Differential effects of alkaloids on memory in rodents

Maternal nicotine exposure promotes hippocampal CeRNA-mediated excitotoxicity and social barriers in adolescent offspring mice

Nicotine, an addictive component of cigarettes, causes cognitive defects, particularly when exposure occurs early in life. However, the exact mechanism through which nicotine causes toxicity and alters synaptic plasticity is still not fully understood. The aim of the current study is to examine how non-coding developmental regulatory RNA impacts the hippocampus of mice offspring whose mothers were exposed to nicotine. Female C57BL/6J mice were given nicotine water from one week before pregnancy until end of lactation. Hippocampal tissue from offspring at 20 days post-birth was used for LncRNA and mRNA microarray analysis. Differential expression of LncRNAs and mRNAs associated with neuronal development were screened and validated, and the CeRNA pathway mediating neuronal synaptic plasticity GM13530/miR-7119-3p/mef2c was predicted using LncBase Predicted v.2. Using protein immunoblotting, Golgi staining and behavioral tests, our findings revealed that nicotine exposure in offspring mice increased hippocampal NMDAR receptor, activated receptor-dependent calcium channels, enhanced the formation of NMDAR/nNOS/PSD95 ternary complexes, increased NO synthesis, mediated p38 activation, induced neuronal excitability toxicity. Furthermore, an epigenetic CeRNA regulatory mechanism was identified, which suppresses Mef2c-mediated synaptic plasticity and leads to modifications in the learning and social behavior of the offspring during adolescence. This study uncovers the way in which maternal nicotine exposure results in neurotoxicity in offspring.

SIRT6 Improves Hippocampal Neurogenesis Following Prolonged Sleep Deprivation Through Modulating Energy Metabolism in Developing rats

OBJECTIVE

Prolonged sleep deprivation is known to have detrimental effects on the hippocampus during development or in adulthood. Furthermore, it is well-established that sleep deprivation disrupts energy metabolism broadly. SIRT6 is a critical regulator of energy metabolism in both central and peripheral tissues. This study aims to investigate the role of SIRT6 in modulating hippocampal neurogenesis following sleep deprivation during development, and elucidate the underlying mechanism.

METHODS

Male Sprague-Dawley rats, aged three weeks, were subjected to 2 weeks of sleep deprivation using the modified multiple platform method. Metabolomic profiling was carried out using the liquid chromatography-electrospray ionization-tandem mass spectrometry (LC‒ESI‒MS/MS). To investigate the role of SIRT6 in energy metabolism, the rats were administered with either the SIRT6-specific inhibitor, OSS128167, or SIRT6-overexpressing adeno-associated virus (AAV). Hippocampal neurogenesis was assessed by immunostaining with markers for neural stem cells (SOX2), immature neurons [doublecortin (DCX)] and newborn cells (BrdU). Sparse labeling of adult neurons was used to determine the density of dendritic spines in the dentate gyrus (DG). The Y-maze and novel object recognition (NOR) tests were performed to evaluate the spatial and recognition memory. SIRT6 expression was examined using immunofluorescence and western blotting (WB). The inhibition of SIRT6 was confirmed by assessing the acetylation of histone 3 lysine 9 (aceH3K9), a well-known substrate of SIRT6, through WB.

RESULTS

Sleep deprivation for a period of two weeks leads to inhibited hippocampal neurogenesis, reduced density of dendritic spines in the DG, and impaired memory, accompanied by decreased SIRT6 expression and disrupted energy metabolism. Similar to sleep deprivation, administration of OSS128167 significantly decreased energy metabolism, leading to reduced neurogenesis and memory dysfunction. Notably, the abnormal hippocampal energy metabolism, neurogenetic pathological changes and memory dysfunction caused by sleep deprivation were alleviated by SIRT6 overexpression in the DG.

CONCLUSION

Our results suggest that SIRT6 plays a critical role in maintaining energy metabolism homeostasis in the hippocampus after sleep deprivation, promoting hippocampal neurogenesis and enhancing memory during development.

