The Role of Noradrenaline in Energy Homeostasis

Obesity is a condition that is associated with excessive weight gain and fat mass storage whose prevalence is increasing within western populations. A variety of co-morbidities are linked to obesity such as type 2 diabetes mellitus, cardiovascular diseases and neurodegenerative disorders, including Alzheimer’s disease and Parkinson’s disease. Together, this contributes to substantial costs of healthcare programs. In non-obese indi- viduals, energy intake and energy expenditure is precisely matched over a long time period in order to maintain energy resources and fat mass. This mechanism, termed energy homeostasis is accomplished by regulatory neuronal networks in the central nervous system (CNS). To better understand and counteract obesity and its co-morbidities, increasing efforts are being made to define the control mechanisms in the CNS, that regulate body weight and energy homeostasis. The focus of this study is the noradrenergic (noradrenaline; NA) modulation of energy homeostasis. Anti-obesity drugs, for example amphetamines, can exert strong anorexigenic effects on eating behaviour in humans. However, these drugs generally affect multiple transmitter and neuromodulator pathways, such as the dopaminergic and serotonergic system, leading to undesired side effects. Pharmacological studies indicate that the anorexigenic effect of amphetamine and related drugs are caused in part by modulation of the NA system. In order to devise strategies and develop specific drugs with minimized side effects in support of weight loss programs, it is critical to understand in detail the mechanisms in the CNS by which NA contributes to energy homeostasis. Besides the well established role of the paraventricular nucleus of the hypothalamus in NA-mediated modulation of food intake, studies indicate that NA input on the homeostatic system in the arcuate nucleus of the hypothalamus (ARC) might also modulate eating behaviour. In the ARC, two key neuronal populations, pro-opiomelanocortin (POMC) and agouti-related peptide (AgRP) expressing neurons sense and integrate peripheral and nutritional signals. Once activated, POMC neurons promote satiety and xi activation of AgRP neurons leads to food intake and decreased energy expenditure. Mechanisms that mediate the possible NA action in the ARC are unknown. In this study, the effect of NA on POMC and AgRP expressing neurons has been investigated. Application of NA inhibits POMC neurons, while AgRP neurons are excited. Pharmacological experiments revealed that these effects are mediated by α2A- and α1A-adrenergic receptors (AR). This suggests a potent NA modulation of food intake. With respect to these effects, afferent projections from NA nuclei and the conditions under which NA is released into the ARC are of greatest interest. As a potential NA source, the locus coeruleus (LC) in the brainstem contains 50% of the NA neurons in CNS. Efferent projections from the LC to the ARC have been identified. Besides the contribution to autonomic functions in general, studies indicate that the LC is also involved in glucose metabolism and the control of brown adipose tissue (BAT). Moreover, BAT thermogenesis is dependent on NA and plasma glucose. Therefore, the effects of changes in extracellular glucose concentrations have been inves- tigated. Around 40% of neurons in the LC responded with increasing spike frequency due to elevated glucose levels, identifying these neurons as glucose-excited. A small subpopulation responded with a moderate inhibition and is considered as glucose- inhibited. Expression of a mutant variant of the ATP dependent potassium channel in mice silenced a large number of LC neurons and abolished responses to glucose. Moreover, sympathetic nerve activity was reduced and led to a white-adipose-tissue-like morphology of BAT, alongside with impairment of thermogenesis. As a consequence of decreased energy expenditure, these mice developed obesity. The modulation of POMC and AgRP neurons by NA indicates a critical role of the catecholamine in the control of energy homeostasis. Moreover, this study reveals that the LC contains glucose-sensing neurons and contributes to the control of glucose metabolism and the activity of BAT. Its projection patterns in the CNS identify the LC as a potential source for NA release into the ARC. These results lead to new insights and the expansion of the current role of NA in the control of energy homeostasis. Importantly, this may help to develop new strategies and drugs with minimized side effects in the treatment of obesity

Long-Term Pioglitazone Treatment Has No Significant Impact on Microglial Activation and Tau Pathology in P301S Mice

Neuroinflammation is one disease hallmark on the road to neurodegeneration in primary tauopathies. Thus, immunomodulation might be a suitable treatment strategy to delay or even prevent the occurrence of symptoms and thus relieve the burden for patients and caregivers. In recent years, the peroxisome proliferator-activated receptor & gamma;(PPAR & gamma;) has received increasing attention as it is immediately involved in the regulation of the immune system and can be targeted by the anti-diabetic drug pioglitazone. Previous studies have shown significant immunomodulation in amyloid-& beta;(A & beta;) mouse models by pioglitazone. In this study, we performed long-term treatment over six months in P301S mice as a tauopathy model with either pioglitazone or placebo. We performed serial 18 kDa translocator protein positron-emission-tomography (TSPO-PET) imaging and terminal immunohistochemistry to assess microglial activation during treatment. Tau pathology was quantified via immunohistochemistry at the end of the study. Long-term pioglitazone treatment had no significant effect on TSPO-PET, immunohistochemistry read-outs of microglial activation, or tau pathology levels in P301S mice. Thus, we conclude that pioglitazone modifies the time course of A & beta;-dependent microglial activation, but does not significantly modulate microglial activation in response to tau pathology

