Distribution and colocalization of NGF and GDNF family ligand receptor mRNAs in dorsal root and nodose ganglion neurons of adult rats.

To understand the dependence of primary sensory neurons on neurotrophic factors, we examined the distribution and colocalization of mRNAs for receptors of nerve growth factor (NGF) and glial cell line-derived neurotrophic factor (GDNF) family ligands in dorsal root ganglion (DRG) and nodose ganglion (NG) neurons of adult rats by in situ hybridization (ISH) histochemistry using serial sections. About 35, 10, and 20% of the lumbar DRG neurons expressed trkA, trkB and trkC mRNAs, respectively. Messenger RNA signals for c-ret, a common signaling receptor of GDNF family ligands, were seen in about 60% of DRG neurons, and some of these neurons expressed trkA, trkB, or trkC mRNAs. Most (97%) of the DRG neurons observed were positive to at least one of these four mRNAs. About 50, 20, and 20% of DRG neurons expressed GDNF family receptor alpha1 (GFR alpha1), GFR alpha2, and GFR alpha3 mRNAs, respectively, and most of these neurons were positive to c-ret mRNA. Interestingly, GFR alpha2 and GFR alpha3 mRNA signals were frequently seen in the same neurons, which lack GFR alpha1 mRNA signals. On the other hand, 98% of NG neurons expressed trkB mRNA and 30-40% of NG neurons co-expressed c-ret and GFR alpha1 mRNAs. However, mRNA signals for other receptors (TrkA, TrkC, GFR alpha2, GFR alpha3) were seen in only a few NG neurons. These findings suggest that all the DRG neurons in adult rats depend on at least one of the NGF and GDNF family ligands, and that some DRG neurons depend on two ligands or more. In contrast, NG neurons were suggested to be divided into two major groups; one group depends on brain-derived neurotrophic factor (BDNF)/neurotrophin-4/5 (NT-4/5), and the other depends on both BDNF/NT-4/5 and GDNF.

Electroacupuncture induces the expression of Fos in rat dorsal horn via capsaicin-insensitive afferents.

Fos is expressed in rat dorsal horn neurons after electroacupuncture (E-acupuncture), but it is unclear which types of afferent fibers are involved in the expression. It is thought that the Fos expression is induced via Adelta afferents rather than C afferents, since the threshold of Adelta afferents to electrical stimulation is much lower than that of unmyelinated ones. Therefore, neonatally capsaicin treated rats lacking many C afferents were examined to clarify this. Fos expression in the dorsal horn after injection of formalin into the hindpaw was severely attenuated by neonatal capsaicin treatment. However, Fos expression after E-acupuncture to the pads of the hindpaw was unaffected by the same treatment. These results suggest that E-acupuncture induces the expression of Fos in the dorsal horn neurons via capsaicin-insensitive afferents, presumably Adelta afferents.

TRPV2-immunoreactive intrinsic neurons in the rat intestine.

Transient receptor potential channel vanilloid subfamily 2 (TRPV2) was shown to receive noxious thermal stimuli (>52 degrees C), and to be expressed in fine myelinated afferent neurons. The mRNA and the immunoreactivity have also been detected in several peripheral tissues. We examined the expression of TRPV2 in the rat intestine. An analysis by transcriptase-polymerase chain reaction (RT-PCR) demonstrated TRPV2 gene expression in the intestine. Many TRPV2-positive neurons were observed in the myenteric plexus by immunohistochemistry. Some of these neurons were positive for calbindin D-28K (CaBP), which is present in intrinsic afferent neurons. TRPV2 immunoreactivity was also observed in nodose ganglion neurons (vagal afferents). These findings suggest that TRPV2 is expressed not only in sensory ganglion neurons, but also in enteric neurons, including primary afferent neurons.