The cholinergic system in mild cognitive impairment and Alzheimer's disease: An in vivo MRI and DTI study

Few studies have investigated in vivo changes of the cholinergic basal forebrain in Alzheimer's disease (AD) and amnestic mild cognitive impairment (MCI), an at risk stage of AD. Even less is known about alterations of cortical projecting fiber tracts associated with basal forebrain atrophy. In this study, we determined regional atrophy within the basal forebrain in 21 patients with AD and 16 subjects with MCI compared to 20 healthy elderly subjects using deformation‐based morphometry of MRI scans. We assessed effects of basal forebrain atrophy on fiber tracts derived from high‐resolution diffusion tensor imaging (DTI) using tract‐based spatial statistics. We localized significant effects relative to a map of cholinergic nuclei in MRI standard space as determined from a postmortem brain. Patients with AD and MCI subjects showed reduced volumes in basal forebrain areas corresponding to anterior medial and lateral, intermediate and posterior nuclei of the Nucleus basalis of Meynert (NbM) as well as in the diagonal band of Broca nuclei (P < 0.01). Effects in MCI subjects were spatially more restricted than in AD, but occurred at similar locations. The volume of the right antero‐lateral NbM nucleus was correlated with intracortical projecting fiber tract integrity such as the corpus callosum, cingulate, and the superior longitudinal, inferior longitudinal, inferior fronto‐occipital, and uncinate fasciculus (P < 0.05, corrected for multiple comparisons). Our findings suggest that a multimodal MRI‐DTI approach is supportive to determine atrophy of cholinergic nuclei and its effect on intracortical projecting fiber tracts in AD. Hum Brain Mapp, 2010. © 2010 Wiley‐Liss, Inc.     

Nerve growth factor receptor immunoreactivity within the nucleus basalis (Ch4) in Parkinson's disease: reduced cell numbers and co-localization with cholinergic neurons.

In a effort to better define the role cholinergic basal forebrain neurons play in human cognitive processes, a quantitative assessment of cholinergic nucleus basalis (Ch4) neurons was carried out in 5 patients with Parkinson's disease (PD; 4 non-demented and 1 demented) and 4 age-matched controls using nerve growth factor (NGF) receptor immunohistochemistry as a direct marker for cholinergic basal forebrain neurons. Virtually all (greater than 90%) NGF receptor-containing neurons co-localize with the specific cholinergic marker choline acetyltransferase (ChAT) within the nucleus basalis in PD. NGF receptor-containing neurons were reduced on average by 68% (range 38.6-87.4%) in the non-demented PD cases and by 88.6% in the demented PD patient. Loss of these neurons was heterogeneous across the nucleus basalis subfields with only the anterolateral and posterior Ch4 subregions demonstrating significant reductions of NGF receptor-containing neurons. The reduction in NGF receptor-containing neurons was accompanied by a decrease of acetylcholinesterase (AChE) containing fibers within temporal cortex and in some cases ChAT immunoreactivity in the basolateral amygdaloid nucleus. The numerous non-cholinergic AChE-rich pyramidal cells which were observed throughout the cortex of aged controls were also virtually absent in PD. Although PD patients exhibited severe reductions in Ch4 neurons, few neuritic plaques or neurofibrillary tangles were observed within the PD cortex or Ch4 and similar numbers of these AD-type pathologies were seen within age-matched controls. This suggests that Ch4 degeneration alone is not sufficient to induce such cytoskeletal abnormalities and that the neuron loss seen within Ch4 in AD and PD may be mediated through different processes. These results, coupled with the extensive basic and clinical literature linking acetylcholine and memory function, further indicate that Ch4 degeneration without additional cortical and/or subcortical pathology is not sufficient to impair cognition in PD. Perhaps additional pathology must be superimposed upon nucleus basalis degeneration to induce dementia in humans.     