[18F]F-DED PET imaging of reactive astrogliosis in neurodegenerative diseases: preclinical proof of concept and first-in-human data

ObjectivesReactive gliosis is a common pathological hallmark of CNS pathology resulting from neurodegeneration and neuroinflammation. In this study we investigate the capability of a novel monoamine oxidase B (MAO-B) PET ligand to monitor reactive astrogliosis in a transgenic mouse model of Alzheimer`s disease (AD). Furthermore, we performed a pilot study in patients with a range of neurodegenerative and neuroinflammatory conditions.MethodsA cross-sectional cohort of 24 transgenic (PS2APP) and 25 wild-type mice (age range: 4.3-21.0 months) underwent 60 min dynamic [F-18]fluorodeprenyl-D2 ([F-18]F-DED), static 18 kDa translocator protein (TSPO, [F-18]GE-180) and beta-amyloid ([F-18]florbetaben) PET imaging. Quantification was performed via image derived input function (IDIF, cardiac input), simplified non-invasive reference tissue modelling (SRTM2, DVR) and late-phase standardized uptake value ratios (SUVr). Immunohistochemical (IHC) analyses of glial fibrillary acidic protein (GFAP) and MAO-B were performed to validate PET imaging by gold standard assessments. Patients belonging to the Alzheimer's disease continuum (AD, n = 2), Parkinson's disease (PD, n = 2), multiple system atrophy (MSA, n = 2), autoimmune encephalitis (n = 1), oligodendroglioma (n = 1) and one healthy control underwent 60 min dynamic [F-18]F-DED PET and the data were analyzed using equivalent quantification strategies.ResultsWe selected the cerebellum as a pseudo-reference region based on the immunohistochemical comparison of age-matched PS2APP and WT mice. Subsequent PET imaging revealed that PS2APP mice showed elevated hippocampal and thalamic [F-18]F-DED DVR when compared to age-matched WT mice at 5 months (thalamus: + 4.3%;p = 0.048), 13 months (hippocampus: + 7.6%, p = 0.022) and 19 months (hippocampus: + 12.3%, p < 0.0001;thalamus: + 15.2%, p < 0.0001). Specific [F-18]F-DED DVR increases of PS2APP mice occurred earlier when compared to signal alterations in TSPO and beta-amyloid PET and [F-18]F-DED DVR correlated with quantitative immunohistochemistry (hippocampus: R = 0.720, p < 0.001;thalamus: R = 0.727, p = 0.002). Preliminary experience in patients showed [F-18]F-DED V-T and SUVr patterns, matching the expected topology of reactive astrogliosis in neurodegenerative (MSA) and neuroinflammatory conditions, whereas the patient with oligodendroglioma and the healthy control indicated [F-18]F-DED binding following the known physiological MAO-B expression in brain.Conclusions[F-18]F-DED PET imaging is a promising approach to assess reactive astrogliosis in AD mouse models and patients with neurological diseases

Transient voltage-activated K+ currents in central antennal lobe neurons: cell type-specific functional properties

In this study we analyzed transient voltage-activated K+currents ( IA) of projection neurons and local interneurons in the antennal lobe of the cockroach Periplaneta americana. The antennal lobe is the first synaptic processing station for olfactory information in insects. Local interneurons are crucial for computing olfactory information and form local synaptic connections exclusively in the antennal lobe, whereas a primary task of the projection neurons is the transfer of preprocessed olfactory information from the antennal lobe to higher order centers in the protocerebrum. The different physiological tasks of these neurons require specialized physiological and morphological neuronal phenotypes. We asked if and how the different physiological phenotypes are reflected in the functional properties of IA, which is crucial for shaping intrinsic electrophysiological properties of neurons. Whole cell patch-clamp recordings from adult male P. americana showed that all their central antennal lobe neurons can generate IA. The current exhibited marked cell type-specific differences in voltage dependence of steady-state activation and inactivation, and differences in inactivation kinetics during sustained depolarization. Pharmacological experiments revealed that IAin all neuron types was partially blocked by α-dendrotoxin and phrixotoxin-2, which are considered blockers with specificity for Shaker- and Shal-type channels, respectively. These findings suggest that IAin each cell type is a mixed current generated by channels of both families. The functional role of IAwas analyzed in experiments under current clamp, in which portions of IAwere blocked by α-dendrotoxin or phrixotoxin-2. These experiments showed that IAcontributes significantly to the intrinsic electrophysiological properties, such as the action potential waveform and membrane excitability.NEW &amp; NOTEWORTHY In the insect olfactory system, projection neurons and local interneurons have task-specific electrophysiological and morphological phenotypes. Voltage-activated potassium channels play a crucial role in shaping functional properties of these neurons. This study revealed marked cell type-specific differences in the biophysical properties of transient voltage-activated potassium currents in central antennal lobe neurons.</jats:p

