Changes In Cholinergic Markers Research Articles

Effect of cerebral small vessel disease on the integrity of cholinergic system in mild cognitive impairment patients: a longitudinal study

We aimed to investigate the effect of cerebral small vessel disease (SVD) on cholinergic system integrity in mild cognitive impairment (MCI) patients. Nucleus basalis of Meynert (NBM) volume and cholinergic pathways integrity was evaluated at baseline, 1-, 2-, and 4-year follow-ups in 40 cognitively unimpaired (CU) participants, 29 MCI patients without SVD, and 23 MCI patients with SVD. We compared cholinergic markers among three groups and examined their associations with SVD burden in MCI patients. We used linear mixed models to assess longitudinal changes in cholinergic markers over time among groups. Mediation analysis was employed to investigate the mediating role of cholinergic system degeneration between SVD and cognitive impairment. Increased mean diffusivity (MD) in medial and lateral pathways was observed in MCI patients with SVD compared to those without SVD and CU participants. Both MCI groups showed decreased NBM volume compared to CU participants, while there was no significant difference between the two MCI groups. Longitudinally, compared to CU participants, MCI patients with SVD displayed a more rapid change in MD in both pathways, but not in NBM volume. Furthermore, SVD burden was associated with cholinergic pathway disruption and its faster rate of change in MCI patients. However, mediation analyses showed that cholinergic pathways did not mediate significant indirect effects of SVD burden on cognitive impairment. Our findings suggest that SVD could accelerate the degeneration of cholinergic pathways in MCI patients. However, they do not provide evidence to support that SVD could contribute to cognitive impairment through cholinergic system injury.

Multiple Anesthesia/Surgery Cannot Impair Reference Memory in Adult Mice.

Postoperative cognitive dysfunction increases mortality and morbidity in perioperative patients. Numerous studies have demonstrated that multiple surgery/anesthesia during the neurodevelopmental period affects cognitive function, whereas a single anesthesia/surgery rarely causes cognitive dysfunction in adults. However, whether adults who undergo multiple anesthesia/surgery over a short period will experience cognitive dysfunction remains unclear. In this study, central nervous system inflammation and changes in cholinergic markers were investigated in adult mice subjected to multiple laparotomy procedures over a short period of time. The results showed that despite the increased expression of IL-6 and TNF-α in the hippocampus after multiple operations and the activation of microglia, multiple anesthesia/surgery did not cause a decline in cognitive function in adult mice. There were no changes in the cholinergic markers after multiple anesthesia/surgery.

Impairments in laterodorsal tegmentum to VTA projections underlie glucocorticoid-triggered reward deficits.

Ventral tegmental area (VTA) activity is critical for reward/reinforcement and is tightly modulated by the laterodorsal tegmentum (LDT). In utero exposure to glucocorticoids (iuGC) triggers prominent motivation deficits but nothing is known about the impact of this exposure in the LDT-VTA circuit. We show that iuGC-rats have long-lasting changes in cholinergic markers in the LDT, together with a decrease in LDT basal neuronal activity. Interestingly, upon LDT stimulation, iuGC animals present a decrease in the magnitude of excitation and an increase in VTA inhibition, as a result of a shift in the type of cells that respond to the stimulus. In agreement with LDT-VTA dysfunction, we show that iuGC animals present motivational deficits that are rescued by selective optogenetic activation of this pathway. Importantly, we also show that LDT-VTA optogenetic stimulation is reinforcing, and that iuGC animals are more susceptible to the reinforcing properties of LDT-VTA stimulation.

Muscarinic receptor binding changes in postmortem Parkinson's disease.