Loss of nerve growth factor receptor-containing neurons in Alzheimer's disease: a quantitative analysis across subregions of the basal forebrain

Magnocellular neurons comprising the Ch1-Ch4 regions of the basal forebrain provide topographic cholinergic innervation to the cerebral cortex, thalamus, and basolateral nucleus of the amygdala. Most quantitative studies analyzing the status of these neurons in Alzheimer's disease (AD) have employed Nissl-stained preparations. These studies principally analyzed large neurons of a prespecified cell diameter. Since basal forebrain neurons atrophy in Alzheimer's disease, an immunocytochemical marker for these neurons would appear to be a better alternative for determining whether there is regionally specific degeneration of cholinergic neurons across subregions of the basal forebrain. Brain sections from seven AD and five aged-matched control patients were immunocytochemically stained with a monoclonal antibody raised against the receptor for nerve growth factor (NGF), a probe which has previously been demonstrated to extensively and exclusively colocalize with cholinergic basal forebrain neurons in humans (17, 25, 35). NGF receptor-immunoreactive neurons within the hippocampal projecting nuclei of the medial septum (Ch1) and vertical limb of the diagonal band (Ch2) were minimally affected in AD as compared to control cases. In contrast, the Ch4 region demonstrated a significant loss of NGF receptor-immunoreactive neurons in AD that inversely correlated (-0.786) with the duration of the disease process. All four subregions of Ch4 were affected in the AD cases with the anterolateral (76.4%), intermediate (62.1%) and posterior divisions (76.5%) demonstrating the greatest reduction in NGF receptor-immunoreactive neurons. Nissl-counterstained sections failed to reveal magnocellular neurons which were not immunoreactive for the NGF receptor, suggesting that reductions in immunocytochemically stained neurons reflects neuron loss and not the failure of viable neurons to synthesize NGF receptors. These data indicate that cholinergic basal forebrain neurons which project to the amygdala, as well as to the temporal, frontobasal, and frontodorsal cortices, are most affected in AD.     

Heterogeneity and selectivity of the degeneration of cholinergic neurons in the basal forebrain of patients with Alzheimer's disease

Cholinergic neurons were studied by immunohistochemistry, with an antiserum against choline acetyltransferase (ChAT), in the basal forebrain (Ch1 to Ch4) of four patients with Alzheimer's disease (AD) and four control subjects. ChAT-positive cell bodies were mapped and counted in Ch1 (medial septal nucleus), Ch2 (vertical nucleus of the diagonal band), Ch3 (horizontal nucleus of the diagonal band) and Ch4 (nucleus basalis of Meynert). Compared to controls, the number of cholinergic neurons in AD patients was reduced by 50% on average. The interindividual variations in cholinergic cell loss were high, neuronal loss ranging from moderate (27%) to severe (63%). Despite the small number of brains studied, a significant correlation was found between the cholinergic cell loss and the degree of intellectual impairment. To determine the selectivity of cholinergic neuronal loss in the basal forebrain of AD patients, NPY-immunoreactive neurons were also investigated. The number of NPY-positive cell bodies was the same in controls and AD patients. The results (1) confirm cholinergic neuron degeneration in the basal forebrain in AD and the relative sparing of these neurons in some patients, (2) indicate that degneration of cholinergic neurons in the basal forebrain contributes to intellectual decline, and (3) show that, in AD, such cholinergic cell loss is selective, since NPY-positive neurons are preserved in the basal forebrain.     

Cholinergic innervation of cortex by the basal forebrain: Cytochemistry and cortical connections of the septal area,diagonal band nuclei,nucleus basalis (Substantia innominata), and hypothalamus in the rhesus monkey

