TrkB signalling in the zinc deficiency model of depression

Molecular neuropsychopharmacology the improvement of their depression scores from various relevant scales. + In wild-type 5-HT+/ 1A mice, the acute administration of the SSRIs escitalopram or fluoxetine decreased the firing rate of dorsal raphe (DR) 5-HT neurons, while the administration of the selective 5-HT1A receptor antagonist WAY100635 reversed this effect. Remarkably, the electrophysiological response induced by both SSRIs + persisted in 5-HT+/ 1A mice pretreated with WAY100635 or −/ − in 5-HT1A mice thereby demonstrating the involvement of another serotonergic receptor type in the inhibitory activity. The observation that the 5-HT2A receptor antagonist MDL100907 also reversed escitalopram-induced decrease in DR 5-HT neuronal activity indicates that the simultaneous blockade of 5-HT1A and 5-HT2A receptors is required to prevent the acute inhibitory effects of SSRIs upon the serotonergic system. It also suggests that the − activity of SSRIs might be enhanced in 5-HT−/ 2A mice after chronic treatment. However, the genetic inactivation of the 5-HT2A receptor significantly attenuated the ability of repeated administration of escitalopram or fluoxetine to increase the firing rate of DR 5-HT neurons and reduced their antidepressant-like effects in the tail suspension test or the novelty suppressed feeding paradigm. Finally, the enhancement of adult hippocampal neurogenesis induced by prolonged administration of SSRIs was blunted in − 5-HT−/ 2A mice. In depressed patients, rs6313 and rs6314 genetic variants were not associated with SSRIs response. We extended this observation to the fact that separately analysed neither escitalopram nor fluoxetine responses were altered for the rs6313. In marked contrast, a trend toward a lower percentage of improvement of depression score was detected after escitalopram treatment in homozygous individuals for the C allele of the rs6314 (p = 0.06). Altogether, these preclinical and clinical data indicate that a functional variant of the 5-HT2A receptor gene may be associated with a poor SSRIs response resulting, at least in part, from an impairment of serotonergic neurotransmission. Although this study has to be completed by determining the consequence of the C allele on the function/expression of the 5-HT2A receptor in the human brain, these results could be of particular importance to select appropriate antidepressant treatment according to the patient’s genotype. Reference(s) [1] Gardier AM, Malagi´e I, Trillat AC, Jacquot C, Artigas F. Role of 5-HT1A autoreceptors in the mechanism of action of serotoninergic antidepressant drugs: recent findings from in vivo microdialysis studies. Fundam Clin Pharmacol. 1996;10(1):16−27.

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[2] Quesseveur G, Nguyen HT, Gardier AM, Guiard BP. 5-HT2 ligands in the treatment of anxiety and depression. Expert Opin Investig Drugs. 2012 Nov;21(11):1701−25. [3] Serretti A, Drago A, De Ronchi D. HTR2A gene variants and psychiatric disorders: a review of current literature and selection of SNPs for future studies. Curr Med Chem. 2007;14(19):2053−69. Review.

P.1.020 The role of CREB/BDNF/TrkB signalling in the zinc deficiency model of depression U. Doboszewska1 ° , B. Szewczyk1 , M. Sowa-Kucma1 , K. Mlyniec2 , G. Nowak1 . 1 Polish Academy of Sciences Institute of Pharmacology, Department of Neurobiology, Krakow, Poland; 2 Jagiellonian University Medical College, Department of Biochemical Toxicology, Krakow, Poland Background: Induced zinc deficiency in adult rats significantly decreases the number of progenitor cells and immature neurons in the dentate gyrus of the rat hippocampus. Zinc deficiency, which occurs during both lactation and adulthood, increases hippocampal apoptosis. This suggests that the trace element zinc may be involved in the regulation of hippocampal neurogenesis during the early stages of life through to adulthood [1]. Neurotrophins are an important class of signalling molecules essential for the development of the central nervous system (CNS). Brain-derived neurotrophic factor (BDNF) is the best characterised of these neurotrophins in terms of its role in synaptic plasticity as well as its potential role in the pathology and treatment of a variety of psychiatric disorders. BDNF gene expression is increased by the transcription factor cyclic AMP response-element binding protein (CREB). Mature BDNF signals via the highaffinity tropomyosine-related kinase B receptor (TrkB). BDNF signalling via TrkB receptors divides into three pathways, all of which converge on the transcription factor CREB, which in turn up-regulates gene expression [2]. Aim: To examine whether zinc deprivation induces changes in the protein levels of the phosphorylated forms of CREB (pCREB), BDNF and TrkB in the prefrontal cortex and hippocampus of rats. Methods: Male Sprague-Dawley rats (5-week-old) were fed a 50 mg Zn/kg (control group) or a 3 mg Zn/kg (zincdeficient group) diet for four weeks. The protein levels of pCREB, BDNF and TrkB were measured using western blotting. Results: Four weeks of dietary zinc deprivation resulted in a significant decrease in the protein levels of pCREB,

