Cholinergic imbalance in the multiple sclerosis hippocampus

Hippocampal pathology was shown to be extensive in multiple sclerosis (MS) and is associated with memory impairment. In this post-mortem study, we investigated hippocampal tissue from MS and Alzheimer's disease (AD) patients and compared these to non-neurological controls. By means of biochemical assessment, (immuno)histochemistry and western blot analyses, we detected substantial alterations in the cholinergic neurotransmitter system in the MS hippocampus, which were different from those in AD hippocampus. In MS hippocampus, activity and protein expression of choline acetyltransferase (ChAT), the acetylcholine synthesizing enzyme, was decreased, while the activity and protein expression of acetylcholinesterase (AChE), the acetylcholine degrading enzyme, was found to be unaltered. In contrast, in AD hippocampus both ChAT and AChE enzyme activity and protein expression was decreased. Our findings reveal an MS-specific cholinergic imbalance in the hippocampus, which may be instrumental in terms of future treatment options for memory problems in this disease.     

Narcoleptic orexin receptor knockout mice express enhanced cholinergic properties in laterodorsal tegmental neurons

Pharmacological studies of narcoleptic canines indicate that exaggerated pontine cholinergic transmission promotes cataplexy. As disruption of orexin (hypocretin) signaling is a primary defect in narcolepsy with cataplexy, we investigated whether markers of cholinergic synaptic transmission might be altered in mice constitutively lacking orexin receptors (double receptor knockout; DKO). mRNA for Choline acetyltransferase (ChAT), vesicular acetylcholine transporter (VAChT) and the high‐affinity choline transporter (CHT1) but not acetylcholinesterase (AChE) was significantly higher in samples from DKO than wild‐type (WT) mice. This was region‐specific; levels were elevated in samples from the laterodorsal tegmental nucleus (LDT) and the fifth motor nucleus (Mo5) but not in whole brainstem samples. Consistent with region‐specific changes, we were unable to detect significant differences in Western blots for ChAT and CHT1 in isolates from brainstem, thalamus and cortex or in ChAT enzymatic activity in the pons. However, using ChAT immunocytochemistry, we found that while the number of cholinergic neurons in the LDT and Mo5 were not different, the intensity of somatic ChAT immunostaining was significantly greater in the LDT, but not Mo5, from DKO than from WT mice. We also found that ChAT activity was significantly reduced in cortical samples from DKO compared with WT mice. Collectively, these findings suggest that the orexins can regulate neurotransmitter expression and that the constitutive absence of orexin signaling results in an up‐regulation of the machinery necessary for cholinergic neurotransmission in a mesopontine population of neurons that have been associated with both normal rapid eye movement sleep and cataplexy.     

Antioxidants Reverse the Changes in the Cholinergic System Caused by L-Tyrosine Administration in Rats

Tyrosinemia type II is an inborn error of metabolism caused by a deficiency in the activity of the enzyme tyrosine aminotransferase, leading to tyrosine accumulation in the body. Although the mechanisms involved are still poorly understood, several studies have showed that higher levels of tyrosine are related to oxidative stress and therefore may affect the cholinergic system. Thus, the aim of this study was to investigate the effects of chronic administration of L-tyrosine on choline acetyltransferase activity (ChAT) and acetylcholinesterase (AChE) in the brain of rats. Moreover, we also examined the effects of one antioxidant treatment (N-acetylcysteine (NAC) + deferoxamine (DFX)) on cholinergic system. Our results showed that the chronic administration of L-tyrosine decreases the ChAT activity in the cerebral cortex, while the AChE activity was increased in the hippocampus, striatum, and cerebral cortex. Moreover, we found that the antioxidant treatment was able to prevent the decrease in the ChAT activity in the cerebral cortex. However, the increase in AChE activity induced by L-tyrosine was partially prevented the in the hippocampus and striatum, but not in the cerebral cortex. Our results also showed no differences in the aversive and spatial memory after chronic administration of L-tyrosine. In conclusion, the results of this study demonstrated an increase in AChE activity in the hippocampus, striatum, and cerebral cortex and an increase of ChAT in the cerebral cortex, without cognitive impairment. Furthermore, the alterations in the cholinergic system were partially prevented by the co-administration of NAC and DFX. Thus, the restored central cholinergic system by antioxidant treatment further supports the view that oxidative stress may be involved in the pathophysiology of tyrosinemia type II.     

