The systems-level organization of cholinergic innervation in the human cerebral cortex and its alterations in Alzheimer's disease

A review of the neurotransmitter system associated with cognitive function of the cerebellum in Parkinson's disease

The dichotomized brain system is a concept that was generalized from the 'dual syndrome hypothesis' to explain the heterogeneity of cognitive impairment, in which anterior and posterior brain systems are independent but partially overlap. The dopaminergic system acts on the anterior brain and is responsible for executive function, working memory, and planning. In contrast, the cholinergic system acts on the posterior brain and is responsible for semantic fluency and visuospatial function. Evidence from dopaminergic/cholinergic imaging or functional neuroimaging has shed significant insight relating to the involvement of the cerebellum in the cognitive process of patients with Parkinson's disease. Previous research has reported evidence that the cerebellum receives both dopaminergic and cholinergic projections. However, whether these two neurotransmitter systems are associated with cognitive function has yet to be fully elucidated. Furthermore, the precise role of the cerebellum in patients with Parkinson's disease and cognitive impairment remains unclear. Therefore, in this review, we summarize the cerebellar dopaminergic and cholinergic projections and their relationships with cognition, as reported by previous studies, and investigated the role of the cerebellum in patients with Parkinson's disease and cognitive impairment, as determined by functional neuroimaging. Our findings will help us to understand the role of the cerebellum in the mechanisms underlying cognitive impairment in Parkinson's disease.

Utilizing mobile robotics for pelvic perturbations to improve balance and cognitive performance in older adults: a randomized controlled trial

Late-life balance disorders remain a severe problem with fatal consequences. Perturbation-based balance training (PBT), a form of rehabilitation that intentionally introduces small, unpredictable disruptions to an individual's gait cycle, can improve balance. The Tethered Pelvic Assist Device (TPAD) is a cable-driven robotic trainer that applies perturbations to the user's pelvis during treadmill walking. Earlier work showcased improved gait stability and the first evidence of increased cognition acutely. The mobile Tethered Pelvic Assist Device (mTPAD), a portable version of the TPAD, applies perturbations to a pelvic belt via a posterior walker during overground gait, as opposed to treadmill walking. Forty healthy older adults were randomly assigned to a control group (CG, n = 20) without mTPAD PBT or an experimental group (EG, n = 20) with mTPAD PBT for a two-day study. Day 1 consisted of baseline anthropometrics, vitals, and functional and cognitive measurements. Day 2 consisted of training with the mTPAD and post-interventional cognitive and functional measurements. Results revealed that the EG significantly outperformed the CG in several cognitive (SDMT-C and TMT-B) and functional (BBS and 4-Stage Balance: one-foot stand) measurements while showcasing increased confidence in mobility based on FES-I. To our knowledge, our study is the first randomized, large group (n = 40) clinical study exploring new mobile perturbation-based robotic gait training technology.

Utilizing Mobile Robotics for Pelvic Perturbations to Improve Balance and Cognitive Performance in Older Adults: A Randomized Controlled Trial

Late-life balance disorders remain a severe problem with fatal consequences. Perturbation-based balance training (PBT), a form of rehabilitation that intentionally introduces small, unpredictable disruptions to an individual's gait cycle, can improve balance. The Tethered Pelvic Assist Device (TPAD) is a cable-driven robotic trainer that applies perturbations to the user's pelvis during treadmill walking. Earlier work showcased improved gait stability and the first evidence of increased cognition acutely. The mobile Tethered Pelvic Assist Device (mTPAD), a portable version of the TPAD, applies perturbations to a pelvic belt via a posterior walker during overground gait, as opposed to treadmill walking. Forty healthy older adults were randomly assigned to a control group (CG, n = 20) without mTPAD PBT or an experimental group (EG, n = 20) with mTPAD PBT for a two-day study. Day 1 consisted of baseline anthropometrics, vitals, and functional and cognitive measurements. Day 2 consisted of training with the mTPAD and post-interventional cognitive and functional measurements. Results revealed that the EG significantly outperformed the CG in cognitive and functional tasks while showcasing increased confidence in mobility. Gait analysis demonstrated that the mTPAD PBT significantly improved mediolateral stability during lateral perturbations. To our knowledge, our study is the first randomized, large group (n = 40) clinical study exploring new mobile perturbation-based robotic gait training technology.

Common Neuroanatomical Substrate of Cholinergic Pathways and Language-Related Brain Regions as an Explanatory Framework for Evaluating the Efficacy of Cholinergic Pharmacotherapy in Post-Stroke Aphasia: A Review

Despite the relative scarcity of studies focusing on pharmacotherapy in aphasia, there is evidence in the literature indicating that remediation of language disorders via pharmaceutical agents could be a promising aphasia treatment option. Among the various agents used to treat chronic aphasic deficits, cholinergic drugs have provided meaningful results. In the current review, we focused on published reports investigating the impact of acetylcholine on language and other cognitive disturbances. It has been suggested that acetylcholine plays an important role in neuroplasticity and is related to several aspects of cognition, such as memory and attention. Moreover, cholinergic input is diffused to a wide network of cortical areas, which have been associated with language sub-processes. This could be a possible explanation for the positive reported outcomes of cholinergic drugs in aphasia recovery, and specifically in distinct language processes, such as naming and comprehension, as well as overall communication competence. However, evidence with regard to functional alterations in specific brain areas after pharmacotherapy is rather limited. Finally, despite the positive results derived from the relevant studies, cholinergic pharmacotherapy treatment in post-stroke aphasia has not been widely implemented. The present review aims to provide an overview of the existing literature in the common neuroanatomical substrate of cholinergic pathways and language related brain areas as a framework for interpreting the efficacy of cholinergic pharmacotherapy interventions in post-stroke aphasia, following an integrated approach by converging evidence from neuroanatomy, neurophysiology, and neuropsychology.

Altered Cholinergic Innervation in De Novo Parkinson's Disease with and without Cognitive Impairment

Background

Altered cholinergic innervation plays a putative role in cognitive impairment in Parkinson's disease (PD) at least in advanced stages. Identification of the relationship between cognitive impairment and cholinergic innervation early in the disease will provide better insight into disease prognosis and possible early intervention.

Objective

The aim was to assess regional cholinergic innervation status in de novo patients with PD, with and without cognitive impairment.

Methods

Fifty‐seven newly diagnosed, treatment‐naive, PD patients (32 men, mean age 64.6 ± 8.2 years) and 10 healthy controls (5 men, mean age 54.6 ± 6.0 years) were included. All participants underwent cholinergic [¹⁸F]fluoroethoxybenzovesamicol positron emission tomography and detailed neuropsychological assessment. PD patients were classified as either cognitively normal (PD‐NC) or mild cognitive impairment (PD‐MCI). Whole brain voxel‐based group comparisons were performed.

Results

Results show bidirectional cholinergic innervation changes in PD. Both PD‐NC and PD‐MCI groups showed significant cortical cholinergic denervation compared to controls (P < 0.05, false discovery rate corrected), primarily in the posterior cortical regions. Higher‐than‐normal binding was most prominent in PD‐NC in both cortical and subcortical regions, including the cerebellum, cingulate cortex, putamen, gyrus rectus, hippocampus, and amygdala.

