Beta-adrenergic receptor binding in human and rat hypothalamus

Analysis of the Glucose-Dependent Transcriptome in Murine Hypothalamic Cells

Glucose provides vital energy for cells and contributes to gene expression. The hypothalamus is key for metabolic homeostasis, but effects of glucose on hypothalamic gene expression have not yet been investigated in detail. Thus, herein, we monitored the glucose-dependent transcriptome in murine hypothalamic mHypoA-2/10 cells by total RNA-seq analysis. A total of 831 genes were up- and 1390 genes were downregulated by at least 50%. Key genes involved in the cholesterol biosynthesis pathway were upregulated, and total cellular cholesterol levels were significantly increased by glucose. Analysis of single genes involved in fundamental cellular signaling processes also suggested a significant impact of glucose. Thus, we chose ≈100 genes involved in signaling and validated the effects of glucose on mRNA levels by qRT-PCR. We identified Gnai1–3, Adyc6, Irs1, Igfr1, Hras, and Elk3 as new glucose-dependent genes. In line with this, cAMP measurements revealed enhanced noradrenalin-induced cAMP levels, and reporter gene assays elevated activity of the insulin-like growth factor at higher glucose levels. Key data of our studies were confirmed in a second hypothalamic cell line. Thus, our findings link extra cellular glucose levels with hypothalamic lipid synthesis and pivotal intracellular signaling processes, which might be of particular interest in situations of continuously increased glucose levels.

Physiological Temperature Changes Fine-Tune 2- Adrenergic Receptor-Induced Cytosolic cAMP Accumulation

Norepinephrine (NE) controls many vital body functions by activating adrenergic receptors (ARs). Average core body temperature (CBT) in mice is 37°C. Of note, CBT fluctuates between 36 and 38°C within 24 hours, but little is known about the effects of CBT changes on the pharmacodynamics of NE. Here, we used Peltier element-controlled incubators and challenged murine hypothalamic mHypoA -2/10 cells with temperature changes of ±1°C. We observed enhanced NE-induced activation of a cAMP-dependent luciferase reporter at 36 compared with 38°C. mRNA analysis and subtype specific antagonists revealed that NE activates β 2- and β 3-AR in mHypoA-2/10 cells. Agonist binding to the β 2-AR was temperature insensitive, but measurements of cytosolic cAMP accumulation revealed an increase in efficacy of 45% ± 27% for NE and of 62% ± 33% for the β 2-AR-selective agonist salmeterol at 36°C. When monitoring NE-promoted cAMP efflux, we observed an increase in the absolute efflux at 36°C. However, the ratio of exported to cytosolic accumulated cAMP is higher at 38°C. We also stimulated cells with NE at 37°C and measured cAMP degradation at 36 and 38°C afterward. We observed increased cAMP degradation at 38°C, indicating enhanced phosphodiesterase activity at higher temperatures. In line with these data, NE-induced activation of the thyreoliberin promoter was found to be enhanced at 36°C. Overall, we show that physiologic temperature changes fine-tune NE-induced cAMP signaling in hypothalamic cells via β 2-AR by modulating cAMP degradation and the ratio of intra- and extracellular cAMP. SIGNIFICANCE STATEMENT: Increasing cytosolic cAMP levels by activation of G protein-coupled receptors (GPCR) such as the β 2-adrenergic receptor (AR) is essential for many body functions. Changes in core body temperature are fundamental and universal factors of mammalian life. This study provides the first data linking physiologically relevant temperature fluctuations to β 2-AR-induced cAMP signaling, highlighting a so far unappreciated role of body temperature as a modulator of the prototypic class A GPCR.

