Abstract
TRPA1 is expressed in small diameter DRG neurons and hair cells, and is proposed to be a receptor for noxious cold (<17 °C) and pungent ingredients such as cinnamaldehyde (CA) and allyl isothiocynate (AI). Recent studies have shown that TRPA1 acts on presynaptic terminals in the substantia gelatinosa of the dorsal horn to increse the glutamate release. It is not fully understood, however, how synaptic transmission through C fibers is eventually modified by the activation of TRPA1 in the SG which exhibits a heterogeneous population of cells. We investigated the effects of CA and AI, on spontaneous and dorsal root-evoked EPSCs in SG neurons, and relationship between the modulatory effects on synaptic transmission and morphological features of recorded neurons. Under voltage-clamp conditions, CA (and AI) dose-dependently increased the frequency and amplitude of sEPSCs while it increased only the frequency of mEPSCs observed in the presence of TTX. On the other hand, CA reversibly inhibited the amplitude of C fiber- but not A δ fiber-evoked monosynaptic EPSCs. In combination with morphological analyze of recorded cells, the excitatory effect of CA was observed in radial and vertical (excitatory) cells but not in islet and central (inhibitory) cells. These results suggest that CA and AI act on TRPA1 receptors expressed in the presynaptic terminals of C fibers to facilitate miniature release in excitatory interneurons in the SG, but inhibit the C fiber-evoked release. [J Physiol Sci. 2008;58 Suppl:S163]