Conclusion

Altered cholinergic innervation is already present in de novo patients with PD. Posterior cortical cholinergic losses were present in all patients independent of cognitive status. Higher‐than‐normal binding in cerebellar, frontal, and subcortical regions in cognitively intact patients may reflect compensatory cholinergic upregulation in early‐stage PD. Limited or failing cholinergic upregulation may play an important role in early, clinically evident cognitive impairment in PD. © 2022 The Authors. Movement Disorders published by Wiley Periodicals LLC on behalf of International Parkinson and Movement Disorder Society

OUP accepted manuscript

Cognitive deficits in Alzheimer’s disease, specifically amnestic (memory dominant) deficits, are associated with cholinergic degeneration in the basal forebrain. The cholinergic nucleus within the basal forebrain, the nucleus basalis of Meynert, exhibits local atrophy and reduced cortical tract integrity on MRI, and reveals amyloid-β and phosphorylated-tau pathology at autopsy. To understand the pathophysiology of nucleus basalis of Meynert atrophy and its neocortical projections in Alzheimer’s disease, we used a combined post-mortem in situ MRI and histopathology approach. A total of 19 Alzheimer’s disease (10 amnestic and nine non-amnestic) and nine non-neurological control donors underwent 3 T T₁-weighted MRI for anatomical delineation and volume assessment of the nucleus basalis of Meynert, and diffusion-weighted imaging for microstructural assessment of the nucleus and its projections. At subsequent brain autopsy, tissue dissection and immunohistochemistry were performed for amyloid-β, phosphorylated-tau and choline acetyltransferase. Compared to controls, we observed an MRI-derived volume reduction and altered microstructural integrity of the nucleus basalis of Meynert in Alzheimer’s disease donors. Furthermore, decreased cholinergic cell density was associated with reduced integrity of the nucleus and its tracts to the temporal lobe, specifically to the temporal pole of the superior temporal gyrus, and the parahippocampal gyrus. Exploratory post hoc subgroup analyses indicated that cholinergic cell density could be associated with cortical tract alterations in amnestic Alzheimer’s disease donors only. Our study illustrates that in Alzheimer’s disease, cholinergic degeneration in the nucleus basalis of Meynert may contribute to damaged cortical projections, specifically to the temporal lobe, leading to cognitive deterioration.

A deep learning toolbox for automatic segmentation of subcortical limbic structures from MRI images

A tool was developed to automatically segment several subcortical limbic structures (nucleus accumbens, basal forebrain, septal nuclei, hypothalamus without mammillary bodies, the mammillary bodies, and fornix) using only a T1-weighted MRI as input. This tool fills an unmet need as there are few, if any, publicly available tools to segment these clinically relevant structures. A U-Net with spatial, intensity, contrast, and noise augmentation was trained using 39 manually labeled MRI data sets. In general, the Dice scores, true positive rates, false discovery rates, and manual-automatic volume correlation were very good relative to comparable tools for other structures. A diverse data set of 698 subjects were segmented using the tool; evaluation of the resulting labelings showed that the tool failed in less than 1% of cases. Test-retest reliability of the tool was excellent. The automatically segmented volume of all structures except mammillary bodies showed effectiveness at detecting either clinical AD effects, age effects, or both. This tool will be publicly released with FreeSurfer (surfer.nmr.mgh.harvard.edu/fswiki/ScLimbic). Together with the other cortical and subcortical limbic segmentations, this tool will allow FreeSurfer to provide a comprehensive view of the limbic system in an automated way.

Effects of Radix Polygalae on Cognitive Decline and Depression in Estradiol Depletion Mouse Model of Menopause

Postmenopausal syndrome refers to symptoms caused by the gradual decrease in female hormones after mid-40 years. As a target organ of estrogen, decrease in estrogen causes various changes in brain function such as a decrease in choline acetyltransferase and brain-derived neurotrophic factor; thus, postmenopausal women experience cognitive decline and more depressive symptoms than age-matched men. Radix Polygalae has been used for memory boosting and as a mood stabilizer and its components have shown neuroprotective, antidepressant, and stress relief properties. In a mouse model of estrogen depletion induced by 4-vinylcyclohexene diepoxide, Radix Polygalae was orally administered for 3 weeks. In these animals, cognitive and depression-related behaviors and molecular changes related to these behaviors were measured in the prefrontal cortex and hippocampus. Radix Polygalae improved working memory and contextual memory and despair-related behaviors in 4-vinylcyclohexene diepoxide-treated mice without increasing serum estradiol levels in this model. In relation to these behaviors, choline acetyltransferase and brain-derived neurotrophic factor in the prefrontal cortex and hippocampus and bcl-2-associated athanogene expression increased in the hippocampus. These results implicate the possible benefit of Radix Polygalae in use as a supplement of estrogen to prevent conditions such as postmenopausal depression and cognitive decline.

Effects of adolescent substance use disorders on central cholinergic function

Adolescence is a transitional period between childhood and adulthood, in which the individual undergoes significant cognitive, behavioral, physical, emotional, and social developmental changes. During this period, adolescents engage in experimentation and risky behaviors such as licit and illicit drug use. Adolescents' high vulnerability to abuse drugs and natural reinforcers leads to greater risk for developing substance use disorders (SUDs) during adulthood. Accumulating evidence indicates that the use and abuse of licit and illicit drugs during adolescence and emerging adulthood can disrupt the cholinergic system and its processes. This review will focus on the effects of peri-adolescent nicotine and/or alcohol use, or exposure, on the cholinergic system during adulthood from preclinical and clinical studies. This review further explores potential cholinergic agents and pharmacological manipulations to counteract peri-adolescent nicotine and/or alcohol abuse.

New Developments in Cholinergic Imaging in Alzheimer and Lewy Body Disorders

PURPOSE OF REVIEW

This paper aims to review novel trends in cholinergic neuroimaging in Alzheimer and Lewy body parkinsonian disorders.

RECENT FINDINGS

The spectrum of cholinergic imaging is expanding with the availability of spatially more precise radioligands that allow assessment of previously less recognized subcortical and cortical structures with more dense cholinergic innervation. In addition, advances in MRI techniques now allow quantitative structural or functional assessment of both the cholinergic forebrain and the pedunculopontine nucleus, which may serve as non-invasive prognostic predictors. Multimodal imaging approaches, such as PET-MRI or multiligand PET offer new insights into the dynamic and interactive roles of the cholinergic system at both local and larger-scale neural network levels.

SUMMARY

Our understanding of the heterogeneous roles of the cholinergic system in age-related diseases is evolving. Multimodal imaging approaches that provide complimentary views of the cholinergic system will be necessary to shed light on the impact of cholinergic degeneration on regional and large-scale neural networks that underpin clinical symptom manifestation in neurodegeneration.

Cholinergic nucleus 4 atrophy and gait impairment in Parkinson's disease

BACKGROUND

There is evidence that cortical cholinergic denervation contributes to gait and balance impairment in Parkinson's Disease (PD), especially reduced gait speed.

OBJECTIVES

The objective of this study was to determine the relationship between cholinergic basal forebrain gray matter density (GMD) and gait in PD patients.

METHODS

We investigated 66 PD patients who underwent a pre-surgical evaluation for a neurosurgical procedure to treat motor symptoms of PD. As part of this evaluation patients had a brain MRI and formal gait assessments. By applying probabilistic maps of the cholinergic basal forebrain to voxel-based morphometry of brain MRI, we calculated gray matter density (GMD) for cholinergic nucleus 4 (Ch4), cholinergic nucleus 1, 2, and 3 (Ch123), and the entire cortex.

