Human voltage-gated Na+ and K+ channel properties underlie sustained fast AP signaling

Enhanced motivated behavior mediated by pharmacological targeting of the FGF14/Nav1.6 complex in nucleus accumbens neurons

Protein/protein interactions (PPI) play crucial roles in neuronal functions. Yet, their potential as drug targets for brain disorders remains underexplored. The fibroblast growth factor 14 (FGF14)/voltage-gated Na+ channel 1.6 (Nav1.6) complex regulates excitability of medium spiny neurons (MSN) of the nucleus accumbens (NAc), a central hub of reward circuitry that controls motivated behaviors. Here, we identified compound 1028 (IUPAC: ethyl 3-(2-(3-(hydroxymethyl)-1H-indol-1-yl)acetamido)benzoate), a brain-permeable small molecule that targets FGF14R117, a critical residue located within a druggable pocket at the FGF14/Nav1.6 PPI interface. We found that 1028 modulates FGF14/Nav1.6 complex assembly and depolarizes the voltage-dependence of Nav1.6 channel inactivation with nanomolar potency by modulating the intramolecular interaction between the III-IV linker and C-terminal domain of the Nav1.6 channel. Consistent with the compound's effects on Nav1.6 channel inactivation, 1028 enhances MSN excitability ex vivo and accumbal neuron firing rate in vivo in murine models. Systemic administration of 1028 maintains behavioral motivation preferentially during motivationally deficient conditions in murine models. These behavioral effects were abrogated by in vivo gene silencing of Fgf14 in the NAc and were accompanied by a selective reduction in accumbal dopamine levels during reward consumption in murine models. These findings underscore the potential to selectively regulate complex behaviors associated with neuropsychiatric disorders through targeting of PPIs in neurons.

Protocol to process fresh human cerebral cortex biopsies for patch-clamp recording and immunostaining

Cerebral cortex biopsies enable the investigation of native developing and mature human brain tissue. Here, we present a protocol to process human cortical biopsies from the surgical theater to the laboratory. We describe steps for the preparation of viable acute slices for patch-clamp recording using dedicated chemical solutions for transport and sectioning. We then explain procedures for tissue fixation and post hoc immunostaining to correlate physiological properties to morphological features and protein detection. For complete details on the use and execution of this protocol, please refer to Libé-Philippot et al.1.

Membrane potential states gate synaptic consolidation in human neocortical tissue

Synaptic mechanisms that contribute to human memory consolidation remain largely unexplored. Consolidation critically relies on sleep. During slow wave sleep, neurons exhibit characteristic membrane potential oscillations known as UP and DOWN states. Coupling of memory reactivation to these slow oscillations promotes consolidation, though the underlying mechanisms remain elusive. Here, we performed axonal and multineuron patch-clamp recordings in acute human brain slices, obtained from neurosurgeries, to show that sleep-like UP and DOWN states modulate axonal action potentials and temporarily enhance synaptic transmission between neocortical pyramidal neurons. Synaptic enhancement by UP and DOWN state sequences facilitates recruitment of postsynaptic action potentials, which in turn results in long-term stabilization of synaptic strength. In contrast, synapses undergo lasting depression if presynaptic neurons fail to recruit postsynaptic action potentials. Our study offers a mechanistic explanation for how coupling of neural activity to slow waves can cause synaptic consolidation, with potential implications for brain stimulation strategies targeting memory performance.

