TREK belongs to a subfamily of tandem pore domain K+ channels, and consists of three subunits, TREK-1, TREK-2 and TRAAK. We examined the distribution of TREK-1, TREK-2 and TRAAK immunoreactive neurons in rat trigeminal sensory neurons. In the trigeminal ganglia, 31%, 43% and 60% of neurons were immunoreactive for TREK-1, TREK-2 and TRAAK, respectively. Mean sizes of TREK-1, TREK-2 and TRAAK immunoreactive trigeminal ganglion neurons were 447+/-185, 445+/-23 and 492+/-12 mm2, respectively. Furthermore, TREK channels were colocalized with cationic TRP channels, TRPV1, TRPV2 and TRPM8. TREK-1 immunoreactive neurons were colocalized with TRPV1 (57%), TRPV2 (11%) and TRPM8 (33%). TREK-2-immunoreactive neurons were colocalized with TRPV1 (33%), TRPV2 (9%) and TRPM8 (19%). TRAAK immunoreactive neurons were colocalized with TRPV1 (47%), TRPV2 (10%) and TRPM8 (22%). The present results revealed that TREK-1, TREK-2 and TRAAK channels colocalized with thermosensitive TRP channels in some small trigeminal ganglion neurons.