The differential effects of emotional or physical stress on pain behaviors or on c-Fos immunoreactivity in paraventricular nucleus or arcuate nucleus.

Although many studies which explore on the interaction between stress and antinociception have been conducted, most of them do not divide stress into emotional stress (ES) and physical stress (PS). In the present study, we investigated the differential effects of ES or PS on pain behaviors or on c-Fos immunoreactivity (IR) in the paraventricular nucleus (PVN) or arcuate nucleus (ArcN) using electrical footshock-witness model. In addition, alteration of pain behaviors or c-Fos IR following stress repetition was examined. The electrical foot shock was applied to PS animal group in one chamber, whereas the witness animal group in another chamber without any electrical foot shock was regarded as an ES. In each group, either single (10 stimuli /10 min/1 day) or repeated stress for 5 consecutive days was applied. Our results suggest that ES and PS appear to play differential roles in the regulation of nociception produced by various types of pain stimuli (formalin, substance P, glutamate or pro-inflammatory cytokines) and on c-Fos IR in the PVN or ArcN. Moreover, such antinociceptive effect or c-Fos IR appears to be modified following stress repetition.