Dendrites Of Pyramidal Neurons Research Articles

Altered projection-specific synaptic remodeling and its modification by oxytocin in an idiopathic autism marmoset model.

Alterations in the experience-dependent and autonomous elaboration of neural circuits are assumed to underlie autism spectrum disorder (ASD), though it is unclear what synaptic traits are responsible. Here, utilizing a valproic acid-induced ASD marmoset model, which shares common molecular features with idiopathic ASD, we investigate changes in the structural dynamics of tuft dendrites of upper-layer pyramidal neurons and adjacent axons in the dorsomedial prefrontal cortex through two-photon microscopy. In model marmosets, dendritic spine turnover is upregulated, and spines are generated in clusters and survived more often than in control marmosets. Presynaptic boutons in local axons, but not in commissural long-range axons, demonstrate hyperdynamic turnover in model marmosets, suggesting alterations in projection-specific plasticity. Intriguingly, nasal oxytocin administration attenuates clustered spine emergence in model marmosets. Enhanced clustered spine generation, possibly unique to certain presynaptic partners, may be associated with ASD and be a potential therapeutic target.

Social hierarchy differentially influences the anxiety-like behaviors and dendritic spine density in prefrontal cortex and limbic areas in male rats

Social hierarchy is a fundamental feature of social organization that can influence brain and emotional processing regarding social ranks. Several areas, including the medial prefrontal cortex (mPFC), the hippocampus, and the basolateral nucleus of the amygdala (BLA), are recognized to be involved in the regulation of emotional processing. However, its delicate structural correlates in brain regions are poorly understood. To address this issue, social hierarchy in home-caged sibling Wistar rats (three male rats/cage) was determined by employing a social confrontation tube test (postnatal weeks 9-12). Then, locomotor activity and anxiety-like behaviors were evaluated using an open-field test (OFT) and elevated plus-maze (EPM) at 13 weeks of age. The rapid Golgi impregnation method was conducted to quantify the spine density of the first secondary branch of the primary dendrite in 20µm length. The results indicated that dominant rats had significantly higher anxiety-like behaviors compared to subordinates, as was evident by lower open-arm entries and time spent in the EPM and lower entries and time spent in the center of OFT. The spine density analysis revealed a significantly higher number of spines in subordinates compared to the dominant rats in dmPFC pyramidal neurons and the apical and basal dendrites of hippocampal CA1 pyramidal neurons. However, the spine density of pyramidal-like neurons in the BLA was higher in dominant rats. Our findings suggest that dominant social rank is associated with higher anxiety and differential density of the dendritic spine in the prefrontal cortex and limbic regions of the brain in male rats.

Structure, biophysics, and circuit function of a "giant" cortical presynaptic terminal.

The hippocampal mossy fiber synapse, formed between axons of dentate gyrus granule cells and dendrites of CA3 pyramidal neurons, is a key synapse in the trisynaptic circuitry of the hippocampus. Because of its comparatively large size, this synapse is accessible to direct presynaptic recording, allowing a rigorous investigation of the biophysical mechanisms of synaptic transmission and plasticity. Furthermore, because of its placement in the very center of the hippocampal memory circuit, this synapse seems to be critically involved in several higher network functions, such as learning, memory, pattern separation, and pattern completion. Recent work based on new technologies in both nanoanatomy and nanophysiology, including presynaptic patch-clamp recording, paired recording, super-resolution light microscopy, and freeze-fracture and "flash-and-freeze" electron microscopy, has provided new insights into the structure, biophysics, and network function of this intriguing synapse. This brings us one step closer to answering a fundamental question in neuroscience: how basic synaptic properties shape higher network computations.

Functional neuroanatomy of basal forebrain projections to the basolateral amygdala: Transmitters, receptors, and neuronal subpopulations.

