Animal models are indispensable for linking human genetic findings to disease mechanisms. Mutations in protocadherin gamma C4 (γC4), one of the 22 isoforms encoded by the protocadherin-γ (Pcdh-γ) gene cluster, cause a human neurodevelopmental syndrome with progressive microcephaly, seizures, and intellectual disability. Here, we established a γC4 mutant mouse model that exhibits motor dysfunction, seizures, reduced brain size, and increased embryonic neuronal apoptosis. Using DOMINO (Double Mutation-Induced Open Reading Frame Switch), a two-step CRISPR/Cas9-based genome-editing strategy, we also generated γC4fl-only mice that retain full-length γC4 while truncating the other 21 Pcdh-γ isoforms. Unlike Pcdh-γ cluster-deficient mice, γC4fl-only mice were viable and fertile. Furthermore, we show that the γC4 constant region (γCR) contributes to the regulation of Purkinje cell dendritic architecture and self-avoidance. Together, these findings indicate that γCR-containing γC4 is required for neuronal survival and dendritic patterning, supporting γC4 as a principal functional isoform within the Pcdh-γ gene cluster.

E1A-like inhibitor of differentiation 1 (EID1), a nuclear coregulator, has been implicated in adipocyte differentiation and lipid metabolism. In vitro, EID1 overexpression suppresses lipid accumulation in preadipocytes; however, its role in thermogenesis in vivo remains unclear. We generated adipose tissue-specific EID1 transgenic (Tg) mice and assessed their thermogenic capacity under cold exposure. During cold exposure, male Tg mice exhibited more than a 7-fold increase in interscapular brown adipose tissue (BAT) glucose uptake, nearly triple the response observed in wild-type (Wt) mice. Core body temperature was better maintained in Tg mice, with attenuated cold-induced decline. Infrared thermography revealed a 5-fold greater increase in BAT temperature in Tg mice than in the Wt controls. These responses were accompanied by robust upregulation of thermogenesis-related genes. These findings highlight EID1 as a dynamic regulator of thermogenic capacity and suggest that modulating its stability and activity may represent a new strategy to improve metabolic health.

Epilepsy arises from disruption of excitation-inhibition (E/I) balance, typically due to excessive excitatory activity. Despite available therapies, a substantial proportion of patients remain treatment resistant. Enhancing inhibitory neuron activity via gene therapy can restore E/I balance and may therefore provide a therapeutic strategy for treatment-resistant epilepsy. Here, we developed a compact 410-bp glutamic acid decarboxylase 67 promoter (cmGAD67) that enables strong, selective transgene expression in inhibitory neurons while preserving adeno-associated virus (AAV) packaging capacity. Systemic delivery of AAV vectors carrying cmGAD67 preferentially targeted parvalbumin interneurons and enabled efficient circuit modulation. To evaluate therapeutic potential, we expressed glutamic acid decarboxylase 65 (GAD65) under the control of cmGAD67 (AAV-GAD65). AAV-GAD65 suppressed abnormal delta oscillations, reduced seizure-like activity, normalized anxiety-like behavior, and improved survival in seizure models. Biochemical analyses confirmed increased GABA levels in the cortex and hippocampus, linking functional improvements to enhanced inhibitory neurotransmitter synthesis. Together, these findings establish the cmGAD67 promoter as a versatile platform for inhibitory neuron-targeted AAV gene delivery and identify AAV-GAD65 as a promising strategy for seizure control and disorders associated with E/I imbalance.

