Cholinergic regulation of object recognition memory

A central role for acetylcholine in entorhinal cortex function and dysfunction with age in humans and mice

Structural and functional changes in the entorhinal cortex (EC) are among the earliest signs of cognitive aging. Here, we ask whether a compromised cholinergic system influences early EC impairments and plays a primary role in EC cognition. We evaluated the relationship between loss of integrity of cholinergic inputs to the EC and cognitive deficits in otherwise healthy humans and mice. Using in vivo imaging (PET/MRI) in older humans and high-resolution imaging in wild-type mice and mice with genetic susceptibility to Alzheimer's disease pathology, we establish that loss of cholinergic input to the EC is, in fact, an early feature in cognitive aging. Through mechanistic studies in mice, we find a central role for EC-projecting cholinergic neurons in the expression of EC-related behaviors. Our data demonstrate that alterations to the cholinergic EC are an early, conserved feature of cognitive aging across species and may serve as an early predictor of cognitive status.

Atypical hippocampal excitatory neurons express and govern object memory

Classically, pyramidal cells of the hippocampus are viewed as flexibly representing spatial and non-spatial information. Recent work has illustrated distinct types of hippocampal excitatory neurons, suggesting that hippocampal representations and functions may be constrained and interpreted by these underlying cell-type identities. In mice, here we reveal a non-pyramidal excitatory neuron type - the "ovoid" neuron - that is spatially adjacent to subiculum pyramidal cells but differs in gene expression, electrophysiology, morphology, and connectivity. Functionally, novel object encounters drive sustained ovoid neuron activity, whereas familiar objects fail to drive activity even months after single-trial learning. Silencing ovoid neurons prevents non-spatial object learning but leaves spatial learning intact, and activating ovoid neurons toggles novel-object seeking to familiar-object seeking. Such function is doubly dissociable from pyramidal neurons, wherein manipulation of pyramidal cells affects spatial assays but not non-spatial learning. Ovoid neurons of the subiculum thus illustrate selective cell-type-specific control of non-spatial memory and behavioral preference.

Traumatic Brain Injury Exacerbates Alcohol Consumption and Neuroinflammation with Decline in Cognition and Cholinergic Activity

Traumatic brain injury (TBI) is a global health challenge, responsible for 30% of injury-related deaths and significantly contributing to disability. Annually, over 50 million TBIs occur worldwide, with most adult patients at emergency departments showing alcohol in their system. TBI is also a known risk factor for alcohol abuse, yet its interaction with alcohol consumption remains poorly understood. In this study, we demonstrate that the fluid percussion injury (FPI) model of TBI in mice significantly increases alcohol consumption and impairs cognitive function. At cellular levels, FPI markedly reduced the number and activity of striatal cholinergic interneurons (CINs) while increasing microglial cells. Notably, depleting microglial cells provided neuroprotection, mitigating cholinergic loss and enhancing cholinergic activity. These findings suggest that TBI may promote alcohol consumption and impair cognitive abilities through microglia activation and consequently reduced cholinergic function. Our research provides critical insights into the mechanisms linking TBI with increased alcohol use and cognitive deficits, potentially guiding future therapeutic strategies.

Moderate capsaicin-containing kochujang alleviates memory impairment through the gut-brain axis in rats with scopolamine-induced amnesia

This study investigated the efficacy and mechanism of traditionally made kochujang(TMK) with different capsaicin levels to alleviate memory impairment in rats with scopolamine-induced amnesia. Sprague-Dawley male rats were administered scopolamine (2 mg/kg bw/day) intraperitoneally to suppress the parasympathetic nervous system(PNS) and induce memory impairment. The rats were divided into four experimental groups, each consuming a diet containing 1 % kochujang in a 43-energy% high-fat diet(HFD) for 8 weeks. The TMK samples used for the study were categorized according to their capsaicin(CPS) content as follows: Low-CPS(0.5 mg%), medium-CPS(1.2 mg%), and high-CPS(1.7 mg%). In addition, factory-made kochujang (FMK; 1.1 mg% capsaicin) was also tested. The effects of kochujang were compared with the Control group(scopolamine), Positive-control(scopolamine+donepezil), and Normal-control(saline) fed HFD. Kochujang consumption reduced body weight and fat mass compared to the Control group. Compared to the Control, memory function measured using passive avoidance, water maze, and novel object recognition tests was enhanced in kochujang-fed rats, especially in the Medium-CPS group, similar to Positive-control. The Medium-CPS and Positive-control groups also exhibited inhibition of hippocampal cell death and increased cholesterol and triglyceride contents and mRNA expression of TNF-α and IL-1β in the brain tissue compared to the Control group. Additionally, TMK elevated short-chain fatty acid, particularly, butyrate concentration in the portal vein. Scopolamine disturbed large intestine cell morphology and gut microbiota composition, and kochujang improved them. Kochujang in the medium-CPS (1.2 mg%) had a more significant impact on the gut microbiota in the interaction analysis between gut microbiota and memory function. In conclusion, kochujang, especially with medium-CPS (1.2 mg%), is a potential dietary intervention to mitigate memory impairment and promote overall cognitive health through improving eubiosis, potentially linked to the gut-brain axis in PNS-suppressed rats.

