A comparative study of three cranial sensory ganglia projecting into the oral cavity: in situ hybridization analyses of neurotrophin receptors and thermosensitive cation channels

Peripheral cranial sensory nerves projecting into the oral cavity receive f ood intake stimuli and transmit sensory signals to the central nervous syst em. To describe and compare the features of the cranial sensory ganglia tha t innervate the oral cavity, i.e., the trigeminal, petrosal, and geniculate ganglia (TG, PG, and GG, respectively), in situ hybridization was conducte d using riboprobes for neurotrophin receptors (TrkA, TrkB, and TrkC), a neu rotransmitter (substance P), and ion channels important for thermosensation (VR1 and TREK-1). In TG, all in six probes yielded positive signals to var ious extent in intensity and frequency. In addition, a strong correlation b etween the expression of VR1 and those of TrkA and substance P was observed as in the case of the dorsal root ganglia. In PG, positive signals to all six probes were also detected, and the correlation of expression was simila r to that shown by TG. On the other hand, most cells in GG were positive to the TrkB probe, and a small number of cells were positive to the TrkC prob e, but no significant signal was observed for the other four probes. These results indicate that TG and PG consist of cells that are heterogeneous in terms of neurotrophin requirement and somatosensory functions, and that GG seems to consist mainly of a homogeneous cell type, gustatory neurons. In c onclusion, TG, PG, and GG, show gene expression characteristics intrinsic t o the three ganglia. It is also concluded that TG and a portion of PG proje ct several types of somatosensory nerves. This is consistent with the findi ng that GG and a portion of PG project gustatory nerves. (C) 2001 Elsevier Science BY. All rights reserved.