Nucleus Basalis Magnocellularis Research Articles

Modulation of the p75NTR during Adolescent Alcohol Exposure Prevents Cholinergic Neuronal Atrophy and Associated Acetylcholine Activity and Behavioral Dysfunction.

Binge alcohol consumption during adolescence can produce lasting deficits in learning and memory while also increasing the susceptibility to substance use disorders. The adolescent intermittent ethanol (AIE) rodent model mimics human adolescent binge drinking and has identified the nucleus basalis magnocellularis (NbM) as a key site of pathology. The NbM is a critical regulator of prefrontal cortical (PFC) cholinergic function and attention. The cholinergic phenotype is controlled pro/mature neurotrophin receptor activation. We sought to determine if p75NTR activity contributes to the loss of cholinergic phenotype in AIE by using a p75NTR modulator (LM11A-31) to inhibit prodegenerative signaling during ethanol exposure. Male and female rats underwent 5 g/kg ethanol (AIE) or water (CON) exposure following 2-day-on 2-day-off cycles from postnatal day 25-57. A subset of these groups also received a protective dose of LM11A-31 (50 mg/kg) during adolescence. Rats were trained on a sustained attention task (SAT) and behaviorally relevant acetylcholine (ACh) activity was recorded in the PFC with a fluorescent indicator (AChGRAB 3.0). AIE produced learning deficits on the SAT, which were spared with LM11A-31. In addition, PFC ACh activity was blunted by AIE, which LM11A-31 corrected. Investigation of NbM ChAT+ and TrkA+ neuronal expression found that AIE led to a reduction of ChAT+TrkA+ neurons, which again LM11A-31 protected. Taken together, these findings demonstrate the p75NTR activity during AIE treatment is a key regulator of cholinergic degeneration.

Neuroprotection of Cholinergic Neurons with a Tau Aggregation Inhibitor and Rivastigmine in an Alzheimer's-like Tauopathy Mouse Model.

Basal forebrain cholinergic dysfunction, most likely linked with tau protein aggregation, is a characteristic feature of Alzheimer's disease (AD). Recent evidence suggests that tau protein is a putative target for the treatment of dementia, and the tau aggregation inhibitor, hydromethylthionine mesylate (HMTM), has emerged as a potential disease-modifying treatment. However, its efficacy was diminished in patients already receiving approved acetylcholinesterase inhibitors. In this study, we ask whether this negative interaction can also be mimicked in experimental tau models of AD and whether the underlying mechanism can be understood. From a previous age profiling study, 6-month-old line 1 (L1) tau transgenic mice were characterized by a severe reduction in several cholinergic markers. We therefore assessed whether long-term pre-exposure with the acetylcholinesterase inhibitor rivastigmine alone and in conjunction with the tau aggregation inhibitor HMTM can reverse cholinergic deficits in L1. Rivastigmine and HMTM, and combinations of the two compounds were administered orally for 11 weeks to both L1 and wild-type mice. The brains were sectioned with a focus on the basal forebrain, motor cortex and hippocampus. Immunohistochemical staining and quantification of choline acetyltransferase (ChAT), tyrosine kinase A (TrkA)-positive neurons and relative optical intensity (ROI) for vesicular acetylcholine transporter (VAChT), and acetylcholinesterase (AChE) reactivity confirmed reversal of the diminished cholinergic phenotype of interneurons (nucleus accumbens, striatum) and projection neurons (medial septum, nucleus basalis magnocellularis) by HMTM, to a greater extent than by rivastigmine alone in L1 mice. Combined administration did not yield additivity but, in most proxies, led to antagonistic effects in which rivastigmine decreased the benefits shown with HMTM alone. Local markers (VAChT and AChE) in target structures of the basal forebrain, motor cortex and hippocampal CA3 seemed to be normalized by HMTM, but not by rivastigmine or the combination of both drugs. HMTM, which was developed as a tau aggregation inhibitor, strongly decreased the tau load in L1 mice, however, not in combination with rivastigmine. Taken together, these data confirm a cholinergic phenotype in L1 tau transgenic mice that resembles the deficits observed in AD patients. This phenotype is reversible by HMTM, but at the same time appears to be subject to a homeostatic regulation induced by chronic pre-treatment with an acetylcholinesterase inhibitor, which interferes with the efficacy of HMTM. The strongest phenotypic reversal coincided with a normalization of the tau load in the cortex and hippocampus of L1, suggesting that tau accumulation underpins the loss of cholinergic markers in the basal forebrain and its projection targets.