Comediation of voltage gating and ion charge in MXene membrane for controllable and selective monovalent cation separation

Artificial ion channels with controllable mono/monovalent cation separation fulfill important roles in biomedicine, ion separation, and energy conversion. However, it remains a daunting challenge to develop an artificial ion channel similar to biological ion channels due to ion-ion competitive transport and lack of ion-gating ability of channels. Here, we report a conductive MXene membrane with polydopamine-confined angstrom-scale channels and propose a voltage gating and ion charge comediation strategy to concurrently achieve gated and selective mono/monovalent cation separation. The membrane shows a highly switchable "on-off" ratio of ∼9.9 for K+ transport and an excellent K+/Li+ selectivity of 40.9, outperforming the ion selectivity of reported membranes with electrical gating (typically 1.5 to 6). Theoretical simulations reveal that the introduced high-charge cations such as Mg2+ enable the preferential distribution of target K+ over competing Li+ at the channel entrance, and the surface potential reduces the ionic transport energy barrier for allowing K+ to pass quickly through the channel.

If you please, draw me a neuron - linking evolutionary tinkering with human neuron evolution

Animal speciation often involves novel behavioral features that rely on nervous system evolution. Human-specific brain features have been proposed to underlie specialized cognitive functions and to be linked, at least in part, to the evolution of synapses, neurons, and circuits of the cerebral cortex. Here, we review recent results showing that, while the human cortex is composed of a repertoire of cells that appears to be largely similar to the one found in other mammals, human cortical neurons do display specialized features at many levels, from gene expression to intrinsic physiological properties. The molecular mechanisms underlying human species-specific neuronal features remain largely unknown but implicate hominid-specific gene duplicates that encode novel molecular modifiers of neuronal function. The identification of human-specific genetic modifiers of neuronal function brings novel insights on brain evolution and function and, could also provide new insights on human species-specific vulnerabilities to brain disorders.

Molecular mechanisms of the specialization of human synapses in the neocortex

Synapses of the neocortex specialized during human evolution to develop over extended timescales, process vast amounts of information and increase connectivity, which is thought to underlie our advanced social and cognitive abilities. These features reflect species-specific regulations of neuron and synapse cell biology. However, despite growing understanding of the human genome and the brain transcriptome at the single-cell level, linking human-specific genetic changes to the specialization of human synapses has remained experimentally challenging. In this review, we describe recent progress in characterizing divergent morphofunctional and developmental properties of human synapses, and we discuss new insights into the underlying molecular mechanisms. We also highlight intersections between evolutionary innovations and disorder-related dysfunctions at the synapse.

The neuroscience of mental illness: Building toward the future

Mental illnesses arise from dysfunction in the brain. Although numerous extraneural factors influence these illnesses, ultimately, it is the science of the brain that will lead to novel therapies. Meanwhile, our understanding of this complex organ is incomplete, leading to the oft-repeated trope that neuroscience has yet to make significant contributions to the care of individuals with mental illnesses. This review seeks to counter this narrative, using specific examples of how neuroscientific advances have contributed to progress in mental health care in the past and how current achievements set the stage for further progress in the future.

State-specific Regulation of Electrical Stimulation in the Intralaminar Thalamus of Macaque Monkeys: Network and Transcriptional Insights into Arousal

Long-range thalamocortical communication is central to anesthesia-induced loss of consciousness and its reversal. However, isolating the specific neural networks connecting thalamic nuclei with various cortical regions for state-specific anesthesia regulation is challenging, with the biological underpinnings still largely unknown. Here, simultaneous electroencephalogram-fuctional magnetic resonance imaging (EEG-fMRI) and deep brain stimulation are applied to the intralaminar thalamus in macaques under finely-tuned propofol anesthesia. This approach led to the identification of an intralaminar-driven network responsible for rapid arousal during slow-wave oscillations. A network-based RNA-sequencing analysis is conducted of region-, layer-, and cell-specific gene expression data from independent transcriptomic atlases and identifies 2489 genes preferentially expressed within this arousal network, notably enriched in potassium channels and excitatory, parvalbumin-expressing neurons, and oligodendrocytes. Comparison with human RNA-sequencing data highlights conserved molecular and cellular architectures that enable the matching of homologous genes, protein interactions, and cell types across primates, providing novel insight into network-focused transcriptional signatures of arousal.

