fMRI of supraspinal areas after morphine and one week pancreatic inflammation in rats

Abdominal pain is a major reason patients seek medical attention yet relatively little is known about neuronal pathways relaying visceral pain. We have previously characterized pathways transmitting information to the brain about visceral pain. Visceral pain arises from second order neurons in lamina X surrounding the spinal cord central canal. Some of the brain regions of interest receiving axonal terminations directly from lamina X were examined in the present study using enhanced functional magnetic resonance imaging (fMRI) before and one week after induction of a rat pancreatitis model with persistent inflammation and behavioral signs of increased nociception. Analysis of imaging data demonstrates an increase in MRI signal for all the regions of interest selected including the rostral ventromedial medulla, dorsal raphe, periaqueductal grey, medial thalamus, and central amygdala as predicted by the anatomical data, as well as increases in the lateral thalamus, cingulate/retrosplenial and parietal cortex. Occipital cortex was not activated above threshold in any condition and served as a negative control. Morphine attenuated the MRI signal, and the morphine effect was antagonized by naloxone in lower brainstem sites. These data confirm activation of these specific regions of interest known as integration sites for nociceptive information important in behavioral, affective, emotional and autonomic responses to ongoing noxious visceral activation.