[Effects of salicylate and quinine on cat primary auditory cortex--spontaneous firing rate]

The effect of salicylate and quinine on the spontaneous firing rate in the cat primary auditory cortex was investigated in 13 healthy cats. Spontaneous firing rates were calculated for each single unit. A dose of 200 mg of sodium salicylate per kg was administered intraperitoneally to six cats, and the findings from the same single unit were recorded prior to application and continuously up to, on average, 6 hours after application. A dose of 100 or 200 mg of quinine hydrochloride per kg was administered intramuscularly to seven cats, and the findings from the same single unit were recorded in the same manner as for the cats treated with sodium salicylate. Twenty one single units in salicylate-treated cats and 29 single units in quinine-treated cats were evaluated. All animals treated with salicylate showed a 20-30 dB threshold shift about 2 hours after application and showed no recovery during the course of the investigation. All animals treated with quinine showed a 10-40 dB threshold shift about 1 hour after application and recovered during the course of the investigation. There was no consistent difference in overall spontaneous firing rate before and after application in either salicylate-treated cats or quinine treated cats. In order to investigate a potential different effect on units with different spontaneous firing rates, we divided the cats into two groups, a high-firing rate group (pre-application firing rate > 1 spike/s) and a low firing rate group (pre-application firing rate < 1 spike/s). A significant decrease in the high-firing rate group (p < 0.05) and a significant increase in the low firing rate (p < 0.01) were observed in salicylate-treated cats. The same tendencies were observed in quinine-treated cats, but only the difference in the low firing rate group was significant (p < 0.05). The difference in the high-firing rate group was close to the significant level (p = 0.055). These changes in spontaneous firing rates in cat primary auditory cortex may be related to the generation of tinnitus.