Aspiration removal of orbitofrontal cortex disrupts cholinergic fibers of passage to anterior cingulate cortex in rhesus macaques.

The study of anthropoid nonhuman primates has provided valuable insights into frontal cortex function in humans, as these primates share similar frontal anatomical subdivisions (Murray et al. 2011). Causal manipulation studies have been instrumental in advancing our understanding of this area. One puzzling finding is that macaques with bilateral aspiration removals of orbitofrontal cortex (OFC) are impaired on tests of cognitive flexibility and emotion regulation, whereas those with bilateral excitotoxic lesions of OFC are not (Rudebeck et al. 2013). This discrepancy is attributed to the inadvertent disruption of fibers of passage by aspiration lesions but not by excitotoxic lesions. Which fibers of passage are responsible for the impairments observed? One candidate is cholinergic fibers originating in the nucleus basalis magnocellularis (NBM) and passing nearby or through OFC on their way to other frontal cortex regions (Kitt et al. 1987). To investigate this possibility, we performed unilateral aspiration lesions of OFC in three macaques, and then compared cholinergic innervation of the anterior cingulate cortex (ACC) between hemispheres. Histological assessment revealed diminished cholinergic innervation in the ACC of hemispheres with OFC lesions relative to intact hemispheres. This finding indicates that aspiration lesions of the OFC disrupt cholinergic fibers of passage, and suggests the possibility that loss of cholinergic inputs to ACC contributes to the impairments in cognitive flexibility and emotion regulation observed after aspiration but not excitotoxic lesions of OFC.

Perioperative Levels of IL8 and IL18, but not IL6, are Associated with Nucleus Basalis Magnocellularis Atrophy Three Months after Surgery

Past studies have observed that brain atrophy may accelerate after surgical procedures. Furthermore, an association of systemic inflammation with neurodegeneration has been described. We hypothesize that postoperative interleukin (IL) levels in circulation as well as the perioperative change in interleukin levels are associated with increased postoperative atrophy in the Nucleus basalis magnocellularis (of Meynert, NBM) which is the major source of cortical acetylcholine. We analyzed data from the BioCog cohort which included patients ≥ 65 years presenting for elective major surgery (≥ 60min). Blood samples were taken before surgery and on the first postoperative day. Magnetic resonance imaging of the brain and neuropsychological assessments were conducted before surgery and after three months follow-up. We used linear regression analysis to determine the association of three interleukins (IL6, IL8 and IL18) with NBM atrophy (in % volume change from baseline before surgery to follow-up), as well as to examine the associations of NBM atrophy and volume with postoperative cognitive ability and perioperative cognitive change. Receiver-operating curves were used to determine the prognostic value of preoperative interleukin levels. For IL8 (N = 97) and IL18 (N = 217), but not IL6 (N = 240), we observed significant associations of higher postoperative IL levels at the first postoperative day with higher NBM atrophy at three months after surgery. Subsequent analyses suggested that in both IL8 and IL18, this association was driven by a more general association of chronically elevated IL levels and NBM atrophy, reflected by preoperative IL concentrations, rather than IL response to surgery, measured as the difference between pre- and postoperative IL concentrations. At follow-up, NBM volume was positively associated with the level of cognitive performance, but NBM atrophy was not significantly related to perioperative cognitive change. Prognostic value of preoperative IL concentrations for NBM atrophy was low. Our results suggest that an association of postoperative interleukin levels with NBM atrophy is driven by preoperatively elevated interleukins due to pre-existing inflammation, rather than perioperative change in interleukin levels in response to surgery and anesthesia. The BioCog study has been registered at clinicaltrials.gov on Oct 15, 2014 (NCT02265263).Graphical

Activation of multiple neuromodulatory systems in alert rats acquiring conditioned taste aversion revealed by positron emission tomography