The projections of the basal forebrain (BF) to the hippocampus and neocortex have been extensively studied and shown to be important for higher cognitive functions, including attention, learning, and memory. Much less is known about the BF projections to the basolateral nuclear complex of the amygdala (BNC), although the cholinergic innervation of this region by the BF is actually far more robust than that of cortical areas. This review will focus on light and electron microscopic tract-tracing and immunohistochemical (IHC) studies, many of which were published in the last decade, that have analyzed the relationship of BF inputs and their receptors to specific neuronal subtypes in the BNC in order to better understand the anatomical substrates of BF-BNC circuitry. The results indicate that BF inputs to the BNC mainly target the basolateral nucleus of the BNC (BL) and arise from cholinergic, GABAergic, and perhaps glutamatergic BF neurons. Cholinergic inputs mainly target dendrites and spines of pyramidal neurons (PNs) that express muscarinic receptors (MRs). MRs are also expressed by cholinergic axons, as well as cortical and thalamic axons that synapse with PN dendrites and spines. BF GABAergic axons to the BL also express MRs and mainly target BL interneurons that contain parvalbumin. It is suggested that BF-BL circuitry could be very important for generating rhythmic oscillations known to be critical for emotional learning. BF cholinergic inputs to the BNC might also contribute to memory formation by activating M1 receptors located on PN dendritic shafts and spines that also express NMDA receptors.

Conditioned morphine tolerance promotes neurogenesis, dendritic remodelling and pro-plasticity molecules in the adult rat hippocampus.

Structural neuroplasticity of the hippocampus in the form of neurogenesis and dendritic remodelling underlying morphine tolerance is still less known. Therefore, in this study, we aimed to assess whether unconditioned- and conditioned-morphine tolerance can trigger structural neuroplasticity in the dorsal and ventral parts of the adult male rat hippocampus. Evaluation of the levels of neurogenesis markers (Ki67 and DCX) by immunohistochemistry shows that conditioned morphine tolerance is sufficient to increase the baseline topographic level of hippocampal neurogenesis in adult rats. Dendritic spine visualization by Golgi staining shows that the behavioural testing paradigms themselves are sufficient to trigger the hippocampus subregion-specific changes in the dendritic remodelling along the apical dendrites of hippocampal CA1 pyramidal neurons and dentate granule cells in adult rats. Quantitative reverse transcription polymerase chain reaction of Bdnf, Trkb, Rac-1 and RhoA mRNA levels as pro-plasticity molecules, shows that the conditioned morphine tolerance is effective in changing Bdnf and RhoA mRNA levels in the ventral hippocampus of adult rats. In summary, we demonstrate that the acquisition of morphine tolerance promotes adult neurogenesis, dendritic remodelling and pro-plasticity molecules such as Bdnf/Trkb in the rat hippocampus. Indeed, the structural neuroplasticity of the hippocampus may underlie the newly formed aberrant memory and could provide the initial basis for understanding the neurobiological mechanisms of morphine-tolerance plasticity in the hippocampus.

Kinetics and functional consequences of BK channels activation by N-type Ca2+ channels in the dendrite of mouse neocortical layer-5 pyramidal neurons.

The back-propagation of an action potential (AP) from the axon/soma to the dendrites plays a central role in dendritic integration. This process involves an intricate orchestration of various ion channels, but a comprehensive understanding of the contribution of each channel type remains elusive. In this study, we leverage ultrafast membrane potential recordings (Vm) and Ca2+ imaging techniques to shed light on the involvement of N-type voltage-gated Ca2+ channels (VGCCs) in layer-5 neocortical pyramidal neurons' apical dendrites. We found a selective interaction between N-type VGCCs and large-conductance Ca2+-activated K+ channels (BK CAKCs). Remarkably, we observe that BK CAKCs are activated within a mere 500 μs after the AP peak, preceding the peak of the Ca2+ current triggered by the AP. Consequently, when N-type VGCCs are inhibited, the early broadening of the AP shape amplifies the activity of other VGCCs, leading to an augmented total Ca2+ influx. A NEURON model, constructed to replicate and support these experimental results, reveals the critical coupling between N-type and BK channels. This study not only redefines the conventional role of N-type VGCCs as primarily involved in presynaptic neurotransmitter release but also establishes their distinct and essential function as activators of BK CAKCs in neuronal dendrites. Furthermore, our results provide original functional validation of a physical interaction between Ca2+ and K+ channels, elucidated through ultrafast kinetic reconstruction. This insight enhances our understanding of the intricate mechanisms governing neuronal signaling and may have far-reaching implications in the field.

