Regional binding of tau and amyloid PET tracers in Down syndrome autopsy brain tissue

INTRODUCTION

Tau pathology is a major age-related event in Down syndrome with Alzheimer's disease (DS-AD). Although recently, several different Tau PET tracers have been developed as biomarkers for AD, these tracers showed different binding properties in Alzheimer disease and other non-AD tauopathies. They have not been yet investigated in tissue obtained postmortem for DS-AD cases. Here, we evaluated the binding characteristics of two Tau PET tracers (³H-MK6240 and ³H-THK5117) and one amyloid (³H-PIB) ligand in the medial frontal gyrus (MFG) and hippocampus (HIPP) in tissue from adults with DS-AD and DS cases with mild cognitive impairment (MCI) compared to sporadic AD.

METHODS

Tau and amyloid autoradiography were performed on paraffin-embedded sections. To confirm respective ligand targets, adjacent sections were immunoreacted for phospho-Tau (AT8) and stained for amyloid staining using Amylo-Glo.

RESULTS

The two Tau tracers showed a significant correlation with each other and with AT8, suggesting that both tracers were binding to Tau deposits. ³H-MK6240 Tau binding correlated with AT8 immunostaining but to a lesser degree than the ³H-THK5117 tracer, suggesting differences in binding sites between the two Tau tracers. ³H-THK5117, ³H-MK6240 and ³H-PIB displayed dense laminar binding in the HIPP and MFG in adult DS brains. A regional difference in Tau binding between adult DS and AD was observed suggesting differential regional Tau deposition in adult DS compared to AD, with higher THK binding density in the MFG in adult with DS compared to AD. No significant correlation was found between ³H-PIB and Amylo-Glo staining in adult DS brains suggesting that the amyloid PIB tracer binds to additional sites.

CONCLUSIONS

This study provides new insights into the regional binding distribution of a first-generation and a second-generation Tau tracer in limbic and neocortical regions in adults with DS, as well as regional differences in Tau binding in adult with DS vs. those with AD. These findings provide new information about the binding properties of two Tau radiotracers for the detection of Tau pathology in adults with DS in vivo and provide valuable data regarding Tau vs. amyloid binding in adult DS compared to AD.

HDAC2 dysregulation in the nucleus basalis of Meynert during the progression of Alzheimer's disease

AIMS

Alzheimer's disease (AD) is characterized by degeneration of cholinergic basal forebrain (CBF) neurons in the nucleus basalis of Meynert (nbM), which provides the major cholinergic input to the cortical mantle and is related to cognitive decline in patients with AD. Cortical histone deacetylase (HDAC) dysregulation has been associated with neuronal degeneration during AD progression. However, whether HDAC alterations play a role in CBF degeneration during AD onset is unknown. We investigated global HDAC protein levels and nuclear HDAC2 immunoreactivity in tissue containing the nbM, changes and their association with neurofibrillary tangles (NFTs) during the progression of AD.

METHODS

We used semi-quantitative western blotting and immunohistochemistry to evaluate HDAC and sirtuin (SIRT) levels in individuals that died with a premortem clinical diagnosis of no cognitive impairment (NCI), mild cognitive impairment (MCI), mild/moderate AD (mAD) or severe AD (sAD). Quantitative immunohistochemistry was used to identify HDAC2 protein levels in individual cholinergic nbM nuclei and their colocalization with the early phosphorylated tau marker AT8, the late-stage apoptotic tau marker TauC3 and Thioflavin-S, a marker of β-pleated sheet structures in NFTs.

RESULTS

In AD patients, HDAC2 protein levels were dysregulated in the basal forebrain region containing cholinergic neurons of the nbM. HDAC2 nuclear immunoreactivity was reduced in individual cholinergic nbM neurons across disease stages. HDAC2 nuclear reactivity correlated with multiple cognitive domains and with NFT formation.

CONCLUSIONS

These findings suggest that HDAC2 dysregulation contributes to cholinergic nbM neuronal dysfunction, NFT pathology, and cognitive decline during clinical progression of AD.

Hippocampal plasticity during the progression of Alzheimer's disease

Neuroplasticity involves molecular and structural changes in central nervous system (CNS) throughout life. The concept of neural organization allows for remodeling as a compensatory mechanism to the early pathobiology of Alzheimer's disease (AD) in an attempt to maintain brain function and cognition during the onset of dementia. The hippocampus, a crucial component of the medial temporal lobe memory circuit, is affected early in AD and displays synaptic and intraneuronal molecular remodeling against a pathological background of extracellular amyloid-beta (Aβ) deposition and intracellular neurofibrillary tangle (NFT) formation in the early stages of AD. Here we discuss human clinical pathological findings supporting the concept that the hippocampus is capable of neural plasticity during mild cognitive impairment (MCI), a prodromal stage of AD and early stage AD.

NGF receptor (p75)-immunoreactivity within hypoglossal motor neurons following axotomy in monkeys

The expression of the p75 nerve growth factor receptor (NGFR) was examined in Rhesus and Cebus monkeys following complete unilateral transections of the hypoglossal nerve. In unoperated and sham-lesioned monkeys, NGF receptor-immunoreactivity was always undetectable within hypoglossal motor neurons. In contrast, monkeys receiving unilateral transections of the hypoglossal nerve displayed numerous NGFR-immunoreactive neurons within ipsilateral hypoglossal motor neurons 1 week post-lesion. The peak expression of NGFR-immunoreactive hypoglossal neurons was seen 4 weeks following the lesion and although fewer, these neurons were still observed in large numbers 10 weeks post-lesion. By 16 weeks post-lesion only a few NGFR-immunoreactive motor neurons were observed. A small number of NGF receptor-immunoreactive neurons were also seen within the contralateral hypoglossal nucleus at post-lesion weeks 4 and 10. These data demonstrate that adult hypoglossal motor neurons express detectable levels of p75 nerve growth factor receptor following hypoglossal nerve transection in monkeys in a manner similar to that previously reported in non-primate species. The synthesis of p75 NGF receptors in these neurons may represent a regeneration-mediated re-expression of NGF receptors which only normally occurs during development.

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

OBJECTIVE

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).

METHODS

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.

RESULTS

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.

CONCLUSIONS

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.

MRI-based volumetric measurement of the substantia innominata in amnestic MCI and mild AD

The substantia innominata (SI) contains the nucleus basalis of Meynert, which provides the major cholinergic innervation to the entire cortical mantel and the amygdala; degeneration of nucleus basalis neurons correlates with cognitive decline in Alzheimer's disease (AD). However, whether SI atrophy occurs in individuals with amnestic mild cognitive impairment (aMCI) has not been examined thoroughly in vivo. In the present study, we developed a new protocol to measure volumetric changes in the SI from magnetic resonance imaging (MRI) scans. Participants consisted of 27 elderly controls with no cognitive impairment (NCI); 33 individuals with aMCI; and 19 patients with mild AD. SI volumes were traced on three consecutive gapless 1mm thick coronal slices. Results showed that SI volume was significantly reduced in the mild AD group compared to both NCI and aMCI participants; however, the NCI and aMCI groups did not differ from each other. Furthermore, a decrease in SI volume was related to impaired performance on declarative memory tasks even when attention was controlled.

Galanin in Alzheimer's disease: neuroinhibitory or neuroprotective?

Galanin (GAL) and GAL receptors (GALRs) are overexpressed in degenerating brain regions associated with cognitive decline in Alzheimer's disease (AD). The functional consequences of GAL plasticity in AD are unclear. GAL inhibits cholinergic transmission in the hippocampus and impairs spatial memory in rodent models, suggesting GAL overexpression exacerbates cognitive impairment in AD. By contrast, gene expression profiling of individual cholinergic basal forebrain (CBF) neurons aspirated from AD tissue revealed that GAL hyperinnervation positively regulates mRNAs that promote CBF neuronal function and survival. GAL also exerts neuroprotective effects in rodent models of neurotoxicity. These data support the growing concept that GAL overexpression preserves CBF neuron function which in turn may slow the onset of AD symptoms. Further elucidation of GAL activity in selectively vulnerable brain regions will help gauge the therapeutic potential of GALR ligands for the treatment of AD.

