ALTERED C-FOS EXPRESSION IN THE PARABRACHIAL NUCLEUS IN A RODENT MODEL OF CFA-INDUCED PERIPHERAL INFLAMMATION

Increases in the expression of immediate early genes have been shown t o occur in the lumbar spinal cord dorsal horn after peripheral inflamm ation. Given that the pontine parabrachial nucleus has been implicated in nociceptive as well as antinociceptive processes and is reciprocal ly connected with the spinal cord dorsal horn, it seems likely that pe ripheral inflammation will cause alterations in immediate early gene e xpression in this nucleus. To test this hypothesis we examined cFos-li ke immunoreactivity in a rodent complete Freund's adjuvant-induced per ipheral inflammatory model of persistent nociception. Unilateral hind paw injections of complete Freund's adjuvant produced inflammation, hy peralgesia of the affected limb, and alterations in open field behavio rs. Immunocytochemical analysis demonstrated a bilateral increase in c Fos-like immunoreactivity in the lateral and Kolliker-Fuse subdivision s of the parabrachial nucleus at 6 and 24 hours postinjection and an i psilateral decrease below basal levels in the Kolliker-Fuse subdivisio n at 96 hours postinjection when compared to saline controls. Taken to gether, these results suggest that select parabrachial neurons are act ivated by noxious somatic inflammation. These active parabrachial neur ons are likely to participate in ascending nociceptive and/or descendi ng antinociceptive pathways. (C) 1996 Wiley-Liss, Inc.