Amygdalar Excitation of Hippocampal Interneurons Can Lead to Emotion-driven Overgeneralization of Context.

Context is central to cognition: Detailed contextual representations enable flexible adjustment of behavior via comparison of the current situation with prior experience. Emotional experiences can greatly enhance contextual memory. However, sufficiently intense emotional signals can have the opposite effect, leading to weaker or less specific memories. How can emotional signals have such intensity-dependent effects? A plausible mechanistic account has emerged from recent anatomical data on the impact of the amygdala on the hippocampus in primates. In hippocampal CA3, the amygdala formed potent synapses on pyramidal neurons, calretinin (CR) interneurons, as well as parvalbumin (PV) interneurons. CR interneurons are known to disinhibit pyramidal neuron dendrites, whereas PV neurons provide strong perisomatic inhibition. This potentially counterintuitive connectivity, enabling amygdala to both enhance and inhibit CA3 activity, may provide a mechanism that can boost or suppress memory in an intensity-dependent way. To investigate this possibility, we simulated this connectivity pattern in a spiking network model. Our simulations revealed that moderate amygdala input can enrich CA3 representations of context through disinhibition via CR interneurons, but strong amygdalar input can impoverish CA3 activity through simultaneous excitation and feedforward inhibition via PV interneurons. Our model revealed an elegant circuit mechanism that mediates an affective "inverted U" phenomenonv: There is an optimal level of amygdalar input that enriches hippocampal context representations, but on either side of this zone, representations are impoverished. This circuit mechanism helps explain why excessive emotional arousal can disrupt contextual memory and lead to overgeneralization, as seen in severe anxiety and posttraumatic stress disorder.

Neurotrophin-3 from the dentate gyrus supports postsynaptic sites of mossy fiber-CA3 synapses and hippocampus-dependent cognitive functions.

At the center of the hippocampal tri-synaptic loop are synapses formed between mossy fiber (MF) terminals from granule cells in the dentate gyrus (DG) and proximal dendrites of CA3 pyramidal neurons. However, the molecular mechanism regulating the development and function of these synapses is poorly understood. In this study, we showed that neurotrophin-3 (NT3) was expressed in nearly all mature granule cells but not CA3 cells. We selectively deleted the NT3-encoding Ntf3 gene in the DG during the first two postnatal weeks to generate a Ntf3 conditional knockout (Ntf3-cKO). Ntf3-cKO mice of both sexes had normal hippocampal cytoarchitecture but displayed impairments in contextual memory, spatial reference memory, and nest building. Furthermore, male Ntf3-cKO mice exhibited anxiety-like behaviors, whereas female Ntf3-cKO showed some mild depressive symptoms. As MF-CA3 synapses are essential for encoding of contextual memory, we examined synaptic transmission at these synapses using ex vivo electrophysiological recordings. We found that Ntf3-cKO mice had impaired basal synaptic transmission due to deficits in excitatory postsynaptic currents mediated by AMPA receptors but normal presynaptic function and intrinsic excitability of CA3 pyramidal neurons. Consistent with this selective postsynaptic deficit, Ntf3-cKO mice had fewer and smaller thorny excrescences on proximal apical dendrites of CA3 neurons and lower GluR1 levels in the stratum lucidum area where MF-CA3 synapses reside but normal MF terminals, compared with control mice. Thus, our study indicates that NT3 expressed in the dentate gyrus is crucial for the postsynaptic structure and function of MF-CA3 synapses and hippocampal-dependent memory.

