Elizabeth J. Cochran

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

In Alzheimers 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.

Loss and atrophy of layer II entorhinal cortex neurons in elderly people with mild cognitive impairment.

Layer II of the entorhinal cortex contains the cells of origin for the perforant path, plays a critical role in memory processing, and consistently degenerates in end‐stage Alzheimers disease. The extent to which neuron loss in layer II of entorhinal cortex is related to mild cognitive impairment without dementia has not been extensively investigated. We analyzed 29 participants who came to autopsy from our ongoing longitudinal study of aging and dementia composed of religious clergy (Religious Orders Study). All individuals underwent detailed clinical evaluation within 12 months of death and were categorized as having no cognitive impairment (n = 8), mild cognitive impairment (n = 10), or mild or moderate Alzheimers disease (n = 11). Sections through the entorhinal cortex were immunoreacted with an antibody directed against a neuron‐specific nuclear protein (NeuN). Stereological counts of NeuN‐immunoreactive stellate cells, their volume, and the volume of layer II entorhinal cortex were estimated. Cases exhibiting no cognitive impairment averaged 639,625 ± 184,600 layer II stellate neurons in the right entorhinal cortex. Individuals with mild cognitive impairment (63.5%; p < 0.0003) and mild or moderate Alzheimers disease (46.06%; p < 0.0017) displayed significant losses of layer II entorhinal cortex neurons relative to those with no cognitive impairment but not relative to each other (p > 0.33). There was also significant atrophy of layer II entorhinal cortex neurons in individuals with mild cognitive impairment (24.1%) and Alzheimers disease (25.1%). The volume of layer II was also reduced in individuals with mild cognitive impairment (26.5%), with a further reduction in those with Alzheimers disease (46.4%). The loss and atrophy of layer II entorhinal cortex neurons significantly correlated with performance on clinical tests of declarative memory. Atrophy of layer II entorhinal cortex and the neurons within this layer significantly correlated with performance on the Mini Mental Status Examination. These data indicate that atrophy and loss of layer II entorhinal cortex neurons occur in elderly subjects with mild cognitive impairment prior to the onset of dementia and suggests that these changes are not exacerbated in early Alzheimers disease. Ann Neurol 2001;49:202–213

Preservation of nucleus basalis neurons containing choline acetyltransferase and the vesicular acetylcholine transporter in the elderly with mild cognitive impairment and early Alzheimer's disease

Immunocytochemistry for choline acetyltransferase (ChAT) and the vesicular acetylcholine transporter (VAChT) was used to examine the expression of these linked cholinergic markers in human basal forebrain, including cases with early stages of Alzheimers disease (AD). Previous neurochemical studies have measured decreased ChAT activity in terminal fields, but little change or even increased levels of VAChT. To determine total cholinergic neuron numbers in the nucleus basalis of Meynert (nbM), stereologic methods were applied to tissue derived from three groups of individuals with varying levels of cognition: no cognitive impairment (NCI), mild cognitive impairment (MCI), and early‐stage Alzheimers disease (AD). Both markers were expressed robustly in nucleus basalis neurons and across all three groups. On average, there was no significant difference between the number of ChAT‐ (210,000) and VAChT‐ (174,000) immunopositive neurons in the nbM per hemisphere in NCI cases for which the biological variation was calculated to be 17%. There was approximately a 15% nonsignificant reduction in the number of cholinergic neurons in the nbM in the AD cases with no decline in MCI cases. The number of ChAT‐ and VAChT‐immunopositive neurons was shown to correlate significantly with the severity of dementia determined by scores on the Mini‐Mental State Examination, but showed no relationship to apolipoprotein E allele status, age, gender, education, or postmortem interval when all clinical groups were combined or evaluated separately. These data suggest that cholinergic neurons, and the coexpression of ChAT and VAChT, are relatively preserved in early stages of AD. J. Comp. Neurol. 411:693–704, 1999.

Relation of cerebral infarctions to dementia and cognitive function in older persons.

Background: Cerebral infarctions are common in older persons but their relationship with dementia and cognitive function remains controversial. Methods: Participants were 164 older Catholic nuns, priests, and brothers who underwent annual clinical evaluation and brain autopsy at death. The authors quantified number and volume of old cerebral infarctions on postmortem examination and determined the association with dementia and cognitive function proximate to death. Analyses controlled for age, sex, and education. Results: A total of 58 (35.4%) subjects had cerebral infarctions: 29 had one infarction and 29 had multiple infarctions. In logistic regression analyses, infarctions increased the odds of dementia twofold (OR 2.12; 95% CI 1.06 to 4.25). The odds of dementia increased by 2.67-fold for multiple infarctions (95% CI 1.08 to 6.61), whereas the odds of dementia with single infarctions increased by 69% (95% CI 0.70 to 4.09). In linear regression analyses, there was a trend for multiple infarctions to be associated with lower global cognitive scores (−0.44 standard units, p = 0.057). Multiple infarctions were related to perceptual speed, visuospatial skills, and working memory, but not to episodic or semantic memory. The authors found similar results with infarction volume. In secondary analyses, only infarctions that were clinically evident during life were associated with dementia and cognitive function. Conclusion: Cerebral infarctions are associated with a twofold increase in odds of dementia. Odds are higher in persons with multiple, large, or clinically evident infarctions. In addition, cerebral infarctions do not affect all cognitive systems equally, showing the strongest association with perceptual speed and the weakest with episodic memory.