Parkinson's disease (PD) is a devastating disorder, affecting approximately 2% of people aged 60 and above. It is marked by progressive neurodegeneration that has long been known to impact dopaminergic cells and circuits, but more recently the acetylcholine system has also been implicated in the complex aetiology and symptomatology of the disease. While broad changes in cholinergic markers have been described, insight into the contribution of specific acetylcholine receptors is less clear. To address this important unknown, in this study we performed [3H] pirenzepine, [3H] 4DAMP, and [3H] AF-DX 384 in situ radioligand binding on postmortem tissues from Brodmann's area 6, 9, 46, and the caudate putamen, from PD and matched controls to detect muscarinic M1, M3, and M1/2/4 receptors, respectively. We found no difference in [3H] pirenzepine binding between PD and controls across all regions assessed. [3H] 4DAMP binding was found to be higher in PD CPu and BA9 than in controls. [3H] AF-DX 384 was higher in BA9 of PD compared with controls. In sum, we show selective increase in M3 receptors in cortical and subcortical regions, as well as increased M2/M4 in cortical area BA9, which together support a role for cholinergic dysfunction in PD.

Centrality of Striatal Cholinergic Transmission in Basal Ganglia Function

Work over the past two decades revealed a previously unexpected role for striatal cholinergic interneurons in the context of basal ganglia function. The recognition that these interneurons are essential in synaptic plasticity and motor learning represents a significant step ahead in deciphering how the striatum processes cortical inputs, and why pathological circumstances cause motor dysfunction. Loss of the reciprocal modulation between dopaminergic inputs and the intrinsic cholinergic innervation within the striatum appears to be the trigger for pathophysiological changes occurring in basal ganglia disorders. Accordingly, there is now compelling evidence showing profound changes in cholinergic markers in these disorders, in particular Parkinson's disease and dystonia. Based on converging experimental and clinical evidence, we provide an overview of the role of striatal cholinergic transmission in physiological and pathological conditions, in the context of the pathogenesis of movement disorders.

In utero methanesulfonyl fluoride differentially affects learning and maze performance in the absence of long-lasting cholinergic changes in the adult rat

There is increasing evidence that acetylcholinesterase (AChE) may have various specific developmental roles in brain development. Nevertheless, specific effects of AChE inhibition during early brain development have not been adequately described. Therefore, methanesulfonyl fluoride (MSF), an irreversible AChE inhibitor that shows high selectivity for the CNS was used to produce AChE inhibition in utero to study subsequent adult behaviors, sleep, and cholinergic markers. Rats exposed to MSF in utero showed a deficit in spatial learning tasks using appetitive motivation but, surprisingly, they performed equally well or better than controls when aversive motivation was used. One hypothesis was that MSF treatment in utero affected the response to stress. Tests of anxiety however showed no differences in basal levels of anxiety. Studies of sleep behavior, however, indicated a higher level of REM sleep which is only seen during the light phase of male rats exposed to MSF in utero as compared to controls. No differences in cholinergic markers in the brains of adults were found except that females exposed to MSF in utero had a higher level of ChAT activity in the synaptosomal fraction of the hippocampus. Even so, whether cholinergic alterations accompany the in utero MSF exposure remains to be determined. The failure to find widespread changes in cholinergic markers in the adult brains suggests changes in behaviors should be further investigated by testing the participation of postsynaptic mechanisms, measuring of cholinergic markers during earlier development periods and the possible participation of other neurotransmitter systems to clearly reveal the role of the cholinergic system following in utero MSF exposure.

Effect of Selective Cholinergic Denervation on the Serotonergic System: Implications for Learning and Memory

The cholinergic system has been widely implicated in cognitive processes and cholinergic loss is a classical hallmark in Alzheimer disease. Increasing evidence supports a role of the serotonergic system in cognition, possibly through a modulation of cholinergic activity. We compared selective cholinergic denervation by administration of the immunotoxin 192 IgG-saporin in the nucleus basalis of Meynert (NBM) with intracerebroventricular (ICV) lesions of the basal forebrain in male rats 7 days after lesioning. NBM lesions induced significant changes in cholinergic markers in the frontal cortex, whereas ICV lesions produced significant decreases in cholinergic markers both in the frontal cortex and hippocampus. Only ICV lesions lead to memory impairments in passive avoidance and Morris water maze tasks. Both models lead to reductions of serotonin levels in the frontal cortex. Similar changes in 5-hydroxytriptophan levels were observed, suggesting a downregulation of the rate-limiting enzyme for the synthesis of serotonin along with the cholinergic deficit. Neither 5-HT1A nor 5-HT1B receptors seem to mediate this process. These data imply that the serotonergic system in the frontal cortex can compensate for diminished cholinergic function and support the investigation of the serotonergic system as a therapeutic target to treat Alzheimer disease.