Conditioned taste aversion (CTA) is an essential ability for animals to consume food safely and is regulated by neuromodulatory systems including the dopamine, noradrenaline, serotonin, and acetylcholine systems. However, because few studies focused on a comprehensive understanding of whole-brain activities, how these neuromodulators contribute to the process of CTA remains an open issue. 18F-fluorodeoxyglucose (FDG)-positron emission tomography (PET) can visualize activated regions within the whole brain simultaneously and noninvasively. This study aimed to understand the mechanisms of CTA, especially focusing on the retrieval process after CTA acquisition by FDG-PET imaging. CTA was established in rats who received an intraoral application of saccharin solution (IOAS) on the first day (Day 1), a LiCl i.p. injection after an IOAS on Day 2, and an IOAS on Day 3 (CTA group). The subtraction images of Day 3 of the SHAM group, which received a 0.9 % NaCl (saline) injection instead of a LiCl on Day 2, from those of Day 3 of the CTA group revealed increases in FDG signals in multiple brain regions including the substantia nigra, ventral tegmental area, locus coeruleus, dorsal raphe, and nucleus basalis magnocellularis, in addition to the hippocampus and nociception-related regions, including the parabrachial nucleus and solitary nucleus. On the other hand, the visceral pain induced by the LiCl injection increased FDG signals in the primary and secondary somatosensory and insular cortices in addition to the parabrachial nucleus and solitary nucleus. These results suggest that the retrieval process of CTA induces brain regions producing neuromodulators and pain-related brainstem.

The Combined Effect of Donepezil and Lovastatin on the Electrical Activity of Hippocampal Pyramidal Neurons in a rat model of Alzheimer’s disease

Background: Donepezil, a noncompetitive acetylcholinesterase inhibitor, is prescribed to treat mild to moderate Alzheimer's disease but it only has moderate performance. Therefore, combination therapies are more effective. There is much evidence suggesting that statins have neuroprotective effects on neurological disorders including Alzheimer's disease. The present study aimed to investigate the combined effects of Donepezil and Lovastatin on the activity of the pyramidal neurons of the CA1 hippocampus.
 Methods: In the present experiment study, adult male rats were divided into 3 groups: Nucleus Basalis Magnocellularis (NBM) lesion (which received electrically- induced lesion (0.5 mA, 3s) in NBM) group, NBM lesion + injection Donepezil 5mg/kg-Lovastatin 10mg/kg, NBM lesion+ injection Donepezil 15mg/kg-Lovastatin 30mg/kg. Spontaneous activity of pyramidal neurons in CA1 region to injection of Donepezil-Lovastatin was investigated in a rat model of Alzheimer's disease.
 Results: The results of this study showed that electrical lesion of NBM leads to a decrease in the activity frequency of pyramidal neurons in the CA1 region. Administration of Donepezil 5mg/kg-Lovastatin 10mg/kg increased the frequency of pyramidal neurons in rat model of Alzheimer's disease.
 Conclusion: The results of this study suggest that co-administration of Donepezil-Lovastatin (low doses) increases the activity of the CA1 pyramidal neurons in a rat model of Alzheimer’s disease.

The TNFR1 antagonist Atrosimab reduces neuronal loss, glial activation and memory deficits in an acute mouse model of neurodegeneration

Tumor necrosis factor alpha (TNF-α) and its key role in modulating immune responses has been widely recognized as a therapeutic target for inflammatory and neurodegenerative diseases. Even though inhibition of TNF-α is beneficial for the treatment of certain inflammatory diseases, total neutralization of TNF-α largely failed in the treatment of neurodegenerative diseases. TNF-α exerts distinct functions depending on interaction with its two TNF receptors, whereby TNF receptor 1 (TNFR1) is associated with neuroinflammation and apoptosis and TNF receptor 2 (TNFR2) with neuroprotection and immune regulation. Here, we investigated the effect of administering the TNFR1-specific antagonist Atrosimab, as strategy to block TNFR1 signaling while maintaining TNFR2 signaling unaltered, in an acute mouse model for neurodegeneration. In this model, a NMDA-induced lesion that mimics various hallmarks of neurodegenerative diseases, such as memory loss and cell death, was created in the nucleus basalis magnocellularis and Atrosimab or control protein was administered centrally. We showed that Atrosimab attenuated cognitive impairments and reduced neuroinflammation and neuronal cell death. Our results demonstrate that Atrosimab is effective in ameliorating disease symptoms in an acute neurodegenerative mouse model. Altogether, our study indicates that Atrosimab may be a promising candidate for the development of a therapeutic strategy for the treatment of neurodegenerative diseases.

