Urethane Improves the Response of Auditory Neurons to Tone.

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 (BW60dBSPL) remained unchanged or decreased, and the average evoked spike of effective frequencies at 60 dB SPL (ES60dBSPL) gradually decreased. Although the average evoked spike of effective frequencies at a tone intensity of 20 dB SPL above MT (ES20dBSPLaboveMT) decreased, the frequency tuning bandwidth at a tone intensity of 20 dB SPL above MT (BW20dBSPLaboveMT) did not change. In addition, the changes in MT, ES60dBSPL, BW60dBSPL, and ES20dBSPLaboveMT increased with the MT in pre-anesthesia awake state (MTpre-anesthesiaawake). In some neurons, the MT was lower, BW60dBSPL was broader, and ES60dBSPL and ES20dBSPLaboveMT were higher in urethane anesthesia state than in pre-anesthesia awake state. During anesthesia, the inhibitory effect of urethane reduced the ES20dBSPLaboveMT, but did not change the MT, characteristic frequency, or BW20dBSPLaboveMT. 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 MTpre-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.

Optimal Pipette Resistance, Seal Resistance, and Zero-Current Membrane Potential for Loose Patch or Breakthrough Whole-Cell Recording in vivo.

In vivo loose patch and breakthrough whole-cell recordings are useful tools for investigating the intrinsic and synaptic properties of neurons. However, the correlation among pipette resistance, seal condition, and recording time is not thoroughly clear. Presently, we investigated the recording time of different pipette resistances and seal conditions in loose patch and breakthrough whole-cell recordings. The recording time did not change with pipette resistance for loose patch recording (Rp-loose) and first increased and then decreased as seal resistance for loose patch recording (Rs-loose) increased. For a high probability of a recording time ≥30 min, the low and high cutoff values of Rs-loose were 21.5 and 36 MΩ, respectively. For neurons with Rs-loose values of 21.5-36 MΩ, the action potential (AP) amplitudes changed slightly 30 min after the seal. The recording time increased as seal resistance for whole-cell recording (Rs-tight) increased and the zero-current membrane potential for breakthrough whole-cell recording (MPzero-current) decreased. For a high probability of a recording time ≥30 min, the cutoff values of Rs-tight and MPzero-current were 2.35 GΩ and -53.5 mV, respectively. The area under the curve (AUC) of the MPzero-current receiver operating characteristic (ROC) curve was larger than that of the Rs-tight ROC curve. For neurons with MPzero-current values ≤ -53.5 mV, the inhibitory or excitatory postsynaptic current amplitudes did not show significant changes 30 min after the seal. In neurons with Rs-tight values ≥2.35 GΩ, the recording time gradually increased and then decreased as the pipette resistance for whole-cell recording (Rp-tight) increased. For the high probability of a recording time ≥30 min, the low and high cutoff values of Rp-tight were 6.15 and 6.45 MΩ, respectively. Together, we concluded that the optimal Rs-loose range is 21.5-36 MΩ, the optimal Rp-tight range is 6.15-6.45 MΩ, and the optimal Rs-tight and MPzero-current values are ≥2.35 GΩ and ≤ -53.5 mV, respectively. Compared with Rs-tight, the MPzero-current value can more accurately discriminate recording times ≥30 min and <30 min.

Contextual and cross-modality modulation of auditory cortical processing through pulvinar mediated suppression.

Lateral posterior nucleus (LP) of thalamus, the rodent homologue of primate pulvinar, projects extensively to sensory cortices. However, its functional role in sensory cortical processing remains largely unclear. Here, bidirectional activity modulations of LP or its projection to the primary auditory cortex (A1) in awake mice reveal that LP improves auditory processing in A1 supragranular-layer neurons by sharpening their receptive fields and frequency tuning, as well as increasing the signal-to-noise ratio (SNR). This is achieved through a subtractive-suppression mechanism, mediated largely by LP-to-A1 axons preferentially innervating specific inhibitory neurons in layer 1 and superficial layers. LP is strongly activated by specific sensory signals relayed from the superior colliculus (SC), contributing to the maintenance and enhancement of A1 processing in the presence of auditory background noise and threatening visual looming stimuli respectively. Thus, a multisensory bottom-up SC-pulvinar-A1 pathway plays a role in contextual and cross-modality modulation of auditory cortical processing.

General anesthetic induced differential changes in latency of auditory evoked potential in the central nucleus of inferior colliculus of mouse.