Serine racemase expression in the pyramidal layer of the hippocampus of rat in the hypertensive encephalopathy modeling

AbstractBackgroundExcessive influence of glutamate on NMDA receptors mediates a cascade of biochemical changes leading to the development of intracellular acidosis, accumulation of free intracellular calcium and activation of a number of enzymes with the formation of free radicals. D‐serine acts as a co‐agonist of NMDA receptors and is involved in learning and memory under normal conditions. However, it has been suggested to play a role in glutamate damage in a number of CNS diseases. The formation of D‐serine in neurons and glial cells occurs with the participation of the enzyme serine racemase (SR) from L‐serine. An increase in the content of SR and the product of its enzymatic reaction, D‐serine, is considered as a process preceding excitotoxicity.MethodHypertensive encephalopathy was modeled on 12‐month‐old rats by the method of exposure to negative longitudinal g‐forces in the caudocranial vector with a force of 9 G for 5 minutes with an interval of 12 hours for 28 days. The following indicators were assessed: behavioral responses, cognitive and mnestic functions, the relative number of neurons with signs of damage, and the level of expression of serine racemase.ResultA morphometric study of the pyramidal layer of the hippocampus revealed a significant increase in the relative area of the immunopositive material in CA1 by 5.5% compared with the control (p<0.05). A feature of the expression of serine racemase in the experimental group was the translocation of immunopositive material, which was determined not only in the cytoplasm of perikaryons, but also in the dendrites of pyramidal neurons. In addition, the nature of expression changed in the experimental group to a moderately pronounced one, and in some pyramidal neurons to a pronounced one. Violation of the cytoarchitectonic of the CA1 zone was manifested in a less compact arrangement of pyramidal neurons, a pattern of spongiosis due to pericellular and perivascular edema, and the acquisition of increased tortuosity by neuronal dendrites.ConclusionHypertensive encephalopathy modeling demonstrates a sharp increase in the relative number of neurons with signs of damage, a decrease in the specific

Longitudinal characterization of behavioral, morphological and transcriptomic changes in a tauopathy mouse model.

Neurodegenerative disorders, such as Alzheimer's disease (AD), have the gradual onset of neurobiological changes preceding clinical diagnosis by decades. To elucidate how brain dysfunction proceeds in neurodegenerative disorders, we performed longitudinal characterization of behavioral, morphological, and transcriptomic changes in a tauopathy mouse model, P301S transgenic mice. P301S mice exhibited cognitive deficits as early as 3 months old, and deficits in social preference and social cognition at 5-6 months. They had a significant decrease of arborization in basal dendrites of hippocampal pyramidal neurons from 3 months and apical dendrites of PFC pyramidal neurons at 9 months. Transcriptomic analysis of genome-wide changes revealed the enrichment of synaptic gene upregulation at 3 months of age, while most of these synaptic genes were downregulated in PFC and hippocampus of P301S mice at 9 months. These time-dependent changes in gene expression may lead to progressive alterations of neuronal structure and function, resulting in the manifestation of behavioral symptoms in tauopathies.

Layer 1 of somatosensory cortex: an important site for input to a tiny cortical compartment.

Neocortical layer 1 has been proposed to be at the center for top-down and bottom-up integration. It is a locus for interactions between long-range inputs, layer 1 interneurons, and apical tuft dendrites of pyramidal neurons. While input to layer 1 has been studied intensively, the level and effect of input to this layer has still not been completely characterized. Here we examined the input to layer 1 of mouse somatosensory cortex with retrograde tracing and optogenetics. Our assays reveal that local input to layer 1 is predominantly from layers 2/3 and 5 pyramidal neurons and interneurons, and that subtypes of local layers 5 and 6b neurons project to layer 1 with different probabilities. Long-range input from sensory-motor cortices to layer 1 of somatosensory cortex arose predominantly from layers 2/3 neurons. Our optogenetic experiments showed that intra-telencephalic layer 5 pyramidal neurons drive layer 1 interneurons but have no effect locally on layer 5 apical tuft dendrites. Dual retrograde tracing revealed that a fraction of local and long-range neurons was both presynaptic to layer 5 neurons and projected to layer 1. Our work highlights the prominent role of local inputs to layer 1 and shows the potential for complex interactions between long-range and local inputs, which are both in position to modify the output of somatosensory cortex.

Structural Organization of Perisomatic Inhibition in the Mouse Medial Prefrontal Cortex.