A confocal microscopic analysis of galaninergic hyperinnervation of cholinergic basal forebrain neurons in Alzheimer's disease

The galanin (GAL) containing peptide fiber system innervates the basal forebrain and has been shown to hyperinnervate remaining cholinergic neurons in Alzheimer's disease (AD). GAL modulates the release of acetylcholine and, therefore, may depress this neurotransmitter in surviving cholinergic basal forebrain (CBF) neurons in AD. The aim of this study was to identify putative synaptic contacts between GAL immunoreactive processes and CBF neurons and evaluate whether these processes hypertrophy in AD patients. We observed by confocal laser microscopy a hyperinnervation of GAL-containing fibers in both AD and Parkinson's disease patients with concurrent AD (PD/AD). Galaninergic fibers were often seen in direct apposition to remaining CBF neurons and enwrapped cholinergic cell soma and dendrites. Our results demonstrate that GAL-containing fibers are in direct apposition to CBF neurons in normal-aged humans and that this phenotype is enhanced in AD and PD/AD, suggesting that direct synaptic contacts occur between GAL-containing fibers and CBF neurons. Because GAL can modulate acetylcholine release from cholinergic neurons, hyperinnervation of GAL fibers in AD and PD/AD patients may further decrease release of acetylcholine from remaining CBF neurons. We propose that therapies based solely on acetylcholinesterase inhibitors may be insufficient to effectively increase cortical levels of acetylcholine.

Synaptic alterations in CA1 in mild Alzheimer disease and mild cognitive impairment

OBJECTIVE

To evaluate the total number of synapses in the stratum radiatum (str rad) of the human hippocampal CA1 subfield in individuals with mild Alzheimer disease (mAD), mild cognitive impairment (MCI), or no cognitive impairment (NCI) and determine if synapse loss is an early event in the progression of the disease.

METHODS

Short postmortem autopsy tissue was obtained, and an unbiased stereologic sampling scheme coupled with transmission electron microscopy was used to directly visualize synaptic contacts.

RESULTS

Individuals with mAD had fewer synapses (55%) than the other two diagnostic groups. Individuals with MCI had a mean synaptic value that was 18% lower than the NCI group mean. The total number of synapses showed a correlation with several cognitive tests including those involving both immediate and delayed recall. Total synaptic numbers showed no relationship to the subject's Braak stage or to APOE genotype. The volume of the str rad was reduced in mAD vs the other two diagnostic groups that were not different from each other.

CONCLUSION

These results strongly support the concept that synapse loss is a structural correlate involved very early in cognitive decline in mild Alzheimer disease (mAD) and supports mild cognitive impairment as a transitional stage between mAD and no cognitive impairment.

Cortical biochemistry in MCI and Alzheimer disease: lack of correlation with clinical diagnosis

OBJECTIVE

Mild cognitive impairment, hypothesized to be prodromal Alzheimer disease (AD), shows abundant senile plaques and neurofibrillary tangles, but its biochemical correlates remain undefined.

METHODS

Biochemical profiles of Abeta, tau, alpha-synuclein, and oxidative pathologies were characterized in middle frontal gyrus, inferior parietal cortex, and entorhinal cortex in postmortem frozen brains from subjects diagnosed antemortem with no cognitive impairment, mild cognitive impairment, or AD.

RESULTS

Insoluble Abeta and tau, as well as tissue isoprostanes, from each brain region analyzed did not correlate with the clinical diagnosis proximate to death, but insoluble Abeta and 8,12-iso-iPF(2alpha)-VI levels from gray matter of all brain regions correlated strongly with the burden of AD pathology, whereas insoluble tau did not.

CONCLUSIONS

The biochemical alterations in cortical tau, Abeta, and isoprostane do not reflect the onset of clinical dementia.

Ectopic galanin expression and normal galanin receptor 2 and galanin receptor 3 mRNA levels in the forebrain of galanin transgenic mice

The functional interactions of the neuropeptide galanin (GAL) occur through its binding to three G protein-coupled receptor subtypes: galanin receptor (GALR) 1, GALR2 and GALR3. Previously, we demonstrated that GALR1 mRNA expression was increased in the CA1 region of the hippocampus and discrete hypothalamic nuclei in galanin transgenic (GAL-tg) mice. This observation suggested a compensatory adjustment in cognate receptors in the face of chronic GAL exposure. To evaluate the molecular alterations to GALR2 and GALR3 in the forebrain of GAL overexpressing mice, we performed complementary quantitative, real-time PCR (qPCR), in situ hybridization, and immunohistochemistry in select forebrain regions of GAL-tg mice to characterize the neuronal distribution and magnitude of GAL mRNA and peptide expression and the consequences of genetically manipulating the neuropeptide GAL on the expression of GALR2 and GALR3 receptors. We found that GAL-tg mice displayed dramatic increases in GAL mRNA and peptide in the frontal cortex, posterior cortex, hippocampus, septal diagonal band complex, amygdala, piriform cortex, and olfactory bulb. Moreover, there was evidence for ectopic neuronal GAL expression in forebrain limbic regions that mediate cognitive and affective behaviors, including the piriform and entorhinal cortex and amygdala. Interestingly, regional qPCR analysis failed to reveal any changes in GALR2 or GALR3 expression in the GAL-tg mice, suggesting that, contrary to GALR1, these receptor genes are not under ligand-mediated regulatory control. The GAL-tg mouse model may provide a useful tool for the investigation of GAL ligand-receptor relationships and their role in normal cognitive and affective functions as well as in the onset of neurological disease.

Estrogen receptor alpha containing neurons in the monkey forebrain: lack of association with calcium binding proteins and choline acetyltransferase

The present study used single and dual immunohistochemistry to determine the topography and chemical phenotype of ERalpha containing neurons within the monkey forebrain utilizing antibodies directed against the full-length human ERalpha (NCL-ER-6F11), calcium-binding proteins calbindin-D(28k), and parvalbumin as well as choline acetyltransferase (ChAT). Our findings demonstrate for the first time ERalpha immunoreactive (-ir) cells in the monkey cerebral cortex (layers I-II) and in the claustrum. In addition, ERalpha-ir cells were seen in the septum, basal forebrain, amygdala and hypothalamus. Double-labeled cells for ERalpha and calbindin-D(28k) were seen only in the ventrolateral part of the ventromedial hypothalamic nucleus. In contrast, the co-localization of ERalpha and parvalbumin or ChAT was not seen in any of the areas of the monkey forebrain examined. These observations suggest that estrogens, at least in part, via ERalpha regulate calbindin-D(28k) hypothalamic but not parvalbumin or ChAT containing neurons in select monkey forebrain regions.

Long-term plastic changes in galanin innervation in the rat basal forebrain

Galanin immunoreactive fibers hyperinnervate remaining cholinergic basal forebrain neurons in Alzheimer's disease, perhaps exacerbating the cholinergic deficit. The purpose of our study is to determine whether a similar phenomenon occurs following intraparenchymal injection of 192 IgG-saporin, a specific cholinergic neurotoxin, within the nucleus of the horizontal limb of the diagonal band of Broca. Immunotoxic lesion produced on average a 31% reduction in cholinergic cell counts ipsilateral to the lesion, compared to the contralateral side. Increased galanin immunoreactivity, suggestive of increased fiber density, was observed within and adjacent to the lesion in 28 out of 36 rats, and this effect persisted across time up to 6 months (the longest time examined). We observed a parallel increase in the number of galanin positive neurons ipsilateral to the lesion, compared to the contralateral side. No correlative change could be detected in the number of galaninergic neurons in the amygdala or the bed nucleus of the stria terminalis. There was no statistically significant correlation between the extent of cholinergic cell loss and the increase in galanin immunoreactivity surrounding the lesion. Yet, since both of these changes persist over time, we suggest that galanin plasticity is triggered by neuronal damage. Our model can be useful to test the role that galanin plays in the regulation of acetylcholine and the efficacy of galanin inhibitors as potential therapeutic interventions in Alzheimer's disease.

