New Approaches for the Study of Orexin Function

Orexin is a neuropeptide produced by a specific subset of neurones located in the lateral hypothalamic area. Mice lacking either prepro‐orexin or orexin receptor 2, as well as those in which orexin‐producing neurones (orexin neurones) are deleted, share a common phenotype: altered sleep–wake regulation and the sudden onset of muscle atonia. These symptoms are similar to the human sleep disorder narcolepsy. In this review, we describe recent advances in the study of orexin function with a particular emphasis on microscopic techniques that better characterise the neuronal networks involving orexin neurones, as well as recent optogenetic approaches that allow for the activation or inhibition of specific neurones by expressing different light‐activated proteins. In particular, the use of orexin/halorhodopsin and orexin/channelrhodopsin‐2 transgenic mice has demonstrated an important role for orexin neurones in regulating the sleep–wake cycle and state of arousal in vivo. Further refinement of these in vitro and in vivo techniques will allow for a more detailed understanding of the interaction of orexin with other neurotransmitter pathways in the brain.     

Attenuated Stress Response to Acute Restraint and Forced Swimming Stress in Arginine Vasopressin 1b Receptor Subtype (Avpr1b) Receptor Knockout Mice and Wild‐Type Mice Treated with a Novel Avpr1b Receptor Antagonist

Arginine vasopressin (AVP) synthesised in the parvocellular region of the hypothalamic paraventricular nucleus and released into the pituitary portal vessels acts on the 1b receptor subtype (Avpr1b) present in anterior pituitary corticotrophs to modulate the release of adrenocorticotrophic hormone (ACTH). Corticotrophin‐releasing hormone is considered the major drive behind ACTH release; however, its action is augmented synergistically by AVP. To determine the extent of vasopressinergic influence in the hypothalamic‐pituitary‐adrenal axis response to restraint and forced swimming stress, we compared the stress hormone levels [plasma ACTH in both stressors and corticosterone (CORT) in restraint stress only] following acute stress in mutant Avpr1b knockout (KO) mice compared to their wild‐type controls following the administration of a novel Avpr1b antagonist. Restraint and forced swimming stress‐induced increases in plasma ACTH were significantly diminished in mice lacking a functional Avpr1b and in wild‐type mice that had been pre‐treated with Avpr1b antagonist. A corresponding decrease in plasma CORT levels was also observed in acute restraint‐stressed knockout male mice, and in Avpr1b‐antagonist‐treated male wild‐type mice. By contrast, plasma CORT levels were not reduced in acutely restraint‐stressed female knockout animals, or in female wild‐type animals pre‐treated with Avpr1b antagonist. These results demonstrate that pharmacological antagonism or inactivation of Avpr1b causes a reduction in the hypothalamic‐pituitary‐adrenal (HPA) axis response, particularly ACTH, to acute restraint and forced swimming stress, and show that Avpr1b knockout mice constitute a model by which to study the contribution of Avpr1b to the HPA axis response to acute stressors.     

Role of Oestrogen Receptors on the Modulation of NADPH‐Diaphorase‐Positive Cell Number in Supraoptic and Paraventricular Nuclei of Ovariectomised Female Rats

Modulation of the nitric oxide producing system (demonstrated via the NADPH‐diaphorase histochemical reaction) by oestradiol has been established in several structures of the rat brain. The present study aimed to explore the possible regulation of NADPH‐diaphorase activity by oestradiol in neurones of the supraoptic (SON) and paraventricular (PVN) nuclei and the role of oestrogen receptors (ERα and ERβ) in this regulation. Adult ovariectomised rats were divided into six groups and injected either with vehicle or a single dose of oestradiol, a selective ERα agonist‐PPT [4,4′,4″‐(4‐propyl‐[1H]‐pyrazole‐1,3,5‐triyl)trisphenol], a selective ERβ agonist‐DPN [2,3‐bis(4‐hydroxyphenyl)‐propionitrile], a selective ERα antagonist‐MPP [1,3‐bis(4‐hydroxyphenyl)‐4‐methyl‐5‐[4‐(2‐piperidinylethoxy)phenol]‐1H‐pyrazole dihydrochloride] or a selective ERβ antagonist‐PHTPP (4‐[2‐phenyl‐5,7‐bis(trifluoromethyl)pyrazolo[1,5‐a]pyrimidin‐3‐yl]phenol). The number of NADPH‐diaphorase positive elements in the SON and the PVN was modulated by both ERs but, depending on the nucleus, ERα and ERβ ligands induced different effects. These results suggest that the regulation of nitrergic system by ERs may play a role in the control of oestrogen‐dependent physiological mechanisms regulated by the SON and the PVN.     