The hippocampus is one of the most important brain regions for memory formation. Memory information is stored in cell populations called memory traces or engrams. However, how these cell populations are formed and selected from among many neurons is unclear. Here, to verify the hypothesis that cell populations are configured by the cellular adhesion molecule clustered protocadherins (Pcdhs), we investigated neuronal activity using immunostaining of the neuronal activity marker c-Fos in hippocampal–cortical regions of mice in which cells expressing Pcdhβ3 are labeled with a fluorescent protein. Reducing Pcdhβ repertoires increased the number of Pcdhβ3+ cells expressing c-Fos. The number of c-Fos+ Pcdhβ3+ cells correlated between hippocampal subregions and between the entorhinal cortex (EC) and hippocampal subregions. Artificial activation of Pcdhβ3+ neurons in the EC induced c-Fos expression in the activated neurons of the EC and Pcdhβ3+ cells of the hippocampus in a projection-dependent manner. These results indicate that cell populations expressing the same Pcdhβ isoforms form functional cell populations and functionally connect hippocampal–cortical regions. These findings suggest that a specific subset of molecules within individual cells latently defines the neuronal populations that encode memory information. Significance statement: The hippocampus is an important brain region for memory formation. Memory information is stored in cell populations called memory traces or engrams. However, the mechanisms underlying the formation of functional cell populations in the hippocampus remain unclear. Here, we show that functional cell populations are latently defined by the molecules clustered protocadherins (Pcdhs) in the hippocampal–cortical regions by observing and manipulating neuronal activity in mice whose cells expressing a specific isoform of Pcdhs are labeled with a fluorescent protein. This study suggests that latent cell populations can function as a fundamental unit for processing information.

Epilepsy often becomes treatment-resistant, partly due to impaired inhibitory neurotransmission and reduced gamma-aminobutyric acid (GABA) function. Enhancing inhibitory neuron activity via gene therapy may restore excitation-inhibition (E/I) balance. We developed a compact 410-bp glutamic acid decarboxylase 67 promoter (cmGAD67) that enables strong, selective transgene expression in inhibitory neurons while preserving AAV packaging capacity. When delivered systemically, AAV vectors carrying cmGAD67 preferentially targeted parvalbumin interneurons and supported effective circuit manipulation. To evaluate therapeutic potential, we expressed glutamic acid decarboxylase 65 (GAD65) under cmGAD67 (AAV-GAD65) in pentylenetetrazole (PTZ) epilepsy models. Systemic AAV-GAD65 suppressed abnormal delta oscillations, reduced seizure-like events, normalized anxiety-like behavior, and improved survival in a severe PTZ paradigm. Biochemical analyses confirmed increased cortical and hippocampal GABA levels, linking behavioral and electrophysiological improvements to enhanced inhibitory neurotransmitter synthesis. Prior clinical evidence indicates that AAV-GAD65 delivery to the subthalamic nucleus is safe and effective in Parkinson's disease. Building on this foundation, our findings establish the cmGAD67 promoter as a powerful platform for inhibitory neuron-targeted AAV gene therapy and highlight AAV-cmGAD67-GAD65 as a promising approach for treatment-resistant epilepsy and other disorders involving disrupted E/I balance. ### Competing Interest Statement Gunma University, with H.H., A.K., and Y.F. listed as inventors, has filed patent applications in the EU (23803614.9), China (202380040106.1), the US (18/865107), and Japan (2024-520489) for the inhibitory neuron-specific promoter described in this study. Japan Agency for Medical Research and Development, JP20dm0207057, JP21dm0207111, JP24wm0625103 Japan Society for the Promotion of Science, 20K06906, 24K10022, 22K06454, 24H01221, 23H02791 Next GIP, JPMJSP2146

The stochastic expression of clustered protocadherin (cPcdh) establishes a single-cell identity fundamental to cellular self/non-self-discrimination. However, it has been challenging to reveal the spatiotemporal patterning of the stochastic cPcdh expression in vivo. We developed XFP (tdTomato or GFP) knock-in mice using a new strategy to enhance XFP expression, which allows us to visualize cPcdhβ3 or 19-positive cells throughout the brain. These mouse lines demonstrate the cell-type selectivity, spatial biases, inter-individual differences, left-right asymmetry, developmental regulation, alteration in pathological or aging brain, and monoallelic expression of stochastic cPcdhβ expression in vivo. Our findings further demonstrate that the cPcdhβ3 expression undergoes significant changes in the mature brain over time. These results demonstrate the potential of these reporter mice to advance our understanding of cPcdh cellular barcode in vivo. ### Competing Interest Statement The authors have declared no competing interest.

