H.W. Lee

Sleep spindles are generated in the absence of T-type calcium channel-mediated low-threshold burst firing of thalamocortical neurons

Significance This study addresses one of the most fundamental issues in sleep rhythm generation. The theory that low-threshold burst firing mediated by T-type calcium channels in thalamocortical neurons is the key component for sleep spindles, has been accepted as dogma and appears throughout the literature. In this study, however, in vivo and in vitro evidence shows that sleep spindles are generated normally in the absence of T-type channels and burst firing in thalamocortical neurons. Furthermore, our data indicate a potentially important role of tonic firing in this rhythm generation. This study advances the knowledge of sleep and vigilance control to another level of understanding. T-type Ca2+ channels in thalamocortical (TC) neurons have long been considered to play a critical role in the genesis of sleep spindles, one of several TC oscillations. A classical model for TC oscillations states that reciprocal interaction between synaptically connected GABAergic thalamic reticular nucleus (TRN) neurons and glutamatergic TC neurons generates oscillations through T-type channel-mediated low-threshold burst firings of neurons in the two nuclei. These oscillations are then transmitted from TC neurons to cortical neurons, contributing to the network of TC oscillations. Unexpectedly, however, we found that both WT and KO mice for CaV3.1, the gene for T-type Ca2+ channels in TC neurons, exhibit typical waxing-and-waning sleep spindle waves at a similar occurrence and with similar amplitudes and episode durations during non-rapid eye movement sleep. Single-unit recording in parallel with electroencephalography in vivo confirmed a complete lack of burst firing in the mutant TC neurons. Of particular interest, the tonic spike frequency in TC neurons was significantly increased during spindle periods compared with nonspindle periods in both genotypes. In contrast, no significant change in burst firing frequency between spindle and nonspindle periods was noted in the WT mice. Furthermore, spindle-like oscillations were readily generated within intrathalamic circuits composed solely of TRN and TC neurons in vitro in both the KO mutant and WT mice. Our findings call into question the essential role of low-threshold burst firings in TC neurons and suggest that tonic firing is important for the generation and propagation of spindle oscillations in the TC circuit.

Bulk Switching Instrumentation Amplifier for a High-Impedance Source in Neural Signal Recording

Flicker noise is the most crucial issue in an instrumentation amplifier (IA) for neural recordings because low-frequency neural signals overlap with the frequency of the amplifiers flicker noise. A Chopping technique, often used to reduce the flicker noise, is not desirable for high-impedance input sources due to the charge injection and clock feedthrough from the MOSFETs of the input chopper to the signal source, resulting in a significant increase in the total input-referred noise. Whereas MOSFETs have less flicker noise at the moment of turning on, and the intrinsic flicker noise can be then reduced by turning on and off the MOSFETs in the IA. This brief proposes a bulk switching IA, which can avoid the input current noise. A prototype IA is implemented in a 65 nm CMOS occupying 0.053 mm2, and it achieves the input-referred noise of 0.74 μVrms (local field potential) for 100 k Ω source impedance, a 3.3 times reduction compared with that of the chopper IAs, while consuming only 3.96 μW from a 1.2 V supply.

CXXC5 plays a role as a transcription activator for myelin genes on oligodendrocyte differentiation

Myelination in corpus callosum plays important role for normal brain functions by transferring neurological information between various brain regions. However, the factors controlling expression of myelin genes in myelination are poorly understood. Here, CXXC5, a recently identified protein with CXXC‐type zinc finger DNA binding motif, was characterized as a transcriptional activator of major myelin genes. We identified expression of CXXC5 expression was increased by Wnt/β‐catenin signaling. CXXC5 specifically expressed in the white matter induced expression of myelin genes through the direct binding of CXXC DNA‐binding motif of CXXC5 on the MBP promoter. During the differentiation of neural stem cells (NSCs) of CXXC5−/− mice, the expressions of myelin genes were simultaneously reduced. The CXXC5−/− mice exhibited severely reduction of myelin genes expression in corpus callosum as well as abnormalities in myelin structure. The disrupted structural integrity of myelin in the CXXC5−/− mice resulted in reduced electrical conduction amplitudes at corpus callosum. These findings indicate that the regulation of myelin genes expression by CXXC5 is important for forming myelin structure involved with axonal electrical signal transfer in the corpus callosum. GLIA 2016;64:350–362

Evolution and persistence of resistance-associated substitutions of hepatitis C virus after direct-acting antiviral treatment failures

Daclatasvir plus asunaprevir (DCV+ASV) treatment is an all‐oral direct‐acting antiviral (DAA) therapy for the genotype 1b HCV‐infected patients. In this study, we investigated how resistance‐associated substitutions (RASs) evolved after treatment failures and assessed the effect of those substitutions on viral fitness. Sequencing of NS5A and NS3 revealed typical RASs after treatment failures. Interestingly, the RASs of NS3 reverted to the wild‐type amino acid within 1 year after treatment failures. However, the RASs of NS5A were stable and did not change. The effect of NS5A and NS3 RASs on viral RNA replication was assessed after mutagenic substitution in the genotype 1b HCV RNA. Among single substitutions, the effect of D168V was more substantial than the others and the effect of the triple mutant combination (D168V+L31V+Y93H) was the most severe. The RAS at NS5A Y93 affected both viral RNA replication and virus production. Finally, the effect of trans‐complementation of NS5A was demonstrated in our co‐transfection experiments and these results suggest that such a trans‐complementation effect of NS5A may help maintain the NS5A RASs for a long time even after cessation of the DAA treatment. In conclusion, the results from this investigation would help understand the emergence and persistence of RASs.