Protein kinase C stabilizes X‐linked inhibitor of apoptosis protein (XIAP) through phosphorylation at Ser87 to suppress apoptotic cell death

Background: Multiple protein kinases have been shown to be involved in the apoptotic neuronal loss of Alzheimer's disease (AD). Although some studies support the role of protein kinase C (PKC) in amyloid precursor protein processing as well as in tau phosphorylation, a direct role for PKC in apoptotic neuronal death remains to be clarified. In the present study, we report on the possible role of PKC in cell survival during conditions of stress through phosphorylation of the X‐linked inhibitor of apoptosis protein (XIAP). Methods: Phosphorylation of XIAP at Ser87 was confirmed by western blot analysis employing phosphorylation dependent anti‐XIAP antibody after incubation of recombinant XIAP with active PKC in vitro. And increased phosphorylation of XIAP at the site was also confirmed in SH‐SY5Y cells treated with PKC activator, phorbol 12‐myristate 13‐acetate (PMA). A mutant XIAP construct in which Ser87 was substituted by Ala, was prepared, and transfected to cells. After the transfection of wild or mutant XIAP, cells viability was evaluated by counting living and dead cells treated with PMA during etoposide‐induced apoptosis. Results: Recombinant XIAP was phosphorylated at Ser⁸⁷ by PKC in vitro and treatment of XIAP‐transfected SH‐SY5Y cells with a PKC activator, phorbol 12‐myristate 13‐acetate (PMA) induced phosphorylation of XIAP at Ser⁸⁷. Pulse chase experiments revealed that, when phosphorylated at Ser⁸⁷, wild‐type XIAP is more stable than XIAP with a Ser87Ala substitution, which is degraded faster. Importantly, the phosphorylation of XIAP at the site by PKC significantly increased cell survival up to approximately 2.5 times under the condition of apoptosis induced by 25 µg/ml etoposide. Conclusion: The findings of the present study indicate a role for PKC, through phosphorylation of XIAP at Ser⁸⁷ and its stabilization, in cell survival under conditions of stress and lend strength to the idea that PKC is crucial in regulating neuronal homeostasis, which may be impaired in AD.     

Regional distribution and cellular localization of β2‐adrenoceptors in the adult zebrafish brain (Danio rerio)

The β₂‐adrenergic receptors (ARs) are G‐protein‐coupled receptors that mediate the physiological responses to adrenaline and noradrenaline. The present study aimed to determine the regional distribution of β₂‐ARs in the adult zebrafish (Danio rerio) brain by means of in vitro autoradiographic and immunohistochemical methods. The immunohistochemical localization of β₂‐ARs, in agreement with the quantitative β‐adrenoceptor autoradiography, showed a wide distribution of β₂‐ARs in the adult zebrafish brain. The cerebellum and the dorsal zone of periventricular hypothalamus exhibited the highest density of [³H]CGP‐12177 binding sites and β₂‐AR immunoreactivity. Neuronal cells strongly stained for β₂‐ARs were found in the periventricular ventral telencephalic area, magnocellular and parvocellular superficial pretectal nuclei (PSm, PSp), occulomotor nucleus (NIII), locus coeruleus (LC), medial octavolateral nucleus (MON), magnocellular octaval nucleus (MaON) reticular formation (SRF, IMRF, IRF), and ganglionic cell layer of cerebellum. Interestingly, in most cases (NIII, LC, MON, MaON, SRF, IMRF, ganglionic cerebellar layer) β₂‐ARs were colocalized with α_2A‐ARs in the same neuron, suggesting their interaction for mediating the physiological functions of nor/adrenaline. Moderate to low labeling of β₂‐ARs was found in neurons in dorsal telencephalic area, optic tectum (TeO), torus semicircularis (TS), and periventricular gray zone of optic tectum (PGZ). In addition to neuronal, glial expression of β₂‐ARs was found in astrocytic fibers located in the central gray and dorsal rhombencephalic midline, in close relation to the ventricle. The autoradiographic and immunohistochemical distribution pattern of β₂‐ARs in the adult zebrafish brain further support the conserved profile of adrenergic/noradrenergic system through vertebrate brain evolution. J. Comp. Neurol. 518:1418–1441, 2010. © 2009 Wiley‐Liss, Inc.     