The organization of projections from the cholinergic neurons of the basal forebrain to neocortex and associated structures was investigated in the rhesus monkey with the help of horseradish peroxidase transport, acetyl-cholinesterase histochemistry, and choline acetyltransferase immunohis-tochemistry. Four groups of neurons contained cholinergic perikarya and were designated as Chl-Ch4. The Ch1 group corresponds to the medial septal nucleus; about 10% of its neurons are cholinergic, and it provides a substantial projection to the hippocampus. The Ch2 group corresponds to the vertical nucleus of the diagonal band; at least 70% of its neurons are cholinergic, and it is the major source of innervation that the hippocampus and hypothalamus receive from the Chl-Ch4 complex. The Ch3 group most closely corresponds to the horizontal nucleus of the diagonal band; only 1% of its neurons can definitely be shown to be cholinergic, and it is the major source of Chl-Ch4 projections to the olfactory bulb. The Ch4 group most closely corresponds to the nucleus basalis of Meynert; at least 90% of its neurons are cholinergic, and it has projections to widespread areas of cortex and to the amygdala. In fact, the Ch4 group provides the single major source of cholinergic innervation for the entire cortical surface. In this respect, it is analogous to the raphe nuclei and to the nucleus locus coeruleus, which constitute the major sources of widespread cortical serotonergic and nor-adrenergic innervation, respectively. The extensive Ch4 group can be divided into several subdivisions. Each subdivision has a preferential set of targets for its projections even though the connection patterns contain considerable overlap. The anteromedial subdivision of Ch4 is the major source of cholinergic projections to areas on the medial aspect of the cerebral hemispheres; the anterolateral Ch4 sub-division is the major source of cholinergic projections to frontoparietal op-ercular areas and to the amygdala; the intermediate Ch4 subdivision pro-vides the major cholinergic input for a variety of dorsal prefrontal, insular, posterior parietal, inferotemporal, and peristriate areas; and the posterior subdivision of Ch4 provides the major cholinergic innervation of superior temporal and immediately adjacent areas. The basal forebrain in the human contains a cytoarchitechture analogous to that of the monkey. The Ch4 group (nucleus basalis) of the human is very extensive and can be subdivided into the same components that were identfied in the monkey brain. Pathological changes in Ch4 neurons have been described in a variety of human disease. In Alzheimer's disease, the relatively selective depression of neocortical cholinergic innervation may be closely associated with the neuronal loss in Ch4, which has also been described inthis condition. In the rhesus monkey, all types of cortical areas receive substantial projections from the hippocampus. Virtually all of this hypothalamic input into neocortex arises from acetylcholinesterase-rich neurons which lack choline acetyltransferase. The hypothalamocortical pathway is therefore acetylcholinesterase-rich but not cholinergic.     

Relationship between corpus callosum atrophy and cerebral metabolic asymmetries in multiple sclerosis.

Corpus callosum (CC) atrophy by magnetic resonance imaging (MRI) is a common finding in multiple sclerosis (MS). In order to examine the relationship between CC atrophy and cortical brain metabolism, we compared the cerebral metabolic rates for glucose (CMRglc), measured by positron emission tomography (PET), of 8 MS patients with evidence of CC atrophy on midsagittal MRI, 8 MS patients without CC atrophy and 10 healthy controls. Results showed no significant differences in supratentorial CMRglc absolute values between the three groups, although a slight metabolic reduction was observed in both MS groups compared with normal controls. By contrast, only patients with CC atrophy showed greater directional metabolic asymmetry than normals, the left frontal, temporal and parietal association cortices being significantly lower than the right. Predominant left hemispheric metabolic reductions were not accompanied by a corresponding left-sided predominance in the extent of MRI-detected demyelinating lesions. Therefore our data suggest that CC atrophy interfers more with left than with right metabolic function.     

Atrophy of the cholinergic basal forebrain in dementia with Lewy bodies and Alzheimer’s disease dementia

Similar to Alzheimer’s disease (AD), dementia with Lewy bodies (DLB) is characterized by a profound degeneration of cortically-projecting cholinergic neurons of the basal forebrain (BF) and associated depletion of cortical cholinergic activity. We aimed to investigate subregional atrophy of the BF in DLB in vivo and compare it to the pattern of BF atrophy in AD. Structural MRI scans of 11 patients with DLB, 11 patients with Alzheimer’s disease, and 22 healthy controls were analysed using a recently developed technique for automated BF morphometry based on high-dimensional image warping and cytoarchitectonic maps of BF cholinergic nuclei. For comparison, hippocampus volume was assessed within the same morphometric framework using recently published consensus criteria for the definition of hippocampus outlines on MRI. The DLB group demonstrated pronounced and subregion-specific atrophy of the BF which was comparable to BF atrophy in AD: volume of the nucleus basalis Meynert was significantly reduced by 20–25 %, whereas rostral BF nuclei were only marginally affected. By contrast, hippocampus volume was markedly less affected in DLB compared to AD. Global cognition as determined by MMSE score was associated with BF volume in AD, but not in DLB, whereas visuoperceptual function as determined by the trail making test was associated with BF volume in DLB, but not in AD. DLB may be characterized by a more selective degeneration of the cholinergic BF compared to AD, which may be related to the differential cognitive profiles in both conditions.     

