Spinal
5-HT3 receptor (5-HT3R) has been implicated in
chronic pain development. The extent to which 5-HT3R contributes to spinal sensitization and diabetic
neuropathic pain (DNP) remains elusive and the mechanisms subserving the effects of 5-HT3R activation on spinal
pain processing during
chronic pain are still unclear. In this study, we evaluated the contribution of spinal 5-HT3R to
pain facilitation and spinal sensitization during DNP, exploiting the role of GABAAR-mediated neurotransmission and glial activation in the effects elicited by intrathecal administration of a 5-HT3R antagonist. Mechanical nociception was evaluated by paw pressure test in
streptozotocin (STZ)-diabetic and control rats after intrathecal (i.t.) administration of a 5-HT3R antagonist (Y25130). The spinal activation of
extracellular signal-regulated kinases (ERKs) pathway and the expression of 5-HT3R,
glial fibrillary acidic protein (GFAP; marker of astroglia activation) and ionized
calcium binding adaptor molecule 1 (IBA-1; marker of microglia activation) were evaluated at the peak maximum effect of Y25130. The involvement of GABAAR-mediated neurotransmission in the behavioral
pain effect of Y25130, was assessed in STZ-diabetic animals receiving i.t. administrations of
muscimol (GABAAR agonist). Intrathecal administration of Y25130 reverted
mechanical hyperalgesia and decreased the activation of ERKs in STZ-diabetic rats, while no effects were observed in control animals. The spinal activation of GABAAR by i.t. administration of
muscimol abolished Y25130-driven antinociception. The expression of IBA-1, GFAP and 5-HT3R was unaltered by treatment. These findings point to a
GABA-mediated pronociceptive role of spinal 5-HT3R during DNP.