiratory Function Following Mid-Cervical Spinal Cord Injury

“…A laparotomy was performed and the abdominal muscle was retracted to expose the diaphragm. Monosynaptic retrograde tracer [40 μl; 0.05%, cholera toxin subunit B (CT-B) conjugated with Alexa Fluor 594 (C34777); ThermoFisher Scientific, Waltham, MA, USA] (n = 4) or trans-synaptic tracer [1.75%, wheat germ agglutinin (WGA) conjugated with Alexa Fluor 594 (W11262); ThermoFisher Scientific] (n = 7) was painted on the bilateral diaphragm [27,28]. At 3 days after tracer painting, the animals were anesthetized with urethane (1.6 g/kg, i.p.)…”

Spinal Interneurons and Forelimb Plasticity after Incomplete Cervical Spinal Cord Injury in Adult Rats

“…A detailed understanding of the neuronal circuits underlying spontaneous recovery can significantly contribute to the design of cell-based and axonal growth-promoting approaches, as well as critical evaluation and prediction of their efficacy. 1,2 Unfortunately, comprehensive neuroanatomical demonstrations of functionally defined intraspinal circuits are lacking, in even the intact spinal cord. 1 The more notable exceptions are studies of spinal bladder, 3 autonomic, 4 and respiratory 1,5 networks, which have employed the transneuronal tracer, pseudorabies virus (PRV), to identify pre-motor spinal interneurons.…”