The anticonvulsant remacemide and its metabolite AR-R12495AA attenuate spinal synaptic transmission and carrageenan-induced inflammation in the young rat

NR2B receptors are involved in the mediation of spinal segmental reflex potentials but not in the cumulative motoneuronal depolarization in vitro

Windup, the frequency dependent build-up of spinal neuronal responses is an electrophysiological model of the development of the central sensitization in the chronic pain states. NR2B subunit containing NMDA-type glutamate receptors are implicated in the windup of dorsal horn neurons, while their role at the motoneuronal level is controversial. The cumulative motoneuronal depolarization in hemisected rat spinal cord preparation is an in vitro model of windup. The role of NR2B receptors in this process, and in the mediation of dorsal root stimulation evoked ventral root reflex potentials was elucidated. Three selective NR2B antagonists; CP-101,606; CI-1041 and Co-101244 (1 microM) were used. They had only weak, but statistically significant inhibitory effect on the early part of ventral root response, and did not influence the cumulative depolarization. On the contrary, non-selective NMDA antagonist APV (40 microM) decreased both responses markedly. We conclude that the pharmacological sensitivities of windup at the sensory and motor levels are different. NR2B containing NMDA receptors have major role in the mediation of the windup of dorsal horn neurons, but their contribution to this phenomenon at the motor level is negligible.

Glutamate uptake inhibition modulates dorsal horn neurotransmission: a comparison between normal and arthritic rats

This study determined the effects of glutamate uptake inhibition on primary-afferent excitatory postsynaptic potentials (DR-EPSPs) in spinal dorsal horn neurones in vitro from naive rats and rats with localised arthritis. The glutamate uptake inhibitor L-PDC (1 mM) significantly reduced DR-EPSP amplitude and duration with a greater reduction in arthritic than in naive rats. The group II/III selective metabotropic glutamate receptor antagonist CPPG (100 microM) reversed L-PDC-induced DR-EPSP inhibition in naive but not arthritic rats. L-AP4 (30 microM), a group III metabotropic agonist, inhibited DR-EPSPs with no difference between naive and arthritic rats. These data suggest the existence of an autoregulatory feedback mechanism that limits spinal postsynaptic excitation especially during inflammation. The putative contribution of metabotropic glutamate receptors to this phenomenon is discussed.

Peripheral inflammation reduces the response of spinal dorsal horn neurons to an NK3 receptor agonist

The neurokinin receptors NK1 and NK3 are involved in processing nociceptive information in the spinal dorsal horn and in central changes following persistent peripheral injury. However, little is known about functional changes in these receptor systems, particularly the NK3 receptor. We have performed intracellular recordings from spinal dorsal horn neurons in vitro, using spinal cords obtained both from control rats and from those with a peripheral inflammation induced by carrageenan. Application of the NK1 receptor agonist, [Sar(9), Met(O2)(11)]Substance P and the NK3 receptor agonist, Senktide, produced slow, long lasting depolarizations. The Senktide- but not [Sar(9), Met(O2)(11)]Substance P-induced depolarizations were significantly smaller in carrageenan-treated rats. These data indicate an altered role for the NK3 receptor in the spinal dorsal horn following acute peripheral inflammation.