Urethane Improves the Response of Auditory Neurons to Tone

Bowan Huang; Linqing Yan; Yan Li; Wenhui Liu; Manhua Liu; Zhongju Xiao; Jinping Huang

doi:10.3389/fncel.2022.855968

Urethane Improves the Response of Auditory Neurons to Tone

Front Cell Neurosci. 2022 Jun 15:16:855968. doi: 10.3389/fncel.2022.855968. eCollection 2022.

Authors

Bowan Huang^{1

2}, Linqing Yan¹, Yan Li¹, Wenhui Liu³, Manhua Liu³, Zhongju Xiao^{1

3}, Jinping Huang³

Affiliations

¹ Department of Physiology, School of Basic Medical Sciences, Southern Medical University, Guangzhou, China.
² Department of Anesthesiology, Shenzhen Traditional Chinese Medicine Hospital, The Fourth Clinical Medical College of Guangzhou University of Chinese Medicine, Shenzhen, China.
³ The Seventh Affiliated Hospital, Southern Medical University, Foshan, China.

Abstract

Urethane has little effect on nervous system and is often used in neuroscience studies. However, the effect of urethane in neurons is not thoroughly clear. In this study, we investigated changes in neuron responses to tones in inferior colliculus during urethane anesthesia. As urethane was metabolized, the best and characteristic frequencies did not obviously change, but the minimal threshold (MT) remained relatively stable or was elevated. The frequency tuning bandwidth at 60 dB SPL (BW_60dBSPL) remained unchanged or decreased, and the average evoked spike of effective frequencies at 60 dB SPL (ES_60dBSPL) gradually decreased. Although the average evoked spike of effective frequencies at a tone intensity of 20 dB SPL above MT (ES_{20dBSPLaboveMT}) decreased, the frequency tuning bandwidth at a tone intensity of 20 dB SPL above MT (BW_{20dBSPLaboveMT}) did not change. In addition, the changes in MT, ES_60dBSPL, BW_60dBSPL, and ES_{20dBSPLaboveMT} increased with the MT in pre-anesthesia awake state (MT_{pre-anesthesiaawake}). In some neurons, the MT was lower, BW_60dBSPL was broader, and ES_60dBSPL and ES_{20dBSPLaboveMT} were higher in urethane anesthesia state than in pre-anesthesia awake state. During anesthesia, the inhibitory effect of urethane reduced the ES_{20dBSPLaboveMT}, but did not change the MT, characteristic frequency, or BW_{20dBSPLaboveMT}. In the recording session with the strongest neuron response, the first spike latency did not decrease, and the spontaneous spike did not increase. Therefore, we conclude that urethane can reduce/not change the MT, increase the evoked spike, or broaden/not change the frequency tuning range, and eventually improve the response of auditory neurons to tone with or without "pushing down" the tonal receptive field in thresholding model. The improved effect increases with the MT_{pre-anesthesiaawake} of neurons. The changes induced by the inhibitory and improved effects of urethane abide by similar regularities, but the change directions are contrary. The improvement mechanism may be likely due to the increase in the ratio of excitatory/inhibitory postsynaptic inputs to neurons.

Keywords: auditory sense; improvement; inferior colliculus; response to tone; urethane.