Orexin neurons regulate physiological functions, including not only energy homeostasis and wakefulness but also motivated behaviors. These neurons play important roles in linking metabolic requirements to such behaviors. However, it is unknown whether these neurons are involved in reward-based choice behavior. We recently developed a transgenic rat line that expresses Cre recombinase exclusively in orexin neurons. Here, we examined the roles of orexin neurons in reward choice behavior under conditions of uncertainty in a gambling test in rats and analyzed the changes in choice behavior when orexin neurons were manipulated using chemogenetic approaches. In the gambling test, chemogenetic activation of orexin neurons resulted in risky arm choice. Positive, but not negative, reward-prediction error contributed to reward-based risky choice when orexin neurons were activated. These risky choice behaviors were canceled by suvorexant, an orexin receptor antagonist. In addition, suvorexant administered alone led to conservative choice behavior. The computational approach revealed that orexin/orexin neurons modulate the learning process and motivational value of rewards. Thus, our data suggest that orexin/orexin neurons affect the processing of reward-prediction error and alter strategy in reward-based decision-making.

Protein kinase C γ (PKCγ), a neuronal isoform present exclusively in the central nervous system, is most abundantly expressed in cerebellar Purkinje cells (PCs). Targeted deletion of PKCγ causes a climbing fiber synapse elimination in developing PCs and motor deficit. However, physiological roles of PKCγ in adult mouse PCs are little understood. In this study, we aimed to unravel the roles of PKCγ in mature mouse PCs by deleting PKCγ from adult mouse PCs of PKCγfl/fl mice via cerebellar injection of adeno-associated virus (AAV) vectors expressing Cre recombinase under the control of the PC-specific L7-6 promoter. Whole cell patch-clamp recording of PCs showed higher intrinsic excitability in PCs virally lacking PKCγ [PKCγ-conditional knockout (PKCγ-cKO) PCs] than in wild-type (WT) mouse PCs in the zebrin-negative module, but not in the zebrin-positive module. AAV-mediated PKCγ re-expression in PKCγ-deficient mouse PCs in the zebrin-negative module restored the enhanced intrinsic excitability to a level comparable to that of wild-type mouse PCs. In parallel with higher intrinsic excitability, we found larger hyperpolarization-activated cyclic nucleotide-gated (HCN) channel currents in PKCγ-cKO PCs located in the zebrin-negative module, compared with those in WT mouse PCs in the same region. However, pharmacological inhibition of the HCN currents did not restore the enhanced intrinsic excitability in PKCγ-cKO PCs in the zebrin-negative module. These results suggested that PKCγ suppresses the intrinsic excitability in zebrin-negative PCs, which is likely independent of the HCN current inhibition.

Orexin neurons regulate physiological functions, including not only energy homeostasis and wakefulness, but also motivated behaviors. These neurons play important roles in linking metabolic requirements to such behaviors. However, it is unknown whether these neurons are involved in reward choice strategy. We recently developed a transgenic rat line that expresses Cre recombinase exclusively in orexin neurons. Here, we examined the roles of orexin neurons in reward choice behavior under conditions of uncertainty in a gambling test in rats, and analyzed the changes in choice behavior when orexin neurons were manipulated using chemogenetic approaches. In the gambling test, cell-specific excitatory manipulation of orexin neurons using chemogenetics resulted in risky arm choice. Positive, but not negative, reward prediction error contributed to reward-based risky choice when orexin neurons were activated. The motivational values of a large reward were also increased when orexin neurons were activated by chemogenetics. Thus, our data suggest that activated orexin neurons affect the processing of reward prediction error and reward value, and alter strategy in reward-based decision-making.

Clustered protocadherin (Pcdh) functions as a cell recognition molecule through the homophilic interaction in the central nervous system. However, its interactions have not yet been visualized in neurons. We previously reported PcdhγB2-Förster resonance energy transfer (FRET) probes to be applicable only to cell lines. Herein, we designed γB2-FRET probes by fusing FRET donor and acceptor fluorescent proteins to a single γB2 molecule and succeeded in visualizing γB2 homophilic interaction in cultured hippocampal neurons. The γB2-FRET probe localized in the soma and neurites, and FRET signals, which were observed at contact sites between neurites, eliminated by ethylene glycol tetraacetic acid (EGTA) addition. Live imaging revealed that the FRET-negative γB2 signals rapidly moved along neurites and soma, whereas the FRET-positive signals remained in place. We observed that the γB2 proteins at synapses rarely interact homophilically. The γB2-FRET probe might allow us to elucidate the function of the homophilic interaction and the cell recognition mechanism.

