Cholinergic Mechanisms in the Cerebral Cortex: Beyond Synaptic Transmission

Basal Forebrain Atrophy, Cortical Thinning, and Amyloid-β Status in Parkinson's disease-Related Cognitive Decline

BACKGROUND

Degeneration of the cortically-projecting cholinergic basal forebrain (cBF) is a well-established pathologic correlate of cognitive decline in Parkinson's disease (PD). In Alzheimer's disease (AD) the effect of cBF degeneration on cognitive decline was found to be mediated by parallel atrophy of denervated cortical areas.

OBJECTIVES

To examine whether the association between cBF degeneration and cognitive decline in PD is mediated by parallel atrophy of cortical areas and whether these associations depend on the presence of comorbid AD pathology.

METHODS

We studied 162 de novo PD patients who underwent serial 3 T magnetic resonance imaging scanning (follow-up: 2.33 ± 1.46 years) within the Parkinson's Progression Markers Initiative. cBF volume and regional cortical thickness were automatically calculated using established procedures. Individual slopes of structural brain changes and cognitive decline were estimated using linear-mixed models. Associations between longitudinal cBF degeneration, regional cortical thinning, and cognitive decline were assessed using regression analyses and mediation effects were assessed using nonparametric bootstrap. Complementary analyses assessed the effect of amyloid-β biomarker positivity on these associations.

RESULTS

After controlling for global brain atrophy, longitudinal cBF degeneration was highly correlated with faster cortical thinning (PFDR  < 0.05), and thinning in cBF-associated cortical areas mediated the association between cBF degeneration and cognitive decline (rcBF-MoCA  = 0.30, P < 0.001). Interestingly, both longitudinal cBF degeneration and its association with cortical thinning were largely independent of amyloid-β status.

CONCLUSIONS

cBF degeneration in PD is linked to parallel thinning of cortical target areas, which mediate the effect on cognitive decline. These associations are independent of amyloid-β status, indicating that they reflect proper features of PD pathophysiology. © 2023 The Authors. Movement Disorders published by Wiley Periodicals LLC on behalf of International Parkinson and Movement Disorder Society.

Basal forebrain cholinergic signalling: development, connectivity and roles in cognition

Acetylcholine plays an essential role in fundamental aspects of cognition. Studies that have mapped the activity and functional connectivity of cholinergic neurons have shown that the axons of basal forebrain cholinergic neurons innervate the pallium with far more topographical and functional organization than was historically appreciated. Together with the results of studies using new probes that allow release of acetylcholine to be detected with high spatial and temporal resolution, these findings have implicated cholinergic networks in 'binding' diverse behaviours that contribute to cognition. Here, we review recent findings on the developmental origins, connectivity and function of cholinergic neurons, and explore the participation of cholinergic signalling in the encoding of cognition-related behaviours.

Molecular Biomarkers of Neuronal Injury in Epilepsy Shared with Neurodegenerative Diseases

In neurodegenerative diseases, changes in neuronal proteins in the cerebrospinal fluid and blood are viewed as potential biomarkers of the primary pathology in the central nervous system (CNS). Recent reports suggest, however, that level of neuronal proteins in fluids also alters in several types of epilepsy in various age groups, including children. With increasing evidence supporting clinical and sub-clinical seizures in Alzheimer's disease, Lewy body dementia, Parkinson's disease, and in other less common neurodegenerative conditions, these findings call into question the specificity of neuronal protein response to neurodegenerative process and urge analysis of the effects of concomitant epilepsy and other comorbidities. In this article, we revisit the evidence for alterations in neuronal proteins in the blood and cerebrospinal fluid associated with epilepsy with and without neurodegenerative diseases. We discuss shared and distinctive characteristics of changes in neuronal markers, review their neurobiological mechanisms, and consider the emerging opportunities and challenges for their future research and diagnostic use.