Enhanced Novel Object Recognition and Spatial Memory in Rats Selectively Bred for High Nicotine Preference

This study examined the influence of genetic background on cognitive performance in a selectively bred high nicotine-preferring (NP) rat line. Using the novel object recognition (NOR), novel location recognition (NLR), and Morris water maze (MWM) tests, we evaluated object memory, spatial memory, and spatial navigation in nicotine-naive NP rats compared to controls. Our results demonstrate that in the NOR test, both male and female NP rats spent more time exploring the novel object (higher discrimination index) compared to sex-matched controls. In the NLR, the discrimination index differed significantly from zero chance (no preference) in both NP males and females but not in controls, indicating enhanced spatial memory in the NP line. During MWM acquisition, the NP groups and control males took a shorter path to reach the platform compared to control females. On the probe trial, the distance traveled in the target quadrant was longer for NP males and females compared to their respective controls, suggesting enhanced spatial navigation and learning in the NP rats. The interesting preference for novel objects and locations displayed by NP rats may indicate a potential novelty-seeking phenotype in this line. These results highlight the complex interplay between genetic factors, cognitive function, and nicotine preference.

Cell-type-specific optogenetic fMRI on basal forebrain reveals functional network basis of behavioral preference

The basal forebrain (BF) is a complex structure that plays key roles in regulating various brain functions. However, it remains unclear how cholinergic and non-cholinergic BF neurons modulate large-scale functional networks and their relevance in intrinsic and extrinsic behaviors. With an optimized awake mouse optogenetic fMRI approach, we revealed that optogenetic stimulation of four BF neuron types evoked distinct cell-type-specific whole-brain BOLD activations, which could be attributed to BF-originated low-dimensional structural networks. Additionally, optogenetic activation of VGLUT2, ChAT, and PV neurons in the BF modulated the preference for locomotion, exploration, and grooming, respectively. Furthermore, we uncovered the functional network basis of the above BF-modulated behavioral preference through a decoding model linking the BF-modulated BOLD activation, low-dimensional structural networks, and behavioral preference. To summarize, we decoded the functional network basis of differential behavioral preferences with cell-type-specific optogenetic fMRI on the BF and provided an avenue for investigating mouse behaviors from a whole-brain view.

Cholinergic-Sensitive Theta Oscillations in Memory Encoding in Mice

Cholinergic regulation of hippocampal theta oscillations has long been proposed to be a potential mechanism underlying hippocampus-dependent memory encoding processes. However, cholinergic transmission has been traditionally associated with type II theta under urethane anesthesia. The mechanisms and behavioral significance of cholinergic regulation of type I theta in freely exploring animals is much less clear. In this study, we examined the potential behavioral significance of cholinergic regulation of theta oscillations in the object location task in male mice that involves training and testing trials and provides an ideal behavioral task to study the underlying memory encoding and retrieval processes, respectively. Cholinergic regulation of hippocampal theta oscillations and the behavioral outcomes was examined by either intrahippocampal infusion of cholinergic receptor antagonists or knocking out cholinergic receptors in excitatory neurons or interneurons. We found that both muscarinic acetylcholine receptors (mAChRs) and α7 nicotinic AChRs (α7 nAChRs) regulated memory encoding by engaging excitatory neurons and interneurons, respectively. There is a transient upregulated theta oscillation at the beginning of individual object exploration events that only occurred in the training trials, but not in the testing trials. This transient upregulated theta is also the only theta component that significantly differed between training and testing trials and was sensitive to mAChR and α7 nAChR antagonists. Thus, our study has revealed a transient cholinergic-sensitive theta component that is specifically associated with memory encoding, but not memory retrieval, in the object location task, providing direct experimental evidence supporting a role for cholinergic-regulated theta oscillations in hippocampus-dependent memory encoding processes.

