Oxidative Stress and Lymphocyte Alterations in Chronic Relapsing Experimental Allergic Encephalomyelitis in the Rat Hippocampus and Protective Effects of an Ethanolamine Phosphate Salt.

Chronic relapsing experimental allergic encephalomyelitis (CR-EAE) exhibits neuropathological and immunological dysfunctions similar to those found in multiple sclerosis (MS) and has been used as an animal model of MS. Inflammatory infiltrates and oxidative stress have been linked to the development of both diseases. Ethanolamine plasmalogen derivates have been shown to be powerful antioxidants and immunomodulators. Therefore, the objective of this study was to analyse inflammatory infiltrates, the state of the oxidative defences and the possible protective effects of calcium, magnesium and phosphate ethanolamine (EAP) in the CR-EAE rat hippocampus. To this aim, we evaluated, by immunohistochemistry, T cell infiltrates, Iba-1+ (a marker of activated microglia) immunoreactivity and TUNEL (+) cells. We also measured the protein levels and activity of the antioxidant enzymes catalase (CAT), superoxide dismutase (SOD), glutathione peroxidase (GP) and glutathione reductase (GR). In addition, reduced (GSH) and oxidized (GSSG) glutathione levels, lipid peroxidation and cholesterol as well as desmosterol content were determined. We found an increase in T cell infiltrates and Iba1+ immunoreactivity, lipid peroxidation, SOD, GP and GR activities as well as enhanced cholesterol levels and a decrease in CAT activity, GSH and desmosterol levels in the first and second attack in the CR-EAE rat hippocampus. Pretreatment of CR-EAE rats with EAP led to a delay in the onset of the clinical signs of the disease as well as a decrease in inflammatory infiltrates and alterations of the antioxidant defences in the hippocampus. Altogether, the present results suggest a protective role of EAP in the CR-EAE rat hippocampus.

A nitric oxide synthase inhibitor, L-NAME, prevents L-arginine-induced downregulation of the rat cortical somatostatinergic system.

Activation of NMDA receptors leads to nitric oxide (NO) synthesis by NO synthase (NOS) from L-arginine. Neuronal NOS colocalizes with somatostatinergic (SRIF) neurons and there is growing evidence of an interaction between NO and the cerebral SRIFergic system in several neurological diseases. Our aim was to study the effect of L-arginine on the regulation of the SRIFergic system in the frontoparietal cortex of male Sprague-Dawley rats. Intraperitoneal administration of L-arginine (150 mg/Kg), twice-daily during eight days, induced a decrease in SRIF receptor density, which was accompanied by a reduction in the capacity of SRIF to stimulate inositol-1,4,5-triphosphate (IP3) accumulation and SRIF-like immunoreactivity (SRIF-LI) levels. To determine if these changes were related to L-arginine-derived NO synthesis, a NOS inhibitor, Nω-nitro-L-arginine methyl ester was coadministered with L-arginine. Its coadministration prevented the reduction in the SRIF receptor density, accumulation of IP3 and SRIF-LI content. These findings indicate that L-arginine induces a deleterious effect on the cortical somatostatinergic system and that the inhibition of NOS could be helpful in some neurological disorders where this neurotransmitter system is affected.

Peptides and food intake.