Increased Acetylcholine Levels and Other Brain Effects in 5XFAD Mice after Treatment with 8,14-Dihydroxy Metabolite of Efavirenz

Efavirenz (EFV), an FDA-approved anti-HIV drug, has off-target binding to CYP46A1, the CNS enzyme which converts cholesterol to 24-hydroxycholesterol. At small doses, EFV allosterically activates CYP46A1 in mice and humans and mitigates some of the Alzheimer's disease manifestations in 5XFAD mice, an animal model. Notably, in vitro, all phase 1 EFV hydroxymetabolites activate CYP46A1 as well and bind either to the allosteric site for EFV, neurotransmitters or both. Herein, we treated 5XFAD mice with 8,14-dihydroxyEFV, the binder to the neurotransmitter allosteric site, which elicits the highest CYP46A1 activation in vitro. We found that treated animals of both sexes had activation of CYP46A1 and cholesterol turnover in the brain, decreased content of the amyloid beta 42 peptide, increased levels of acetyl-CoA and acetylcholine, and altered expression of the brain marker proteins. In addition, male mice had improved performance in the Barnes Maze test and increased expression of the acetylcholine-related genes. This work expands our knowledge of the beneficial CYP46A1 activation effects and demonstrates that 8,14-dihydroxyEFV crosses the blood-brain barrier and has therapeutic potential as a CYP46A1 activator.

Structural characterization of polysaccharide purified from Hericium erinaceus fermented mycelium and its pharmacological basis for application in Alzheimer's disease: Oxidative stress related calcium homeostasis

The purified polysaccharides from Hericium erinaceus fermented mycelium entitled with PHEB was analyzed and it was mainly composed of six glycosidic bonds. It has been confirmed to show the relieving activity against Alzheimer's Disease (AD)- just as behaviors of B6C3-Tg (APPswePSEN1d E9)/Nju double transgenic [Genotype: (Appswe)T, (Psen1) T] (APP/PS1) mice. Six-week PHEB administration significantly improved the cognitive behavior of mice. Brain injury, amyloid beta deposition and tau hyperphosphorylation were alleviated in PHEB-treated AD mice without changes in other tissues. PHEB alleviated the oxidative stress in brains of AD mice via regulation the Nrf2 and its downstream kinase, which further improved the cholinergic system function. Proteomics and bioinformatics analysis showed that the therapeutic effect of PHEB is achieved by regulating calcium homeostasis mediated by oxidative stress. Furthermore, PHEB regulated the CaMK II/IV to achieve the calcium homeostasis in brains; and ultimately to show the anti-AD property.

The Effect of the APOE-ε4 Allele on the Cholinergic Circuitry for Subjects With Different Levels of Cognitive Impairment

Background: Cholinergic deficiency has been suggested to associate with the abnormal accumulation of Aβ and tau for patients with Alzheimer's disease (AD). However, no studies have investigated the effect of APOE-ε4 and group differences in modulating the cholinergic basal forebrain-amygdala network for subjects with different levels of cognitive impairment. We evaluated the effect of APOE-ε4 on the cholinergic structural association and the neurocognitive performance for subjects with different levels of cognitive impairment. Methods: We used the structural brain magnetic resonance imaging scans from the Alzheimer's Disease Neuroimaging Initiative dataset. The study included cognitively normal (CN, n = 167) subjects and subjects with significant memory concern (SMC, n = 96), early mild cognitive impairment (EMCI, n = 146), late cognitive impairment (LMCI, n = 138), and AD (n = 121). Subjects were further categorized according to the APOE-ε4 allele carrier status. The main effects of APOE-ε4 and group difference on the brain volumetric measurements were assessed. Regression analyses were conducted to evaluate the associations among cholinergic structural changes, APOE-ε4 status, and cognitive performance. Results: We found that APOE-ε4 carriers in the disease group showed higher brain atrophy than non-carriers in the cholinergic pathway, while there is no difference between carriers and non-carriers in the CN group. APOE-ε4 allele carriers in the disease groups also exhibited a stronger cholinergic structural correlation than non-carriers did, while there is no difference between the carriers and non-carriers in the CN subjects. Disease subjects exhibited a stronger structural correlation in the cholinergic pathway than CN subjects did. Moreover, APOE-ε4 allele carriers in the disease group exhibited a stronger correlation between the volumetric changes and cognitive performance than non-carriers did, while there is no difference between carriers and non-carriers in CN subjects. Disease subjects exhibited a stronger correlation between the volumetric changes and cognitive performance than CN subjects did. Conclusion: Our results confirmed the effect of APOE-ε4 on and group differences in the associations with the cholinergic structural changes that may reflect impaired brain function underlying neurocognitive degeneration in AD.

