Expression ofFosintheRatForebrain Following Experimental ToothMovement

Orthodontic tooth movement isknowntocause painanddiscomfort topatients. Mechanically induced inflammatory responses intheperiodontium areassumed toberelated tothemechanism ofpainsensation. An immediate-early gene, c-fos, that isexpressed within some neurons following synaptic activation, iswidely usedasa marker forneuronal activity following noxious orinno- cuousstimulation. We haverecently demonstrated that experimental tooth movementproduced Fosinduction in theipsilateral trigeminal subnucleus caudalis andinthe bilateral lateral parabrachial nucleus, whichisknowntobe involved inthetransmission ofnociceptive information. As afurther step, weinvestigated thedistribution ofFos-like immunoreactive neurons intheupperbrainregions. Twenty-four hoursafter thecommencement ofthe experimental tooth movement, theFos-like immunoreactive neurons appeared inthecentral nucleus oftheamygdala (Ce), paraventricular nucleus ofthehypothalamus (PVH), andparaventricular nucleus ofthethalamus (PV)ofthe experimental rats. Thenumbers ofthelabeled neurons were significantly increased by639%(P<0.001) and644%(P< 0.001) intheipsilateral andcontralateral sides oftheCe, respectively, by292%(P<0.001) and307%(P<0.001) inthe ipsilateral andcontralateral sides ofthePVH,andby264% (P<0.0001) inthePVwithrespect toshamcontrol rats. Theseresults suggest thatnociceptive information caused byexperimental tooth movement mightbetransmitted and modulated inseveral regions oftheforebrain.