Presynaptic markers of cholinergic function in the rat brain: relationship with age and cognitive status

The nature of age-related changes in cholinergic function and their relationship to age-related behavioral decline were examined in the present study. Male Fischer-344 rats of four ages (four, 11, 17 and 23 months) were tested in a battery of cognitive tasks. Discrete microdissections of brain areas involved in cognitive function were performed, and activity of choline acetyltransferase and levels of hemicholinium-3 binding were determined to assess the integrity of cholinergic innervation. Age-related changes in cholinergic markers occurred predominantly in the medial septal area and its target areas (hippocampus and cingulate cortex), and were also present in the posterior caudate. However, most of the age-related changes in cholinergic markers were already present at ages at which behavioral impairment was not yet maximal. There were some consistent correlations between behavioral and neurochemical measures, independent of age, but these accounted for relatively small proportions of variance in behavioral performance. For most of these correlations, lower levels of presynaptic cholinergic markers were related to better behavioral performance. In brain areas in which correlations changed with age, lower levels of presynaptic cholinergic markers were associated with better performance in young rats, whereas higher levels were associated with better performance in aged rats. Recent lesion studies using a toxin selective for basal forebrain cholinergic neurons have suggested that these neurons do not play as central a role in learning and memory in young and aged animals as was previously thought. When considered in this context, the present results suggest that preserved cholinergic function in old age might act indirectly to sustain cognitive ability. Changes in cholinergic function may represent one of a number of age-related neurobiological events that underlie behavioral impairments, or may be a permissive factor for other age-related processes that are more directly responsible for cognitive impairments.

Long term changes in brain cholinergic markers and nerve growth factor levels after partial immunolesion

There are deficits in cholinergic basal forebrain neurons (CBFNs) in the aged brain and patients suffering Alzheimer's disease associated with a partial loss of the CBFNs. To mimic this partial loss and assess its long term effects on residual cholinergic activity and resultant target-derived nerve growth factor (NGF) levels, we produced a partial immunolesion to CBFNs with 192 IgG-saporin, an immunotoxin selectively taken up by p75 NTR-bearing neurons. We measured two cholinergic markers, choline acetyltransferase (ChAT) and acetylcholinesterase (AChE) activity, and NGF protein levels at 10 days, 1, 6 and 12 months postlesion. There were no significant changes in the cholinergic markers and the NGF protein levels in the sham-treated animal controls during the one year experiment. Ten days after 192 IgG-saporin treatment, ChAT activity decreased to 35–50% of controls in the olfactory bulb, hippocampus, and cortex. There was a minor but significant recovery of ChAT activity one year after the immunolesion in the hippocampus. Changes in AChE activity mirrored the ChAT changes but were less robust. There were transient increases in NGF protein levels in the hippocampus and cortex that returned to basal levels at 6 months and 12 months postlesion, respectively. In summary, partial immunolesions resulted in partial region-specific and time-dependent recoveries of cholinergic activity in the target areas of the basal forebrain after a partial elimination of CBFNs and a return to basal levels of NGF protein consistent with the hypothesis that the remaining CBFNs compensated for losses of ChAT and NGF due to changes in cholinergic innervation of basal forebrain target areas.

Developmental cholinotoxicity of lead: loss of septal cholinergic neurons and long-term changes in cholinergic innervation of the hippocampus in perinatally lead-exposed rats

