Pregabalin and gabapentin reduce release of substance P and CGRP from rat spinal tissues only after inflammation or activation of protein kinase C

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Abstract
Gabapentin and pregabalin are amino acid derivatives of γ-amino butyric acid that have anticonvulsant, analgesic, and anxiolytic-like properties in animal models. The mechanisms of these effects, however, are not well understood. To ascertain whether these drugs have effects on sensory neurons, we studied their actions on capsaicin-evoked release of the sensory neuropeptides, substance P and calcitonin gene-related peptide from rat spinal cord slices in vitro. Although release of immunoreactive peptides from non-inflamed animals was not altered by either drug, prior in vivo treatment by intraplantar injection of complete Freund's adjuvant enhanced release from spinal tissues in vitro, which was attenuated by gabapentin and pregabalin. These drugs also reduced release of immunoreactive neuropeptides in spinal tissues pretreated in vitro with the protein kinase C activator, phorbol 12,13-dibutyrate. Our results suggest that gabapentin and pregabalin modulate the release of sensory neuropeptides, but only under conditions corresponding to significant inflammation-induced sensitization of the spinal cord.