L-alpha-amino adipic acid provokes depression-like behaviour and a stress related increase in dendritic spine density in the pre-limbic cortex and hippocampus in rodents.

Astrocyte dysfunction is implicated in clinical depression. There is a paucity of animal models to assess the role of astrocytes in depression pathogenesis. Refinement of an existing model is described here. Administration of the astrocytic toxin L-alpha aminoadipic acid (L-AAA) to the pre-limbic cortex (PLC) was assessed in rats and mice in tests of anxiety and depression related behaviours. Delivery of L-AAA to the PLC of Wistar rats produced an increase in immobility in the forced swimming test (FST) and reduced exploration in the open field. Delivery to the CA3 subfield of the hippocampus produced a deficit in the novel object relocation task. Delivery of single or two successive doses of L-AAA to the PLC of C57Bl6/J mice was sufficient to induce an increase in immobility in the mouse tail suspension (TST) and FST independently of administration of anaesthetic agent or the surgical procedure. In both mice and rats, L-AAA produced a reduction in immunoreactivity of the astrocytic marker glial fibrillary acidic protein (GFAP) for up to 72 h. L-AAA provoked an increase in the density of apical and basal dendritic spines in mice exposed to the FST when compared to non-FST controls. In summary, L-AAA provokes a region-dependent change in behaviour, a reduction in GFAP immunoreactivity and FST-provoked increased in dendritic spine density in the PLC. This model may be further employed to assess the impact of astroglial integrity on the structural plasticity of neurons and the effect of antidepressant agents on L-AAA-related changes.

Inhibitors of the NMDA-Nitric Oxide Signaling Pathway Protect Against Neuronal Atrophy and Synapse Loss Provoked by l-alpha Aminoadipic Acid-treated Astrocytes.

The impact of treating astrocytes with the astrocytic toxin l-alpha amino adipic acid (L-AAA) on neuronal outgrowth, complexity and synapse formation was assessed, using a model of astrocyte-neuronal interaction. Treatment of rat primary cortical neurons with conditioned media (CM) derived from astrocytes treated with L-AAA reduced neuronal complexity and synapse formation. L-AAA provoked a reduction in the expression of glial fibrillary acid protein (GFAP) and a reduction in ATP-linked mitochondrial respiration in astrocytic cells. As the NMDA-R/PSD-95/NOS signaling pathway is implicated in regulating the structural plasticity of neurons, treatment of neuronal cultures with the neuronal nitric oxide synthase (nNOS) inhibitor 1-[2-(trifluoromethyl)phenyl] imidazole (TRIM) [100 nM] was assessed and observed to protect against L-AAA-treated astrocytic CM-induced reduction in neuronal complexity and synapse loss. Treatment with the NMDA-R antagonist ketamine protected against the CM-induced loss of synapse formation whereas the novel PSD-95/nNOS inhibitors 2-((1H-benzo[d] [1,2,3]triazol-5-ylamino) methyl)-4,6-dichlorophenol (IC87201) and 4-(3,5-dichloro-2-hydroxy-benzylamino)-2-hydroxybenzoic acid (ZL006) protected against synapse loss with partial protection against reduced neurite outgrowth. Furthermore, L-AAA delivery to the pre-limbic cortex (PLC) of mice was found to increase dendritic spine density and treatment with ZL006 reduced this effect. In summary, L-AAA-induced astrocyte impairment leads to a loss of neuronal complexity and synapse loss in vitro and increased dendritic spine density in vivo that may be reversed by inhibitors of the NMDA-R/PSD-95/NOS pathway. The results have implications for understanding astrocytic-neuronal interaction and the search for drug candidates that may provide therapeutic approaches for brain disorders associated with astrocytic histopathology.