NOXIOUS COLORECTAL DISTENSION INDUCED-C-FOS PROTEIN IN LIMBIC BRAIN STRUCTURES IN THE RAT

Colorectal distention is a non-invasive stimulus used to study viscera l pain processing in the nervous system. In this study, immunocytochem ical labeling for the immediate-early gene, c-Fos, was used to map lim bic brain structures involved in processing visceral pain. Rats receiv ed noxious colorectal distention while loosely restrained or loose res traint without distention (control). The brains were immunostained and the density of Fos-labeled nuclei within areas of the brain associate d with limbic function were examined. Many cortical (cingulate; retros plenial; insular; perirhinal; entorhinal) and subcortical (periaqueduc tal gray; locus coeruleus; lateral parabrachial area; paraventricular, anterodorsal and centromedian thalamic nuclei; lateral septal area; d orsomedial hypothalamus; cortical amygdala; subiculum) areas were labe led in the control rats, but significantly more Fos was observed in th ese areas following noxious colorectal distention (CRD). Additional ar eas were labeled following CRD but not restraint (e.g. infralimbic and prelimbic cortices; mediodorsal thalamic nuclueus; central amygdaloid nucleus). The results show that noxious visceral stimuli result in Fo s expression in limbic structures that exceeds that induced by restrai nt stress, suggesting that different pathways and circuits are recruit ed by stimuli which can produce similar emotional responses.