ABSTRACT
Brief cochlear excitotoxicity produces temporary neural swelling and transient deficits in auditory sensitivity; however, the consequences of long-lasting excitotoxic insult have not been tested. Chronic intra-cochlear infusion of the glutamate agonist AMPA (a-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid) resulted in functional deficits in the sound-evoked auditory brainstem response, as well as in behavioral measures of hearing. The electrophysiological deficits were similar to those observed following acute infusion of AMPA into the cochlea; however, the concentration-response curve was significantly shifted as a consequence of the slower infusion rate used with chronic cochlear administration. As observed following acute excitotoxic insult, complete functional recovery was evident within 7 days of discontinuing the AMPA infusion. Distortion product otoacoustic emissions were not affected by chronic AMPA infusion, suggesting that trauma to outer hair cells did not contribute to AMPA-induced deficits in acoustic sensitivity. Results from the current experiment address the permanence of deficits induced by chronic (14 day) excitotoxic insult as well as deficits in psychophysical detection of longer duration acoustic signals.
Subject(s)
Cochlea/drug effects , Cochlear Nerve/drug effects , Excitatory Amino Acid Agonists/toxicity , Hearing Loss, Sensorineural/chemically induced , alpha-Amino-3-hydroxy-5-methyl-4-isoxazolepropionic Acid/toxicity , Animals , Audiometry, Evoked Response , Auditory Threshold/drug effects , Cochlea/pathology , Cochlea/physiology , Evoked Potentials, Auditory, Brain Stem/drug effects , Excitatory Amino Acid Agonists/pharmacology , Female , Guinea Pigs , Hair Cells, Auditory, Outer/drug effects , Male , Neomycin/pharmacology , Otoacoustic Emissions, Spontaneous/drug effects , Otoacoustic Emissions, Spontaneous/physiology , Protein Synthesis Inhibitors/pharmacology , alpha-Amino-3-hydroxy-5-methyl-4-isoxazolepropionic Acid/pharmacologyABSTRACT
There is evidence that Japanese macaques (Macaca fuscata) are extremely sensitive to dynamic changes in the relative amplitudes of coo call harmonics during discrimination tests. To verify this evidence using more controlled stimulus configurations, the authors examined threshold sensitivity of macaque monkeys to amplitude increments added to the standard level of coo call harmonics. Psychophysical threshold determination methods paralleled those used previously to determine macaque sensitivity to amplitude increments added to vowel-like stimuli. Variation was detectable although thresholds were elevated relative to those obtained with vowel-like stimuli in another investigation (C. G. Le Prell, A. J. Niemiec, & D. B. Moody, 2001). This elevation was probably a function of natural amplitude modulation in the standard stimuli.