Apolipoprotein E immunoreactivity in neurons and neurofibrillary degeneration of aged non-demented and Alzheimer's disease patients

Apolipoprotein E (ApoE) genotype is a risk factor for Alzheimer's disease (AD) but its relationship with neurofibrillary degeneration remains obscure. To further analyze this relationship, hippocampal, entorhinal, temporopolar, and insular cortices of 10 non-demented and 7 Alzheimer disease brains were studied with both light and electron microscopy. Focus was directed on pretangles and neurons starting to accumulate tangles. ApoE immunolabeling in neurons and tangles was independent of ApoE individual genotype. The majority of the neurons in all of the brains were ApoE-negative, but virtually every brain also contained groups of ApoE-immunoreactive neurons, with diffuse cytoplasmic labeling. Most of the ApoE-positive tangles were extracellular, but a few tangles were shown to be intraneuronal when studied ultrastructurally. No ApoE immunoreactivity was found in neuropil threads, as well as in neurites associated with senile plaques. Double protocols with both AT-8 and anti-ApoE antibodies, performed to determine whether ApoE-positive neurons were pretangle neurons, did not detect cytoplasmic AT-8 in ApoE-positive neurons. Though careful electron microscopy studies found ApoE reaction product in an occasional ApoE-positive pretangle-like neuron and a few intracellular tangles, these findings do not support that ApoE is necessary for the accumulation of hyperphosphorylated tau protein. The more consistent colocalization of anti-ApoE and AT-8 in extracellular tangles reveals that ApoE mainly binds to tangles once they are in the extracellular space, in a manner similar to that described for amyloid fibrils.

Down-regulation of trkA mRNA within nucleus basalis neurons in individuals with mild cognitive impairment and Alzheimer's disease

Recent studies indicate that trkA expression is reduced in end-stage Alzheimer's disease (AD). However, understanding the neuropathologic correlates of early cognitive decline, as well as the changes that underlie the transition from nondemented mild cognitive impairment (MCI) to AD, are more critical neurobiological challenges. In these regards, the present study examined the expression of trkA mRNA in individuals diagnosed with MCI and AD from a cohort of people enrolled in a Religious Orders Study. Individuals with MCI and AD displayed significant reductions in trkA mRNA relative to aged-matched controls, indicating that alterations in trkA gene expression occur early in the disease process. The magnitude of change was similar in MCI and AD cases, suggesting that further loss of trkA mRNA is not necessarily associated with the transition of individuals from nondemented MCI to AD. The loss of trkA mRNA was not associated with education, apolipoprotein E allele status, gender, Braak score, global cognitive score or Mini-Mental Status Examination. In contrast, the loss of trkA mRNA in MCI and AD was significantly correlated with function on a variety of episodic memory tests.

Neuropathology of mice carrying mutant APP(swe) and/or PS1(M146L) transgenes: alterations in the p75(NTR) cholinergic basal forebrain septohippocampal pathway

Cholinergic basal forebrain (CBF) projection systems are defective in late Alzheimer's disease (AD). We examined the brains of 12-month-old singly and doubly transgenic mice overexpressing mutant amyloid precursor protein (APP(swe)) and/or presenilin-1 (PS1(M146L)) to investigate the effects of these AD-related genes on plaque and tangle pathology, astrocytic expression, and the CBF projection system. Two types of beta-amyloid (Abeta)-immunoreactive (ir) plaques were observed: type 1 were darkly stained oval and elongated deposits of Abeta, and type 2 were diffuse plaques containing amyloid fibrils. APP(swe) and PS1(M146L) mouse brains contained some type 1 plaques, while the doubly transgenic (APP(swe)/PS1(M146L)) mice displayed a greater abundance of types 1 and 2 plaques. Sections immunostained for the p75 NGF receptor (p75(NTR)) revealed circular patches scattered throughout the cortex and hippocampus of the APP(swe)/PS1(M146L) mice that contained Abeta, were innervated by p75(NTR)-ir neurites, but displayed virtually no immunopositive neurons. Tau pathology was not seen in any transgenic genotype, although a massive glial response occurred in the APP(swe)/PS1(M146L) mice associated with amyloid plaques. Stereology revealed a significant increase in p75(NTR)-ir medial septal neurons in the APP(swe) and PS1(M146L) singly transgenic mice compared to the APP(swe)/PS1(M146L) mice. No differences in size or optical density of p75(NTR)-ir neurons were observed in these three mutants. p75(NTR)-ir fibers in hippocampus and cortex were more pronounced in the APP(swe) and PS1(M146L) mice, while the APP(swe)/PS1(M146L) mice showed the least p75(NTR)-ir fiber staining. These findings suggest a neurotrophic role for mutant APP and PS1 upon cholinergic hippocampal projection neurons at 12 months of age.

Tau-66: evidence for a novel tau conformation in Alzheimer's disease

We have characterized a novel monoclonal antibody, Tau-66, raised against recombinant human tau. Immunohistochemistry using Tau-66 reveals a somatic-neuronal stain in the superior temporal gyrus (STG) that is more intense in Alzheimer's disease (AD) brain than in normal brain. In hippocampus, Tau-66 yields a pattern similar to STG, except that neurofibrillary lesions are preferentially stained if present. In mild AD cases, Tau-66 stains plaques lacking obvious dystrophic neurites (termed herein 'diffuse reticulated plaques') in STG and the hippocampus. Enzyme-linked immunosorbent assay (ELISA) analysis reveals that Tau-66 is specific for tau, as there is no cross-reactivity with MAP2, tubulin, Abeta(1-40), or Abeta(1-42), although Tau-66 fails to react with tau or any other polypeptide on western blots. The epitope of Tau-66, as assessed by ELISA testing of tau deletion mutants, appears discontinuous, requiring residues 155-244 and 305-314. Tau-66 reactivity exhibits buffer and temperature sensitivity in an ELISA format and is readily abolished by SDS treatment. Taken together these lines of evidence indicate that the Tau-66 epitope is conformation-dependent, perhaps involving a close interaction of the proline-rich and the third microtubule-binding regions. This is the first indication that tau can undergo this novel folding event and that this conformation of tau is involved in AD pathology.

Distribution of galaninergic immunoreactivity in the brain of the mouse

The distribution of galaninergic immunoreactive (-ir) profiles was studied in the brain of colchicine-pretreated and non-pretreated mice. Galanin (GAL)-ir neurons and fibers were observed throughout all encephalic vesicles. Telencephalic GAL-ir neurons were found in the olfactory bulb, cerebral cortex, lateral and medial septum, diagonal band of Broca, nucleus basalis of Meynert, bed nucleus of stria terminalis, amygdala, and hippocampus. The thalamus displayed GAL-ir neurons within the anterodorsal, paraventricular, central lateral, paracentral, and central medial nuclei. GAL-ir neurons were found in several regions of the hypothalamus. In the midbrain, GAL-ir neurons appeared in the pretectal olivary nucleus, oculomotor nucleus, the medial and lateral lemniscus, periaqueductal gray, and the interpeduncular nucleus. The pons contained GAL-ir neurons within the dorsal subcoeruleus, locus coeruleus, and dorsal raphe. In the medulla oblongata, GAL-ir neurons appear in the anterodorsal and dorsal cochlear nuclei, salivatory nucleus, A5 noradrenergic cells, gigantocellular nucleus, inferior olive, solitary tract nucleus, dorsal vagal motor and hypoglossal nuclei. Only GAL-ir fibers were seen in the lateral habenula nucleus, substantia nigra, parabrachial complex, cerebellum, spinal trigeminal tract, as well as the motor root of the trigeminal and facial nerves. GAL-ir was also observed in several circumventricular organs. The widespread distribution of galanin in the mouse brain suggests that this neuropeptide plays a role in the regulation of cognitive and homeostatic functions.