Current Progress on Central Cholinergic Receptors as Therapeutic Targets for Alzheimer's Disease

Acetylcholine (ACh) is ubiquitously present in the nervous system and has been involved in the regulation of various brain functions. By modulating synaptic transmission and promoting synaptic plasticity, particularly in the hippocampus and cortex, ACh plays a pivotal role in the regulation of learning and memory. These procognitive actions of ACh are mediated by the neuronal muscarinic and nicotinic cholinergic receptors. The impairment of cholinergic transmission leads to cognitive decline associated with aging and dementia. Therefore, the cholinergic system has been of prime focus when concerned with Alzheimer's disease (AD), the most common cause of dementia. In AD, the extensive destruction of cholinergic neurons occurs by amyloid-β plaques and tau protein-rich neurofibrillary tangles. Amyloid-β also blocks cholinergic receptors and obstructs neuronal signaling. This makes the central cholinergic system an important target for the development of drugs for AD. In fact, centrally acting cholinesterase inhibitors like donepezil and rivastigmine are approved for the treatment of AD, although the outcome is not satisfactory. Therefore, identification of specific subtypes of cholinergic receptors involved in the pathogenesis of AD is essential to develop future drugs. Also, the identification of endogenous rescue mechanisms to the cholinergic system can pave the way for new drug development. In this article, we discussed the neuroanatomy of the central cholinergic system. Further, various subtypes of muscarinic and nicotinic receptors involved in the cognition and pathophysiology of AD are described in detail. The article also reviewed primary neurotransmitters that regulate cognitive processes by modulating basal forebrain cholinergic projection neurons.

Integrative metabolomics science in Alzheimer's disease: Relevance and future perspectives

Alzheimer's disease (AD) is determined by various pathophysiological mechanisms starting 10-25 years before the onset of clinical symptoms. As multiple functionally interconnected molecular/cellular pathways appear disrupted in AD, the exploitation of high-throughput unbiased omics sciences is critical to elucidating the precise pathogenesis of AD. Among different omics, metabolomics is a fast-growing discipline allowing for the simultaneous detection and quantification of hundreds/thousands of perturbed metabolites in tissues or biofluids, reproducing the fluctuations of multiple networks affected by a disease. Here, we seek to critically depict the main metabolomics methodologies with the aim of identifying new potential AD biomarkers and further elucidating AD pathophysiological mechanisms. From a systems biology perspective, as metabolic alterations can occur before the development of clinical signs, metabolomics - coupled with existing accessible biomarkers used for AD screening and diagnosis - can support early disease diagnosis and help develop individualized treatment plans. Presently, the majority of metabolomic analyses emphasized that lipid metabolism is the most consistently altered pathway in AD pathogenesis. The possibility that metabolomics may reveal crucial steps in AD pathogenesis is undermined by the difficulty in discriminating between the causal or epiphenomenal or compensatory nature of metabolic findings.

Selective Menin Deletion in the Hippocampal CA1 Region Leads to Disruption of Contextual Memory in the MEN1 Conditional Knockout Mouse: Behavioral Restoration and Gain of Function following the Reintroduction of MEN1 Gene

Cholinergic neuronal networks in the hippocampus play a key role in the regulation of learning and memory in mammals. Perturbations of these networks, in turn, underlie neurodegenerative diseases. However, the mechanisms remain largely undefined. We have recently demonstrated that an in vitro MEN1 gene deletion perturbs nicotinic cholinergic plasticity at the hippocampal glutamatergic synapses. Furthermore, MEN1 neuronal conditional knockout in freely behaving animals has also been shown to result in learning and memory deficits, though the evidence remains equivocal. In this study, using an AVV viral vector transcription approach, we provide direct evidence that MEN1 gene deletion in the CA1 region of the hippocampus indeed leads to contextual fear conditioning deficits in conditional knockout animals. This loss of function was, however, recovered when the same animals were re-injected to overexpress MEN1. This study provides the first direct evidence for the sufficiency and necessity of MEN1 in fear conditioning, and further endorses the role of menin in the regulation of cholinergic synaptic machinery in the hippocampus. These data underscore the importance of further exploring and revisiting the cholinergic hypothesis that underlies neurodegenerative diseases that affect learning and memory.