Estrogen pendulum in schizophrenia and Alzheimer's disease: Review of therapeutic benefits and outstanding questions

Although produced largely in the periphery, gonadal steroids play a key role in regulating the development and functions of the central nervous system and have been implicated in several chronic neuropsychiatric disorders, with schizophrenia and Alzheimer's disease (AD) most prominent. Despite major differences in pathobiology and clinical manifestations, in both conditions, estrogen transpires primarily with protective effects, buffering the onset and progression of diseases at various levels. As a result, estrogen replacement therapy (ERT) emerges as one of the most widely discussed adjuvant interventions. In this review, we revisit evidence supporting the protective role of estrogen in schizophrenia and AD and consider putative cellular and molecular mechanisms. We explore the underlying functional processes relevant to the manifestation of these devastating conditions, with a focus on synaptic transmission and plasticity mechanisms. We discuss specific effects of estrogen deficit on neurotransmitter systems such as cholinergic, dopaminergic, serotoninergic, and glutamatergic. While the evidence from both, preclinical and clinical reports, in general, are supportive of the protective effects of estrogen from cognitive decline to synaptic pathology, numerous questions remain, calling for further research.

Integrated phylogeny of the human brain and pathobiology of Alzheimer's disease: A unifying hypothesis

The disproportionate evolutionary expansion of the human cerebral cortex with reinforcement of cholinergic innervations warranted a major rise in the functional and metabolic load of the conserved basal forebrain (BF) cholinergic system. Given that acetylcholine (ACh) regulates properties of the microtubule-associated protein (MAP) tau and promotes non-amyloidogenic processing of amyloid precursor protein (APP), growing neocortex predicts higher demands for ACh, while the emerging role of BF cholinergic projections in Aβ clearance infers greater exposure of source neurons and their innervation fields to amyloid pathology. The higher exposure of evolutionary most recent cortical areas to the amyloid pathology of Alzheimer's disease (AD) with synaptic impairments and atrophy, therefore, might involve attenuated homeostatic effects of BF cholinergic projections, in addition to fall-outs of inherent processes of expanding association areas. This unifying model, thus, views amyloid pathology and loss of cholinergic cells as a quid pro quo of the allometric evolution of the human brain, which in combination with increase in life expectancy overwhelm the fine homeostatic balance and trigger the disease process.

Brain-derived neurotrophic factor (BDNF) promotes molecular polarization and differentiation of immature neuroblastoma cells into definitive neurons

Throughout development, neuronal progenitors undergo complex transformation into polarized nerve cells, warranting the directional flow of information in the neural grid. The majority of neuronal polarization studies have been carried out on rodent-derived precursor cells, programmed to develop into neurons. Unlike rodent neuronal cells, SH-SY5Y cells derived from human bone marrow present a sub-clone of neuroblastoma line, with their transformation into neuron-like cells showing a range of highly instructive neurobiological characteristics. We applied two-step retinoic acid (RA) and brain-derived neurotrophic factor (BDNF) protocol to monitor the conversion of undifferentiated SH-SY5Y into neuron-like cells with distinctly polarized axon-dendritic morphology and formation of bona fide synaptic connections. We show that BDNF is a key driver and regulator of the expression of axonal marker tau and dendritic microtubule-associated protein-2 (MAP2), with their sorting to distinct cellular compartments. Using selective kinase inhibitors downregulating BDNF-TrkB signaling, we demonstrate that constitutive activation of TrkB receptor is essential for the maintenance of established polarization morphology. Importantly, the proximity ligation assay applied in our preparation demonstrates that differentiating neuron-like cells develop elaborate synaptic connections enriched with hallmark pre- and postsynaptic proteins. Described herein findings highlight several fundamental processes related to neuronal polarization and synaptogenesis in human-derived cells, which are of major relevance to neurobiology and translational neuroscience.

Myrtus communis subsp. communis improved cognitive functions in ovariectomized diabetic rats

AIM

The purpose of this study was to investigate the possible effects of Myrtus communis subsp. communis (MC) on cognitive impairment in ovariectomized diabetic rats.

MATERIAL AND METHOD

Female Sprague-Dawley rats were divided into 5 groups consisting of 15 rats each; Control (C), Diabetes (D), Ovariectomy and diabetes (OVX + D), Ovariectomy, diabetes and donepezil (OVX + D + Don), Ovariectomy, diabetes and Myrtus communis subsp. communis (OVX + D + MC). Blood glucose measurements were made at the beginning and end of the experiments. The animals underwent the novel object recognition test (NORT) and their performance was evaluated. In hippocampal tissues; amyloid beta (Aβ) and neprilysin levels, acetylcholinesterase (AChE), and choline acetyltransferase (ChAT) activities, polysialylated neural cell adhesion molecule (PSA-NCAM), α7 subunit of neuronal nicotinic acetylcholine receptor (α7-nAChR) and brain derived neurotrophic factor (BDNF) gene expressions were examined.