AbstractFunctional neural circuits in the cerebral cortex are established through specific neural connections between excitatory and various inhibitory cell types. However, the molecular mechanisms underlying synaptic partner recognition remain unclear. In this study, we examined the impact of clustered protocadherin-γ (cPcdhγ) gene deletion in parvalbumin-positive (PV+) cells on intralaminar and translaminar neural circuits formed between PV+and pyramidal (Pyr) cells in the primary visual cortex (V1) of male and female mice. First, we used whole-cell recordings and laser-scan photostimulation with caged glutamate to map excitatory inputs from layer 2/3 to layer 6. We found thatcPcdhγ-deficient PV+cells in layer 2/3 received normal translaminar inputs from Pyr cells through layers 2/3–6. Second, to further elucidate the effect on PV+-Pyr microcircuits within intralaminar layer 2/3, we conducted multiple whole-cell recordings. While the overall connection probability of PV+-Pyr cells remained largely unchanged, the connectivity of PV+-Pyr was significantly different between control and PV+-specificcPcdhγ-conditional knock-out (PV-cKO) mice. In control mice, the number of reciprocally connected PV+cells was significantly higher than PV+cells connected one way to Pyr cells, a difference that was not significant inPV-cKOmice. Interestingly, the proportion of highly reciprocally connected PV+cells to Pyr cells with large unitary IPSC (uIPSC) amplitudes was reduced inPV-cKOmice. Conversely, the proportion of middle reciprocally connected PV+cells to Pyr cells with large uIPSC amplitudes increased compared with control mice. This study demonstrated thatcPcdhγin PV+cells modulates their reciprocity with Pyr cells in the cortex.

Neurons form dense neural circuits by connecting to each other via synapses and exchange information through synaptic receptors to sustain brain activities. Excitatory postsynapses form and mature on spines composed predominantly of actin, while inhibitory synapses are formed directly on the shafts of dendrites where both actin and microtubules (MTs) are present. Thus, it is the accumulation of specific proteins that characterizes inhibitory synapses. In this study, we explored the mechanisms that enable efficient protein accumulation at inhibitory postsynapse. We found that some inhibitory synapses function to recruit the plus end of MTs. One of the synaptic organizers, Teneurin-2 (TEN2), tends to localize to such MT-rich synapses and recruits MTs to inhibitory postsynapses via interaction with MT plus-end tracking proteins EBs. This recruitment mechanism provides a platform for the exocytosis of GABAA receptors. These regulatory mechanisms could lead to a better understanding of the pathogenesis of disorders such as schizophrenia and autism, which are caused by excitatory/inhibitory (E/I) imbalances during synaptogenesis.

Feedback projections from the secondary motor cortex (M2) to the primary motor and sensory cortices are essential for behavior selection and sensory perception. Intratelencephalic (IT) cells in layer 5 (L5) contribute feedback projections to diverse cortical areas. Here we show that L5 IT cells participating in feedback connections to layer 1 (L1) exhibit distinct projection patterns, genetic profiles, and electrophysiological properties relative to other L5 IT cells. An analysis of the MouseLight database found that L5 IT cells preferentially targeting L1 project broadly to more cortical regions, including the perirhinal and auditory cortices, and innervate a larger volume of striatum than the other L5 IT cells. We found experimentally that in upper L5 (L5a), ER81 (ETV1) was found more often in L1-preferring IT cells, and in IT cells projecting to perirhinal/auditory regions than those projecting to primary motor or somatosensory regions. The perirhinal region-projecting L5a IT cells were synaptically connected to each other and displayed lower input resistance than contra-M2 projecting IT cells including L1-preferring and nonpreferring cells. Our findings suggest that M2-L5a IT L1-preferring cells exhibit stronger ER81 expression and broader cortical/striatal projection fields than do cells that do not preferentially target L1.

