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Galanin receptor-1 modulates 5-hydroxtryptamine-1A signaling via heterodimerization.

Previous biochemical, cardiovascular and behavioral work has given evidence for the existence of antagonistic galanin receptor-5-HT1A receptor interactions in the brain. In this study we investigated the existence of GalR1-5-HT1A receptor heteromers and their functional characteristics. In mammalian cells transfected with GFP2-tagged 5-HT1A receptor and YFP-tagged GalR1 receptor, a proximity-based fluorescence resonance energy transfer technique was used and it has been demonstrated that GalR1-5-HT1A receptors heteromerize. Furthermore, signaling by either the mitogen-activated protein kinase (MAPK) or adenylyl cyclase (AC) pathways by these heteromers indicates a trans-inhibition phenomenon through their interacting interface via allosteric mechanisms that block the development of an excessive activation of G(i/o) and an exaggerated inhibition of AC or stimulation of MAPK activity. The presence of these heteromers in the discrete brain regions is postulated based on the existence of GalR-5-HT1A receptor-receptor interactions previously described in the brain and gives rise to explore possible novel therapeutic strategies for treatment of depression by targeting the GalR1-5-HT1A heteromers.

On the existence and function of galanin receptor heteromers in the central nervous system

Galanin receptor (GalR) subtypes 1–3 linked to central galanin neurons may form heteromers with each other and other types of G protein-coupled receptors in the central nervous system (CNS). These heteromers may be one molecular mechanism for galanin peptides and their N-terminal fragments (gal 1-15) to modulate the function of different types of glia–neuronal networks in the CNS, especially the emotional and the cardiovascular networks. GalR–5-HT1A heteromers likely exist with antagonistic GalR–5-HT1A receptor–receptor interactions in the ascending midbrain raphe 5-HT neuron systems and their target regions. They represent a novel target for antidepressant drugs. Evidence is given for the existence of GalR1–5-HT1A heteromers in cellular models with trans-inhibition of the protomer signaling. A GalR1–GalR2 heteromer is proposed to be a galanin N-terminal fragment preferring receptor (1-15) in the CNS. Furthermore, a GalR1–GalR2–5-HT1A heterotrimer is postulated to explain why only galanin (1-15) but not galanin (1-29) can antagonistically modulate the 5-HT1A receptors in the dorsal hippocampus rich in gal fragment binding sites. The results underline a putative role of different types of GalR–5-HT1A heteroreceptor complexes in depression. GalR antagonists may also have therapeutic actions in depression by blocking the antagonistic GalR–NPYY1 receptor interactions in putative GalR–NPYY1 receptor heteromers in the CNS resulting in increases in NPYY1 transmission and antidepressant effects. In contrast the galanin fragment receptor (a postulated GalR1–GalR2 heteromer) appears to be linked to the NPYY2 receptor enhancing the affinity of the NPYY2 binding sites in a putative GalR1–GalR2–NPYY2 heterotrimer. Finally, putative GalR–α2-adrenoreceptor heteromers with antagonistic receptor–receptor interactions may be a widespread mechanism in the CNS for integration of galanin and noradrenaline signals also of likely relevance for depression.

Dietary lutein/zeaxanthin partially reduces photoaging and photocarcinogenesis in chronically UVB-irradiated Skh-1 hairless mice.

Lutein and zeaxanthin are xanthophyll carotenoids with potent antioxidant properties protecting the skin from acute photodamage. This study extended the investigation to chronic photodamage and photocarcinogenesis. Mice received either a lutein/zeaxanthin-supplemented diet or a standard nonsupplemented diet. Dorsal skin of female Skh-1 hairless mice was exposed to UVB radiation with a cumulative dose of 16,000 mJ/cm2 for photoaging and 30,200 mJ/cm2 for photocarcinogenesis. Clinical evaluations were performed weekly, and the animals were sacrificed 24 h after the last UVB exposure. For photoaging experiments, skin fold thickness, suprapapillary plate thickness, mast cell counts and dermal desmosine content were evaluated. For photocarcinogenesis, samples of tumors larger than 2 mm were analyzed for histological characterization, hyperproliferation index, tumor multiplicity, total tumor volume and tumor-free survival time. Results of the photoaging experiment revealed that skin fold thickness and number of infiltrating mast cells following UVB irradiation were significantly less in lutein/zeaxanthin-treated mice when compared to irradiated animals fed the standard diet. The results of the photocarcinogenesis experiment were increased tumor-free survival time, reduced tumor multiplicity and total tumor volume in lutein/zeaxanthin-treated mice in comparison with control irradiated animals fed the standard diet. These data demonstrate that dietary lutein/zeaxanthin supplementation protects the skin against UVB-induced photoaging and photocarcinogenesis.

