Inhibitory Synaptic Inputs Activated By On-BF And Off-BF Frequencies Are Co-sharpening Frequency Tuning Of Mouse Inferior Colliculus Neurons:in Vivo Intracellular Recording

Frequency is one of the sound signal parameters and it plays an important role in transmitting sound information, frequency tuning is an important function of auditory neurons. By comparing the shape of the frequency tuning curves (FTC) between peripheral and central auditory neurons, it shows that the central auditory neurons have stronger ability to frequency tuning and analyzing than the peripheral auditory neurons. The mechanism underlying sharpening frequency tuning of the auditory neurons is not completely clear because of lacking of the direct experimental evidences affecting sharpening frequency tuning through interaction between excitatory and inhibitory synaptic inputs. Therefore, we probed co-sharpening role of the inhibitory synaptic inputs activated by on-BF and off-BF frequencies in sharpening frequency tuning of mouse inferior colliculus (IC) neurons with in vivo intracellular recording in present study.Total of87neurons were obtained from inferior colliculi of31adult and healthy mice (Mus musculus, Km) anesthetized by Nembutal (0.02mL/g b.wt.), the ranges of the recording depth (μm) and best frequency (BF)(kHz) of the neurons (n=53) were633-1950(1368.4±364.1) and7-47(22.3±10.9), respectively. By analyzing frequency tuning of53among87neurons, they could be classified into two types, which type one (n=25,47.16%) had lateral inhibitory areas (LIA) at low or/and high limbs of their excitatory frequency tuning curve (EFTC) and type two (n=28,52.83%) had no LIA at both sides of EFTC. Under two-tone stimulation condition, the inhibitions activated by both on-BF and off-BF frequencies can sharpen the EFTC of these neurons. In addition, sharpening of FTCs of28neurons without LIA at any one side of FTC mainly depends on the inhibition activated by on-BF frequency and is concerned perhaps with lateral inhibition (LI) from some auditory centers below IC.By comparison of degrees of sharpening frequency tuning through inhibitions activated severally by on-and off-BF frequencies, there exists a statistically significant difference (p<0.05) between two inhibitions. These results suggested that inhibitory synaptic inputs activated by on-BF and off-BF frequencies were co-sharpening frequency tuning of mouse inferior colliculus neurons.