Galanin transgenic mice display cognitive and neurochemical deficits characteristic of Alzheimer's disease

Galanin is a neuropeptide with multiple inhibitory actions on neurotransmission and memory. In Alzheimer's disease (AD), increased galanin-containing fibers hyperinnervate cholinergic neurons within the basal forebrain in association with a decline in cognition. We generated transgenic mice (GAL-tg) that overexpress galanin under the control of the dopamine beta-hydroxylase promoter to study the neurochemical and behavioral sequelae of a mouse model of galanin overexpression in AD. Overexpression of galanin was associated with a reduction in the number of identifiable neurons producing acetylcholine in the horizontal limb of the diagonal band. Behavioral phenotyping indicated that GAL-tgs displayed normal general health and sensory and motor abilities; however, GAL-tg mice showed selective performance deficits on the Morris spatial navigational task and the social transmission of food preference olfactory memory test. These results suggest that elevated expression of galanin contributes to the neurochemical and cognitive impairments characteristic of 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 Alzheimer's 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 Alzheimer's 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 Alzheimer's 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 Alzheimer's 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 Alzheimer's 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 Alzheimer's disease.

Novel method to quantify neuropil threads in brains from elders with or without cognitive impairment

Pathological alterations in dendrites and axons (i.e., neuritic pathologies) occur in the normal aging brain as well as in brains from elders with mild cognitive impairment and neurodegenerative dementia. These alterations may correlate with clinical measures of cognitive abilities, but the contribution of neuropil threads (NTs), which constitute 85-90% of cortical tau pathology, has not been clear because of the lack of quantitative methodologies. We combined quantitative fractionation and image analysis to devise a strategy for measuring the burden of tau-rich NTs in the entorhinal and perirhinal cortex of brains from elders with and without cognitive impairment, including dementia due to Alzheimer's disease (AD). On the basis of data presented here using this novel strategy, we conclude that this quantitative imaging technique will facilitate efforts to determine the behavioral correlations of neuritic lesions in AD and other brain disorders.

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 Alzheimer's 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.

Age-related decreases in GTP-cyclohydrolase-I immunoreactive neurons in the monkey and human substantia nigra

Guanosine triphosphate cyclohydrolase I (GTPCHI) is a critical enzyme in catecholamine function and is rate limiting for the synthesis of the catecholamine co-factor tetrahydrobiopterin. The present study assessed the distribution of GTPCHI immunoreactivity (-ir) within the monkey and human ventral midbrain and determined whether its expression is altered as a function of age. Light and confocal microscopic analyses revealed that young monkeys and humans displayed GTPCHI-ir within melanin-containing and tyrosine-hydroxylase-ir neurons in primate substantia nigra. Stereological counts revealed that there was a 67.4% reduction in GTPCHI-ir neuronal number, a 63.5% reduction in GTPCHI-ir neuronal density, and a 37.6% reduction in neuronal volume in aged monkeys relative to young cohorts. Similar age-related changes were seen in humans, in whom there were significant reductions in the number of GTPCHI-ir nigral neurons in middle age (58.4%) and aged (81.5%) cases relative to young cohorts. The density of GTPCHI-ir neurons within the nigra was similarly reduced in middle-aged (63.0%) and aged (81.8%) cases. In contrast to monkeys, aged humans did not display shrinkage in the volume of GTPCHI-ir nigral neurons. The presence of numerous melanin-positive, but GTPCHI-ir immunonegative, neurons in the aged monkey and human nigra indicates that these decreases represent an age-related phenotypic downregulation of this enzyme and not a loss of neurons per se. These data indicate that there is a dramatic decrease in GTPCHI-ir in nonhuman primates and humans as a function of age and that loss of this enzyme may be partly responsible for the age-related decrease in dopaminergic tone within nigrostriatal systems.

Galanin regulates the postnatal survival of a subset of basal forebrain cholinergic neurons

The neuropeptide galanin colocalizes with choline acetyltransferase, the synthetic enzyme for acetylcholine, in a subset of cholinergic neurons in the basal forebrain of rodents. Chronic intracerebroventricular infusion of nerve growth factor induces a 3- to 4-fold increase in galanin gene expression in these neurons. Here we report the loss of a third of cholinergic neurons in the medial septum and vertical limb diagonal band of the basal forebrain of adult mice carrying a targeted loss-of-function mutation in the galanin gene. These deficits are associated with a 2-fold increase in the number of apoptotic cells in the forebrain at postnatal day seven. This loss is associated with marked age-dependent deficits in stimulated acetylcholine release, performance in the Morris water maze, and induction of long-term potentiation in the CA1 region of the hippocampus. These data provide unexpected evidence that galanin plays a trophic role to regulate the development and function of a subset of septohippocampal cholinergic neurons.

Galanin receptor plasticity within the nucleus basalis in early and late Alzheimer's disease: an in vitro autoradiographic analysis

Hypertrophy of fibers containing galanin (GAL), the inhibitory neurotransmitter of acetylcholine, occur on remaining cholinergic nucleus basalis neurons in late stage Alzheimer's disease (AD). The present investigation evaluated whether changes in the number of GAL receptors (GALR) were detectable within the nucleus basalis in the early or late stage of AD when compared to age-matched controls. Postmortem neuropathological specimens were obtained at autopsy from three groups: late AD, early (possible) AD, and normal (age-matched controls) human subjects. Autoradiography of GALR binding was performed on human brain sections from each of the three groups. Analysis of autoradiographic images show no change in the distribution of ([125])hGAL binding sites in early AD cases throughout the nucleus basalis. In contrast, the number of ([125])hGAL binding sites was increased over the anterior nucleus basalis subfield in late stage AD. A region-of-interest densitometric analysis of the anterior nucleus basalis in the late stage AD cases depict an increase in the number of ([125])hGAL binding sites by approximately two-three-fold when compared to normal (age-matched controls). Quantitative measures of ([125])hGAL binding densities were not significantly different in the anterolateral, intermediate or posterior nucleus basalis subsectors of early or late stage AD when compared to age-matched controls. These observations show that the occurrence of overexpression of GALRs coincide with earlier reports showing galaninergic fibers hyperinnervating surviving cholinergic basal forebrain neurons in late stage AD.

Reduction in TrkA-immunoreactive neurons is not associated with an overexpression of galaninergic fibers within the nucleus basalis in Down's syndrome

Down's syndrome (DS) individuals develop neuropathological features similar to Alzheimer's disease (AD), including degeneration of cholinergic basal forebrain (CBF) neurons. In AD a reduction in CBF/trkA-containing neurons has been suggested to trigger a hyperexpression of galaninergic fibers within the nucleus basalis subfield of the basal forebrain. The present study examined the interrelationship between reductions in CBF/trkA-containing neurons and the overexpression of galaninergic fibers within the nucleus basalis in DS. Within the nucleus basalis stereologic evaluation revealed a 46% reduction in the number of trkA-immunopositive neurons, whereas optical density measurements displayed a nonsignificant 18% reduction in neuronal trkA immunoreactivity in DS as compared with age-matched controls. Western blot analysis also showed a significant reduction in cortical trkA protein levels in DS. A semiquantitative examination of galaninergic fibers in the nucleus basalis revealed only a modest hypertrophy of galaninergic fibers within the nucleus basalis in DS. The present findings indicate a significant reduction in trkA within the nucleus basalis and cortex with only a moderate hypertrophy of galaninergic fibers in DS. These observations suggest that DS may not be an exact genetic model for investigation of changes in the AD basal forebrain.

