The cholinergic system and hippocampal plasticity

5-Fluorouracil Impairs Transmission of Acetylcholine in the Hippocampus and Induces Cognitive Impairments in Mice

BACKGROUND

Chemotherapy-induced cognitive impairments are a significant adverse sequela of cancer treatment. The potential mechanism of chemotherapy-induced cognitive impairments remains elusive. The present study evaluated the impact of a commonly utilized chemotherapy agent, 5-fluorouracil (5-FU), on acetylcholine (ACh) levels in the hippocampus.

METHODS

5-FU was injected into mice once a day for 10 days to create a mouse model of chemotherapy-induced cognitive impairment. Microdialysis and HPLC-MS/MS were used to determine hippocampal ACh levels. Biocytin injection and patch-clamp recordings were performed on cholinergic (ChAT) neurons in the medial septum (MS) to observe their morphological and electrophysiological changes. Chemogenetic tools were used to activate ChAT neurons in the MS. The acetylcholinesterase inhibitor donepezil was injected i.p. into mice to elevate ACh levels in the brain.

RESULTS

Cognitive performance in mice was impaired after 5-FU treatment, accompanied by reduced ACh release in the hippocampus. The administration of 5-FU led to compromised structural integrity and diminished activity of ChAT neurons in the MS. Chemogenetic stimulation of MS ChAT neurons ameliorated the cognitive impairments. The administration of donepezil also reduced the cognitive impairments caused by 5-FU.

CONCLUSIONS

5-FU therapy caused cognitive impairments in mice by affecting the neuronal structure and activity of ChAT neurons in the MS. Inducing the increase of ACh levels could be a promising therapeutic approach for addressing 5-FU treatment-induced cognitive impairments.

Electrophysiological insights into Alzheimer's disease: A review of human and animal studies

This review highlights the crucial role of neuroelectrophysiology in illuminating the mechanisms underlying Alzheimer's disease (AD) pathogenesis and progression, emphasizing its potential to inform the development of effective treatments. Electrophysiological techniques provide unparalleled precision in exploring the intricate networks affected by AD, offering insights into the synaptic dysfunction, network alterations, and oscillatory abnormalities that characterize the disease. We discuss a range of electrophysiological methods, from non-invasive clinical techniques like electroencephalography and magnetoencephalography to invasive recordings in animal models. By drawing on findings from these studies, we demonstrate how electrophysiological research has deepened our understanding of AD-related network disruptions, paving the way for targeted therapeutic interventions. Moreover, we underscore the potential of electrophysiological modalities to play a pivotal role in evaluating treatment efficacy. Integrating electrophysiological data with clinical neuroimaging and longitudinal studies holds promise for a more comprehensive understanding of AD, enabling early detection and the development of personalized treatment strategies. This expanded research landscape offers new avenues for unraveling the complexities of AD and advancing therapeutic approaches.

PLB2Tau mice are impaired in novel and temporal object recognition and show corresponding traits in brain MRI

Recent clinical trials targeting tau protein aggregation have heightened interest in tau-based therapies for dementia. Success of such treatments depends crucially on translation from non-clinical animal models. Here, we present the age profile of the PLB2Tau knock-in model of fronto-temporal dementia in terms of cognition, and by utilising a directly translatable magnetic resonance imaging approach. Separate cohorts of mice aged 3, 6 and 12 months were tested in an object recognition protocol interrogating visual, spatial, and temporal discrimination in consecutive tests. Upon completion of their behavioural testing, animals were recorded in a 7 T MRI for brain structural integrity and diffusion tensor imaging (DTI) analysis. We report that PLB2Tau mice presented with an age-dependent deficit in novel object discrimination relative to wild-type controls at 6 and 12 months. Spatial and temporal discrimination, though not significantly different from controls, appeared extremely challenging for PLB2Tau subjects, especially at 12 months, since they explored objects less than controls and were devoid of memory. Controls readily recalled all relevant object-related information. At the same time, the T2 weighted voxel-based image analysis revealed a progressive shrinkage of total brain volumes in 6- and 12-month-old PLB2Tau mice as well as relative striatal, but not hippocampal volumes. A regional DTI analysis yielded only reduced mean diffusivity of the fimbria, but not CA1 or dentate gyrus, amygdala, cingulate cortex, or corpus callosum. These data confirm the PLB2Tau mouse as a translationally useful model for dementia research and suggest the importance of the hippocampal input as a determinant for novel object discrimination.

Structural Neuroimaging and Molecular Signatures of Drug-Naive Depression With Melancholic Features

Objectives: Melancholic depression (MD) is a common subtype of major depressive disorder (MDD). It is difficult to treat because its neurobiological basis is poorly understood. Therefore, to investigate whether MD patients have any structural changes in gray matter (GM) and the molecular foundation of these changes, we combined voxel-based morphometry (VBM) analysis with neurotransmitter system-derived mapping from public data. Methods: 137 drug-naive MDD patients and 75 healthy controls (HCs) were recruited for structural magnetic resonance imaging. The imaging results were analyzed using VBM analysis. MDD patients were then divided into MD and nonmelancholic depression (NMD) subgroups according to their scores on the Montgomery-Asberg Depression Rating Scale (MADRS) and the Hamilton Depression Rating Scale. Next, we analyzed the spatial correlation between the changes in the gray matter volume (GMV) maps and the neurotransmitter receptor/transporter protein density maps provided by the JuSpace toolbox. Results: Compared to HCs, patients with MD had significant GMV reduction in the bilateral hippocampus, bilateral thalamus, right amygdala, and right posterior cingulate cortex (PCC)/precuneus. Compared to patients with NMD, MD patients had significant GMV reduction in the bilateral PCC/precuneus and lateral occipital cortex. Moreover, compared to HCs, changes in GMV introduced by MD were spatially associated with the serotonin transporter, cannabinoid receptor, and μ-opioid receptor. Compared to NMD patients, changes in GMV introduced by MD were spatially associated with the vesicular acetylcholine transporter. Conclusion: The present study discovered abnormal GMV alterations in patients with subtypes of depression. We also found a series of neurotransmitter receptors that may be associated with the alterations. The findings of the current study may provide a more comprehensive understanding of the molecular mechanisms underlying the structural abnormalities in subtypes of depression and potentially offer new insights into developing new therapeutic strategies.

Selenium toxicity in fishes: A current perspective

Anthropogenic activities have led to increased levels of contaminants that pose significant threats to aquatic organisms, particularly fishes. One such contaminant is Selenium (Se), a metalloid which is released by various industrial activities including mining and fossil fuel combustion. Selenium is crucial for various physiological functions, however it can bioaccumulate and become toxic at elevated concentrations. Given that fishes are key predators in aquatic ecosystems and a major protein source for humans, Se accumulation raises considerable ecological and food safety concerns. Selenium induces toxicity at the cellular level by disrupting the balance between reactive oxygen species (ROS) production and antioxidant capacity leading to oxidative damage. Chronic exposure to elevated Se impairs a wide range of critical physiological functions including metabolism, growth and reproduction. Selenium is also a potent teratogen and induces various types of adverse developmental effects in fishes, mainly due to its maternal transfer to the eggs. Moreover, that can persist across generations. Furthermore, Se-induced oxidative stress in the brain is a major driver of its neurotoxicity, which leads to impairment of several ecologically important behaviours in fishes including cognition and memory functions, social preference and interactions, and anxiety response. Our review provides an up-to-date and in-depth analysis of the various adverse physiological effects of Se in fishes, while identifying knowledge gaps that need to be addressed in future research for greater insights into the impact of Se in aquatic ecosystems.

The dopamine analogue CA140 alleviates AD pathology, neuroinflammation, and rescues synaptic/cognitive functions by modulating DRD1 signaling or directly binding to Abeta

BACKGROUND

We recently reported that the dopamine (DA) analogue CA140 modulates neuroinflammatory responses in lipopolysaccharide-injected wild-type (WT) mice and in 3-month-old 5xFAD mice, a model of Alzheimer's disease (AD). However, the effects of CA140 on Aβ/tau pathology and synaptic/cognitive function and its molecular mechanisms of action are unknown.

METHODS

To investigate the effects of CA140 on cognitive and synaptic function and AD pathology, 3-month-old WT mice or 8-month-old (aged) 5xFAD mice were injected with vehicle (10% DMSO) or CA140 (30 mg/kg, i.p.) daily for 10, 14, or 17 days. Behavioral tests, ELISA, electrophysiology, RNA sequencing, real-time PCR, Golgi staining, immunofluorescence staining, and western blotting were conducted.

RESULTS

In aged 5xFAD mice, a model of AD pathology, CA140 treatment significantly reduced Aβ/tau fibrillation, Aβ plaque number, tau hyperphosphorylation, and neuroinflammation by inhibiting NLRP3 activation. In addition, CA140 treatment downregulated the expression of cxcl10, a marker of AD-associated reactive astrocytes (RAs), and c1qa, a marker of the interaction of RAs with disease-associated microglia (DAMs) in 5xFAD mice. CA140 treatment also suppressed the mRNA levels of s100β and cxcl10, markers of AD-associated RAs, in primary astrocytes from 5xFAD mice. In primary microglial cells from 5xFAD mice, CA140 treatment increased the mRNA levels of markers of homeostatic microglia (cx3cr1 and p2ry12) and decreased the mRNA levels of a marker of proliferative region-associated microglia (gpnmb) and a marker of lipid-droplet-accumulating microglia (cln3). Importantly, CA140 treatment rescued scopolamine (SCO)-mediated deficits in long-term memory, dendritic spine number, and LTP impairment. In aged 5xFAD mice, these effects of CA140 treatment on cognitive/synaptic function and AD pathology were regulated by dopamine D1 receptor (DRD1)/Elk1 signaling. In primary hippocampal neurons and WT mice, CA140 treatment promoted long-term memory and dendritic spine formation via effects on DRD1/CaMKIIα and/or ERK signaling.