Cholinergic regulation of object recognition memory.

Object recognition memory refers to a basic memory mechanism to identify and recall various features of objects. This memory has been investigated by numerous studies in human, primates and rodents to elucidate the neuropsychological underpinnings in mammalian memory, as well as provide the diagnosis of dementia in some neurological diseases, such as Alzheimer’s disease and Parkinson’s disease. Since Alzheimer’s disease at the early stage is reported to be accompanied with cholinergic cell loss and impairment in recognition memory, the central cholinergic system has been studied to investigate the neural mechanism underlying recognition memory. Previous studies have suggested an important role of cholinergic neurons in the acquisition of some variants of object recognition memory in rodents. Cholinergic neurons in the medial septum and ventral diagonal band of Broca that project mainly to the hippocampus and parahippocampal area are related to recognition memory for object location. Cholinergic projections from the nucleus basalis magnocellularis innervating the entire cortex are associated with recognition memory for object identification. Especially, the brain regions that receive cholinergic projections, such as the perirhinal cortex and prefrontal cortex, are involved in recognition memory for object-in-place memory and object recency. In addition, experimental studies using rodent models for Alzheimer’s disease have reported that neurodegeneration within the central cholinergic system causes a deficit in object recognition memory. Elucidating how various types of object recognition memory are regulated by distinct cholinergic cell groups is necessary to clarify the neuronal mechanism for recognition memory and the development of therapeutic treatments for dementia.

Effects of Memantine on the Spontaneous Firing Frequency of Hippocampal CA1 Pyramidal Neurons in Intact and Alzheimer Rat Model: An Electrophysiological Study.

Memantine (MEM) is a noncompetitive N-methyl-D-aspartate receptor (NMDAR) antagonist clinically used for the treatment of Alzheimer disease (AD) in mild to severe conditions. The present study was conducted to investigate the effects of memantine on the spontaneous firing frequency of CA1 pyramidal neurons in rats caused by an electrical lesion of Nucleus Basalis Magnocellularis (NBM). Then, this model of AD rats was compared with the intact adult male rats. In this study, adult male rats were divided into two groups. Group I (lesion of NBM, n=53) includes the following subgroups: lesion+saline, sham+saline, lesion+MEM 5 mg/kg, lesion+MEM 10 mg/kg, and lesion+MEM 20mg/kg. Group II (intact, n=48) includes the following subgroups: intact+saline, intact+MEM 3mg/kg, intact+MEM 5mg/kg, and intact+MEM 10mg/kg. Extracellular single-unit recording (15 min baseline+105 min after MEM or saline) was performed under urethane-anesthetized rats. The results showed that the mean frequency of CA1 pyramidal neurons after saline in the lesion+saline (P<0.001) group significantly decreases compared with the intact+saline and sham+saline groups. In addition, after saline and memantine, the mean frequency of CA1 pyramidal neurons in the lesion+MEM 10 mg/kg (P<0.01) and lesion+MEM 20 mg/kg (P<0.001) groups significantly increased compared with the lesion+saline group. Also, the mean frequencies of CA1 pyramidal neurons in the intact+MEM 10 mg/kg (P<0.001) group significantly decreased compared with the intact+saline group. Results showed that memantine increases the electrical activity of CA1 pyramidal neurons in a rat model of AD. Furthermore, in the intact adult male rats, the low-dose memantine, contrary to high dose, does not decrease the electrical activity of CA1 pyramidal neurons.

Cannabinoid Receptors and Glial Response Following a Basal Forebrain Cholinergic Lesion.