Comparative study of the expression of cholinergic system components in the CNS of experimental autoimmune encephalomyelitis mice: Acute vs remitting phase

Acetylcholine (ACh) is involved in the modulation of the inflammatory response. ACh levels are regulated by its synthesizing enzyme, choline acetyltransferase (ChAT), and by its hydrolyzing enzymes, mainly acetylcholinesterase (AChE) and butyrylcholinesterase (BuChE). A more comprehensive understanding of the cholinergic system in experimental autoimmune encephalomyelitis (EAE) disease progression could pave the path for the development of therapies to ameliorate multiple sclerosis (MS). In this work, we analyzed possible alterations of the CNS cholinergic system in the neuroinflammation process by using a MOG‐induced EAE mice model. MOG‐ and vehicle‐treated animals were studied at acute and remitting phases. We examined neuropathology and analyzed mRNA expression of ChAT, AChE and the α7 subunit of the nicotinic acetylcholine receptor (α7nAChR), as well as AChE and BuChE enzyme activities, in brain and spinal cord sections during disease progression. The mRNA expression and enzyme activities of these cholinergic markers were up‐ or down‐regulated in many cholinergic areas and other brain areas of EAE mice in the acute and remitting phases of the disease. BuChE was present in a higher proportion of astroglia and microglia/macrophage cells in the EAE remitting group. The observed changes in cholinergic markers expression and cellular localization in the CNS during EAE disease progression suggests their potential involvement in the development of the neuroinflammatory process and may lay the ground to consider cholinergic system components as putative anti‐inflammatory therapeutic targets for MS.     

Impairment of cholinergic neurotransmission in adult and aged transgenic Tg2576 mouse brain expressing the Swedish mutation of human beta-amyloid precursor protein

To address the question of whether beta-amyloid peptides also affect cholinergic neurotransmission in vivo, brain tissue from transgenic Tg2576 mice with Alzheimer plaque pathology at ages ranging from 7 to 24 months were examined by immuno- and histochemical staining for choline acetyltransferase (ChAT) and acetycholinesterase (AChE), by assaying cholinergic enzyme activities and high-affinity choline uptake as well muscarinic and nicotinic cholinergic receptor binding levels by quantitative autoradiography. Cortical and hippocampal activities of AChE and ChAT were not different between transgenic mice and non-transgenic littermates regardless of the postnatal ages examined. However, high-affinity choline uptake was reduced in the hippocampus of 21-month-old transgenic mice. In brains of 8-month-old transgenic mice which do not yet demonstrate cortical beta-amyloids, reduced binding levels of cortical and hippocampal M1-muscarinic cholinergic receptors were observed, which were still reduced in 17-month-old transgenic mouse brains with high plaque load as compared to non-transgenic littermates. M2-muscarinic cholinergic receptor binding was hardly affected in brains from 8-month-old transgenic mice, but in 17-month-old transgenic mice reduced cortical and hippocampal binding levels were observed as compared to non-transgenic controls. Decreased cortical nicotinic cholinergic receptor binding was detected in 17-month-old transgenic mice. The development of changes in cholinergic synaptic markers in transgenic Tg2576 mouse brain before the onset of progressive plaque deposition provides in vivo evidence of a modulatory role of soluble beta-amyloid on cholinergic neurotransmission and may be referred to the deficits in learning and memory also observed in these mice before significant plaque load.     