Antagonists of the Vasopressin V1 Receptor and of the β(1)-Adrenoceptor Inhibit Cytotoxic Brain Edema in Stroke by Effects on Astrocytes - but the Mechanisms Differ

Brain edema is a serious complication in ischemic stroke because even relatively small changes in brain volume can compromise cerebral blood flow or result in compression of vital brain structures on account of the fixed volume of the rigid skull. Literature data indicate that administration of either antagonists of the V1 vasopressin (AVP) receptor or the β1-adrenergic receptor are able to reduce edema or infarct size when administered after the onset of ischemia, a key advantage for possible clinical use. The present review discusses possible mechanisms, focusing on the role of NKCC1, an astrocytic cotransporter of Na(+), K(+), 2Cl(-) and water and its activation by highly increased extracellular K(+) concentrations in the development of cytotoxic cell swelling. However, it also mentions that due to a 3/2 ratio between Na(+) release and K(+) uptake by the Na(+),K(+)-ATPase driving NKCC1 brain extracellular fluid can become hypertonic, which may facilitate water entry across the blood-brain barrier, essential for development of edema. It shows that brain edema does not develop until during reperfusion, which can be explained by lack of metabolic energy during ischemia. V1 antagonists are likely to protect against cytotoxic edema formation by inhibiting AVP enhancement of NKCC1-mediated uptake of ions and water, whereas β1-adrenergic antagonists prevent edema formation because β1-adrenergic stimulation alone is responsible for stimulation of the Na(+),K(+)-ATPase driving NKCC1, first and foremost due to decrease in extracellular Ca(2+) concentration. Inhibition of NKCC1 also has adverse effects, e.g. on memory and the treatment should probably be of shortest possible duration.

Galanin activated Gi/o-proteins in human and rat central nervous systems

The neuropeptide galanin (GAL) is involved in the control of hormone secretion, nociception, feeding behavior, attention, learning and memory. The anatomical localization of galanin receptors in the brain has been described using autoradiography and immunohistochemistry, but both techniques are limited by the availability of specific radioligands or antibodies. Functional autoradiography provides an alternative method by combining anatomical resolution and information of the activity mediated by G-protein coupled receptors. The present study analyzes the functional GAL receptors coupled to Gi/o-proteins in human and rat brain nuclei using [(35)S]GTPγS autoradiography. The results show the anatomical distribution of Gi/o-proteins activated by GAL receptors that trigger intracellular signaling mechanisms. The activity mediated by GAL receptors in human and rat brain showed a good correlation of the net stimulation in areas such as spinal cord, periaqueductal gray, putamen, CA3 layers of hippocampus, substantia nigra and diverse thalamic nuclei. The functional GAL receptors coupled to Gi/o-proteins showed a similar pattern for both species in most of the areas analyzed, but some discrete nuclei showed differences in the activity mediated by GAL, such as the ventroposteromedial thalamic nucleus, or areas that regulate learning and memory processes in the hippocampus. Taken into consideration the present results, the rat could be used as an experimental model for the study of the physiological role of GAL-mediated neurotransmission and the modulation of GAL receptors activity in the human CNS.

G protein-coupled receptors in the hypothalamic paraventricular and supraoptic nuclei--serpentine gateways to neuroendocrine homeostasis

G protein-coupled receptors (GPCRs) are the largest family of transmembrane receptors in the mammalian genome. They are activated by a multitude of different ligands that elicit rapid intracellular responses to regulate cell function. Unsurprisingly, a large proportion of therapeutic agents target these receptors. The paraventricular nucleus (PVN) and supraoptic nucleus (SON) of the hypothalamus are important mediators in homeostatic control. Many modulators of PVN/SON activity, including neurotransmitters and hormones act via GPCRs--in fact over 100 non-chemosensory GPCRs have been detected in either the PVN or SON. This review provides a comprehensive summary of the expression of GPCRs within the PVN/SON, including data from recent transcriptomic studies that potentially expand the repertoire of GPCRs that may have functional roles in these hypothalamic nuclei. We also present some aspects of the regulation and known roles of GPCRs in PVN/SON, which are likely complemented by the activity of 'orphan' GPCRs.