Application of feedback‐controlled bolus plus infusion (FC‐B/I) method for quantitative PET imaging of dopamine transporters with [18F]β‐CFT‐FE in conscious monkey brain

The competitive inhibition of dopamine transporters (DAT) with cocaine, a specific DAT inhibitor, was evaluated with a feedback‐controlled bolus plus infusion (FC‐B/I) method using animal positron emission tomography (PET) in the living brain of conscious monkey. 2β‐Carbomethoxy‐3β‐(4‐fluorophenyl)‐8‐(2‐[¹⁸F]fluoroethyl) nortropane ([¹⁸F]β‐CFT‐FE; Harada et al. [2004] Synapse 54:37–45) was used for this study because it provided specific, fast, and reversible kinetic properties to DAT in the striatum. In FC‐B/I method, the real‐time image reconstruction was started just after intravenous bolus injection of [¹⁸F]β‐CFT‐FE to generate a time‐activity curve in the striatum, and the infusion rate was adjusted to achieve an equilibrium state of the striatal radioactivity concentrations by means of a feedback‐control algorithm. The first equilibrium state in the brain was reached within 20 min after the infusion start. Intravenous administration of cocaine at the doses of 0.02, 0.1, and 0.5 mg/kg shifted the equilibrium radioactivity level to the second equilibrium state in a dose‐dependent manner, while no significant alterations was observed in the cerebellum. The present results demonstrated that the combined use of FC‐B/I method and PET probe with fast kinetics like [¹⁸F]β‐CFT‐FE could be useful to assess the occupancy of drugs in the living brain with PET. Synapse, 2013. © 2012 Wiley Periodicals, Inc.     

The N‐terminal fragment of the β‐amyloid precursor protein of Alzheimer's disease (N‐APP) binds to phosphoinositide‐rich domains on the surface of hippocampal neurons

The function of the β‐amyloid precursor protein (APP) of Alzheimer's disease is poorly understood. The secreted ectodomain fragment of APP (sAPPα) can be readily cleaved to produce a small N‐terminal fragment (N‐APP) that contains heparin‐binding and metal‐binding domains and that has been found to have biological activity. In the present study, we examined whether N‐APP can bind to lipids. We found that N‐APP binds selectively to phosphoinositides (PIPs) but poorly to most other lipids. Phosphatidylinositol 4,5‐bisphosphate (PI(4,5)P₂)‐rich microdomains were identified on the extracellular surface of neurons and glia in primary hippocampal cultures. N‐APP bound to neurons and colocalized with PIPs on the cell surface. Furthermore, the binding of N‐APP to neurons increased the level of cell‐surface PI(4,5)P₂ and phosphatidylinositol 3,4,5‐trisphosphate. However, PIPs were not the principal cell‐surface binding site for N‐APP, because N‐APP binding to neurons was not inhibited by a short‐acyl‐chain PIP analogue, and N‐APP did not bind to glial cells which also possessed PI(4,5)P₂ on the cell surface. The data are explained by a model in which N‐APP binds to two distinct components on neurons, one of which is an unidentified receptor and the second of which is a PIP lipid, which binds more weakly to a distinct site within N‐APP. Our data provide further support for the idea that N‐APP may be an important mediator of APP's biological activity. © 2014 Wiley Periodicals, Inc.     

