Involvement of posterior hypothalamic CaMKII-positive neurons in ADHD-like behaviors in mice.

This study explores the behavioral effects of modulating CaMKII-positive (CaMKII+) neurons in the posterior hypothalamus (PH). Utilizing a chemogenetic approach in mice, we discovered that the activation of CaMKII + neurons within the PH is associated with heightened locomotor activity, reduced social interaction, and impulsive behavior unrelated to anxiety or avoidance. These observed behaviors share a significant resemblance with characteristics commonly found in attention deficit and hyperactivity disorder (ADHD). Notably, treatment with clonidine, which is frequently prescribed for ADHD, effectively reduced impulsive behaviors in our mouse model. Our findings uncover the role of the PH that has not been previously explored and suggest a possible involvement of the PH in the manifestation of ADHD-like behaviors.

Histone variant H2BE enhances chromatin accessibility in neurons to promote synaptic gene expression and long-term memory.

Histone proteins affect gene expression through multiple mechanisms, including through exchange with histone variants. Recent findings link histone variants to neurological disorders, yet few are well studied in the brain. Most notably, widely expressed variants of H2B remain elusive. We applied recently developed antibodies, biochemical assays, and sequencing approaches to reveal broad expression of the H2B variant H2BE and defined its role in regulating chromatin structure, neuronal transcription, and mouse behavior. We find that H2BE is enriched at promoters, and a single unique amino acid allows it to dramatically enhance chromatin accessibility. Further, we show that H2BE is critical for synaptic gene expression and long-term memory. Together, these data reveal a mechanism linking histone variants to chromatin accessibility, transcriptional regulation, neuronal function, and memory. This work further identifies a widely expressed H2B variant and uncovers a single histone amino acid with profound effects on genomic structure.

Infralimbic activity during REM sleep facilitates fear extinction memory.

Rapid eye movement (REM) sleep is known to facilitate fear extinction and play a protective role against fearful memories.1,2 Consequently, disruption of REM sleep after a traumatic event may increase the risk for developing PTSD.3,4 However, the underlying mechanisms by which REM sleep promotes extinction of aversive memories remain largely unknown. The infralimbic cortex (IL) is a key brain structure for the consolidation of extinction memory.5 Using calcium imaging, we found in mice that most IL pyramidal neurons are intensively activated during REM sleep. Optogenetically suppressing the IL specifically during REM sleep within a 4-h window after auditory-cued fear conditioning impaired extinction memory consolidation. In contrast, REM-specific IL inhibition after extinction learning did not affect the extinction memory. Whole-cell patch-clamp recordings demonstrated that inactivating IL neurons during REM sleep depresses their excitability. Together, our findings suggest that REM sleep after fear conditioning facilitates fear extinction by enhancing IL excitability and highlight the importance of REM sleep in the aftermath of traumatic events for protecting against traumatic memories.

Histone variant H2BE enhances chromatin accessibility in neurons to promote synaptic gene expression and long-term memory.

Regulation of histone proteins affects gene expression through multiple mechanisms including exchange with histone variants. However, widely expressed variants of H2B remain elusive. Recent findings link histone variants to neurological disorders, yet few are well studied in the brain. We applied new tools including novel antibodies, biochemical assays, and sequencing approaches to reveal broad expression of the H2B variant H2BE, and defined its role in regulating chromatin structure, neuronal transcription, and mouse behavior. We find that H2BE is enriched at promoters and a single unique amino acid allows it to dramatically enhance chromatin accessibility. Lastly, we show that H2BE is critical for synaptic gene expression and long-term memory. Together, these data reveal a novel mechanism linking histone variants to chromatin regulation, neuronal function, and memory. This work further identifies the first widely expressed H2B variant and uncovers a single histone amino acid with profound effects on genomic structure.

Distributed processing for value-based choice by prelimbic circuits targeting anterior-posterior dorsal striatal subregions in male mice.

Fronto-striatal circuits have been implicated in cognitive control of behavioral output for social and appetitive rewards. The functional diversity of prefrontal cortical populations is strongly dependent on their synaptic targets, with control of motor output mediated by connectivity to dorsal striatum. Despite evidence for functional diversity along the anterior-posterior striatal axis, it is unclear how distinct fronto-striatal sub-circuits support value-based choice. Here we found segregated prefrontal populations defined by anterior/posterior dorsomedial striatal target. During a feedback-based 2-alternative choice task, single-photon imaging revealed circuit-specific representations of task-relevant information with prelimbic neurons targeting anterior DMS (PL::A-DMS) robustly modulated during choices and negative outcomes, while prelimbic neurons targeting posterior DMS (PL::P-DMS) encoded internal representations of value and positive outcomes contingent on prior choice. Consistent with this distributed coding, optogenetic inhibition of PL::A-DMS circuits strongly impacted choice monitoring and responses to negative outcomes while inhibition of PL::P-DMS impaired task engagement and strategies following positive outcomes. Together our data uncover PL populations engaged in distributed processing for value-based choice.

