Journal of Neuroscience, Vol 8, 1767-1775, Copyright © 1988 by Society for Neuroscience
The intermediolateral cell column of the thoracic spinal cord is comprised of target-specific subnuclei: evidence from retrograde transport studies and immunohistochemistry
NM Appel and RP Elde
Department of Cell Biology and Neuroanatomy, University of Minnesota, Minneapolis 55455.
In this study we examined the hypothesis that the intermediolateral cell
column (IML) of the thoracic spinal cord, the nucleus from which
preganglionic sympathetic neurons originate, provides an anatomical
substrate through which selective regulation of sympathetic nervous system
targets is accomplished. Preganglionic sympathetic neurons of rats were
retrogradely labeled by the simultaneous exposure of the cervical
sympathetic trunk (CST) and the adrenal medulla to Fluoro-Gold and True
blue, contrasting fluorescent dyes. Retrograde labeling from these sites
revealed 2 populations of sympathetic preganglionic neurons in IML whose
distribution overlapped between segments T1 and T4. In regions where these
2 groups of retrogradely labeled neurons overlapped, sympathoadrenal
preganglionic (SAP) neurons occupied the most lateral aspect of the
nucleus. It was also determined whether individual retrogradely labeled
neurons within these two groups sent axon collaterals to both the CST and
adrenal medulla. Diamidino yellow, a fluorescent retrograde tracer dye that
labels only nuclei, was substituted for Fluoro-Gold and used in combination
with True blue to simultaneously label preganglionic sympathetic neurons
projecting to either the CST or adrenal medulla. No double-labeled cell
bodies were observed in spinal cords of rats treated in this manner. Thus
it appeared that the efferent projections of these 2 cell populations in
IML were target-specific. Immunohistochemical analysis of the relationship
between nerve fibers in the IML and preganglionic sympathetic neurons was
also undertaken in an attempt to classify further these 2 populations of
sympathetic preganglionic neurons. Equal proportions of identified CST and
SAP neurons appeared to be apposed by varicosities immunoreactive for
either somatostatin or serotonin. On the other hand, when the comparison
was based on whether oxytocin- immunoreactive varicosities appeared to
appose these 2 populations of retrogradely labeled sympathetic neurons, a
highly significant difference was revealed. That is,
oxytocin-immunoreactive fibers and terminals appeared to avoid SAP neurons.
Thus these data support the hypothesis that an anatomical substrate exists
in spinal cord IML whereby selective regulation of sympathetic nervous
system targets may be mediated. Moreover, the lack of
oxytocin-immunoreactive varicosities apposing SAP neurons in IML suggests
that if the paraventricular nucleus innervates SAP neurons in IML, it does
so via a population of neurons that do not use oxytocin as a
neurotransmitter.
Previous Article | Next Article