Estrogen receptor immunoreactivity within subregions of the rat forebrain: neuronal distribution and association with perikarya containing choline acetyltransferase

Administration of the neuroactive steroid hormone estrogen has been shown to effect cholinergic basal forebrain neuronal function. Antibodies directed against the estrogen receptor alpha (ERalpha) revealed dark (type 1) and light (type 2) nuclear positive neurons within the islands of Calleja, endopiriform nucleus, lateral septum, subfields of the cholinergic basal forebrain, bed nucleus of the stria terminalis, striohypothalamic region, medial preoptic region, periventricular, ventromedial, arcuate and tuberal mammillary nuclei of the hypothalamus, reuniens and anterior medial thalamic nuclei, amygdaloid complex, piriform cortex and subfornical organ. In contrast, only a few scattered ERalpha labeled neurons were found in cortex and hippocampus. ERalpha stained cell bodies were not seen in the striatum. Counts of ERalpha labeled neurons in intact female rats revealed significantly more type 2 neurons within the basal forebrain subfields. Quantitation of ERalpha immunoreactive neurons revealed a significant decrease in the relative number of type 1 neurons within the medial septum (MS), horizontal limb of the diagonal band (HDB) and substantia innominata/nucleus basalis (SI/NB) following ovariectomy. Quantitation following choline acetyltransferease (ChAT) immunohistochemistry revealed a significant decrease in the number of ChAT positive neurons within the MS, HDB and SI/NB, but not VDB following ovariectomy. Following ovx, the percentage of double labeled cholinergic basal forebrain neurons also declined significantly within the MS, VDB, HDB and SI/NB. These observations suggest that estrogen effects a subpopulation of cholinergic basal forebrain neurons and may provide insight into the biologic actions of this steroid in Alzheimer's disease.

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 Alzheimer's 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 Alzheimer's 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.

Clinicopathological findings following intraventricular glial-derived neurotrophic factor treatment in a patient with Parkinson's disease

As part of a safety and tolerability study, a 65-year-old man with Parkinson's disease (PD) received monthly intracerebroventricular injections of glial-derived neurotrophic factor (GDNF). His parkinsonism continued to worsen following intracerebroventricular GDNF treatment. Side effects included nausea, loss of appetite, tingling, L'hermitte's sign, intermittent hallucinations, depression, and inappropriate sexual conduct. There was no evidence of significant regeneration of nigrostriatal neurons or intraparenchymal diffusion of the intracerebroventricular GDNF to relevant brain regions. Alternative GDNF delivery systems should be explored.

Entorhinal cortex beta-amyloid load in individuals with mild cognitive impairment

The deposition of beta-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 beta-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 Alzheimer's disease (AD). beta-amyloid staining was seen in 12 of the 20 NCI, in 10 of 12 MCI, and in all 12 AD cases within the EC. beta-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 beta-amyloid imunoreactivity. Despite the heterogeneity of beta-amyloid loads within the clinical groups, decomposing an analysis of variance revealed a significant difference across groups in mean beta-amyloid load within the EC based upon a linear trend analysis. Multiple comparisons testing revealed that NCI individuals had a significantly lower mean beta-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 beta-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.

Immunocytochemical localization of the dopamine transporter in human brain

The dopamine transporter (DAT) was localized in normal human brain tissue by light microscopic immunocytochemistry by using highly specific monoclonal antibodies. Regional distribution of DAT was found in areas with established dopaminergic circuitry, e.g., mesostriatal, mesolimbic, and mesocortical pathways. Mesencephalic DAT-immunoreactivity was enriched in the dendrites and cell bodies of neurons in the substantia nigra pars compacta and ventral tegmental area. Staining in the striatum and nucleus accumbens was dense and heterogeneous. Mesocortical DAT immunoreactivity in motor, premotor, anterior cingulate, prefrontal, entorhinal/perirhinal, insular, and visual cortices was detected in scattered varicose and a few nonvaricose fibers. Varicose fibers were relatively enriched in the basolateral and central subnuclei of amygdala, with sparser fibers in lateral and basomedial subnuclei. Double-labeling studies combining DAT and tyrosine hydroxylase (TH) immunostaining in the ventral mesencephalon showed two subpopulations of dopaminergic neurons differentiated by the presence or absence of DAT-immunoreactivity in the A9 and A10 cell groups. In other dopaminergic cell groups (All, A13-A15), TH-positive hypothalamic neurons showed no detectable DAT-immunoreactivity. However, fine DAT-immunoreactive axons were scattered throughout the hypothalamus, particularly concentrated along the medial border, with more coarse axons present along the lateral border. These findings demonstrate that most mesotelencephalic dopamine neurons of human brain express high levels of DAT throughout their entire somatodendritic and axonal domains, whereas a smaller subpopulation of mesencephalic dopamine cells and all hypothalamic dopamine cell groups examined express little or no DAT. These data indicate that different subpopulations of dopaminergic neurons use different mechanisms to regulate their extracellular dopamine levels.

Dopamine transporter-immunoreactive neurons decrease with age in the human substantia nigra

Unbiased disector stereologic cell counting was applied to sections from the human substantia nigra that were immunostained by using a monoclonal antibody against the dopamine transporter (DAT). This antibody was found to penetrate the full thickness of the stained section. Quantification of the number of DAT immunostained neurons was performed in human cases stratified into three age groups, young (ages 0-49 years), middle aged (ages 50-69 years), and aged (ages 70-85 years). The number of DAT-immunoreactive nigral neurons was normalized for each case by constructing a ratio of the number of DAT-containing neurons to total number of neuromelanin-containing cells in each subject's sample. Three types of DAT nigral neurons were seen: type 1, intensely stained; type 2, lightly stained; and type 3, DAT-immunonegative neuromelanin-containing perikarya. By 50 years of age, the number of type 1 neurons decreased significantly (P < 0.0001), whereas the number of type 2 neurons increased with age (P < 0.0001). Type 3 neurons also increased with age (P < 0.01), although less robustly than type 2 neurons. Type 1 neurons decreased by 11.2% per decade, and the total number of nigral neurons (types 1-3) decreased by 6.7% per decade. Relative to the young group, there were 75% and 88% reductions in type 1 neurons in the middle-aged and aged groups, respectively. This contrasts with the 35% and 41% reductions in total number of neuromelanin-containing neurons seen in middle-aged and aged groups, respectively. The young group had significantly more type 1 neurons and fewer type 2 neurons compared with middle-aged and aged participants. Post-hoc analyses indicated that the young group had significantly fewer type 3 neurons compared with middle-aged and aged participants. These findings demonstrate an age-related reduction in the number of substantia nigra DAT-immunoreactive neurons. Therefore, insight into the mechanisms regulating the rate of DAT synthesis may aid in our understanding of the decline of DATs with aging and its functional significance.

Distribution and retrograde transport of trophic factors in the central nervous system: functional implications for the treatment of neurodegenerative diseases

Neurotrophins play a crucial role in the maintenance, survival and selective vulnerability of various neuronal populations within the normal and diseased brain. Several families of growth promoting substances have been identified within the central nervous system (CNS) including the superfamily of nerve growth factor related neurotrophin factors, glial derived neurotrophic factor (GDNF) and ciliary neurotrophic factor (CNTF). In addition, other non-neuronal growth factors such as fibroblast growth factor (FGF) have also been identified. This article reviews the trophic anatomy of these factors within the CNS. Intraventricular and intraparenchymal injections of exogenous nerve growth factor result in retrograde labeling mainly within the cholinergic basal forebrain. Distribution of brain derived neurotrophic factor (BDNF) following intraventricular injection is minimal due to the binding to the trkB receptor along the ventricular wall. In contrast, intraparenchymal injections of BDNF results in widespread retrograde transport throughout the CNS. BDNF has also been shown to be transported anterogradely within the CNS. Infusion of GDNF into the CNS results in retrograde transport limited to the nigrostriatal pathway. Hippocampal injections of NT-3 retrogradely label mainly basal forebrain neurons. Retrograde transport of radiolabeled CNTF has only been observed in sensory neurons of the sciatic nerve. Following intraventricular and intraparenchymal infusion of radiolabeled bFGF, retrograde neuronal labeling was found in the telecephalon, diencephalon, mesencephalon and pons. In contrast retrograde labeling for aFGF was found only in the hypothalamus and midbrain. Since select neurotrophins traffic anterogradely and retrogradely within the nervous system, these proteins could be used to treat neurological diseases such as Alzheimer's disease, Parkinson's disease and amyotrophic lateral sclerosis.