RESULTS

Reduced Ch4 GMD was associated with reduced Fast Walking Speed in the "on" medication state (FWSON, p = 0.004). Bilateral cortical GMD was also associated with FWSON (p = 0.009), but Ch123 GMD was not (p = 0.1). Bilateral cortical GMD was not associated with FWSON after adjusting for Ch4 GMD (p = 0.44). While Ch4 GMD was not associated with improvement in Timed Up and Go (TUG) or Cognitive TUG in the "on" medication state, reduced Ch4 GMD was associated with greater percent worsening based on dual tasks (p = 0.021).

CONCLUSIONS

Reduced Ch4 GMD is associated with slower gait speed in PD and greater percent worsening in TUG during dual tasks in patients with PD. These findings have implications for planning of future clinical trials investigating cholinergic therapies to improve gait impairment in PD.

Neuropathologic features associated with basal forebrain atrophy in Alzheimer disease

OBJECTIVE

To study the neuropathologic correlates of cholinergic basal forebrain (BF) atrophy as determined using antemortem MRI in the Alzheimer disease (AD) spectrum.

METHODS

We determined associations between BF volume from antemortem MRI brain scans and postmortem assessment of neuropathologic features, including neuritic plaques, neurofibrillary tangles (NFTs), Lewy body (LB) pathology, and TDP-43, in 64 cases of the Alzheimer's Disease Neuroimaging Initiative cohort. For comparison, we assessed neuropathologic features associated with hippocampal and parahippocampal gyrus atrophy. In addition to region of interest-based analysis, we determined the association of neuropathologic features with whole brain gray matter volume using regionally unbiased voxel-based volumetry.

RESULTS

BF atrophy was associated with Thal amyloid phases (95% confidence interval [CI] -0.49 to -0.01, p = 0.049) and presence of LB pathology (95% CI -0.54 to -0.06, p = 0.015), as well as with the degree of LB pathology within the nucleus basalis Meynert (95% CI -0.54 to -0.07, p = 0.025). These effects were no longer significant after false discovery rate (FDR) correction. Hippocampal atrophy was significantly associated with the presence of TDP-43 pathology (95% CI -0.61 to -0.17, p = 0.003; surviving FDR correction), in addition to dentate gyrus NFT load (95% CI -0.49 to -0.01, p = 0.044; uncorrected). Voxel-based analysis confirmed spatially restricted effects of Thal phases and presence of LB pathology on BF volume.

CONCLUSIONS

These findings indicate that neuropathologic correlates of regional atrophy differ substantially between different brain regions that are typically involved in AD-related neurodegeneration, including different susceptibilities to common comorbid pathologies.

Dystonia and dopamine: From phenomenology to pathophysiology

A line of evidence suggests that the pathophysiology of dystonia involves the striatum, whose activity is modulated among other neurotransmitters, by the dopaminergic system. However, the link between dystonia and dopamine appears complex and remains unclear. Here, we propose a physiological approach to investigate the clinical and experimental data supporting a role of the dopaminergic system in the pathophysiology of dystonic syndromes. Because dystonia is a disorder of motor routines, we first focus on the role of dopamine and striatum in procedural learning. Second, we consider the phenomenology of dystonia from every angle in order to search for features giving food for thought regarding the pathophysiology of the disorder. Then, for each dystonic phenotype, we review, when available, the experimental and imaging data supporting a connection with the dopaminergic system. Finally, we propose a putative model in which the different phenotypes could be explained by changes in the balance between the direct and indirect striato-pallidal pathways, a process critically controlled by the level of dopamine within the striatum. Search strategy and selection criteria References for this article were identified through searches in PubMed with the search terms « dystonia », « dopamine", « striatum », « basal ganglia », « imaging data », « animal model », « procedural learning », « pathophysiology », and « plasticity » from 1998 until 2018. Articles were also identified through searches of the authors' own files. Only selected papers published in English were reviewed. The final reference list was generated on the basis of originality and relevance to the broad scope of this review.

Molecular Imaging of the Cholinergic System in Parkinson's Disease

One of the first identified neurotransmitters in the brain, acetylcholine, is an important modulator that drives changes in neuronal and glial activity. For more than two decades, the main focus of molecular imaging of the cholinergic system in Parkinson's disease (PD) has been on cognitive changes. Imaging studies have confirmed that degeneration of the cholinergic system is a major determinant of dementia in PD. Within the last decade, the focus is expanding to studying cholinergic correlates of mobility impairments, dyskinesias, olfaction, sleep, visual hallucinations and risk taking behavior in this disorder. These studies increasingly recognize that the regional topography of cholinergic brain areas associates with specific functions. In parallel with this trend, more recent molecular cholinergic imaging approaches are investigating cholinergic modulatory functions and contributions to large-scale brain network functions. A novel area of research is imaging cholinergic innervation functions of peripheral autonomic organs that may have the potential of future prodromal diagnosis of PD. Finally, emerging evidence of hypercholinergic activity in prodromal and symptomatic leucine-rich repeat kinase 2 PD may reflect neuronal cholinergic compensation versus a response to neuro-inflammation. Molecular imaging of the cholinergic system has led to many new insights in the etiology of dopamine non-responsive symptoms of PD (more "malignant" hypocholinergic disease phenotype) and is poised to guide and evaluate future cholinergic drug development in this disorder.

Recent advances in cholinergic imaging and cognitive decline-Revisiting the cholinergic hypothesis of dementia

PURPOSE OF REVIEW

Although the cholinergic hypothesis of dementia provided a successful paradigm for the development of new drugs for dementia, this hypothesis has waned in popularity. Cholinergic brain imaging may provide novel insights into the viability of this hypothesis.

RECENT FINDINGS

Cholinergic receptor and forebrain volumetric studies suggest an important role of the cholinergic system in maintaining brain network integrity that may deteriorate with cognitive decline in Alzheimer disease (AD) and Lewy body disorders (LBD). Bidirectional changes in regional receptor expression may suggest the presence of compensatory responses to neurodegenerative injury. Cholinergic system changes are more complex in LBD because of additional subcortical degenerations compared to AD. Cholinergic-dopaminergic interactions affect attentional, verbal learning and executive functions, and impairments in these two transmitter systems may jointly increase the risk of dementia in Parkinson disease.

SUMMARY

The cholinergic hypothesis is evolving from a primary focus on memory toward expanded cognitive functions modulated by regionally more complex and interactive brain networks. Cholinergic network adaptation may serve as a novel research target in neurodegeneration.

Alzheimer's Disease, Acetylcholine and Oestrogen

Common types of dementia occurring in old age are associated with the loss of cholinergic activity from basal forebrain neurons projecting to the cerebral cortex. In Alzheimer's disease this loss correlates with cognitive decline, and in dementia with Lewy bodies with neuropsychiatric features such a hallucinations. New therapies aimed at restoring the levels of acetylcholine, such as the cholinesterase inhibitors tacrine or donepezil, provide some symptomatic benefit and may also be protective. Similar symptomatic and protective effects of oestrogen may operate through stimulation of the affected cholinergic neurons. These neurons have oestrogen receptors and, in animal models, oestrogen elevates cortical cholinergic activity. Cholinergic control of vasodilation is also affected by oestrogen. Declining oestrogen in postmenopausal women is thus likely to contribute to age-related cognitive decline and increased risk of Alzheimer's via cholinergic mechanisms. In addition to accumulating evidence of the protective effect of oestrogen in Alzheimer's, there is already a report that oestrogen replacement therapy enhances the response of female patients to cholinergic medication (eg, tacrine).