Presynaptic HCN channel activity is required for the expression of long-term potentiation at lateral amygdala to basal amygdala synapses.

Recently, we reported that auditory fear conditioning leads to the presynaptic potentiation at lateral amygdala to basal amygdala (LA-BA) synapses that shares the mechanism with high-frequency stimulation (HFS)-induced long-term potentiation (LTP) ex vivo. In the present study, we further examined the molecular mechanisms underlying the HFS-induced presynaptic LTP. We found that a presynaptic elevation of Ca2+ was required for the LTP induction. Interestingly, the blockade of presynaptic but not postsynaptic HCN channels with ZD7288 completely abolished LTP induction. While ZD7288 did not alter basal synaptic transmission, the blocker fully reversed previously established LTP, indicating that HCN channels are also required for the maintenance of LTP. Indeed, HCN3 and HCN4 channels were preferentially localized in the presynaptic boutons of LA afferents. Furthermore, an inhibition of either GABAB receptors or GIRK channels eliminated the inhibitory effect of HCN blockade on the LTP induction. Collectively, we suggest that activation of presynaptic HCN channels may counteract membrane hyperpolarization during tetanic stimulation, and thereby contributes to the presynaptic LTP at LA-BA synapses.

Auditory fear conditioning facilitates neurotransmitter release at lateral amygdala to basal amygdala synapses.

The lateral amygdala (LA) is a main sensory input site from the cortical and thalamic regions. In turn, LA glutamatergic pyramidal neurons strongly project to the basal amygdala (BA). Although it is well known that auditory fear conditioning involves synaptic potentiation in the LA, it is not clear whether the LA-BA synaptic transmission is modified upon auditory fear conditioning. Here we found that high-frequency stimulation ex vivo resulted in long-term potentiation (LTP) with a concomitant enhancement of neurotransmitter release at LA-BA synapses. Auditory fear conditioning also led to the presynaptic facilitation at LA-BA synapses. Meanwhile, AMPA/NMDA current ratio was not changed upon fear conditioning, excluding the involvement of postsynaptic mechanism. Notably, fear conditioning occluded electrically induced ex vivo LTP in the LA-BA pathway, indicating that the conditioning and electrically induced LTP share common mechanisms. Our findings suggest that the presynaptic potentiation of LA-BA synapses may be involved in fear conditioning.

Striatal Low-Threshold Spiking Interneurons Regulate Goal-Directed Learning.

The dorsomedial striatum (DMS) is critically involved in motor control and reward processing, but the specific neural circuit mediators are poorly understood. Recent evidence highlights the extensive connectivity of low-threshold spiking interneurons (LTSIs) within local striatal circuitry; however, the in vivo function of LTSIs remains largely unexplored. We employed fiber photometry to assess LTSI calcium activity in a range of DMS-mediated behaviors, uncovering specific reward-related activity that is down-modulated during goal-directed learning. Using two mechanistically distinct manipulations, we demonstrated that this down-modulation of LTSI activity is critical for acquisition of novel contingencies, but not for their modification. In contrast, continued LTSI activation slowed instrumental learning. Similar manipulations of fast-spiking interneurons did not reproduce these effects, implying a specific function of LTSIs. Finally, we revealed a role for the γ-aminobutyric acid (GABA)ergic functions of LTSIs in learning. Together, our data provide new insights into this striatal interneuron subclass as important gatekeepers of goal-directed learning.

Integrated anatomical and physiological mapping of striatal afferent projections.

The dorsomedial striatum, a key site of reward-sensitive motor output, receives extensive afferent input from cortex, thalamus and midbrain. These projections are integrated by striatal microcircuits containing both spiny projection neurons and local circuit interneurons. To explore target cell specificity of these projections, we compared inputs onto D1-dopamine receptor-positive spiny neurons, parvalbumin-positive fast-spiking interneurons and somatostatin-positive low-threshold-spiking interneurons, using cell type-specific rabies virus tracing and optogenetic-mediated projection neuron recruitment in mice. While the relative proportion of retrogradely labelled projection neurons was similar between target cell types, the convergence of inputs was systematically higher for projections onto fast-spiking interneurons. Rabies virus is frequently used to assess cell-specific anatomical connectivity but it is unclear how this correlates to synaptic connectivity and efficacy. To test this, we compared tracing data with target cell-specific measures of synaptic efficacy for anterior cingulate cortex and parafascicular thalamic projections using novel quantitative optogenetic measures. We found that target-specific patterns of convergence were extensively modified according to region of projection neuron origin and postsynaptic cell type. Furthermore, we observed significant divergence between cell type-specific anatomical connectivity and measures of excitatory synaptic strength, particularly for low-threshold-spiking interneurons. Taken together, this suggests a basic uniform connectivity map for striatal afferent inputs upon which presynaptic-postsynaptic interactions impose substantial diversity of physiological connectivity.