Haloperidol alters rat CNS cholinergic system: enzymatic and morphological analyses

Chemical and morphological changes in cholinergic marker enzymes, acetylcholinesterase (AChE), and choline acetyltransferase (ChAT) of striatum, hippocampus, and cerebral cortex were studied following haloperidol treatment of rats. After short-term (7-21 days) haloperidol treatment, the levels of both enzymes (AChE and ChAT) were increased in striatum and hippocampus (greater than 25%), but not in cortex. After long-term (+40 days) haloperidol treatment, the level of AChE activity returned to control levels in all brain areas, whereas the levels of striatal and hippocampal ChAT decreased by 26% and 29%, respectively. No change in levels of both enzymes was detected after acute treatment (single dose) of haloperidol or chronic treatment with either clozapine or imipramine. Morphological analysis of cholinergic neurons and their processes using monoclonal antibody to ChAT showed two types of changes following 40 days of haloperidol treatment. First, parallel to the observed decrease in the levels of ChAT activity there was a visual decrease in the immunoreactivity in neurons as well as in their processes in striatum and hippocampus. Second, there was an apparent reduction in the size and number of stained neurons and their processes. No changes were seen in immunoreactivity after an acute treatment with haloperidol. These results indicate that the chronic haloperidol treatment in rats causes changes in central cholinergic systems that may be relevant to the pathophysiology of schizophrenia and its treatment.     

The Role of Apolipoprotein E and Ethanol Exposure in Age-Related Changes in Choline Acetyltransferase and Brain-Derived Neurotrophic Factor Expression in the Mouse Hippocampus

Disruption of apolipoprotein E (APOE) is responsible for age-dependent neurodegeneration and cognitive impairment. Elderly individuals are more sensitive than young individuals to the effects of ethanol (EtOH), particularly those affecting cognition. We investigated the role of APOE deficiency and EtOH exposure on age-dependent alterations in choline acetyltransferase (ChAT) and brain-derived neurotrophic factor (BDNF) mRNA and protein expression in the mouse hippocampus. Three-month-old (young) and 12-month-old (aged) ApoE-knockout (ApoE-KO) and wild-type (WT) mice were treated with saline or 2 g/kg EtOH, and the bilateral hippocampus was collected after 60 min for real-time PCR and western blotting analyses. ChAT (P < 0.01) and BDNF (P < 0.01) expression were significantly decreased in both young and aged saline- and EtOH-treated ApoE-KO mice versus young and aged saline- and EtOH-treated WT mice. Aged saline- and EtOH-treated ApoE-KO mice exhibited greater differences in ChAT and BDNF expression (P < 0.01) than young saline- and EtOH-treated ApoE-KO mice. Aged EtOH-treated WT mice also exhibited larger decreases in BDNF expression (P < 0.01)—but not in ChAT expression—than young EtOH-treated WT mice. EtOH decreased ChAT and BDNF expression in both young (P < 0.01) and aged (P < 0.01) ApoE-KO mice versus EtOH-free ApoE-KO mice of the same age. EtOH also decreased BDNF expression in aged (P < 0.01) WT mice versus EtOH-free aged WT mice. In summary, these results suggest that APOE deficiency and EtOH exposure cause age-dependent decreases in ChAT and BDNF in the hippocampus. Importantly, the decreases in ChAT and BDNF were greater in aged EtOH-treated mice, particularly those lacking APOE, raising the possibility that APOE-deficient individuals who consume alcohol may be at greater risk of memory deficit.     

Cortical cholinergic decline parallels the progression of Borna virus encephalitis.

Borna disease virus (BDV)-induced meningoencephalitis is associated with the dysfunction of the cholinergic system. Temporal development of this cholinergic decline during pre-encephalitic and encephalitic stages of BDV infection remains however elusive. Changes in choline acetyltransferase (ChAT) and acetylcholinesterase (AChE) activities were therefore determined in the cerebral cortex, hippocampus, striatum, amygdala and cholinergic basal forebrain nuclei (ChBFN) of rats infected with BDV. Immunocytochemistry for ChAT and vesicular acetylcholine transporter (VAChT) was employed to identify morphological consequences of BDV infection on cholinergic neurons. Whereas both ChAT and AChE activities changed only slightly under pre-encephalitic conditions, the encephalitic stage was characterized by a significant decrease of ChAT activity in the cerebral cortex, horizontal diagonal band of Broca (hDBB), hippocampus and amygdala concomitant with a marked reduction of AChE activity in the cerebral cortex, hDBB and hippocampus. The striatum and medial septum remained unaffected. ChAT and VAChT immunocytochemistry revealed prominent axonal degeneration in affected cortical and limbic projection areas of ChBFN. In summary, our data indicate progressive deterioration of forebrain cholinergic systems that parallels the progression of BDV encephalitis.     