CONCLUSIONS

Our results indicate that CA140 improves neuronal/synaptic/cognitive function and ameliorates Aβ/tau pathology and neuroinflammation by modulating DRD1 signaling in primary hippocampal neurons, primary astrocytes/microglia, WT mice, and aged 5xFAD mice.

Complexity decline of hippocampal CA1 circuit model due to cholinergic deficiency associated with Alzheimer's disease

A hallmark of Alzheimer's disease (AD) is cholinergic system dysfunction, directly affecting the hippocampal neurons. Previous experiments have demonstrated that reduced complexity is one significant effect of AD on electroencephalography (EEG). Motivated by these, this study explores reduced EEG complexity of cholinergic deficiency in AD by neurocomputation. We first construct a new hippocampal CA1 circuit model with cholinergic action. M-current I M and calcium-activated potassium current I AHP are newly introduced in the model to describe cholinergic input from the medial septum. Then, by enhancing I M and I AHP to mimic cholinergic deficiency, how cholinergic deficiency influences the model complexity is investigated by sample entropy (SampEn) and approximate entropy (ApEn). Numerical results show a more severe cholinergic deficit with lower model complexity. Furthermore, we conclude that the decline of SampEn and ApEn is due to the greatly diminished excitability of model neurons. These suggest that decreased neuronal excitability due to cholinergic impairment may contribute to reduced EEG complexity in AD. Subsequently, statistical analysis between simulated AD patients and normal control (NC) groups demonstrates that SampEn and auto-mutual-information (AMI) decrease rates significantly differ. Compared to NC, AD patients have a lower SampEn and a less negative AMI decline rate. These imply a low rate of new-generation information in AD brains with cholinergic deficits. Interestingly, the statistical correlation between SampEn and AMI is analyzed, and they have a large negative Pearson correlation coefficient. Thus, AMI reduction rates may be a complementary tool for complex analysis. Our modeling and complex analysis are expected to provide a deeper understanding of the reduced EEG complexity resulting from cholinergic deficiency.

Updating functional brain units: Insights far beyond Luria

This paper reviews Luria's model of the three functional units of the brain. To meet this objective, several issues were reviewed: the theory of functional systems and the contributions of phylogenesis and embryogenesis to the brain's functional organization. This review revealed several facts. In the first place, the relationship/integration of basic homeostatic needs with complex forms of behavior. Secondly, the multi-scale hierarchical and distributed organization of the brain and interactions between cells and systems. Thirdly, the phylogenetic role of exaptation, especially in basal ganglia and cerebellum expansion. Finally, the tripartite embryogenetic organization of the brain: rhinic, limbic/paralimbic, and supralimbic zones. Obviously, these principles of brain organization are in contradiction with attempts to establish separate functional brain units. The proposed new model is made up of two large integrated complexes: a primordial-limbic complex (Luria's Unit I) and a telencephalic-cortical complex (Luria's Units II and III). As a result, five functional units were delineated: Unit I. Primordial or preferential (brainstem), for life-support, behavioral modulation, and waking regulation; Unit II. Limbic and paralimbic systems, for emotions and hedonic evaluation (danger and relevance detection and contribution to reward/motivational processing) and the creation of cognitive maps (contextual memory, navigation, and generativity [imagination]); Unit III. Telencephalic-cortical, for sensorimotor and cognitive processing (gnosis, praxis, language, calculation, etc.), semantic and episodic (contextual) memory processing, and multimodal conscious agency; Unit IV. Basal ganglia systems, for behavior selection and reinforcement (reward-oriented behavior); Unit V. Cerebellar systems, for the prediction/anticipation (orthometric supervision) of the outcome of an action. The proposed brain units are nothing more than abstractions within the brain's simultaneous and distributed physiological processes. As function transcends anatomy, the model necessarily involves transition and overlap between structures. Beyond the classic approaches, this review includes information on recent systemic perspectives on functional brain organization. The limitations of this review are discussed.

Early exposure to trans fat causes cognitive impairment by modulating the expression of proteins associated with oxidative stress and synaptic plasticity in Drosophila melanogaster

Evidence has shown that consuming trans fatty acids (TFA) during development leads to their incorporation into the nervous tissue, resulting in neurological changes in flies. In this study, Drosophila melanogaster was exposed to different concentrations of hydrogenated vegetable fat (HVF) during development: substitute hydrogenated vegetable fat (SHVF), HVF 10 %, and HVF 20 %. The objective was to evaluate the effects of early trans fat exposure on cognition and associated pathways in flies. The results showed that early TFA exposure provoked a cerebral redox imbalance, as confirmed by increased reactive species (HVF 10 and 20 %) and lipid peroxidation (SHVF, HVF 10, and 20 %), reduced nuclear factor erythroid 2-related factor 2 immunoreactivity (HVF 10 and 20 %), and increased heat shock protein 70 (HVF 20 %), which was possibly responsible for decreasing superoxide dismutase (SHVF, HVF 10, and 20 %) and catalase (HVF 20 %) activities. Furthermore, the presence of TFA in nervous tissue impaired learning (HVF 10 and 20 %) and memory at 6 and 24 h (SHVF, HVF 10, and 20 %). These cognitive impairments may be linked to reduced Shank levels (HVF 20 %) and increased acetylcholinesterase activity (SHVF, HVF 10 and 20 %) observed. Our findings demonstrate that early exposure to trans fat leads to cerebral redox imbalance, altering proteins associated with stress, synaptic plasticity, and the cholinergic system, consequently leading to cognitive impairment in flies.

The effects of choline supplementation in mothers with hypothyroidism on the alteration of cognitive-behavioral, long-term potentiation, morphology, and apoptosis in the hippocampus of pre-pubertal offspring rats

The mother's thyroid hormone status during gestation and the first few months after delivery can play a crucial role in maturation during the brain development of the child. Transient abnormalities in thyroid function at birth indicate developmental and cognitive disorders in adulthood. Choline supplementation during gestation and the perinatal period in rats causes long-lasting memory improvement in the offspring. However, it remains unclear whether choline is able to restore the deficits in rats with maternal hypothyroidism. The aim of this study was to evaluate the effects of choline supplementation on the alteration of cognitive-behavioral function, long-term potentiation (LTP), and morphological changes as well as apoptosis in pre-pubertal offspring rats. To induce hypothyroidism, 6-propyl-2-thiouracil was added to the drinking water from the 6th day of gestation to the 21st postnatal day (PND). Choline treatment was started twice a day on the first day of the gestation until PND 21 via gavage. LTP recording and Morris water maze (MWM) test were conducted at PND 28. Then, the rats were sacrificed to assess their brains. The results revealed that developmental thyroid hormone deficiency impaired spatial learning and memory and reduced LTP (both: P < 0.001). Choline treatment alleviated LTP (P < 0.001), as well as learning and memory deficits (P < 0.01) in both male and female hypothyroid rats. However, no significant changes were observed in the number of caspase-3 stained cells in choline-receiving hypothyroid groups. The results revealed that developmental thyroid hormone deficiency impaired spatial learning and memory and reduced LTP. Choline treatment alleviated LTP, as well as learning and memory deficits in both male and female hypothyroid rats.

An essential role for the RNA helicase DDX6 in NMDA receptor-dependent gene silencing and dendritic spine shrinkage

MicroRNAs (miRNAs) repress translation of target mRNAs by associating with Argonaute (Ago) proteins in the RNA-induced silencing complex (RISC) to modulate protein expression. Specific miRNAs are required for NMDA receptor (NMDAR)-dependent synaptic plasticity by repressing the translation of proteins involved in dendritic spine morphogenesis. Rapid NMDAR-dependent silencing of Limk1 is essential for spine shrinkage and requires Ago2 phosphorylation at S387. Not all gene silencing events are modulated by S387 phosphorylation, and the mechanisms that govern the selection of specific mRNAs for silencing downstream of S387 phosphorylation are unknown. Here, we show that NMDAR-dependent S387 phosphorylation causes a rapid and transient increase in the association of Ago2 with Limk1, but not Apt1 mRNA. The specific increase in Limk1 mRNA binding to Ago2 requires recruitment of the helicase DDX6 to RISC. Furthermore, we show that DDX6 is required for NMDAR-dependent silencing of Limk1 via miR-134, but not Apt1 via miR-138, and is essential for NMDAR-dependent spine shrinkage. This work defines a novel mechanism for the rapid transduction of NMDAR stimulation into miRNA-mediated translational repression of specific genes to control dendritic spine morphology.