Role of galanin and galanin(1–15) on central cardiovascular control

Galanin and the N-terminal fragment Galanin(1-15) are involved in central cardiovascular regulation. The present paper reviews the recent cardiovascular results obtained by intracisternal injections of Galanin and Galanin(1-15) showing that: (A) the Galanin antagonist M40 blocks the central cardiovascular responses induced by Galanin(1-15) but not those elicited by Galanin; (B) both Galanin and Galanin(1-15) induce the expression of c-Fos in cardiovascular nuclei of the medulla oblongata with different temporal and spatial profiles; (C) the cardiovascular action of Galanin(1-15), but not Galanin, is mediated by peripheral beta-receptor stimulation; (D) and it is demonstrated an antagonistic Galanin/alpha2-adrenoceptors interaction as well as a differential modulation of central cardiovascular responses of Angiotensin II by Galanin or Galanin(1-15). All these data strengthen the involvement of both Galanin molecules as neuromodulators on central cardiovascular regulation.

A Role for Galanin N-Terminal Fragment (1–15) in Anxiety- and Depression-Related Behaviors in Rats

Background: Galanin (GAL) plays a role in mood regulation. In this study we analyzed the action of the active N-terminal fragment [GAL(1–15)] in anxiety- and depression-related behavioral tests in rats. Methods: The effect of GAL(1–15) was analyzed in the forced swimming test, tail suspension test, open field test, and light/dark test. The proximity of GAL1 and GAL2 receptors was examined with the proximity ligation assay (PLA). We tested the GAL receptors involved in GAL(1–15) effects with the GAL2 receptor antagonist M871 and with an in vivo model of siRNA GAL2 receptor knockdown or siRNA GAL1 receptor knockdown rats. The effects of GAL(1–15) were also studied in the cell line RN33B. Results: GAL(1–15) induced strong depression-like and anxiogenic-like effects in all the tests. These effects were stronger than the ones induced by GAL. The involvement of the GAL2 receptor was demonstrated with M871 and with the siRNA GAL2 receptor knockdown rats. The PLA indicated the possible existence of GAL1 and GAL2 heteroreceptor complexes in the dorsal hippocampus and especially in the dorsal raphe nucleus. In the siRNA GAL1 receptor knockdown rats the behavioral actions of GAL(1–15) disappeared, and in the siRNA GAL2 receptor knockdown rats the reductions of the behavioral actions of GAL(1–15) was linked to a disappearance of PLA. In the cell line RN33B, GAL(1–15) decreased 5-HT immunoreactivity more strongly than GAL. Conclusions: Our results indicate that GAL(1–15) exerts strong depression-related and anxiogenic-like effects and may give the basis for the development of drugs targeting GAL1 and GAL2 heteroreceptor complexes in the raphe-limbic system for the treatment of depression and anxiety.

Galanin–neuropeptide Y (NPY) interactions in central cardiovascular control: involvement of the NPY Y1 receptor subtype

The interactions between neuropeptide Y (NPY), specifically through NPY Y1 and Y2 receptor subtypes, and galanin [GAL(1–29)] have been analysed at the cardiovascular level. The cardiovascular effects of intracisternal coinjections of GAL(1–29) with NPY or NPY Y1 or Y2 agonists, as well as quantitative receptor autoradiography of the binding characteristics of NPY Y1 and Y2 receptor subtypes in the nucleus of the solitary tract (NTS), in the presence or absence of GAL(1–29), have been investigated. The effects of coinjections of GAL(1–29) and the NPY Y1 agonist on the expression of c‐FOS immunoreactivity in the NTS were also studied. The coinjection of NPY with GAL(1–29) induced a significant vasopressor and tachycardic action with a maximum 40% increase (P < 0.001). The coinjection of the NPY Y1 agonist and GAL(1–29) induced a similar increase in mean arterial pressure and heart rate as did NPY plus GAL(1–29), actions that were not observed with the NPY Y2 agonist plus GAL(1–29). GAL(1–29), 3 nm, significantly and substantially (by ∼ 40%) decreased NPY Y1 agonist binding in the NTS. This effect was significantly blocked (P < 0.01) in the presence of the specific galanin antagonist M35. The NPY Y2 agonist binding was not modified in the presence of GAL(1–29). At the c‐FOS level, the coinjection of NPY Y1 and GAL(1–29) significantly reduced the c‐FOS‐immunoreactive response induced by either of the two peptides. The present findings suggest the existence of a modulatory antagonistic effect of GAL(1–29) mediated via galanin receptors on the NPY Y1 receptor subtype and its signalling within the NTS.

