5-HT Neurons Integrate GABA and Dopamine Inputs to Regulate Meal Initiation

Obesity is a growing global health epidemic with limited effective therapeutics. Serotonin (5-HT) is one major neurotransmitter which remains an excellent target for new weight-loss therapies, but there remains a gap in knowledge on the mechanisms involved in 5-HT produced in the dorsal Raphe nucleus (DRN) and its involvement in meal initiation. Using a closed-loop optogenetic feeding paradigm, we showed that the 5-HT DRN ◊arcuate nucleus (ARH) circuit plays an important role in regulating meal initiation. Incorporating electrophysiology and ChannelRhodopsin-2-Assisted Circuit Mapping, we demonstrated that 5-HT DRN neurons receive inhibitory input partially from GABAergic neurons in the DRN, and the 5-HT response to GABAergic inputs can be enhanced by hunger. Additionally, deletion of the GABA A receptor subunit in 5-HT neurons inhibits meal initiation with no effect on the satiation process. Finally, we identified the instrumental role of dopaminergic inputs via dopamine receptor D2 in 5-HT DRN neurons in enhancing the response to GABA-induced feeding. Thus, our results indicate that 5-HT DRN neurons are inhibited by synergistic inhibitory actions of GABA and dopamine, which allows for the initiation of a meal.

Anoctamin 4 channel currents activate glucose-inhibited neurons in the mouse ventromedial hypothalamus during hypoglycemia

Glucose is the basic fuel essential for maintenance of viability and functionality of all cells. However, some neurons - namely, glucose-inhibited (GI) neurons - paradoxically increase their firing activity in low-glucose conditions and decrease that activity in high-glucose conditions. The ionic mechanisms mediating electric responses of GI neurons to glucose fluctuations remain unclear. Here, we showed that currents mediated by the anoctamin 4 (Ano4) channel are only detected in GI neurons in the ventromedial hypothalamic nucleus (VMH) and are functionally required for their activation in response to low glucose. Genetic disruption of the Ano4 gene in VMH neurons reduced blood glucose and impaired counterregulatory responses during hypoglycemia in mice. Activation of VMHAno4 neurons increased food intake and blood glucose, while chronic inhibition of VMHAno4 neurons ameliorated hyperglycemia in a type 1 diabetic mouse model. Finally, we showed that VMHAno4 neurons represent a unique orexigenic VMH population and transmit a positive valence, while stimulation of neurons that do not express Ano4 in the VMH (VMHnon-Ano4) suppress feeding and transmit a negative valence. Together, our results indicate that the Ano4 channel and VMHAno4 neurons are potential therapeutic targets for human diseases with abnormal feeding behavior or glucose imbalance.

SK3 in POMC neurons plays a sexually dimorphic role in energy and glucose homeostasis

BACKGROUND

Pro-opiomelanocortin (POMC) neurons play a sexually dimorphic role in body weight and glucose balance. However, the mechanisms for the sex differences in POMC neuron functions are not fully understood.

RESULTS

We detected small conductance calcium-activated potassium (SK) current in POMC neurons. Secondary analysis of published single-cell RNA-Seq data showed that POMC neurons abundantly express SK3, one SK channel subunit. To test whether SK3 in POMC neurons regulates POMC neuron functions on energy and glucose homeostasis, we used a Cre-loxP strategy to delete SK3 specifically from mature POMC neurons. POMC-specific deletion of SK3 did not affect body weight in either male or female mice. Interestingly, male mutant mice showed not only decreased food intake but also decreased physical activity, resulting in unchanged body weight. Further, POMC-specific SK3 deficiency impaired glucose balance specifically in female mice but not in male mice. Finally, no sex differences were detected in the expression of SK3 and SK current in total POMC neurons. However, we found higher SK current but lower SK3 positive neuron population in male POMC neurons co-expressing estrogen receptor α (ERα) compared to that in females.

CONCLUSION

These results revealed a sexually dimorphic role of SK3 in POMC neurons in both energy and glucose homeostasis independent of body weight control, which was associated with the sex difference of SK current in a subpopulation of POMC + ERα + neurons.