Hippocampal acetylcholine receptor activation-dependent long-term depression in streptozotocin-induced diabetic rats

Cholinergic innervation of the hippocampus correlates with memory formation. In a well-established animal model of type 1 diabetes mellitus, obtained by injecting young adult rats with streptozotocin (STZ), reductions have been reported in the expression of acetylcholine receptors and choline acetyltransferase. In this study, we showed that long-term synaptic depression (LTD) induced by carbachol (CCh), a nonselective cholinergic receptor agonist, at Schaffer collateral-CA1 synapses in hippocampal slices was significantly weaker in streptozotocin-induced diabetic rats (STZ rats) than in age-matched control rats. No significant change was observed in the paired-pulse ratio between before and 80 min after the application of CCh in control and STZ rats. Moreover, CCh-induced LTD in control and STZ rats was not affected by an NMDA receptor antagonist. Although the application of CCh down-regulated the surface expression of GluA2 in the hippocampus of control rats, but not STZ rats. Therefore, the present results suggest that acetylcholine receptor-mediated LTD in STZ rats requires the internalization of AMPA receptors on the postsynaptic surface and their intracellular effects in the hippocampus.

The looming threat of profenofos organophosphate and microbes in action for their sustainable degradation

Organophosphates are the most extensively used class of pesticides to deal with increasing pest diversity and produce more on limited terrestrial areas to feed the ever-expanding global population. Profenofos, an organophosphate group of non-systematic insecticides and acaricides, is used to combat aphids, cotton bollworms, tobacco budworms, beet armyworms, spider mites, and lygus bugs. Profenofos was inducted into the system as a replacement for chlorpyrifos due to its lower toxicity and half-life. It has become a significant environmental concern due to its widespread presence. It accumulates in various environmental components, contaminating food, water, and air. As a neurotoxic poison, it inhibits acetylcholinesterase receptor activity, leading to dizziness, paralysis, and pest death. It also affects other eukaryotes, such as pollinators, birds, mammals, and invertebrates, affecting ecosystem functioning. Microbes directly expose themselves to profenofos and adapt to these toxic compounds over time. Microbes use these toxic compounds as carbon and energy sources and it is a sustainable and economical method to eliminate profenofos from the environment. This article explores the studies and developments in the bioremediation of profenofos, its impact on plants, pollinators, and humans, and the policies and laws related to pesticide regulation. The goal is to raise awareness about the global threat of profenofos and the role of policymakers in managing pesticide mismanagement.

Ethanol extract of Evodia lepta Merr. ameliorates cognitive impairment through inhibiting NLRP3 inflammasome in scopolamine-treated mice

Evodia lepta Merr. (Evodia lepta) is a well-known traditional Chinese medicine, which has been widely used in herbal tea. We previously reported that the coumarin compounds from the root of Evodia lepta exhibited neuroprotective effects. However, whether Evodia lepta could inhibit NLRP3 inflammasome in dementia was still unknown. In this study, the components of the Evodia lepta extract were identified by HPLC-Q-TOF HRMS. We employed a scopolamine-treated mouse model. Evodia lepta extract (10 or 20 mg/kg) and donepezil were treated by gavage once a day for 14 consecutive days. Following the behavioral tests, oxidative stress levels were measured. Then, Western blot and immunofluorescence analysis were used to evaluate the expressions of NLRP3 inflammasome. 14 major components of the Evodia lepta extract were identified by HPLC-Q-TOF HRMS. The results of Morris water maze, object recognition task and open field test indicated that Evodia lepta extract could ameliorate cognitive impairment in scopolamine-treated mice. Evodia lepta extract improved cholinergic system. Moreover, Evodia lepta extract improved the expressions of PSD95 and BDNF. Evodia lepta extract suppressed neuronal oxidative stress and apoptosis. In addition, Evodia lepta extract inhibited NLRP3 inflammasome in the hippocampus of scopolamine-treated mice. Evodia lepta extract could protect against cognitive impairment by inhibiting NLRP3 inflammasome in scopolamine-treated mice.

Neuromodulation via muscarinic acetylcholine pathway can facilitate distinct, complementary, and sequential roles for NREM and REM states during sleep-dependent memory consolidation

Across vertebrate species, sleep consists of repeating cycles of NREM followed by REM. However, the respective functions of NREM, REM, and their stereotypic cycling pattern are not well understood. Using a simplified biophysical network model, we show that NREM and REM sleep can play differential and critical roles in memory consolidation primarily regulated, based on state-specific changes in cholinergic signaling. Within this network, decreasing and increasing muscarinic acetylcholine (ACh) signaling during bouts of NREM and REM, respectively, differentially alters neuronal excitability and excitatory/inhibitory balance. During NREM, deactivation of inhibitory neurons leads to network-wide disinhibition and bursts of synchronized activity led by firing in engram neurons. These features strengthen connections from the original engram neurons to less-active network neurons. In contrast, during REM, an increase in network inhibition suppresses firing in all but the most-active excitatory neurons, leading to competitive strengthening/pruning of the memory trace. We tested the predictions of the model against in vivo recordings from mouse hippocampus during active sleep-dependent memory storage. Consistent with modeling results, we find that functional connectivity between CA1 neurons changes differentially at transition from NREM to REM sleep during learning. Returning to the model, we find that an iterative sequence of state-specific activations during NREM/REM cycling is essential for memory storage in the network, serving a critical role during simultaneous consolidation of multiple memories. Together these results provide a testable mechanistic hypothesis for the respective roles of NREM and REM sleep, and their universal relative timing, in memory consolidation.

Significance statement

Using a simplified computational model and in vivo recordings from mouse hippocampus, we show that NREM and REM sleep can play differential roles in memory consolidation. The specific neurophysiological features of the two sleep states allow for expansion of memory traces (during NREM) and prevention of overlap between different memory traces (during REM). These features are likely essential in the context of storing more than one new memory simultaneously within a brain network.

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.

Memory Recovery Effect of a New Bioactive Innovative Combination in Rats with Experimental Dementia

Alzheimer's disease manifests as a complex pathological condition, with neuroinflammation, oxidative stress and cholinergic dysfunction being a few of the many pathological changes. Due to the complexity of the disease, current therapeutic strategies aim at a multitargeted approach, often relying on a combination of substances with versatile and complementary effects. In the present study, a unique combination of α-lipoic acid, citicoline, extracts of leaves from olive tree and green tea, vitamin D3, selenium and an immune-supporting complex was tested in scopolamine-induced dementia in rats. Using behavioral and biochemical methods, we assessed the effects of the combination on learning and memory, and elucidated the mechanisms of these effects. Our results showed that, compared to its components, the experimental combination was most efficient in improving short- and long-term memory as assessed by the step-through method as well as spatial memory as assessed by T-maze and Barnes maze underlined by decreases in AChE activity (p < 0.05) and LPO (p < 0.001), increases in SOD activity in the cortex (p < 0.05) and increases in catalase (p < 0.05) and GPx (p < 0.01) activities and BDNF (p < 0.001) and pCREB (p < 0.05) levels in the hippocampus. No significant histopathological changes or blood parameter changes were detected, making the experimental combination an effective and safe candidate in a multitargeted treatment of AD.

Acetylcholine facilitates localized synaptic potentiation and location specific feature binding

Forebrain acetylcholine (ACh) signaling has been shown to drive attention and learning. Recent experimental evidence of spatially and temporally constrained cholinergic signaling has sparked interest to investigate how it facilitates stimulus-induced learning. We use biophysical excitatory-inhibitory (E-I) multi-module neural network models to show that external stimuli and ACh signaling can mediate spatially constrained synaptic potentiation patterns. The effects of ACh on neural excitability are simulated by varying the conductance of a muscarinic receptor-regulated hyperpolarizing slow K+ current (m-current). Each network module consists of an E-I network with local excitatory connectivity and global inhibitory connectivity. The modules are interconnected with plastic excitatory synaptic connections, that change via a spike-timing-dependent plasticity (STDP) rule. Our results indicate that spatially constrained ACh release influences the information flow represented by network dynamics resulting in selective reorganization of inter-module interactions. Moreover the information flow depends on the level of synchrony in the network. For highly synchronous networks, the more excitable module leads firing in the less excitable one resulting in strengthening of the outgoing connections from the former and weakening of its incoming synapses. For networks with more noisy firing patterns, activity in high ACh regions is prone to induce feedback firing of synchronous volleys and thus strengthening of the incoming synapses to the more excitable region and weakening of outgoing synapses. Overall, these results suggest that spatially and directionally specific plasticity patterns, as are presumed necessary for feature binding, can be mediated by spatially constrained ACh release.

Ex Vivo Electrochemical Monitoring of Cholinergic Signaling in the Mouse Colon Using an Enzyme-Based Biosensor

Cholinergic signaling, i.e., neurotransmission mediated by acetylcholine, is involved in a host of physiological processes, including learning and memory. Cholinergic dysfunction is commonly associated with neurodegenerative diseases, including Alzheimer's disease. In the gut, acetylcholine acts as an excitatory neuromuscular signaler to mediate smooth muscle contraction, which facilitates peristaltic propulsion. Gastrointestinal dysfunction has also been associated with Alzheimer's disease. This research focuses on the preparation of an electrochemical enzyme-based biosensor to monitor cholinergic signaling in the gut and its application for measuring electrically stimulated acetylcholine release in the mouse colon ex vivo. The biosensors were prepared by platinizing Pt microelectrodes through potential cycling in a potassium hexachloroplatinate (IV) solution to roughen the electrode surface and improve adhesion of the multienzyme film. These electrodes were then modified with a permselective poly(m-phenylenediamine) polymer film, which blocks electroactive interferents from reaching the underlying substrate while remaining permeable to small molecules like H2O2. A multienzyme film containing choline oxidase and acetylcholinesterase was then drop-cast on these modified electrodes. The sensor responds to acetylcholine and choline through the enzymatic production of H2O2, which is electrochemically oxidized to produce an increase in current with increasing acetylcholine or choline concentration. Important figures of merit include a sensitivity of 190 ± 10 mA mol-1 L cm-2, a limit of detection of 0.8 μmol L-1, and a batch reproducibility of 6.1% relative standard deviation at room temperature. These sensors were used to detect electrically stimulated acetylcholine release from mouse myenteric ganglia in the presence and absence of tetrodotoxin and neostigmine, an acetylcholinesterase inhibitor.