192 IgG—Saporin-induced Loss of Cholinergic Neurons in the Septum Abolishes Cholinergic Sprouting After Unilateral Entorhinal Lesion in the Rat

After unilateral lesion of the entorhinal cortex, cholinergic septohippocampal fibres are believed to sprout in the denervated outer molecular layer of the rat dentate gyrus. This cholinergic sprouting has been demonstrated by acetylcholinesterase (AChE) histochemistry, a method said selectively to label cholinergic septohippocampal fibres in the hippocampus. However, a recent report has questioned this concept, suggesting that AChE may not be an adequate marker to monitor cholinergic sprouting and that other, non-cholinergic axons sprouting after entorhinal cortex lesion cause the dense AChE-positive band in the denervated outer molecular layer. In order to determine the contribution of cholinergic septohippocampal fibres to the dense AChE band appearing after entorhinal cortex lesion, the neurotoxin 192 IgG-saporin, known to destroy cholinergic neurons in the basal forebrain selectively, was used. Rats received bilateral injections of 192 IgG-saporin into the lateral ventricles 3 weeks before entorhinal cortex lesion, simultaneously with entorhinal cortex lesion, or 8 weeks after entorhinal cortex lesion. lmmunocytochemistry for choline acetyltransferase (ChAT) and in situ hybridization for ChAT mRNA demonstrated the loss of cholinergic neurons in the medial septum and diagonal band after 192 IgG-saporin treatment. The cholinergic sprouting response in the molecular layer, as visualized with AChE histochemistry, was abolished in all animals treated with immunotoxin. These data indicate that the dense AChE band forming after entorhinal cortex lesion represents the sprouting of cholinergic septohippocampal fibres.     

APP/PS1双转基因小鼠早期记忆功能障碍与胆碱能系统的关系研究

目的观察转APP/PS1基因阿尔茨海默病小鼠(APP/PS1小鼠)早期空间学习记忆功能及乙酰胆碱能系统的变化以及两者之间的相关性,探讨阿尔茨海默病早期学习记忆障碍的发病机制。方法应用Morris水迷宫法评定3月龄APP/PS1小鼠及相应野生型(WT)小鼠的空间学习记忆功能;采用免疫组织化学及组织化学染色方法检测脑组织中β-淀粉样蛋白(Aβ)斑块沉积情况;采用ELISA法检测脑组织中乙酰胆碱(ACh)含量以及胆碱乙酰转移酶(ChAT)和乙酰胆碱酯酶(AChE)活性,并探讨小鼠脑组织中ACh含量与其空间记忆能力、ChAT活性的相关性。结果水迷宫评定结果显示两组小鼠到达平台的潜伏期无统计学差异(P>0.05);APP/PS1小鼠在目标象限的游泳时间百分比〔(29.02±4.27)%〕和距离百分比〔(28.85±3.77)%〕较WT小鼠均下降(P<0.05)。APP/PS1小鼠脑组织中尚无Aβ斑块的沉积。APP/PS1小鼠脑组织中ACh含量〔(45.23±1.40)ng/g prot〕和ChAT活性〔(279.53±12.13)U/g组织湿重〕均较WT小鼠〔分别为(54.08±4.84)ng/gprot、(315.84±11.32)U/g组织湿重〕显著降低(P<0.05),两组小鼠脑组织中AChE活性无统计学差异(P>0.05)。小鼠脑组织中ACh含量与其空间记忆功能(目标象限航行时间百分比、目标象限航行路程百分比)呈正相关(r=0.861、r=0.874,P<0.05),ACh含量与ChAT活性呈正相关(r=0.926,P<0.05)。结论 APP/PS1小鼠空间记忆功能障碍、ACh含量减少和ChAT活性降低可发生于Aβ斑块沉积之前。脑组织中ACh含量减少和ChAT活性降低可能与APP/PS1小鼠记忆功能损害密切相关。     