The effects of perinatal lead exposure on choline acetyltransferase-immunoreactive (ChAT-IR) cell counts in the medial septum and AChE-positive fiber counts in the hippocampus were examined in relation to changes in cholinergic markers in the septohippocampal pathway of the rat. Maternal exposure to 0.2% lead acetate in drinking water from gestational day 16 through weaning at post-natal day 21 (P21) induced in the offspring a 30% reduction in septal ChAT activity and a 20% reduction in ChAT-IR cell profile counts in the medial septum/vertical diagonal band (MS/vDB). These changes were seen as early as P7, persisted through 2 months post-exposure (P81), and were followed by recovery of ChAT activity but not the ChAT-IR cell numbers, at 3 months post-exposure (P112). The loss of ChAT activity and ChAT-IR neurons in the septum was temporally associated with a reduction of ChAT activity (30%), hemicholinium-3 (HC-3) binding (40%), and AChE-positive fiber counts (13–15%) in the hippocampus. The hippocampal ChAT activity and AChE-positive fiber counts returned to control levels by P112 whereas HC-3 binding was restored to normal levels by P200. These results indicate that perinatal, low-level lead exposure induces loss of septohippocampal cholinergic projection neurons in neonate animals, resulting in a deficit in hippocampal cholinergic innervation that persists into young adulthood. The disruption of cholinergic septohippocampal system may be an important factor in lasting cognitive impairments associated with early Pb exposure.

Differential changes in cholinergic markers from selected brain regions after specific immunolesion of the rat cholinergic basal forebrain system

The aim of this study was to characterize the effects of cortical cholinergic denervation on cholinergic parameters in the cerebral cortex and basal forebrain using a novel immunotoxin (conjugate of the monoclonal antibody 192IgG against the low-affinity nerve growth factor receptor armed with cytotoxin saporin) to efficiently and selectively lesion cholinergic neurons in rat basal forebrain. Seven days following an intracerebroventricular injection of the cholinergic immunotoxin 192IgG-saporin the binding levels of nicotinic and M1- and M2-muscarinic acetylcholine receptors (mAChR), high-affinity choline uptake sites, as well as the m1-m4 mAChR mRNA were determined in coronal brain sections by both receptor autoradiography and in situ hybridization, and quantified by image analysis. Hemicholinium-3 binding to high-affinity choline uptake sites was decreased by up to 45% in all cortical regions and in the hippocampus after a single injection of the immunotoxin compared to controls. In contrast, M1-mAChR sites were increased over the corresponding control value in the anterior parts of cingulate, frontal, and piriform cortex by about 20%, in the hindlimb/forelimb areas (18%), in the parietal cortex (35%), in the occipital cortex area 2 (17%), as well as in the temporal cortex (25%) following immunolesion. M2-mAChR levels were found to be significantly increased in the posterior part of the parietal cortex area 1 (by about 22%) and in the occipital cortex area 2 (20%) only. With respect to laminar cortical localization, M2-mAChRs and choline uptake sites were altered in all cortical layers, whereas M1-mAChRs were preferentially affected in the upper cortical layers by the immunolesion. The increase in M1-mAChR binding in the temporal and occipital cortex as a consequence of the immunolesion was complemented by an increase in the amount of m1 and m3 mAChR mRNA of about 20% in these regions. The elevated levels of M2-mAChR sites in the occipital and temporal cortex following immunolesion were accompanied by an increase in the m4 (by 25%) but not m2 mAChR mRNA. There was no effect of the immunolesion on the m1-m4 mAChR mRNA in frontal cortical regions. in the basal forebrain, however, immunolesioning caused about a 40% decrease in the level of m2 mAChR mRNA in the medial and lateral septum as well as in the vertical and horizontal limb of the diagonal band, whereas M1- and M2-mAChR binding and the levels of m1, m3, and m4 mAChR mRNA were not affected by the immunolesion in any of the basal forebrain nuclei studied.(ABSTRACT TRUNCATED AT 400 WORDS)

