Reduction In Choline Acetyltransferase Activity Research Articles

The effects of gestational and lactational exposure to Nonylphenol on c-jun, and c-fos expression and learning and memory in hippocampus of male F1 rat.

Objective(s):To investigate the effects of Nonylphenol (NP) in pups from dams exposed during gestational and lactational periods on immediate early genes (c-jun, c-fos) in hippocampus and the learning and memory of F1 rats.Materials and Methods:Twenty eight pregnant dams, stratified by pregnancy date, were randomly assigned into 4 groups, which were gavaged with NP at the doses of 50 mg/kg/day, 100 mg/kg/day, 200 mg/kg/day and groundnut oil, respectively. Step-down avoidance test, and learning and memory effects of NP were evaluated on 8-weeks-old pups. The expressions of c-jun and c-fos and the activities of choline acetyltransferase (ChAT) and acetylcholinesterase (AchE) were evaluated in hippocampus of pups.Results:Compared to the control, reaction time (RT) that pups spent to jump to the platform was longer (P=0.02), the number of errors were higher (P=0.01), and the step-down latency was shorter in the 200 mg/kg/day NP-treated group (P=0.04). Exposure to NP induced a significant reduction in ChAT activity in hippocampus in the 100 (P=0.005) and 200 mg/kg/day NP-treated groups (P=0.002), whereas exposure to 200 mg/kg/day caused a significant increase in AchE activity (P=0.004); a dose–response relationship was revealed between ChAT and AchE activities and NP exposure in the hippocampus of pups (r=-0.821, P=0.01; r=0.757, P=0.04). Exposure to NP in the 100 and 200 mg/kg/day NP-treated groups exhibited an increase in number of c-fos and c-jun positive cells.Conclusion:Exposure to NP might negatively affect learning and memory ability in F1 rats, possibly due to the alterations in the expression of c-jun and c-fos, and ChAT, AchE activities in hippocampus of pups.

Exenatide reduces TNF-α expression and improves hippocampal neuron numbers and memory in streptozotocin treated rats

Recent studies suggest a possible link between type 2 diabetes and Alzheimer's disease (AD). Glucogan-like peptide 1 (GLP-1) facilitates insulin release from pancreas under hyperglycemic conditions. In addition to its metabolic effects, GLP-1 and its long-lasting analogs, including exenatide can stimulate neurogenesis and improve cognition in rodent AD model. The aim of the present study was to investigate the effects of exenatide on hippocampal cellularity, cognitive performance and inflammation response in a rat model of AD. Fourteen rats were used to create AD model using intracerebroventricular (ICV) streptozotocin (STZ) infusion while 7 rats were administered 0.9% NaCl only (sham-operated group). Following stereotaxic surgery, STZ received rats were randomly distributed into two groups, and treated with either saline or exenatide 20µgr/kg/day through intraperitoneally for two weeks. Then, cognitive performance (passive avoidance learning), brain tumor necrosis factor alpha (TNF-α) levels, choline acetyltransferase (ChAT) activity and hippocampal neuronal count were determined. While the brain TNF-α levels were significantly high in the saline-treated STZ group, exenatide treatment suppressed the increase in TNF-α levels. Saline-treated STZ group showed reduced ChAT activity compared to sham group. However, exenatide significantly preserved brain ChAT activity. The cognitive performance was also impaired in saline group while exenatide improved memory in rats. Moreover, exenatide treatment significantly prevented the decrease in hippocampal neurons. Overall, the results of the present study clearly indicated exenatide might have beneficial effects on impaired cognitive performance and hippocampal neuronal viability in AD by suppressing the inflammation response and increasing cholinergic activity.

Hippocampal acetylcholine depletion has no effect on anxiety, spatial novelty preference, or differential reward for low rates of responding (DRL) performance in rats.

We investigated the role of the septo-hippocampal cholinergic projection in anxiety, spatial novelty preference, and differential reward for low rates of responding (DRL) performance. Cholinergic neurons of the rat medial septum (MS) and the vertical limb of the diagonal band of Broca (VDB) were lesioned using the selective immunotoxin, 192 IgG-saporin. Rats were then tested on several behavioral tests previously shown to be sensitive to either (a) hippocampal lesions or (b) nonselective MS/VDB lesions which target both cholinergic and γ-aminobutyric acid (GABA)-ergic projections, or both. Saporin lesions substantially reduced hippocampal cholinergic innervation, resulting in an absence of acetyl cholinesterase staining and markedly reduced choline acetyltransferase activity (mean reduction: 80 ± 5%; range: 50–97%). However, the saporin-lesioned rats did not differ from control rats in any of the behavioral tests. Thus we found no evidence from these lesion studies that the septo-hippocampal cholinergic projection plays an essential role in anxiety, spatial novelty preference, or DRL.

