Rafael Benoliel

Actions of intrathecal diphtheria toxin-substance P fusion protein on models of persistent pain.

Substance P (SP) plays a central role in the transduction of second messenger signals from primary afferent nociceptive terminals to second-order neurons in the spinal cord. We have tested a recombinant engineered diphtheria toxin/SP fusion protein (DAB389SP) in acute and chronic pain models in the rat. DAB389SP binds to the SP receptor (SPR) and is internalized and kills SPR-expressing cells by blocking cellular protein synthesis. DAB389SP delivery was by intrathecal infusion, of varying duration, at the lumbar level. In the chronic constriction injury model of neuropathic pain a significant reduction in mechanically induced hyperalgesia was obtained. This effect was less marked in an acute carageenan inflammation model. Although other pain characteristics (mechano-allodynia, cold-allodynia, and heat-hyperalgesia) showed some improvement, these were less pronounced. Immunocytochemistry revealed a toxin-induced reduction in lamina I, of SPR and of NMDA NR1 subunit receptor expressing neurons, and of c-Fos, an inducible molecular marker of persistent nociceptive activity. The use of cytotoxic fusion proteins to target specific cell types may be of considerable benefit in the study of nociception and the treatment of chronic pain.

Neuropeptide Y in trigeminal ganglion following chronic constriction injury of the rat infraorbital nerve : is there correlation to somatosensory parameters?

&NA; The aim of this study was to investigate neuropeptide Y (NPY) levels in trigeminal ganglia following infraorbital nerve injury. Two experimental procedures were performed in three groups of rats: a unilateral chronic constriction injury (CCI) to the infraorbital nerve (n=13), nerve manipulation without CCI (n=13) and unoperated controls (n=8). All rats underwent baseline and regular assessment of mechanical withdrawal threshold (Von Frey) and reaction to pin prick as well as free behavior evaluations. CCI to the infraorbital nerve induced significant hyperalgesia and allodynia within 9–12 days. At 6 days seven rats were euthanized and trigeminal ganglia harvested for immunocytochemical (ICC) studies. The study was ended at 14 days when all rats were euthanized and their ganglia harvested for ICC and radioimmunoassay (RIA) studies. An increase in NPY levels was seen in the ipsilateral ganglia of manipulated and CCI rats at 6 days, when rats displayed no pain‐related behavior. At 14 days, ICC and RIA both detected significant increases in NPY levels in the ipsilateral ganglia of CCI and manipulated rats but not in unoperated controls. The possible roles of NPY in pain modulation and nerve injury are discussed in light of these findings.

Co-localization of N-methyl-D-aspartate receptors and substance P (neurokinin-1) receptors in rat spinal cord

Glutamate, substance P (SP), and their receptors have been implicated in the initiation and maintenance of persistent pain through an interaction at second order spinal cord neurons. Employing well-characterized antibodies to the SP receptor and the N-methyl-D-aspartate receptor (NR1 subunit, splice variant missing exon 22), we demonstrate co-localization of these receptors on second order neurons at cervical, thoracic, lumbar, and sacral spinal cord levels. The co-localization was marked in lamina I of the dorsal horn at all levels and in the intermediolateral nucleus of the thoraco-lumbar spinal cord nuclei associated with autonomic function.

Chapter 11 – Neuropathic orofacial pain

Neuropathic orofacial pain (NOP) is a challenging diagnostic problem. In some cases, symptomatology may be similar to that seen with dental pathology, resulting in unwarranted dental treatment. Rarely, NOP can herald serious disease or central tumors, and early diagnosis can be life-saving. The following review outlines the classification, clinical presentation, pathophysiology, and treatment of the more common NOP entities.