Mapping of the basal forebrain cholinergic system of the dog: A choline acetyltransferase immunohistochemical study

In an effort to produce a canine model of basal forebrain ischemia with memory deficits, we have shown that dogs possess a medial striate artery that perfuses basal forebrain territory, homologous to the human recurrent artery of Heubner. In the present study, we set out to delineate the precise topography of the cholinergic neurons in the canine forebrain, a neuronal system implicated in cognitive and memory functions. Floating coronal sections, derived from the head of the caudate nucleus to the rostral border of the hippocampus, were stained for choline acetyltransferase using a monoclonal antibody. Representative sections from one dog brain were drawn. These outlines were used for measurement of cell density, cell size, number of processes, and cell roundness. Choline acetyltransferase-positive neurons constituted four major subdivisions within the basal forebrain. A relatively dense population of cholinergic neurons was present in the medial septal nucleus (Ch1). A continuum of densely packed cells was also delineated within the vertical (Ch2) and horizontal (Ch3) nuclei of the diagonal band of Broca. A fourth group of heterogeneously packed cholinergic neurons represented the nucleus basalis magnocellularis (Ch4). Except for the caudal component of the Ch4 population, the forebrain cholinergic corticopetal system was located within the perfusion territory of the medial striate arteries. The Ch4 cell group in dogs is better defined than that of rodents but is not as sharply demarcated as in human and nonhuman primates. Our findings indicate that the dog may serve as an excellent model for assessing neurological and memory deficits, which, in humans, results from hypoperfusion of the recurrent artery of Heubner. © 1996 Wiley-Liss, Inc.     

NGF receptor gene expression is decreased in the nucleus basalis in Alzheimer's disease

Basal forebrain neuronal atrophy in Alzheimer's disease (AD) may be caused by a deficit in the NGF responsiveness of magnocellular cholinergic neurons which project to the cerebral cortex and hippocampal formation. We have used in situ hybridization to show that NGF-receptor (NGF-R) mRNA-positive neurons are lost within all divisions of the nucleus basalis of Meynert (Ch4 cell group) in AD patients as compared to normal aged controls. The posterior division of the nucleus basalis showed the largest decrease in NGF-R mRNA hybridization in the disease, with no overlap in neuronal number between AD cases and normal controls. Northern (RNA) blotting showed decreased levels of NGF-R mRNA in the nucleus basalis in the disease. No differences in the number of NGF-R mRNA-positive neurons between normal aged and AD patients were detected within the NGF-responsive cell groups of the medial septum (Ch1) and nucleus of the vertical limb of the diagonal band (Ch2). These results show that NGF-R gene expression is selectively reduced within basal forebrain neuronal populations which exhibit degenerative changes in AD.     

Nerve growth factor receptor immunoreactivity in the nonhuman primate (Cebus apella): distribution, morphology, and colocalization with cholinergic enzymes

A monoclonal antibody raised against the receptor for nerve growth factor (NGF) was used to examine the distribution and morphology of NGF receptor-containing neurons within the central nervous system of Cebus apella monkeys. Most somata demonstrating positive immunoreactivity were localized within the Ch1-4 regions of the basal forebrain. Neurons in the Ch1 region displayed morphological features typical of cholinergic medial septal neurons. These perikarya were primarily vertically oriented (40-50 micron along the vertical axis) with both apical and basal neuritic processes. Magnocellular (40-50 micron) neurons within the Ch2 (vertical limb of the diagonal band), Ch3 (horizontal limb of the diagonal band) and Ch4 (nucleus basalis of Meynert) regions were multipolar and had rounded perikarya that often displayed an eccentric nucleus. Fibers presumably originating from the Ch1-2 regions were observed throughout the fimbria-fornix system and were found to terminate preferentially within the CA1 and CA3 regions of the hippocampal formation and within the dentate gyrus of the hippocampus. An intense fiber network was also observed in the olfactory tubercle and other rhinencephalic structures, presumably originating from the Ch3 region of the basal forebrain. Beaded processes emanating from the Ch4 region primarily coursed within the external capsule and terminated preferentially within layers I, II, and IV of the cerebral cortex. In a pattern similar to that of cortical acetylcholinesterase (AChE) staining, NGF receptor immunopositive fibers were oriented in a tangential plane within the molecular layer of the cortex and in both a radial and tangential fashion within the cortical granular cell layers. In addition to neural innervation, there was an extensive vascular apposition by NGF receptor-containing neurites on both large caliber vessels and microcapillaries. NGF receptor immunoreactivity was extensively, but not exclusively, colocalized with choline acetyltransferase (ChAT) and AChE in the basal forebrain. A small population of cholinergic neurons were observed that were not NGF receptor-immunoreactive. Conversely, a few NGF receptor-containing neurons that were noncholinergic were also observed in this brain region. NGF receptor-containing somata were also identified in the putamen. The number of immunoreactive neurons observed in this structure, however, would not appear to be sufficient to account for the homologous NGF receptor binding densities described in rodents.(ABSTRACT TRUNCATED AT 250 WORDS)     

