Vanilloid receptor 1-like receptor-immunoreactive primary sensory neurons in the rat trigeminal nervous system
Section snippets
Animals
The TGs, brainstems, maxillae, mandibles and facial skins were obtained from six male Sprague–Dawley rats (200–300 g; Charles River, Japan). Rats were anesthetized with ether to the level at which respiration was markedly suppressed (i.e. respiration had stopped for 30 s or more), and perfused transvascularly with 50 ml of saline followed by 500 ml of 4% formaldehyde in 0.1 M phosphate buffer (pH 7.4). The materials were dissected and postfixed with the same fixative for 30 min. Maxillae and
The distribution of primary sensory neurons in the trigeminal ganglion and mesencephalic trigeminal tract nucleus
Two types of staining pattern were observed in TG neurons. In strongly stained neurons, VRL-1 immunoreactivity (IR) was detected throughout the cytoplasm (Fig. 1A, B). The immunoreactivity was restricted to the plasma membrane in lightly stained neurons (Fig. 1A). In a previous study, however, lightly stained neurons were also observed in the dorsal columns of the spinal cord. VRL-1 is unlikely to act as a noxious heat transducer in such neurons. In this study, therefore, lightly stained
Discussion
The present study demonstrated that VRL-1 IR was localized to primary sensory neurons in the TG. In the Mes5, virtually all neurons were devoid of the immunoreactivity. Because Mes5 neurons are considered to be the exclusive source of trigeminal proprioceptors innervating masticatory muscles and periodontal ligaments,1., 17. it is likely that most trigeminal proprioceptors are devoid of the candidate transducer for high-threshold heat responses. We also showed that orofacial structures
Conclusions
We have described VRL-1 IR in TG and Mes5 primary sensory neurons. The immunoreactivity was detected in 14% of TG cells, while Mes5 neurons were almost devoid of VRL-1 IR. The VRL-1-IR TG cells were mostly medium to large in size. They probably innervate orofacial structures and project to the superficial laminae of the medullary dorsal horn. Co-expression of CGRP was common among the VRL-1-IR tooth pulp neurons and cutaneous neurons. VRL-1-IR TG neurons that co-expressed parvalbumin IR
Acknowledgements
We are very grateful to Dr David Julius (Department of Cellular and Molecular Pharmacology, University of California) for the kind gift of the anti-VRL-1 serum.
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