Aims: To specify the regions of the brain stem that are characterized
by changes in substance P (SP)-like immunoreactivity following
activation of capsaicin-sensitive afferents innervating temporomandibular
joint (TMJ) tissues in New Zealand rabbits. Methods:
Capsaicin, an activator of small-diameter unmyelinated and thinly
myelinated nociceptive afferent fibers, was administered unilaterally
to the right TMJ of experimental animals. Another group
received vehicle solution and served as controls. The animals were
sacrificed 6 hours post-treatment through transcardial perfusion.
Their brain stems were removed and sectioned, and SP-like
immunoreactivity was assessed in serial horizontal sections.
Results: A decrease in brain stem SP-like immunoreactivity
occurred ipsilateral to capsaicin application. This reduction was
primarily localized in brain stem regions that correspond to the
trigeminal main sensory nucleus, as well as subnucleus oralis,
interpolaris, and caudalis of the trigeminal spinal tract nucleus.
Conclusion: The present study revealed central nervous system
changes following TMJ capsaicin treatment in rabbits.