title: Characteristics of laser stimulation by near infrared pulses of retinal and vestibular primary neurons.
abstract: OBJECTIVE
  The optical stimulation of neurons from pulsed infrared lasers has appeared over the last years as an alternative to classical electric stimulations based on conventional electrodes. Laser stimulation could provide a better spatial selectivity allowing single-cell stimulation without prerequisite contact. In this work we present relevant physical characteristics of a non-lethal stimulation of cultured mouse vestibular and retinal ganglion neurons by single infrared laser pulses.
  
  
  METHODS
  Vestibular and retinal ganglion neurons were stimulated by a 100-400 mW pulsed laser diode beam (wavelengths at 1,470, 1,535, 1,875 nm) launched into a multimode optical fiber positioned at a few hundred micrometers away from the neurons. Ionic exchange measurements at the neuron membrane were achieved by whole-cell patch-clamp recordings. Stimulation and damage thresholds, duration and repetition rate of stimulation and temperature were investigated.
  
  
  RESULTS
  All three lasers induced safe and reproducible action potentials (APs) on both types of neurons. The radiant exposure thresholds required to elicit APs range from 15 ± 5 to 100 ± 5 J cm(-2) depending on the laser power and on the pulse duration. The damage thresholds, observed by a vital dye, were significantly greater than the stimulation thresholds. In the pulse duration range of our study (2-30 milliseconds), similar effects were observed for the three lasers. Measurements of the local temperature of the neuron area show that radiant exposures required for reliable stimulations at various pulse durations or laser powers correspond to a temperature increase from 22 °C (room temperature) to 55-60 °C. Stimulations by laser pulses at repetition rate of 1, 2, and 10 Hz during 10 minutes confirmed that the neurons were not damaged and were able to survive such temperatures.
  
  
  CONCLUSIONS
  These results show that infrared laser radiations provide a possible way to safely stimulate retinal and vestibular ganglion neurons. A similar temperature threshold is required to trigger neurons independently of variable energy thresholds, suggesting that an absolute temperature is required.
authors.affiliation: Institut d'Electronique du Sud, CNRS UMR5214, Université Montpellier 2, Montpellier, France.
authors.forename: Jean-Michel
authors.initials: JM
authors.lastname: Bec
authors.forename: Emmanuelle S
authors.initials: ES
authors.lastname: Albert
authors.forename: Isabelle
authors.initials: I
authors.lastname: Marc
authors.forename: Gilles
authors.initials: G
authors.lastname: Desmadryl
authors.forename: Cécile
authors.initials: C
authors.lastname: Travo
authors.forename: Agnès
authors.initials: A
authors.lastname: Muller
authors.forename: Christian
authors.initials: C
authors.lastname: Chabbert
authors.forename: Fabrice
authors.initials: F
authors.lastname: Bardin
authors.forename: Michel
authors.initials: M
authors.lastname: Dumas
mesh_terms: D000200:Action Potentials / Q000528:radiation effects; D000818:Animals; D002478:Cells, Cultured; D005336:Fiber Optic Technology; D054023:Lasers, Semiconductor / Q000009:adverse effects; D008027:Light / Q000009:adverse effects; D051379:Mice; D008810:Mice, Inbred C57BL; D018408:Patch-Clamp Techniques; D010775:Photic Stimulation / Q000009:adverse effects / Q000295:instrumentation / Q000379:methods; D051381:Rats; D017208:Rats, Wistar; D012165:Retinal Ganglion Cells / Q000528:radiation effects*; D013696:Temperature; D014725:Vestibular Nerve / Q000528:radiation effects*