Cholinergic degeneration is associated with increased plaque deposition and cognitive impairment in APPswe/PS1dE9 mice

Cholinergic dysfunction and deposition of plaques containing amyloid β-peptides (Aβ) are two of the characteristics of Alzheimer's disease. Here, we combine APPswe/PS1dE9 (APP/PS1) mice with the cholinergic immunotoxin mu p75-saporin (SAP) to integrate partial basal forebrain cholinergic degeneration and the neuropathology of APP/PS1 mice. By 6 months of age, APP/PS1 mice and wild type littermates (Wt) received intracerebroventricular injection of 0.6μg SAP (lesion) or PBS (sham). Two months following surgery, APP/PS1 mice treated with SAP were significantly impaired compared to sham treated APP/PS1 mice in a behavioural paradigm addressing working memory. Conversely, the performance of Wt mice was unaffected by SAP treatment. Choline acetyltransferase activity was reduced in the hippocampus and frontal cortex following SAP treatment. The selective effect of a mild SAP lesion in APP/PS1 mice was not due to a more extensive cholinergic degeneration since the reduction in choline acetyltransferase activity was similar following SAP treatment in APP/PS1 mice and Wt. Interestingly, plaque load was significantly increased in SAP treated APP/PS1 mice relative to sham lesioned APP/PS1 mice. Additionally, APP/PS1 mice treated with SAP showed a tendency towards an increased level of soluble and insoluble Aβ1-40 and Aβ1-42 measured in brain tissue homogenate. Our results suggest that the combination of cholinergic degeneration and Aβ overexpression in the APP/PS1 mouse model results in cognitive decline and accelerated plaque burden. SAP treated APP/PS1 mice might thus constitute an improved model of Alzheimer's disease-like neuropathology and cognitive deficits compared to the conventional APP/PS1 model without selective removal of basal forebrain cholinergic neurons.

The effects of bilateral common carotid artery occlusion on expression of peripherin and choline acetyltransferase activity in C57BL/6 mice

Peripherin is a 57-kDa type III neuronal intermediate filament protein that appears to play a role in neurite elongation during development and axonal regeneration. Its role in the pathogenesis of cognitive deficits caused by cerebral ischemia is unknown. The purpose of this study was to investigate the location and level of peripherin expression in the central nervous system in response to transient global cerebral ischemia, and the resultant effect of peripherin expression on the cholinergic neurons and Choline acetyltransferase (ChAT) activity in this mouse model of ischemia. Transient global cerebral ischemia was induced in C57BL/6 mice by 20-min bilateral common carotid artery occlusion (BCCAO) with microclips. The resulting impairment of spatial learning and memory was investigated by Morris water maze testing. Peripherin expression was evaluated by immunostaining and Western Blot assay of brain sections. Peripherin expression increased in neurons of the cortex, hippocampus, and thalamus after BCCAO. By double immunofluorescence staining, neurons showed a cytoplasmic co-localization of peripherin and MAP-2, but not of peripherin and GFAP. ChAT activity was determined spectrophotometrically using the assay kit. There was significantly decreased ChAT activity in the cerebral cortex, hippocampus and thalamus in mice of the BCCAO group (p<0.05), compared with the sham group. After BCCAO, peripherin overexpression was significantly correlated with reduction in ChAT activity (r=−0.929; p<0.01), spatial learning and memory were impaired, and peripherin expression was induced in neurons but not astrocytes. Thus, peripherin appears to be a participant in learning and memory impairment in mice.