The mechanisms for controlling food intake involve mainly an interplay between gut, brain, and adipose tissue (AT), among the major organs. Parasympathetic, sympathetic, and other systems are required for communication between the brain satiety center, gut, and AT. These neuronal circuits include a variety of peptides and hormones, being ghrelin the only orexigenic molecule known, whereas the plethora of other factors are inhibitors of appetite, suggesting its physiological relevance in the regulation of food intake and energy homeostasis. Nutrients generated by food digestion have been proposed to activate G-protein-coupled receptors on the luminal side of enteroendocrine cells, e.g., the L-cells. This stimulates the release of gut hormones into the circulation such as glucagon-like peptide-1 (GLP-1), oxyntomodulin, pancreatic polypeptides, peptide tyrosine tyrosine, and cholecystokinin, which inhibit appetite. Ghrelin is a peptide secreted from the stomach and, in contrast to other gut hormones, plasma levels decrease after a meal and potently stimulate food intake. Other circulating factors such as insulin and leptin relay information regarding long-term energy stores. Both hormones circulate at proportional levels to body fat content, enter the CNS proportionally to their plasma levels, and reduce food intake. Circulating hormones can influence the activity of the arcuate nucleus (ARC) neurons of the hypothalamus, after passing across the median eminence. Circulating factors such as gut hormones may also influence the nucleus of the tractus solitarius (NTS) through the adjacent circumventricular organ. On the other hand, gastrointestinal vagal afferents converge in the NTS of the brainstem. Neural projections from the NTS, in turn, carry signals to the hypothalamus. The ARC acts as an integrative center, with two major subpopulations of neurons influencing appetite, one of them coexpressing neuropeptide Y and agouti-related protein (AgRP) that increases food intake, whereas the other subpopulation coexpresses pro-opiomelanocortin (POMC) and cocaine and amphetamine-regulated transcript that inhibits food intake. AgRP antagonizes the effects of the POMC product, α-melanocyte-stimulating hormone (α-MSH). Both populations project to areas important in the regulation of food intake, including the hypothalamic paraventricular nucleus, which also receives important inputs from other hypothalamic nuclei.

Vitamin E deficiency impairs the somatostatinergic receptor-effector system and leads to phosphotyrosine phosphatase overactivation and cell death in the rat hippocampus.

Vitamin E plays an essential role in maintaining the structure and function of the nervous system, and its deficiency, commonly associated with fat malabsorption diseases, may reduce neuronal survival. We previously demonstrated that the somatostatinergic system, implicated in neuronal survival control, can be modulated by α-tocopherol in the rat dentate gyrus, increasing cyclic adenosine monophosphate response element binding protein phosphorylation. To gain a better understanding of the molecular actions of tocopherols and examine the link among vitamin E, somatostatin and neuronal survival, we have investigated the effects of a deficiency and subsequent administration of tocopherol on the somatostatin signaling pathway and neuronal survival in the rat hippocampus. No changes in somatostatin expression were detected in vitamin-E-deficient rats. These rats, however, showed a significant increase in the somatostatin receptor density and dissociation constant, which correlated with a significant increase in the protein levels of somatostatin receptors. Nevertheless, vitamin E deficiency impaired the ability of the somatostatin receptors to couple to the effectors adenylyl cyclase and phosphotyrosine phosphatase by diminishing Gi protein functionality. Furthermore, vitamin E deficiency significantly increased phosphotyrosine phosphatase activity and PTPη expression, as well as PKCδ activation, and decreased extracellular-signal-regulated kinase phosphorylation. All these changes were accompanied by an increase in neuronal cell death. Subsequent α-tocopherol administration partially or completely reversed all these values to control levels. Altogether, our results prove the importance of vitamin E homeostasis in the somatostatin receptor-effector system and suggest a possible mechanism by which this vitamin may regulate the neuronal cell survival in the adult hippocampus.

Leptin-induced downregulation of the rat hippocampal somatostatinergic system may potentiate its anorexigenic effects.

The learning and memory mechanisms in the hippocampus translate hormonal signals of energy balance into behavioral outcomes involved in the regulation of food intake. As leptin and its receptors are expressed in the hippocampus and somatostatin (SRIF), an orexigenic neuropeptide, may inhibit leptin-mediated suppression of food intake in other brain areas, we asked whether chronic leptin infusion induces changes in the hippocampal somatostatinergic system and whether these modifications are involved in leptin-mediated effects. We studied 18 male Wistar rats divided into three groups: controls (C), treated intracerebroventricularly (icv) with leptin (12 µg/day) for 14 days (L) and a pair-fed group (PF) that received the same amount of food consumed by the L group. Food restriction increased whereas leptin decreased the hippocampal SRIF receptor density, due to changes in SRIF receptor 2 protein levels. These changes in the PF group were concurrent with an increase of hippocampal G protein-coupled receptor kinase 2 protein levels and activation of Akt and cyclic AMP response element binding protein. The inhibitory effect of SRIF on adenylyl cyclase (AC) activity, however, was decreased in L rats, coincident with lower G inhibitory α3 and higher AC-I levels as well as signal transducer and activator of transcription factor 3 activation. In addition, 20 male Wistar rats were included to analyze whether the leptin antagonist L39A/D40A/F41A and the SRIF receptor agonist SMS 201-995 modify SRIF signaling and food intake, respectively. Administration of L39A/D40A/F41A reversed changes in SRIF signaling, whereas SMS 201-995 ameliorated food consumption in L. Altogether, these results suggest that increased somatostatinergic tone in PF rats may be a mechanism to improve the hippocampal orexigenic effects in a situation of metabolic demand, whereas down-regulation of this system in L rats may represent a mechanism to enhance the anorexigenic effects of leptin.