Loss of cholinergic input to the entorhinal cortex is an early indicator of cognitive impairment in natural aging of humans and mice

In a series of translational experiments using fully quantitative positron emission tomography (PET) imaging with a new tracer specific for the vesicular acetylcholine transporter ([18F]VAT) in vivo in humans, and genetically targeted cholinergic markers in mice, we evaluated whether changes to the cholinergic system were an early feature of age-related cognitive decline. We found that deficits in cholinergic innervation of the entorhinal cortex (EC) and decline in performance on behavioral tasks engaging the EC are, strikingly, early features of the aging process. In human studies, we recruited older adult volunteers that were physically healthy and without prior clinical diagnosis of cognitive impairment. Using [18F]VAT PET imaging, we demonstrate that there is measurable loss of cholinergic inputs to the EC that can serve as an early signature of decline in EC cognitive performance. These deficits are specific to the cholinergic circuit between the medial septum and vertical limb of the diagonal band (MS/vDB; CH1/2) to the EC. Using diffusion imaging, we further demonstrate impaired structural connectivity in the tracts between the MS/vDB and EC in older adults with mild cognitive impairment. Experiments in mouse, designed to parallel and extend upon the human studies, used high resolution imaging to evaluate cholinergic terminal density and immediate early gene (IEG) activity of EC neurons in healthy aging mice and in mice with genetic susceptibility to accelerated accumulation amyloid beta plaques and hyperphosphorylated mouse tau. Across species and aging conditions, we find that the integrity of cholinergic projections to the EC directly correlates with the extent of EC activation and with performance on EC-related object recognition memory tasks. Silencing EC-projecting cholinergic neurons in young, healthy mice during the object-location memory task impairs object recognition performance, mimicking aging. Taken together we identify a role for acetylcholine in normal EC function and establish loss of cholinergic input to the EC as an early, conserved feature of age-related cognitive decline in both humans and rodents.

Local Thyroid Hormone Action in Brain Development

Proper brain development essentially depends on the timed availability of sufficient amounts of thyroid hormone (TH). This, in turn, necessitates a tightly regulated expression of TH signaling components such as TH transporters, deiodinases, and TH receptors in a brain region- and cell-specific manner from early developmental stages onwards. Abnormal TH levels during critical stages, as well as mutations in TH signaling components that alter the global and/or local thyroidal state, result in detrimental consequences for brain development and neurological functions that involve alterations in central neurotransmitter systems. Thus, the question as to how TH signaling is implicated in the development and maturation of different neurotransmitter and neuromodulator systems has gained increasing attention. In this review, we first summarize the current knowledge on the regulation of TH signaling components during brain development. We then present recent advances in our understanding on how altered TH signaling compromises the development of cortical glutamatergic neurons, inhibitory GABAergic interneurons, cholinergic and dopaminergic neurons. Thereby, we highlight novel mechanistic insights and point out open questions in this evolving research field.

Nicotinic acetylcholine receptors and learning and memory deficits in Neuroinflammatory diseases

Animal survival depends on cognitive abilities such as learning and memory to adapt to environmental changes. Memory functions require an enhanced activity and connectivity of a particular arrangement of engram neurons, supported by the concerted action of neurons, glia, and vascular cells. The deterioration of the cholinergic system is a common occurrence in neurological conditions exacerbated by aging such as traumatic brain injury (TBI), posttraumatic stress disorder (PTSD), Alzheimer's disease (AD), and Parkinson's disease (PD). Cotinine is a cholinergic modulator with neuroprotective, antidepressant, anti-inflammatory, antioxidant, and memory-enhancing effects. Current evidence suggests Cotinine's beneficial effects on cognition results from the positive modulation of the α7-nicotinic acetylcholine receptors (nAChRs) and the inhibition of the toll-like receptors (TLRs). The α7nAChR affects brain functions by modulating the function of neurons, glia, endothelial, immune, and dendritic cells and regulates inhibitory and excitatory neurotransmission throughout the GABA interneurons. In addition, Cotinine acting on the α7 nAChRs and TLR reduces neuroinflammation by inhibiting the release of pro-inflammatory cytokines by the immune cells. Also, α7nAChRs stimulate signaling pathways supporting structural, biochemical, electrochemical, and cellular changes in the Central nervous system during the cognitive processes, including Neurogenesis. Here, the mechanisms of memory formation as well as potential mechanisms of action of Cotinine on memory preservation in aging and neurological diseases are discussed.

