The microRNA-455 Null Mouse Has Memory Deficit and Increased Anxiety, Targeting Key Genes Involved in Alzheimer’s Disease

The complete molecular mechanisms underlying the pathophysiology of Alzheimer’s disease (AD) remain to be elucidated. Recently, microRNA-455-3p has been identified as a circulating biomarker of early AD, with increased expression in post-mortem brain tissue of AD patients. MicroRNA-455-3p also directly targets and down-regulates APP, with the overexpression of miR-455-3p suppressing its toxic effects. Here, we show that miR-455-3p expression decreases with age in the brains of wild-type mice. We generated a miR-455 null mouse utilising CRISPR-Cas9 to explore its function further. Loss of miR-455 resulted in increased weight gain, potentially indicative of metabolic disturbances. Furthermore, performance on the novel object recognition task diminished significantly in miR-455 null mice (p = 0.004), indicating deficits in recognition memory. A slight increase in anxiety was also captured on the open field test. BACE1 and TAU were identified as new direct targets for miR-455-3p, with overexpression of miR-455-3p leading to a reduction in the expression of APP, BACE1 and TAU in neuroblastoma cells. In the hippocampus of miR-455 null mice at 14 months of age, the levels of protein for APP, BACE1 and TAU were all increased. Such findings reinforce the involvement of miR-455 in AD progression and demonstrate its action on cognitive performance.

Inhibition of PDE4 by Roflumilast ameliorates sleep deprivation-induced cognitive dysfunction in C57BL/6J mice

Sleep deprivation interferes with long-term memory and cognitive functions by over-activation of phosphodiesterase (PDE) enzymes. PDE4 is a non-redundant regulator of the cyclic nucleotides (cAMP), is densely expressed in the hippocampus, and is involved in learning and memory processes. In the present study, we investigated the effects of Roflumilast (ROF), a PDE4 inhibitor, on sleep deprivation induced cognitive dysfunction in a mouse model. Memory assessment was performed using a novel object recognition task and the cAMP level was estimated by ELISA. The alterations in the expressions of PDE4B, amyloid beta, CREB, BDNF, and synaptic proteins (Synapsin I, SAP 97, PSD 95) were assessed to gain insights on the possible mechanisms of action of ROF using the western blot technique. Results show that ROF reverse SD induced cognitive decline in mice. ROF down-regulated PDE4B and amyloid beta expressions. Additionally, ROF improved cAMP levels and the expressions of synapsin I, SAP 97, and PSD 95 in the hippocampal region of SD mice. Taken together, these results suggest that ROF can suppress the deleterious effects of SD-induced cognitive dysfunction via PDE4-mediated cAMP/CREB/BDNF cascade.

Immune system challenge improves recognition memory and reverses malaria-induced cognitive impairment in mice

The immune system plays a role in the maintenance of healthy neurocognitive function. Different patterns of immune response triggered by distinct stimuli may affect nervous functions through regulatory or deregulatory signals, depending on the properties of the exogenous immunogens. Here, we investigate the effect of immune stimulation on cognitive-behavioural parameters in healthy mice and its impact on cognitive sequelae resulting from non-severe experimental malaria. We show that immune modulation induced by a specific combination of immune stimuli that induce a type 2 immune response can enhance long-term recognition memory in healthy adult mice subjected to novel object recognition task (NORT) and reverse a lack of recognition ability in NORT and anxiety-like behaviour in a light/dark task that result from a single episode of mild Plasmodium berghei ANKA malaria. Our findings suggest a potential use of immunogens for boosting and recovering recognition memory that may be impaired by chronic and infectious diseases and by the effects of ageing.

Transient Astrocytic Gq Signaling Underlies Remote Memory Enhancement

Astrocytes elicit transient Ca2+ elevations induced by G protein-coupled receptors (GPCRs), yet their role in vivo remains unknown. To address this, transgenic mice with astrocytic expression of the optogenetic Gq-type GPCR, Optoα1AR, were established, in which transient Ca2+ elevations similar to those in wild type mice were induced by brief blue light illumination. Activation of cortical astrocytes resulted in an adenosine A1 receptor-dependent inhibition of neuronal activity. Moreover, sensory stimulation with astrocytic activation induced long-term depression of sensory evoked response. At the behavioral level, repeated astrocytic activation in the anterior cortex gradually affected novel open field exploratory behavior, and remote memory was enhanced in a novel object recognition task. These effects were blocked by A1 receptor antagonism. Together, we demonstrate that GPCR-triggered Ca2+ elevation in cortical astrocytes has causal impacts on neuronal activity and behavior.