Analysis of neuronal Ca2+ handling properties by combining perforated patch clamp recordings and the added buffer approach

Ca2+ functions as an important intracellular signal for a wide range of cellular processes. These processes are selectively activated by controlled spatiotemporal dynamics of the free cytosolic Ca2+. Intracellular Ca2+ dynamics are regulated by numerous cellular parameters. Here, we established a new way to determine neuronal Ca2+ handling properties by combining the 'added buffer' approach [1] with perforated patch-clamp recordings [2]. Since the added buffer approach typically employs the standard whole-cell configuration for concentration-controlled Ca2+ indicator loading, it only allows for the reliable estimation of the immobile fraction of intracellular Ca2+ buffers. Furthermore, crucial components of intracellular signaling pathways are being washed out during prolonged whole-cell recordings, leading to cellular deterioration. By combining the added buffer approach with perforated patch-clamp recordings, these issues are circumvented, allowing the precise quantification of the cellular Ca2+ handling properties, including immobile as well as mobile Ca2+ buffers

Antagonistic modulation of NPY/AgRP and POMC neurons in the arcuate nucleus by noradrenalin

In the arcuate nucleus of the hypothalamus (ARH) satiety signaling (anorexigenic) proopiomelanocortin (POMC)-expressing and hunger signaling (orexigenic) agouti-related peptide (AgRP)-expressing neurons are key components of the neuronal circuits that control food intake and energy homeostasis. Here, we assessed whether the catecholamine noradrenalin directly modulates the activity of these neurons in mice. Perforated patch clamp recordings showed that noradrenalin changes the activity of these functionally antagonistic neurons in opposite ways, increasing the activity of the orexigenic NPY/AgRP neurons and decreasing the activity of the anorexigenic POMC neurons. Cell type-specific transcriptomics and pharmacological experiments revealed that the opposing effect on these neurons is mediated by the activation of excitatory alpha(1A)- and beta- adrenergic receptors in NPY/AgRP neurons, while POMC neurons are inhibited via alpha(2A) adrenergic receptors. Thus, the coordinated differential modulation of the key hypothalamic neurons in control of energy homeostasis assigns noradrenalin an important role to promote feeding

Neuronal Actin Dynamics, Spine Density and Neuronal Dendritic Complexity Are Regulated by CAP2

Actin remodeling is crucial for dendritic spine development, morphology and density. CAP2 is a regulator of actin dynamics through sequestering G-actin and severing F-actin. In a mouse model, ablation of CAP2 leads to cardiovascular defects and delayed wound healing. This report investigates the role of CAP2 in the brain using Cap2(gt)/(gt) mice. Dendritic complexity, the number and morphology of dendritic spines were altered in Cap2(gt)/(gt) with increased number of excitatory synapses. This was accompanied by increased F-actin content and F-actin accumulation in cultured Cap2(gt)/(gt) neurons. Moreover, reduced surface GluA1 was observed in mutant neurons under basal condition and after induction of chemical LTP. Additionally, we show an interaction between CAP2 and n-cofilin, presumably mediated through the C-terminal domain of CAP2 and dependent on cofilin Ser3 phosphorylation. In vivo, the consequences of this interaction were altered phosphorylated cofilin levels and formation of cofilin aggregates in the neurons. Thus, our studies identify a novel role of CAP2 in neuronal development and neuronal actin dynamics

Cortical circuit dysfunction in a mouse model of alpha-synucleinopathy in vivo

Blumenstock et al. report brain state-dependent hyperreactivity in somatosensory cortex months after striatal seeding of alpha-synuclein preformed fibrils. A concerted reduction of GAD67 positive interneurons argues for excitation/inhibition imbalance as a driver of cortical network dysfunction. Considerable fluctuations in cognitive performance and eventual dementia are an important characteristic of alpha-synucleinopathies, such as Parkinson's disease and Lewy Body dementia and are linked to cortical dysfunction. The presence of misfolded and aggregated alpha-synuclein in the cerebral cortex of patients has been suggested to play a crucial role in this process. However, the consequences of a-synuclein accumulation on the function of cortical networks at cellular resolution in vivo are largely unknown. Here, we induced robust a-synuclein pathology in the cerebral cortex using the striatal seeding model in wild-type mice. Nine months after a single intrastriatal injection of a-synuclein preformed fibrils, we observed profound alterations of the function of layer 2/3 cortical neurons in somatosensory cortex by in vivo two-photon calcium imaging in awake mice. We detected increased spontaneous activity levels, an enhanced response to whisking and increased synchrony. Stereological analyses revealed a reduction in glutamic acid decarboxylase 67-positive inhibitory neurons in the somatosensory cortex of mice injected with preformed fibrils. Importantly, these findings point to a disturbed excitation/inhibition balance as a relevant driver of circuit dysfunction, potentially underlying cognitive changes in alpha-synucleinopathies