The Relationship between Choline Acetyltransferase and Nitric Oxide Synthase Isoform Expression in Alzheimer’s Disease

Nitric oxide (NO) plays an important role in cholinergic neurotransmission and has been implicated in the progression of Alzheimer’s disease (AD). Cholinergic neurotransmission has been associated with regulation of NO synthase (NOS) expression, and we determined previously that NO modulates choline acetyltransferase (ChAT) expression. In spite of the important links identified between NOS and ChAT, little is known about the relationship between these two enzymes in AD. Therefore in the present study, we compared the expression levels of ChAT and NOS in necropsy brain of individuals with AD and non-demented controls. ChAT and NOS levels were assessed in control and AD caudate, nucleus basalis of Meynert (nbM), cortex and hippocampus by radioenzymatic assay, immunoblot analysis and RT-PCR. We detected a significant decrease in ChAT activity in the cortex of AD cases, but no alterations in NOS activity were observed in any of the brain regions examined. At the mRNA level, no significant decrease in total ChAT mRNA was detected but the decrease in M-ChAT mRNA levels approached significance in the nbM. No difference in nNOS and iNOS mRNA and protein levels was observed between control and AD tissue in any of the four brain regions sampled, but a statistically significant decrease in eNOS mRNA levels was detected in both the cortex and hippocampus of AD brain. Finally, the levels of ChAT and NOS activity, protein or mRNA isoforms did not correlate in most of the brain regions examined, but a reduction in ChAT activity and eNOS mRNA in basal forebrain projection regions was observed. These data suggest that in general, there is no correlation between the levels of NOS and ChAT in control or AD subjects, but a reduction in eNOS levels in the hippocampus and cortex indicates there could be an interaction between eNOS containing cells and basal forebrain projections neurons in AD.

David Bowen, 1940–2011

David Bowen, 1940–2011

Precuneus amyloid burden is associated with reduced cholinergic activity in Alzheimer disease

This study examined the relationship between postmortem precuneus cholinergic enzyme activity, Pittsburgh compound B (PiB) binding, and soluble amyloid-β concentration in mild cognitive impairment (MCI) and Alzheimer disease (AD). Choline acetyltransferase (ChAT) activity, [(3)H]PiB binding, and soluble amyloid-β(1-42) (Aβ42) concentration were quantified in precuneus tissue samples harvested postmortem from subjects with no cognitive impairment (NCI), MCI, and mild AD and correlated with their last antemortem Mini-Mental State Examination (MMSE) score and postmortem pathologic evaluation according to the National Institute on Aging-Reagan criteria, recommendations of the Consortium to Establish a Registry for Alzheimer's Disease, and Braak stage. Precuneus ChAT activity was lower in AD than in NCI and was comparable between MCI and NCI. Precuneus [(3)H]PiB binding and soluble Aβ42 levels were elevated in MCI and significantly higher in AD than in NCI. Across all case subjects, reduced ChAT activity was associated with increased [(3)H]PiB binding, increased soluble Aβ42, lower MMSE score, presence of the APOE*4 allele, and more advanced AD pathology. Despite accumulating amyloid burden, cholinergic enzyme activity is stable in the precuneus during prodromal AD. A decline in precuneus ChAT activity occurs only in clinical AD, when PiB binding and soluble Aβ42 levels are substantially elevated compared with those in MCI. Anti-amyloid interventions in MCI case subjects with a positive PiB PET scan may aid in reducing cholinergic deficits and cognitive decline later in the disease process.

Different β-amyloid oligomer assemblies in Alzheimer brains correlate with age of disease onset and impaired cholinergic activity

In this study, we examined the relationship between various β-amyloid (Aβ) oligomer assemblies in autopsy brain with the levels of fibrillar Aβ and cholinergic synaptic function. Brain tissues obtained from the frontal cortex of 14 Alzheimer's disease (AD) patients grouped into early-onset AD (EOAD) and late-onset AD (LOAD) and 12 age-matched control subjects were used to extract and quantify Aβ oligomers in soluble (TBS), detergent soluble (TBST), and insoluble (GuHCl) fractions. The predominant oligomeric Aβ assemblies detected were dodecamers, decamers, and pentamers, and different patterns of expression were observed between EOAD and LOAD patients. There was no association between any of the detected Aβ oligomer assemblies and fibrillar Aβ levels measured by N-methyl[3H] 2-(40-methylaminophenyl)-6-hydroxy-benzothiazole ([3H]PIB) binding. Levels of pentamers in the soluble fraction significantly correlated with a reduction in choline acetyltransferase activity in AD patients. The number of nicotinic acetylcholine receptors negatively correlated with the total amount of Aβ oligomers in the insoluble fraction in EOAD patients, and with decamers in the soluble fraction in LOAD patients. These novel findings suggest that distinct Aβ oligomers induce impairment of cholinergic neurotransmission in AD pathogenesis.