Optogenetic activation of septal GABAergic afferents entrains neuronal firing in the medial habenula.

The medial habenula (MHb) plays an important role in nicotine-related behaviors such as nicotine aversion and withdrawal. The MHb receives GABAergic input from the medial septum/diagonal band of Broca (MS/DB), yet the synaptic mechanism that regulates MHb activity is unclear. GABA (γ -aminobutyric acid) is a major inhibitory neurotransmitter activating both GABAA receptors and GABAB receptors. Depending on intracellular chloride concentration, however, GABAA receptors also function in an excitatory manner. In the absence of various synaptic inputs, we found that MHb neurons displayed spontaneous tonic firing at a rate of about ~4.4 Hz. Optogenetic stimulation of MS/DB inputs to the MHb evoked GABAA receptor-mediated synaptic currents, which produced stimulus-locked neuronal firing. Subsequent delayed yet lasting activation of GABAB receptors attenuated the intrinsic tonic firing. Consequently, septal GABAergic input alone orchestrates both excitatory GABAA and inhibitory GABAB receptors, thereby entraining the firing of MHb neurons.

Promotion of Cortical Neurogenesis from the Neural Stem Cells in the Adult Mouse Subcallosal Zone.

Neurogenesis occurs spontaneously in the subventricular zone (SVZ) of the lateral ventricle in adult rodent brain, but it has long been debated whether there is sufficient adult neurogenesis in human SVZ. Subcallosal zone (SCZ), a posterior continuum of SVZ closely associated with posterior regions of cortical white matter, has also been reported to contain adult neural stem cells (aNSCs) in both rodents and humans. However, little is known whether SCZ-derived aNSC (SCZ-aNSCs) can produce cortical neurons following brain injury. We found that SCZ-aNSCs exhibited limited neuronal differentiation potential in culture and after transplantation in mice. Neuroblasts derived from SCZ initially migrated toward injured cortex regions following brain injury, but later exhibited apoptosis. Overexpression of anti-apoptotic bcl-xL in the SCZ by retroviral infection rescued neuroblasts from cell death in the injured cortex, but neuronal maturation was still limited, resulting in atrophy. In combination with Bcl-xL, infusion of brain-derived neurotropic factor rescued atrophy, and importantly, a subset of such SCZ-aNSCs differentiated and attained morphological and physiological characteristics of mature, excitatory neurons. These results suggest that the combination of anti-apoptotic and neurotrophic factors might enable the use of aNSCs derived from the SCZ in cortical neurogenesis for neural replacement therapy.

Learning-induced synaptic potentiation in implanted neural precursor cell-derived neurons.

Neuronal loss caused by neurodegenerative diseases, traumatic brain injury and stroke results in cognitive dysfunctioning. Implantation of neural stem/precursor cells (NPCs) can improve the brain function by replacing lost neurons. Proper synaptic integration following neuronal differentiation of implanted cells is believed to be a prerequisite for the functional recovery. In the present study, we characterized the functional properties of immortalized neural progenitor HiB5 cells implanted into the rat hippocampus with chemically induced lesion. The implanted HiB5 cells migrated toward CA1 pyramidal layer and differentiated into vGluT1-positive glutamatergic neurons with morphological and electrophysiological properties of endogenous CA1 pyramidal cells. Functional synaptic integration of HiB5 cell-derived neurons was also evidenced by immunohistochemical and electrophysiological data. Lesion-caused memory deficit was significantly recovered after the implantation when assessed by inhibitory avoidance (IA) learning. Remarkably, IA learning preferentially produced long-term potentiation (LTP) at the synapses onto HiB5 cell-derived neurons, which occluded paring protocol-induced LTP ex vivo. We conclude that the implanted HiB5 cell-derived neurons actively participate in learning process through LTP formation, thereby counteracting lesion-mediated memory impairment.

Regional differences in acute corticosterone-induced dendritic remodeling in the rat brain and their behavioral consequences.