RESULTS

Animals with ovariectomy and diabetes showed increased levels of blood glucose, AChE activity and Aβ levels, and decreased neprilysin levels, ChAT activity, α7-nAChR, PSA-NCAM and BDNF gene expressions in parallel with a decrease in NORT performance score. On the other hand, in the MC-treated OVX + D group, there was a significant decrease observed in blood glucose levels and AChE activities while there was improvement in NORT performances and an increase in hippocampal ChAT activity, neprilysin levels, α7-nAChR, PSA-NCAM and BDNF expressions.

CONCLUSION

These results suggest that MC extract could improve cognitive and neuronal functions with its anticholinesterase and antihyperglycemic properties.

Rostral intralaminar thalamic deep brain stimulation ameliorates memory deficits and dendritic regression in β-amyloid-infused rats

Rostral intralaminar thalamic deep brain stimulation (ILN-DBS) has been shown to enhance attention and cognition through neuronal activation and brain plasticity. We examined whether rostral ILN-DBS can also attenuate memory deficits and impaired synaptic plasticity and protect glutamatergic transmission in the rat intraventricular β-amyloid (Aβ) infusion model of Alzheimer's disease (AD). Spatial memory was tested in the Morris water maze (MWM), while structural synaptic plasticity and glutamatergic transmission strength were estimated by measuring dendritic spine densities in dye-injected neurons and tissue expression levels of postsynaptic density protein 95 (PSD-95) in medial prefrontal cortex (mPFC) and hippocampus. All these assessments were compared among the naïve control rats, AD rats, and AD rats with ILN-DBS. We found that a single rostral ILN-DBS treatment significantly improved MWM performance and reversed PSD-95 expression reductions in the mPFC and hippocampal region of Aβ-infused rats. In addition, ILN-DBS preserved dendritic spine densities on mPFC and hippocampal pyramidal neurons. In fact, MWM performance, PSD-95 expression levels, and dendritic spine densities did not differ between naïve control and rostral ILN-DBS treatment groups, indicating near complete amelioration of Aβ-induced spatial memory impairments and dendritic regression. These findings suggest that the ILN is critical for modulating glutamatergic transmission, neural plasticity, and spatial memory functions through widespread effects on distributed brain regions. Further, these findings provide a rationale for examining the therapeutic efficacy of ILN-DBS in AD patients.

Cholinergic modulation of striatal microcircuits

The purpose of this review is to bridge the gap between earlier literature on striatal cholinergic interneurons and mechanisms of microcircuit interaction demonstrated with the use of newly available tools. It is well known that the main source of the high level of acetylcholine in the striatum, compared to other brain regions, is the cholinergic interneurons. These interneurons provide an extensive local innervation that suggests they may be a key modulator of striatal microcircuits. Supporting this idea requires the consideration of functional properties of these interneurons, their influence on medium spiny neurons, other interneurons, and interactions with other synaptic regulators. Here, we underline the effects of intrastriatal and extrastriatal afferents onto cholinergic interneurons and discuss the activation of pre‐ and postsynaptic muscarinic and nicotinic receptors that participate in the modulation of intrastriatal neuronal interactions. We further address recent findings about corelease of other transmitters in cholinergic interneurons and actions of these interneurons in striosome and matrix compartments. In addition, we summarize recent evidence on acetylcholine‐mediated striatal synaptic plasticity and propose roles for cholinergic interneurons in normal striatal physiology. A short examination of their role in neurological disorders such as Parkinson's, Huntington's, and Tourette's pathologies and dystonia is also included.

Can Arginase Inhibitors Be the Answer to Therapeutic Challenges in Alzheimer's Disease?

While the extensive hunt for therapeutics combating Alzheimer's disease (AD) has fallen short of delivering effective treatments, breakthroughs towards understanding the disease mechanisms and identifying areas for future research have nevertheless been enabled. The majority of clinical trials with β- and γ-secretase modulators have been suspended from additional studies or terminated due to toxicity issues and health concerns. The lack of progress in developing innovative AD therapies has also prompted a resurgence of interest in more traditional symptomatic treatments with cholinesterase inhibitors and N-methyl-D-aspartate receptor antagonists, as well as in the research of immune response modulators. Recently, evidence has emerged showing that inhibitors of arginine metabolism and in particular blockers of arginase, an enzyme that catalyzes the breakdown of L-arginine, could present an effective therapeutic candidate for halting the progression of AD and boosting cognition and memory. In this commentary, we present a brief overview of reports on arginase inhibitors in AD mouse models and discuss emerging advantages and areas for careful consideration on the road to clinical translation.

