Processing of Paired Click-Tone Stimulation in the Mice Inferior Colliculus

Abstract

The inferior colliculus (IC) is known as a neuronal structure involved in the integration of acoustic information in the ascending auditory pathway. However, the processing of paired acoustic stimuli containing different sound types, especially when they are applied closely, in the IC remains poorly studied. We here firstly investigated the IC neuronal response to the paired stimuli comprising click and pure tone with different inter-stimulus (click-tone) intervals using in vivo loose-patch recordings in anesthetized BALB/c mice. It was found that the total acoustic evoked spike counts decreased under certain click-tone interval conditions on some neurons with or without click-induced supra-threshold responses. Application of click could enhance the minimum threshold of the neurons responding to the tone in a pair without changing other characteristics of the neuronal tone receptive fields. We further studied the paired acoustic stimuli evoked excitatory/inhibitory inputs, IC neurons received, by holding the membrane potential at -70/0 mV using in vivo whole-cell voltage-clamp techniques. The curvature and peak amplitude of the excitatory/inhibitory post-synaptic current (EPSC/IPSC) could be almost unchanged under different inter-stimulus interval conditions. Instead of showing the summation of synaptic inputs, most recorded neurons only had the EPSC/IPSC with the amplitude similar as the bigger one evoked by click or tone in a pair when the inter-stimulus interval was small. We speculated that the IC could inherit the paired click-tone information which had been integrated before reaching it.

Bilateral Interactions in the Mouse Dorsal Inferior Colliculus Enhance the Ipsilateral Neuronal Responses and Binaural Hearing

“…The synaptic responses were not the same as those from the extracellular recordings in terms of the distribution of neuron types ( Figures 4 – 7 ). Generally, synaptic changes would likely be more sensitive ( Liu et al, 2019 ; Wang et al, 2019 ; Wu et al, 2021 ). Therefore, some subthreshold modulation was not reflected in spikes.…”

“…The surgical procedures used for mouse electrophysiological recordings were similar to those methods that we previously reported ( Wei et al, 2018 ; Liu et al, 2019 ; Wang et al, 2019 ; Wu et al, 2021 ). Mice were anaesthetized with pentobarbital (60–80 mg/kg, i. p., Sigma, United States) and atropine (0.25 mg/kg, s. c., Nandao, China).…”

Synaptic excitation underlies processing of paired stimulation in the mouse inferior colliculus

“…Because binaural synaptic responses tended to be contra‐preferred even when contralateral intensities were attenuated by 0–30 dB SPL and still had lager synaptic currents than those evoked ipsilaterally. As a result, this type of neurons seemed to prefer the EPSC with the amplitude similar to the bigger one evoked by a tone (Figure 10a, middle row; 10b, pathway N), such as contralateral stimulation, in a pair when the interval was small (Wang et al., 2019; Wei et al., 2018).…”

“…For electrophysiological recording experiments preparation, all mice were subjected to surgeries following our previously reported methods (Wang et al., 2019; Wei et al., 2018; Xiong et al., 2013). Mice were anesthetized with sodium pentobarbital (60–70 mg/kg, Nandao, Hainan, China) via intraperitoneal injections after tracheal mucous secretion was reduced by atropine sulfate (0.25 mg/kg, i.h., Nandao, Hainan, China).…”

“…The location of the recorded neuron was confirmed by iontophoretically applied biocytin (1–10 nA for 300 ms ON and 300 ms OFF for 30 min) using microiontophoresis (Neurophore BH‐2; Harvard, Holliston, MA, United States) (Wang et al., 2019). Each mouse was sacrificed with an overdose of sodium pentobarbital (120 mg/kg, i.p.)…”