Regionally specific modulation of brain apolipoprotein E in the mouse during the estrous cycle and by exogenous 17beta estradiol.

Studies have suggested that 17beta estradiol (E2) can modify apolipoprotein E (apoE) expression. The current study determined if apoE protein varied in different regions of the mouse brain as a function of the estrous cycle and if E2 could increase apoE protein expression. In this study apoE concentration was lowest on estrus in the hippocampus, cingulate cortex and frontal cortex. In contrast, apoE concentration was highest on estrus in the olfactory bulb and cerebellum. There were no differences in the striatal apoE expression throughout the estrous cycle. Exogenous E2 significantly raised tissue levels of apoE in the olfactory bulb and cerebellum at 5 days after treatment. There was a slight, but nonsignificant increase in cortical expression of apoE and no change in striatum. Immunocytochemical localization studies found estrogen receptor alpha (ERalpha) and estrogen receptor beta (ERbeta) in cortical neurons and glia. In the cerebellum and olfactory bulb, ERbeta was seen primarily in glia. ERalpha was not observed in the cerebellum and was rare in the olfactory bulb. Neither ERalpha nor ERbeta was seen in the striatum. Our data show regional differences in the production of apoE throughout the estrous cycle. In addition, exogenous E2 has regionally specific effects on apoE expression. Regional variability in apoE production appears to vary as a function of the estrogen receptor subtype.

Effects of hormone replacement therapy on olfactory sensitivity: cross-sectional and longitudinal studies.

OBJECTIVE: To determine whether hormone replacement therapy (HRT) preserved or improved olfactory sensitivity in healthy postmenopausal women. METHODS: Sixty-two postmenopausal women participated in a cross-sectional study of olfactory sensitivity involving detection, intensity discrimination, quality discrimination and two measures of quality recognition. In addition, 24 postmenopausal women participated in a longitudinal study of olfactory sensitivity. This study allowed for the measurement of estrogen effects (while holding practice effects constant) and the measurement of practice effects (while holding HRT conditions constant). RESULTS: In the cross-sectional study, we were unable to detect any differences between those receiving HRT and those not receiving HRT. Duration of exposure to HRT was examined by selecting women who had 5 or more years of exposure to their HRT regimen. Even after the data were reorganized into those for opposed- and unopposed-estrogen use, we were unable to detect any differences. However, olfactory threshold increased as a function of increasing age, regardless of HRT status. A gradual decrease in ability to detect odors was observed from the 4th to the 6th decade, with a greater decrease between the 6th and 7th decades. In the longitudinal study, no effects of HRT were detected even when practice effects were uncontrolled. Practice effects were assessed both between and within subjects. No effects of practice were detected when initial baseline performance was used as a covariate. CONCLUSION: Although prophylactic HRT has been suggested to be associated with improved olfactory function, we find that its use in healthy postmenopausal women does not enhance performance in a wide range of olfactory tasks.

Apolipoprotein E is upregulated in olfactory bulb glia following peripheral receptor lesion in mice.

Apolipoprotein E (apoE), a lipid transporting protein, has been postulated to participate in nerve regeneration. To better clarify apoE function in the olfactory system, we evaluated the amount and distribution of apoE in the olfactory bulb following olfactory nerve lesion in mice. Olfactory nerve was lesioned in 2- to 4-month-old mice by intranasal irrigation with Triton X-100. Olfactory bulbs were collected at 0, 3, 7, 21, 42, and 56 days postlesion, and both apoE concentrations and apoE distribution were determined. ApoE levels, as determined by immunoblot analysis, were twofold greater than normal during nerve degeneration at 3 days. ApoE levels remained elevated by approximately 1.5 times normal levels at 7 through 21 days after injury and returned to baseline by 56 days. Immunocytochemical studies supported these observations. ApoE immunoreactivity was prominent on the olfactory nerve at 3 days after lesion and decreased to baseline levels at later time periods. Double-labeling immunocytochemical studies confirmed that both reactive astroglia and microglia produced detectable amounts of apoE following the lesion. Return of apoE expression to baseline paralleled measures of olfactory nerve maturation as measured by olfactory marker protein. These data suggest that apoE increases concurrent with nerve degeneration. ApoE may facilitate efficient regeneration perhaps by recycling lipids from degenerating fibers for use by growing axons. The association of apoE genotype with dementing illnesses may represent a diminished ability to support a lifetime of nerve regeneration.

Volumetric and horseradish peroxidase tracing analysis of rat olfactory bulb following reversible olfactory nerve lesions.