Alleviation of Trigeminal Nociception Using p75 Neurotrophin Receptor Targeted Lentiviral Interference Therapy

Acute and chronic trigeminal (TG) neuropathies are the cause of considerable distress, with limited treatments available at present. Nociceptive neurons enriched with the vanilloid type 1 receptor (VR1) partake in pain sensation and sensitization in the TG system. While VR1 blockers with anti-nociceptive potential are of substantial medical interest, their use remains limited due to poor selectivity and lack of cell-targeting capabilities. This study describes a methodology for the alleviation of nociception via targeted depletion of VR1 in TG sensory neurons in rats. In cultured TG ganglion neurons, VR1 expression was virtually abolished by lentiviral short hairpin RNA (LV-VR1). By decorating GFP encoding LV (LV-GFP) and LV-VR1 with IgG192 for targeting TG sensory neurons enriched with the p75 neurotrophin receptor (p75NTR), transduction of a reporter GFP and VR1 depletion was achieved after injection of targeted vectors into the whisker pad. In IgG192/LV-VR1-injected rats, the behavioral response to capsaicin exposure as well as Erk 1/2 phosphorylation and VR1 current activation by capsaicin were significantly reduced. This pioneering investigation, thus, provides a proof of principle for a means of attenuating TG nociception, revealing therapeutic potential.

A second wind for the cholinergic system in Alzheimer's therapy

Notwithstanding tremendous research efforts, the cause of Alzheimer's disease (AD) remains elusive and there is no curative treatment. The cholinergic hypothesis presented 35 years ago was the first major evidence-based hypothesis on the etiology of AD. It proposed that the depletion of brain acetylcholine was a primary cause of cognitive decline in advanced age and AD. It relied on a series of observations obtained in aged animals, elderly, and AD patients that pointed to dysfunctions of cholinergic basal forebrain, similarities between cognitive impairments induced by anticholinergic drugs and those found in advanced age and AD, and beneficial effects of drugs stimulating cholinergic activity. This review revisits these major results to show how this hypothesis provided the drive for the development of anticholinesterase inhibitor-based therapies of AD, the almost exclusively approved treatment in use despite transient and modest efficacy. New ideas for improving cholinergic therapies are also compared and discussed in light of the current revival of the cholinergic hypothesis on the basis of two sets of evidence from new animal models and refined imagery techniques in humans. First, human and animal studies agree in detecting signs of cholinergic dysfunctions much earlier than initially believed. Second, alterations of the cholinergic system are deeply intertwined with its reactive responses, providing the brain with efficient compensatory mechanisms to delay the conversion into AD. Active research in this field should provide new insight into development of multitherapies incorporating cholinergic manipulation, as well as early biomarkers of AD enabling earlier diagnostics. This is of prime importance to counteract a disease that is now recognized to start early in adult life.

New dimensions of connectomics and network plasticity in the central nervous system

Cellular network architecture plays a crucial role as the structural substrate for the brain functions. Therefore, it represents the main rationale for the emerging field of connectomics, defined as the comprehensive study of all aspects of central nervous system connectivity. Accordingly, in the present paper the main emphasis will be on the communication processes in the brain, namely wiring transmission (WT), i.e. the mapping of the communication channels made by cell components such as axons and synapses, and volume transmission (VT), i.e. the chemical signal diffusion along the interstitial brain fluid pathways. Considering both processes can further expand the connectomics concept, since both WT-connectomics and VT-connectomics contribute to the structure of the brain connectome. A consensus exists that such a structure follows a hierarchical or nested architecture, and macro-, meso- and microscales have been defined. In this respect, however, several lines of evidence indicate that a nanoscale (nano-connectomics) should also be considered to capture direct protein-protein allosteric interactions such as those occurring, for example, in receptor-receptor interactions at the plasma membrane level. In addition, emerging evidence points to novel mechanisms likely playing a significant role in the modulation of intercellular connectivity, increasing the plasticity of the system and adding complexity to its structure. In particular, the roamer type of VT (i.e. the intercellular transfer of RNA, proteins and receptors by extracellular vesicles) will be discussed since it allowed us to introduce a new concept of 'transient changes of cell phenotype', that is the transient acquisition of new signal release capabilities and/or new recognition/decoding apparatuses.

