NeuroImage
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Objective measure of pain is valuable in drug discovery research and development of analgesics. Spinal cord is an important relay of the pain pathway, and fMRI offers an excellent opportunity to quantify pain using activation in the spinal cord induced by painful stimuli. fMRI literature of cervical spinal cord with regard to the spatial extent, in both longitudinal and cross-sectional directions, of neuronal activation induced by noxious stimulation is ambiguous. This study investigates the feasibility of developing a robust pain assay using fMRI in the cervical spinal cord in alpha-chloralose anesthetized rats subjected to transcutaneous noxious electrical stimulation of the forepaw. ⋯ Spatially, the fMRI signal extended approximately 9 mm in the longitudinal direction, covering C(4)-C(8) segments, coinciding with the synapse location of afferent terminals from the stimulated site. In the cross-sectional direction, the signal change is localized predominantly to the ipsilateral dorsal region. This study demonstrates that cervical spinal cord fMRI can be performed reliably in anesthetized rats offering it as a potential tool for analgesic drug development.
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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. ⋯ 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.