Deficits in spatial learning and memory is associated with hippocampal volume loss in aged apolipoprotein E4 mice

Apolipoprotein E ε4 (ApoE4) has been implicated as a potential genetic risk factor for dementia. In this study, we investigate the effect of ApoE4 on learning and memory, changes in brain volume and neuroinflammatory responses in brain of ApoE4 transgenic mice. Four groups of male mice with ApoE4 and age-matched wild type (WT) (6-, 12-, 18- and 24-month) were studied. Spatial learning and retaining of mice was examined in the Morris Water Maze (MWM). Changes in brain volume (including the whole brain, hippocampus, cortex, total ventricles, and caudate putamen) were assessed by using 7T small animal MRI. Neuroinflammatory responses were analyzed by measuring the levels of microglia (Iba-1), iNOS, TNFα, and IL-6 quantitatively. In the MWM, ApoE4 mice showed longer escape latency (p < 0.05) and swim distance (p < 0.05) at age 12 month and older, comparing with the WT mice. They also demonstrated poor memory retention in the probe test (p < 0.05). Brain atrophy was significant in ApoE4 mice than age-matched WT mice (18 months: 0.079 ± 0.004 versus 0.086 ± 0.003, p = 0.018; and 24 months: 0.074 ± 0.005 versus 0.084 ± 0.006, p = 0.008). The expression of Iba-1, iNOS, and TNFα in hippocampus and cortex were significantly higher in ApoE4 mice than in WT mice at 12 months and older. These data suggest that ApoE4 plays an important role in learning and memory impairment. These deficits are associated with neuroinflammatory responses that may in turn lead to atrophy in hippocampus and cortex.     

Chronic intraventricular injections of nerve growth factor elevate hippocampal choline acetyltransferase activity in adult rats with partial septo-hippocampal lesions

Nerve growth factor (NGF) was injected intraventricularly during 4 weeks into adult rats with unilateral partial lesions of the cholinergic septo-hippocampal pathway. On the lesioned side, NGF treatment elevated choline acetyltransferase (ChAT) activity up to 60% above the activity measured on the lesioned side of cytochrome c-treated controls. On the unlesioned side, NGF treatment increased ChAT activity only to an insignificant degree. ChAT activity in the septum of NGF-treated animals was increased by 60% as compared to controls. The NGF-induced increases on the lesioned side and in the septum were not accompanied by elevations in acetylcholinesterase (AChE) activity. Furthermore, histochemical analysis revealed no difference in AChE staining pattern or intensity between NGF-treated and control animals. The lack of effect on AChE strongly suggests that the increases in ChAT activity in hippocampus and septum are due to an elevation of ChAT activity within cholinergic neurons surviving the lesion rather than to a promotion of sprouting of cholinergic fibers.     

Low-dose nicotine facilitates spatial memory in ApoE-knockout mice in the radial arm maze

Here, we investigated the effects of nicotine on spatial memory in ApoE-knockout (ApoE-KO) and wild-type (WT) mice in a radial arm maze. Training occurred on three consecutive days and the test was performed on day 4, with one trial per day. Then on day 4, animals were administered nicotine (0.1, 0.25, 0.5, and 1.0 mg/kg) or the antagonist of nicotinic receptors (nAChRs) mecamylamine (MEC 2 mg/kg) alone or together with 0.1 mg/kg nicotine. The number of errors in the first eight choices was recorded. The results were that 0.1 mg/kg nicotine decreased errors in ApoE-KO mice, while 0.1 and 0.25 mg/kg nicotine reduced errors in WT mice, indicating that lower doses of nicotine elicit a memory improvement. In contrast, 1.0 mg/kg nicotine increased errors in WT mice, but not in ApoE-KO mice. MEC alone had no noticeable effect on errors in either strain of mice. However, co-administration of 0.1 mg/kg nicotine and MEC increased errors and reduced the effects of nicotine in WT mice, but not in ApoE-KO mice. Our study found a biphasic effect of nicotine in WT mice: it improves spatial memory at lower doses and impairs it at a higher dose. In ApoE-KO mice, nicotine improves memory at a low dose and has no effect at a higher dose, suggesting that the ApoE deficiency may influence the efficacy of nicotine. Moreover, a reversal of nicotinic effects with MEC was seen in WT mice, indicating the likelihood of the involvement of nAChRs in the spatial-memory response to nicotine.     