Choline Acetyltransferase Activity in Vascular Dementia and Stroke

Background/Aim: Alterations in cholinergic activity have not been systematically studied in types of cerebrovascular disease. We examined cholinergic function at postmortem, focussing on stroke and vascular dementia (VaD). Methods: Post-mortem brain tissue was studied from 61 patients with stroke or VaD (13 infarct dementia; 8 stroke/no dementia; 11 sub-cortical ischaemic VaD, SIVD; 29 VaD and concurrent Alzheimer’s disease, AD), 12 patients with AD and 23 controls. Choline acetyltransferase (ChAT) was measured in Brodmann areas (BA) 9 and 20/21. Results: There were significant reductions in ChAT activity in patients with VaD and concurrent AD compared to age-matched controls (BA9: t = 2.7, p = 0.009; BA20/21: t = 4.67, p = 0.000). In patients with infarct dementia, there was a significant 27% increase in ChAT activity in BA9 (t = 2.1, p = 0.047), but not in BA20/21 (t = 1.67, p = 0.106), compared to the age-matched control group. There was no relationship between ChAT activity and cognition in the VaD patients. Conclusions: Loss of cholinergic function is only evident in VaD patients with concurrent AD. A novel increase in cholinergic activity was identified in patients with infarct dementia, which may create important new treatment opportunities.

Reduction of Choline Acetyltransferase Activity in Primary Visual Cortex in Mild to Moderate Alzheimer's Disease

Cholinergic deficits in the primary visual cortex (PVC) may underlie some of the abnormalities in visual processing and global cognitive performance in Alzheimer's disease (AD). To correlate measures of general cognition (Mini-Mental State Examination and Global Cognitive Score) and visuospatial function with choline acetyltransferase (ChAT) and acetylcholinesterase (AChE) activities, and nerve growth factor protein levels in the PVC. The ChAT and AChE enzyme assays and a nerve growth factor protein enzyme-linked immunoabsorbent assay were performed on PVC tissue samples from subjects clinically diagnosed as having mild cognitive impairment (MCI), AD, or no cognitive impairment (NCI). Nuns, priests and brothers enrolled in the Religious Order Study, with annual premortem records of neuropsychological testing. Significant differences in ChAT activity, but not in AChE activity or nerve growth factor protein levels, were found among diagnostic groups (P = .049). The ChAT activity was lower in AD than in MCI or NCI (P<.01); MCI was not different from NCI. The PVC ChAT activity correlated with measures of overall cognitive function (Mini-Mental State Examination and Global Cognitive Score), but less so with a composite measure of visuospatial function. The reduction in ChAT activity in the PVC of mild to moderate AD, but not in MCI, might serve to distinguish between clinical and preclinical forms of the disease. It appears that this change relates to generalized cognitive abnormalities but not specifically to visuospatial function.

Alternative therapy of Alzheimer’s disease via supplementation with choline acetyltransferase

Much evidence indicates that the memory and cognitive deficits of patients with Alzheimer’s disease are closely associated with dysfunction of central cholinergic system. The degree of reduction of choline acetyltransferase activity in cerebral cholinergic neurons is significantly correlated with the severity of dementia or cognitive impairments observed in Alzheimer’s disease. Therefore, Alzheimer’s disease may be slowed by supplementation of exogenous choline acetyltransferase. Here we show that choline acetyltransferase mediated by TAT protein transduction domain passes through the blood–brain barrier and enters the neurons in mice, increasing choline acetyltransferase and neurotransmitter acetylcholine contents. The recombination TAT-choline acetyltransferase fusion protein injected intravenously improves the memory and cognitive dysfunction in Alzheimer’s disease model mice induced by amyloid-β peptide. Our results imply a novel and potentially effective way for Alzheimer’s disease therapy.