NSC-34 Motor Neuron-Like Cells Are Unsuitable as Experimental Model for Glutamate-Mediated Excitotoxicity

Glutamate-induced excitotoxicity is a major contributor to motor neuron degeneration in the pathogenesis of amyotrophic lateral sclerosis (ALS). The spinal cord × Neuroblastoma hybrid cell line (NSC-34) is often used as a bona fide cellular model to investigate the physiopathological mechanisms of ALS. However, the physiological response of NSC-34 to glutamate remains insufficiently described. In this study, we evaluated the relevance of differentiated NSC-34 (NSC-34D) as an in vitro model for glutamate excitotoxicity studies. NSC-34D showed morphological and physiological properties of motor neuron-like cells and expressed glutamate receptor subunits GluA1-4, GluN1 and GluN2A/D. Despite these diverse characteristics, no specific effect of glutamate was observed on cultured NSC-34D survival and morphology, in contrast to what has been described in primary culture of motor neurons (MN). Moreover, a small non sustained increase in the concentration of intracellular calcium was observed in NSC-34D after exposure to glutamate compared to primary MN. Our findings, together with the inability to obtain cultures containing only differentiated cells, suggest that the motor neuron-like NSC-34 cell line is not a suitable in vitro model to study glutamate-induced excitotoxicity. We suggest that the use of primary cultures of MN is more suitable than NSC-34 cell line to explore the pathogenesis of glutamate-mediated excitotoxicity at the cellular level in ALS and other motor neuron diseases.

Cognitive Impairment and Electroconvulsive Therapy in Geriatric Depression, What Could be the Role of Rivastigmine? A Case Series

Electroconvulsive therapy (ECT), albeit highly effective in treating depression, is frequently associated with cognitive impairment, either temporary or more persistent. Especially in older patients, who generally respond even better, serious cognitive impairment during the course of ECT may lead to premature termination of ECT. Treatment of this cognitive impairment is of utmost importance. In this case series report, we present the effect of rivastigmine, an acetylcholinesterase inhibitor, on cognitive impairment in three older, severely depressed patients during or after a course of ECT. An improvement of cognitive functioning, in particular a decline of confusional symptoms, was observed in two patients with structural brain alterations associated with aging. In the other patient, who suffered primarily from amnesia, no effect of rivastigmine was observed. These preliminary results emphasize the need for detailed profiling of cognitive impairment when developing a research design to study the potential benefits of rivastigmine in the prevention or treatment of cognitive impairment in severely depressed patients treated with ECT.

Cholinergic modulation of stimulus-driven attentional capture

Distraction is one of the main problems encountered by people with degenerative diseases that are associated with reduced cortical cholinergic innervations. We examined the effects of donepezil, a cholinesterase inhibitor, on stimulus-driven attentional capture. Reflexive attention shifts to a distractor are usually elicited by abrupt peripheral changes. This bottom-up shift of attention to a salient item is thought to be the result of relatively inflexible hardwired mechanisms. Thirty young male participants were randomly allocated to one of two groups: placebo first/donepezil second session or the opposite. They were asked to locate a target appearing above and below fixation whilst a peripheral distractor moved abruptly (motion-jitter attentional capture condition) or not (baseline condition). A classical attentional capture effect was observed under placebo: moving distractors interfered with the task in slowing down response times as compared to the baseline condition with fixed distractors. Increased interference from moving distractors was found under donepezil. We suggest that attentional capture in our paradigm likely involved low level mechanisms such as automatic reflexive orienting. Peripheral motion-jitter elicited a rapid reflexive orienting response initiated by a cholinergic signal from the brainstem pedunculo-pontine nucleus that activates nicotinic receptors in the superior colliculus.

Distinguishing attentional gain and tuning in young and older adults

Here we examined with functional magnetic resonance imaging (fMRI) whether advanced age affects 2 mechanisms of attention that are widely thought to enhance signal processing in the sensory neocortex: gain and tuning. Healthy young and older adults discriminated faces under varying levels of object competition while fMRI was acquired. In young adults, cortical response magnitude to attended faces was maintained despite increasing competition, consistent with gain. Cortical response selectivity, indexed from repetition suppression, also increased only for attended faces despite increasing competition, consistent with tuning. Older adults exhibited intact gain, but altered tuning, with extrastriate cortical tuning determined by object salience rather than attention. Moreover, the magnitude of this susceptibility to stimulus-driven processing was associated with a redistribution of attention-driven competitive processes to the frontal cortices. These data indicate that although both gain and tuning are modulated by increased perceptual competition, they are functionally dissociable in the extrastriate cortices, exhibit differential susceptibility to advanced aging, and spare the frontal cortices a considerable processing burden through early selection.

Butyrylcholinesterase: impact on symptoms and progression of cognitive impairment

The most successful approach for treating people with Alzheimer's disease to date has been by improving cholinergic transmission using cholinesterase inhibitors. Many of these drugs selectively inhibit acetylcholinesterase but some agents inhibit both acetylcholinesterase and butyrylcholinesterase. Recent evidence from studies examining butyrylcholinesterase in post mortem brain samples from dementia patients and examining the relationship between butyrylcholinesterase polymorphisms and the progression of cognitive impairment in dementia with Lewy bodies and Alzheimer's disease add to a body of work suggesting that butyrylcholinesterase is present in key brain areas and may influence the maturation of plaques in Alzheimer's disease. These accumulating data suggest that butyrylcholinesterase contributes to disease progression in people with dementia, which may be particularly important in individuals with more severe dementia as butyrylcholinesterase activity increases with disease development. It is a priority for future clinical trials to determine whether agents which inhibit butyrylcholinesterase and acetylcholinesterase have a greater clinical efficacy.

Association of basal forebrain volumes and cognition in normal aging

The basal forebrain cholinergic system (BFCS) is known to undergo moderate neurodegenerative alterations during normal aging and severe atrophy in Alzheimer's disease (AD). It has been suggested that functional and structural alterations of the BFCS mediate cognitive performance in normal aging and AD. But, it is still unclear to what extend age-associated cognitive decline can be related to BFCS in normal aging. We analyzed the relationship between BFCS volume and cognition using MRI and a comprehensive neuropsychological test battery in a cohort of 43 healthy elderly subjects spanning the age range from 60 to 85 years. Most notably, we found significant associations between general intelligence and BFCS volumes, specifically within areas corresponding to posterior nuclei of the nucleus basalis of Meynert (Ch4p) and the nucleus subputaminalis (NSP). Associations between specific cognitive domains and BFCS volumes were less pronounced. Supplementary analyses demonstrated that especially the volume of NSP but also the volume of Ch4p was related to the volume of widespread temporal, frontal, and parietal gray and white matter regions. Volumes of these gray and white matter regions were also related to general intelligence. Higher volumes of Ch4p and NSP may enhance the effectiveness of acetylcholine supply in related gray and white matter regions underlying general intelligence and hence explain the observed association between the volume of Ch4p as well as NSP and general intelligence. Since general intelligence is known to attenuate the degree of age-associated cognitive decline and the risk of developing late-onset AD, the BFCS might, besides the specific contribution to the pathophysiology in AD, constitute a mechanism of brain resilience in normal aging.

