Experimental erbium laser surgery in the guinea pig cochlea : its use in the study of afferent cochlear neurotransmitters

Microiontophoretic techniques were used to examine the changes in activity of inner half cell afferents in the guinea pig following circumscribed penetration of cochlear bone with erbium:YSGG laser pulses. Neuronal responses to the application of the glutamate agonists N-methyl-D-aspartate (NMDA) and alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA) before laser use and after return to normal spontaneous activity were equivalent, implying total reversibility of the changes occurring. Suppression of laser-induced hair cell activity was possible with NMDA and AMPA receptor antagonists and lasted 10-15 min. These findings suggest a transmitter-related increase of neuronal activity. Our results show that use of the erbium laser in inner ear microsurgery might be possible with low risk if the amount of energy applied is kept under a safe limit of 10 J/cm2.