ID 104177
Author
Hiura, Akio Oral Histology, School of Dentistry, University of Tokushima KAKEN Search Researchers
Nakagawa, Hiroshi Dentistry for Oersons with Disability, Tokushima niversity Hospital, University of Tokushima Tokushima University Educator and Researcher Directory KAKEN Search Researchers
Keywords
Noxious heat
Noxious mechanical stimulus
Withdrawal response
Inflammatory pain
Content Type
Journal Article
Description
The aim of the present study was to investigate the cause of normal response behaviors to noxious heat despite the marked loss of small neurons in the dorsal root ganglion (DRG) as a result of neonatal capsaicin treatment. Capsaicin (50 mg/kg) was injected subcutaneously (s.c.) into mice on either day P2 or P15; control mice received a vehicle injection. Twenty days after the capsaicin injection, 2% carrageenan (20 μL) was injected into the right hind paw of each animal. Twenty-four hours after the carrageenan injection, behavioral tests using noxious heat stimuli (NHS; Hargreaves method) and noxious mechanical stimuli (NMS; von Frey method) were performed using the control and capsaicin-treated mice. Pre-carrageenan measurements were used as the baseline values for each group. After the experiments, the mice were perfused with a mixture of 4% paraformaldehyde and 0.2% picric acid in a 0.1-M phosphate buffer (pH 7.4). The L4 and L5 DRGs were extracted, sectioned using a cryostat, and immunostained using a TRPV1 antibody and reacted with isolectin IB4. The P2 capsaicin-injected mice exhibited a marked increase in their analgesic responses to NHS, compared with both their baseline values and the respective control mice. Both the capsaicin-treated and control animals exhibited significant hyperalgesia in response to NMS. Naturally, the control P15 mice exhibited a shorter response time to NHS than their baseline values, while the capsaicin-injected P15 mice exhibited increased algesia comparable to the baseline values of the control. The capsaicin-injected mice also exhibited algesia in response to NMS. The number of TRPV1-immunoreactive (ir) small neurons decreased by 90% in the P2 capsaicin-injected mice and 45% in the P15 capsaicin-injected mice, whereas an increase in IB4-positive neurons was seen in both the P2 and P15 capsaicin-injected mice. In association with the decrease in larger neurons, the numbers of smaller neurons were increased in both P2 and P15 capsaicin-injected mice. TRPV1-ir small neurons are closely correlated with inflammatory heat pain perception, suggesting the enhancement of an unknown acute noxious heat sensor in the present study. The present findings indicate that noxious mechanical stimuli can be sensed despite the presence or absence of TRPV1-ir or IB4-positive neurons.
Journal Title
WebmedCentral NEUROSCIENCES
ISSN
20461690
Publisher
WebmedCentral
Volume
3
Issue
12
Start Page
WMC003727
Published Date
2012-12-06
Remark
Article URL: http://www.webmedcentral.com/article_view/3727

This is an open-access article distributed under the terms of the Creative Commons Attribution
License(CC-BY), which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.
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DOI (Published Version)
URL ( Publisher's Version )
FullText File
language
eng
TextVersion
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departments
Oral Sciences
University Hospital