Telencephalic cholinergic system of the New World monkey (Cebus apella): morphological and cytoarchitectonic assessment and analysis of the projection to the amygdala

While the cholinergic projection from the nucleus basalis to the cortical mantle has received considerable attention, a similar projection to the magnocellular basal nucleus of the amygdala has not been studied in such detail. The present study analyzed the cholinergic basal forebrain projection to the amygdala in the Cebus apella monkey by using combined tract-tracing and immunocytochemical techniques. As a foundation for this assessment, the morphological and cytoarchitectonic organization of the cholinergic telencephalic system of the New World C. apella monkey was examined by using choline acetyltransferase (ChAT) immunocytochemistry. Although there were minor differences, the telencephalic cholinergic system of Cebus monkeys is similar to that seen in Old World nonhuman primates. ChAT-immunoreactive neurons were observed throughout the Ch1-4 regions of the basal forebrain, with subdivisions of the Ch4 region similar to those previously described (Mesulam et al., '83a). Most cholinergic neurons were hyperchromic and magnocellular; however, some neurons were parvicellular. Like most species, cholinergic neurons were also observed throughout the striatum. However, unlike in rodents, cholinergic perikarya were not observed within the cortex or hippocampus. To analyze the cholinergic fiber projections from the basal forebrain to the amygdala, monkeys received an intraamygdaloid injection of the retrograde tracer horseradish peroxidase conjugated to wheat germ agglutinin. Retrogradely labeled neurons that colocalized ChAT or acetylcholinesterase (AChE) were found predominantly in the anterolateral portion of the CH4 region. Fewer double-labeled neurons were found in the anteromedial and intermediate portion of CH4 and in the CH3 region. Neurons that exhibited retrograde labeling were only occasionally discerned in the posterior portions of the CH4 region, in the medullary laminae of the globus pallidus, or lodged within the internal capsule. These data are discussed in terms of the putative role this cholinergic input might play in cognitive processing in primates.     

Crossed unilateral lesions of medial forebrain bundle and either inferior temporal or frontal cortex impair object recognition memory in Rhesus monkeys

In monkeys, section of the fornix, amygdala and anterior temporal stem results in a severe anterograde amnesia. Immunolesions of the cholinergic cells of the basal forebrain suggest that this amnesia is a result of isolating the inferior temporal cortex and medial temporal lobe from their cholinergic basal forebrain afferents. In this experiment, six monkeys were trained in a delayed match-to-sample task and then received a section of the medial forebrain bundle in one hemisphere and an ablation of either the frontal or inferior temporal cortex in the opposite hemisphere. All the animals were severely impaired in the performance of this task following this surgery, and the severity of the impairment was independent of the cortical area from which the medial forebrain bundle was disconnected. These results support a model of fronto-temporal interaction via the basal forebrain in new learning, in which midbrain sites related to reward modulate the cholinergic basal forebrain activity.     

Neonatal electrolytic lesions of the basal forebrain stunt plasticity in mouse barrel field cortex

Previous studies have shown that neonatal electrolytic lesions of basal forebrain cholinergic projections in mice lead to a transient cholinergic depletion of neocortex and to permanent alterations in cortical cytoarchitecture and in cognitive performance. The present study examines whether neonatal electrolytic lesions of the basal forebrain modify neocortical plasticity. Using cytochrome oxidase histochemistry, we compared cross-sectional areas of individual barrels in the barrel field of four groups of postnatal day 8 (P8) old mice that on P1 received either (1) right electrolytic lesions of the basal forebrain, (2) left C row 1-4 whisker follicle ablations, (3) combined lesion treatments or (4) ice anesthesia only. The size of barrels in basal forebrain lesioned animals was not significantly different from controls. However, the plastic response to whisker removal was compromised in basal forebrain lesioned animals. An index of plasticity, the ratio of row D/row C areas, was reduced significantly in the combined nBM lesioned/follicle ablation group. Compared to whisker-lesioned mice, the expansion in rows B and D and the shrinkage in the lesioned row C area were diminished in the combined treatment group. The present findings correspond to those from a study of rats injected with a cholinergic immunotoxin [Cereb. Cortex 8 (1998) 63]. These results suggest that cholinergic inputs play a role in regulating plasticity as well as in the morphogenesis of mouse sensory-motor cortex.     