Neural restrictive silencer factor and choline acetyltransferase expression in cerebral tissue of Alzheimer's Disease patients: A pilot study

Decreased Choline Acetyltransferase (ChAT) brain level is one of the main biochemical disorders in Alzheimer’s Disease (AD). In rodents, recent data show that the CHAT gene can be regulated by a neural restrictive silencer factor (NRSF). The aim of the present work was to evaluate the gene and protein expression of CHAT and NRSF in frontal, temporal, entorhinal and parietal cortices of AD patient brains. Four brains from patients with AD and four brains from subjects without dementia were studied. Cerebral tissues were obtained and processed by the guanidine isothiocyanate method for RNA extraction. CHAT and NRSF gene and protein expression were determined by reverse transcription-polymerase chain reaction (RT-PCR) and Western blotting. CHAT gene expression levels were 39% lower in AD patients as compared to the control group (p < 0.05, U test). ChAT protein levels were reduced by 17% (p = 0.02, U test). NRSF gene expression levels were 86% higher in the AD group (p = 0.001, U test) as compared to the control group. In the AD subjects, the NRSF protein levels were 57% higher (p > 0.05, U test) than in the control subjects. These findings suggest for the first time that in the brain of AD patients high NRSF protein levels are related to low CHAT gene expression levels.

Simultaneous separation, identification and activity evaluation of three butyrylcholinesterase inhibitors from Plumula nelumbinis using on-line HPLC-UV coupled with ESI-IT-TOF-MS and BChE biochemical detection

We have firstly established a method of high-performance liquid chromatography-ultraviolet analysis coupled with electrospray ionization-ion trap-time-of-flight mass spectrometry and butyrylcholinesterase biochemical detection (HPLC-UV-ESI-IT-TOF-MS-BChEBCD). Applying this on-line method to the identification of BChE inhibitors in a Plumula nelumbinis sample, three alkaloids, namely liensinine, isoliensinine, and neferine, have been detected as having a strong BChE inhibition activity for the first time; in addition, norisoliensinine and 6-hydroxynorisoliensinine were proposed as two new compounds identified by their UV and MS data. The HPLC fingerprint, the MS fragments of the components, and the BChE activity profile could be simultaneously recorded during real-time analysis of complex samples using this on-line approach. Tacrine, a BChE inhibitor, was used as a positive reference compound, and its detection limit in the biochemical detection system was 1 nmol. The BChE activity of 1g of P. nelumbinis sample was equal to that of 127.88 μmol tacrine. The proposed on-line method has been validated as having good precision and reproducibility, and could be used to rapidly identify BChE inhibitors and to screen potential drugs for the treatment of Alzheimer's disease in complicated samples.

Role of nicotinic acetylcholine receptors in the effects of cocaine-paired contextual stimuli on impulsive decision making in rats

RATIONALE

Chronic cocaine exposure produces unconditioned enhancement in impulsive decision making; however, little is known about the effects of cocaine-paired conditioned stimuli on this behavior. Thus, this study explored the effects of cocaine-paired contextual stimuli on impulsive decision making and the contribution of nicotinic acetylcholine receptors (nAChRs) to this phenomenon.

METHODS

Rats were trained to achieve stable performance on a delay discounting task, which involved lever press-based choice between a single food pellet (small reward) available immediately and three food pellets (large reward) available after a 10-, 20-, 40-, or 60-s time delay. Rats then received Pavlovian context-cocaine (15 mg/kg, i.p.) and context-saline (1 ml/kg, i.p.) pairings in two other, distinct contexts. Subsequently, delay discounting task performance was assessed in the previously cocaine-paired or saline-paired context following pretreatment with saline or cocaine (15 mg/kg, Experiment 1) or with saline or the nAChR antagonist, mecamylamine (0.2 and 2 mg/kg, Experiment 2), using counterbalanced within-subjects testing designs.

RESULTS

Independent of cocaine pretreatment, rats exhibited greater decrease in preference for the large reward as a function of delay duration in the cocaine-paired context, relative to the saline-paired context. Furthermore, systemic mecamylamine pretreatment dose-dependently attenuated the decrease in preference for the large reward in the cocaine-paired context, but not in the saline-paired context, as compared to saline.

CONCLUSION

Cocaine-paired contextual stimuli evoke a state of impulsive decision making, which requires nAChR stimulation. Drug context-induced impulsivity likely increases the propensity for drug relapse in cocaine users, making the nAChR an interesting target for drug relapse prevention.

Chronic treatment with a GPR30 antagonist impairs acquisition of a spatial learning task in young female rats

We hypothesize that the beneficial effects of estradiol on cognitive performance may be mediated through GPR30, a putative membrane target of estrogens. Recently we showed that administration of a selective GPR30 agonist (G-1) to ovariectomized rats enhanced acquisition of a delayed matching-to-position (DMP) T-maze task and increased potassium-stimulated acetylcholine release in the hippocampus, similar to estradiol (E2) (Hammond et al., 2009). The present study tested whether treating with a selective GPR30 antagonist (G-15) would impair spatial learning in gonadally intact rats and in ovariectomized (OVX) rats treated with E2. As predicted, G-15 dose-dependently impaired DMP acquisition both in gonadally intact rats and in OVX rats treated with E2. G-15 specifically reduced the rate of acquisition, and this effect was associated with an increased predisposition to adopt a persistent turn. In contrast, G-15 alone at the highest dose had no significant effect on DMP acquisition in OVX controls. The effects were task dependent, as similar effects of G-15 were not observed in gonadally intact rats tested on an operant discrimination/reversal learning task motivated by the same food reward. This suggests that the effects on DMP acquisition were not due to effects on motivation for food. Effects of G-15 on DMP acquisition were similar to previously published work showing significant impairment produced by selective cholinergic denervation of the hippocampus. These data suggest that GPR30 can play an important role in mediating the effects of estradiol on spatial learning, possibly by mediating estradiol effects on basal forebrain cholinergic function.

Chronic administration of tibolone modulates anxiety-like behavior and enhances cognitive performance in ovariectomized rats

Hormone replacement therapy (HRT) may be prescribed to prevent the symptoms of menopause. This therapy may include estrogenic and/or progestin components and may increase the incidence of endometrial and breast cancers. Tibolone (TIB), which is also made up of estrogen and progestin components, is often used to reduce the impact of HRT. However, the effect of TIB on the processes of learning, memory and anxiety has yet to be fully elucidated. The aim of this study was to evaluate the long-term effect on learning, memory processes and anxiety in ovariectomized rats caused by different doses of TIB (0 mg/kg, 0.01 mg/kg, 0.1 mg/kg 1.0 mg/kg and 10 mg/kg, administered daily via the oral route for 18 weeks). Two behavioral animal models, the autoshaping and T maze models were employed. The concentrations of acetyl choline transferase (ChAT) and tryptophan hydroxylase (TPH) in the hippocampus were directly measured by Western blot. No significant changes were observed in the autoshaping model and spontaneous activity test. In the T maze, increased latency was observed with TIB doses of 1 and 10 mg/kg compared to the vehicle. We observed that the ChAT content decreased with increasing doses of TIB, whereas TPH content increased with doses of 1 and 10 mg/kg of TIB. These data indicate that high doses of TIB improved emotional learning, which may be related to the modulation of the cholinergic and serotonergic systems by TIB.