Galanin expression within the basal forebrain in Alzheimer's disease. Comments on therapeutic potential

The inhibitory neuropeptide galanin has widespread distribution throughout the central nervous system. Studies indicate that galanin modulates cognition by regulating cholinergic basal forebrain (CBF) neuron function. The chemoanatomic organization of galanin within the mammalian CBF differs across species. In monkeys, all CBF neurons coexpress galanin, whereas in apes and humans galanin is found within a separate population of interneurons that are in close apposition to the CBF perikarya. Pharmacologic investigations revealed a low and high affinity galanin receptor within the basal forebrain in humans. In vitro autoradiographic investigations of the primate brain indicate that galanin receptors are concentrated within the anterior subfields of the CBF as well as bed nucleus of the stria terminalis, amygdala, and entorhinal cortex. Galaninergic fibers hyperinnervate remaining CBF neurons in Alzheimer's disease. Because galanin inhibits the release of acetylcholine in the hippocampus, it has been suggested that the overexpression of galanin in Alzheimer's disease may downregulate the production of acetylcholine within CBF perikarya, further exacerbating cholinergic cellular dysfunction in this disorder. These observations suggest that the development of a potent galanin antagonist would be a useful step towards the successful pharmacologic treatment of Alzheimer's disease.

Age-related declines in nigral neuronal function correlate with motor impairments in rhesus monkeys

Although the role of dopamine dysfunction is well established in Parkinson's disease, the effect of nigrostriatal degeneration on motor performance during normal aging is less well understood. In this study, aged rhesus monkeys (25-27 years old) displayed significant impairments relative to young (3-5 years old) cohorts in motor function as assessed on a fine motor task and home cage activity. Additionally, the clinical motor function of aged monkeys was impaired relative to young monkeys as assessed on a clinical rating scale. Unbiased stereologic measurements of the substantia nigra revealed a significant age-related loss of tyrosine hydroxylase-immunoreactive (TH-ir; 50.3%) and dopamine transporter-immunoreactive (DAT-ir; 33.2%) nigral neurons. The monkeys performance on the fine motor task and on the clinical rating scale was correlated with TH-ir neuronal counts. The number of DAT-ir nigral neurons was correlated with activity and clinical rating scale scores. Our results suggest that age-related motor impairments in nonhuman primates are associated with spontaneous decreases in TH-ir and DAT-ir nigral cells. The correlation of motor deficits with the loss of TH-ir and DAT-ir nigral neurons suggests that aged nonhuman primates may provide a useful model for mimicking changes seen in human aging and early Parkinson's disease.

Tyrosine kinase A, galanin and nitric oxide synthase within basal forebrain neurons in the rat

Cholinergic basal forebrain neurons appear to play a key role in cognition and attention. In rat, basal forebrain neurons express multiple proteins including the high-affinity signal transducing tyrosine kinase A receptor for nerve growth factor, the neuropeptide galanin and nitric oxide synthase, a marker for the novel neurotransmitter nitric oxide. The present study was undertaken to define the relationship between neurons expressing each of these markers within the medial septum-vertical limb of the diagonal band, horizontal limb of the diagonal band and nucleus basalis in colchicine pre-treated rats. Tyrosine kinase A-immunopositive neurons were seen throughout all subfields of the basal forebrain. In contrast, nitric oxide synthase- and galanin-immunoreactive neurons were mainly distributed within the septal-diagonal band complex. Co-localization experiments revealed that virtually all nitric oxide synthase-positive neurons (visualized by nicotinamide adenine dinucleotide phosphate-diaphorase histochemistry) also contained tyrosine kinase A, whereas many fewer tyrosine kinase A neurons were nicotinamide adenine dinucleotide phosphate-diaphorase positive within the medial septum-vertical limb of the diagonal band. Within the horizontal limb of the diagonal band, numerous nicotinamide adenine dinucleotide phosphate-diaphorase neurons expressed tyrosine kinase A, whereas only a small number of tyrosine kinase A neurons contained nicotinamide adenine dinucleotide phosphate-diaphorase. Within the nucleus basalis very few neurons were nicotinamide adenine dinucleotide phosphate-diaphorase reactive, and a minor number contained tyrosine kinase A. Additional co-localization experiments revealed minor percentages of neurons containing nicotinamide adenine dinucleotide phosphate-diaphorase and galanin immunoreactivity within the various subfields of the basal forebrain. Within the horizontal limb of the diagonal band minor numbers of nicotinamide adenine dinucleotide phosphate-diaphorase-reactive perikarya displayed galanin. Similarly, only a few galanin-containing neurons expressed nicotinamide adenine dinucleotide phosphate-diaphorase. The existence of tyrosine kinase A, nitric oxide synthase and galanin within select neuronal subgroups of the cholinergic basal forebrain suggests that these perikarya are responsive to a complex set of chemical signals. A greater understanding of the chemical signature of the cholinergic basal forebrain neurons will provide the insight required to develop novel pharmacological approaches aimed at preventing or slowing the degenerative processes that effect these neurons in aging and pathologic disorders.

Fetal nigral grafts survive and mediate clinical benefit in a patient with Parkinson's disease

We have previously demonstrated that fetal nigral grafts can survive, reinnervate the striatum, and mediate clinically relevant recovery in a patient with Parkinson's disease (PD). Most previous autopsy cases have failed to identify meaningful numbers of viable grafted cells suggesting that differences in critical transplant variables determine graft viability. The present study evaluated the structural and functional correlates of fetal nigral transplantation in a second PD patient who received fetal nigral grafts according to our previously published transplant protocol. A 61-year-old woman with severe PD received bilateral fetal nigral grafts to the postcommissural putamen from seven donor fetuses (four right side and three left side) aged 6.5-9 weeks postconception. This patient died 19 months after surgery from a cause unrelated to the transplant surgery. Her postoperative clinical course was characterized by improved motor and activities of daily living scores during "off time," reduced "off time," and increased "on" time without dyskinesia. Positron emission tomography (PET) scans revealed a bilateral and progressive increase in fluorodopa (FD) uptake within the grafted putamen. Postmortem examination of the right hemisphere revealed large oval-shaped grafts containing more than 138,000 tyrosine-hydroxylase-immunoreactive (TH-ir) neurons. Grafted cells formed a seamless border with the host and provided dense TH-ir innervation to 78% of the host postcommissural putamen. Graft-mediated sprouting of host fibers was not observed. These data provide essential confirmation that, under appropriate transplant conditions, grafted nigral neurons can survive, reinnervate the host striatum, and provide clinical benefit to PD patients. These findings also support the concept that improved motor function and striatal FD uptake on PET after nigral grafting in PD are the result of the viability of grafted neurons and graft-derived reinnervation of the host striatum.

m2 muscarinic acetylcholine receptor-immunoreactive neurons are not reduced within the nucleus basalis in Alzheimer's disease: relationship with cholinergic and galaninergic perikarya