Cold exposure increases the biosynthesis and proteolytic processing of prothyrotropin-releasing hormone in the hypothalamic paraventricular nucleus via beta-adrenoreceptors

Different physiological conditions affect the biosynthesis and processing of hypophysiotropic proTRH in the hypothalamic paraventricular nucleus, and consequently the output of TRH. Early studies suggest that norepinephrine (NE) mediates the cold-induced activation of the hypothalamic-pituitary-thyroid axis at a central level. However, the specific role of NE on the biosynthesis and processing of proTRH has not been fully investigated. In this study, we found that NE affects gene transcription, protein biosynthesis, and secretion in TRH neurons in vitro; these changes were coupled with an up-regulation of prohormone convertase enzymes (PC) 1/3 and PC2. In vivo, NE is the main mediator of the cold-induced activation of the hypothalamic-pituitary-thyroid axis at the hypothalamic level, in which it potently stimulates the biosynthesis and proteolytic processing of proTRH through a coordinated up-regulation of the PCs. This activation occurs via beta-adrenoreceptors and phosphorylated cAMP response element binding signaling. In contrast, alpha-adrenoreceptors regulate TRH secretion but not proTRH biosynthesis and processing. Therefore, this study provides novel information on the molecular mechanisms of control of hypophysiotropic TRH biosynthesis.

Noradrenaline excites and inhibits GABAergic transmission in parvocellular neurons of rat hypothalamic paraventricular nucleus

Noradrenaline (NA) is a major neurotransmitter that regulates many neuroendocrine and sympathetic autonomic functions of the hypothalamic paraventricular nucleus (PVN). Previously NA has been shown to increase the frequency of excitatory synaptic activity of parvocellular neurons within the PVN, but little is known about its effects on inhibitory synaptic activity. In this work, we studied the effects of NA (1-100 microM) on the spontaneous inhibitory synaptic currents (sIPSC) of type II PVN neurons in brain slices of the rat using the whole cell patch-clamp technique. Spontaneous IPSCs were observed from most type II neurons (n = 121) identified by their anatomical location within the PVN and their electrophysiological properties. Bath application of NA (100 microM) increased sIPSC frequency by 256% in 59% of the neurons. This effect was blocked by prazosin (2-20 microM), the alpha(1)-adrenoceptor antagonist and mimicked by phenylephrine (10-100 microM), the alpha(1)-adrenoceptor agonist. However, in 33% of the neurons, NA decreased sIPSC frequency by 54%, and this effect was blocked by yohimbine (2-20 microM), the alpha(2)-adrenoceptor antagonist and mimicked by clonidine (50 microM), the alpha(2)-adrenoceptor agonist. The Na(+) channel blocker, tetrodotoxin (0.1 microM) blocked the alpha(1)-adrenoceptor-mediated effect, but not the alpha(2)-adreonoceptor-mediated one. Both of the stimulatory and inhibitory effects of NA on sIPSC frequency were observed in individual neurons when tested with NA alone, or both phenylephrine and clonidine. Furthermore, in most neurons that showed the stimulatory effects, the inhibitory effects of NA were unmasked after blocking the stimulatory effects by prazosin or tetrodotoxin. These data indicate that tonic GABAergic inputs to the majority of type II PVN neurons are under a dual noradrenergic modulation, the increase in sIPSC frequency via somatic or dendritic alpha(1)-adrenoceptors and the decrease in sIPSC frequency via axonal terminal alpha(2)-adrenoceptors on the presynaptic GABAergic neurons.

Relationships between beta- and alpha2-adrenoceptors and G coupling proteins in the human brain: effects of age and suicide

Interactions between brain alpha2- and beta-adrenoceptors are of interest in physiological (aging) and pathological (major depression) processes involving both receptors. In this study, total beta-adrenoceptors and beta1/2-subtypes were quantitated in postmortem human brains to investigate their relationships with alpha2A-adrenoceptors and specific G proteins during the process of aging and in brains of suicide victims. Analysis of [3H]CGP12177 binding, in the presence of CGP20712A (beta1-antagonist), indicated that the predominant beta-adrenoceptor in the frontal cortex is the beta1-subtype (65-75%). The density of total beta- (r=-0.60, n=44) or beta1-adrenoceptors (r=-0.78, n=22), but not the beta2-subtype, declined with aging (3-80 years). The density of total beta- or beta1-adrenoceptors, but not the beta2-subtype, correlated with the number of alpha2-adrenoceptors quantitated in the same brains with the agonist [3H]UK14304 (r=0.71-0.81) or the antagonist [3H]RX821002 (r=0.61-0.66). Interestingly, the ratios alpha2/beta- or alpha2/beta1-adrenoceptors did not correlate with the age of the subject at death, indicating that the proportion of alpha2/beta-adrenoceptors in brain remains rather constant during the process of aging. The density of beta-adrenoceptors correlated with the immunodensity of G(alpha)s (r=0.55) and Gbeta (r=0.61) proteins, and that of alpha2-adrenoceptors with those of G(alpha)i1/2 (r=0.88) and Gbeta (r=0.65). In brains of suicides, compared to controls, the ratio between alpha2- and beta- or beta1-adrenoceptors (alpha2-full agonist sites/beta-sites) was greater (1.3- to 2.0-fold; P<0.05). The results demonstrate a close interdependence between brain alpha2- and beta-adrenoceptors during aging, and in brains of suicides. The quantitation of the alpha2A/beta-adrenoceptor ratio could represent a relevant neurochemical index in the study of brain pathologies in which both receptors are involved.