Cholinergic modulation of sensory perception and plasticity

Sensory systems are highly plastic, but the mechanisms of sensory plasticity remain unclear. People with vision or hearing loss demonstrate significant neural network reorganization that promotes adaptive changes in other sensory modalities as well as in their ability to combine information across the different senses (i.e., multisensory integration. Furthermore, sensory network remodeling is necessary for sensory restoration after a period of sensory deprivation. Acetylcholine is a powerful regulator of sensory plasticity, and studies suggest that cholinergic medications may improve visual and auditory abilities by facilitating sensory network plasticity. There are currently no approved therapeutics for sensory loss that target neuroplasticity. This review explores the systems-level effects of cholinergic signaling on human visual and auditory perception, with a focus on functional performance, sensory disorders, and neural activity. Understanding the role of acetylcholine in sensory plasticity will be essential for developing targeted treatments for sensory restoration.

ARG1-expressing microglia show a distinct molecular signature and modulate postnatal development and function of the mouse brain

Molecular diversity of microglia, the resident immune cells in the CNS, is reported. Whether microglial subsets characterized by the expression of specific proteins constitute subtypes with distinct functions has not been fully elucidated. Here we describe a microglial subtype expressing the enzyme arginase-1 (ARG1; that is, ARG1⁺ microglia) that is found predominantly in the basal forebrain and ventral striatum during early postnatal mouse development. ARG1⁺ microglia are enriched in phagocytic inclusions and exhibit a distinct molecular signature, including upregulation of genes such as Apoe, Clec7a, Igf1, Lgals3 and Mgl2, compared to ARG1^- microglia. Microglial-specific knockdown of Arg1 results in deficient cholinergic innervation and impaired dendritic spine maturation in the hippocampus where cholinergic neurons project, which in turn results in impaired long-term potentiation and cognitive behavioral deficiencies in female mice. Our results expand on microglia diversity and provide insights into microglia subtype-specific functions.

Vesicular acetylcholine transporter in the basal forebrain improves cognitive impairment in chronic cerebral hypoperfusion rats by modulating theta oscillations in the hippocampus

The cholinergic transmission in the medial septum and ventral limb of the diagonal band of broca (MS/VDB)-hippocampal circuit and its associated theta oscillations play a crucial role in chronic cerebral hypoperfusion (CCH)-related cognitive impairment. However, the contribution and mechanism of the vesicular acetylcholine transporter (VAChT), a vital protein that regulates acetylcholine (ACh) release, in CCH-related cognitive impairment are not well understood. To investigate this, we established a rat model of CCH by performing 2-vessel occlusion (2-VO) and overexpressed VAChT in the MS/VDB via stereotaxic injection of adeno-associated virus (AAV). We evaluated the cognitive function of the rats using the Morris Water Maze (MWM) and Novel Object Recognition Test (NOR). We employed enzyme-linked immunosorbent assay (ELISA), Western blot (WB), and immunohistochemistry (IHC) to assess hippocampal cholinergic levels. We also conducted in vivo local field potentials (LFPs) recording experiments to evaluate changes in hippocampal theta oscillations and synchrony. Our findings showed that VAChT overexpression shortened the escape latency in the hidden platform test, increased swimming time in the platform quadrant in probe trains, and increased the recognition index (RI) in NOR. Moreover, VAChT overexpression increased hippocampal cholinergic levels, improved theta oscillations, and improved the synchrony of theta oscillations between CA1 and CA3 in CCH rats. These results suggest that VAChT plays a protective role in CCH-induced cognitive deficits by regulating cholinergic transmission in the MS/VDB-hippocampal circuit and promoting hippocampal theta oscillations. Therefore, VAChT could be a promising therapeutic target for treating CCH-related cognitive impairments.

Contextual fear expression engages a complex set of interactions between ventromedial prefrontal cortex cholinergic, glutamatergic, nitrergic and cannabinergic signaling

Rats re-exposed to an environment previously associated with the onset of shocks evoke a set of conditioned defensive responses in preparation to an eventual flight or fight reaction. Ventromedial prefrontal cortex (vmPFC) is mutually important for controlling the behavioral/physiological consequences of stress exposure and the one's ability to satisfactorily undergo spatial navigation. While cholinergic, cannabinergic and glutamatergic/nitrergic neurotransmissions within the vmPFC are shown as important for modulating both behavioral and autonomic defensive responses, there is a gap on how these systems would interact to ultimately coordinate such conditioned reactions. Then, males Wistar rats had guide cannulas bilaterally implanted to allow drugs to be administered in vmPFC 10 min before their re-exposure to the conditioning chamber where three shocks were delivered at the intensity of 0.85 mA for 2 s two days ago. A femoral catheter was implanted for cardiovascular recordings the day before fear retrieval test. It was found that the increment of freezing behavior and autonomic responses induced by vmPFC infusion of neostigmine (acetylcholinesterase inhibitor) were prevented by prior infusion of a transient receptor potential vanilloid type 1 (TRPV1) antagonist, N-methyl-d-aspartate receptor antagonist, neuronal nitric oxide synthase inhibitor, nitric oxide scavenger and soluble guanylate cyclase inhibitor. A type 3 muscarinic receptor antagonist was unable to prevent the boosting in conditioned responses triggered by a TRPV1 agonist and a cannabinoid receptors type 1 antagonist. Altogether, our results suggest that expression of contextual conditioned responses involves a complex set of signaling steps comprising different but complementary neurotransmitter pathways.

A bibliometric analysis of global research status and trends in neuromodulation techniques in the treatment of autism spectrum disorder

BACKGROUND

Autism spectrum disorder (ASD) is a neurodevelopmental disease which has risen to become the main cause of childhood disability, placing a heavy burden on families and society. To date, the treatment of patients with ASD remains a complicated problem, for which neuromodulation techniques are a promising solution. This study analyzed the global research situation of neuromodulation techniques in the treatment of ASD from 1992 to 2022, aiming to explore the global research status and frontier trends in this field.

METHODS

The Web of Science (WoS) was searched for literature related to neuromodulation techniques for ASD from 1992 to October 2022. A knowledge atlas to analyze collaboration among countries, institutions, authors, publishing journals, reference co-citation patterns, keyword co-occurrence, keyword clustering, and burst keywords was constructed using Rstudio software, CiteSpace, and VOSviewer.

RESULTS

In total, 392 publications related to the treatment of ASD using neuromodulation techniques were included. Despite some fluctuations, the number of publications in this field has shown a growing trend in recent years. The United States and Deakin University are the leading country and institution in this field, respectively. The greatest contributing authors are Peter G Enticott, Manuel F Casanova, and Paul B Fitzgerald et al. The most prolific and cited journal is Brain Stimulation and the most commonly co-cited journal is The Journal of Autism and Developmental Disorders. The most frequently cited article was that of Simone Rossi (Safety, ethical considerations, and application guidelines for the use of transverse magnetic stimulation in clinical practice and research, 2009). "Obsessive-compulsive disorder," "transcranial direct current stimulation," "working memory," "double blind" and "adolescent" were identified as hotspots and frontier trends of neuromodulation techniques in the treatment of ASD.

CONCLUSION

The application of neuromodulation techniques for ASD has attracted the attention of researchers worldwide. Restoring the social ability and improving the comorbid symptoms in autistic children and adults have always been the focus of research. Neuromodulation techniques have demonstrated significant advantages and effects on these issues. Transcranial magnetic stimulation (TMS) and transcranial direct current stimulation (tDCS) are new therapeutic methods introduced in recent years, and are also directions for further exploration.

Hippocampal cholinergic receptors and the mTOR participation in fear-motivated inhibitory avoidance extinction memory

Evidence has demonstrated the hippocampal cholinergic system and the mammalian target of rapamycin (mTOR) participation during the memory formation of aversive events. This study assessed the role of these systems in the hippocampus for the extinction memory process by submitting male Wistar rats to fear-motivated step-down inhibitory avoidance (IA). The post-extinction session administration of the nicotinic and muscarinic cholinergic receptor antagonists, mecamylamine and scopolamine, respectively, both at doses of 2 µg/µl/side, and rapamycin, an mTOR inhibitor (0.02 µg/µl/side), into the CA1 region of the dorsal hippocampus, impaired the IA extinction memory. Furthermore, the nicotinic and muscarinic cholinergic receptor agonists, nicotine and muscarine, respectively, had a dose-dependent effect on the IA extinction memory when administered intra-CA1, immediately after the extinction session. Nicotine (0.6 µg/µl/side) and muscarine (0.02 µg/µl/side), respectively, had no effect, while the higher doses (6 and 2 µg/µl/side, respectively) impaired the IA extinction memory. Interestingly, the co-administration of muscarine at the lower dose blocked the impairment that was induced by rapamycin. This effect was not observed when nicotine at the lower dose was co-administered. These results have demonstrated the participation of the cholinergic receptors and mTOR in the hippocampus for IA extinction, and that the cholinergic agonists had a dose-dependent effect on the IA extinction memory. This study provides insights related to the behavioural aspects and the neurobiological properties underlying the early stage of fear-motivated IA extinction memory consolidation and suggests that there is hippocampal muscarinic receptor participation independent of mTOR in this memory process.

