Noxious heat receptors present in cold-sensory cells in rats

• Published in: Neuroscience letters 2004-04, Vol.359 (1), p.33-36
• Main Authors: Okazawa, Makoto, Inoue, Wataru, Hori, Aiko, Hosokawa, Hiroshi, Matsumura, Kiyoshi, Kobayashi, Shigeo
• Format: Article
• Language: English
• Subjects: Animals; Biological and medical sciences; Ca 2+ imaging; Cells, Cultured; Coding–decoding system; Cold Temperature; Dorsal root ganglion; Fundamental and applied biological sciences. Psychology; Ganglia, Spinal - chemistry; Ganglia, Spinal - physiology; Hot Temperature; Ion Channels - analysis; Ion Channels - physiology; Neoplasm Proteins - analysis; Neoplasm Proteins - physiology; Patch clamp; Rats; Receptors, Drug - analysis; Receptors, Drug - physiology; Somesthesis and somesthetic pathways (proprioception, exteroception, nociception); interoception; electrolocation. Sensory receptors; Thermoreceptors - chemistry; Thermoreceptors - physiology; Transducer; TRPM Cation Channels; Vertebrates: nervous system and sense organs
• ISSN: 0304-3940; 1872-7972
• DOI: 10.1016/j.neulet.2004.01.074

Noxious heat above ∼45 °C applied on cold spots evokes a paradoxical cold sensation by activating cold fibers. It remains unresolved whether cold receptors respond to heat as well, or whether noxious-heat receptors and cold receptors coexist in the same fiber. Recently, noxious heat receptors (TRPV1) and cold receptors (TRPM8) have been cloned. It is controversial, however, whether TRPV1 and TRPM8 coexist in the same sensory neuron. Here, we investigate colocalization of these receptors in dorsal root ganglion (DRG) of rats. TRPV1 was expressed in 29% of TRPM8-positive cells in DRG sections. In Ca 2+ imaging, noxious heat excited many of the cold-sensitive cells in culture. In a whole-cell current-clamp mode, noxious heat, capsaicin, cooling and menthol all evoked receptor potentials and impulses in a subset of DRG neurons. This colocalization of TRPV1 and TRPM8 in a DRG neuron may be the basis for the paradoxical cold sensation.