Gabra5 plays a sexually dimorphic role in POMC neuron activity and glucose balance

Pro-opiomelanocortin (POMC) neurons are important for the regulation of body weight and glucose balance. The inhibitory tone to POMC neurons is mediated primarily by the GABA receptors. However, the detailed mechanisms and functions of GABA receptors are not well understood. The α5 subunit of GABAA receptor, Gabra5, is reported to regulate feeding, and we found that Gabra5 is highly expressed in POMC neurons. To explore the function of Gabra5 in POMC neurons, we knocked down Gabra5 specifically from mature hypothalamic POMC neurons using the clustered regularly interspaced short palindromic repeats (CRISPR)-Cas9 strategy. This POMC-specific knock-down of Gabra5 did not affect body weight or food intake in either male or female mice. Interestingly, the loss of Gabra5 caused significant increases in the firing frequency and resting membrane potential, and a decrease in the amplitude of the miniature inhibitory postsynaptic current (mIPSC) in male POMC neurons. However, the loss of Gabra5 only modestly decreased the frequency of mIPSC in female POMC neurons. Consistently, POMC-specific knock-down of Gabra5 significantly improved glucose tolerance in male mice but not in female mice. These results revealed a sexually dimorphic role of Gabra5 in POMC neuron activity and glucose balance, independent of body weight control.

Temporal and spatially controlled APP transgene expression using Cre-dependent alleles

Although a large number of mouse models have been made to study Alzheimer's disease, only a handful allow experimental control over the location or timing of the protein being used to drive pathology. Other fields have used the Cre and the tamoxifen-inducible CreER driver lines to achieve precise spatial and temporal control over gene deletion and transgene expression, yet these tools have not been widely used in studies of neurodegeneration. Here, we describe two strategies for harnessing the wide range of Cre and CreER driver lines to control expression of disease-associated amyloid precursor protein (APP) in modeling Alzheimer's amyloid pathology. We show that CreER-based spatial and temporal control over APP expression can be achieved with existing lines by combining a Cre driver with a tetracycline-transactivator (tTA)-dependent APP responder using a Cre-to-tTA converter line. We then describe a new mouse line that places APP expression under direct control of Cre recombinase using an intervening lox-stop-lox cassette. Mating this allele with a CreER driver allows both spatial and temporal control over APP expression, and with it, amyloid onset. This article has an associated First Person interview with the first author of the paper.

Free-floating Immunostaining of Mouse Brains

Immunohistochemical staining of mouse brains is a routine technique commonly used in neuroscience to investigate central mechanisms underlying the regulation of energy metabolism and other neurobiological processes. However, the quality, reliability, and reproducibility of brain histology results may vary among laboratories. For each staining experiment, it is necessary to optimize the key procedures based on differences in species, tissues, targeted proteins, and the working conditions of the reagents. This paper demonstrates a reliable workflow in detail, including intra-aortic perfusion, brain sectioning, free-floating immunostaining, tissue mounting, and imaging, which can be followed easily by researchers in this field. Also discussed are how to modify these procedures to satisfy the individual needs of researchers. To illustrate the reliability and efficiency of this protocol, perineuronal nets were stained with biotin-labeled Wisteria florbunda agglutinin (WFA) and arginine vasopressin (AVP) with an anti-AVP antibody in the mouse brain. Finally, the critical details for the entire procedure have been addressed, and the advantages of this protocol compared to those of other protocols. Taken together, this paper presents an optimized protocol for free-floating immunostaining of mouse brain tissue. Following this protocol makes this process easier for both junior and senior scientists to improve the quality, reliability, and reproducibility of immunostaining studies.

Early-Derived Murine Macrophages Temporarily Renounce Tissue Identity during Acute Systemic Inflammation

In mice, a subset of cardiac macrophages and Kupffer cells derive from fetal precursors, seed the developing tissues, self-renew locally, and persist into adulthood. In this study we investigated how these cells survive acute systemic inflammation. In both tissues, early-derived subsets rapidly responded to acute systemic inflammation by assuming a temporary nonclassical activation state featuring upregulation of both proinflammatory (Il1b, Tnf, Nfkb1), and anti-inflammatory (Il10, Il4ra, Nfkbiz) genes. During this process, transcription factor genes associated with myeloid identity (Spi1, Zeb2) were upregulated, whereas those associated with tissue specificity (Nr1h3 for Kupffer cells and Nfatc2 and Irf4 for cardiac macrophages) were downregulated, suggesting that the cells reasserted their myeloid identity but renounced their tissue identity. Most of these changes in gene expression reverted to steady-state levels postresolution. We conclude that these early-derived macrophage subsets are resilient in the face of acute stress by temporary loss of adaptation to local tissue-specific niches while reasserting their generic myeloid identity.