Genetically-determined responses of central cholinergic markers: the effects of ethanol on inbred strains of mice

The present study investigated differences in cholinergic function which might contribute to genetic differences in the effects of ethanol on inbred mice. Choline acetyltransferase (ChAT), acetylcholinesterase (AChE) activity and [3H]-quinuclidinyl benzilate (QNB) binding were assessed in several brain areas after administration of ethanol (4.6 g/Kg). ChAT in striatum and septum of C57BL/6 mouse strain exhibit greater sensitivity to ethanol as compared to BALB/c mouse strain. While BALB/c limbic system and related structures showed greater sensitivity to ethanol as compared to C57BL/6 strain. Our previous studies indicated that acute ethanol administration in C57BL/6 mice increased striatal ChAT activity (up to 22% with 60 min latency, Durkin et al., 1982). This augmentation in ChAT activity induced by ethanol was associated with non-synchronous decreases in kinetic characteristics of QNB binding in striatum. In contrast, no such changes were seen in BALB/c striatum (except we noted an increase in Kd up to 90 min after acute ethanol treatment). Similar significant increases in ChAT activity were also observed in C57BL/6 septum 165 min after ethanol administration. However, the septum in BALB/c mice did not exhibit comparable changes. Ethanol did increase ChAT activity in several brain areas of both strains. The areas included the hippocampus, temporal limbic cortex and piriform cortex or paleocortex. Interestingly, the latencies to increased ChAT activity in these areas were much shorter in BALB/c than in C57 mice. The kinetic characteristics of QNB binding sites (Bmax and Kd) and AChE activity were unchanged in all brain areas and did not differ by strain except as otherwise indicated. These data indicate that genetic differences in ethanol preference and sensitivity in these strains are accompanied by differential sensitivity of ChAT to acute ethanol. Genotypic variations in dopaminergiccholinergic interactions in striatum and hippocampus (Durkin et al., 1983), and septum (Kempf et al., 1985), temporal limbic and piriform cortex, could contribute to genetic differences in cholinergic sensitivity to ethanol. In addition, different blood-brain barrier and membrane properties might also contribute to genetic differences in the sensitivity of cholinergic function to ethanol. The differential effects on ChAT activity might participate in genetic differences in memory disorders (limbic system and related structures) and motor incoordination (basal ganglia) following high dose alcohol administration.     

Impairment of Basal Forebrain Cholinergic Neurons Associated with Aging and Long-Term Loss of Ovarian Function