The endocannabinoid system modulates learning, memory, and neuroinflammatory processes, playing a key role in neurodegeneration, including Alzheimer's disease (AD). Previous results in a rat lesion model of AD showed modulation of endocannabinoid receptor activity in the basalo-cortical pathway following a specific lesion of basal forebrain cholinergic neurons (BFCNs), indicating that the glial neuroinflammatory response accompanying the lesion is related to endocannabinoid signaling. In this study, 7 days after the lesion, decreased astrocyte and increased microglia immunoreactivities (GFAP and Iba-1) were observed, indicating microglia-mediated neuroinflammation. Using autoradiographic studies, the density and functional coupling to G-proteins of endocannabinoid receptor subtypes were studied in tissue sections from different brain areas where microglia density increased, using CB1 and CB2 selective agonists and antagonists. In the presence of the specific CB1 receptor antagonist, SR141716A, [3H]CP55,940 binding (receptor density) was completely blocked in a dose-dependent manner, while the selective CB2 receptor antagonist, SR144528, inhibited binding to 25%, at best. [35S]GTPγS autoradiography (receptor coupling to Gi/0-proteins) evoked by CP55,940 (CB1/CB2 agonist) and HU308 (more selective for CB2) was abolished by SR141716A in all areas, while SR144528 blocked up to 51.8% of the coupling to Gi/0-proteins evoked by CP55,940 restricted to the nucleus basalis magnocellularis. Together, these results demonstrate that there are increased microglia and decreased astrocyte immunoreactivities 1 week after a specific deletion of BFCNs, which projects to cortical areas, where the CB1 receptor coupling to Gi/0-proteins is upregulated. However, at the lesion site, the area with the highest neuroinflammatory response, there is also a limited contribution of CB2.

The Effect of Lovastatin on the Electrophysiological Properties of CA1 Pyramidal Neurons in a Rat Model of Alzheimer Disease

Background: Statins are widely used to control the level of plasma cholesterol. There is growing evidence that statins reduce the prevalence of Alzheimer disease (AD) and dementia. Objectives: The present study evaluated the effect of lovastatin treatment on neuronal responses of pyramidal cells of the CA1 region of the hippocampus in a rat model of AD. Methods: Rats randomly separated into 4 groups (n = 10): the lesion group of nucleus basalis magnocellularis (NBM) that received destruction by an electrical method (0.5 mA, 3 seconds) and lovastatin groups [lesion + lovastatin (10, 20, and 30 mg/kg)]. An in vivo single-unit recording method was used in rats anesthetized with urethane. After 15 minutes of baseline recording from pyramidal neurons in the CA1 region of the hippocampus, intraperitoneal injections of lovastatin and dimethyl sulfoxide (DMSO) were administered, and neuronal response to administration of lovastatin continued to be recorded for 105 minutes. Results: Acute injection of 30-mg/kg lovastatin excited 11 out of 17 neurons and inhibited 2 neurons. On the other hand, intraperitoneal injection of lovastatin in the highest dose resulted in increased spontaneous activity in the CA1 region of the hippocampus. Conclusions: The acute use of lovastatin increases the neuronal frequency in the pyramidal neurons of the CA1 region of the hippocampus.

Handling and novel object recognition modulate fear response and endocannabinoid signaling in nucleus basalis magnocellularis.

Storage of aversive memories is of utmost importance for survival, allowing animals to avoid upcoming similar stimuli. However, without reinforcement, the learned avoidance response gradually decreases over time. Although the molecular mechanisms controlling this extinction process are not well known, there is evidence that the endocannabinoid system plays a key role through CB1 receptor‐mediated modulation of cholinergic signaling. In this study, we measured fear extinction throughout 7 months using naïve rats, assessed in passive avoidance (PA) test in a non‐reinforced manner. Then, we evaluated the effect of gentle handling and non‐aversive novel object recognition test (NORT) on the extinction and expression of fear memories by measuring passive avoidance responses. Neurochemical correlates were analyzed by functional autoradiography for cannabinoid, cholinergic, and dopaminergic receptors. Despite results showing a gradual decrease of passive avoidance response, it did not fully disappear even after 7 months, indicating the robustness of this process. Meanwhile, in rats that received gentle handling or performed NORT after receiving the PA aversive stimulus, extinction occurred within a week. In contrast, gentle handling performed before receiving the aversive stimulus exacerbated fear expression and triggered escape response in PA. The neurochemical analysis showed increased cannabinoid and cholinergic activity in the nucleus basalis magnocellularis (NBM) in rats that had performed only PA, as opposed to rats that received gentle handling before PA. Additionally, a correlation between CB1 mediated‐signaling in the NBM and freezing in PA was found, suggesting that the endocannabinoid system might be responsible for modulating fear response induced by aversive memories.