Effects of the antipsychotic drug haloperidol on the somastostatinergic system in SH-SY5Y neuroblastoma cells.

Antipsychotics are established drugs in schizophrenia treatment which, however, are not free of side effects. Lipid rafts are critical for normal brain function. Several G protein-coupled receptors, such as somatostatin (SRIF) receptors, have been shown to localize to lipid rafts. The aim of this study was to investigate whether haloperidol treatment affects the composition and functionality of lipid rafts in SH-SY5Y neuroblastoma cells. Haloperidol inhibited cholesterol biosynthesis, leading to a marked reduction in cell cholesterol content and to an accumulation of sterol intermediates, particularly cholesta-8,14-dien-3beta-ol. These changes were accompanied by a loss of flotillin-1 and Fyn from the lipid rafts. We next studied the functionality of the SRIF receptor. Treatment with haloperidol reduced the inhibitory effect of SRIF on adenylyl cyclase (AC) activity. On the other side, haloperidol decreased basal AC activity but increased forskolin-stimulated AC activity. Addition of free cholesterol to the culture medium abrogated the effects of haloperidol on lipid raft composition and SRIF signaling whereas the AC response to forskolin remained elevated. The results show that haloperidol, by affecting cholesterol homeostasis, ultimately alters SRIF signaling and AC activity, which might have physiological consequences.

17Beta-estradiol protects depletion of rat temporal cortex somatostatinergic system by beta-amyloid.

Estradiol prevents amyloid-beta peptide (Abeta)-induced cell death through estrogen receptors (ERs) and modulates somatostatin (SRIF) responsiveness in the rat brain. As intracerebroventricular (ICV) Abeta25-35 administration reduces SRIFergic tone in the temporal cortex of ovariectomized (Ovx) rats, we asked whether 17beta-estradiol (E2) treatment can restore the Abeta25-35 induced changes in SRIF content, SRIF receptor density and adenylyl cyclase (AC) activity, as well as if these effects are mediated by ERs. E2 treatment did not change Abeta25-35 levels in the temporal cortex, but partially restored the SRIFergic parameters affected by Abeta insult and decreased cell death, which was correlated with Akt activation. The ER antagonist ICI 182,780 prevented the protective effect of E2 on sst2 levels, but did not modify SRIF levels. Furthermore, ICI 182,780 treatment further decreased sst2 protein and mRNA levels when administered alone to Abeta25-35-treated rats, suggesting that it may block the effects of endogenous estrogens. These findings indicate that E2 protects the temporal cortical SRIFergic system from Abeta-induced depletion independently of Abeta accumulation.

Differential effects of ethanol ingestion on somatostatin content, somatostatin receptors and adenylyl cyclase activity in the frontoparietal cortex of virgin and parturient rats.

Chronic ethanol ingestion decreases the number of somatostatin (SRIF) receptors in the rat frontoparietal cortex and female sex hormones modulate the effects of ethanol in the brain. Therefore, we investigated the differential effects of ethanol consumption on the SRIFergic system in the frontoparietal cortex of virgin and parturient rats given ethanol in their drinking water before and during gestation. In parturient rats, ethanol consumption decreased the density of SRIF receptors (25%, p<0.01 vs control parturient group) whereas the SRIF-like immunoreactivity (SRIF-LI) content was increased (140%, p<0.01). In virgin rats, ethanol ingestion decreased the density of SRIF receptors (42%, p<0.01) more than in alcoholic parturient rats. SRIF-LI levels were unaffected. The inhibitory effect of SRIF on basal and forskolin-stimulated adenylyl cyclase was significantly lower in alcoholic virgin rats as compared to alcoholic parturient rats. No differences in the levels of the G inhibitory (Gi) alpha1 and Gialpha2 proteins were observed among the experimental groups. These results suggest that gestation may confer partial resistance to the ethanol-induced effect on the SRIFergic system.