Lesions of the ventral ascending noradrenergic bundles decrease the stress response to occlusal disharmony in rats

► We investigated the relationship between the response of the hypothalamic–pituitary–adrenal axis and the ventral ascending noradrenergic bundles in rats with occlusal disharmony. ► We examined changes in extracellular noradrenaline in the hypothalamic paraventricular nucleus and plasma corticosterone following occlusal disharmony in rats injected with 6-hydroxydopamine. ► 6-hydroxydopamine microinjection into the ventral ascending noradrenergic bundles reduced the magnitude of the responses of extracellular noradrenaline in the paraventricular nucleus and the plasma corticosterone to occlusal disharmony. Occlusal disharmony induced by placing an acryl cap on the lower incisors of rats is perceived as chronic stress. This chronic stress activates corticotropin-releasing hormone (CRH) neurons in the hypothalamic paraventricular nucleus (PVN), resulting in stimulation of the hypothalamic–pituitary–adrenal (HPA) axis. The ventral ascending noradrenergic bundles (V-NAB) from the brainstem innervate the PVN. To investigate the relationship between the response of the HPA axis and the V-NAB, we examined changes in extracellular noradrenaline (NA) in the PVN and plasma corticosterone, the final output of the HPA axis, following occlusal disharmony in rats injected with 6-hydroxydopamine (6-OHDA), a specific catecholamine neurotoxin. 6-OHDA microinjection into the V-NAB reduced the magnitude of the responses of extracellular NA in the PVN and the plasma corticosterone to occlusal disharmony. Our results suggest that V-NAB to the PVN are involved in occlusal disharmony-induced activation of the HPA axis.