Olfactory receptor neurons can regenerate from basal stem cells. Receptor neuron lesion causes degenerative changes in the olfactory bulb followed by regeneration as new olfactory receptor axons innervate the olfactory bulb. To our knowledge, parametric analyses of morphometric changes in the olfactory bulb during degeneration and regeneration do not exist except in abstract form. To better characterize olfactory bulb response, we performed morphometric analysis in rats following reversible olfactory nerve lesion with diethyldithiocarbamate. We also performed anterograde tracing of the olfactory nerve with wheatgerm agglutinin linked to horseradish peroxidase. Results of morphometry and tracing were complementary. The glomerular layer and external plexiform layer showed shrinkage of 45 and 26%, respectively, at 9 days. No significant shrinkage occurred in any other layer. Individual glomeruli shrank by 40-50% at 3 and 9 days following lesion. These data show that degenerative changes occur both in the glomeruli and transneuronally in the external plexiform layer. Olfactory nerve regeneration (identified by WGA-HRP transport) paralleled volumetric recovery. Recovery occurred first in ventral and lateral glomeruli between 9 and 16 days followed by recovery in medial and dorsal glomeruli. These data indicate substantial transynaptic degeneration in the olfactory bulb and a heretofore unrecognized gradient in olfactory nerve regeneration that can be used to systematically study recovery of a cortical structure.

Response of the olfactory bulb antioxidant system following diethyldithiocarbamate (DDTC) administration in rats.

This study was designed in order to evaluate alterations in the reactive oxygen species (ROS) scavenging system in olfactory bulb, dorsal neocortex and cerebellum for 6 weeks following a single subcutaneous dose (600 mg kg-1) of diethyldithiocarbamate (DDTC) to rats. A single dose of DDTC caused substantial damage to the olfactory epithelium and degeneration within the olfactory bulb. The epithelium regenerates, followed by regeneration in the olfactory bulb. The mean olfactory bulb weight decreased significantly 3 days after DDTC administration and gradually recovered to control values in 6 weeks. The DDTC-induced lesion of the olfactory nerve resulted in significant changes in glutathione (GSH) and antioxidant enzyme activities in olfactory bulb. In contrast, no significant changes were found in either cerebellum or dorsal neocortex. These observations indicate that a single dose of DDTC selectively affected the ROS scavenging system of the olfactory bulb. Moreover, these changes persisted for at least 6 weeks, which includes regeneration and synaptogenesis. Olfactory bulb GSH concentrations decreased significantly by 47 +/- 4%, glutathione reductase activity decreased by 18 +/- 3% and catalase activity increased by 27 +/- 7% over the 6 weeks. Superoxide dismutase activity decreased significantly in olfactory bulb of rats by 32 +/- 6% at 3 days following the lesion and then recovered and increased by 38 +/- 3% at 3 weeks. Olfactory bulb malondialdehyde concentrations were elevated (298 +/- 67%) throughout the post-lesion survival period, although this change did not reach the stringent statistical significance level required in this study. These data suggest that increased ROS flux perturbs the olfactory bulb antioxidant defense system during olfactory nerve regeneration.

Apolipoprotein E immunoreactivity in human and mouse olfactory bulb.

We evaluated the distribution of apolipoprotein E (apoE) immunoreactivity in mouse and human olfactory bulbs. ApoE immunoreactivity was present in the olfactory nerve and around the glomeruli. Immunoreactivity was seen in somata that appeared to be glial. No neuronal staining was seen. The apoE immunoreactivity was also present in the mouse olfactory bulb subependymal layer. The specificity of immunoreactivity was confirmed with apoE-deficient mice (apoE gene knock-out mice, apoE KO) which did not display any immunoreactivity. The presence of apoE around glomeruli and nerve suggest that apoE is associated with the continuous degeneration and regeneration processes that occur in the olfactory nerve. Experimental manipulation of the olfactory nerve may be a useful technique to determine the functions of apoE in a well-defined neural system.

Cancer treatment and growth cone-associated protein in human olfactory bulb glomeruli.

