Mean number of Fos-positive neurons produced within the caudal TBNC and upper cervical dorsal horn after injection of mustard oil (20% solution, 25 μl) into the TMJ region expressed as a function of the distance from the obex in HE2 and LE2 rats. a = P < 0.05, b = P < 0.01 HE2 versus LE2. Abbreviations: C1, first cervical segment; C2, second cervical segment; Vc, trigeminal subnucleus caudalis; Vi, trigeminal subnucleus interpolaris.