Specific neuronal subpopulations in the amygdala of macaque monkeys express high levels of nonphosphorylated neurofilaments

Pyramidal neurons in the neocortex that express nonphosphorylated neurofilaments (NPNFs) are especially vulnerable to degeneration in Alzheimer’s disease. Since the basolateral nuclear complex of the amygdala (BNC) and cortical nuclear complex of the amygdala (CNC) are cortex-like structures, containing both pyramidal (PNs) and nonpyramidal neurons (NPNs), it is of interest to determine which cell types in the primate BNC and CNC are NPNF+. We also studied NPNF expression in the non-cortex-like nuclei of the amygdala (central and medial nuclei). Digitized images of sections through fetal, newborn, infant, and adult macaque brains stained for NPNFs, obtained from the Macaque Brain Resource (MacBrainResource, MBR), were analyzed. The pattern of NPNF immunoreactivity (NPNF-ir) in the BNC, CNC, and medial nucleus was essentially identical in all four age groups, but there were some age-dependent differences in the central nucleus. All BNC and CNC nuclei contained a moderate density of NPNF+ NPNs. Both the somata and the entire dendritic arborizations of these NPNs were stained. PNs with robust NPNF-ir in their somata and proximal dendrites were only seen in the basal magnocellular nucleus, where it appeared that virtually every PN was NPNF+. This pattern of NPNF expression is distinct from that seen in the mammalian neocortex, where NPNF+ neurons are almost entirely PNs, but is very similar to that seen in a recent study of the rat BNC. These findings, in conjunction with the cortical data, suggest the possibility that NPNF+ neuronal subpopulations in the BNC and CNC might be especially vulnerable in Alzheimer’s disease.

Different cholinergic cell groups in the basal forebrain regulate social interaction and social recognition memory

Social behaviour is a complex construct that is reported to include several components of social approach, interaction and recognition memory. Alzheimer’s disease (AD) is mainly characterized by progressive dementia and is accompanied by cognitive impairments, including a decline in social ability. The cholinergic system is a potential constituent for the neural mechanisms underlying social behaviour, and impaired social ability in AD may have a cholinergic basis. However, the involvement of cholinergic function in social behaviour has not yet been fully understood. Here, we performed a selective elimination of cholinergic cell groups in the basal forebrain in mice to examine the role of cholinergic function in social interaction and social recognition memory by using the three-chamber test. Elimination of cholinergic neurons in the medial septum (MS) and vertical diagonal band of Broca (vDB) caused impairment in social interaction, whereas ablating cholinergic neurons in the nucleus basalis magnocellularis (NBM) impaired social recognition memory. These impairments were restored by treatment with cholinesterase inhibitors, leading to cholinergic system activation. Our findings indicate distinct roles of MS/vDB and NBM cholinergic neurons in social interaction and social recognition memory, suggesting that cholinergic dysfunction may explain social ability deficits associated with AD symptoms.

Acetylcholine from the nucleus basalis magnocellularis facilitates the retrieval of well-established memory

Retrieval deficit of long-term memory is a cardinal symptom of dementia and has been proposed to associate with abnormalities in the central cholinergic system. Difficulty in the retrieval of memory is experienced by healthy individuals and not limited to patients with neurological disorders that result in forgetfulness. The difficulty of retrieving memories is associated with various factors, such as how often the event was experienced or remembered, but it is unclear how the cholinergic system plays a role in the retrieval of memory formed by a daily routine (accumulated experience). To investigate this point, we trained rats moderately (for a week) or extensively (for a month) to detect a visual cue in a two-alternative forced-choice task. First, we confirmed the well-established memory in the extensively trained group was more resistant to the retrieval problem than recently acquired memory in the moderately trained group. Next, we tested the effect of a cholinesterase inhibitor, donepezil, on the retrieval of memory after a long no-task period in extensively trained rats. Pre-administration of donepezil improved performance and reduced the latency of task initiation compared to the saline-treated group. Finally, we lesioned cholinergic neurons of the nucleus basalis magnocellularis (NBM), which project to the entire neocortex, by injecting the cholinergic toxin 192 IgG-saporin. NBM-lesioned rats showed severely impaired task initiation and performance. These abilities recovered as the trials progressed, though they never reached the level observed in rats with intact NBM. These results suggest that acetylcholine released from the NBM contributes to the retrieval of well-established memory developed by a daily routine.