BACKGROUND: Growth cone-associated protein (GAP43) is found in growing axons and we hypothesized that systemic treatment with antineoplastic agents should disrupt regeneration of olfactory receptor cells. Disruption of regeneration should be evidenced by decreased presence of growing axons in the olfactory bulb. OBJECTIVE: To evaluate GAP43 in human olfactory bulb in normal controls and in individuals receiving treatment for neoplasms. DESIGN: Immunocytochemical studies were performed on autopsied human olfactory bulbs to identify both GAP43 and olfactory marker protein immunoreactivity. The former recognizes growing axons and the latter is a definitive marker of adult olfactory nerve. SUBJECTS: Twenty-seven subjects were evaluated. Seven had received either antineoplastic agents and/or x-irradiation of the whole head. Four subjects were young, untreated controls, 10 were age matched to the treated group, and 2 had neoplasms but did not receive antineoplastic agents or irradiation of the head. In addition, 3 subjects with end-stage renal disease were immunostained. RESULTS: Subjects treated with antineoplastic agents or x-irradiation of the whole head displayed no statistically significant loss of olfactory bulb glomeruli, but GAP43 immunoreactivity was markedly reduced in all but 1 subject (P<.32). The subjects with end-stage kidney disease showed frank loss of both GAP43 immunoreactivity and olfactory glomeruli. CONCLUSIONS: Treatment with antineoplastic agents apparently does not damage olfactory epithelium directly but inhibits growth of new axons into the olfactory bulb. This observation suggests that the quality of olfactory experience may change during the course of treatment with antineoplastic agents because the olfactory nerve is not replaced.

Hemianopsia in dementia with Lewy bodies.

OBJECTIVE: To describe the pathologic changes that caused a left homonymous hemianopsia in a patient with dementia with Lewy bodies. DESIGN: Report of a case and postmortem studies. MAIN OUTCOME AND RESULTS: A 66-year-old woman experienced parkinsonism and left homonymous hemianopsia early in the course of a rapidly progressive dementia that culminated in death only 21 months after the onset of her symptoms. Postmortem examination revealed pathologic features consistent with the diagnosis of dementia with Lewy bodies. The only apparent explanation for her visual field deficit was a disproportionately large number of neurofibrillary tangles in the right striate, peristriate, and inferotemporal cortices. CONCLUSION: A clinically obvious homonymous hemianopsia can result from the occipital and inferotemporal cortical degeneration in dementia with Lewy bodies.

Beta-amyloid precursor protein-like immunoreactivity is upregulated during olfactory nerve regeneration in adult rats.

Beta-amyloid precursor protein (APP) is the source of beta-amyloid, which forms the cores of senile plaques in Alzheimer's Disease. However, the function of this precursor protein is currently unknown and an adult animal in which this protein varied substantially would be valuable. We used subcutaneous diethyldithiocarbamate to reversibly lesion the olfactory epithelium in adult rats and found that whole-bulb levels of APP-like immunoreactivity significantly decreased after the lesion, then increased reaching almost five-fold normal levels six weeks after treatment. Growth cone associated protein (GAP43) decreased when the nerve degenerated, then increased, replicating previous studies of olfactory nerve regeneration. Immunocytochemical techniques identified APP immunoreactive perikarya and fibers in and around glomeruli at three days to one week post-lesion and upregulation of APP-like immunoreactivity in mitral cells and dendrites at five weeks. Olfactory nerve regeneration appears to be a useful in vivo model system to understand the regulation of APP-like proteins.

The distribution of amyloid beta protein deposition in the corpus striatum of patients with Alzheimer's disease.

The distribution of amyloid beta peptide (A beta) was quantified in the corpus striatum and pallidum of 10 patients with Alzheimer's disease (AD) and three patients with both Alzheimer's disease and Parkinson's disease (AD-PD). A beta occurred almost exclusively in plaques that did not have neurites or amyloid cores. Caudate, accumbens nuclei and rostral putamen contained more of the diffuse plaques than did caudal putamen. No diffuse plaques were found in the neighbouring globus pallidus. This distribution of A beta deposition may reflect the distribution of diseased synaptic cortical afferents rather than a putative vascular source of A beta.

Olfactory mucosal lesions following subcutaneous diethyldithiocarbamate (DDTC).

We found that a single 600 mg/kg subcutaneous dose of the chelating agent diethyldithiocarbamate (DDTC) in rats caused severe damage of the olfactory epithelium. Damage was characterized by degeneration of the receptor cells but sparing of basal cells. This degeneration was characterized centrally (in the olfactory bulb) by 50% shrinkage of glomeruli. Reactive gliosis, as judged by immunoreactivity for glial fibrillary acidic protein, was prominent in the glomeruli at one week. Glomeruli areas had recovered to control values and gliosis in glomeruli had decreased by five weeks after injection. This recovery corresponds to sparing of the regenerative cell of the olfactory epithelium. We hypothesized that DDTC may act by disrupting xenobiotic metabolic pathways requiring divalent cations.