Entorhinal Cortex β-Amyloid Load in Individuals with Mild Cognitive Impairment

Abstract The deposition of β-amyloid within the entorhinal cortex (EC) may play a key role in the development of mild cognitive impairment (MCI) in the elderly. To examine the relationship of β-amyloid deposition to MCI, EC tissue immunostained for this protein was quantitated from a cohort of aged Catholic religious clergy with a clinical diagnosis of MCI and compared to those with no cognitive impairment (NCI) and Alzheimers disease (AD). β-amyloid staining was seen in 12 of the 20 NCI, in 10 of 12 MCI, and in all 12 AD cases within the EC. β-amyloid immunoreactivity displayed two patterns within the EC: (1) a crescent-shaped band within layers 3–4 or (2) bilaminar staining mainly within layers 2–3 and 5–6. Ten cases failed to display any detectable β-amyloid imunoreactivity. Despite the heterogeneity of β-amyloid loads within the clinical groups, decomposing an analysis of variance revealed a significant difference across groups in mean β-amyloid load within the EC based upon a linear trend analysis. Multiple comparisons testing revealed that NCI individuals had a significantly lower mean β-amyloid load (1.32) than AD individuals (4.55). The MCI individuals had a mean intermediate (2.60) load between NCI and AD, but not statistically distinguishable from the mean for either NCI or AD. Spearman rank correlation showed a trend for decreasing MMSE with increasing amyloid load that failed to reach statistical significance. Since many NCI cases displayed β-amyloid loads equal to or greater than that seen in some MCI and some AD cases, it is mostly likely that deposition of this protein is not the sole pathogenic event underlying cognitive impairment in the elderly.

Parahippocampal tau pathology in healthy aging, mild cognitive impairment, and early Alzheimer's disease.

Abnormally phosphorylated tau accumulates as neurofibrillary tangles and neuropil threads in older persons with and without Alzheimers disease. The relationship between neurofibrillary tangles and neuropil threads and how they relate to cognitive function is unknown. This study investigated the relationship between phosphorylated tau lesions and cognitive function in 31 persons participating in the Religious Orders Study, a prospective, longitudinal clinicopathological study of aging and Alzheimers disease. All subjects underwent detailed neuropsychological performance testing within a year of death and evidenced a spectrum of cognitive performance ranging from normal abilities to mild dementia. Measures of neurofibrillary tangle density and phosphorylated tau immunoreactive structures (predominantly neuropil threads) in the entorhinal and perirhinal cortices by quantitative image analysis were significantly correlated (r = 0.5). In multiple linear regression analyses controlling for age, sex, and education, parahippocampal neurofibrillary tangles and neuropil threads were significantly lower in persons without cognitive impairment compared to those with mild cognitive impairment and/or Alzheimers disease. Further, neurofibrillary tangles were significantly correlated to measures of episodic memory but not other cognitive abilities; neuropil tangles were not significantly related to memory or other cognitive functions. These data indicate that phosphorylated tau pathology in the ventromedial temporal lobe develop prior to the onset of clinical dementia and their presence is associated with cognitive impairment, particularly impairment of episodic memory.

Loss of nucleus basalis neurons containing trkA immunoreactivity in individuals with mild cognitive impairment and early Alzheimer's disease

Recent studies indicate that there is a marked reduction in trkA–containing nucleus basalis neurons in end–stage Alzheimers disease (AD). We used unbiased stereological counting procedures to determine whether these changes extend to individuals with mild cognitive impairment (MCI) without dementia from a cohort of people enrolled in the Religious Orders Study. Thirty people (average age 84.7 years) came to autopsy. All individuals were cognitively tested within 12 months of death (average MMSE 24.2). Clinically, 9 had no cognitive impairment (NCI), 12 were categorized with MCI, and 9 had probable AD The average number of trkA–immunoreactive neurons in persons with NCI was 196, 632 ± 12,093 (n = 9), for those with MCI it was 106,110 ± 14,565, and for those with AD it was 86,978 ± 12,141. Multiple comparisons showed that both those with MCI and those with AD had significant loss in the number of trkA–containing neurons compared to those with NCI (46% decrease for MCI, 56% for AD). An analysis of variance revealed that the total number of neurons containing trkA immunoreactivity was related to diagnostic classification (P < 0.001), with a significant reduction in AD and MCI compared to NCI but without a significant difference between MCI and AD. Cell density was similarly related to diagnostic classification (P < 0.001). There was a significant correlation with the Boston Naming Test and with a global score measure of cognitive function. The number of trkA–immunoreactive neurons was not correlated with MMSE, age at death, education, apolipoprotein E allele status, gender, or Braak score. These data indicate that alterations in the number of nucleus basalis neurons containing trkA immunoreactivity occurs early and are not accelerated from the transition from MCI to mild AD. J. Comp. Neurol. 427:19–30, 2000.