Specific Phospholipid Modulation by Muscarinic Signaling in a Rat Lesion Model of Alzheimer's Disease.

Alzheimer’s disease (AD) represents the most common cause of dementia worldwide and has been consistently associated with the loss of basal forebrain cholinergic neurons (BFCNs) leading to impaired cholinergic neurotransmission, aberrant synaptic function, and altered structural lipid metabolism. In this sense, membrane phospholipids (PLs) can be used for de novo synthesis of choline (Ch) for the further obtaining of acetylcholine (ACh) when its availability is compromised. Specific lipid species involved in the metabolism of Ch have been identified as possible biomarkers of phenoconversion to AD. Using a rat model of BFCN lesion, we have evaluated the lipid composition and muscarinic signaling in brain areas related to cognitive processes. The loss of BFCN resulted in alterations of varied lipid species related to Ch metabolism at nucleus basalis magnocellularis (NMB) and cortical projection areas. The activity of muscarinic receptors (mAChR) was decreased in the NMB and increased in the hippocampus according to the subcellular distribution of M1/M2 mAChR which could explain the learning and memory impairment reported in this AD rat model. These results suggest that the modulation of specific lipid metabolic routes could represent an alternative therapeutic strategy to potentiate cholinergic neurotransmission and preserve cell membrane integrity in AD.

Modulation of prefrontal cortex function by basal forebrain cholinergic and GABAergic neurons at the behavioral and molecular level.

The present research aimed to study the effects of selective immunolesions of cholinergic or gamma-aminobutyric acid (GABA)ergic neurons in the nucleus basalis magnocellularis (NBM) on memory function as well as cholinergic activity and the level of expression of glutamatergic [NR2B subunit of N-methyl-D-aspartate(NMDA)] receptors in the medial prefrontal cortex (mPFC) and hippocampus of behaviorally characterized rats. In behavioral experiments, working memory was assessed by a spatial alternation testing procedure in a plus-maze, and acquisition and retention of spatial memory was evaluated in a Morris water maze. The rats were divided into three groups: the NBM cholinergic, GABAergic immunolesioned groups and the normal control group. Cholin acetyltransferase or parvalbumin staining of the NBM and acetylcholinesterase staining of the mPFC and hippocampal sections were performed to visualize the effects of immunotoxins. The electrophoresis and immunoblotting were run to evaluate the effect of NBM lesions on the amount of the NR2B subunit of NMDA receptors. The results indicate that the immunolesion of cholinergic NBM neurons impair spatial working memory, as well as long-term spatial memory which is accompanied by significant changes in glutamatergic (the NR2B subunit of NMDA receptor) and cholinergic markers in the mPFC, whereas immunolesion of GABAergic NBM neurons does not affect long-term spatial memory, it does though cause the impairment of working memory with a reduction of the NMDA NR2B receptor signaling in the mPFC. The present results demonstrate that the cholinergic and GABAergic NBM cell groups play diverse and complementary roles and are integrated in distinct NBM-mPFC networks that may play different roles in mPFC memory function.

Effect of Nucleus Basalis Magnocellularis Lesions on Memory and Hippocampal Brain-Derived Neurotrophic Factor, IL-1β, Glucose, and Corticosterone Levels in Adult Rats

Background: The nucleus basalis magnocellularis (NBM) sends projections to the hippocampus that are implicated in learning and memory formation. Despite ample evidence proposing that cognitive function impairment related to neurodegeneration, it may result from alteration of biochemical substances. We aimed to investigate the effects of NBM lesions on the hippocampal interleukin-1beta (IL-1β), brain-derived neurotrophic factor (BDNF), and corticosterone levels, as inflammation markers, and hallmarks of neurodegeneration, stress, and metabolic status. Methods: Thirty-six male Wistar rats were randomly put in control, sham, and NBM-lesioned groups. After inducing the lesion using an intra-NBM injection of 10 μg ibotenic acid (5 μg/μL, each side) in rats, memory was estimated using the passive avoidance test. Moreover, serum and hippocampal IL-1β levels, as well as the hippocampal corticosterone, BDNF, and glucose levels were measured after 42 days. Results: Findings indicated a significant impairment of retention at different intervals in the NBM-lesioned group. BDNF decreased whereas corticosterone, glucose, and IL-1β levels increased in the hippocampus. Also, the levels of serum IL-1β, hippocampal BDNF, corticosterone, and glucose had significant correlations with hippocampal IL-1β levels. Conclusion: The synchronous alterations of some hippocampal factors, including BDNF, corticosterone, IL-1β, and glucose, caused by NBM lesion suggest that their interaction might play a significant role in neurodegeneration and relevant learning and memory impairments.