Perisomatic inhibition profoundly controls neural function. However, the structural organization of inhibitory circuits giving rise to the perisomatic inhibition in the higher-order cortices is not completely known. Here, we performed a comprehensive analysis of those GABAergic cells in the medial prefrontal cortex (mPFC) that provide inputs onto the somata and proximal dendrites of pyramidal neurons. Our results show that most GABAergic axonal varicosities contacting the perisomatic region of superficial (layer 2/3) and deep (layer 5) pyramidal cells express parvalbumin (PV) or cannabinoid receptor type 1 (CB1). Further, we found that the ratio of PV/CB1 GABAergic inputs is larger on the somatic membrane surface of pyramidal tract neurons in comparison with those projecting to the contralateral hemisphere. Our morphologic analysis of in vitro labeled PV+ basket cells (PVBC) and CCK/CB1+ basket cells (CCKBC) revealed differences in many features. PVBC dendrites and axons arborized preferentially within the layer where their soma was located. In contrast, the axons of CCKBCs expanded throughout layers, although their dendrites were found preferentially either in superficial or deep layers. Finally, using anterograde trans-synaptic tracing we observed that PVBCs are preferentially innervated by thalamic and basal amygdala afferents in layers 5a and 5b, respectively. Thus, our results suggest that PVBCs can control the local circuit operation in a layer-specific manner via their characteristic arborization, whereas CCKBCs rather provide cross-layer inhibition in the mPFC.SIGNIFICANCE STATEMENT Inhibitory cells in cortical circuits are crucial for the precise control of local network activity. Nevertheless, in higher-order cortical areas that are involved in cognitive functions like decision-making, working memory, and cognitive flexibility, the structural organization of inhibitory cell circuits is not completely understood. In this study we show that perisomatic inhibitory control of excitatory cells in the medial prefrontal cortex is performed by two types of basket cells endowed with different morphologic properties that provide inhibitory inputs with distinct layer specificity on cells projecting to disparate areas. Revealing this difference in innervation strategy of the two basket cell types is a key step toward understanding how they fulfill their distinct roles in cortical network operations.

Optogenetic stimulation shapes dendritic trees of infragranular cortical pyramidal cells.

Spontaneous or experimentally evoked activity can lead to changes in length and/or branching of neocortical pyramidal cell dendrites. For instance, an early postnatal overexpression of certain AMPA or kainate glutamate receptor subunits leads to larger amplitudes of depolarizing events driven by spontaneous activity, and this increases apical dendritic complexity. Whether stimulation frequency has a role is less clear. In this study, we report that the expression of channelrhodopsin2-eYFP was followed by a 5-day optogenetic stimulation from DIV 5-10 or 11-15 in organotypic cultures of rat visual cortex-evoked dendritic remodeling. Stimulation at 0.05 Hz, at a frequency range of spontaneous calcium oscillations known to occur in the early postnatal neocortex in vivo until eye opening, had no effect. Stimulation with 0.5 Hz, a frequency at which the cortex in vivo adopts after eye opening, unexpectedly caused shorter and somewhat less branched apical dendrites of infragranular pyramidal neurons. The outcome resembles the remodeling of corticothalamic and callosal projection neurons of layers VI and V, which in the adult have apical dendrites no longer terminating in layer I. Exposure to 2.5 Hz, a frequency not occurring naturally during the time windows, evoked dendritic damage. The results suggested that optogenetic stimulation at a biologically meaningful frequency for the selected developmental stage can influence dendrite growth, but contrary to expectation, the optogenetic stimulation decreased dendritic growth.

Creatine supplementation protects spatial memory and long-term potentiation against chronic restraint stress.

Stress contributes to numerous psychopathologies, including memory impairment, and threatens one's well-being. It has been reported that creatine supplementation potentially influences cognitive processing. Hence, in this study, we examined the effects of creatine supplementation on memory, synaptic plasticity, and neuronal arborization in the CA1 region of the hippocampus in rats under chronic restraint stress (CRS). Thirty-two adult male Wistar rats (8 weeks old) weighing 200-250 g were randomly divided into four groups (n = 8/per group): control, stress, creatine, and stress + creatine. CRS was induced for 6 h per day for 14 days, and creatine supplementation was carried out by dissolving creatine (2 g/kg body weight per day) in the animals' drinking water for 14 days. We used the Barnes maze and shuttle box for spatial and passive avoidance memory examination. The in-vivo field potential recording and Golgi-Cox staining were also used to investigate long-term potentiation (LTP) and dendrite arborization in the CA1 pyramidal neurons. Chronic stress impaired spatial memory, dysregulated LTP parameters, and decreased the number of dendrites in the CA1 pyramidal neurons of stressed rats, and creatine supplementation modified these effects in stressed rats. It seems that creatine supplementation can improve spatial memory deficits and synaptic plasticity loss induced by CRS in hippocampal CA1 neurons, possibly by reducing the dendrite arborization damages. However, understanding its mechanism needs further investigation.

