MEMBRANE AND CELLULAR BIOPHYSICSExcitation of primary afferent neurons by near-infrared light in vitroKatz, Elizabeth J.a; Ilev, Ilko K.a; Krauthamer, Victora; Kim, Do Hyuna; Weinreich, Daniela bAuthor Information aFood and Drug Administration, Center for Devices and Radiological Health, Silver Spring bDepartment of Pharmacology, School of Medicine, Baltimore, Maryland, USA Correspondence to Dr Elizabeth J. Katz, Food and Drug Administration, 10903 New Hampshire Ave., Building 62, Silver Spring, MD 20993, USA Tel: +1 301 796 2495; fax: +1 301 827 8112; e-mail: firstname.lastname@example.org Received 23 February 2010 accepted 11 April 2010 NeuroReport: June 23rd, 2010 - Volume 21 - Issue 9 - p 662-666 doi: 10.1097/WNR.0b013e32833add3a Buy Metrics Abstract Near-infrared light therapy is an emerging neurostimulation technology, but its cellular mechanism of action remains unresolved. Using standard intracellular recording techniques, we observed that 5–10 ms pulses of 1889 nm light depolarized the membrane potential for hundreds of milliseconds in more than 85% of dorsal root ganglion and nodose ganglion neurons tested. The laser-evoked depolarizations (LEDs) exhibited complex, multiphasic kinetics comprising fast and slow components. There was no discernable difference in the LEDs in intact ganglion neurons and in acutely isolated neurons. Thus, the LED sensor seems to reside within the neuronal membrane. The near-uniform distribution of responsive neurons increased membrane conductance, and the negative reversal potential value (−41±2.9 mV) suggests that LED is unrelated to the activation of heat-sensitive transient receptor potential cation channel subfamily V member 1 channels. The long duration of LEDs favors an involvement of second messengers. © 2010 Lippincott Williams & Wilkins, Inc.