Chronic Ethanol Exposure Potentiates Cholinergic Neurotransmission in the Basolateral Amygdala

Chronic intermittent ethanol (CIE) exposure dysregulates glutamatergic and GABAergic neurotransmission, facilitating basolateral amygdala (BLA) pyramidal neuron hyperexcitability and the expression of anxiety during withdrawal. It is unknown whether ethanol-induced alterations in nucleus basalis magnocellularis (NBM) cholinergic projections to the BLA mediate anxiety-related behaviors through direct modulation of GABA and glutamate afferents. Following 10 days of CIE exposure and 24 h of withdrawal, we recorded GABAergic and glutamatergic synaptic responses in BLA pyramidal neurons with electrophysiology, assessed total protein expression of cholinergic markers, and quantified acetylcholine and choline concentrations using a colorimetric assay. We measured α7 nicotinic acetylcholine receptor (nAChR) dependent modulation of presynaptic function at distinct inputs in AIR- and CIE-exposed BLA coronal slices as a functional read-out of cholinergic neurotransmission. CIE/withdrawal upregulates the endogenous activity of α7 nAChRs, facilitating release at both GABAergic’ local’ interneuron and glutamatergic synaptic responses to stria terminalis (ST) stimulation, with no effect at GABAergic lateral paracapsular cells (LPCs). CIE caused a three-fold increase in BLA acetylcholine concentration, with no changes in α7 nAChR or cholinergic marker expression. These data illustrate that α7 nAChR-dependent changes in presynaptic function serve as a proxy for CIE-dependent alterations in synaptic acetylcholine levels. Thus, cholinergic projections appear to mediate CIE-induced alterations at GABA/glutamate inputs.

Disruption of Cholinergic Circuits as an Area for Targeted Drug Treatment of Alzheimer's Disease: In Vivo Assessment of Short-Term Plasticity in Rat Brain.

The search for new therapeutics for the treatment of Alzheimer’s disease (AD) is still in progress. Aberrant pathways of synaptic transmission in basal forebrain cholinergic neural circuits are thought to be associated with the progression of AD. However, the effect of amyloid-beta (Aβ) on short-term plasticity (STP) of cholinergic circuits in the nucleus basalis magnocellularis (NBM) is largely unknown. STP assessment in rat brain cholinergic circuitry may indicate a new target for AD cholinergic therapeutics. Thus, we aimed to study in vivo electrophysiological patterns of synaptic activity in NBM-hippocampus and NBM-basolateral amygdala circuits associated with AD-like neurodegeneration. The extracellular single-unit recordings of responses from the hippocampal and basolateral amygdala neurons to high-frequency stimulation (HFS) of the NBM were performed after intracerebroventricular injection of Aβ 25–35. We found that after Aβ 25–35 exposure the number of hippocampal neurons exhibiting inhibitory responses to HFS of NBM is decreased. The reverse tendency was seen in the basolateral amygdala inhibitory neural populations, whereas the number of amygdala neurons with excitatory responses decreased. The low intensity of inhibitory and excitatory responses during HFS and post-stimulus period is probably due to the anomalous basal synaptic transmission and excitability of hippocampal and amygdala neurons. These functional changes were accompanied by structural alteration of hippocampal, amygdala, and NBM neurons. We have thus demonstrated that Aβ 25–35 induces STP disruption in NBM-hippocampus and NBM-basolateral amygdala circuits as manifested by unbalanced excitatory/inhibitory responses and their frequency. The results of this study may contribute to a better understanding of synaptic integrity. We believe that advancing our understanding of in vivo mechanisms of synaptic plasticity disruption in specific neural circuits could lead to effective drug searches for AD treatment.