RESUMO
The lack of truly robust analgesics for chronic pain is owed, in part, to the lack of an animal model that reflects the clinical pain state and of a mechanism-based, objective neurological indicator of pain. The present study examined stimulus-evoked brain activation with functional magnetic resonance imaging in male and female cynomolgus macaques following unilateral L7 spinal nerve ligation and the effects of clinical analgesics pregabalin, duloxetine, and morphine on brain activation in these macaques. A modified straight leg raise test was used to assess pain severity in awake animals and to evoke regional brain activation in anesthetized animals. The potential effects of clinical analgesics on both awake pain behavior and regional brain activation were examined. Following spinal nerve ligation, both male and female macaques showed significantly decreased ipsilateral straight leg raise thresholds, suggesting the presence of radicular-like pain. Morphine treatment increased straight leg raise thresholds in both males and females whereas duloxetine and pregabalin did not. In male macaques, the ipsilateral straight leg raise activated contralateral insular and somatosensory cortex (Ins/SII), and thalamus. In female macaques, the ipsilateral leg raise activated cingulate cortex and contralateral insular and somatosensory cortex. Straight leg raises of the contralateral, unligated leg did not evoke brain activation. Morphine reduced activation in all brain regions in both male and female macaques. In males, neither pregabalin nor duloxetine decreased brain activation compared with vehicle treatment. In females, however, pregabalin and duloxetine decreased the activation of cingulate cortex compared with vehicle treatment. The current findings suggest a differential activation of brain areas depending on sex following a peripheral nerve injury. Differential brain activation observed in this study could underlie qualitative sexual dimorphism in clinical chronic pain perception and responses to analgesics. Future pain management approaches for neuropathic pain will need to consider potential sex differences in pain mechanism and treatment efficacy.
RESUMO
The red blood cells (RBCs) of vertebrates have evolved into two basic shapes, with nucleated nonmammalian RBCs having a biconvex ellipsoidal shape and anuclear mammalian RBCs having a biconcave disk shape. In contrast, camelid RBCs are flat ellipsoids with reduced membrane deformability, suggesting altered membrane skeletal organization. However, the mechanisms responsible for their elliptocytic shape and reduced deformability have not been determined. We here showed that in alpaca RBCs, protein 4.1R, a major component of the membrane skeleton, contains an alternatively spliced exon 14-derived cassette (e14) not observed in the highly conserved 80 kDa 4.1R of other highly deformable biconcave mammalian RBCs. The inclusion of this exon, along with the preceding unordered proline- and glutamic acid-rich peptide (PE), results in a larger and unique 90 kDa camelid 4.1R. Human 4.1R containing e14 and PE, but not PE alone, showed markedly increased ability to form a spectrin-actin-4.1R ternary complex in viscosity assays. A similar facilitated ternary complex was formed by human 4.1R possessing a duplication of the spectrin-actin-binding domain, one of the mutations known to cause human hereditary elliptocytosis. The e14- and PE-containing mutant also exhibited an increased binding affinity to ß-spectrin compared with WT 4.1R. Taken together, these findings indicate that 4.1R protein with the e14 cassette results in the formation and maintenance of a hyperstable membrane skeleton, resulting in rigid red ellipsoidal cells in camelid species, and suggest that membrane structure is evolutionarily regulated by alternative splicing of exons in the 4.1R gene.