The role of neuromodulators in selective attention

Several classes of neurotransmitters exert modulatory effects on a broad and diverse population of neurons throughout the brain. Some of these neuromodulators, especially acetylcholine and dopamine, have long been implicated in the neural control of selective attention. We review recent evidence and evolving ideas about the importance of these neuromodulatory systems in attention, particularly visual selective attention. We conclude that, although our understanding of their role in the neural circuitry of selective attention remains rudimentary, recent research has begun to suggest unique contributions of neuromodulators to different forms of attention, such as bottom-up and top-down attention.

Donepezil plus estradiol treatment enhances learning and delay-dependent memory performance by young ovariectomized rats with partial loss of septal cholinergic neurons

Effects of estrogen therapy on cognitive performance appear to diminish with age and time following the loss of ovarian function. We hypothesize that this is due to a reduction in basal forebrain cholinergic function and that treatment with a cholinergic enhancer can reverse the effect. This study tested whether combining the cholinesterase inhibitor donepezil with estradiol treatment can enhance/restore estradiol effects on cognitive performance in young ovariectomized rats with selective lesions of septal cholinergic neurons. 192IgG-saporin was injected directly into the medial septum to produce selective cholinergic lesions. Rats were then treated with donepezil (Don, daily injections of 3mg/kg/day, i.p.) or vehicle, and then with 17β-estradiol (E2, administered by silastic capsule implanted s.c.) or an empty capsule. Rats were trained on a delayed matching-to-position (DMP) T-maze task which previous studies have shown is sensitive to ovariectomy and estrogen replacement. Results show that neither estradiol nor donepezil alone significantly enhanced acquisition of the DMP task in rats with cholinergic lesions. Combination therapy was effective, however, depending on the severity of the lesion. Don+E2 significantly enhanced acquisition of the task in rats with partial lesions (<50% loss of cholinergic neurons), but not in rats with severe lesions. This effect was due largely to a reduction in perseverative behavior. Don+E2 also improved working memory in rats with partial lesions, as evidenced by significantly better performance than controls during increased intertrial delays. These findings suggest that even partial loss of septal cholinergic neurons can reduce effects of estrogen therapy on cognitive performance, and demonstrate that combining a cholinesterase inhibitor with estrogen therapy can help to restore beneficial effects on performance. We propose that combination therapy may have similar beneficial effects in women, particularly in older women who have not used estrogen therapy for many years and are beginning to show signs of cognitive impairment or early Alzheimer's disease.

The pathological process underlying Alzheimer's disease in individuals under thirty

Brains of 42 individuals between the ages of 4 and 29 were examined with antibodies (AT8, 4G8) and silver stains for the presence of intraneuronal and extracellular protein aggregates associated with Alzheimer's disease. Thirty-eight of 42 (38/42) cases displayed abnormally phosphorylated tau protein (pretangle material) in nerve cells or in portions of their cellular processes, and 41/42 individuals showed no extracellular amyloid-β protein deposition or neuritic plaques-an individual with Down syndrome was the only exception. In 16/42 cases abnormal tau was found in the transentorhinal region, and in 3/42 cases this site was Gallyas-positive for isolated NFTs (NFT stage I). Of 26 cases that lacked abnormal tau in the transentorhinal region, 4 did not show pretangle material at subcortical sites. The remaining 22 of these same 26 cases, however, had subcortical lesions confined to non-thalamic nuclei with diffuse projections to the cerebral cortex, and, remarkably, in 19/22 individuals the pretangle material was confined to the noradrenergic coeruleus/subcoeruleus complex. Assuming the pretangle alterations are not transient and do not regress, these findings may indicate that the Alzheimer's disease-related pathological process leading to neurofibrillary tangle formation does not begin in the cerebral cortex but, rather, in select subcortical nuclei, and it may start quite early, i.e., before puberty or in early young adulthood.

Transcriptomic effects of depleted uranium on acetylcholine and cholesterol metabolisms in Alzheimer's disease model

Some heavy metals, or aluminium, could participate in the development of Alzheimer disease (AD). Depleted uranium (DU), another heavy metal, modulates the cholinergic system and the cholesterol metabolism in the brain of rats, but without neurological disorders. The aim of this study was to determine what happens in organisms exposed to DU that will/are developing the AD. This study was thus performed on a transgenic mouse model for human amyloid precursor protein (APP), the Tg2576 strain. The possible effects of DU through drinking water (20 mg/L) over an 8-month period were analyzed on acetylcholine and cholesterol metabolisms at gene level in the cerebral cortex. The mRNA levels of choline acetyl transferase (ChAT) vesicular acetylcholine transporter (VAChT) and ATP-binding cassette transporter A1 (ABC A1) decreased in control Tg2576 mice in comparison with wild-type mice (respectively -89%, -86% and -44%, p < 0.05). Chronic exposure of Tg2576 mice to DU increased mRNA levels of ChAT (+189%, p < 0.05), VAChT (+120%, p < 0.05) and ABC A1 (+52%, p < 0.05) compared to control Tg2576 mice. Overall, these modifications of acetylcholine and cholesterol metabolisms did not lead to increased disturbances that are specific of AD, suggesting that chronic DU exposure did not worsen the pathology in this experimental model.

Failing to ignore: paradoxical neural effects of perceptual load on early attentional selection in normal aging

We examined visual selective attention under perceptual load--simultaneous presentation of task-relevant and -irrelevant information--in healthy young and older adult human participants to determine whether age differences are observable at early stages of selection in the visual cortices. Participants viewed 50/50 superimposed face/place images and judged whether the faces were male or female, rendering places perceptible but task-irrelevant. Each stimulus was repeated, allowing us to index dynamic stimulus-driven competition from places. Consistent with intact early selection in young adults, we observed no adaptation to unattended places in parahippocampal place area (PPA) and significant adaptation to attended faces in fusiform face area (FFA). Older adults, however, exhibited both PPA adaptation to places and weak FFA adaptation to faces. We also probed participants' associative recognition for face-place pairs post-task. Older adults with better place recognition memory scores were found to exhibit both the largest magnitudes of PPA adaptation and the smallest magnitudes of FFA adaptation on the attention task. In a control study, we removed the competing perceptual information to decrease perceptual load. These data revealed that the initial age-related impairments in selective attention were not due to a general decline in visual cortical selectivity; both young and older adults exhibited robust FFA adaptation and neither group exhibited PPA adaptation to repeated faces. Accordingly, distracting information does not merely interfere with attended input in older adults, but is co-encoded along with the contents of attended input, to the extent that this information can subsequently be recovered from recognition memory.

GPR30 is positioned to mediate estrogen effects on basal forebrain cholinergic neurons and cognitive performance

Beneficial effects of estrogen therapy on cognitive performance diminish with age and time following the loss of ovarian function. This has led to the 'Window of Opportunity' hypothesis, which states that estrogen therapy must be administered within a limited period of time following menopause in order to be effective. Effects of estrogen therapy on cognitive performance are due, at least in part, to the effects on cholinergic afferents innervating the hippocampus and cortex, and it has been suggested that the loss of estrogen effect with age and time following menopause is due to a substantial reduction in the function of these projections. The mechanisms that underlie the effects are not clear. GPR30 is a novel G-protein coupled estrogen receptor that is expressed in the brain and other tissues. Our recent studies show that GPR30 is expressed in areas of the brain important for spatial learning, memory, and attention. In addition, GPR30 in expressed by the vast majority of cholinergic neurons in the basal forebrain, and appears to be an important regulator of basal forebrain cholinergic function. We hypothesize that GPR30 plays an important role in mediating direct effects of estradiol on basal forebrain cholinergic neurons, with corresponding effects on cognitive performance. Hence, GPR30 may be an important target for developing new therapies that can enhance or restore estrogen effects on cognitive performance in older women. Here we briefly review the cholinergic hypothesis and summarize our findings to date showing effects of a GPR30 agonist and antagonist on basal forebrain cholinergic function and cognitive performance.