The neuropeptide oxytocin (Oxt) plays important roles in modulating social behaviors. Oxt receptor (Oxtr) is abundantly expressed in the brain and its relationship to socio-behavioral controls has been extensively studied using mouse brains. Several genetic tools to visualize and/or manipulate Oxtr-expressing cells, such as fluorescent reporters and Cre recombinase drivers, have been generated by ES-cell based gene targeting or bacterial artificial chromosome (BAC) transgenesis. However, these mouse lines displayed some differences in their Oxtr expression profiles probably because of the complex context and integrity of their genomic configurations in each line. Here, we apply our sophisticated genome-editing techniques to the Oxtr locus, systematically generating a series of knock-in mouse lines, in which its endogenous transcriptional regulations are intactly preserved and evaluate their expression profiles to ensure the reliability of our new tools. We employ the epitope tagging strategy, with which C-terminally fused tags can be detected by highly specific antibodies, to successfully visualize the Oxtr protein distribution on the neural membrane with super-resolution imaging for the first time. By using T2A self-cleaving peptide sequences, we also induce proper expressions of tdTomato reporter, codon-improved Cre recombinase (iCre), and spatiotemporally inducible Cre-ERT2 in Oxtr-expressing neurons. Electrophysiological recordings from tdTomato-positive cells in the reporter mice support the validity of our tool design. Retro-orbital injections of AAV-PHP.eB vector into the Cre line further enabled visualization of recombinase activities in the appropriate brain regions. Moreover, the first-time Cre-ERT2 line drives Cre-mediated recombination in a spatiotemporally controlled manner on tamoxifen (TMX) administration. These tools thus provide an excellent resource for future functional studies in Oxt-responsive neurons and should prove of broad interest in the field.

Ketone body β-hydroxybutyrate (βOHB) and fibroblast growth factor-21 (FGF21) have been proposed to mediate systemic metabolic response to fasting. However, it remains elusive about the signaling elicited by ketone and FGF21 in the heart. Stimulation of neonatal rat cardiomyocytes with βOHB and FGF21 induced peroxisome proliferator-activated receptor α (PPARα) and PGC1α expression along with the phosphorylation of LKB1 and AMPK. βOHB and FGF21 induced transcription of peroxisome proliferator-activated receptor response element (PPRE)-containing genes through an activation of PPARα. Additionally, βOHB and FGF21 induced the expression of Nrf2, a master regulator for oxidative stress response, and catalase and Ucp2 genes. We evaluated the oxidative stress response gene expression after 24 h fast in global Fgf21-null (Fgf21−/−) mice, cardiomyocyte-specific FGF21-null (cmFgf21−/−) mice, wild-type (WT), and Fgf21fl/fl littermates. Fgf21−/− mice but not cmFgf21−/− mice had unexpectedly higher serum βOHB levels, and higher expression levels of PPARα and oxidative stress response genes than WT mice or Fgf21fl/fl littermates. Notably, expression levels of oxidative stress response genes were significantly correlated with serum βOHB and PGC1α levels in both WT and Fgf21−/− mice. These findings suggest that fasting-induced βOHB and circulating FGF21 coordinately regulate oxidative stress response gene expression in the heart.

Transgenic animals expressing fluorescent proteins are widely used to label specific cells and proteins. By using a split Cre recombinase fused with mCherry-binding nanobodies or designed ankyrin repeat proteins, we created Cre recombinase dependent on red fluorescent protein (RFP) (Cre-DOR). Functional binding units for monomeric RFPs are different from those for polymeric RFPs. We confirmed selective target RFP-dependent gene expression in the mouse cerebral cortex using stereotaxic injection of adeno-associated virus vectors. In estrogen receptor-beta (Esr2)-mRFP1 mice and gastrin-releasing peptide receptor (Grpr)-mRFP1 rats, we confirmed that Cre-DOR can be used for selective tracing of the neural projection from RFP-expressing specific neurons. Cellular localization of RFPs affects recombination efficiency of Cre-DOR, and light and chemical-induced nuclear translocation of an RFP-fused protein can modulate Cre-DOR efficiency. Our results provide a method for manipulating gene expression in specific cells expressing RFPs and expand the repertory of nanobody-based genetic tools.

