On the presence and functional significance of sympathetic premotor neurons with collateralized spinal axons in the rat


  • D.G.S. Farmer
  • N. Pracejus
  • B. Dempsey
  • A. Turner
  • P. Bokiniec
  • J.F.R. Paton
  • A.E. Pickering
  • J. Burguet
  • P. Andrey
  • A.K. Goodchild
  • R.M. McAllen
  • S. McMullan


  • Journal of Physiology


  • J Physiol 597 (13): 3407-3423


  • Here we investigate the extent of spinal axon collateralization of rat RVLM sympathetic premotor neurons and its functional consequences. In anatomical tracing experiments, two recombinant herpes viral vectors with retrograde tropism and expressing different fluorophores were injected into the intermediolateral column at upper thoracic and lower thoracic levels. Histological analysis revealed that ~21% of RVLM bulbospinal neurons were retrogradely labelled by both vectors, indicating substantial axonal collateralisation to disparate spinal segments. In functional experiments, another virus with retrograde tropism, a canine adenovirus expressing Cre recombinase, was injected into the left intermediolateral horn around the thoracolumbar junction, while a Cre-dependent viral vector encoding Channelrhodopsin2 under LoxP control was injected into the ipsilateral RVLM. In subsequent terminal experiments blue laser light (473 nm x 20 ms pulses at 10 mW) was used to activate RVLM neurons that had been transduced by both vectors. Stimulus-locked activation, at appropriate latencies, was recorded in the following pairs of sympathetic nerves: forelimb and hindlimb muscle sympathetic fibres; cardiac and either hindlimb muscle or lumbar sympathetic nerves. The latter result demonstrates that axon collaterals of lumbar-projecting RVLM neurons project to, and excite, both functionally similar (forelimb and hindlimb muscle) and functionally dissimilar (lumbar and cardiac) preganglionic neurons. Together, these findings show that the axons of a significant proportion of RVLM neurons collateralise widely within the spinal cord, and that they may excite preganglionic neurons of more than one functional class.