The cholinergic system in mild cognitive impairment and Alzheimer's disease: an in vivo MRI and DTI study

Few studies have investigated in vivo changes of the cholinergic basal forebrain in Alzheimer's disease (AD) and amnestic mild cognitive impairment (MCI), an at risk stage of AD. Even less is known about alterations of cortical projecting fiber tracts associated with basal forebrain atrophy. In this study, we determined regional atrophy within the basal forebrain in 21 patients with AD and 16 subjects with MCI compared to 20 healthy elderly subjects using deformation-based morphometry of MRI scans. We assessed effects of basal forebrain atrophy on fiber tracts derived from high-resolution diffusion tensor imaging (DTI) using tract-based spatial statistics. We localized significant effects relative to a map of cholinergic nuclei in MRI standard space as determined from a postmortem brain. Patients with AD and MCI subjects showed reduced volumes in basal forebrain areas corresponding to anterior medial and lateral, intermediate and posterior nuclei of the Nucleus basalis of Meynert (NbM) as well as in the diagonal band of Broca nuclei (P < 0.01). Effects in MCI subjects were spatially more restricted than in AD, but occurred at similar locations. The volume of the right antero-lateral NbM nucleus was correlated with intracortical projecting fiber tract integrity such as the corpus callosum, cingulate, and the superior longitudinal, inferior longitudinal, inferior fronto-occipital, and uncinate fasciculus (P < 0.05, corrected for multiple comparisons). Our findings suggest that a multimodal MRI-DTI approach is supportive to determine atrophy of cholinergic nuclei and its effect on intracortical projecting fiber tracts in AD.

Altered neural cholinergic receptor systems in cocaine-addicted subjects

Changes in the brain's cholinergic receptor systems underlie several neuropsychiatric disorders, including Alzheimer's disease, schizophrenia, and depression. An emerging preclinical literature also reveals that acetylcoholine may have an important function in addictive processes, including reward, learning, and memory. This study was designed to assess alterations in cholinergic receptor systems in limbic regions of abstinent cocaine-addicted subjects compared with healthy controls. On three separate days, 23 1- to 6-week abstinent, cocaine- (and mostly nicotine-) addicted subjects and 22 sex-, age-, and race-matched control subjects were administered the muscarinic and nicotinic cholinergic agonist physostigmine, the muscarinic antagonist scopolamine, and saline. Regional cerebral blood flow (rCBF) after each infusion was determined using single photon emission-computed tomography. Both cholinergic probes induced rCBF changes (p<0.005) in relatively distinct, cholinergic-rich, limbic brain regions. After physostigmine, cocaine-addicted subjects showed altered rCBF, relative to controls, in limbic regions, including the left hippocampus, left amygdala, and right insula. Group differences in the right dorsolateral prefrontal cortex, posterior cingulate, and middle temporal gyrus were also evident. Scopolamine also revealed group differences in the left hippocampus and right insula as well as the posterior cingulate and middle temporal gyrus. Cocaine addicted and controls differ in their subcortical, limbic, and cortical response to cholinergic probes in areas relevant to craving, learning, and memory. Cholinergic systems may offer a pharmacologic target for cocaine addiction treatment.

Estrogen therapy and cognition: a review of the cholinergic hypothesis

The pros and cons of estrogen therapy for use in postmenopausal women continue to be a major topic of debate in women's health. Much of this debate focuses on the potential benefits vs. harm of estrogen therapy on the brain and the risks for cognitive impairment associated with aging and Alzheimer's disease. Many animal and human studies suggest that estrogens can have significant beneficial effects on brain aging and cognition and reduce the risk of Alzheimer's-related dementia; however, others disagree. Important discoveries have been made, and hypotheses have emerged that may explain some of the inconsistencies. This review focuses on the cholinergic hypothesis, specifically on evidence that beneficial effects of estrogens on brain aging and cognition are related to interactions with cholinergic projections emanating from the basal forebrain. These cholinergic projections play an important role in learning and attentional processes, and their function is known to decline with advanced age and in association with Alzheimer's disease. Evidence suggests that many of the effects of estrogens on neuronal plasticity and function and cognitive performance are related to or rely upon interactions with these cholinergic projections; however, studies also suggest that the effectiveness of estrogen therapy decreases with age and time after loss of ovarian function. We propose a model in which deficits in basal forebrain cholinergic function contribute to age-related changes in the response to estrogen therapy. Based on this model, we propose that cholinergic-enhancing drugs, used in combination with an appropriate estrogen-containing drug regimen, may be a viable therapeutic strategy for use in older postmenopausal women with early evidence of mild cognitive decline.

A comparative perspective on minicolumns and inhibitory GABAergic interneurons in the neocortex

Neocortical columns are functional and morphological units whose architecture may have been under selective evolutionary pressure in different mammalian lineages in response to encephalization and specializations of cognitive abilities. Inhibitory interneurons make a substantial contribution to the morphology and distribution of minicolumns within the cortex. In this context, we review differences in minicolumns and GABAergic interneurons among species and discuss possible implications for signaling among and within minicolumns. Furthermore, we discuss how abnormalities of both minicolumn disposition and inhibitory interneurons might be associated with neuropathological processes, such as Alzheimer's disease, autism, and schizophrenia. Specifically, we explore the possibility that phylogenetic variability in calcium-binding protein-expressing interneuron subtypes is directly related to differences in minicolumn morphology among species and might contribute to neuropathological susceptibility in humans.

Action of estrogen on survival of basal forebrain cholinergic neurons: promoting amelioration

Extensive studies during the past two decades provide compelling evidence that the gonadal steroid, estrogen, has the potential to affect the viability of basal forebrain cholinergic neurons. These observations reflect a unique ameliorative feature of estrogen as it restores and protects the cholinergic neurons against noxious stimuli or neurodegenerative processes. Hence, we first address the ameliorative function of estrogen on basal forebrain cholinergic neurons such as the actions of estrogen on neuronal plasticity of cholinergic neurons, estrogen-induced memory enhancement and the ameliorative role of estrogen on cholinergic neuron related neurodegenerative processes such as Alzheimer's disease. Second, we survey recent data as to possible mechanisms underlying the ameliorative actions of estrogen; influencing the amyloid precursor protein processing, enhancement in neurotrophin receptor signaling and estrogen-induced non-classical actions on second messenger systems. In addition, clinical relevance, pitfalls and future aspects of estrogen therapy on basal forebrain cholinergic neurons will be discussed.

