Zingerone enhances glutamatergic spontaneous excitatory transmission by activating TRPA1 but not TRPV1 channels in the adult rat substantia gelatinosa

Abstract

Transient receptor potential (TRP) channels are thought to play a role in regulating nociceptive transmission to spinal substantia gelatinosa (SG) neurons. It remains to be unveiled whether the TRP channels in the central nervous system are different in property from those involved in receiving nociceptive stimuli in the peripheral nervous system. We examined the effect of the vanilloid compound zingerone, which activates TRPV1 channels in the cell body of a primary afferent neuron, on glutamatergic excitatory transmission in the SG neurons of adult rat spinal cord slices by using the whole cell patch-clamp technique. Bath-applied zingerone reversibly and concentration-dependently increased spontaneous excitatory postsynaptic current (EPSC) frequency. This effect was accompanied by an inward current at -70 mV that was resistant to glutamate receptor antagonists. These zingerone effects were repeated and persisted in Na(+)-channel blocker tetrodotoxin-, La(3+)-, or IP3-induced Ca(2+)-release inhibitor 2-aminoethoxydiphenyl borate-containing or Ca(2+)-free Krebs solution. Zingerone activity was resistant to the selective TRPV1 antagonist capsazepine but sensitive to the nonselective TRP antagonist ruthenium red, the TRPA1 antagonist HC-030031, and the Ca(2+)-induced Ca(2+)-release inhibitor dantrolene. TRPA1 agonist allyl isothiocyanate but not capsaicin inhibited the facilitatory effect of zingerone. On the other hand, zingerone reduced monosynaptically evoked EPSC amplitudes, as did TRPA1 agonists. Like allyl isothiocyanate, zingerone enhanced GABAergic spontaneous inhibitory transmission in a manner sensitive to tetrodotoxin. We conclude that zingerone presynaptically facilitates spontaneous excitatory transmission, probably through Ca(2+)-induced Ca(2+)-release mechanisms, and produces a membrane depolarization in SG neurons by activating TRPA1 but not TRPV1 channels.

Spontaneous l-glutamate release enhancement in rat substantia gelatinosa neurons by (−)-carvone and (+)-carvone which activate different types of TRP channel

“…Capsazepine itself did not affect sEPSC frequency and amplitude, as reported previously (for example, see Ref. [13]). Unlike the TRPV1 antagonist, a TRPA1 antagonist HC-030031 (50 mM) inhibited the facilitatory effect of (þ)-carvone but not (À)-carvone on excitatory transmission ( Fig.…”

“…HC-030031 itself did not affect sEPSC frequency and amplitude, as reported previously (for example, see Ref. [13]). …”

“…Slice preparations from the adult rat spinal cord were prepared as described elsewhere [4,10,13]. Briefly, male SpragueeDawley rats (6e8 weeks old) were anesthetized with urethane (1.2 g/kg, i.p.…”

“…Blind whole-cell voltage-clamp recordings from SG neurons were made at a holding potential (V H ) of À70 mV with a patchpipette, as done previously [4,10,13]. The patch-pipette solution used (in mM) was composed of K-gluconate, 135; CaCl 2 , 0.5; MgCl 2 , 2; KCl, 5; EGTA, 5; HEPES, 5; and Mg-ATP, 5 (pH ¼ 7.2).…”

“…We have suggested that there may be a difference in property between TRP channels in the central terminal and cell body of primary-afferent neuron. For instance, eugenol, zingerone and olvanil (the synthetic oleic acid homologue of capsaicin) activated TRPV1 channels in its cell body [15e17] but not the spinal cord SG [7,8,13]. Gonçalves et al [18] have recently reported that a monoterpene ketone (À)-carvone contained in spearmint increases intracellular Ca 2þ concentration in rat primaryafferent neurons in a manner sensitive to a TRPV1 antagonist capsazepine, indicating an involvement of TRPV1 channels.…”