Novel effects on memory observed following unilateral intracranial administration of okadaic acid, cyclosporin A, FK506 and [MeVal4]CyA

Effects Following Intracerebroventricular Injection of Immunosuppressant Cyclosporine A On Inhibitory Avoidance Learning and Memory in Mice

Background:

Protein phosphatase-2B or calcineurin (CN) is the main phosphatase and a critical regulator of cellular pathways for learning, memory, and plasticity. Cyclosporine A(CyA), a phosphatase and peptidyl-prolyl cis/trans isomerase inhibitor, is a common immune suppressant extensively used in tissue transplantation. To further clarify the role of CN in different stages of learning and memory, the aim of the present study was to evaluate the role of CyA in an inhibitory avoidance (IA) model in mice.

Materials and Methods:

Using intracerebroventricular (ICV) injection of different doses of CyA (0.5, 5, and 50 nM) at different periods (pre-/post-training and pre-test), the effect of the drug was evaluated in a step-down IA paradigm. The latency of step-down (sec) was considered a criterion for memory performance.

Results:

The pre-training injections of CyA (0.5, 5 nM), however not of 50 nM, impaired IA learning acquisition. The post-training injection of high-dose CyA (50 nM) impaired memory consolidation. The pre-test ICV CyA injection did not impair memory retrieval; the ICV injection of CyA caused no change in locomotion.

Conclusion:

These findings suggest that CyA selectively interferes with acquisition, retention, but not retrieval, of information processing in mice. Given the crucial role of CN in common signaling pathway of memory performance and cognition, it could be a probable therapeutic target in the treatment of a wide variety of neurological conditions involving memory.

Lead dysregulates serine/threonine protein phosphatases in human neurons

It is well established that lead (Pb) exposure in humans leads to learning and memory impairment. However, the biological and molecular mechanisms are still not clearly understood. When over activated, serine/threonine protein phosphatases are known to function as a constraint on learning and memory. Activation of these phosphatases can also result in cytoskeletal changes that will adversely affect learning and memory. We investigated the effects of Pb exposure on these phosphatases in primary cultures of human neurons. Neurons were exposed to physiologically relevant concentrations of Pb (5, 10, 20 and 40 μg/dL) and total phosphatase and PP2A activities were determined in neuronal lysate using para-nitrophenyl phosphate (pNPP), and a PP2A-specific phosphopeptide as substrates. Expression of various serine/threonine phosphatases, tau and its phosphorylation state were determined by Western blot (WB) and immunocytochemistry (ICC). We found that the total phosphatase activity in the neuronal lysate was increased by 30–50% by all the concentrations of Pb tested. PP2A activity was increased by 5 μg/dL Pb only. PP1 expression was increased (ranging from 25–50%) by 10, 20 and 40 μg/dL of Pb. PP2B expression was increased substantially (up to 2.5-fold) by 10 μg/dL Pb, whereas, higher concentrations did not show any effect. On the other hand, Pb (at all concentrations used) decreased expression of PP2A and PP5. Pb exposure induced substantial hyperphosphorylation of tau at serine 199/202 by 5 and 10 μg/dL Pb, and Threonine 231 at higher doses. Expression of total tau was mostly unaffected by lead. Immunocytochemistry data confirmed the WB results of expression of PP1, PP2A, tau protein and the phosphorylation of tau. These results support our hypothesis that Pb exposure up regulates some of the serine/threonine phosphatases (PP1 and PP2B) that are known to impair memory formation, and suggest a novel mechanism of Pb neurotoxicity.

Effects of intrahippocampal administration of the phosphatase inhibitor okadaic acid: Dual effects on memory formation

Protein phosphorylation mediated by serine-threonine kinases in the hippocampus is crucial to the synaptic modifications believed to underlie memory formation. The role of phosphatases has been the focus of comparatively little study.

Olanzapine attenuates the okadaic acid-induced spatial memory impairment and hippocampal cell death in rats

It is hypothesized that olanzapine, an atypical antipsychotic drug, has beneficial effects on cognitive impairment and neuropathological changes in treating neurodegenerative diseases. In the present study, we investigated the effects of chronic administration of olanzapine on the spatial memory impairment and hippocampal cell death induced by the direct injection of okadaic acid (OA), a potent neurotoxin, into the rat hippocampus. After being pretreated with olanzapine (0.5 or 2 mg/kg/day, i.p.) for 2 weeks, the rats were unilaterally microinjected with OA (100 ng) into the hippocampus, and then were continuously administrated with olanzapine for an additional week The rats were trained on a spatial memory task in an eight-arm radial maze before OA administration, and tested on the same task 18 h after the last olanzapine injection. After the behavioral test, the rats were killed for Nissl staining and terminal deoxynucleutidyl transferase-mediated biotinylated UTP nick end labeling staining. OA significantly induced spatial memory impairment, and caused pyramidal cell loss in the CAI and apoptotic cell death in the hippocampus. Olanzapine significantly attenuated OA-induced spatial memory impairment and the OA-induced neuropathological changes in the hippocampus. These findings suggest that olanzapine may have therapeutic effects in treatment of cognitive impairment and neuropathological changes of schizophrenia and other neurodegenerative diseases.

The role of protein phosphatase-1 in the modulation of synaptic and structural plasticity

Synaptic plasticity is a phenomenon contributing to changes in the efficacy of neuronal transmission. These changes are widely believed to be a major cellular basis for learning and memory. Protein phosphorylation is a key biochemical process involved in synaptic plasticity that operates through a tight balance between the action of protein kinases and protein phosphatases (PPs). Although the majority of research in this field has concentrated primarily on protein kinases, the significant role of PPs is becoming increasingly apparent. This review examines one such phosphatase, PP1, and highlights recent advances in the understanding of its intervention in synaptic and structural plasticity and the mechanisms of learning and memory.