Use of a near-infrared diode laser to activate mouse cutaneous nociceptors in vitro.
A skin-nerve preparation is useful for study of heat transduction mechanisms of A- and C-high threshold primary afferents (nociceptors), but the small dimension and liquid environment of the skin organ bath do not readily accommodate conventional noxious heat delivery systems. For these reasons, a 980 nm (near-infrared) diode laser was tested for activation and differentiation of cutaneous afferents. Current to the laser driver was varied. Exposure time and area, angle of approach, and stand-off distance from the bath solution surface were held constant. Seventy-eight fibers were classified by: conduction velocity, mechanical threshold, and responsiveness to laser radiation. A subset of the sampled fibers was also tested for sensitivity to convective heat. Most C (30/43) and a few A (6/25) nociceptors responded to laser irradiation. All low mechanical threshold primary afferents (10/10) were unresponsive to laser irradiation. Laser-sensitive fibers responded to convective heat, whereas laser-insensitive fibers did not. Laser-induced responses were consistent with literature reports of responses to traditional heat stimulation. Laser stimulation proved to be a rapid, unobtrusive method for reproducible heat stimulation of primary afferents of the mouse skin-nerve preparation. It is effective for defining subpopulations of primary afferent fibers and holds promise as a tool for gauging modification of C-fiber activity.
Department of Cell and Molecular Physiology, School of Medicine, University of North Carolina at Chapel Hill, 115 Mason Farm Road, Chapel Hill, NC 27599-7545, United States. pribisko@med.unc.edu
Alaine L
AL
Pribisko
Edward R
ER
Perl
D000200:Action Potentials / Q000502:physiology*; D000367:Age Factors; D000818:Animals; D001703:Biophysics; D005260:Female; D066298:In Vitro Techniques; D007834:Lasers / Q000009:adverse effects*; D054023:Lasers, Semiconductor; D051379:Mice; D008810:Mice, Inbred C57BL; D009412:Nerve Fibers / Q000502:physiology*; D009619:Nociceptors / Q000502:physiology*; D010812:Physical Stimulation / Q000379:methods; D012684:Sensory Thresholds / Q000502:physiology; D012867:Skin / Q000294:innervation*; D013314:Stress, Mechanical; D013694:Temperament; D017833:Visceral Afferents / Q000502:physiology