Sterubin protects against chemically-induced Alzheimer's disease by reducing biomarkers of inflammation- IL-6/ IL-β/ TNF-α and oxidative stress- SOD/MDA in rats

Sterubin, a flavanone is an active chemical compound that possesses neuroprotective activity. The current investigation was intended to assess the sterubin effect in scopolamine-activated Alzheimer's disease. The rats were induced with scopolamine (1.5 mg/kg) followed by treatment with sterubin (10 mg/kg) for 14 days. Behavioural analysis was predictable by the Y-maze test and Morris water test. Biochemical variables like nitric oxide acetylcholinesterase, Choline acetyltransferase, antioxidant markers like superoxide dismutase, glutathione transferase, malondialdehyde, catalase, and myeloperoxidase activity, neuroinflammatory markers such as tumor necrosis factor-alpha, nuclear factor kappa B, interferon-gamma, interleukin (IL-1β), and IL-6 were measured. The result stated that sterubin reversed the oxidative stress parameters, increased motor performance, and lowered the inflammatory markers in scopolamine-induced rats. The study demonstrated that sterubin possesses neuroprotective, anti-inflammatory, and antioxidant properties which can be used as a beneficial medication in AD.

The dependence of acetylcholine on dynamic changes in the membrane potential and an action potential during spike timing-dependent plasticity induction in the hippocampus

The hippocampus is an important area for memory encoding and retrieval and is the location of spike timing-dependent plasticity (STDP), a basic phenomenon of learning and memory. STDP is facilitated if acetylcholine (ACh) is released from cholinergic neurons during attentional processes. However, it is unclear how ACh influences postsynaptic changes during STDP induction and determines the STDP magnitude. To address these issues, we obtained patch clamp recordings from CA1 pyramidal neurons to evaluate the postsynaptic changes during stimuli injection in Schaffer collaterals by quantifying baseline amplitudes (i.e., the lowest values elicited by paired pulses comprising STDP stimuli) and action potentials. The results showed that baseline amplitudes were elevated if eserine was applied in the presence of picrotoxin. In addition, muscarinic ACh receptors (mAChRs) contributed more to the baseline amplitude elevation than nicotinic AChRs (nAChRs). Moreover, the magnitude of the STDP depended on the magnitude of the baseline amplitude. However, in the absence of picrotoxin, baseline amplitudes were balanced, regardless of the ACh concentration, resulting in a similar magnitude of the STDP, except under the nAChR alone-activated condition, which showed a larger STDP and lower baseline amplitude induction. This was due to broadened widths of action potentials. These results suggest that activation of mAChRs and nAChRs, which are effective for baseline amplitudes and action potentials, respectively, plays an important role in postsynaptic changes during memory consolidation.

Effect of ivabradine on cognitive functions of rats with scopolamine-induced dementia

Alzheimer's disease is among the challenging diseases to social and healthcare systems because no treatment has been achieved yet. Although the ambiguous pathological mechanism underlying this disorder, ion channel dysfunction is one of the recently accepted possible mechanism. Hyperpolarization-activated cyclic nucleotide-gated (HCN) channels play important roles in cellular excitability and synaptic transmission. Ivabradine (Iva), an HCN blocker, is acting on HCN channels, and is clinically used for angina and arrhythmia. The current study aimed to investigate the therapeutic effects of Iva against scopolamine (Sco) induced dementia. To test our hypothesis, Sco and Iva injected rats were tested for behavioural changes, followed by ELISA and histopathological analysis of the hippocampus. Induced dementia was confirmed by behavioural tests, inflammatory cytokines and oxidative stress tests and histopathological signs of neurodegeneration, multifocal deposition of congo red stained amyloid beta plaques and the decreased optical density of HCN1 immunoreactivity. Iva ameliorated the scopolamine-induced dysfunction, the hippocampus restored its normal healthy neurons, the amyloid plaques disappeared and the optical density of HCN1 immunoreactivity increased in hippocampal cells. The results suggested that blockage of HCN1 channels might underly the Iva therapeutic effect. Therefore, Iva might have beneficial effects on neurological disorders linked to HCN channelopathies.

The interaction between hippocampal cholinergic and nitrergic neurotransmission coordinates NMDA-dependent behavior and autonomic changes induced by contextual fear retrieval

RATIONALE

Re-exposing an animal to an environment previously paired with an aversive stimulus evokes large alterations in behavioral and cardiovascular parameters. Dorsal hippocampus (dHC) receives important cholinergic inputs from the basal forebrain, and respective acetylcholine (ACh) levels are described to influence defensive behavior. Activation of muscarinic M1 and M3 receptors facilitates autonomic and behavioral responses along threats. Evidence show activation of cholinergic receptors promoting formation of nitric oxide (NO) and cyclic guanosine monophosphate (cGMP) in dHC. Altogether, the action of ACh and NO on conditioned responses appears to converge within dHC.

OBJECTIVES

As answer about how ACh and NO interact to modulate defensive responses has so far been barely addressed, we aimed to shed additional light on this topic.

METHODS

Male Wistar rats had guide cannula implanted into the dHC before being submitted to the contextual fear conditioning (3footshocks/085 mA/2 s). A catheter was implanted in the femoral artery the next day for cardiovascular recordings. Drugs were delivered into dHC 10 min before contextual re-exposure, which occurred 48 h after the conditioning procedure.

RESULTS

Neostigmine (Neo) amplified the retrieval of conditioned responses. Neo effects (1 nmol) were prevented by the prior infusion of a M1-M3 antagonist (fumarate), a neuronal nitric oxide synthase inhibitor (NPLA), a NO scavenger (cPTIO), a guanylyl cyclase inhibitor (ODQ), and a NMDA antagonist (AP-7). Pretreatment with a selective M1 antagonist (pirenzepine) only prevented the increase in autonomic responses induced by Neo.

CONCLUSION

The results show that modulation in the retrieval of contextual fear responses involves coordination of the dHC M1-M3/NO/cGMP/NMDA pathway.

Antidepressant, anti-amnesic and vasoprotective effect of Bombax costatum Pellegr. & Vuillet aqueous stem bark extract on chronic mild unpredictable stress induced in rat

ETHNOPHARMACOLOGICAL RELEVANCE

Bombax costatum Pellegr. & Vuillet is used traditionally in Northern Cameroon to treat memory impairment, anxiety, insomnia and depression.

AIM OF THE STUDY

Investigating the effect of Bombax costatum stem bark aqueous extract (BC) on depression associated with amnesia and vascular disorder, using a chronic mild unpredictable stress (CMUS) model in rats for 30 days.

MATERIALS AND METHODS

Sucrose Preference Test (SPT), Forced Swimming Test (FST), corticosteronemia, brain serotonin and dopamine level were evaluated as indices of antidepressant-like effect. The Novel Object Recognition Task (NOR), the Morris Water Maze (MWM) and acetylcholinesterase activity in the hippocampus were also used to verify memory integrity. Oxidative and nitrosative stress markers, the lipid profile and atherogenic index were estimated in blood serum to assess vasoprotective effect. Chlorophenylalanine and haloperidol, were used to delineate the extract's mechanism of action.

RESULTS

CMUS induced a decrease in sucrose preference and swimming time in the SPT and FST respectively while BC (27.5 and 55 mg/kg) increased sucrose preference and swimming time. Increments in these parameters were however reversed by the treatment of rats with chlorophenylalanine a serotonin synthesis inhibitor and haloperidol a D2 receptor antagonist. An increase in blood corticosterone level, prefrontal cortex malondialdehyde and nitric oxide concentrations were reversed by the extract. Moreover, BC increased the time spent in the target quadrant of the MWM test and the discrimination index in the NOR test. This was associated with an increase in hippocampus superoxide dismutase and catalase levels, a decrease in acetylcholine esterase level, total blood cholesterol and atherogenicity index compared to CMUS group.

CONCLUSION

Thirty days CMUS induces a depressive state in rats. BC reverses this condition when administered alongside stress exposure. This antidepressive effect is associated with antiamnesic, antioxidant and vasoprotective actions, suggesting its use as a potential candidate in the management of major depressive disorder.

Cholinergic Internal and Projection Systems of Hippocampus and Neocortex Critical for Early Spatial Memory Consolidation in Normal and Chronic Cerebral Hypoperfusion Conditions in Rats with Different Abilities to Consolidation: The Role of Cholinergic Interneurons of the Hippocampus

The role of cholinergic projection systems of the neocortex and hippocampus in memory consolidation in healthy and neuropathological conditions has been subject to intensive research. On the contrary, the significance of cholinergic cortical and hippocampal interneurons in learning has hardly been studied. We aimed to evaluate the role of both cholinergic projection neurons and interneurons of the neocortex and hippocampus at an early stage of spatial memory consolidation (2s1) in normal and chronic brain hypoperfusion conditions. Control rats and rats subjected to permanent two-vessel occlusion were trained with the Morris water maze, and the activity of membrane-bound and water-soluble choline acetyltransferase was evaluated in the sub-fractions of ‘light’ and ‘heavy’ synaptosomes of the neocortex and hippocampus, in which the presynapses of cholinergic projections and interneurons, respectively, are concentrated. Animals were ranked into quartiles according to their performance on stage 2s1. We found: (1) quartile-dependent cholinergic composition of 2s1 function and dynamics of cholinergic synaptic plasticity under cerebral hypoperfusion; (2) cholinergic hippocampal interneurons are necessary for successful 2s1 consolidation; (3) cholinergic neocortical interneurons and projections can be critical for 2s1 consolidation in less learning rats. We conclude that targeted modulation of cholinergic synaptic activity in the hippocampus and neocortex can be effective in reversing the cognitive disturbance of cerebral hypoperfusion. We discuss the possible ways to restore the impaired spatial memory 2s1 in the presence of cerebral hypoperfusion.