RiboTag: Ribosomal Tagging Strategy to Analyze Cell-Type-Specific mRNA Expression In Vivo

Ribosome tagging has become a very useful in vivo approach for analyzing gene expression and mRNA translation in specific cell types that are difficult and time consuming to isolate by conventional methods. The approach is based on selectively expressing a hemagglutinin A (HA)-tagged ribosomal protein in a target cell type and then using antibodies against HA to purify the polysomes and associated mRNAs from the target cell. The original approach makes use of a mouse line (RiboTag) harboring a modified allele of Rpl22 (Rpl22-HA) that is induced by the action of Cre recombinase. The Rpl22-HA gene can also be introduced into the animal by stereotaxic injection of an AAV-DIO-Rpl22-HA that is then activated in Cre-expressing cells. Both methods for tagging ribosomes facilitate the immunoprecipitation of ribosome-bound mRNAs and their analysis by qRT-PCR or RNA-Seq. This protocol will discuss the technical procedures and describe important considerations relevant to the analysis of the data. © 2019 by John Wiley & Sons, Inc.

Lrp4 in astrocytes modulates glutamatergic transmission

Neurotransmission requires precise control of neurotransmitter release from axon terminals. This process is regulated by glial cells; however, underlying mechanisms are not fully understood. Here we report that glutamate release in the brain is impaired in mice lacking low density lipoprotein receptor-related protein 4 (Lrp4), a protein critical for neuromuscular junction formation. Electrophysiological studies indicate compromised release probability in astrocyte-specific Lrp4 knockout mice. Lrp4 mutant astrocytes suppress glutamate transmission by enhancing the release of ATP, whose levels are elevated in the hippocampus of Lrp4 mutant mice. Consequently, the mutant mice are impaired in locomotor activity and spatial memory and are resistant to seizure induction. These impairments could be ameliorated by adenosine A1 receptor antagonist. The results reveal a critical role of Lrp4, in response to agrin, in modulating astrocytic ATP release and synaptic transmission. Our study provides insight into the interaction between neurons and astrocytes for synaptic homeostasis and/or plasticity.

ERBB3-mediated regulation of Bergmann glia proliferation in cerebellar lamination

Cortical lamination is crucial for the assembly of cerebellar circuitry. In this process, granule neurons (GNs) migrate along Bergmann glia (BG), which are specialized astroglial cells, from the external granule layer to the internal granule layer. However, the molecular mechanisms underlying BG development are not well understood. Here, we show that GFAP::Cre;Erbb3(F/F) mice, which lack Erbb3 in both radial glia and neurons, exhibit impairments in balance and motor coordination. Cerebellar lamination is aberrant, with misplaced Purkinje neurons and GN clusters. These phenotypes were not observed in Math1::CreER(T2);Erbb3(F/F) mice, where the Erbb3 gene was deleted in GNs, suggesting involvement of non-neuronal Erbb3 in cerebellar lamination. Mechanistic studies indicate that ERBB3 is crucial for the proliferation of BG, which are required for GN migration. These observations identify a crucial role for ERBB3 in cerebellar lamination and reveal a novel mechanism that regulates BG development.

Reversal of behavioral deficits and synaptic dysfunction in mice overexpressing neuregulin 1

Neuregulin 1 (Nrg1) is a susceptibility gene of schizophrenia, a disabling mental illness that affects 1% of the general population. Here, we show that ctoNrg1 mice, which mimic high levels of NRG1 observed in forebrain regions of schizophrenic patients, exhibit behavioral deficits and hypofunction of glutamatergic and GABAergic pathways. Intriguingly, these deficits were diminished when NRG1 expression returned to normal in adult mice, suggesting that damage which occurred during development is recoverable. Conversely, increase of NRG1 in adulthood was sufficient to cause glutamatergic impairment and behavioral deficits. We found that the glutamatergic impairment by NRG1 overexpression required LIM domain kinase 1 (LIMK1), which was activated in mutant mice, identifying a pathological mechanism. These observations demonstrate that synaptic dysfunction and behavioral deficits in ctoNrg1 mice require continuous NRG1 abnormality in adulthood, suggesting that relevant schizophrenia may benefit from therapeutic intervention to restore NRG1 signaling.

Strained-layer epitaxy of germanium-silicon alloys

Despite the dominant position of silicon in semiconductor electronics, its use is ultimately limited by its incompatibility with other semiconducting materials. Strained-layer epitaxy overcomes problems of crystallographic compatibility and produces high-quality heterostructures of germanium-silicon layers on silicon. This opens the door to a range of electronic and photonic devices that are based on bandstructure physics.

