Article ID | Journal | Published Year | Pages | File Type |
---|---|---|---|---|
4327740 | Brain Research | 2009 | 14 Pages |
Abstract
The anterior ethmoidal nerve (AEN) innervates the nasal passages and external nares, and serves as the afferent limb of the nasopharyngeal and diving responses. However, although 65% of the AEN is composed of unmyelinated fibers, it has not been determined whether this afferent signal is carried by unmyelinated or myelinated fibers. We used the transganglionic tracers WGA-HRP, IB4-HRP, and CTB-HRP to trace the central projections of the AEN of the rat. Interpretation of the labeling patterns suggests that AEN unmyelinated fibers project primarily to the ventral tip of the ipsilateral medullary dorsal horn (MDH) at the level of the area postrema. Other unmyelinated projections were to the ventral paratrigeminal nucleus and ventrolateral medulla, specifically the Bötzinger and RVLM/C1 regions. Myelinated AEN fibers projected to the ventral paratrigeminal and mesencephalic trigeminal nuclei. Stimulating the nasal passages of urethane-anesthetized rats with ammonia vapors produced the nasopharyngeal response that included apnea, bradycardia and an increase in arterial blood pressure. Central projections of the AEN co-localized with neurons within both MDH and RVLM/C1 that were activated by nasal stimulation. Within the ventral MDH the density of AEN terminal projections positively correlated with the rostral-caudal location of activated neurons, especially at and just caudal to the obex. We conclude that unmyelinated AEN terminal projections are involved in the activation of neurons in the MDH and ventrolateral medulla that participate in the nasopharyngeal response in the rat. We also found that IB4-HRP was a much less robust tracer than WGA-HRP.
Keywords
CTB-HRPanterior ethmoidal nerveSp5IAENParatrigeminal nucleusMe5WGA-HRPWGATMBIB4MDHNTSRVLMSDHHRPCTBBSASp5rostral ventrolateral medullabovine serum albumintetramethylbenzidineSpinal trigeminal tractmedullary dorsal hornSpinal dorsal hornHeart ratemean arterial blood pressureBötzinger complexrespiratory ratemapnucleus ambiguusnucleus tractus solitariusMesencephalic trigeminal nucleusfacial nucleusDiving responseHorseradish peroxidaseWheat germ agglutinin
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Authors
Michael P. Hollandsworth, Karyn M. DiNovo, Paul F. McCulloch,