BACKGROUND: Glucocorticoid released by stressful stimuli elicits various stress responses. Acute treatment with a single dose of corticosterone (CORT; predominant glucocorticoid of rats) alone has previously been shown to trigger anxiety behavior and robust dendritic hypertrophy of neurons in the basolateral amygdala (BLA). Neurons in the medial prefrontal cortex (mPFC) are also known to be highly sensitive to stress and regulate anxiety-like behaviors. Nevertheless, we know less about acute CORT-induced structural changes of other brain regions and their behavioral outcomes. In addition, the temporal profile of acute CORT effects remains to be examined. The current study investigates time course changes of dendritic architectures in the stress vulnerable brain areas, the BLA and mPFC, and their behavioral consequences after acute treatment with a single dose of CORT. RESULTS: Acute CORT treatment produced delayed onset of dendritic remodeling in the opposite direction in the BLA and mPFC with different time courses. Acute CORT induced dendritic hypertrophy of BLA spiny neurons, which was paralleled by heightened anxiety, both peaked 12 days after the treatment. Meanwhile, CORT-induced dendritic atrophy of mPFC pyramidal neurons peaked on day 6, concomitantly with impaired working memory. Both changed dendritic morphologies and altered behavioral outcomes were fully recovered. CONCLUSION: Our results suggest that stress-induced heightened anxiety appears to be a functional consequence of dendritic remodeling of BLA neurons but not that of mPFC. Instead, stress-induced dendritic atrophy of mPFC neurons is relevant to working memory deficit. Therefore, structural changes in the BLA and the mPFC might be specifically associated with distinct behavioral symptoms observed in stress-related mental disorders. Remarkably, stress-induced dendritic remodeling in the BLA as well as mPFC is readily reversible. The related behavioral outcomes also follow the similar time course in a reversible manner. Therefore, further studies on the cellular mechanism for the plasticity of dendrites architecture might provide new insight into the etiological factors for stress-related mental illness such as posttraumatic stress disorder (PTSD).

HCN channel activity-dependent modulation of inhibitory synaptic transmission in the rat basolateral amygdala.

Hyperpolarization-activated cyclic nucleotide-gated (HCN) channels are expressed in the central nervous system and play a regulatory role in neuronal excitability. In the present study, we examined a physiological role of HCN channels in the rat basolateral amygdala (BLA). In vitro electrophysiological studies showed that ZD7288 decreased spontaneous inhibitory postsynaptic current (sIPSC) without changing miniature IPSC (mIPSC). HCN channel blockade also attenuated feedback inhibitions in BLA principal neurons. However, blockade of HCN channel had little effects on spontaneous excitatory postsynaptic current (sEPSC) and mEPSC. Therefore, HCN channel appeared to decrease BLA excitability by increasing the action potential-dependent inhibitory control over the BLA principal neurons. Anxiety is reported to be influenced by neuronal excitability in the BLA and inhibitory synaptic transmission is thought to play a pivotal role in regulating overall excitability of the amygdala. As expected, blockade of HCN channels by targeted injection of ZD7288 to the BLA increased anxiety-like behavior under elevated plus maze test. Our results suggest that HCN channel activity can modulate the GABAergic synaptic transmission in the BLA, which in turn control the amygdala-related emotional behaviors such as anxiety.

Neuroprotective effects of roasted licorice, not raw form, on neuronal injury in gerbil hippocampus after transient forebrain ischemia.

AIM: To observe neuroprotective effects of raw and roasted licorice against hypoxia and ischemic damage. METHODS: When elucidating the protective effects of raw and roasted licorice, we analyzed the lactate dehydrogenase (LDH) release using PC12 cells after hypoxia in an in vitro study and after transient forebrain ischemia in an in vivo study on Mongolian gerbils. RESULTS: Raw and roasted licorice significantly reduced LDH release from PC12 cells exposed to an hypoxic chamber for 1 h. In the roasted licorice-treated group, the decrease of LDH release was more pronounced compared to that of the raw licorice-treated group. In roasted licorice-treated animals, approximately 66%-71% of CA1 pyramidal cells in the ischemic hippocampus were stained with cresyl violet compared to the control group. However, in the raw licorice-treated animals, no significant neuroprotection against ischemic damage was shown. In addition, ischemic animals in roasted licorice-treated group maintained the Cu, Zn-superoxide dismutase (SOD1) activity and protein levels compared to the control group, while in raw licorice-treated group SOD1 activity and protein levels were reduced significantly. High pressure liquid chromatography analysis showed that non-polar compounds containing glycyrrhizin-degraded products, such as glycyrrhetinic acid (GA) and glycyrrhetinic acid monoglucuronide (GM), were increased in roasted licorice. CONCLUSION: Roasted licorice had neuroprotective effects against ischemic damage by maintaining the SOD1 levels. In addition, the difference in protective ability between raw and roasted licorice may be associated with non-polar compounds, such as GA and GM.