Cognitive and neurological deficits induced by early and prolonged basal forebrain cholinergic hypofunction in rats

In the present study we examined the long-term effects of neonatal lesion of basal forebrain cholinergic neurons induced by intracerebroventricular injections of the immunotoxin 192 IgG saporin. Animals were then characterised behaviourally, electrophysiologically and molecularly. Cognitive effects were evaluated in the social transmission of food preferences, a non-spatial associative memory task. Electrophysiological effects were assessed by recording of cortical electroencephalographic (EEG) patterns. In addition, we measured the levels of proteins whose abnormal expression has been associated with neurodegeneration such as amyloid precursor protein (APP), presenilin 1 and 2 (PS-1, PS-2), and cyclooxygenases (COX-1 and COX-2). In animals lesioned on postnatal day 7 and tested 6 months thereafter, memory impairment in the social transmission of food preferences was evident, as well as a significant reduction of choline acetyltransferase activity in hippocampus and neocortex. Furthermore, similar to what observed in Alzheimer-like dementia, EEG cortical patterns in lesioned rats presented changes in α, β and δ activities. Levels of APP protein and mRNA were not affected by the treatment. Levels of hippocampal COX-2 protein and mRNA were significantly decreased whereas COX-1 remained unaltered. PS-1 and PS-2 transcripts were reduced in hippocampus and neocortex. These findings indicate that neonatal and permanent basal forebrain cholinergic hypofunction is sufficient to induce behavioural and neuropathological abnormalities. This animal model could represent a valid tool to evaluate the role played by abnormal cholinergic maturation in later vulnerability to neuropathological processes associated with cognitive decline and, possibly, to Alzheimer-like dementia.

Choline transporter 1 maintains cholinergic function in choline acetyltransferase haploinsufficiency.

Choline acetyltransferase (ChAT), the enzyme that synthesizes the neurotransmitter acetylcholine (ACh), is thought to be present in kinetic excess in cholinergic neurons. The rate-limiting factor in ACh production is the provision of choline to ChAT. Cholinergic neurons are relatively unique in their expression of the choline transporter 1 (CHT1), which exhibits high-affinity for choline and catalyzes its uptake from the extracellular space to the neuron. Multiple lines of evidence indicate that the activity of CHT1 is a key determinant of choline supply for ACh synthesis. We examined the interaction of ChAT and ChT activity using mice heterozygous for a null mutation in the Chat gene (Chat+/-). In these mice, brain ChAT activity was reduced by 40-50% relative to the wild type, but brain ACh levels as well as ACh content and depolarization-evoked ACh release in hippocampal slices were normal. However, the amount of choline taken up by CHT1 and ACh synthesized de novo from choline transported by CHT1 in hippocampal slices, as well as levels of CHT1 mRNA in the septum and CHT1 protein in several regions of the CNS, were 50-100% higher in Chat+/- than in Chat+/+ mice. Thus, haploinsufficiency of ChAT leads to an increased expression of CHT1. Increased ChT activity may compensate for the reduced ChAT activity in Chat+/- mice, contributing to the maintenance of apparently normal cholinergic function as reflected by normal performance of these mice in several behavioral assays.

Effects of sex hormones, forskolin, and nicotine on choline acetyltransferase activity in human isolated placenta.

The activity of choline acetyltransferase (ChAT) was investigated in the human placenta before and after long-term incubation (24 h) to test the effects of sex hormones, nicotine and forskolin. ChAT activity differed considerably between the amnion (0.03 micromol/mg protein/h) and the villus (0.56). After long-term incubation, ChAT activity persisted in the latter but declined in the amnion. Neither sex hormones (beta-estradiol, testosterone, progesterone; 10 or 100 nM each) nor follicle stimulating hormone and luteinizing hormone (FSH/LH; 8.4 U/ml each) modified ChAT activity. Also nicotine (1 nM-100 microM) did not affect ChAT activity. Forskolin, an activitor of adenylyl cyclase, reduced ChAT activity in the villus but not in amnion. The present model offers the possibility to investigate ChAT regulation in intact tissue under long-term incubation. The risks of maternal smoking during pregnancy cannot be attributed to an effect of nicotine on placental ChAT activity. Differences in the regulation of ChAT appear to exist between neuronal and nonneuronal cells.

Cholinergic changes in the APP23 transgenic mouse model of cerebral amyloidosis.