Inhibition of spontaneous inhibitory postsynaptic currents (IPSC) by noradrenaline in rat supraoptic neurons through presynaptic alpha2-adrenoceptors

It has been shown that noradrenergic activation has great influence on the activities of hypothalamic supraoptic neurons. No direct evidence has been reported on the presynaptic effects of adrenoceptors in the actions of noradrenaline on supraoptic neurons, although postsynaptic mechanisms have been studied extensively. In the present study, we explored presynaptic effects of noradrenaline on the supraoptic neurons by measuring spontaneous inhibitory postsynaptic currents (IPSC) with the whole-cell patch-clamp technique. Noradrenaline reduced the frequency of IPSCs in a dose-dependent (10(-9) to 10(-3) M) and reversible manner. Noradrenaline did not affect the amplitude of IPSCs at concentrations of 10(-9) to 10(-5) M, but reduced the amplitude of IPSCs at high concentrations (10(-4) and 10(-3) M). The inhibitory effects of noradrenaline were mimicked by the alpha2-agonist clonidine (10(-4) M), but not by the alpha1-agonist methoxamine (10(-4) M) nor by the beta-agonist isoproterenol (10(-4) M). Moreover, the inhibitory effects of noradrenaline on IPSCs were blocked by the non-selective alpha antagonist phentolamine (10(-4) M) or the selective alpha2-antagonist yohimbine (10(-4) M), but not by the alpha1-antagonist prazosin (10(-4) M). These results suggest that noradrena-line inhibits release of GABA from the presynaptic GABAergic terminals of the supraoptic neurons by activating presynaptic alpha2-adrenoceptors and such presynaptic mechanisms may play a role in the excitatory control of SON neurons by noradrenergic neurons.

Beta-adrenergic receptor subtypes in human pineal gland

The secretion of melatonin by the pineal has been promoted as a direct monitor of adrenergic function in depressive illness. However, discrepant findings have been reported, possibly reflecting a complex adrenergic regulation of pineal output. In order to clarify the anatomical localization and relative density of beta-adrenergic receptors and their subtypes in human pineal, quantitative autoradiographic analysis was conducted of beta-adrenergic receptors in postmortem specimens using the high affinity radioligand 125I-pindolol. Dense specific binding was found throughout the gland. beta 1 -adrenergic receptors were more numerous, but beta 2-receptors were present in an overlapping anatomical distribution with beta 1-receptors.

Beta-adrenergic receptor binding in frontal cortex from suicide victims

Beta-adrenergic binding in frontal cortex samples from suicide victims has been reported to be increased, unaltered, and decreased compared to matched controls. Subject's diagnoses and drug exposures in these studies were not equivalently documented and were possibly different. In the present study, diagnostic and symptomatic information was systematically collected from family members of 15 subjects committing suicide and 15 matched controls using standardized interview techniques. The goal was to test the hypothesis that alterations in beta-adrenergic binding were more likely to be found in subjects with evidence of depressive disorders. [125I]pindolol binding in frontal cortex was found to be significantly lower in the group committing suicide compared to the matched controls (21.1 +/- 1.1 fmol/mg protein vs. 24.8 +/- 0.8 fmol/mg protein, p < .02). However, no diagnostic subgroup among the suicide victims appeared distinct.