Antisense knock down of TRPA1, but not TRPM8, alleviates cold hyperalgesia after spinal nerve ligation in rats.
Patients with neuropathic pain frequently experience hypersensitivity to cold stimulation. However, the underlying mechanisms of this enhanced sensitivity to cold are not well understood. After partial nerve injury, the transient receptor potential ion channel TRPV1 increases in the intact small dorsal root ganglion (DRG) neurons in several neuropathic pain models. In the present study, we precisely examined the incidence of cold hyperalgesia and the changes of TRPA1 and TRPM8 expression in the L4 and L5 DRG following L5 spinal nerve ligation (SNL), because it is likely that the activation of two distinct populations of TRPA1- and TRPM8-expressing small neurons underlie the sensation of cold. We first confirmed that L5 SNL rats developed cold hyperalgesia for more than 14 days after surgery. In the nearby uninjured L4 DRG, TRPA1 mRNA expression increased in trkA-expressing small-to-medium diameter neurons from the 1st to 14th day after the L5 SNL. This upregulation corresponded well with the development and maintenance of nerve injury-induced cold hyperalgesia of the hind paw. In contrast, there was no change in the expression of the TRPM8 mRNA/protein in the L4 DRG throughout the 2-week time course of the experiment. In the injured L5 DRG, on the other hand, both TRPA1 and TRPM8 expression decreased over 2 weeks after ligation. Furthermore, intrathecal administration of TRPA1, but not TRPM8, antisense oligodeoxynucleotide suppressed the L5 SNL-induced cold hyperalgesia. Our data suggest that increased TRPA1 in uninjured primary afferent neurons may contribute to the exaggerated response to cold observed in the neuropathic pain model.
Department of Anatomy and Neuroscience, Hyogo College of Medicine, 1-1 Mukogawa-cho, Nishinomiya, Hyogo 663-8501, Japan.
Hirokazu
H
Katsura
Koichi
K
Obata
Toshiyuki
T
Mizushima
Hiroki
H
Yamanaka
Kimiko
K
Kobayashi
Yi
Y
Dai
Tetsuo
T
Fukuoka
Atsushi
A
Tokunaga
Masafumi
M
Sakagami
Koichi
K
Noguchi
D000818:Animals; D017487:Ankyrins; D002121:Calcium Channel Blockers / Q000627:therapeutic use; D015220:Calcium Channels / Q000096:biosynthesis / Q000235:genetics* / Q000502:physiology; D003080:Cold Temperature; D018390:Gene Targeting; D006614:Hindlimb; D006930:Hyperalgesia / Q000235:genetics / Q000378:metabolism* / Q000503:physiopathology / Q000628:therapy; D008026:Ligation; D008297:Male; D016376:Oligonucleotides, Antisense / Q000235:genetics / Q000627:therapeutic use*; D010147:Pain Measurement / Q000379:methods; D051381:Rats; D017207:Rats, Sprague-Dawley; D013127:Spinal Nerves / Q000166:cytology / Q000378:metabolism; D000074025:TRPA1 Cation Channel; D050052:TRPC Cation Channels; D050053:TRPM Cation Channels / Q000096:biosynthesis / Q000235:genetics* / Q000502:physiology; D013997:Time Factors
D017487:Ankyrins; D002121:Calcium Channel Blockers; D015220:Calcium Channels; D016376:Oligonucleotides, Antisense; D000074025:TRPA1 Cation Channel; D050052:TRPC Cation Channels; D050053:TRPM Cation Channels; C480976:Trpa1 protein, rat; C498947:Trpm8 protein, rat