Droxidopa for the Short‐Term Treatment of Symptomatic Neurogenic Orthostatic Hypotension in Parkinson's Disease (nOH306B)

Neurogenic orthostatic hypotension (nOH) results from failure of norepinephrine responses to postural change to maintain standing systolic blood pressure (s‐SBP). Droxidopa is an oral prodrug of norepinephrine. Study nOH306 enrolled patients with Parkinson's disease (PD) and symptomatic nOH. Subjects underwent up to 2 weeks of double‐blind titration of droxidopa or placebo, followed by 8 weeks of double‐blind maintenance treatment (100‐600 mg thrice‐daily). For the initial 51 subjects (study nOH306A, previously reported), the primary efficacy measure, Orthostatic Hypotension Questionnaire (OHQ) composite score, did not demonstrate significant change versus placebo at maintenance week 8. For the subsequent 171 subjects (study nOH306B, reported here), the primary efficacy measure was change versus placebo on item 1 (“dizziness, lightheadedness, feeling faint, or feeling like you might black out”) of the Orthostatic Hypotension Symptom Assessment (OHSA) subsection of the OHQ at maintenance week 1. At week 1, mean (standard deviation) improvement on OHSA item 1 was 2.3 (2.95) for droxidopa versus 1.3 (3.16) for placebo (P = 0.018). In addition, mean increase in s‐SBP at week 1 was 6.4 (18.85) for droxidopa versus 0.7 (20.18) mmHg for placebo (nominal P value: 0.032). Differences in change in OHSA item 1 scores from baseline to maintenance weeks 2, 4, and 8 were not statistically significant. Adverse‐event (AE) incidence was similar across groups, but 12.4% of droxidopa and 6.1% of placebo subjects withdrew because of AEs. The most common AEs on droxidopa (vs. placebo) were headache (13.5% vs. 7.3%) and dizziness (10.1% vs. 4.9%). Study nOH306B demonstrated subjective (OHSA item 1) and objective (s‐SBP) evidence of short‐term droxidopa efficacy (vs. placebo) for symptomatic nOH in PD. © 2014 The Authors. Movement Disorders published by Wiley Periodicals, Inc. on behalf of International Parkinson and Movement Disorder Society.     

Functional and structural correlates of the aging brain: Relating visual cortex (V1) gamma band responses to age‐related structural change

The gamma band response is thought to be a key neural signature of information processing in the mammalian brain, yet little is known about how age‐related maturation influences the γ‐band response. Recent MRI‐based studies have shown that brain maturation is accompanied by clear structural changes in both gray and white matter, yet the correspondence of these changes to brain function is unclear. The objective of this study was to relate visual cortex (V1) γ‐band responses to age‐related structural change. We evaluated MEG measured γ‐band responses to contrast gratings stimuli and structural MRIs from participants observed from two separate research centers (MEG lab at CUBRIC, Cardiff University, UK, and the Lurie Family Foundations MEG Imaging Center, (CHOP) at the Children's Hospital of Philadelphia). Pooled participant data (N = 59) ranged in age from 8.7 to 45.3 years. We assessed linear associations between age and MEG γ‐band frequency and amplitude, as well as between age and MRI volumetric parameters of the occipital lobe. Our MEG findings revealed a significant negative correlation for gamma band frequency versus age. Volumetric brain analysis from the occipital lobe also revealed significant negative correlations between age and the cortical thickness of pericalcarine and cuneus areas. Our functional MEG and structural MRI findings shows regionally specific changes due to maturation and may thus be informative for understanding physiological processes of neural development, maturation, and age‐related decline. In addition, this study represents (to our knowledge), the first published demonstration of multicenter data sharing across MEG centers. Hum Brain Mapp 33:2035–2046, 2012. © 2011 Wiley Periodicals, Inc.