D-cycloserine rescues scopolamine-induced deficits in cognitive flexibility in rats measured by the attentional set-shifting task

Cognitive flexibility facilitates adaptions to a changing environment in humans and animals and can be assessed with the attentional set shifting task (ASST). In various learning paradigms for laboratory rodents, the partial NMDA receptor agonist D-cycloserine has been found to have pro-cognitive effects. However, D-cycloserine has not yet been investigated for its effects on cognitive flexibility. The aim of the present study was to determine whether D-cycloserine is able to improve cognitive flexibility measured by the ASST in rats. Rats were first pre-treated with the muscarinic antagonist scopolamine (0.5 mg/kg) before the D-cycloserine administrations (20 mg/kg) to induce deficits in ASST performance. Our findings showed impaired ASST performance after scopolamine administration with significant effects on reversal phases and extra-dimensional shift. D-cycloserine treatment selectively improved the performance in the extra-dimensional shift and the last reversal phase, where scopolamine effects were most pronounced. These findings suggest that D-cycloserine can rescue deficits in cognitive flexibility.

Effects of Artemisia macrocephala Jacquem on Memory Deficits and Brain Oxidative Stress in Streptozotocin-Induced Diabetic Mice

Different species of Artemisia have been reported to have therapeutic potential in treating various health disorders, including diabetes and memory dysfunction. The present study was planned to evaluate the effects of Artemisia macrocephala Jacquem crude extract and its subfractions as antiamnesic agents in streptozotocin-induced (STZ) diabetic mice. The in vivo behavioral studies were performed using the Y Maze test and novel object recognition test (NORT) test at doses of 100 and 200 mg/kg of crude extract and 75 and 150 mg/kg of fractions. The in vitro and ex vivo anticholinesterase activities, along with biochemical parameters (superoxide dismutase, catalase, glutathione and lipid peroxidation) in the brain, were evaluated. Blood glucose levels were monitored with a glucometer; crude extract and fractions reduced the glucose level considerably, with some differences in the extent of their efficacies. The crude extract and fractions demonstrated significant inhibitory activity against cholinesterases (AChE and BuChE) in vitro. Crude, chloroform and ethyl acetate extract were found to be more potent than the other fractions, with IC50 of Crd-Am = 116.36 ± 1.48 and 240.52 ± 1.35 µg/mL, Chl-Am = 52.68 ± 1.09 and 57.45 ± 1.39 µg/mL and Et-Am = 75.19 ± 1.02 and 116.58 ± 1.09 µg/mL, respectively. Oxidative stress biomarkers like superoxide dismutase, catalase and glutathione levels were elevated, whereas MDA levels were reduced by crude extract and all fractions with little difference in their respective values. The Y-maze test and novel object recognition test demonstrated declines in memory impairment in groups (n = 6) treated with crude extract and fractions as compared to STZ diabetic (amnesic) group. The most active fraction, Chl-Am, was also subjected to isolation of bioactive compounds; three compounds were obtained in pure state and designated as AB-I, AB-II and AB-III. Overall, the results of the study showed that Artemisia macrocephala Jacquem enhanced the memory impairment associated with diabetes, elevated acetylcholine levels and ameliorated oxidative stress. Further studies are needed to explore the beneficial role of the secondary metabolites isolated in the present study as memory enhancers. Toxicological aspects of the extracts are also important and need to be evaluated in other animal models.

Effects of Moringa oleifera in Two Independents Formulation and as Neuroprotective Agent Against Scopolamine-Induced Memory Impairment in Mice

Background

The cognitive deficit has frequently been found in the elderly population. Several studies have shown that every single part of Moringa oleifera, including leaves, roots, and seeds, has abundant micronutrients, such as flavonoids, which improve the neurobehavioral capacity. However, herb parts that display optimal neuropharmacological properties remain unknown.

Objective

We investigate whether M. oleifera seed oil (MOO) or aqueous M. oleifera leaves extracts (MOEs) may ameliorate memory impairment in mice induced with scopolamine (Sco). Additionally, the phytochemical analyses of those two independent formulations were analyzed.

Methods

In this study, 2 ml/kg body weight (BW) of MOO and 500 mg/kg BW of MOE were orally administered to the mice for 28 days, followed by intraperitoneal injection of Sco (1 mg/kg) at the day 22–28 to induce cognitive impairment in those mice.