Mitochondrial BNIP3 upregulation precedes endonuclease G translocation in hippocampal neuronal death following oxygen-glucose deprivation

Background

Caspase-independent apoptotic pathways are suggested as a mechanism for the delayed neuronal death following ischemic insult. However, the underlying signalling mechanisms are largely unknown. Recent studies imply the involvement of several mitochondrial proteins, including endonuclease G (EndoG) and Bcl-2/adenovirus E1B 19 kDa-interacting protein (BNIP3), in the pathway of non-neuronal cells.

Results

In this report, using western blot analysis and immunocytochemistry, we found that EndoG upregulates and translocates from mitochondria to nucleus in a time-dependent manner in cultured hippocampal neurons following oxygen-glucose deprivation (OGD). Moreover, the translocation of EndoG occurs hours before the observable nuclear pyknosis. Importantly, the mitochondrial upregulation of BNIP3 precedes the translocation of EndoG. Forced expression of BNIP3 increases the nuclear translocation of EndoG and neuronal death while knockdown of BNIP3 decreases the OGD-induced nuclear translocation of EndoG and neuronal death.

Conclusion

These results suggest that BNIP3 and EndoG play important roles in hippocampal neuronal apoptosis following ischemia, and mitochondrial BNIP3 is a signal protein upstream of EndoG that can induce neuronal death.

In Situ Studies of the Interaction of Dislocations with Point Defects during Annealing of Ion Implanted Si/SiGe/Si (001) Heterostructures

: Strained layer heterostructures provide ideal systems with which to study the dynamics of dislocation motion via in situ transmission electron microscopy, as the geometry, strain state, and kinetics can be characterized and directly controlled. We discuss how these structures are used to study dislocation-point defect interactions, emphasizing the experimental requirements necessary for quantification of dislocation motion. Following ion implantation, different concentrations and types of point defects are introduced within the SiGe epilayer depending on the implantation species, energy, and current density. By annealing samples in situ in the transmission electron microscope (TEM) following implantation, we can directly observe dislocation motion and quantify the effect of dislocation-point defect interactions on dislocation velocities. We find that dislocation motion is impeded if the implantation dose peak lies within the epilayer, as dislocations pin at point defect atmospheres. Shallow BF2 implantation into the sample capping layer results in more complicated behavior. For low current density implants, dislocation velocities may be dramatically increased; at higher current densities the magnitude of this increase is significantly smaller. Implantation of different ions separately implicates fluorine as the species responsible for the observed increases in dislocation velocities, presumably due to an electrical effect on the rate of dislocation kink nucleation.

Vectorially oriented monolayers of the cytochrome c/cytochrome oxidase bimolecular complex

Vectorially oriented monolayers of yeast cytochrome c and its bimolecular complex with bovine heart cytochrome c oxidase have been formed by self-assembly from solution. Both quartz and Ge/Si multilayer substrates were chemical vapor deposited with an amine-terminated alkylsiloxane monolayer that was then reacted with a hetero-bifunctional cross-linking reagent, and the resulting maleimide endgroup surface then provided for covalent interactions with the naturally occurring single surface cysteine 102 of the yeast cytochrome c. The bimolecular complex was formed by further incubating these cytochrome c monolayers in detergent-solubilized cytochrome oxidase. The sequential formation of such monolayers and the vectorially oriented nature of the cytochrome oxidase was studied via meridional x-ray diffraction, which directly provided electron density profiles of the protein(s) along the axis normal to the substrate plane. The nature of these profiles is consistent with previous work performed on vectorially oriented monolayers of either cytochrome c or cytochrome oxidase alone. Furthermore, optical spectroscopy has indicated that the rate of binding of cytochrome oxidase to the cytochrome c monolayer is an order of magnitude faster than the binding of cytochrome oxidase to an amine-terminated surface that was meant to mimic the ring of lysine residues around the heme edge of cytochrome c, which are known to be involved in the binding of this protein to cytochrome oxidase.