Distribution of amyloid in the brainstem of patients with Alzheimer disease.

A4 protein (beta-protein, beta-amyloid) deposits were identified with silver stains in postmortem brainstem sections from 13 patients with Alzheimer disease (AD), 6 patients with mixed Alzheimer disease and Parkinson disease (AD-PD), 5 disease controls, and 2 elderly controls. A rostro-caudal gradient of A4 was found in patients with AD and AD-PD, such that A4 was most prevalent in the midbrain and least prevalent in the medulla. The brainstem of the controls contained little or no A4. The midbrain tectum and tegmentum contained the greatest densities of A4, but the red nucleus and substantia nigra pars reticulata were largely spared. This distribution of A4 suggests that A4 deposition is a function of synaptic connectivity rather than passive diffusion from vascular sources.

Olfactory bulb lesions in Alzheimer's disease.

The olfactory bulb (OB), with its comparatively simple and well-delineated connectivity, presents an interesting system for examining cell-specific pathology in neurologic degenerative disorders such as Alzheimer's disease (AD). We have found that in AD the large, efferently projecting neurons (mitral cells) of the OB degenerate, typically without classical Alzheimer neurofibrillary changes. In some cases, with less severe neocortical pathology, the terminal arborizations of olfactory nerve appear hyperplastic and are associated with focal accumulations of A-4 (beta-amyloid) immunoreactivity that are not detectable by standard amyloid stains. These abnormalities may represent a pathologic manifestation of normally occurring plasticity in the olfactory system.

Muscarinic cholinoceptive neurons in the frontal cortex in Alzheimer's disease.

The cellular distribution of muscarinic acetylcholine receptor protein in the frontal cortex of Alzheimer (AD) patients, age-matched and middle-aged controls was assessed quantitatively by means of immunohistochemistry using the monoclonal antibody M35. As shown previously in biopsy cortices, mainly layer II/III and V pyramidal neurons were immunolabeled. Neither distribution nor numbers of labeled cells displayed significant differences between the groups investigated. This is in accordance with the results of ligand binding studies that mostly failed to reveal different binding characteristics in AD compared to controls. Muscarinic and nicotinic receptor proteins have been shown to be colocalized in many cholinoceptive pyramidal neurons. Since nicotinic receptors--in contrast to muscarinic receptor proteins--are severely reduced in AD, this indicates a selective impairment of nicotinic receptor expression and not a significant death of cholinoceptive neurons per se.

Nicotinic cholinoceptive neurons of the frontal cortex are reduced in Alzheimer's disease.

The cellular distribution of nicotinic acetylcholine receptors was studied in the frontal cortex (area 10) of 1) Alzheimer patients and compared to 2) age-matched and 3) middle-aged controls using the monoclonal antibody WF 6 and an immunoperoxidase protocol. Statistical analysis revealed significant differences between the number of labeled neurons among all three groups tested (middle-aged controls greater than aged controls greater than Alzheimer cases). No differences were seen for cresyl violet-stained samples. These findings underline that the nicotinic receptor decrease found with radioligand binding may reflect a postsynaptic in addition to a presynaptic component.

Hippocampal lesions in dominantly inherited Alzheimer's disease.

We compared hippocampal lesions in three pedigrees of Familial Alzheimer's Disease (FAD). In these pedigrees, the disease is inherited as an autosomal dominant disorder and has been linked to DNA markers on chromosome 21. In eight cases of FAD (four from one pedigree and two each from two others) we quantified neurofibrillary tangles (NFT) and senile plaques (SP) in hippocampal subdivision CA1-4, subiculum, presubiculum, and dentate gyrus. We observed consistent patterns of the distribution of lesions: The highest density of NFT and SP was present in CA1-2; virtually no SP or NFT were present in presubiculum; SP diameter was consistently greatest in CA4. We found no overall differences among pedigrees in total densities of NFT and SP, but statistical analyses disclosed that an uncommon type of SP was disproportionately present in two pedigrees. This type of SP was usually restricted to CA4, had a marked amyloid core devoid of argyrophilic neurites. These studies also disclosed inter- and intrafamilial heterogeneity of lesion distribution (including congophilic angiopathy and cerebellar plaques) in these three pedigrees.

Cellular distribution and expression of cortical acetylcholine receptors in aging and Alzheimer's disease.