Reduced somatostatin-like immunoreactivity in cerebral cortex in nonfamilial dysphasic dementia

A nonfamilial syndrome is described in two middle-aged men who presented with progressive aphasia without incipient signs of cognitive impairment. In each case, 2 years elapsed before progressive functional decline or behavioral disabilities supervened. Radiologic studies documented asymmetric left cerebral atrophy that was progressive. The structure of the language disintegration was distinctive and not like that in Alzheimer's disease. Pathologic studies performed at postmortem examination of one patient documented asymmetric cerebral atrophy with nonspecific histopathologic changes. Biochemical studies revealed normal tissue levels of choline acetyltransferase activity, but reduced somatostatin-like immunoreactivity. Since cerebral somatostatin is largely present in intrinsic cortical neurons, while cholinergic innervation is largely derived from the basal forebrain, these findings suggest that nonfamilial dysphasic dementia may be an example of a distinct class of dementia due to intrinsic cortical degeneration, with sparing of the basal forebrain.     

The distribution pattern of pathology and cholinergic deficits in amygdaloid complex in Alzheimer's disease and dementia with Lewy bodies

We studied the distribution pattern of pathology and cholinergic deficits in the subnuclei of the amygdaloid complex (AC) in five patients with Alzheimer's disease (AD), eight with dementia with Lewy bodies (DLB) and five normal controls. In controls, the basal nucleus contained the highest choline acetyltransferase activity; the activity in the lateral and central nuclei and those in the cortical, medial and accessory basal nuclei were comparable. In AD, there was a significant decrease in choline acetyltransferase activity in the accessory basal and lateral nuclei, in DLB a significant decrease was observed in the accessory basal, lateral and cortical nuclei. Compared to controls the hyperphosphorylated tau-pathology burden was significantly higher in the basal, central and medial nuclei in AD and in the central, cortical, lateral and medial nuclei in DLB. The amyloid plaque burden was significantly higher in the accessory basal, basal, lateral and cortical nuclei in AD and in all nuclei in DLB. The α-synuclein burden was significantly higher in all nuclei in both AD and DLB. Compared to AD α-synuclein burden was higher in all nuclei in DLB. There were no correlations between the distribution pattern of hyperphosphorylated tau-pathology, amyloid plaques and α-synuclein-positive structures, and choline acetyltransferase activity, except the lateral nucleus in DLB. In conclusion we found no relationship between the pattern of cholinergic deficits and the distribution pattern of lesions in the AC of patients with AD or DLB. Cholinergic deficits were more prominent in the nuclei of basolateral (BL) group in AD, whereas the nuclei of both BL and corticomedial groups were involved in DLB, which may be due to the involvement of both basal forebrain and brainstem cholinergic nuclei in the latter.     

Mapping hemispheric asymmetries of the macaque cerebral cortex during early brain development

Studying cortical hemispheric asymmetries during the dynamic early postnatal stages in macaque monkeys (with close phylogenetic relationship to humans) would increase our limited understanding on the possible origins, developmental trajectories, and evolutional mechanisms of brain asymmetries in nonhuman primates, but remains a blind spot to the community. Via cortical surface‐based morphometry, we comprehensively analyze hemispheric structural asymmetries in 134 longitudinal MRI scans from birth to 20 months of age from 32 healthy macaque monkeys. We reveal that most clusters of hemispheric asymmetries of cortical properties, such as surface area, cortical thickness, sulcal depth, and vertex positions, expand in the first 4 months of life, and evolve only moderately thereafter. Prominent hemispheric asymmetries are found at the inferior frontal gyrus, precentral gyrus, posterior temporal cortex, superior temporal gyrus (STG), superior temporal sulcus (STS), and cingulate cortex. Specifically, the left planum temporale and left STG consistently have larger area and thicker cortices than those on the right hemisphere, while the right STS, right cingulate cortex, and right anterior insula are consistently deeper than the left ones, partially consistent with the findings in human infants and adults. Our results thus provide a valuable reference in studying early brain development and evolution.     