Beta-caryophyllene, a CB2R selective agonist, protects against cognitive impairment caused by neuro-inflammation and not in dementia due to ageing induced by mitochondrial dysfunction

Background: Dementia is a neurodegenerative disorder majorly evidenced by cognitive impairment. Although there are many types of dementia, the common underlying etiological factors in all the types are neuro-inflammation or ageing induced apoptosis. β-caryophyllene, a cannabinoid type-2 receptor agonist has reported to have promising neuroprotective effects in cerebral ischemia and neuro-inflammation. Objective: In the present study, we evaluated the effects of β-caryophyllene, against animal models of dementia whose etiology mimicked neuro-inflammation and ageing. Method: Two doses (50 and 100 mg/kg of body weight) of β-caryophyllene given orally were tested against AlCl3-induced dementia in male Sprague Dawley (SD) rats using Morris water maze test. Subsequently, the effect of the drug was assessed for episodic memory in female SD rats using novel object recognition task in doxorubicin-induced neuro-inflammation and male SD rats for chemobrain model. Moreover, its effects were evaluated in D-galactose-induced mitochondrial dysfunction leading to dementia. Results: β-caryophyllene, at both the doses, showed significant improvement in memory when assessed using parameters like target quadrant entries, escape latency and path efficiency in Morris water maze test for spatial memory. In the doxorubicin-induced chemobrain model, β-caryophyllene at 100 mg/kg significantly elevated acetylcholinesterase and catalase levels and lowered lipid peroxidation compared to the disease control. In the novel object recognition task, β-caryophyllene at 100 mg/kg significantly improved recognition index and discrimination index in the treated animals compared to the disease control, with a significant increase in catalase and decrease in lipid peroxidation in both hippocampus and frontal cortex. However, in D-galactose-induced mitochondrial dysfunction model, β-caryophyllene failed to show positive effects when spatial memory was assessed. It also failed to improve D-galactose induced diminished mitochondrial complex I and II activities. Conclusion: Hence, we conclude that β-caryophyllene at 100 mg/kg protects against dementia induced by neuro-inflammation with no effect on neuronal aging induced by mitochondrial dysfunction.

Microglia control glutamatergic synapses in the adult mouse hippocampus

ABSTRACTMicroglial cells are active players in regulating synaptic development and plasticity in the brain. However, how these cells influence the normal functioning of synapses is largely unknown. In this study, we characterized the effects of pharmacological depletion of microglia, achieved by administration of PLX5622, on hippocampal CA3-CA1 synapses of adult wild type mice. Following microglial depletion, we observed a reduction of spontaneous and evoked glutamatergic activity associated with a decrease of dendritic spine density. We also observed the appearance of immature synaptic features accompanied by higher levels of plasticity. In addition, microglia depleted mice showed a deficit in the acquisition of the Novel Object Recognition task. Remarkably, microglial repopulation after PLX5622 withdrawal was associated with the recovery of hippocampal synapses and learning functions. Altogether, these data demonstrate that microglia contribute to normal synaptic functioning in the adult brain and that their removal induces reversible changes in synaptic organization and activity of glutamatergic synapses.

Dissociating the effects of distraction and proactive interference on object memory through tests of novelty preference

Encoding information into memory is sensitive to distraction while retrieving that memory may be compromised by proactive interference from pre-existing memories. These two debilitating effects are common in neuropsychiatric conditions, but modelling them preclinically to date is slow as it requires prolonged operant training. A step change would be the validation of functionally equivalent but fast, simple, high-throughput tasks based on spontaneous behaviour. Here, we show that spontaneous object preference testing meets these requirements in the subchronic phencyclidine rat model for cognitive impairments associated with schizophrenia. Subchronic phencyclidine rats show clear memory sensitivity to distraction in the standard novel object recognition task. However, due to this, standard novel object recognition task cannot assess proactive interference. Therefore, we compared subchronic phencyclidine performance in standard novel object recognition task to that using the continuous novel object recognition task, which offers minimal distraction, allowing disease-relevant memory deficits to be assessed directly. We first determined that subchronic phencyclidine treatment did not affect whisker movements during object exploration. Subchronic phencyclidine rats exhibited the expected distraction standard novel object recognition task effect but had intact performance on the first continuous novel object recognition task trial, effectively dissociating distraction using two novel object recognition task variants. In remaining continuous novel object recognition task trials, the cumulative discrimination index for subchronic phencyclidine rats was above chance throughout, but, importantly, their detection of object novelty was increasingly impaired relative to controls. We attribute this effect to the accumulation of proactive interference. This is the first demonstration that increased sensitivity to distraction and proactive interference, both key cognitive impairments in schizophrenia, can be dissociated in the subchronic phencyclidine rat using two variants of the same fast, simple, spontaneous object memory paradigm.