Cholinergic stimulation enhances neural activity associated with encoding but reduces neural activity associated with retrieval in humans

The cerebral cholinergic system is centrally involved in memory formation. Studies in rodents suggest that cholinergic stimulation may facilitate encoding of new information but may interfere with retrieval. We investigated the effect of cholinergic stimulation on encoding and retrieval of episodic memory in humans. We also tested whether the putative benefit of cholinergic stimulation on memory function depends on individual baseline performance. Since such effects were expected to be greatest in an older population resulting from an age-related degeneration of the cholinergic system, we recruited 22 healthy older subjects (51-68 years) for an event-related functional magnetic resonance imaging experiment. In two separate scanning sessions, subjects encoded and retrieved items and their spatial context under cholinergic stimulation or placebo with the acetylcholine-esterase inhibitor physostigmine or saline being administered intravenously in a double-blind cross-over design. Baseline performance was recorded at a separate occasion without scanning. Cholinergic stimulation enhanced neural activity for successful versus unsuccessful spatial context encoding in the right hippocampus but reduced activity for successful versus unsuccessful spatial context retrieval in the right amygdala. These data may bridge the gap between rodent and human studies by showing that also in man cholinergic stimulation enhances encoding but interferes with retrieval on a neural level. Furthermore, baseline performance negatively correlated with the effect of cholinergic stimulation. Thus, participants who were worse at baseline benefited more from cholinergic stimulation than those who had better baseline values, indicating that a cholinergic deficit contributes to the memory decline even in healthy older subjects.

Prefrontal brain morphology and executive function in healthy and depressed elderly

OBJECTIVES

Late-life depression is known to correlate independently with decreased brain volumes in anterior cingulate, gyrus rectus and orbitofrontal cortex and with executive dysfunction, but the relationship between morphometry of reduced volume regions and executive dysfunction has not been well defined.

METHODS

Nondepressed and depressed elders completed five executive tests, a standard panel of laboratory tests and magnetic resonance imaging. Images of the prefrontal cortex were manually masked and automatically segmented and regional brain volumes were calculated. Executive scores and error rates were regressed on bilateral white and gray matter volumes of anterior cingulate, gyrus rectus and orbitofrontal.

RESULTS

Gyrus rectus was associated positively with scores on sequencing and nonverbal abstract reasoning, and negatively with two fluency error scores. Four positive interactions indicated that performance of controls was more closely associated with increased volume than that of depressed patients. Anterior cingulate was associated positively with two nonverbal reasoning tasks and with three positive interactions. Orbitofrontal volumes were negatively associated with correct responses and errors on two fluency tasks. One interaction showed controls' performance decreased more than depressed patients with increased volume.

CONCLUSIONS

Individual executive tasks correlate positively with volumes of anterior cingulate and gyrus rectus regions and negatively with orbitofrontal region. The orbitofrontal relationship suggests a loss of inhibitory control with decreased volume because both correct and incorrect answers on fluency tasks increased per unit decrease in volume.

The role of acetylcholine in cocaine addiction

Central nervous system cholinergic neurons arise from several discrete sources, project to multiple brain regions, and exert specific effects on reward, learning, and memory. These processes are critical for the development and persistence of addictive disorders. Although other neurotransmitters, including dopamine, glutamate, and serotonin, have been the primary focus of drug research to date, a growing preclinical literature reveals a critical role of acetylcholine (ACh) in the experience and progression of drug use. This review will present and integrate the findings regarding the role of ACh in drug dependence, with a primary focus on cocaine and the muscarinic ACh system. Mesostriatal ACh appears to mediate reinforcement through its effect on reward, satiation, and aversion, and chronic cocaine administration produces neuroadaptive changes in the striatum. ACh is further involved in the acquisition of conditional associations that underlie cocaine self-administration and context-dependent sensitization, the acquisition of associations in conditioned learning, and drug procurement through its effects on arousal and attention. Long-term cocaine use may induce neuronal alterations in the brain that affect the ACh system and impair executive function, possibly contributing to the disruptions in decision making that characterize this population. These primarily preclinical studies suggest that ACh exerts a myriad of effects on the addictive process and that persistent changes to the ACh system following chronic drug use may exacerbate the risk of relapse during recovery. Ultimately, ACh modulation may be a potential target for pharmacological treatment interventions in cocaine-addicted subjects. However, the complicated neurocircuitry of the cholinergic system, the multiple ACh receptor subtypes, the confluence of excitatory and inhibitory ACh inputs, and the unique properties of the striatal cholinergic interneurons suggest that a precise target of cholinergic manipulation will be required to impact substance use in the clinical population.

Regulation of the NMDA receptor-mediated synaptic response by acetylcholinesterase inhibitors and its impairment in an animal model of Alzheimer's disease

The cholinergic system is crucial for cognitive processes and the deficient acetylcholine (ACh) function has been implicated in Alzheimer's disease (AD). Inhibitors of acetylcholinesterase (AChE), which act to enhance cholinergic function by prolonging the action of endogenously released ACh, have been used as the major therapy of AD. To understand the functional roles of cholinergic enhancement in prefrontal cortex (PFC), a key brain region for cognition, we examined the impact of AChE inhibitors in PFC neurons on synaptic responses mediated by the NMDA receptor (NMDAR), an important player in learning and memory. We found that AChE inhibitors produced a strong and persistent reduction of the amplitude of NMDA receptor-mediated excitatory postsynaptic current (NMDAR-EPSC). This effect was mainly mediated by nicotinic ACh receptors, and through a Ca(2+)-dependent mechanism. Inhibition of extracellular signal-regulated kinases (ERK) abolished the regulation of NMDAR function by AChE inhibitors, suggesting the involvement of ERK. In the transgenic mouse model of AD overexpressing mutant beta-amyloid precursor protein (APP), the effect of AChE inhibitors on NMDAR-EPSC was significantly impaired, which was associated with their diminished effect on ERK activation. Taken together, these results suggest that one of the key targets of endogenous ACh involved in cognition is the NMDAR-mediated transmission. Loss of the regulation of synaptic NMDAR responses by endogenous ACh may contribute to the cognitive deficiency in AD.

Computer-assisted 3D reconstruction of the human basal forebrain complex

The basal forebrain complex (BFC) is a small but intricate structure. Its organization and function is hard to investigate using conventional methods, especially in humans. By combining new methods of research we present a comprehensive overview of this complex, in order to better understand its function in normal and diseased brains.

Dopaminergic and adrenergic toxicities on SK-N-MC human neuroblastoma cells are mediated through G protein signaling and oxidative stress

Dopamine and norepinephrine are neurotransmitters which participate in various regulatory functions of the human brain. These functions are lost in neurodegenerative diseases including Parkinson's disease and Alzheimer's disease. In this study, we used SK-N-MC neuroblastoma cells to investigate the cytotoxicities of high concentrations of dopamine and norepinephrine on neuronal cells. Dopamine, norepinephrine, as well as their corresponding synthetic agonists (SKF38393 and isoproterenol, respectively) triggered SK-N-MC cell death when applied at 50-100 muM persistently for 2 days. This catecholamine-induced cell death appears to be neuronal specific, as demonstrated by their inabilities of triggering apoptosis of A549 lung carcinoma cells and Cos-7 kidney fibroblasts. By pretreating SK-N-MC cells with target-specific inhibitors before administration of catecholamine, components of G protein signaling (i.e. G( s )/cAMP/PKA), monoamine oxidases, nitric oxide synthase, c-Jun N-terminal kinase and oxidative stress were found to be involved in this dopamine/norepinephrine-induced cytotoxicity, which subsequently led to caspase-dependent and -independent apoptotic responses as well as DNA degradation. In contrast, agonists of G( i )-coupled dopamine receptors and adrenergic receptors (quinpirole and UK14,304, respectively) were incapable of triggering apoptosis of SK-N-MC cells. Our results suggest that both G protein (G( s ))-mediated signaling cascade and oxidative stress participate in the dopamine/norepinephrine-induced neuronal apoptosis.