Genomic, molecular, and cellular divergence of the human brain

While many core biological processes are conserved across species, the human brain has evolved with unique capacities. Current understanding of the neurobiological mechanisms that endow human traits as well as associated vulnerabilities remains limited. However, emerging data have illuminated species divergence in DNA elements and genome organization, in molecular, morphological, and functional features of conserved neural cell types, as well as temporal differences in brain development. Here, we summarize recent data on unique features of the human brain and their complex implications for the study and treatment of brain diseases. We also consider key outstanding questions in the field and discuss the technologies and foundational knowledge that will be required to accelerate understanding of human neurobiology.

Aging-associated weakening of the action potential in fast-spiking interneurons in the human neocortex

Aging is associated with the slowdown of neuronal processing and cognitive performance in the brain; however, the exact cellular mechanisms behind this deterioration in humans are poorly elucidated. Recordings in human acute brain slices prepared from tissue resected during brain surgery enable the investigation of neuronal changes with age. Although neocortical fast-spiking cells are widely implicated in neuronal network activities underlying cognitive processes, they are vulnerable to neurodegeneration. Herein, we analyzed the electrical properties of 147 fast-spiking interneurons in neocortex samples resected in brain surgery from 106 patients aged 11-84 years. By studying the electrophysiological features of action potentials and passive membrane properties, we report that action potential overshoot significantly decreases and spike half-width increases with age. Moreover, the action potential maximum-rise speed (but not the repolarization speed or the afterhyperpolarization amplitude) significantly changed with age, suggesting a particular weakening of the sodium channel current generated in the soma. Cell passive membrane properties measured as the input resistance, membrane time constant, and cell capacitance remained unaffected by senescence. Thus, we conclude that the action potential in fast-spiking interneurons shows a significant weakening in the human neocortex with age. This may contribute to the deterioration of cortical functions by aging.

LRRC37B is a human modifier of voltage-gated sodium channels and axon excitability in cortical neurons

The enhanced cognitive abilities characterizing the human species result from specialized features of neurons and circuits. Here, we report that the hominid-specific gene LRRC37B encodes a receptor expressed in human cortical pyramidal neurons (CPNs) and selectively localized to the axon initial segment (AIS), the subcellular compartment triggering action potentials. Ectopic expression of LRRC37B in mouse CPNs in vivo leads to reduced intrinsic excitability, a distinctive feature of some classes of human CPNs. Molecularly, LRRC37B binds to the secreted ligand FGF13A and to the voltage-gated sodium channel (Nav) β-subunit SCN1B. LRRC37B concentrates inhibitory effects of FGF13A on Nav channel function, thereby reducing excitability, specifically at the AIS level. Electrophysiological recordings in adult human cortical slices reveal lower neuronal excitability in human CPNs expressing LRRC37B. LRRC37B thus acts as a species-specific modifier of human neuron excitability, linking human genome and cell evolution, with important implications for human brain function and diseases.

Structural and functional specializations of human fast-spiking neurons support fast cortical signaling

Fast-spiking interneurons (FSINs) provide fast inhibition that synchronizes neuronal activity and is critical for cognitive function. Fast synchronization frequencies are evolutionary conserved in the expanded human neocortex despite larger neuron-to-neuron distances that challenge fast input-output transfer functions of FSINs. Here, we test in human neurons from neurosurgery tissue, which mechanistic specializations of human FSINs explain their fast-signaling properties in human cortex. With morphological reconstructions, multipatch recordings, and biophysical modeling, we find that despite threefold longer dendritic path, human FSINs maintain fast inhibition between connected pyramidal neurons through several mechanisms: stronger synapse strength of excitatory inputs, larger dendrite diameter with reduced complexity, faster AP initiation, and faster and larger inhibitory output, while Na+ current activation/inactivation properties are similar. These adaptations underlie short input-output delays in fast inhibition of human pyramidal neurons through FSINs, explaining how cortical synchronization frequencies are conserved despite expanded and sparse network topology of human cortex.