Activation of
glutamate receptors and glial cells in the spinal dorsal horn are two fundamental processes involved in the pathogenesis of various
pain conditions, including
neuropathic pain induced by injury to the peripheral or central nervous systems. Numerous studies have demonstrated that
minocycline treatment attenuates allodynic and hyperalgesic behaviors induced by tissue
inflammation or nerve injury. However, the synaptic mechanisms by which
minocycline prevents
hyperalgesia are not fully understood. We recently reported that deficient
glutamate uptake by glial
glutamate transporters (GTs) is key for the enhanced activation of
N-methyl-d-aspartate (
NMDA) receptors in the spinal sensory synapses of rats receiving partial sciatic nerve
ligation (pSNL). In this study, we investigated how
minocycline affects activation of
NMDA receptors in the spinal sensory synapses in rats with pSNL by whole cell recordings of
NMDA currents in spinal laminea I and II neurons from spinal slices. The effects of
minocycline treatments on the dorsal horn expression of glial GTs and astrocyte marker
glial fibrillary acidic protein (GFAP) were analyzed by immunohistochemistry. We demonstrated that normalized activation of
NMDA receptors in synapses activated by both weak and strong peripheral input in the spinal dorsal horn is temporally associated with attenuated
mechanical allodynia in rats with pSNL receiving
intraperitoneal injection of
minocycline.
Minocycline ameliorated both the downregulation of glial GT expression and the activation of astrocytes induced by pSNL in the spinal dorsal horn. We further revealed that preventing deficient glial
glutamate uptake at the synapse is crucial for preserving the normalized activation of
NMDA receptors in the spinal sensory synapses in pSNL rats treated with
minocycline. Our studies suggest that glial GTs may be a potential target for the development of
analgesics.