Differential rostral projections of caudal brainstem neurons receiving trigeminal input after masseter inflammation

Tetsuya Ikeda, Ryuji Terayama, Seong Suk Jue, Shinichi Sugiyo, Ronald Dubner, Ke Ren

Research output: Contribution to journalArticle

32 Citations (Scopus)

Abstract

To understand the functional significance of orofacial injury-induced neuronal activation, this study examined the rostral projection of caudal brainstem neurons that were activated by masseteric inflammation. Rats were injected with a retrograde tracer, Fluorogold, into the nucleus submedius of the thalamus (Sm), parabrachial nucleus (PB), lateral hypothalamus (LH), or medial ventroposterior thalamic nucleus (VPM) 7 days before injection of an inflammatory agent, complete Freund's adjuvant (CFA), into the masseter muscle. Rats were perfused at 2 hours after inflammation, and brainstem tissues were processed for Fos-Fluorogold double immunocytochemistry. Although there was no difference in Fos expression among the four groups (n = 4 per site), the rostral projection of Fos-positive neurons showed dramatic differences. In the ventral portion of the trigeminal subnuclei interpolaris/caudalis (Vi/Vc) transition zone, the percentage of Fos-positive neurons projecting to the Sm (39.7%) was significantly higher than that projecting to the LH (5.4%) or VPM (5.6%; P < .001). The anesthesia alone also induced Fos expression in ventral Vi/Vc neurons, but these neurons did not project to Sm. In the caudal laminated Vc and dorsal Vi/Vc, the PB was the major site of rostral projection of Fos-positive neurons. In the caudal ventrolateral medulla and nucleus tractus solitarius, Fos-positive neurons projected to the Sm, PB, and LH. Most VPM-projecting neurons examined did not show Fos-like immunoreactivity after masseter inflammation. These findings emphasize the importance of the trigeminal Vi/Vc transition zone in response to orofacial deep tissue injury. Furthermore, the results differentiate the ventral and dorsal portions of the Vi/Vc transition zone, in that the Sm received projection mainly from activated neurons in the ventral Vi/Vc. The activation of Vi/Vc neurons and associated ascending pathways may facilitate somatoautonomic and somatovisceral integration and descending pain modulation after orofacial deep tissue injury.

Original languageEnglish
Pages (from-to)220-233
Number of pages14
JournalJournal of Comparative Neurology
Volume465
Issue number2
DOIs
Publication statusPublished - Oct 13 2003

Keywords

  • Fluorogold
  • Freund's adjuvant
  • Nucleus submedius
  • Trigeminal transition zone

ASJC Scopus subject areas

  • Neuroscience(all)

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