Apolipoprotein E 4 allele, AD pathology, and the clinical expression of Alzheimer's disease

Objective: To test the hypothesis that the APOE ε4 allele is associated with the clinical manifestations of AD through an association with the pathologic hallmarks of disease. Methods: Participants were older Catholic nuns, priests, and brothers who agreed to annual neurologic and neuropsychological evaluation for AD and other common neurologic conditions and brain autopsy at the time of death. There were 77 persons without dementia and 51 with probable AD; 38 participants had one or more ε4 alleles. Results: In logistic regression analyses, controlling for age, sex, and education, the ε4 allele was strongly associated with the likelihood of clinical AD (odds = 3.46, 95% CI = 1.44 to 8.33). However, controlling for the effect of AD pathology, the association of the ε allele with clinical AD was reduced by >50% and was no longer significant (odds = 1.58, 95% CI = 0.56 to 4.43). Similarly, in linear regression analyses, controlling for age, sex, and education, the ε4 allele was strongly associated with level of cognitive function proximate to death (regression coefficient = −0.477, p = 0.005). However, after controlling for the effect of AD pathology, the association of the ε4 allele with level of cognition was reduced by >80% and was no longer significant (regression coefficient = −0.093). Similar results were found in analyses using separate measures of neuritic plaques, diffuse plaques, and neurofibrillary tangles, and in analyses of five different cognitive systems (episodic memory, semantic memory, working memory, perceptual speed, and visuospatial ability). Conclusions: The APOE ε4 allele appears to be associated with the clinical manifestations of AD through an association with the pathologic hallmarks of AD rather than another mechanism.

Loss of basal forebrain P75NTR immunoreactivity in subjects with mild cognitive impairment and Alzheimer's disease

The long‐held belief that degeneration of the cholinergic basal forebrain was central to Alzheimers disease (AD) pathogenesis and occurred early in the disease process has been questioned recently. In this regard, changes in some cholinergic basal forebrain (CBF) markers (e.g. the high affinity trkA receptor) but not others (e.g., cortical choline acetyltransferase [ChAT] activity, the number of ChAT and vesicular acetylcholine transporter‐immunoreactive neurons) suggest specific phenotypic changes, but not frank neuronal degeneration, early in the disease process. The present study examined the expression of the low affinity p75 neurotrophin receptor (p75NTR), an excellent marker of CBF neurons, in postmortem tissue derived from clinically well‐characterized individuals who have been classified as having no cognitive impairment (NCI), mild cognitive impairment (MCI), and mild AD. Relative to NCI individuals, a significant and similar reduction in the number of nucleus basalis p75NTR‐immunoreactive neurons was seen in individuals with MCI (38%) and mild AD (43%). The number of p75NTR‐immunoreactive nucleus basalis neurons was significantly correlated with performance on the Mini‐Mental State Exam, a Global Cognitive Test score, as well as some individual tests of working memory and attention. These data, together with previous reports, support the concept that phenotypic changes, but not frank neuronal degeneration, occur early in cognitive decline. Although there was no difference in p75NTR CBF cell reduction between MCI and AD, it remains to be determined whether these findings lend support to the hypothesis that MCI is a prodromal stage of AD. J. Comp. Neurol. 443:136–153, 2002.

Galaninergic innervation of the cholinergic vertical limb of the diagonal band (Ch2) and bed nucleus of the stria terminalis in aging, Alzheimer's disease and down's syndrome

The galanin (GAL) containing peptide fiber system circuit which innervates acetylcholine containing basal forebrain neurons has been shown to hypertrophy and hyperinnervate remaining cholinergic Ch4 perikarya in Alzheimers disease (AD). The present study examined whether a similar hyperinnervation occurs within the cholinergic vertical limb of the diagonal band nucleus (Ch2), a portion of the basal forebrain which, unlike Ch4, exhibits only modest degeneration in AD. Furthermore, we evaluated whether GAL hyperinnervation occurs within the basal forebrain in Downs syndrome, a genetic disorder with extensive AD-like pathology including cholinergic basal forebrain neuron degeneration. The present study revealed that virtually all Ch2 neurons were GAL immunonegative. However, this region was innervated by GAL immunoreactive (ir) interneurons and fibers associated with a major galaninergic pathway which travels through the substantia innominata enroute to the hypothalamus, bed nucleus of the stria terminalis as well as vertical limb of diagonal band nucleus. GAL-ir fibers coursing within this fiber bundle hypertrophied in AD relative to age matched controls and the Downs cases. Within the putative Ch2 terminal zones in AD, many of the remaining cholinergic neurons were hyperinnervated by GAL despite the modest reduction in Ch2 neurons. In contrast, GAL-ir fibers were not hypertrophied in Downs syndrome despite extensive cholinergic cell loss within Ch4. Taken together these findings suggest that extensive cholinergic basal forebrain cell loss alone is not sufficient to trigger the basal forebrain GAL plasticity response found in AD.