Effects of Smart Drugs on Cholinergic System and Non-Neuronal Acetylcholine in the Mouse Hippocampus: Histopathological Approach

In recent years, people in the United States and other countries have been using smart drugs, called nootropic or cognitive enhancers, to improve concentration and memory learning skills. However, these drugs were originally prescribed for attention-deficit hyperactivity disorder and dementia, and their efficacy in healthy people has not yet been established. We focused on acetylcholine in the hippocampus, which is responsible for memory learning, and elucidate the long-term effects of smart drugs on the neural circuits. Smart drugs were administered orally in normal young mice for seven weeks. The hippocampus was sectioned and compared histologically by hematoxylin and eosin (HE) staining, immunohistochemistry for acetylcholine, and immunoelectron microscopy. There were no significant changes in acetylcholinesterase staining. However, in HE, we found perivascular edema, and choline acetyltransferase staining showed increased staining throughout the hippocampus and new signal induction in the perivascular area in the CA3, especially in the aniracetam and α-glyceryl phosphoryl choline group. Additionally, new muscarinic acetylcholine receptor signals were observed in the CA1 due to smart drug intake, suggesting that vasodilation might cause neuronal activation by increasing the influx of nutrients and oxygen. Moreover, these results suggest a possible new mechanism of acetylcholine-mediated neural circuit activation by smart drug intake.

Hippocampal acetylcholine modulates stress-related behaviors independent of specific cholinergic inputs

Acetylcholine (ACh) levels are elevated in actively depressed subjects. Conversely, antagonism of either nicotinic or muscarinic ACh receptors can have antidepressant effects in humans and decrease stress-relevant behaviors in rodents. Consistent with a role for ACh in mediating maladaptive responses to stress, brain ACh levels increase in response to stressful challenges, whereas systemically blocking acetylcholinesterase (AChE, the primary ACh degradative enzyme) elicits depression-like symptoms in human subjects, and selectively blocking AChE in the hippocampus increases relevant behaviors in rodents. We used an ACh sensor to characterize stress-evoked ACh release, then used chemogenetic, optogenetic and pharmacological approaches to determine whether cholinergic inputs from the medial septum/diagonal bands of Broca (MSDBB) or ChAT-positive neurons intrinsic to the hippocampus mediate stress-relevant behaviors in mice. Chemogenetic inhibition or activation of MSDBB cholinergic neurons did not result in significant behavioral effects, while inhibition attenuated the behavioral effects of physostigmine. In contrast, optogenetic stimulation of septohippocampal terminals or selective chemogenetic activation of ChAT-positive inputs to hippocampus increased stress-related behaviors. Finally, stimulation of sparse ChAT-positive hippocampal neurons increased stress-related behaviors in one ChAT-Cre line, which were attenuated by local infusion of cholinergic antagonists. These studies suggest that ACh signaling results in maladaptive behavioral responses to stress if the balance of signaling is shifted toward increased hippocampal engagement.

Anticholinergics: A potential option for preventing posttraumatic epilepsy

Interest in the use of anticholinergics to prevent the development of epilepsy after traumatic brain injury (TBI) has grown since recent basic studies have shown their effectiveness in modifying the epileptogenic process. These studies demonstrated that treatment with anticholinergics, in the acute phase after brain injury, decreases seizure frequency, and severity, and the number of spontaneous recurrent seizures (SRS). Therefore, anticholinergics may reduce the risk of developing posttraumatic epilepsy (PTE). In this brief review, we summarize the role of the cholinergic system in epilepsy and the key findings from using anticholinergic drugs to prevent PTE in animal models and new clinical trial protocols. Furthermore, we discuss why treatment with anticholinergics is more likely to prevent PTE than treatment for other epilepsies.

Effects of Cigarette Smoking on Resting-State Functional Connectivity of the Nucleus Basalis of Meynert in Mild Cognitive Impairment

Background: Mild cognitive impairment (MCI) is the prodromal phase of Alzheimer’s disease (AD) and has a high risk of progression to AD. Cigarette smoking is one of the important modifiable risk factors in AD progression. Cholinergic dysfunction, especially the nucleus basalis of Meynert (NBM), is the converging target connecting smoking and AD. However, how cigarette smoking affects NBM connectivity in MCI remains unclear.

Objective: This study aimed to evaluate the interaction effects of condition (non-smoking vs. smoking) and diagnosis [cognitively normal (CN) vs. MCI] based on the resting-state functional connectivity (rsFC) of the NBM.

Methods: After propensity score matching, we included 86 non-smoking CN, 44 smoking CN, 62 non-smoking MCI, and 32 smoking MCI. All subjects underwent structural and functional magnetic resonance imaging scans and neuropsychological tests. The seed-based rsFC of the NBM with the whole-brain voxel was calculated. Furthermore, the mixed effect analysis was performed to explore the interaction effects between condition and diagnosis on rsFC of the NBM.

Results: The interaction effects of condition × diagnosis on rsFC of the NBM were observed in the bilateral prefrontal cortex (PFC), bilateral supplementary motor area (SMA), and right precuneus/middle occipital gyrus (MOG). Specifically, the smoking CN showed decreased rsFC between left NBM and PFC and increased rsFC between left NBM and SMA compared with non-smoking CN and smoking MCI. The smoking MCI showed reduced rsFC between right NBM and precuneus/MOG compared with non-smoking MCI. Additionally, rsFC between the NBM and SMA showed a significant negative correlation with Wechsler Memory Scale-Logical Memory (WMS-LM) immediate recall in smoking CN (r = −0.321, p = 0.041).

Conclusion: Our findings indicate that chronic nicotine exposure through smoking may lead to functional connectivity disruption between the NBM and precuneus in MCI patients. The distinct alteration patterns on NBM connectivity in CN smokers and MCI smokers suggest that cigarette smoking has different influences on normal and impaired cognition.

A new arylsulfanyl-benzo-2,1,3-thiadiazoles derivative produces an anti-amnesic effect in mice by modulating acetylcholinesterase activity

The aim of the present study was investigate the binding affinity of 5-((4-methoxyphenyl)thio)benzo[c][1,2,5]thiadiazole (MTDZ) with acetylcholinesterase (AChE). We also evaluated the effect of MTDZ against scopolamine (SCO)-induced amnesia in mice and we looked at the toxicological potential of this compound in mice. The binding affinity of MTDZ with AChE was investigated by molecular docking analyses. For an experimental model, male Swiss mice were treated daily with MTDZ (10 mg/kg, intragastrically (i.g.)) or canola oil (10 ml/kg, i.g.), and induced, 30 min later, with injection of SCO (0.4 mg/kg, intraperitoneally (i.p.)) or saline (0.9%, 5 ml/kg, i.p.) daily. From day 1 to day 10, mice were submitted to the behavioral tasks (Barnes maze, open-field, object recognition and location, Y-maze and step-down inhibitory avoidance tasks), 30 min after induction with SCO. On the tenth day, the animals were euthanized and blood was collected for the analysis of biochemical markers (creatinine, aspartate (AST), and alanine (ALT) aminotransferase). MTDZ interacts with residues of the AChE active site. SCO caused amnesia in mice by changing behavioral tasks. MTDZ treatment attenuated the behavioral changes caused by SCO. In ex vivo assay, MTDZ also protected against the alteration of AChE activity, reactive species (RS) levels, thiobarbituric acid reative species (TBARS) levels, catalase (CAT) activity in tissues, as well as in transaminase activities of plasma caused by SCO in mice. In conclusion, MTDZ presented anti-amnesic action through modulation of the cholinergic system and provided protection from kidney and liver damage caused by SCO.

Choline chloride modulates learning, memory, and synaptic plasticity impairments in maternally separated adolescent male rats

Maternal separation (MS) is a model to induce permanent alternations in the central nervous system (CNS) and is associated with increased levels of anxiety and cognitive deficiencies. Since Methyl donor choline (Ch) has been shown to play a significant role in learning and memory and enhances synaptic plasticity, the authors hypothesized that Ch may attenuate MS-induced impairments in synaptic plasticity and cognitive performance. Rat pups underwent a MS protocol for 180 min/day from postnatal day (PND) 1 to 21. Ch was administered subcutaneously (100 mg/kg, 21 days) to the Choline chloride and MS + Choline chloride groups from PND 29 to 49. Anxiety-like behavior, recognition memory, spatial and passive avoidance learning and memory were measured in the adolescent rats. In addition, evoked field excitatory postsynaptic potentials (fEPSP) were recorded from the CA1 region of the hippocampus. MS induced higher anxiety-like behavior in the animals. It also impaired learning and memory. However, MS had no effect on locomotor activity. Subcutaneous administration of Ch attenuated MS-induced cognitive deficits and enhanced the learning and memory of MS rats. Ch also decreased anxiety-like behavior in the open field test. The present results showed that long-term potentiation (LTP) was induced in all groups except MS and MS + saline animals. However, Ch injection induced LTP and had maintenance in MS + choline chloride, but it was not statistically significant compared with the MS group. In summary, the present findings indicate that MS can interfere with normal animal's cognition and subcutaneous of Ch may be considered an appropriate therapeutic strategy for promoting cognitive dysfunctions in MS animals.