Results

The Sco group showed memory retention impairment represented by the Y-maze and novel object recognition tests, significant enhancement of acetylcholine esterase (AChE) activity in hippocampus tissue (p < 0.0001), and increased the level of total antioxidant capacity (TAOC) in serum. Interestingly, the Sco-induced memory defect was improved and completely blunted the AChE exacerbation in Sco+MOO-treated mice (p < 0.0001), although the TAOC level was comparable among the groups. Mechanistically, both tropomyosin receptor kinase B (TrkB), as a brain-derived neurotrophic factor-receptor, and nuclear factor-kappa-light-chain-enhancer of activated B cells (NF-κB) protein expressions were enhanced with the hippocampus isolated from the Sco group. Nonetheless, pretreatment with MOO only, but not with MOE, ameliorated the enhanced protein expression levels of TrkB and NF-κB (p < 0.05 and p = 0.09, respectively).

Conclusion

Our data reveal that MOO is preferable to MOE as a neuroprotective as evidenced by improving memory impairment. This effect, at least in part, through inhibiting the AChE and NF-κB activities and modulating the TrkB expression level.

Non-motor connections of the pedunculopontine nucleus of the rat and human brain

INTRODUCTION

The connections of the pedunculopontine nucleus (PPN) with motor areas of the central nervous system (CNS) are well described in the literature, in contrast relations with non-motor areas are lacking. Thus, the aim of the present study is to define the non-motor connections of the PPN in rats using the fluoro-gold (FG) tracer and compare the presence of these connections in healthy human adults using diffusion tensor tractography (DTI).

MATERIALS AND METHODS

We injected FG into the PPN of 12 rats. The non-motor connections of the PPN with cortical, subcortical, and brainstem structures were documented. The non-motor connections of the rats were compared with the DTI obtained from 35 healthy adults.

RESULTS

The results of the tract-tracing study in the rat showed that the PPN was connected to non-motor cortical (cingulate, somatosensory, visual, auditory, medial frontal cortices), subcortical (amygdala, hypothalamus, thalamus, habenular, and bed nucleus of stria terminalis), and brainstem (medullary reticular, trigeminal spinal, external cuneate, pontine reticular, vestibular, superior and inferior colliculus, locus ceruleus, periaqueductal gray, parabrachial, dorsal raphe, pretectal, lateral lemniscus nuclei, and the contralateral PPN) structures. The DTI obtained from healthy adults showed similar PPN non-motor connections as in rats.

CONCLUSION

Understanding the connections of the PPN with non-motor cortical, subcortical, and brainstem areas of the CNS will enrich our knowledge of its contribution in various circuits and the areas that PPN activity can influence. Further, it will provide insight into the role of Parkinson's disease and related disorders and explain the non-motor complications which occur subsequent to deep brain stimulation (DBS) of the PPN.

Cotinine: Pharmacologically Active Metabolite of Nicotine and Neural Mechanisms for Its Actions

Tobacco use disorder continues to be a leading public health issue and cause of premature death in the United States. Nicotine is considered as the major tobacco alkaloid causing addiction through its actions on nicotinic acetylcholine receptors (nAChRs). Current pharmacotherapies targeting nicotine's effects produce only modest effectiveness in promoting cessation, highlighting the critical need for a better understanding of mechanisms of nicotine addiction to inform future treatments. There is growing interest in identifying potential contributions of non-nicotine components to tobacco reinforcement. Cotinine is a minor alkaloid, but the major metabolite of nicotine that can act as a weak agonist of nAChRs. Accumulating evidence indicates that cotinine produces diverse effects and may contribute to effects of nicotine. In this review, we summarize findings implicating cotinine as a neuroactive metabolite of nicotine and discuss available evidence regarding potential mechanisms underlying its effects. Preclinical findings reveal that cotinine crosses the blood brain barrier and interacts with both nAChRs and non-nAChRs in the nervous system, and produces neuropharmacological and behavioral effects. Clinical studies suggest that cotinine is psychoactive in humans. However, reviewing evidence regarding mechanisms underlying effects of cotinine provides a mixed picture with a lack of consensus. Therefore, more research is warranted in order to provide better insight into the actions of cotinine and its contribution to tobacco addiction.