plays a pivotal role in the regulation of functions such as pain and the sleep and wake cycle by modulating neural activities of the ventrolateral periaqueductal gray (vlPAG). Electrophysiological stud-ies have shown that cholinergic effects are inconsistent among recorded neurons, particularly in the depolariza-tion and hyperpolarization of the resting membrane potential (RMP). This discrepancy may be due to the neural subtype-dependent cholinergic modulation of the RMP. To examine this possibility, we performed whole-cell patch-clamp recordings from subtype-identified neurons using vesicular GABA transporter (VGAT)-Venus x Ch AT-TdTomato rats and elucidated cellular mechanisms of cholinergic effects on the RMP. The application of car-bachol hyperpolarized the RMP of cholinergic neurons in a dose-dependent manner but had much less of an effect on other neural subtypes, including GABAergic/glycinergic and glutamatergic neurons. Cholinergic hyper-polarization was accompanied by a decrease in input resistance. These cholinergic effects were blocked by AF-DX384 or gallamine and were mimicked by arecaidine but-2-ynyl ester tosylate, suggesting that the carbachol-induced hyperpolarization of the RMP in cholinergic neurons is mediated via M2 receptors. Tertiapin suppressed the carbachol-induced G protein-activated inwardly rectifying potassium channel (GIRK) currents and hyperpolar-ization of the RMP in cholinergic neurons. Intracellular application of GDP-b-S blocked the carbachol-induced hyperpolarization of the RMP. Neostigmine slowly hyperpolarized the RMP in cholinergic neurons. These results suggest that neural firing of vlPAG cholinergic neurons is suppressed by GIRK currents induced via M2 receptor activation, and this negative feedback regulation of cholinergic neuronal activities can be induced by acetyl-choline, which is intrinsically released in the vlPAG.(c) 2022 IBRO. Published by Elsevier Ltd. All rights reserved.

In mature neurons, excitatory synapses are formed on the dendritic spine, whereas inhibitory synapses are formed on the dendritic shaft. Thus, it is primarily the accumulation of synaptic proteins that characterizes inhibitory synapses as distinct from non-synaptic regions. Protein accumulation is achieved by a combination of microtubule (MT)-based transport by kinesins and lateral diffusion across the plasma membrane; however, how and when proteins are released from kinesins remains unclear. Using primary cultured hippocampal neurons, we found that Teneurin-2 (TEN2) promotes synaptic protein accumulation by recruiting MTs via the representative MT plus end-tracking protein, EB1. MTs recruitment was enhanced when the extracellular domain of TEN2 successfully chose partners, and the lateral diffusion of TEN2 was inhibited. Conversely, if TEN2 partner choice is not achieved, MTs are not recruited, and thus synaptogenesis is not followed. Our study revealed that cargo release from kinesins through TEN2-MTs interactions supports the continuity from partner choice to synaptogenesis, which is a critical step in synaptic maturation.

The nucleus accumbens (NAc) receives cortical projections principally from the insular cortex (IC) and medial prefrontal cortex (mPFC). Among NAc neurons, cholinergic interneurons (ChNs) regulate the activities of medium spiny neurons (MSNs), which make up ~ 95% of NAc neurons, by modulating their firing and synaptic properties. However, little is known about the synaptic mechanisms, including their cell-type-dependent corticoaccumbal projection properties and cholinergic effects on the NAc core. Here, we performed whole-cell patch-clamp recordings from NAc MSNs and ChNs in acute brain slice preparations obtained from rats that received an AAV5-hSyn-ChR2(H134R)-mCherry injection into the IC or mPFC. Light stimulation of IC or mPFC axons induced comparable phase-locked excitatory postsynaptic currents (EPSCs) in MSNs. On the other hand, ChNs showed consistent EPSCs evoked by light stimulation of mPFC axons, whereas light stimulation of IC axons evoked much smaller EPSCs, which often showed failure in ChNs. Light-evoked EPSCs were abolished by tetrodotoxin and were recovered by 4-aminopyridine, suggesting that corticoaccumbal projections monosynaptically induce EPSCs in MSNs and ChNs. Carbachol effectively suppressed the amplitude of EPSCs in MSNs and ChNs evoked by light stimulation of IC or mPFC axons and in ChNs evoked by stimulating mPFC axons. The carbachol-induced suppression was recovered by atropine or pirenzepine, while preapplication of gallamine, J104129, PD102807, or AF-DX384 did not block the carbachol-induced EPSC suppression. These results suggest that NAc MSNs and ChNs are differentially regulated by excitatory projections from the IC and mPFC and that these corticoaccumbal excitatory inputs are modulated by M1 receptor activation.