Confirming the effect of general anesthetic on brainstem auditory evoked potential (BAEP) is important to interpret BAEP data, elucidate the neuroanatomical sites of action of general anesthetic and monitor the effect of general anesthetic. However, the effect of general anesthetic on BAEP is not thoroughly understood, which may be due to unreasonable acoustic stimulation scheme. This study aimed to redesign acoustic stimulation scheme and attempted to test our hypothesis that general anesthetic induces differential changes in BAEP latency in mouse. Auditory evoked potential in the central nucleus of inferior colliculus (AEP-ICC) was used to represent BAEP. Every 10 min after pentobarbital anesthesia, AEP-ICC was recorded by delivering tones with a rate of 1/s, and pentobarbital blood concentration (PBC) was measured, until the mice awoke. AEP-ICC latency to 80-dB SPL sounds (L80) and latency change in nerve fibers (ΔL) did not present regular changes, and AEP-ICC latency to 50-dB SPL sounds (L50) and latency change in synapses (ΔI) gradually decreased as pentobarbital was metabolized. L50 and ΔI changes were exponentially associated with decreased PBC, and L50 showed a linear relationship with ΔI. We conclude that, general anesthetic acts on auditory brainstem; general anesthetic does not alter L80 and ΔL but increases L50 and ΔI; L80 and ΔL can evaluate the function of auditory brainstem and its inferior structures under general anesthesia; L50 and ΔI exponentially reflect the blood concentration of a general anesthetic.

Synaptic Mechanisms for Bandwidth Tuning in Awake Mouse Primary Auditory Cortex.

Spatial size tuning in the visual cortex has been considered as an important neuronal functional property for sensory perception. However, an analogous mechanism in the auditory system has remained controversial. In the present study, cell-attached recordings in the primary auditory cortex (A1) of awake mice revealed that excitatory neurons can be categorized into three types according to their bandwidth tuning profiles in response to band-passed noise (BPN) stimuli: nonmonotonic (NM), flat, and monotonic, with the latter two considered as non-tuned for bandwidth. The prevalence of bandwidth-tuned (i.e., NM) neurons increases significantly from layer 4 to layer 2/3. With sequential cell-attached and whole-cell voltage-clamp recordings from the same neurons, we found that the bandwidth preference of excitatory neurons is largely determined by the excitatory synaptic input they receive, and that the bandwidth selectivity is further enhanced by flatly tuned inhibition observed in all cells. The latter can be attributed at least partially to the flat tuning of parvalbumin inhibitory neurons. The tuning of auditory cortical neurons for bandwidth of BPN may contribute to the processing of complex sounds.

Regioselective Atomic Rearrangement of Ag-Pt Octahedral Catalysts by Chemical Vapor-Assisted Treatment.

Thermal annealing is a common, and often much-needed, process to optimize the surface structure and composition of bimetallic nanoparticles for high catalytic performance. Such thermal treatment is often carried out either in air or under an inert atmosphere by a trial-and-error approach. Herewith, we present a new chemical vapor-assisted treatment, which can preserve the octahedral morphology of Ag-Pt nanoparticles while modifying the surface into preferred composition arrangements with site-selectivity for high catalytic activity. In situ environmental transmission electron microscope (ETEM) study reveals a relatively homogeneous distribution of Ag and Pt is generated on the surface of Ag-Pt nanoparticles upon exposure to carbon monoxide (CO), whereas Pt atoms preferably segregate to the edge regions when the gas atmosphere is switched to argon. Density functional theory (DFT) calculations suggest stabilization of Pt atoms is energetically favored in the form of mixed surface alloys when CO vapor is present. Without CO, Ag and Pt phase separate under the similar mild treatment condition. There exists a close correlation between the tunable surface structures and the catalytic activities of Ag-Pt octahedral nanoparticles.

Latency of auditory evoked potential monitoring the effects of general anesthetics on nerve fibers and synapses.

Auditory evoked potential (AEP) is an effective index for the effects of general anesthetics. However, it's unknown if AEP can differentiate the effects of general anesthetics on nerve fibers and synapses. Presently, we investigated AEP latency and amplitude changes to different acoustic intensities during pentobarbital anesthesia. Latency more regularly changed than amplitude during anesthesia. AEP Latency monotonically decreased with acoustic intensity increase (i.e., latency-intensity curve) and could be fitted to an exponential decay equation, which showed two components, the theoretical minimum latency and stimulus-dependent delay. From the latency-intensity curves, the changes of these two components (∆L and ∆I) were extracted during anesthesia. ∆L and ∆I monitored the effect of pentobarbital on nerve fibers and synapses. Pentobarbital can induce anesthesia, and two side effects, hypoxemia and hypothermia. The hypoxemia was not related with ∆L and ∆I. However, ∆L was changed by the hypothermia, whereas ∆I was changed by the hypothermia and anesthesia. Therefore, we conclude that, AEP latency is superior to amplitude for the effects of general anesthetics, ∆L monitors the effect of hypothermia on nerve fibers, and ∆I monitors a combined effect of anesthesia and hypothermia on synapses. When eliminating the temperature factor, ∆I monitors the anesthesia effect on synapses.