Journal of Neuroscience, Vol 6, 1220-1226, Copyright © 1986 by Society for Neuroscience
Opioid peptide immunoreactivity in spinal and trigeminal dorsal horn neurons projecting to the parabrachial nucleus in the rat
DG Standaert, SJ Watson, RA Houghten and CB Saper
The parabrachial nucleus (PB) is the major relay for ascending visceral
afferent information from the nucleus of the solitary tract to the
forebrain. We have recently found that PB in the rat also receives a
substantial afferent projection from neurons in the marginal zone of the
entire length of the spinal and trigeminal dorsal horn. Immunoreactive
perikarya stained with antisera against several neuropeptides--including
dynorphin, enkephalins, and substance P--have been identified in the
marginal zone. We therefore investigated the chemical specificity of the
spinoparabrachial projection by combining fluorescent retrograde tracing
with immunofluorescence for substance P, dynorphin A1-17, met-enkephalin,
and two enkephalin precursor fragments (proenkephalin 192-203 and peptide
E). Following PB injections of fluorescent dyes, about half of the
retrogradely labeled neurons in the marginal zone stained with antisera
against either dynorphin or enkephalin series peptides. Elution-restaining
experiments indicated that the dynorphin- and enkephalin-immunoreactivities
were contained within separate populations of marginal zone neurons. We
could not identify any substance P-immunoreactive perikarya in the marginal
zone, but substance P-immunoreactive fibers were seen in close apposition
to retrogradely labeled, opioid-immunoreactive cell bodies and dendrites.
These results indicate that the dynorphin- and enkephalin- immunoreactive
perikarya in the marginal zone of the dorsal horn represent independent
neuronal populations. These opioid-immunoreactive neurons, which are
believed to have extensive local collateral connections, are the main
source of a long ascending projection to the parabrachial nucleus in the
rat. Furthermore, opioid neurons in the marginal zone may receive substance
P-immunoreactive primary sensory afferents.