The distribution of profiles containing the m2-muscarinic acetylcholine receptor within the aged human basal forebrain and its relationship to cholinergic and noncholinerigc neurons and alterations in Alzheimer's disease (AD) was investigated by using an m2-specific monoclonal antibody (Levey et al. [1995] J. Comp. Neurol. 351:339-356). Immunocytochemistry revealed that the m2 receptor protein is expressed primarily in noncholinergic multipolar neurons (mean+/-S.E.M.; 355.7+/-15.4 microm2) located primarily outside the cholinergic nucleus basalis subfields. Dual-stained sections from the septal/diagonal band complex revealed that m2 was detected in only 14% of choline acetyltransferase-labeled neurons, whereas only 13% of m2-stained neurons colocalized choline acetyltransferase. Within the nucleus basalis, choline acetyltransferase was found in 35% of the m2-labeled neurons, whereas only 6% of choline acetyltransferase-stained perikarya were dual labeled for m2. Although we did not visualize colocalization of m2+/choline acetyltransferase-immunonegative neurons and the inhibitory neuropeptide galanin, galaninergic fibers coursed in close apposition to m2+ cells. Cell counts demonstrated that 90% of choline acetyltransferase-labeled striatal neurons expressed the m2 receptor. Despite the extensive reduction in cholinergic basal forebrain neurons, cell counts of the relative number ofm2-immunoreactive neurons within the nucleus basalis complex from aged controls and AD patients revealed that the m2 neurons are spared. Finally, our findings suggest that most m2 receptors in the cholinergic basal forebrain are located on noncholinergic structures; therefore, they are not the major source of m2 receptors in the cortex. Thus, the reduced levels of the m2 receptor seen in AD cortex probably reflect changes in other neuronal populations.

Characterization and localization of galanin receptors in human entorhinal cortex

The neuropeptide galanin (GAL) has a widespread distribution throughout the human cortex. The entorhinal cortex (ENT) plays a crucial role in the transfer of cortico-cortical information related to memory and displays severe degeneration in Alzheimer's disease (AD). However, very little is known about the pharmacology of the GAL receptor (GALR) in normal human ENT. Therefore, we pharmacologically visualized their distribution and characterized GALRs using in vitro receptor autoradiography and radioligand binding assays. Autoradiograms revealed intense GALR labeling, mainly in the substantia innominata, hypothalamus, the bed nucleus of the stria terminalis and within layers 2 and 4 of the ENT. Kinetic experiments showed that saturation of GALR sites by [125I]GAL (human) (hGAL) occurred within 2 h and that this binding readily reversed in the presence of a GTP analog, but not in the presence of excess unlabeled hGAL. Analysis of [125I]hGAL binding data from saturation experiments gave KD values of 98.6+/-21.6 pM, Bmax values of 52.9+/-32.4 fmol/mg protein and identified a high and low affinity state of the GALR. The presence of 5'-guanylylimidodiphosphate (GppNHp) or NaCl reduced the agonist labeling of hGALR in ENT membranes.

Carrier mediated delivery of NGF: alterations in basal forebrain neurons in aged rats revealed using antibodies against low and high affinity NGF receptors

The distribution of low and high affinity nerve growth factor (NGF) receptors was investigated in the basal forebrain during aging and NGF treatment. A peripheral administration model for NGF was utilized. NGF was conjugated to a transferrin receptor antibody (OX-26-NGF), and this conjugate was injected into the tail vein of aged Fischer 344 male rats (24 months) twice weekly for 5 weeks (equivalent to 50 microg of NGF/injection). Controls were injected with a non-conjugated mixture of OX-26 and NGF. The aged rats treated with conjugate showed a significant increase in cell size of p75- and trkA-immunoreactive neurons in the medial septal nucleus and vertical limb of the diagonal band as compared to controls. A significant increase in cell size of trkA-immunoreactive neurons was also observed in the horizontal limb of the diagonal band in rats treated with conjugate. Rats treated with conjugate also showed a significant increase in overall staining density for p75 and trkA antibodies in the medial septal nucleus as compared to controls. A significant increase in staining density of p75-immunoreactive structures was also observed in the vertical and horizontal limbs of the diagonal band. Therefore, treatment with OX-26-NGF conjugate has regional effects on both the low and high affinity NGF receptors in terms of cell body size and staining density in the basal forebrain of aged rats. The current findings support the idea that this delivery system might be useful in therapeutic approaches involving the delivery of neurotrophic factors and other large molecules into the brain.

Grafts of EGF-responsive neural stem cells derived from GFAP-hNGF transgenic mice: trophic and tropic effects in a rodent model of Huntington's disease

The present study examined whether implants of epidermal growth factor (EGF)-responsive stems cells derived from transgenic mice in which the glial fibrillary acid protein (GFAP) promoter directs the expression of human nerve growth factor (hNGF) could prevent the degeneration of striatal neurons in a rodent model of Huntington's disease (HD). Rats received intrastriatal transplants of GFAP-hNGF stem cells or control stem cells followed 9 days later by an intrastriatal injection of quinolinic acid (QA). Nissl stains revealed large striatal lesions in rats receiving control grafts, which, on average, encompassed 12.78 mm3. The size of the lesion was significantly reduced (1.92 mm3) in rats receiving lesions and GFAP-hNGF transplants. Rats receiving QA lesions and GFAP-hNGF-secreting grafts stem cell grafts displayed a sparing of striatal neurons immunoreactive (ir) for glutamic acid decarboxylase, choline acetyltransferase, and neurons histochemically positive for nicotinamide adenosine diphosphate. Intrastriatal GFAP-hNGF-secreting implants also induced a robust sprouting of cholinergic fibers from subjacent basal forebrain neurons. The lesioned striatum in control-grafted animals displayed numerous p75 neurotrophin-ir (p75NTR) astrocytes, which enveloped host vasculature. In rats receiving GFAP-hNGF-secreting stem cell grafts, the astroglial staining pattern was absent. By using a mouse-specific probe, stem cells were identified in all animals. These data indicate that cellular delivery of hNGF by genetic modification of stem cells can prevent the degeneration of vulnerable striatal neural populations, including those destined to die in a rodent model of HD, and supports the emerging concept that this technology may be a valuable therapeutic strategy for patients suffering from this disease.

Parvalbumin-immunoreactive neurons in the hippocampal formation of Alzheimer's diseased brain

The number and topographic distribution of immunocytochemically stained parvalbumin interneurons was determined in the hippocampal formation of control and Alzheimer's diseased brain. In control hippocampus, parvalbumin interneurons were aspiny and pleomorphic, with extensive dendritic arbors. In dentate gyrus, parvalbumin cells, as well as a dense plexus of fibers and puncta, were associated with the granule cell layer. A few cells also occupied the molecular layer. In strata oriens and pyramidale of CA1-CA3 subfields, parvalbumin neurons gave rise to dendrites that extended into adjacent strata. Densely stained puncta and beaded fibers occupied stratum pyramidale, with less dense staining in adjacent strata oriens and radiatum. Virtually no parvalbumin profiles were observed in stratum lacunosum-moleculare or the alveus. Numerous polymorphic parvalbumin neurons and a dense plexus of fibers and puncta characterized the deep layer of the subiculum and the lamina principalis externa of the presubiculum. In Alzheimer's diseased hippocampus, there was an approximate 60% decrease in the number of parvalbumin interneurons in the dentate gyrus/CA4 subfield (P<0.01) and subfields CA1-CA2 (P<0.01). In contrast, parvalbumin neurons did not statistically decline in subfields CA3, subiculum or presubiculum in Alzheimer's diseased brains relative to controls. Concurrent staining with Thioflavin-S histochemistry did not reveal degenerative changes within parvalbumin-stained profiles. These findings reveal that parvalbumin interneurons within specific hippocampal subfields are selectively vulnerable in Alzheimer's disease. This vulnerability may be related to their differential connectivity, e.g., those regions connectionally related to the cerebral cortex (dentate gyrus and CA1) are more vulnerable than those regions connectionally related to subcortical loci (subiculum and presubiculum).

