Olvanil And Piperine, On Spontaneous Excitatory Synaptic Transmission In Adult Rat Spinal Substantia Gelatinosa Neurons

Objective:Transient receptor potential (TRP) channels such as TRPV1 and TRPA1 channels play an important role in transmitting nociceptive information to the CNS from periphery through primary-afferent fibers. Capsaicin-like drug olvanil and piperine, both of which are known to activate TRPV1 channels in the soma of DRG neurons and alleviate pain. RTX activates both substantia gelatinosa (SG; laminaⅡof Rexed) neurons in the central terminal and the soma of DRG neurons, alleviating pain. SG neurons play an important role in modulating nociceptive transmission to the CNS. We examined the effects of Olvanil and piperine, to address the issue whether they can activate TPR channel in SG neuron and alleviate pain.Methods:Male adult Sprague-Dawley rats (6-8 weeks old) were anesthetized with urethane (1.2g/kg, intraperitoneal), and then lumbosacral laminectomy was performed. The lumbosacral spinal cord (L1-S3) was removed and mounted on a vibrating microslicer and then a 600-800μm thick transverse slice was cut. Olvanil, piperine, TRPV1 channel antagonist capsazepine and TRPA1 channel antagonist HC-030031 were applied by superfusion with a change in solutions in the recording chamber. The blind whole-cell patch-clamp technique was applied to the SG neurons of the slices.Results:Bath-applied olvanil for 5 min in a range of 0.1-40μM did not affect the frequency and amplitude of spontaneous excitatory postsynaptic current (sEPSC) and unchanged holding currents at a holding potential of-70 mV. On the other hand, piperine superfused for 2 min increased the frequency of sEPSC in a dose-dependent manner with a half-maximal effective concentration value of 52.3μM (Hill coefficient =4.54) and a small increase in its amplitude. The sEPSC frequency increase produced by piperine was reversible, although there was a tendency for the second application of piperine 20 min or 1 hour later to have a small effect than that of the first application. The piperine effect was inhibited by a TRPV1 channel antagonist capsazepine (10μM) or a TRPA1 channel antagonist HC-030031 (50μM).Conclusion:It is concluded that piperine but not olvanil activates both TRPV1 and TRPA1 channels in the central terminals of DRG neurons, resulting in an increase in the spontaneous release of L-glutamate onto SG neurons. This result support that there are different types of TRPV1 or TRPA1 channels in each of the soma and central terminals of the DRG neurons.