Responses of pyramidal cell somata and apical dendrites in mouse visual cortex over multiple days

The apical dendrites of pyramidal neurons in sensory cortex receive primarily top-down signals from associative and motor regions, while cell bodies and nearby dendrites are heavily targeted by locally recurrent or bottom-up inputs from the sensory periphery. Based on these differences, a number of theories in computational neuroscience postulate a unique role for apical dendrites in learning. However, due to technical challenges in data collection, little data is available for comparing the responses of apical dendrites to cell bodies over multiple days. Here we present a dataset collected through the Allen Institute Mindscope’s OpenScope program that addresses this need. This dataset comprises high-quality two-photon calcium imaging from the apical dendrites and the cell bodies of visual cortical pyramidal neurons, acquired over multiple days in awake, behaving mice that were presented with visual stimuli. Many of the cell bodies and dendrite segments were tracked over days, enabling analyses of how their responses change over time. This dataset allows neuroscientists to explore the differences between apical and somatic processing and plasticity.

Cortico-cortical feedback engages active dendrites in visual cortex

Sensory processing in the neocortex requires both feedforward and feedback information flow between cortical areas1. In feedback processing, higher-level representations provide contextual information to lower levels, and facilitate perceptual functions such as contour integration and figure–ground segmentation2,3. However, we have limited understanding of the circuit and cellular mechanisms that mediate feedback influence. Here we use long-range all-optical connectivity mapping in mice to show that feedback influence from the lateromedial higher visual area (LM) to the primary visual cortex (V1) is spatially organized. When the source and target of feedback represent the same area of visual space, feedback is relatively suppressive. By contrast, when the source is offset from the target in visual space, feedback is relatively facilitating. Two-photon calcium imaging data show that this facilitating feedback is nonlinearly integrated in the apical tuft dendrites of V1 pyramidal neurons: retinotopically offset (surround) visual stimuli drive local dendritic calcium signals indicative of regenerative events, and two-photon optogenetic activation of LM neurons projecting to identified feedback-recipient spines in V1 can drive similar branch-specific local calcium signals. Our results show how neocortical feedback connectivity and nonlinear dendritic integration can together form a substrate to support both predictive and cooperative contextual interactions.

Control of contextual memory through interneuronal α5-GABAA receptors.

γ-Aminobutyric acid type A receptors that incorporate α5 subunits (α5-GABAARs) are highly enriched in the hippocampus and are strongly implicated in control of learning and memory. Receptors located on pyramidal neuron dendrites have long been considered responsible, but here we report that mice in which α5-GABAARs have been eliminated from pyramidal neurons (α5-pyr-KO) continue to form strong spatial engrams and that they remain as sensitive as their pseudo-wild-type (p-WT) littermates to etomidate-induced suppression of place cells and spatial engrams. By contrast, mice with selective knockout in interneurons (α5-i-KO) no longer exhibit etomidate-induced suppression of place cells. In addition, the strength of spatial engrams is lower in α5-i-KO mice than p-WT littermates under control conditions. Consistent with the established role of the hippocampus in contextual fear conditioning, α5-i-KO mice resisted etomidate's suppression of freezing to context, but so too did α5-pyr-KO mice, supporting a role for extra-hippocampal regions in the development of contextual fear memory. Overall, our results indicate that interneuronal α5-GABAARs serve a physiological role in promoting spatial learning and that they mediate suppression of hippocampus-dependent contextual memory by etomidate.

Ankyrin-B is lipid-modified by S-palmitoylation to promote dendritic membrane scaffolding of voltage-gated sodium channel NaV1.2 in neurons.

