EFFECTS OF QUININE ON NEURAL ACTIVITY IN CAT PRIMARY AUDITORY-CORTEX

The effect of systemically applied quinine on single-unit firing activ ity in primary auditory cortex was investigated in seven cats. A dose of 100 or 200 mg/kg of quinine hydrochloride was administered intramus cularly and recordings from the same units were performed prior to app lication and continuously up to on average 5.5 h after administration. All animals showed 10-40 dB of threshold shift about 30 min after adm inistration and some animals showed recovery during the course of the investigation. Significant increases were found in spontaneous firing rates for low-firing-rate units (initial firing rate < 1 spike/s). For high-firing-rate units (initial firing rate > 1 spike/s) no significa nt changes were observed. There were no significant changes in modal a nd mean interspike interval. The time-to-rebound peak in the autocorre lation function for spontaneous firings was not altered significantly. The rate of burst occurrence showed no significant change. The best m odulation frequency in response to stimulation with periodic click tra ins decreased after administration, but the limiting rate did not chan ge. Peak cross-correlation coefficients for the spontaneous firings of simultaneously recorded cells showed a significant increase and the c orrelogram's central peak was significantly narrower after quinine app lication. Dose effects were only present for cross-correlation results and temporal modulation transfer functions. The results for both spon taneous firing rate, peak width in the cross-correlogram and click sti mulation were similar to those observed in salicylate-treated cats (Oc hi and Eggermont, 1996). The other findings were different from those observed after salicylate. It is obvious that the effects of quinine o n the auditory system are not the same as those of salicylate. The inc reased synchronization of the spontaneous firings across different neu rons observed after application of both drugs may be related to tinnit us.