Urocanic acid facilitates acquisition of object recognition memory in mice

Trans-urocanic acid (UCA), an isomer of cis-UCA that is located in the skin, has recently been reported to have a role in short-term working memory and in the consolidation, reconsolidation and retrieval of long-term memory. However, its effect on memory acquisition remains unclear. In the present study, the effect of UCA on short-term and long-term memory acquisition in mice was investigated using novel object recognition (NOR) and object location recognition (OLR) protocols that each involved three stages: habituation, sampling and testing. UCA was intraperitoneally injected 0.5 h pre-sampling, and the discrimination index during subsequent testing was determined in NOR and OLR tasks. The results showed that 10 mg/kg UCA significantly facilitated short-term and long-term memory acquisition in both types of tasks. Furthermore, 30 mg/kg UCA significantly facilitated long-term memory acquisition in the NOR task and tended to facilitate long-term memory acquisition in the OLR tasks but did not facilitate short-term memory acquisition in either task. Additionally, the enhancing role of UCA on memory acquisition was not dependent on changes of nonspecific responses, e.g. exploratory behavior and locomotor activity. The current study suggests that UCA facilitates short-term and long-term recognition memory acquisition, which further extends the functional role of UCA in the brain function.

N-acetyl-5-methoxykynuramine enhance object location and working memory performances via modulating CaMKII, ERK and CREB phosphorylation

OBJECTIVES

Melatonin (MEL) has been reported to enhance cognitive performance. Recently, we have demonstrated that a MEL metabolite N-acetyl-5-methoxykynuramine (AMK) promoted the formation of long-term object recognition memory more potently than MEL. Here, we examined the effects of 1 mg/kg MEL and AMK on both object location memory and spatial working memory. We also investigated the effects of the same dose of these drugs on relative phosphorylation/activation levels of memory-related proteins in the hippocampus (HP), the perirhinal cortex (PRC) and the medial prefrontal cortex (mPFC).

METHODS

Object location memory and spatial working memory were assessed using the object location task and the Y-maze spontaneous alternation task, respectively. Relative phosphorylation/activation levels of memory-related proteins were assessed using western blot analysis.

RESULTS

AMK, as well as MEL, enhanced object location memory and spatial working memory. AMK increased the phosphorylation of cAMP-response element-binding protein (CREB) in both the HP and the mPFC 2 h after the treatment. AMK also increased the phosphorylation of extracellular signal-regulated kinases (ERKs) but decreased that of Ca2+/calmodulin-dependent protein kinases II (CaMKIIs) in the PRC and the mPFC 30 min after the treatment. MEL increased CREB phosphorylation in the HP 2 h after the treatment, whereas no detectable changes in the other proteins examined were observed.

CONCLUSION

These results suggested the possibility that AMK exerts stronger memory-enhancing effects than MEL by more remarkably altering the activation of memory-related proteins such as ERKs, CaMKIIs and CREB in broader brain regions, including the HP, mPFC and PRC, compared to MEL.

Cholinergic neurons in the basal forebrain are involved in behavioral abnormalities associated with Cul3 deficiency: Role of prefrontal cortex projections in cognitive deficits

Loss-of-function mutations of the gene Cul3 have been identified as a risk factor for autism-spectrum disorder (ASD), but the pathogenic mechanisms are not well understood. Conditional Cul3 ablation in cholinergic neurons of mice (ChatCRECul3F/+) recapitulated ASD-like social and sensory gating phenotypes and caused significant cognitive impairments, with diminished activity of cholinergic neurons in the basal forebrain (BF). Chemogenetic inhibition of BF cholinergic neurons in healthy mice induced similar social and cognitive deficits. Conversely, chemogenetic stimulation of BF cholinergic neurons in ChatCRECul3F/+ mice reversed abnormalities in sensory gating and cognition. Cortical hypofunction was also found after ChAT-specific Cul3 ablation and stimulation of cholinergic projections from the BF to the prefrontal cortex (PFC) mitigated cognitive deficits. Overall, we demonstrate that cholinergic dysfunction due to Cul3 deficiency is involved in ASD-like behavioral abnormalities, and that BF cholinergic neurons are particularly critical for cognitive component through their projections to the PFC.