Neuronal ankyrin-B is an intracellular scaffolding protein that plays multiple roles in the axon. By contrast, relatively little is known about the function of ankyrin-B in dendrites, where ankyrin-B is also localized in mature neurons. Recently, we showed that ankyrin-B acts as a scaffold for the voltage-gated sodium channel, NaV1.2, in dendrites of neocortical pyramidal neurons. How ankyrin-B is itself targeted to the dendritic membrane is not well understood. Here, we report that ankyrin-B is lipid-modified by S-palmitoylation to promote dendritic localization of NaV1.2. We identify the palmitoyl acyl transferase zDHHC17 as a key mediator of ankyrin-B palmitoylation in heterologous cells and in neurons. Additionally, we find that zDHHC17 regulates ankyrin-B protein levels independently of its S-acylation function through a conserved binding mechanism between the ANK repeat domain of zDHHC17 and the zDHHC ankyrin-repeat binding motif of ankyrin-B. We subsequently identify five cysteines in the N-terminal ankyrin repeat domain of ankyrin-B that are necessary for ankyrin-B palmitoylation. Mutation of these five cysteines to alanines not only abolishes ankyrin-B palmitoylation, but also prevents ankyrin-B from scaffolding NaV1.2 at dendritic membranes of neurons due to ankyrin-B's inability to localize properly at dendrites. Thus, we show palmitoylation is critical for localization and function of ankyrin-B at dendrites. Strikingly, loss of ankyrin-B palmitoylation does not affect ankyrin-B-mediated axonal cargo transport of synaptic vesicle synaptotagmin-1 in neurons. This is the first demonstration of S-palmitoylation of ankyrin-B as an underlying mechanism required for ankyrin-B localization and function in scaffolding NaV1.2 at dendrites.

The L1 cell adhesion molecule constrains dendritic spine density in pyramidal neurons of the mouse cerebral cortex.

A novel function for the L1 cell adhesion molecule, which binds the actin adaptor protein Ankyrin was identified in constraining dendritic spine density on pyramidal neurons in the mouse neocortex. In an L1-null mouse mutant increased spine density was observed on apical but not basal dendrites of pyramidal neurons in diverse cortical areas (prefrontal cortex layer 2/3, motor cortex layer 5, visual cortex layer 4. The Ankyrin binding motif (FIGQY) in the L1 cytoplasmic domain was critical for spine regulation, as demonstrated by increased spine density and altered spine morphology in the prefrontal cortex of a mouse knock-in mutant (L1YH) harboring a tyrosine (Y) to histidine (H) mutation in the FIGQY motif, which disrupted L1-Ankyrin association. This mutation is a known variant in the human L1 syndrome of intellectual disability. L1 was localized by immunofluorescence staining to spine heads and dendrites of cortical pyramidal neurons. L1 coimmunoprecipitated with Ankyrin B (220 kDa isoform) from lysates of wild type but not L1YH forebrain. This study provides insight into the molecular mechanism of spine regulation and underscores the potential for this adhesion molecule to regulate cognitive and other L1-related functions that are abnormal in the L1 syndrome.

Toward the unknown: consciousness and pain.

Studies of consciousness are hindered by the complexity of the brain, but it is possible to study the consciousness of a sensation, namely pain. Three systems are necessary to experience pain: the somatosensory system conveys information about an injury to the thalamus where an awareness of the injury but not the painfulness emerges. The thalamus distributes the information to the affective system, which modulates the intensity of the pain, and to the cognitive system that imparts attention to the pain. Imaging of patients in pain and those experiencing placebo and hypnosis-induced analgesia shows that two essential cortical circuits for pain and attention are located within the anterior cingulate cortex. The circuits are activated when a high-frequency input results in the development of a long-term potentiation (LTP) at synapses on the apical dendrites of pyramidal neurons. The LTP acts via α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA) and N-methyl-D-aspartate (NMDA) receptors, and an anterior cingulate cortex-specific type-1 adenylate cyclase is necessary for both the LTP and the pain. The apical dendrites form an extensive network such that the input from serious injuries results in the emergence of a local field potential. Using mouse models, I propose experiments designed to test the hypothesis that the local field potential is necessary and sufficient for the consciousness of pain.