Alzheimer's Disease (AD) is a neurodegenerative disorder that is characterized by extracellular deposits of amyloid-beta peptide (Abeta) and a severe depletion of the cholinergic system, although the relationship between these two events is poorly understood. In the neocortex, there is a loss of cholinergic fibers and receptors and a decrease of both choline acetyltransferase (ChAT) and acetylcholinesterase enzyme activities. The nucleus basalis of Meynert (NBM), which provides the major cholinergic input to the neocortex, undergoes profound neuron loss in AD. In the present study, we have examined the cholinergic alterations in amyloid precursor protein transgenic mice (APP23), a mouse model of cerebral beta-amyloidosis. In aged APP23 mice, our results reveal modest decreases in cortical cholinergic enzyme activity compared with age-matched wild-type mice. Total cholinergic fiber length was more severely affected, with 29 and 35% decreases in the neocortex of aged APP23 mice compared with age-matched wild-type mice and young transgenic mice, respectively. However, there was no loss of cholinergic basal forebrain neurons in these aged APP23 mice, suggesting that the cortical cholinergic deficit in APP23 mice is locally induced by the deposition of amyloid and is not caused by a loss of cholinergic basal forebrain neurons. To study the impact of cholinergic basal forebrain degeneration on cortical amyloid deposition, we performed unilateral NBM lesions in adult APP23 mice. Three to 8 months after lesioning, a 38% reduction in ChAT activity and significant cholinergic fiber loss were observed in the ipsilateral frontal cortex. There was a 19% decrease in Abeta levels of the ipsilateral compared with contralateral frontal cortex with no change in the ratio of Abeta40 to Abeta42. We conclude that the severe cholinergic deficit in AD is caused by both the loss of cholinergic basal forebrain neurons and locally by cerebral amyloidosis in the neocortex. Moreover, our results suggest that disruption of the basal cholinergic forebrain system does not promote cerebral amyloidosis in APP23 transgenic mice.

Cholinergic Changes in the APP23 Transgenic Mouse Model of Cerebral Amyloidosis

Alzheimer's Disease (AD) is a neurodegenerative disorder that is characterized by extracellular deposits of amyloid-beta peptide (Abeta) and a severe depletion of the cholinergic system, although the relationship between these two events is poorly understood. In the neocortex, there is a loss of cholinergic fibers and receptors and a decrease of both choline acetyltransferase (ChAT) and acetylcholinesterase enzyme activities. The nucleus basalis of Meynert (NBM), which provides the major cholinergic input to the neocortex, undergoes profound neuron loss in AD. In the present study, we have examined the cholinergic alterations in amyloid precursor protein transgenic mice (APP23), a mouse model of cerebral beta-amyloidosis. In aged APP23 mice, our results reveal modest decreases in cortical cholinergic enzyme activity compared with age-matched wild-type mice. Total cholinergic fiber length was more severely affected, with 29 and 35% decreases in the neocortex of aged APP23 mice compared with age-matched wild-type mice and young transgenic mice, respectively. However, there was no loss of cholinergic basal forebrain neurons in these aged APP23 mice, suggesting that the cortical cholinergic deficit in APP23 mice is locally induced by the deposition of amyloid and is not caused by a loss of cholinergic basal forebrain neurons. To study the impact of cholinergic basal forebrain degeneration on cortical amyloid deposition, we performed unilateral NBM lesions in adult APP23 mice. Three to 8 months after lesioning, a 38% reduction in ChAT activity and significant cholinergic fiber loss were observed in the ipsilateral frontal cortex. There was a 19% decrease in Abeta levels of the ipsilateral compared with contralateral frontal cortex with no change in the ratio of Abeta40 to Abeta42. We conclude that the severe cholinergic deficit in AD is caused by both the loss of cholinergic basal forebrain neurons and locally by cerebral amyloidosis in the neocortex. Moreover, our results suggest that disruption of the basal cholinergic forebrain system does not promote cerebral amyloidosis in APP23 transgenic mice.

Upregulation of choline acetyltransferase activity in hippocampus and frontal cortex of elderly subjects with mild cognitive impairment.

In Alzheimer's disease (AD), loss of cortical and hippocampal choline acetyltransferase (ChAT) activity has been correlated with dementia severity and disease duration, and it forms the basis for current therapies. However, the extent to which reductions in ChAT activity are associated with early cognitive decline has not been well established. We quantified ChAT activity in the hippocampus and four cortical regions (superior frontal, inferior parietal, superior temporal, and anterior cingulate) of 58 individuals diagnosed with no cognitive impairment (NCI; n = 26; mean age 81.4 +/- 7.3 years), mild cognitive impairment (MCI; n = 18; mean age 84.5 +/- 5.7), or mild AD (n =14; mean age 86.3 +/- 6.6). Inferior parietal cortex ChAT activity was also assessed in 12 subjects with end-stage AD (mean age 81.4 +/- 4.3 years) and compared to inferior parietal cortex ChAT levels of the other three groups. Only the end-stage AD group had ChAT levels reduced below normal. In individuals with MCI and mild AD, ChAT activity was unchanged in the inferior parietal, superior temporal, and anterior cingulate cortices compared to NCI. In contrast, ChAT activity in the superior frontal cortex was significantly elevated above normal controls in MCI subjects, whereas the mild AD group was not different from NCI or MCI. Hippocampal ChAT activity was significantly higher in MCI subjects than in either NCI or AD. Our results suggest that cognitive deficits in MCI and early AD are not associated with the loss of ChAT and occur despite regionally specific upregulation. Thus, the earliest cognitive deficits in AD involve brain changes other than simply cholinergic system loss. Of importance, the cholinergic system is capable of compensatory responses during the early stage of dementia. The upregulation in frontal cortex and hippocampal ChAT activity could be an important factor in preventing the transition of MCI subjects to AD.