Receptor–receptor interactions in central cardiovascular regulation. Focus on neuropeptide/α2-adrenoreceptor interactions in the nucleus tractus solitarius

Summary.The nucleus tractus solitarii (NTS) is a key nucleus in central cardiovascular control. In this mechanism it is well known the role of the α2-adrenoreceptors for the modulation of the autonomic pathways. Moreover a number of neuropeptides described in the NTS, including Neuropeptide Y (NPY), Galanin (GAL) and Angiotensin II (Ang II), have different roles in regulating the cardiovascular function within this nucleus. We show in this review several data which help to understand how these neuropeptides (NPY, GAL and Ang II) could modulate the cardiovascular responses mediated through α2-adrenoreceptors in the NTS. Also we show for the first time the interactions between neuropeptides in the brain, specifically the interactions between NPY, GAL, and Ang II, and its functional relevance for central cardiovascular regulation. These data strength the role of neuropeptides on central autonomic control and provide some evidences to understand the neurochemical mechanisms involved in the cardiovascular responses from the NTS.

Region specific galanin receptor/neuropeptide Y Y1 receptor interactions in the tel- and diencephalon of the rat. Relevance for food consumption.

The aim of this work was to determine the interactions between NPY and GAL receptor (GALR) subtypes in the hypothalamus and the amygdala using quantitative receptor autoradiography to analyze the binding characteristics of NPY-Y1 and Y2 receptor subtypes in the presence and absence of GAL. Food intake in satiated animals was evaluated after intraventricular co-injections of GAL and NPY-Y1 or Y2 agonists. The expression of c-Fos IR in both regions was also investigated. GAL decreases NPY-Y1 agonist binding in the arcuate nucleus by about 15% (p<0.01), but increases NPY-Y1 agonist binding in amygdala (18%) (p<0.01). These effects were blocked with the GAL antagonist M35. Y2-agonist binding was not modified by GAL. GAL blocked the food intake induced by the Y1 agonist (p<0.01). Co-injections of Y1 agonist and GAL also reduced the c-Fos expression induced by the Y1 agonist in the arcuate nucleus and the dorsomedial hypothalamic nucleus but increased c-Fos expression in amygdala. These results indicate the existence of antagonistic interactions between GALR and NPY-Y1 receptors in the hypothalamus and their functional relevance for food intake. In contrast, a facilitatory interaction between GALR and Y1 receptors exists in the amygdala which may be of relevance for fear related behaviour.

Galanin receptor 2-neuropeptide Y Y1 receptor interactions in the amygdala lead to increased anxiolytic actions

Galanin (GAL) and neuropeptide Y (NPY) are neuropeptides involved in behaviors associated with anxiety. Both neuropeptides interact in several central functions. However, the potential behavioral and cellular interactions between them in anxiety are unknown. GAL was found to act through GAL receptor 2 (GALR2) to enhance NPYY1 receptor (NPYY1R)-mediated anxiolytic behaviors in rats. Using receptor autoradiography, c-Fos expression and in situ proximity ligation assay, the medial paracapsular intercalated nuclei of the amygdala were determined to be a key area in the interaction probably involving the formation of GALR2/NPYY1R heteroreceptor complexes. In cell cultures costimulation of GALR2 and NPYY1R induced changes in the functions of these receptors. The changes involved a potentiation of the decrease in the phosphorylation of CREB induced by NPYY1R and a delay in the internalization of NPYY1R. These results indicate that GALR2/NPYY1R interactions can provide a novel integrative amygdaloid mechanism in anxiety.

Neurochemical Modulation of Central Cardiovascular Control: The Integrative Role of Galanin

Galanin (GAL) is a peptide involved in multiple functions, including central cardiovascular control. In this review, the role of GAL and its fragments in the modulation of cardiovascular neuronal networks in the nucleus of the solitary tract is presented, including its interaction with the classical neurotransmitters and other neuropeptides involved in cardiovascular responses in this nucleus. First, we describe the cardiovascular responses of GAL and the pathway involved in these responses. Then we summarize findings obtained in our laboratory on how GAL, through its receptors, interacts with two other neuropeptides--Neuropeptide Y and Angiotensin II and their receptors--as they have particularly conspicuous cardiovascular effects. All these results strengthen the role of GAL in central cardiovascular control and indicate the existence of interactions among GAL receptor subtypes and alpha2-adrenergic receptors, AT1, and Y1 receptor subtypes. These interactions are crucial for understanding the integrative mechanisms responsible for the organization of the cardiovascular responses from the NTS.