Neuroscience Letters 457 (2009) 12–15 Contents lists available at ScienceDirect Neuroscience Letters journal homepage: www.elsevier.com/locate/neulet Effects of chronic fluoxetine treatment on the rat somatosensory cortex: Activation and induction of neuronal structural plasticity R. Guirado, E. Varea, E. Castillo-Gómez, M.A. Gómez-Climent, L. Rovira-Esteban, J.M. Blasco-Ibá ˜ nez, C. Crespo, F.J. Martínez-Guijarro, J. Nàcher ∗ Neurobiology Unit and Program in Basic and Applied Neurosciences, Cell Biology Dpt., Universitat de València., Spain article info Article history: Received 3 February 2009 Received in revised form 27 March 2009 Accepted 30 March 2009 Keywords: Spine density Structural plasticity c-fos GAD67 Antidepressant PSA-NCAM abstract Recent hypotheses support the idea that disruption of normal neuronal plasticity mechanisms underlies depression and other psychiatric disorders, and that antidepressant treatment may counteract these changes. In a previous report we found that chronic fluoxetine treatment increases the expression of the polysialylated form of the neural cell adhesion molecule (PSA-NCAM), a molecule involved in neuronal structural plasticity, in the somatosensory cortex. In the present study we intended to find whether, in fact, cell activation and neuronal structural remodeling occur in parallel to changes in the expression of this molecule. Using immunohistochemistry, we found that chronic fluoxetine treatment caused an increase in the expression of the early expression gene c-fos. Golgi staining revealed that this treatment also increased spine density in the principal apical dendrite of pyramidal neurons. These results indicate that, apart from the medial prefrontal cortex or the hippocampus, other cortical regions can respond to chronic antidepressant treatment undergoing neuronal structural plasticity. © 2009 Elsevier Ireland Ltd. All rights reserved. Although the neurobiological bases of depression are not well understood, it has been proposed that dysfunction of the mech- anisms of neuronal plasticity may be involved [3,6]. Moreover, antidepressant drugs may act by normalizing this neural plastic- ity [6,5,13]. Structural plastic processes, such as dendritic or spine remodelling, have been observed in animal models of depres- sion [12,37] and after antidepressant treatment [10], specially in the amygdala, the hippocampus and the medial prefrontal cortex (mPFC) (see [24] for review). This structural remodelling may be mediated by changes in the expression of cytoskeletal proteins or cell adhesion molecules, such as the polysialylated form of the neural cell adhesion molecule (PSA-NCAM) [2,8,30]. In fact, the antidepressant fluoxetine, a serotonin reuptake inhibitor, increases the expression of PSA-NCAM in the mPFC, the hippocampal CA3 stratum lucidum and the visual and somatosensory cortices [38,39]. To date, there is no direct evidence that the somatosensory cortex is affected by depression, although animal models of this mental disorder show alterations in the physiology of this cortical region [35] and antidepressants modulate somatosensory-related functions when administered locally [15]. The finding of an altered expression of PSA-NCAM in the somatosensory cortex after chronic ∗ Corresponding author at: Neurobiology, Cell Biology Dpt., Universitat de Valèn- cia, Dr. Moliner, 50, Burjassot, 46100, Valencia, Spain. Tel.: +34 96 354 3241; fax: +34 96 354 3404. E-mail address: nacher@uv.es (J. Nàcher). treatment with fluoxetine [39] has prompted us to study whether the structure and activity of this cortical region is also modified after antidepressant treatment. We have used twelve male Sprague–Dawley rats (4 months old, 320 ± 50 g, Harlan Iberica), which were chronically injected intraperitoneally either with the antidepressant fluoxetine (n = 6, 10 mg/kg), or with saline solution (n = 6), during 14 days (once daily at 10.00 am). All animal experimentation was conducted in accordance with the European Communities Council Directive of 24 November 1986 (86/609/EEC). Rats were perfused transcar- dially under deep chloral hydrate anaesthesia (chloral hydrate at 4%, 1 mL/100 g) with saline and then 4% paraformaldehyde in sodium phosphate buffer (PB 0.1 M, pH 7.4). After perfusion, the brains were extracted and stored in PB until used. In order to study cellular activation in the somatosensory cor- tex the left hemisphere was cut into 50 m thick sections with a freezing sliding microtome and immunohistochemically stained for the immediate early gene c-fos. Briefly, sections were incu- bated with 5% normal donkey serum (NDS) (Abcys) in PBS with 0.2% Triton-X100 (Sigma) for 1h, and then overnight with rab- bit polyclonal anti-c-fos K25 (1:2000; Santa Cruz Biotechnology, Inc.). After washing, sections were incubated for 30 min with bio- tinilated donkey anti-rabbit IgG (1:200; Jackson Immunoresearch), followed by an avidin-biotin-peroxidase complex (ABC, Vector Lab- oratories) for 30 min in PBS. Color development was achieved by incubating with 3,3 ′ -diaminobenzidine tetrahydrochloride (DAB, Sigma) for 4 min. All the sections were coded to avoid any bias and, 0304-3940/$ – see front matter © 2009 Elsevier Ireland Ltd. All rights reserved. doi:10.1016/j.neulet.2009.03.104