Treatment with 7-nitroindazole enhances kainic acid induced cholinergic neurotoxicity in the rat striatum: a neuroprotective role for neuronal nitric oxide.

1. In this study we investigated the effect of 7-nitroindazole (7-NI), a preferential inhibitor of neuronal nitric oxide synthase (nNOS), on kainic acid (KA) induced neurotoxicity in rats. Choline acetyltransferase activity (CAT), a cholinergic marker, and histological changes were employed to assess neurotoxicity. 2. In control rats, the local intrastriatal injection of 0.5 microg of KA reduced CAT from 22.9 +/- 2.2 to 14.7 +/- 2.0 nmol/h/mg tissue ((38 +/- 6)% reduction) (P < 0.001). Greater reductions in CAT were observed with 1 and 2 microg of KA ((70 +/- 6)% and (80 +/- 3)%, respectively). 7-NI aggravated KA-induced cholinergic and histological damage. KA reduced CAT by (68.2 +/- 4)% in 7-NI-treated rats, by (38 +/- 6)% in saline-treated controls, and by (41 +/- 4)% in peanut-oil- (7-NI-vehicle-) treated rats (P = 0.0047). 3. After KA, CAT activity averaged 14.3 +/- 2.0 in peanut-oil-treated rats and 7.9 +/- 1.0 nmol/h/mg tissue in 7-NI- (peanut-oil-) treated rats (P = 0.015). Similarly to changes in CAT, 7-NI treatment aggravated KA-induced histological changes indicative of neuronal damage (acute ischemic neuronal changes, disorganization of myelinated fibers bundle, and vacuolation changes of the neuropil). Treatment with 7-NI was not associated with increased mortality. 4. Our findings suggest that neuronal NO plays a neuroprotective action on excitotoxicity.

Lesion of caudate-putamen interneurons with kainic acid alters dopamine and serotonin metabolism in the olfactory tubercle of the rat.

1. The existence of functional interrelationships between dorsal and ventral regions of the rat striatum was investigated. Kainic acid (KA) was employed to induce neuronal lesions in the more dorsal striatum, the caudate-putamen (CP). Only one CP (one side) received KA. KA-induced neurotoxicity at the site of injection (CP) was evidenced by reductions in choline-acetyltransferase activity and in GABA levels, and by increases in the ratios metabolite/monoamine for dopamine (DA) and serotonin (5-HT). 2. In addition to the well-known local effects, direct stereotaxic injection of KA into the CP produced distant effects in the ipsilateral olfactory tubercle (OT). A dose-dependent increase in the levels of 3,4-dihydroxyphenylacetic acid (DOPAC), homovanillic acid (HVA), and 5-hydroxyindoleacetic acid (5-HIAA) and decreases in DA and 5-HT concentrations were observed in the OT ipsilateral to the CP injected with KA. With 1, 2, 3, and 4 microg of KA, the ratio DOPAC+HVA/DA in the OT was 30, 79, 140, and 173% higher, respectively, than control levels. With 2, 3, and 4 microg of KA, the levels of 5-HIAA were approximately 30, 60, and 120% higher than control values, and the changes in 5-HIAA were associated with significant reductions in 5-HT concentrations. 3. Our results suggest that the dorsal part of the striatum exerts important regulatory functions over the most ventral striatal region, the OT. Destruction of CP interneurons by KA leads to disinhibition of DA and 5-HT activities to the OT. The functional interactions between dorsal and ventral striatal regions may play a role in the integration of fundamental life-preserving, motivational, and goal-directed olfactory motor behaviors of rodents.