Leptin-induced downregulation of the rat hippocampal somatostatinergic system may potentiate its anorexigenic effects Arancha Perianes-Cachero a , Emma Burgos-Ramos b,d , Lilian Puebla-Jiménez a , Sandra Canelles b,d , María Paz Viveros e , Virginia Mela b,d,e , Julie A. Chowen b,d , Jesús Argente b,c,d , Eduardo Arilla-Ferreiro a,⇑ , Vicente Barrios b,d,⇑ a Neurobiochemistry Unit, Department of Biochemistry and Molecular Biology, Facultad de Medicina, Universidad de Alcalá, Alcalá de Henares, E-28871 Madrid, Spain b Department of Endocrinology, Hospital Infantil Universitario Niño Jesús, Instituto de Investigación La Princesa, Madrid, Spain c Department of Pediatrics, Universidad Autónoma de Madrid, E-28009 Madrid, Spain d Centro de Investigación Biomédica en Red de Fisiopatología Obesidad y Nutrición (CIBERobn), Instituto de Salud Carlos III, E-28009 Madrid, Spain e Department of Physiology (Animal Physiology II), Faculty of Biology, Universidad Complutense de Madrid, E-28040 Madrid, Spain article info Article history: Received 16 May 2012 Received in revised form 24 September 2012 Accepted 30 September 2012 Available online 13 October 2012 Keywords: Hippocampus Food restriction Leptin Somatostatin Somatostatin receptor abstract 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 lep- tin-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 lg/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, coinci- dent with lower G inhibitory a3 and higher AC-I levels as well as signal transducer and activator of tran- scription 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 somatostat- inergic 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. Ó 2012 Elsevier Ltd. All rights reserved. 1. Introduction Recent evidence points towards a role of the hippocampus, a brain area critical in learning and memory functions, in energy regulation (Davidson et al., 2009). This potential role is based on the presence of receptors for hormones involved in the regulation of food intake (Paulus et al., 2005), on the negative effects of satu- rated fat-rich diets on hippocampal oxidative stress and cognitive processes related to energy homeostasis (Morrison et al., 2010) and on the impairment of functional plasticity in obesity (Grillo et al., 2011). In addition, hippocampal damage in rats is related to augmented appetite and food responses, leading to increased body weight (Davidson et al., 2010). Moreover, amnesic patients seem to be unable to inhibit the intake of a second meal because of the absence of memory of the recent meal (Higgs, 2005). Somatostatin (SRIF), one of the most abundant peptides in the central nervous system (CNS), has a role in modulating different 0197-0186/$ - see front matter Ó 2012 Elsevier Ltd. All rights reserved. http://dx.doi.org/10.1016/j.neuint.2012.09.019 Abbreviations: AC, adenylyl cyclase; CREB, cyclic AMP response element binding protein; Gi, GTP-binding inhibitory protein; GRK, G-protein-coupled receptor kinase; IFNc, interferon-c; IL, interleukin; SDS, sodium dodecyl sulfate; SOCS3, suppressor of cytokine signaling 3; SRIF, somatostatin, SRIF-LI, somatostatin-like immunoreactivity; sst, somatostatin receptor subtype; STAT3, signal transducer and activator of transcription factor 3; TTBS, Tris-Tween buffered saline. ⇑ Corresponding authors. Tel.: +34 91 8854509; fax: +34 91 8854585 (E. Arilla- Ferreiro), tel.: +34 91 5035900; fax: +34 91 5035939 (V. Barrios). E-mail addresses: eduardo.arilla@uah.es (E. Arilla-Ferreiro), vbarrios@telefonica. net (V. Barrios). Neurochemistry International 61 (2012) 1385–1396 Contents lists available at SciVerse ScienceDirect Neurochemistry International journal homepage: www.elsevier.com/locate/nci