P.2.032 - ZL006 has antidepressant effects and attenuates changes in dendritic spines associated with astrocytic impairment in mice

Abstract

The NMDA receptor (NMDA-R) remains a promising target for treating CNS disorders including depression. Directly targeting NMDA-R is however liable to produce unwanted adverse effects. Previous studies demonstrate that nitric oxide (NO) synthase inhibitors are capable of attenuating behavioural deficits in preclinical animal models of depression. We hypothesise that uncoupling neuronal NO synthase from the NMDA-R through the scaffolding postsynaptic density protein 95 (PSD-95) produces antidepressant effects similar to NMDA-R antagonists and NO synthase inhibitors [1]. Small-molecule inhibitors of the PSD-95/nNOS interaction, 2-((1H-benzo-[d]-[1,2,3] triazol-5-ylamino)-methyl)-4,6dichlorophenol (IC87201) and 4-(3,5-dichloro-2-hydroxy-benzylamino)-2-hydroxybenzoic acid (ZL006) produced sustained antidepressant-like responses in the forced swimming test (FST) and tail suspension test (TST) following intraperitoneal administration in mice [2]. This investigation extends preliminary findings by further assessing the antidepressant-related effects of these compounds. Stereotactic delivery of the astrocytic toxin L-alpha-amino adipic acid (L-AAA) to the pre-limbic cortex (PLC) provokes depressive-like behaviour in the FST and reduced immunoreactivity of the astrocytic marker glial fibrillary acidic protein (GFAP) in mice. L-AAA-induced astrocytic dysfunction in the PLC has been proposed as a useful animal model of astrocyte impairment in depression [3]. We investigate if L-AAA-induced alterations in cortical dendritic spine morphology are associated with depression-related behaviours. The aims of this study were to determine (i) the antidepressant-like properties of ZL006 in the FST following L-AAA-induced astrocytic impairment in the PLC, and (ii) the corresponding changes to dendritic spines in the mouse PLC. L-AAA (50 μg/μl; 1μl, or control PBS) was stereotactically delivered to the PLC of C57Bl/6 mice. Mice were treated with vehicle or ZL006 (10 mg/kg injected intraperitoneally) 48h following L-AAA delivery and exposed to FST at 72h. Animals were subsequently transcardially perfused. Post mortem GFAP immunoreactivity and Golgi-cox dendritic spine analyses (superGolgi Kit, Bioenno Tech) were performed on coronal sections. Image stacks were analysed and spines were quantified and classified morphologically as mushroom, thin or stubby using NeuronStudio. Data are expressed as mean and standard error of the mean and analysed by ANOVA and Student Newman Keuls post-hoc test where P 72h following L-AAA administration mice displayed increased immobility time in the FST, indicative of depression-related behaviour. ZL006 attenuated the increased immobility time observed in the FST in keeping with its previously reported antidepressant effects. As expected, L-AAA reduced GFAP immunoreactivity in the PLC. A decrease in thin and mushroom spines was observed on neuronal dendrites 72h following L-AAA administration. ZL006 treatment alone had no effect on dendritic spine density but opposed changes to thin and mushroom spines on basal dendrites in L-AAA treated mice. These results demonstrate that astrocyte impairment in the PLC provokes a depression-related phenotype and changes in dendritic spine morphology and treatment with ZL006 can attenuate such behavioural and structural changes. Further investigation is essential to assess the functional impact of such changes and the consequences for neuronal connectivity and regional brain function. These data contribute to a growing body of evidence linking astrocyte impairment to depression-related behaviours, supporting the hypothesis that selectively targeting the NMDA-R/PSD-95/nNOS complex produces antidepressant effects.