title: Intraorbital optic nerve stimulation with penetrating electrodes: in vivo electrophysiology study in rabbits.
abstract: OBJECTIVE
  To investigate the response properties of the electrically evoked potentials (EEPs) elicited by intraorbital optic nerve stimulation with penetrating electrodes using different stimulus parameters.
  
  
  METHODS
  Visually evoked potentials (VEPs) were recorded as a control and for comparative purposes. Teflon-coated tungsten wire electrodes (100 microm core-diameter, 300 microm exposed tip) were inserted intraorbitally into the optic nerve. A charge-balanced biphasic current was delivered to the optic nerve via inserted wire electrodes in 26 anaesthetized rabbits. EEPs were recorded by epidural electrodes placed over the visual cortex. The charge density threshold for eliciting EEPs was determined. Stimulus pulse amplitude, duration, frequency and waveform were varied to study their effects on EEPs. After the experiments, the stimulated optic nerves were examined histologically for examination of implantation position of the stimulating electrode into the optic nerve tissue.
  
  
  RESULTS
  EEPs were successfully elicited by intraorbital optic nerve stimulation with penetrating electrodes. The measured amplitude of the first large positive peak (P1) was smaller and the latency of P1 was shorter compared with VEPs. The measured charge density threshold to elicit EEPs was 21.36 +/- 5.64 microC/cm(2). The amplitude of P1 increased and the latency of P1 decreased with increasing pulse amplitude of fixed duration stimuli. The amplitude of P1 increased with increasing pulse duration of fixed amplitude stimuli. For fixed charge stimuli, the amplitude of P1 decreased and the latency of P1 increased as the pulse duration increased. As frequency of stimuli varied from 1 to 10 Hz, the amplitude of P1 decreased monotonically. Among the different charge-balanced biphasic pulse stimulating waveforms, the symmetrical cathode-first biphasic pulse elicited the largest amplitude of P1.
  
  
  CONCLUSIONS
  Our study demonstrates that intraorbital optic nerve stimulation with different stimulus parameters by penetrating electrodes can evoke cortical responses with different properties. The short-duration symmetrical cathode-first biphasic pulses of current with low frequencies are more efficacious in eliciting electrophysiological responses in the visual cortex than other stimulating waveforms.
authors.affiliation: Institute for Laser Medicine and Bio-Photonics, Department of Biomedical Engineering, Shanghai Jiao Tong University, 800 Dong-Chuan Road, Shanghai, 200240, China.
authors.forename: Liming
authors.initials: L
authors.lastname: Li
authors.forename: Pengjia
authors.initials: P
authors.lastname: Cao
authors.forename: Mingjie
authors.initials: M
authors.lastname: Sun
authors.forename: Xinyu
authors.initials: X
authors.lastname: Chai
authors.forename: Kaijie
authors.initials: K
authors.lastname: Wu
authors.forename: Xun
authors.initials: X
authors.lastname: Xu
authors.forename: Xiaoxin
authors.initials: X
authors.lastname: Li
authors.forename: Qiushi
authors.initials: Q
authors.lastname: Ren
mesh_terms: D000818:Animals; D004558:Electric Stimulation / Q000379:methods*; D004567:Electrodes, Implanted; D005074:Evoked Potentials, Visual / Q000502:physiology*; D009900:Optic Nerve / Q000502:physiology*; D009915:Orbit; D010775:Photic Stimulation / Q000379:methods*; D011817:Rabbits; D014793:Visual Cortex / Q000502:physiology*