Recent studies suggest that women are at greater risk for Alzheimer's disease than men and that estrogen replacement can help to reduce the risk and severity of Alzheimer's-related dementia in postmenopausal women. We have hypothesized that the increased risk for Alzheimer's-related dementia is due, in part, to the loss of ovarian function in postmenopausal women and to the effects that decreased levels of ovarian hormones have on basal forebrain cholinergic function. In the present study, the effects of aging and ovariectomy on cholinergic neurons in the rat basal forebrain were examined to determine (1) whether aging differentially affects cholinergic neurons in the basal forebrain of males vs females, and (2) whether long-term loss of ovarian function produces deficits in basal forebrain cholinergic function beyond those associated with aging and sex. In part I of the study, gonadally intact male and female rats were sacrificed at 13, 19, and 25 months of age and the effects of aging on cholinergic neurons in the medial septum (MS) and nucleus basalis magnocellularis (NBM) were compared. In part II of the study, female rats were ovariectomized at 13 months of age and then sacrificed 3 and 6 months later along with gonadally intact, age-matched controls. Adjacent sections through the MS and NBM were processed for either immunocytochemical detection of choline acetyltransferase (ChAT) and p75NTR-like immunoreactivity or forin situhybridization detection and quantification of ChAT and trkA mRNA. Results from part I revealed no significant effects of age on the relative size or density of cholinergic neurons in the MS and NBM of gonadally intact animals. Likewise, no significant effects on the relative numbers of cholinergic neurons expressing p75NTR protein were detected. However, a significant decrease in trkA mRNA was detected in the MS of gonadally intact females, but not males, between 13 and 25 months of age. No significant effects of aging on ChAT mRNA were detected. Results from part II revealed significant decreases in both ChAT and trkA mRNA in the MS and NBM of female rats sacrificed 6 months, but not 3 months, following ovariectomy relative to age-matched, gonadally intact controls. Short-term estrogen replacement initiated 6 months following ovariectomy and administered for 3 days prior to sacrifice partially restored ChAT mRNA levels in the MS and trkA mRNA levels in the NBM. These findings suggest that ovarian hormones play a role in maintaining normal levels of ChAT and trkA expression in the MS and NBM. The fact that ChAT mRNA was decreased in the MS and NBM at 6 months following ovariectomy suggests that long-term loss of ovarian function produces a decrease in the functional status of basal forebrain cholinergic neurons projecting to the hippocampus and cortex. In addition, we hypothesize that the decreases in trkA mRNA detected both in the MS as a function of aging, and in the MS and NBM in response to ovariectomy, reflect decreases in the production of high affinity nerve growth factor (NGF) receptors, and a decrease in the responsiveness of the cholinergic neurons to endogenous NGF. This, in turn, may increase the susceptibility of the cholinergic neurons to the effects of aging and disease and thereby contribute to basal forebrain cholinergic decline. We conclude that long-term loss of ovarian function combined with aging has a negative impact on basal forebrain cholinergic neurons. These effects may contribute to the risk and severity of cognitive decline associated with aging and Alzheimer's disease in postmenopausal women.     

Changes in the septohippocampal cholinergic system following removal of molar teeth in the aged SAMP8 mouse

We investigated the effect of dysfunctional teeth on age-related changes in the septohippocampal cholinergic system by assessing acetylcholine (ACh) release and choline acetyltransferase (ChAT) activity in the hippocampus and ChAT immunohistochemistry in the medial septal nucleus and the vertical limb of the diagonal band in young-adult and aged SAMP8 mice after removal of their upper molar teeth (molarless condition). Aged molarless mice showed decreased ACh release and ChAT activity in the hippocampus and a reduced number of ChAT-immunopositive neurons in the medial septal nucleus compared to age-matched control mice, whereas these effects were not seen in young-adult mice. The results suggest that the molarless condition in aged SAMP8 mice may enhance an age-related decline in the septohippocampal cholinergic system.     

Increased activity of choline acetyltransferase and acetylcholinesterase in actively epileptic human cerebral cortex

We measured the activities of the cholinergic marker synthetic and catabolic enzymes choline acetyltransferase (ChAT) and acetylcholinesterase (AChE) in surgical specimens obtained from 38 patients immediately following anterior temporal lobectomy for intractable epilepsy. Samples from patients with actively spiking lateral temporal cortex were compared to non-spiking lateral temporal cortex obtained from patients in whom the epileptic discharges were confined to the hippocampus. Mean activities of ChAT and AChE were increased by 25% (P less than 0.01) and 30% (P less than 0.025) respectively in the spiking vs. non-spiking cortex. We suggest that the above-normal activity of these cholinergic marker enzymes may reflect sprouting of cholinergic nerve terminals in spontaneously spiking cortex of some patients and/or increased acetylcholine metabolism secondary to the stimulatory effect of the ongoing epileptic discharge.