Cerebral and Retinal Neurovascular Changes: A Biomarker for Alzheimer's Disease

Objectives

Biomarker quest for Alzheimer’s disease (AD) has gone a long way by studying various anatomical, physiological and biochemical parameters for detecting disease onset and predicting prognosis. Almost all the studies converge on the single hypothesis of the amyloid and Tau pathway. Recently, vascular hypothesis has evolved drawing attention towards a complex dynamic anatomical and physiological entity, neuro-vascular (NV) unit. Pathological changes at this level, altering the normal physiology such as auto-regulation and dynamics of blood brain barrier have been hypothesized as a probable basis for AD. This paper attempts to review the existing data on the vascular hypothesis and the current trends in analyzing the NV unit in AD.

Design

This review initially focuses on the cerebral NV coupling followed by the retinal neurovascular coupling that mirrors the cerebral pathophysiology. The pathophysiology and the potential tools to diagnose AD at the level of NV unit are analyzed. Further, it examines the drawbacks in existing methods for analyzing the same.

Findings

None of the current studies have emphasized the importance of studying the complex dynamic NV unit as a whole. This review strongly recommends the combination of vascular and neuro-glial parameters using objective methods for estimating the physiological and pathological changes in the NV unit.

Discussion and conclusion

This review highlights the importance of retina for non-invasive estimation of the same. Also, novel algorithms for retinal image analysis have been proposed. The purpose of this review is to highlight the importance of retinal findings in neurodegenerative disorders and to create awareness among the neuroophthalmologists, of the potential benefits of ophthalmological tools in screening dementia patients.

Quantitative mapping of microtubule-associated protein 2c (MAP2c) phosphorylation and regulatory protein 14-3-3ζ-binding sites reveals key differences between MAP2c and its homolog Tau

Microtubule-associated protein 2c (MAP2c) is involved in neuronal development and is less characterized than its homolog Tau, which has various roles in neurodegeneration. Using NMR methods providing single-residue resolution and quantitative comparison, we investigated molecular interactions important for the regulatory roles of MAP2c in microtubule dynamics. We found that MAP2c and Tau significantly differ in the position and kinetics of sites that are phosphorylated by cAMP-dependent protein kinase (PKA), even in highly homologous regions. We determined the binding sites of unphosphorylated and phosphorylated MAP2c responsible for interactions with the regulatory protein 14-3-3ζ. Differences in phosphorylation and in charge distribution between MAP2c and Tau suggested that both MAP2c and Tau respond to the same signal (phosphorylation by PKA) but have different downstream effects, indicating a signaling branch point for controlling microtubule stability. Although the interactions of phosphorylated Tau with 14-3-3ζ are supposed to be a major factor in microtubule destabilization, the binding of 14-3-3ζ to MAP2c enhanced by PKA-mediated phosphorylation is likely to influence microtubule-MAP2c binding much less, in agreement with the results of our tubulin co-sedimentation measurements. The specific location of the major MAP2c phosphorylation site in a region homologous to the muscarinic receptor-binding site of Tau suggests that MAP2c also may regulate processes other than microtubule dynamics.

Low-Affinity Neurotrophin Receptor p75 Promotes the Transduction of Targeted Lentiviral Vectors to Cholinergic Neurons of Rat Basal Forebrain

Basal forebrain cholinergic neurons (BFCNs) are one of the most affected neuronal types in Alzheimer's disease (AD), with their extensive loss documented at late stages of the pathology. While discriminatory provision of neuroprotective agents and trophic factors to these cells is thought to be of substantial therapeutic potential, the intricate topography and structure of the forebrain cholinergic system imposes a major challenge. To overcome this, we took advantage of the physiological enrichment of BFCNs with a low-affinity p75 neurotrophin receptor (p75NTR) for their targeting by lentiviral vectors within the intact brain of adult rat. Herein, a method is described that affords selective and effective transduction of BFCNs with a green fluorescence protein (GFP) reporter, which combines streptavidin-biotin technology with anti-p75NTR antibody-coated lentiviral vectors. Specific GFP expression in cholinergic neurons was attained in the medial septum and nuclei of the diagonal band Broca after a single intraventricular administration of such targeted vectors. Bioelectrical activity of GFP-labeled neurons was proven to be unchanged. Thus, proof of principle is obtained for the utility of the low-affinity p75NTR for targeted transduction of vectors to BFCNs in vivo.