Effects of nucleus basalis lesion on muscarinic receptor subtypes

The cholinergic system in the central nervous system is an important component of the neural circuitry of learning, memory and cognition. A decline of cholinergic innervation in the human brain is a characteristic feature of dementia of Alzheimer's type. In this study, changes in cholinergic markers were studied after a unilateral lesion of the nucleus basalis magnocellularis (nbM). Acetylcholinesterase (AChE) histochemistry showed a loss of cortical AChE-containing neurons, and choline acetyltransferase (ChAT) immunohistochemistry demonstrated a loss of cholinergic cells in nbM. The localizations of muscarinic M1 and M2 receptors using [3H]pirenzepine ([3H]PZ) and [3H]AF-DX 384, respectively, were studied by quantitative autoradiography 1, 2, 4 and 6 weeks following unilateral ibotenic acid lesion of nbM. A significant decrease in [3H]PZ binding sites was observed at postlesion week 1 in the parietal and temporal cortices. The decrease in [3H]AF-DX 384 binding sites on the lesioned side was observed throughout frontal, parietal and temporal cortices after postlesion week 1, with a significant increase after 6 weeks, possibly as result of loss of presynaptic receptors and upregulation of postsynaptic ones. Moreover, laminar distribution after nbM lesion shows that M1 and M2 receptor binding sites are more affected in superficial layers (I,II,III) than in the deep layers (IV,V,VI), depending on ligand, postlesion period and cortical region. Furthermore, nbM lesion causes a higher deficit of M2 receptors than of M1 receptors. These data suggest the existence of a presynaptic population as well as a postsynaptic population of M1 and M2 receptors which are differently affected after unilateral nbM lesion.

The effect of aluminum on markers for synaptic neurotransmission, cyclic AMP, and neurofilaments in a neuroblastoma × glioma hybridoma (NG108-15)

The effects of the neurotoxin aluminum on markers of synaptic neurotransmission, adenosine 3′,5′-monophosphate, and neurofilaments have been evaluated in a neuroblastoma × glioma hybridoma (NG108-15). Cells were exposed for 4 days to 2 mM aluminum lactate, a concentration that did not suppress growth. Compared to controls, the activity of choline acetyltransferase was significantly increased by 37% associated with an up-regulation in enzyme activity ( V max). Muscarinic receptors, measured by [ 3H]QNB binding, were reduced by 41%. In contrast, the activities of acetylcholinesterase and glutamate decarboxylase were not significantly changed. Aluminum raised the level of cyclic AMP by 20%, although adenylate cyclase activity was unchanged. Small amounts of both phosphorylated and non-phosphorylated neurofilaments were detected in NG108-15 cells. Aluminum intoxication, however, did not alter the quantity, ultrastructure, or immunoreactivity of neurofilaments. Our results demonstrate the capability of aluminum to produce selected changes in cholinergic markers and levels of cyclic AMP in a rapidly dividing cell line.

Changes in cholinergic markers following kainic acid lesion of the ventral globus pallidus in rat.

Choline acetyltransferase (CAT) and glutamate decarboxylase (GAD) activities and [3H] quinuclidinyl benzilate ([3H]QNB) binding were determined in the rat frontal cortex following damage to the basal forebrain cholinergic system. Pre- and postsynaptic changes in the cholinergic system with the passage of time were also studied. After a unilateral injection of kainic acid into the right ventral globus pallidus, the GAD levels remained unaffected, but the CAT levels decreased to 63.4% after 7 days. After 12 weeks, the CAT levels had returned to 87% of the control value. The Bmax of [3H]QNB binding for the muscarinic receptor was higher in the ipsilateral cortex up to 4 weeks. On the other hand, the KD value at 12 weeks was higher without a change in the Bmax of the [3H]QNB binding. These findings might indicate an ongoing compensatory receptor mechanism of denervation supersensitivity as a response to early changes in presynaptic cholinergic activity and the production of postsynaptic effect with presynaptic cholinergic damage over a long period of time.

GLUCOSE METABOLISM AND ACETYLCHOLINE SYNTHESIS IN RELATION TO NEURONAL ACTIVITY IN ALZHEIMER'S DISEASE

The metabolism of (U- 14C) glucose and its incorporation into acetylcholine were determined in vitro in fresh cortical biopsy samples from patients with Alzheimer's disease and controls. Synthesis of 14C acetylcholine was significantly reduced (60% and 67% reduction under stimulated and resting conditions, respectively) without significant changes in the overall metabolism of glucose (as measured by 14CO 2 production). Acetylcholine synthesis was directly related to the activity of choline acetyltransferase. The changes in cholinergic markers reflected the severity of psychological defects. Acetylcholine synthesis was not reduced in biopsy samples from patients suffering from presenile dementia with no histological evidence of Alzheimer's disease.