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Molecular neuropsychopharmacology

BDNF and TrkB in the hippocampus but not in the prefrontal cortex. The level of pCREB protein was decreased by 91% whereas the level of BDNF protein was decreased by 73% in the hippocampus of the zinc-deficient rats when compared with that of the control animals. At the same time point a decrease (by 40%) in TrkB protein was observed in the hippocampus of the zinc-deficient group compared to the control group. Conclusions: The previous studies indicated that dietary-induced zinc deficiency leads to the development of depressive like behaviour (e.g. increase in the immobility time in the forced swim test) and that experimentally induced zinc deficiency might be a model of depression. The present data suggests that pCREB, BDNF and TrkB expression is modulated by zinc deficiency and that the decreased expression of these proteins after dietary zinc deprivation is linked to the depressive like behaviour in the zinc deficiency paradigm. It seems that the hippocampus, the region of the brain that plays a critical role in neurogenesis, is more susceptible to the biochemical changes caused by zinc deficiency than the prefrontal cortex. This is consistent with data obtained during experiments where acute and chronic stress paradigms were found to decrease the expression of BDNF in the rodent hippocampus [1]. Reference(s) [1] Levenson, C.W., Morris, D., 2011. Zinc and neurogenesis: making new neurons from development to adulthood. Adc Nutr 2, 96–100. [2] Autry, A.E., Monteggia, L.M., 2012. Brain-derived neurotrophic factor and neuropsychiatric disorders. Pharmacol Rev 64, 238–258. P.1.021 Chronic administration of haloperidol in rats and its effect on microglial cell density and whole brain weight and volume

emission tomography (PET) radiotracer, which acts as a marker of neuroinflammation [2]. While these are changes since the start of medication, it is not possible to differentiate between changes arising from medication and those occurring with the progression of the disease. Here we dose na¨ıve rats with haloperidol (Hal) to test the hypotheses that anitpsychotic drugs induce brain volume loss and microglial activation. Methods: We used subcutaneous drug pellets to slowly release Hal over a two-week period in randomised mixed cages of control (n = 9) and medicated (n = 9) male Sprague Dawley rats. The drug pellets released a 0.05 mg/kg/day dose, control animals were implanted with a placebo pellet. The dose used is a comparatively low dose in terms of preclinical literature, with a similarly low D2 receptor occupancy when compared with clinical data (calculated from Samha et al., 2008 [3]). Following perfusion, brains were dissected for post mortem analysis. The weights of brains were measured and whole brain volumes were calculated using water displacement. The brain tissue was then processed for immunohistochemistry, where changes in microglial cell number were determined to assess neuroinflammatory associated changes. Results: Here we show that there is a significant reduction in both brain weight and volume in Hal treated animals (2.57 g (±0.088 SEM), 1583.3 mm3 (±105.4 SEM)) when compared with placebo controls (2.78 g (±0.111 SEM), 2166.7 mm3 (±153.7 SEM)) (p < 0.05, independent samples t-test). Immunohistochemical quantification of colocalised Iba-1 and DAPI stains was used to determine the number of microglial cells in the following 800 mm2 regions of interest (ROIs); the prefrontal cortex, hippocampus and ventral striatum. There was a consistent increase in microglial number across the 3 regions in drug treated animals (see table), which trended toward significance (p = 0.07). Mean Iba-1 positive cells counts in cortical ROIs PFC (±SEM)

Hippocampus (±SEM)

Striatum (±SEM)

59.0 (±11.1) 62.0 (±12.4)

25.3 (±5.1) 51.3 (±13.2)

69.2 (±16.1) 85.3 (±19.4)

P.S. Bloomfield1 ° , O.D. Howes1 , V. de Paola2 . 1 MRC Clinical Sciences Centre, Psychiatric Imaging, London, United Kingdom; 2 MRC Clinical Sciences Centre, Neuroplasticity and Disease, London, United Kingdom

Placebo Haloperidol

Introduction: Patients with schizophrenia are routinely prescribed antipsychotic medication. Magnetic resonance imaging (MRI) in newly medicated patients has demonstrated how, over a 5 year period, there is an average whole brain structural deficit of 8%, with regional losses of up to 20%, when compared to baseline [1]. Another study investigating schizophrenic patients demonstrate an increase in binding with the [C11 ]PK11195 positron

Conclusions: The results we have seen here show how a low dose of a typical antipsychotic medication is able to produce significant changes in the brains of na¨ıve rats. Further investigation is required to determine the full effects of these changes and the mechanism involved. An experiment investigating the effects of a higher dose regime is in progress and will be used to investigate inflammatory changes further alongside