Connections of the hippocampal formation in humans: II. The endfolial fiber pathway

We investigated the anatomical connections of the pyramidal neurons located within the hilar region of the dentate gyrus of the human hippocampus, neurons which do not have a rodent equivalent. The myeloarchitectural patterns of the human hippocampus indicated the presence of a distinct fiber pathway, the endfolial fiber pathway, in the stratum oriens of the hilus and field CA3. By using the fluorescent lipophilic dye DiI in formalin-fixed human hippocampal tissue, we demonstrated that this is a continuous fiber pathway between the deep hilar region and CA2. This fiber pathway did not enter the fimbria or alveus along the entire distance of the traced pathway and ran exclusively in the stratum oriens of the hilus and CA3. Tracing studies with biocytin in in vitro human hippocampal slices indicated that the hilar and CA3 pyramidal neurons contributed to this pathway. Out distally in field CA3, the long transverse fibers became short and choppy, suggesting that they were beginning to move out of the plane of the tissue slice. Numerous fibers from this pathway were seen crossing the pyramidal layer. Based on comparative studies, we propose that the endfolial fiber system is a component of the hilar Schaffer collateral system in humans. The presence of a significant Schaffer collateral system from the pyramidal neurons in the hilar region would indicate that these neurons are anatomically related to the CA3 pyramidal neurons. Therefore, we suggest the inclusion of the human hilar pyramidal neurons within Lorente de No's field CA3 and, in particular, within subfield CA3c.

Plasticity of galaninergic fibers following neurotoxic damage within the rat basal forebrain: initial observations

Galanin immunoreactive fibers hypertrophy and hyperinnervate remaining cholinergic basal forebrain neurons within the septum-diagonal band complex in Alzheimer's disease. The present investigation determined whether a similar hyperinnervation of galanin immunoreactive fibers occurs following intraparenchymal injections of ibotenic acid within the cholinergic medial septum or diagonal band nucleus in young adult rats. Sections through the medial septum and the diagonal band were either concurrently immunostained for galanin and the low-affinity p75 neurotrophin receptor (an excellent marker of cholinergic basal forebrain neurons) or single stained for choline acetyltransferase. Following chemical lesion, an increase in the density of galanin immunoreactivity was seen within the medial septum on the lesion, as opposed to the contralateral control side. In contrast, within diagonal band-lesioned animals, the increase in galanin immunoreactivity was low to moderate. In either lesion paradigm we did not observe hyperinnervation of remaining cholinergic basal forebrain neurons. In fact, there was no correlation between the galanin hypertrophy and the amount of cholinergic cell loss. We hypothesize that galanin hyperinnervation within the cholinergic basal forebrain may provide a protective effect by down-regulating acetylcholine release following brain insult.

Reduction in p140-TrkA receptor protein within the nucleus basalis and cortex in Alzheimer's disease

It has been hypothesized that the diminished transport of nerve growth factor (NGF) seen within cholinergic basal forebrain (CBF) neurons in Alzheimer's disease (AD) results from a defect in the expression of its high-affinity trkA receptor. The present study used an anti-human trkA-specific monoclonal antibody (mAb 5C3) that recognizes the NGF docking site, combined with quantitative optical densitometry, to evaluate whether expression of the trkA protein is altered within the nucleus basalis and its cortical projection sites in AD. In normal aged humans, trkA immunoreactivity revealed a continuum of positive neurons extending throughout all CBF subfields. In addition, trkA-positive neurons were scattered throughout the olfactory tubercle and striatum. These regions also displayed intense trkA neuropil staining. Although fewer in total number, remaining CBF perikarya in AD displayed a significant decrease in trkA levels relative to aged controls. Biochemical analysis revealed a significant reduction in trkA protein within both the nucleus basalis and the frontal cortex in AD relative to aged controls. In contrast, trkA levels in the caudate nucleus were unaffected. The decrease in trkA protein in conjunction with our recent observations that the message for trkA is reduced within individual CBF neurons in AD supports the concept that defects in the production and/or utilization of the trkA receptor may be a key event mediating degeneration of NGF-responsive CBF neurons in this disease.

Presenilin-1 protein expression in familial and sporadic Alzheimer's disease

Mutations of the presenilin PS1 and PS2 genes are closely linked to aggressive forms of early-onset (< 60 years) familial Alzheimer's disease. A highly specific monoclonal antibody was developed to identify and characterize the native PS1 protein. Western blot analyses revealed a predominant 32-kd immunoreactive polypeptide in a variety of samples, including PC12 cells transfected with human PS1 complementary DNA, brain biopsy specimens from demented patients, and postmortem samples of frontal neocortex from early-onset familial Alzheimer's disease cases (PS1 and PS2), late-onset sporadic Alzheimer's disease cases, and cases of other degenerative disorders. This truncated polypeptide contains the N-terminus of PS1 and appeared unchanged across cases. In 2 early-onset cases linked to missense mutations in the PS1 gene, a PS1 immunoreactive protein (approximately 49 kd) accumulated in the frontal cortex. This protein was similar in size to full-length PS1 protein present in transfected cells overexpressing PS1 complementary DNA, and in lymphocytes from an affected individual with a deletion of exon 9 of the PS1 gene, suggesting that mutations of the PS1 gene peturb the endoproteolytic processing of the protein. Immunohistochemical studies of control brains revealed that PS1 is expressed primarily in neurons, with the protein localized in the soma and dendritic processes. In contrast, PS1 showed striking localization to the neuropathology in early-onset familial Alzheimer's disease and sporadic Alzheimers' disease cases. PS1 immunoreactivity was present in the neuritic component of senile plaques as well as in neurofibrillary tangles. Localization of PS1 immunoreactivity in familial and sporadic Alzheimer's disease suggests that genetically heterogeneous forms of the disease share a common pathophysiology involving PS1 protein.

Cellular delivery of NGF does not alter the expression of beta-amyloid immunoreactivity in young or aged nonhuman primates

The present study determined whether grafts of nerve growth factor-producing fibroblasts alter the expression of beta-amyloid in young or aged nonhuman primates. Aged monkeys serve as an animal model which normally exhibits beta-amyloid-laden plaques. Three young adult (7-12 years of age) and three aged (24-29 years of age) rhesus monkeys received intraventricular implants of polymer-encapsulated cells that were genetically modified to secrete human recombinant nerve growth factor (NGF). Three young adult and three aged rhesus monkeys received identical treatment except that the grafted cells were not genetically modified and thus differed only by a single gene construct. Five additional aged rhesus monkeys were ungrafted and also served as controls. Three to four weeks posttransplantation, young monkeys did not display beta-amyloid-immunoreactive profiles within any CNS structure regardless of treatment. Qualitative observations revealed that aged monkeys displayed numerous beta-amyloid plaque-like structures within the amygdala and hippocampus as well as limbic and neocortices. The amount of beta-amyloid immunoreactivity (beta-amyloid load) was quantified bilaterally within the temporal neocortex of these animals. The beta-amyloid load within the temporal neocortex of aged monkeys was highly variable but did not differ across treatment groups. These data indicate that chronic short-term administration of NGF does not affect the expression of beta-amyloid in the young or the aged primate brain.

Decreased trkA gene expression within basal forebrain neurons in Alzheimer's disease

In situ hybridization for TrkA mRNA was combined with quantitative optical densitometry to evaluate whether the expression of this gene is altered within cholinergic basal forebrain neurons (CBF) in Alzheimer's disease (AD). TrkA mRNA within individual nucleus basalis neurons was significantly reduced (66%) in AD cases relative to aged controls. Reverse transcription polymerase chain reaction quantitative analyses confirmed that TrkA mRNA levels decreased markedly in AD. In contrast, expression of the gene coding for for the low affinity p75NTR was not significantly altered in AD relative to aged controls. These data indicate that there is a selective defect in trkA gene expression in AD, supporting the hypothesis that the degeneration of CBF neurons seen in this disease results from impaired nerve growth factor trophic support.