Synergistic and additive effects of enriched environment and lithium on the generation of new cells in adult mouse hippocampus

Synergistic but not additive effect between ACPA and lithium in the dorsal hippocampal region on spatial learning and memory in rats: Isobolographic analyses

Lithium and cannabinoids can disrupt learning and memory performance. The goal of the present study is to investigate the additive or synergistic effect of lithium and cannabinoid combination doses on spatial learning and memory in rats by isobolographic analyses. Although several studies have suggested synergistic effects of cannabinoids or lithium in response to other compounds, in most of them isobolographic analyses were not used; Thus, there is a need for more detailed studies using isobolographic analyses. In this study, spatial memory was evaluated in the Morris Water Maze (MWM) apparatus by eight trials in the training day and one trial in the test day. Lithium was injected intraperitoneal and ACPA (cannabinoid type 1 receptor agonist) was injected into the dorsal hippocampal region (intra-CA1). For the isobolographic analyses, the ED50 of lithium (2.5 mg/kg) and ACPA (0.5 μg/rat) was measured by linear regression analysis, considering the doses were tested in our previous research. The results showed that, combinations of low, medium and high doses of lithium (0.312 mg/kg, 0.625 mg/kg and 1.25 mg/kg, respectively) and ACPA (0.0625 μg/rat, 0.125 μg/rat and 0.25 μg/rat, respectively) had synergistic but not additive effect on spatial learning and spatial memory. In conclusion, we suggest that combination doses of lithium and ACPA have synergistic but not additive effect on spatial learning and memory in the rat's dorsal hippocampal region.

Lithium activates brain phospholipase A2 and improves memory in rats: implications for Alzheimer's disease

Phospholipase A2 (Pla2) is required for memory retrieval, and its inhibition in the hippocampus has been reported to impair memory acquisition in rats. Moreover, cognitive decline and memory deficits showed to be reduced in animal models after lithium treatment, prompting us to evaluate possible links between Pla2, lithium and memory. Here, we evaluated the possible modulation of Pla2 activity by a long-term treatment of rats with low doses of lithium and its impact in memory. Wistar rats were trained for the inhibitory avoidance task, treated with lithium for 100 days and tested for perdurability of long-term memory. Hippocampal samples were used for quantifying the expression of 19 brain-expressed Pla2 genes and for evaluating the enzymatic activity of Pla2 using group-specific radio-enzymatic assays. Our data pointed to a significant perdurability of long-term memory, which correlated with increased transcriptional and enzymatic activities of certain members of the Pla2 family (iPla2 and sPla2) after the chronic lithium treatment. Our data suggest new possible targets of lithium, add more information on its pharmacological activity and reinforce the possible use of low doses of lithium for the treatment of neurodegenerative conditions such as the Alzheimer's disease.

Long-Term Lithium Treatment Increases cPLA₂ and iPLA₂ Activity in Cultured Cortical and Hippocampal Neurons

Background: Experimental evidence supports the neuroprotective properties of lithium, with implications for the treatment and prevention of dementia and other neurodegenerative disorders. Lithium modulates critical intracellular pathways related to neurotrophic support, inflammatory response, autophagy and apoptosis. There is additional evidence indicating that lithium may also affect membrane homeostasis. Objective: To investigate the effect of lithium on cytosolic phospholipase A₂ (PLA₂) activity, a key player on membrane phospholipid turnover which has been found to be reduced in blood and brain tissue of patients with Alzheimer’s disease (AD). Methods: Primary cultures of cortical and hippocampal neurons were treated for 7 days with different concentrations of lithium chloride (0.02 mM, 0.2 mM and 2 mM). A radio-enzymatic assay was used to determine the total activity of PLA₂ and two PLA₂ subtypes: cytosolic calcium-dependent (cPLA₂); and calcium-independent (iPLA₂). Results: cPLA₂ activity increased by 82% (0.02 mM; p = 0.05) and 26% (0.2 mM; p = 0.04) in cortical neurons and by 61% (0.2 mM; p = 0.03) and 57% (2 mM; p = 0.04) in hippocampal neurons. iPLA₂ activity was increased by 7% (0.2 mM; p = 0.04) and 13% (2 mM; p = 0.05) in cortical neurons and by 141% (0.02 mM; p = 0.0198) in hippocampal neurons. Conclusion: long-term lithium treatment increases membrane phospholipid metabolism in neurons through the activation of total, c- and iPLA₂. This effect is more prominent at sub-therapeutic concentrations of lithium, and the activation of distinct cytosolic PLA₂ subtypes is tissue specific, i.e., iPLA₂ in hippocampal neurons, and cPLA₂ in cortical neurons. Because PLA₂ activities are reported to be reduced in Alzheimer’s disease (AD) and bipolar disorder (BD), the present findings provide a possible mechanism by which long-term lithium treatment may be useful in the prevention of the disease.