Neuroimaging findings in Alzheimer's disease

In the present article, the neuroimaging findings in Alzheimer's disease are summarized and experimental data from animals relating to metabolic changes in Alzheimer's disease (AD), particularly in the frontobasal cholinergic projections onto the cerebral cortex, are reviewed. Changes in glucose metabolism as well as in cerebral blood flow (CBF) are specific for AD, in which the parietotemporal association cortex shows metabolic suppression. This finding is used as a diagnostic aid in the clinical application of single photon emission computed tomography. In rare cases, limited suppression of metabolism and blood flow is also found in the unilateral medial temporal lobe or parietal lobe. Statistically, approximately 80% of cases of AD show a typical parietotemporal suppression pattern of CBF. This cortical metabolic and circulatory suppression has been attributed to cholinergic deprivation from the basal forebrain Mynert nucleus. Animal experiments have revealed transient cortical suppression of glucose metabolism in the frontal cortex after destruction of the basal forebrain cholinergic neurons by ibotenic acid. This suppression persists for approximately 1 week and returns to normal 1 month after operation. Thus, the typical neuroimaging findings in AD would not be due to deficient cholinergic projections from the basal forebrain.     

Long-term reversal of cholinergic neuronal decline in aged non-human primates by lentiviral NGF gene delivery

Spontaneous atrophy of basal forebrain cholinergic neurons occurs with aging in the non-human primate brain. Short-term reversal of this atrophy has been reported following ex vivo nerve growth factor (NGF) gene delivery, but long-term effects of in vivo NGF gene delivery in the aged primate brain have not to date been examined. We tested the hypothesis that long-term lentiviral NGF intraparenchymal gene delivery would reverse age-related cholinergic decline, without induction of adverse effects previously observed following sustained intracerebroventricular growth factor protein exposure. Three aged rhesus monkeys underwent intraparenchymal lentiviral NGF gene delivery to the cholinergic basal forebrain. 1 year later, cholinergic neuronal numbers were quantified stereologically and compared to findings in four controls, non-treated aged monkeys and four young adult monkeys. Safety was assessed on several variables related to growth factor exposure. We now report that lentiviral gene delivery of NGF to the aged primate basal forebrain sustains gene expression for at least 1 year, and significantly restores cholinergic neuronal markers to levels of young monkeys. Aging resulted in a significant 17% reduction (p < 0.05) in the number of neurons labeled for the cholinergic marker p75 among basal forebrain neurons. Lentiviral NGF gene delivery induced significant (p < 0.05) and nearly complete recovery of p75-labeled neuronal numbers in aged subjects to levels observed in young monkeys. Similarly, the size of cholinergic neurons in aged monkeys was significantly reduced by 16% compared to young subjects (p < 0.05), and lentiviral NGF delivery to aged subjects induced complete recovery of neuronal size. Intraparenchymal NGF gene delivery over a one-year period did not result in systemic leakage of NGF, activation of inflammatory markers in the brain, pain, weight loss, Schwann cell migration, or formation of anti-NGF antibodies. These findings indicate that extended trophic support to neurons in the non-human primate brain reverses age-related neuronal atrophy. These findings also support the safety and feasibility of lentiviral NGF gene transfer for potential testing in human clinical trials to protect degenerating cholinergic neurons in Alzheimer's disease.     

Aphasia and dementia

Primary progressive aphasia (PPA) is an uncommon neurodegenerative syndrome characterized by a relatively isolated dissolution of language function at the beginning, followed by deterioration of general cognitive function and of activities of daily living after 2 or more years. On account of neuropathological and clinical findings, PPA is supposed to form part of the spectrum of frontotemporal lobar degeneration. We present a case study of a 66-year-old woman with a probable fluent progressive aphasia. She initially experienced word amnesia and developed after 2 - 3 years gradual regression of word comprehension, over-fluent speech with semantic paraphasias, and at last generalized dementia. In addition to minor bilateral cortical volume reduction on CCT, MRI showed left temporal lobe atrophy involving hippocampus, SPECT revealed reduced uptake left frontal and temporal.     

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 accomplanied 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. Seven days after a single dose of the 192IgG-saporin immunotoxin there was no change in the level of cortical nicotinic acetylcholine receptor sites in any of the regions studied compared to corresponding controls. The region-specific changes in the level of M₁- and M₂-mAChRs, as well as corresponding receptor gene expression and the lack of effects on cortical nicotinic receptors, may be part of an adaptive mechanism in response to cholinergic degeneration. These data further support the usefulness of the 192IgG-saporin conjugate as an appropriate tool to produce cortical cholinergic dysfunction. © 1995 Wiley-Liss, Inc.