Ligand binding studies show marked reductions of nicotinic, but not of muscarinic binding sites in Alzheimer's disease. Using monoclonal antibodies we studied immunohistochemically the expression of the respective receptor proteins in the frontal cortex of middle-aged (55 +/- 5 yr) controls, age-matched controls (73 +/- 6 yr), and patients with Alzheimer's disease (74 +/- 5 yr). Density of nicotinic cholinoceptive neurons was 8000/mm3 for middle-aged controls and 4000/mm3 for age-matched controls, but only 900/mm3 in Alzheimer's brains (p less than 0.0001). Densities of muscarinic cholinoceptive and of Nissl-stained neurons were not significantly different between the groups, pointing to a selective decrease of nicotinic receptor protein expression in cortical neurons with aging and in Alzheimer's disease.

Transient impairment of recognition memory following ibotenic-acid lesions of the basal forebrain in macaques.

To assess the contributions of the basal forebrain cholinergic nuclei to visual recognition memory in macaques, we compared the effects of lesions of (a) the nucleus basalis of Meynert, (b) the medial septal and diagonal band nuclei, and (c) all nuclei combined on performance of delayed nonmatching-to-sample with trial-unique stimuli. Whereas monkeys with the separate lesions did not differ from each other or from normal control animals, those with combined lesions showed a significant impairment. With time and extended practice, however, the performance of the animals with combined lesions recovered to normal levels. During the recovery period, these monkeys showed an initially increased sensitivity to scopolamine that later dissipated, at which time they also failed to show the improvement that follows physostigmine administration in normal animals. Postmortem assessment of cortical choline acetyltransferase activity revealed that only the group with combined lesions had significant depletion of this enzyme. The results suggest that (1) the basal forebrain cholinergic system participates in mnemonic processes in primates and that (2) extensive damage to this system is necessary before impairments in recognition memory, even transient ones, can be observed.

Changes in size of motor axons in hereditary canine spinal muscular atrophy.

Hereditary canine spinal muscular atrophy (HCSMA), a dominantly inherited disorder of motor neurons, has three phenotypes: accelerated, intermediate, and chronic. In the accelerated and intermediate phenotypes, axonal sizes in ventral roots were smaller than in controls. Reductions in axonal size occurred primarily in large axons, and the frequency of small-caliber axons was increased. In HCSMA, nerve fiber shape, i.e., circularity, was reduced, and the relative thickness of the myelin sheath as a function of axonal caliber was decreased. The density of fibers in motor nerves was increased, making it unlikely that a selective loss of large-caliber axons explained the increased frequency of small-caliber axons. These observations suggest that, in HCSMA, changes in axonal size in motor nerves are associated with both growth arrest and axonal atrophy.

Mu opiate receptors are selectively labelled by [3H]carfentanil in human and rat brain.

[11C]Carfentanil is a potent opioid agonist currently in use as a specific PET (position emission tomography) scan radioligand for brain mu opioid receptors. In order to investigate the receptor interactions of carfentanil in detail [3H]carfentanil was used as a radioligand for labelling receptors in rat and human brain tissue homogenates. [3H]Carfentanil was found to bind saturably and with high affinity (KD = 0.08 +/- 0.01 nM) to membranes prepared from human cortical (Bmax = 42 +/- 3 fmol/mg) and thalamic (Bmax = 84 +/- 3 fmol/mg) tissues and rat cortex (Bmax = 82 +/- 4 fmol/mg) and diencephalon (Bmax = 105 +/- 5 fmol/mg). Association (1.23 +/- 0.19 X 10(10) Mol-1 X min-1 and dissociation rate (0.19 +/- 0.03 min-1) constants were determined in human cortical tissues; results from studies in rat cortical, and rat diencephalon tissue homogenates produced similar kinetic rate constants. Competition studies with a variety of drugs indicated that [3H]carfentanil interacts primarily with mu opioid receptors in the four tissues studied; the affinities of a series of non-radioactive opioid ligands were essentially identical in the four tissues (correlation coefficients = 0.88-0.93). Naloxone, morphine, DAGO [( D-Ala2-MePhe4-Gly-ol5]enkephalin), DADL [( D-Ala2-D-Leu5]enkephalin) and EKC (ehtylketazocine) potently displaced specific [3H]carfentanil binding with nM potency while the kappa agonist U-69593, the sigma agonists (+)-SKF 10047, (+)-3-PPP [3-hydroxyphenyl)-N-propylpiperidine) and haloperidol and PCP (phencyclidine) were less potent displacing agents. The higher affinities of DAGO and morphine versus DADL for the [3H]carfentanil binding sites indicates that delta opioid receptors are not being labelled.(ABSTRACT TRUNCATED AT 250 WORDS)