Evaluation of the Activity of Choline Acetyltransferase From Different Synaptosomal Fractions at the Distinct Stages of Spatial Learning in the Morris Water Maze

Accumulated data have evidenced that brain cholinergic circuits play a crucial role in learning and memory; however, our knowledge about the participation of neocortical and hippocampal cholinergic systems in spatial learning needs to be refined. The aim of this study was to evaluate the association of the activity of membrane-bound and soluble choline acetyltransferase (ChAT) in the synaptosomal sub-fractions of the neocortex and hippocampus with performance of the spatial navigation task in the Morris water maze at different temporal stages of memory trace formation. To identify distinct stages of memory formation, rats were trained using a 5-day protocol with four trials per day. The mean escape latency for each trial was collected, and the entire dataset was subjected to principal component analysis. Based on the Morris water maze protocol, there were three relatively distinct stages of memory formation: days 1-2, day 3, and days 4-5. The remotely stored memory trace tested in repeated and reversal learning beginning on day 19 (14 days after the end of initial learning) was associated at the individual level mainly with performance during the second trial on day 21 (the third day or repeated or reversal learning). The ChAT activity data suggest the participation of cortical cholinergic projections mainly in the first stage of spatial learning (automatic sensory processing) and the involvement of hippocampal interneurons in the second stage (error-corrected learning). Cholinergic cortical interneurons participated mainly in the stage of asymptotic performance (days 4-5). It is advisable to evaluate other signalling pathways at the identified stages of memory formation.

Effects of prenatal ethanol exposure on choline-induced long-term depression in the hippocampus

Choline is an essential nutrient under evaluation as a cognitive enhancing treatment for fetal alcohol spectrum disorders (FASD) in clinical trials. As a result, there is increased pressure to identify therapeutic mechanism(s) of action. Choline is not only a precursor for several essential cell membrane components and signaling molecules but also has the potential to directly affect synaptic mechanisms that are believed important for cognitive processes. In the current work, we study how the direct application of choline can affect synaptic transmission in the dentate gyrus (DG) of hippocampal slices obtained from adolescent (postnatal days 21-28) Sprague-Dawley rats (Rattus norvegicus). The acute administration of choline chloride (2 mM) reliably induced a long-term depression (LTD) of field excitatory postsynaptic potentials (fEPSPs) in the DG in vitro. The depression required the involvement of M1 receptors, and the magnitude of the effect was similar in slices obtained from male and female animals. To further study the impact of choline in an animal model of FASD, we examined offspring from dams fed an ethanol-containing diet (35.5% ethanol-derived calories) throughout gestation. In slices from the adolescent animals that experienced prenatal ethanol exposure (PNEE), we found that the choline induced an LTD that uniquely involved the activation of N-methyl-d-aspartate (NMDA) and M1 receptors. This study provides a novel insight into how choline can modulate hippocampal transmission at the level of the synapse and that it can have unique effects following PNEE.NEW & NOTEWORTHY Choline supplementation is a nutraceutical therapy with significant potential for a variety of developmental disorders; however, the mechanisms involved in its therapeutic effects remain poorly understood. Our research shows that choline directly impacts synaptic communication in the brain, inducing a long-term depression of synaptic efficacy in brain slices. The depression is equivalent in male and female animals, involves M1 receptors in control animals, but uniquely involves NMDA receptors in a model of FASD.

Human Three-Finger Protein Lypd6 Is a Negative Modulator of the Cholinergic System in the Brain

Lypd6 is a GPI-tethered protein from the Ly-6/uPAR family expressed in the brain. Lypd6 enhances the Wnt/β-catenin signaling, although its action on nicotinic acetylcholine receptors (nAChRs) have been also proposed. To investigate a cholinergic activity of Lypd6, we studied a recombinant water-soluble variant of the human protein (ws-Lypd6) containing isolated “three-finger” LU-domain. Experiments at different nAChR subtypes expressed in Xenopus oocytes revealed the negative allosteric modulatory activity of ws-Lypd6. Ws-Lypd6 inhibited ACh-evoked currents at α3β4- and α7-nAChRs with IC₅₀ of ∼35 and 10 μM, respectively, and the maximal amplitude of inhibition of 30–50%. EC₅₀ of ACh at α3β4-nAChRs (∼30 μM) was not changed in the presence of 35 μM ws-Lypd6, while the maximal amplitude of ACh-evoked current was reduced by ∼20%. Ws-Lypd6 did not elicit currents through nAChRs in the absence of ACh. Application of 1 μM ws-Lypd6 significantly inhibited (up to ∼28%) choline-evoked current at α7-nAChRs in rat hippocampal slices. Similar to snake neurotoxin α-bungarotoxin, ws-Lypd6 suppressed the long-term potentiation (LTP) in mouse hippocampal slices. Colocalization of endogenous GPI-tethered Lypd6 with α3β4- and α7-nAChRs was detected in primary cortical and hippocampal neurons. Ws-Lypd6 interaction with the extracellular domain of α7-nAChR was modeled using the ensemble protein-protein docking protocol. The interaction of all three Lypd6 loops (“fingers”) with the entrance to the orthosteric ligand-binding site and the loop C of the primary receptor subunit was predicted. The results obtained allow us to consider Lypd6 as the endogenous negative modulator involved in the regulation of the cholinergic system in the brain.

Effects of trophic 2,2', 4,4'-tetrabromodiphenyl ether (BDE-47) exposure in Oreochromis niloticus: A multiple biomarkers analysis

Polybrominated diphenyl esters are emerging environmental contaminants with few toxicological data, being a concern for the scientific community. This study evaluated the effects of BDE-47 on the health of Oreochromis niloticus fish. The animals were exposed to three doses of BDE-47 (0, 0.253, 2.53, 25.3 ng g^-1) every 10 days, for 80 days. The BDE-47 affected the hepatosomatic and gonadosomatic index in female and the condition factor by intermediate dose in both sexes. The levels of estradiol decreased and the T4 are increased, but the vitellogenin production was not modulated in male individuals. Changes in AChE, GST, LPO and histopathology were observed while the integrated biomarker response index suggests that the lowest dose of BDE-47 compromised the activity of antioxidant enzymes. The oral exposure to BDE-47 in environmental concentrations is toxic to O. niloticus and the use of multiple biomarkers is an attribution in ecotoxicology studies and biomonitoring programs.

Scopolamine prevents aberrant mossy fiber sprouting and facilitates remission of epilepsy after brain injury

Prevention or modification of acquired epilepsy in patients at risk is an urgent, yet unmet, clinical need. Following acute brain insults, there is an increased risk of mesial temporal lobe epilepsy (mTLE), which is often associated with debilitating comorbidities and reduced life expectancy. The latent period between brain injury and the onset of epilepsy may offer a therapeutic window for interfering with epileptogenesis. The pilocarpine model of mTLE is widely used in the search for novel antiepileptogenic treatments. Recent biochemical studies indicated that cholinergic mechanisms play a role in the epileptogenic alterations induced by status epilepticus (SE) in this and other models of mTLE, which prompted us to evaluate whether treatment with the muscarinic antagonist scopolamine during the latent period after SE is capable of preventing or modifying epilepsy and associated behavioral and cognitive alterations in female Sprague-Dawley rats. First, in silico pharmacokinetic modeling was used to select a dosing protocol by which M-receptor inhibitory brain levels of scopolamine are maintained during prolonged treatment. This protocol was verified by drug analysis in vivo. Rats were then treated twice daily with scopolamine over 17 days after SE, followed by drug wash-out and behavioral and video/EEG monitoring up to ~6 months after SE. Compared to vehicle controls, rats that were treated with scopolamine during the latent period exhibited a significantly lower incidence of spontaneous recurrent seizures during periods of intermittent recording in the chronic phase of epilepsy, less behavioral excitability, less cognitive impairment, and significantly reduced aberrant mossy fiber sprouting in the hippocampus. The present data may indicate that scopolamine exerts antiepileptogenic/disease-modifying activity in the lithium-pilocarpine rat model, possibly involving increased remission of epilepsy as a new mechanism of disease-modification. For evaluating the rigor of the present data, we envision a study that more thoroughly addresses the gender bias and video-EEG recording limitations of the present study.

Inhibition of Matrix Metalloproteinase 9 Activity Promotes Synaptogenesis in the Hippocampus

Information coding in the hippocampus relies on the interplay between various neuronal ensembles. We discovered that the application of a cholinergic agonist, carbachol (Cch), which triggers oscillatory activity in the gamma range, induces the activity of matrix metalloproteinase 9 (MMP-9)—an enzyme necessary for the maintenance of synaptic plasticity. Using electrophysiological recordings in hippocampal organotypic slices, we show that Cch potentiates the frequency of miniature inhibitory and excitatory postsynaptic currents (mIPSCs and mEPSCs, respectively) in CA1 neurons and this effect is MMP-9 dependent. Interestingly, though MMP-9 inhibition prevents the potentiation of inhibitory events, it further boosts the frequency of excitatory mEPSCs. Such enhancement of the frequency of excitatory events is a result of increased synaptogenesis onto CA1 neurons. Thus, the function of MMP-9 in cholinergically induced plasticity in the hippocampus is to maintain the fine-tuned balance between the excitatory and the inhibitory synaptic transmission.