Vectorially oriented monolayers of detergent-solubilized Ca(2+) -ATPase from sarcoplasmic reticulum

A method for tethering proteins to solid surfaces has been utilized to form vectorially oriented monolayers of the detergent-solubilized integral membrane protein Ca(2+) -ATPase from the sarcoplasmic reticulum (SR). Bifunctional, organic self-assembled monolayers (SAMs) possessing "headgroup" binding specificity for the substrate and "endgroup" binding specificity for the enzyme were utilized to tether the enzyme to the substrate. Specifically, an amine-terminated 11-siloxyundecaneamine SAM was found to bind the Ca(2+)-ATPase primarily electrostatically. The Ca(2+)-ATPase was labeled with the fluorescent probe 5-(2-[(iodoacetyl)amino]ethyl)aminonaphthalene-1-sulfonic acid before monolayer formation. Consequently, fluorescence measurements performed on amine-terminated SAM/enzyme monolayers formed on quartz substrates served to establish the nature of protein binding. Formation of the monolayers on inorganic multilayer substrates fabricated by molecular beam epitaxy made it possible to use x-ray interferometry to determine the profile structure for the system, which was proved correct by x-ray holography. The profile structures established the vectorial orientation of the Ca(2+)-ATPase within these monolayers, to a spatial resolution of approximately 12 A. Such vectorially oriented monolayers of detergent-solubilized Ca(2+)-ATPase from SR make possible a wide variety of correlative structure/function studies, which would serve to elucidate the mechanism of Ca(2+) transport by this enzyme.

Theory of reflectivity of an asymmetric mirror

By using the concept of transfer matrices and Bloch waves, we have derived a set of equations that provide insight into the operation of asymmetric Bragg reflectors that have been demonstrated to be useful in achieving high reflectivities in strained-material systems. These equations will be useful in the design of asymmetric mirrors and can be used to compare the trade-offs between the conventional, symmetric (quarter-wavelength), and asymmetric mirrors.

Evaluating the effect of co-contraction in optimization models

The effect of co-contraction of antagonist muscles on spinal compression force is estimated using Karush-Kuhn-Tucker (K-K-T) multipliers. Co-contraction is modelled as an incremental increase in the lower bounds on the allowable muscle forces in an optimization model formation. The K-K-T multipliers associated with each lower bound provide an estimate of the partial derivate of the optimal objective function value with respect to a change in the lower bound. A model whose objective function is spinal compression force is analyzed to estimate the effect of co-contraction on spinal compression force. While the effect depends on the specific muscle and task under consideration, the marginal effect of co-contraction on spinal compression force can be as high as 5.52 N additional spinal compression force for every additional N of muscle force. Paradoxically, the co-contraction may slightly decrease predicted spinal compression in special circumstances.

Vectorially oriented membrane protein monolayers: profile structures via x-ray interferometry/holography

X-ray interferometry/holography was applied to meridional x-ray diffraction data to determine uniquely the profile structures of a single monolayer of an integral membrane protein and a peripheral membrane protein, each tethered to the surface of a solid inorganic substrate. Bifunctional, organic self-assembled monolayers (SAMs) were utilized to tether the proteins to the surface of Ge/Si multilayer substrates, fabricated by molecular beam epitaxy, to facilitate the interferometric/holographic x-ray structure determination. The peripheral membrane protein yeast cytochrome c was covalently tethered to the surface of a sulfhydryl-terminated 11-siloxyundecanethiol SAM via a disulfide linkage with residue 102. The detergent-solubilized, photosynthetic reaction center integral membrane protein was electrostatically tethered to the surface of an analogous amine-terminated SAM. Optical absorption measurements performed on these two tethered protein monolayer systems were consistent with the x-ray diffraction results indicating the reversible formation of densely packed single monolayers of each fully functional membrane protein on the surface of the respective SAM. The importance of utilizing the organic self-assembled monolayers (as opposed to Langmuir-Blodgett) lies in their ability to tether specifically both soluble peripheral membrane proteins and detergent-solubilized integral membrane proteins. The vectorial orientations of the cytochrome c and the reaction center molecules were readily distinguishable in the profile structure of each monolayer at a spatial resolution of 7 A.

Biomechanical model calculation of muscle contraction forces: a double linear programming method

This paper presents a novel scheme for the use of linear programming to calculate muscle contraction forces in models describing musculoskeletal system biomechanics. Models of this kind are frequently found in the biomechanics literature. In most cases they involve muscle contraction force calculations that are statically indeterminate, and hence use optimization techniques to make those calculations. We present a linear programming optimization technique that solves a two-objective problem with two sequential linear programs. We use the technique here to minimize muscle intensity and joint compression force, since those are commonly used objectives. The two linear program model has the advantages of low computation cost, ready implementation on a micro-computer, and stable solutions. We show how to solve the model analytically in simple cases. We also discuss the use of the dual problem of linear programming to gain understanding of the solution it provides.