Muscarinic acetylcholine receptor M1 mutations causing neurodevelopmental disorder and epilepsy

De novo rare damaging variants in genes involved in critical developmental pathways, notably regulation of synaptic transmission, have emerged as a frequent cause of neurodevelopmental disorders (NDD). NDD show great locus heterogeneity and for many of the associated genes, there is substantial phenotypic diversity, including epilepsy, intellectual disability, autism spectrum disorder, movement disorders, and combinations thereof. We report two unrelated patients, a young girl with early-onset refractory epilepsy, severe disability, and progressive cerebral and cerebellar atrophy, and a second girl with mild dysmorphism, global developmental delay, and moderate intellectual disability in whom trio-based whole-exome sequencing analysis uncovered de novo missense variants in CHRM1. Biochemical analyses of one of the NDD-associated variants proved that it caused a reduction in protein levels and impaired cellular trafficking. In addition, the mutated receptor showed defective activation of intracellular signaling pathways. Our data strengthen the concept that brain-reduced muscarinic signaling lowers the seizure threshold and severely impairs neurodevelopment.

Neuroprotective effects of quercetin produced by an endophytic fungus Nigrospora oryzae isolated from Tinospora cordifolia

AIMS

Alzheimer's disease is considered one of the most prevalent neurodegenerative disorders and dementia is the core symptom of this disease. This study was aimed to test the bioactive compounds produced by endophytic fungus for the inhibition of acetylcholinesterase (AChE) activity and to identify the compound responsible for this activity.

METHODS AND RESULTS

Endophytic fungi were isolated from the medicinal plant Tinospora cordifolia and screened for AChE inhibition and antioxidant activity. The extract of one of the isolates Nigrospora oryzae (GL15) showed maximum AChE inhibition as well as antioxidant activity. The compound responsible for AChE inhibition (fraction 3) was identified as quercetin based on UV, FTIR spectra, HPLC and ESI-MS analyses. Furthermore, the identification of quercetin in the extract of fraction 3 was confirmed by ¹ H NMR analysis. This extract showed anti-dementia-like activity in scopolamine (SCO) model. The minimal effective dose of the extract of fraction 3 modulated the SCO-provoked cognitive deficits such as impairments in spatial recognition memory and latency period in Y-maze test and passive avoidance test, respectively. The SCO-induced modulation in cholinergic pathway was ameliorated by the extract of N. oryzae in hippocampus, resulting in decrease in AChE activity and restoration of cytoarchitecture of hippocampus.

CONCLUSIONS

The bioactive compound quercetin produced by N. oryzae may cure the learning and memory shortfalls via AChE-mediated mechanism in experimental mice.

SIGNIFICANCE AND IMPACT OF THE STUDY

The endophytic fungus N. oryzae serves as a potential source for the bioactive compound quercetin, which plays an important role in the management of Alzheimer's disease.

Presynaptic Inhibitory Effects of Acetylcholine in the Hippocampus: A 40-Year Evolution of a Serendipitous Finding

Cholinergic regulation of hippocampal circuit activity has been an active area of neurophysiological research for decades. The prominent cholinergic innervation of intrinsic hippocampal circuitry, potent effects of cholinomimetic drugs, and behavioral responses to cholinergic modulation of hippocampal circuitry have driven investigators to discover diverse cellular actions of acetylcholine in distinct sites within hippocampal circuitry. Further research has illuminated how these actions organize circuit activity to optimize encoding of new information, promote consolidation, and coordinate this with recall of prior memories. The development of the hippocampal slice preparation was a major advance that accelerated knowledge of how hippocampal circuits functioned and how acetylcholine modulated these circuits. Using this preparation in the early 1980s, we made a serendipitous finding of a novel presynaptic inhibitory effect of acetylcholine on Schaffer collaterals, the projections from CA3 pyramidal neurons to dendrites of CA1 pyramidal cells. We characterized this effect at cellular and pharmacological levels, published the findings in the first volume of the Journal of Neuroscience, and proceeded to pursue other scientific directions. We were surprised and thrilled to see that, nearly 40 years later, the paper is still being cited and downloaded because the data became an integral piece of the foundation of the science of cholinergic regulation of hippocampal function in learning and memory. This Progressions article is a story of how single laboratory findings evolve through time to be confirmed, challenged, and reinterpreted by other laboratories to eventually become part of the basis of fundamental concepts related to important brain functions.

Central Administration of Ampelopsin A Isolated from Vitis vinifera Ameliorates Cognitive and Memory Function in a Scopolamine-Induced Dementia Model

Neurodegenerative diseases are characterized by the progressive degeneration of the function of the central nervous system or peripheral nervous system and the decline of cognition and memory abilities. The dysfunctions of the cognitive and memory battery are closely related to inhibitions of neurotrophic factor (BDNF) and brain-derived cAMP response element-binding protein (CREB) to associate with the cholinergic system and long-term potentiation. Vitis vinifera, the common grapevine, is viewed as the important dietary source of stilbenoids, particularly the widely-studied monomeric resveratrol to be used as a natural compound with wide-ranging therapeutic benefits on neurodegenerative diseases. Here we found that ampelopsin A is a major compound in V. vinifera and it has neuroprotective effects on experimental animals. Bath application of ampelopsin A (10 ng/µL) restores the long-term potentiation (LTP) impairment induced by scopolamine (100 μM) in hippocampal CA3-CA1 synapses. Based on these results, we administered the ampelopsin A (10 ng/µL, three times a week) into the third ventricle of the brain in C57BL/6 mice for a month. Chronic administration of ampelopsin A into the brain ameliorated cognitive memory-behaviors in mice given scopolamine (0.8 mg/kg, i.p.). Studies of mice’s hippocampi showed that the response of ampelopsin A was responsible for the restoration of the cholinergic deficits and molecular signal cascades via BDNF/CREB pathways. In conclusion, the central administration of ampelopsin A contributes to increasing neurocognitive and neuroprotective effects on intrinsic neuronal excitability and behaviors, partly through elevated BDNF/CREB-related signaling.

Consolidation of memory traces in cultured cortical networks requires low cholinergic tone, synchronized activity and high network excitability

In systems consolidation, encoded memories are replayed by the hippocampus during slow-wave sleep (SWS), and permanently stored in the neocortex. Declarative memory consolidation is believed to benefit from the oscillatory rhythms and low cholinergic tone observed in this sleep stage, but underlying mechanisms remain unclear. To clarify the role of cholinergic modulation and synchronized activity in memory consolidation, we applied repeated electrical stimulation in mature cultures of dissociated rat cortical neurons with high or low cholinergic tone, mimicking the cue replay observed during systems consolidation under distinct cholinergic concentrations. In the absence of cholinergic input, these cultures display activity patterns hallmarked by network bursts, synchronized events reminiscent of the low frequency oscillations observed during SWS. They display stable activity and connectivity, which mutually interact and achieve an equilibrium. Electrical stimulation reforms the equilibrium to include the stimulus response, a phenomenon interpreted as memory trace formation. Without cholinergic input, activity was burst-dominated. First application of a stimulus induced significant connectivity changes, while subsequent repetition no longer affected connectivity. Presenting a second stimulus at a different electrode had the same effect, whereas returning to the initial stimuli did not induce further connectivity alterations, indicating that the second stimulus did not erase the 'memory trace' of the first. Distinctively, cultures with high cholinergic tone displayed reduced network excitability and dispersed firing, and electrical stimulation did not induce significant connectivity changes. We conclude that low cholinergic tone facilitates memory formation and consolidation, possibly through enhanced network excitability. Network bursts or SWS oscillations may merely reflect high network excitability.

Long-term effects of early postnatal nicotine exposure on cholinergic function in the mouse hippocampal CA1 region

In rodent models of smoking during pregnancy, early postnatal nicotine exposure results in impaired hippocampus-dependent memory, but the underlying mechanism remains elusive. Given that hippocampal cholinergic systems modulate memory and rapid development of hippocampal cholinergic systems occurs during nicotine exposure, here we investigated its impacts on cholinergic function. Both nicotinic and muscarinic activation produce transient or long-lasting depression of excitatory synaptic transmission in the hippocampal CA1 region. We found that postnatal nicotine exposure impairs both the induction and nicotinic modulation of NMDAR-dependent long-term depression (LTD). Activation of muscarinic receptors decreases excitatory synaptic transmission and CA1 network activity in both wild-type and α2 knockout mice. These muscarinic effects are still observed in nicotine-exposed mice. M1 muscarinic receptor activity is required for mGluR-dependent LTD. Early postnatal nicotine exposure has no effect on mGluR-dependent LTD induction, suggesting that it has no effect on the function of m1 muscarinic receptors involved in this form of LTD. Our results demonstrate that early postnatal nicotine exposure has more pronounced effects on nicotinic function than muscarinic function in the hippocampal CA1 region. Thus, impaired hippocampus-dependent memory may arise from the developmental disruption of nicotinic cholinergic systems in the hippocampal CA1 region.